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Research and development on accelerator-driven transmutation system at JAERI
Nuclear Engineering and Design 230 (2004) 209–222
Research and development on accelerator-driven transmutation system at JAERI Toshinobu Sasa∗ , Hiroyuki Oigawa, Kazufumi Tsujimoto, Kenji Nishihara, Kenji Kikuchi, Yuji Kurata, Shigeru Saito, Masatoshi Futakawa, Makoto Umeno, Nobuo Ouchi, Yasuo Arai, Kazuo Minato, Hideki Takano Japan Atomic Energy Research Institute, 2-4, Shirakata-Shirane, Tokai, Ibaraki 319-1195, Japan Received 8 May 2003; received in revised form 3 October 2003; accepted 25 November 2003
Abstract Japan Atomic Energy Research Institute carries out research and development on accelerator-driven system (ADS) to transmute minor actinides and long-lived fission products in high-level radioactive waste. The system is composed of high intensity proton accelerator, lead-bismuth spallation target and lead-bismuth cooled subcritical core with nitride fuel. About 2500 kg of minor actinide is loaded into the subcritical core. Annual transmutation amount using this system is 250 kg with 800 MW of thermal output. This transmutation amount corresponds to the amount of minor actinides produced from 10 units of 1GWe power reactors annually. A superconducting linear accelerator with the beam power of 20–30 MW is connected to drive the subcritical core. To maximize the transmutation efficiency, the nitride fuel without uranium, such as (Np, Am, Pu)N, is selected. The nitride fuel irradiated in the ADS is reprocessed by pyrochemical process followed by the re-fabrication of nitride fuel. Many research and development activities are under way and planned in the fields of subcritical core design, spallation target technology, lead-bismuth handling technology, accelerator development, and minor actinide fuel development. Especially, to study and evaluate the feasibility of the ADS from physics and engineering aspects, the transmutation experimental facility (TEF) is proposed under a framework of the High-Intensity Proton Accelerator Project. © 2004 Elsevier B.V. All rights reserved.
1. Introduction In 1988, the Japan Atomic Energy Commission launched a long term R&D program named Options Making Extra Gains from Actinides and fission products (OMEGA) for partitioning and transmutation of long-lived radioactive nuclides. In the OMEGA program, Japan Atomic Energy Research Institute (JAERI) has proposed a double-strata fuel cycle con∗ Corresponding author. Tel.: +81-29-282-6436; fax: +82-29-282-6438. E-mail address: [email protected] (T. Sasa).
cept (Takano et al., 2000) which consists of two fuel cycles; current commercial fuel cycle and dedicated fuel cycle for the transmutation of minor actinides (MA) and long lived fission products (LLFP). By the double-strata fuel cycle that illustrated in Fig. 1, no significant modification is required to the current fuel cycle, and long-lived nuclides are confined into the second-strata small cycle that is optimized to the transmutation of MA and LLFP. JAERI proposes an accelerator-driven system (ADS) for the effective transmutation of MA and LLFP. When the fuel is mainly composed of MA, a delayed neutron fraction, which influences the safety operation of crit-
0029-5493/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.nucengdes.2003.11.033
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In this paper, research and development (R&D) on the ADS at JAERI is reviewed and future plans are also presented.
2. Code development for ADS neutronic performance analysis
Fig. 1. Double strata fuel cycle concept.
ical reactor, becomes lower than that of conventional nuclear reactors. In the case of ADS, the delayed neutron fraction does not directly affect the operation in comparison with a critical reactor because of the subcriticality of the system. There also exists a wide margin of reactivity to install various compositions of MA that are related to the burn-up profile and the types of spent fuel. JAERI proposes a lead–bismuth (Pb–Bi) target/coolant system as a primary candidate of the ADS (Tsujimoto et al., 2000). A proton beam of 1.5 GeV–20 MW is injected and the system is designed to generate 800 MW of thermal power. To realize the ADS, there are many technical subjects; the neutronics of the subcritical core driven by spallation neutrons, the engineering application of the high power spallation target, the development and the operation of the intense proton accelerator, MA nitride fuel fabrication and so on. To solve these technical issues relevant to the ADS development, construction of the transmutation experimental facility (TEF) is planned under the Japan Proton Accelerator Research Complex (J-PARC) Project that is directed by JAERI and High Energy Accelerator Research Organization (KEK) (The Joint Project Team of JAERI and KEK, 1999).
The incident particle of ADS is a proton with energy around 1 GeV and reactions in spallation target mainly occur in the energy range above 100 MeV. Reactions in such high energy region are different from those considered in conventional reactor analysis. On the other hand, in the fuel surrounding the target, most of reactions occur below several tens MeV. For the design study of ADS, calculations in the wide energy range from electron volt or kilo electron volt up to giga electron volt must be performed to analyze specific neutronics parameters such as spallation neutron yield from the spallation target, spatial and energy distribution of the spallation neutrons, heat deposition distribution, time evolution of the isotope composition of the fuel and the subcriticality of the core, particle flux and power density distribution in the subcritical core, decay heat of the spallation target and fuel, coolant void reactivity, Doppler coefficient and so on. To analyze these parameters, an analysis code system named “Accelerator-driven Transmutation Reactor Analysis code System (ATRAS)” to analyze the neutronics and burn-up properties of ADS was developed (Sasa et al., 1999). ATRAS is an integrated code system that performs the following analyses: • spallation, evaporation and high energy fission reactions in high energy region; • proton, neutron and pion transport in high energy region; • neutron reactions and transport in low energy region; and • core burn-up in low energy region. The structure of the ATRAS is illustrated in Fig. 2. Analysis codes included in ATRAS are connected to each other through CCCC format binary file (O’Dell, 1977). In ATRAS, hadronic cascade processes that occur in the energy range from MeV to GeV are calculated with the NMTC/JAERI97 (Takada et al., 1998).
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Fig. 2. Structure of the ATRAS code system.
NMTC/JAERI97 calculates hadronic cascade processes, such as a intra-nuclear cascade process, an evaporation process and a high energy fission process. An isobar model and a pre-equilibrium model can also be considered. A high energy fission model, nucleon–nucleon reaction cross sections and level density parameters were revised and applied to the NMTC/JAERI97. When neutrons produced from hadronic cascade processes are slowed down below a cut-off energy, that can be arbitrary defined by user, they are scored into a neutron history file. The position, direction, energy and importance of the cut-off neutrons are recorded. The FSOURCE code was developed to create a fixed neutron source file for a succeeding neutron transport analysis by the deterministic method. FSOURCE generates the spatial, energy and angular distributions of the cut-off neutrons from the history file. The angular distribution of the cut-off neutrons is expressed in the form of a Legendre polynomial. The number of energy groups and the order of the Legendre polynomial can be arbitrary specified by user. To transport the neutrons below cutoff energy, the two-dimensional discrete ordinate transport code TWODANT (Alcouffe et al., 1990) is prepared. It is difficult to solve fixed neutron source problem with
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fissile material by Monte Carlo method. Source neutrons are multiplied as a function of neutron multiplication factor and this requires very long computation time to obtain the results. Therefore, for the calculation models containing fissile material, a deterministic analysis code TWODANT is selected and included into ATRAS. One unique function of ATRAS is its capability of burn-up analysis for accelerator-driven systems. It is important to determine the burn-up characteristics of ADS transmutor, since it specifies the efficiency of transmutation. And it should be ensured that the burn-up reactivity change does not cause the core to become critical. The BURNER code, the burn-up calculation module in the VENTURE (CCC-459, 1980) code system, is included into ATRAS. When the user uses BURNER together with TWODANT, it is possible to obtain the burn-up characteristics by using the energy spectrum and flux distribution taking account of the spallation neutron source. In the BURNER code, the user can easily modify the burn-up and decay chain of the nuclides and apply the latest data to the analysis. The program CHFUEL was developed to simulate the fuel exchange at the end of the burn-up cycle. The neutron group cross section set for the ATRAS code system was prepared from the JENDL-3.2 (Nakagawa et al., 1995) cross section library. About 150 nuclides that are necessary to analyze the JAERIproposed ADS were selected from the JENDL-3.2 library. Higher actinides such as Bk and Cf, long-lived fission products and lanthanides that would mix with MA in a dry reprocessing process were also included. Average cross sections of fission products were prepared as a lumped fission product. These lumped fission product cross sections are used to consider the nuclides which are not explicitly considered in the burn-up chain. Nuclides required for the analysis of the systems using 232 Th–233 U fuel were also prepared. The effective cross sections for the deterministic neutron transport and burn-up calculation in the low energy region are prepared by the CSAS module in the SCALE-4 (CCC-545, 1990) code system. Heterogeneity of the fuel pin configuration and correction of the self-shielding factor can be considered to construct the effective cross section files. A utility program MKISO was prepared to convert the effective microscopic cross-section file from the SCALE standard AMPX format to the CCCC format.
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To obtain the neutronics and burn-up characteristics of ADS, several calculation codes in ATRAS are used. To facilitate the data input, we developed a pre-processing program named “ATRAS driver” and included it into ATRAS. The user needs to specify the calculation model only once into the input data file of the ATRAS driver. Then, the ATRAS driver creates input data files for the calculation codes used in the analysis. Parameters those are required for the heterogeneous cell calculation and the analysis by TWODANT can be specified into the input data file of the ATRAS driver. The ATRAS code system adopts the CCCC format binary files to save disk space and access time, but these files are unreadable for the user. Furthermore, some calculation results like the neutron energy spectrum are listed in separate files from the hadronic cascade code and neutron transport code. A post-processing program “ATRAS utility” was created to read the binary files and calculate the results such as a particle energy spectrum from high energy region to low energy region, reaction rates and actinide inventories at each burn-up step. The decay heat and the radiotoxicity of residual MA in the spent fuel can also be analyzed by the ATRAS utility.
3. ADS transmutation plant design The reference ADS design proposed by JAERI (Tsujimoto et al., 2000) is the 800 MWth fast subcritical core fueled with MA nitride, cooled by Pb–Bi eutectic and driven by the spallation neutron source using Pb–Bi target and proton accelerator as shown in Fig. 3. About 250 kg of MA can be burned annually by fission reactions, which corresponds to the amount of MA produced in 10 Units of LWRs whose burn-up is 33,000 MWD/t. The current reference design of the subcritical core consists of one fuel zone. It is convenient to manage the spent fuel and fuel reloading. However, it also gives rather higher power peaking value than that of multi fuel zone core. To reduce the peaking factor especially for the radial one, two approaches were examined. First method is separation of fuel section into two zones by changing Pu mixing ratio. Another way is location of Pb–Bi buffer zone between the spallation target section and the fuel section. Fig. 4 shows a
Fig. 3. Conceptual design of ADS (800 MWth).
comparison of radial power density distribution at the beginning of first cycle. From the further analysis results, latest core configuration illustrated in Fig. 5 is arranged (Tsujimoto et al., 2004).
Fig. 4. Comparison of radial power distribution.
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Fig. 5. Subcritical core configuration.
In this reference design, maximum value of the effective multiplication factor, keff , is set at 0.95. To achieve the above mentioned thermal power with this keff , a high-power proton beam, at least 22 MW, is required. Moreover, taking account of the burn-up reactivity swing, keff will be deteriorated to 0.93, where a proton beam of about 30 MW is necessary. The adequate subcritical level of the ADS must be defined by considering several reactivity factors (Kim et al., 2002), such as system cool down from operation temperature to refueling temperature, unusual coolant temperature rise and coolant intrusion into beam duct, and uncertainties caused from measurement and calculation. Based on our reference design of ADS, sum of the estimated reactivity factors were determined about 2.5% k/k. It means that the initial keff of our proposed ADS can increase from 0.95 to 0.97. The re-arrangement of the system parameters is in progress. To supply a powerful proton beam, a superconducting linear accelerator should be developed. Considering the energy efficiency of a neutron source, the specification of the proton beam, 1.5 GeV × 15–20 mA,
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is temporally chosen, though the acceleration energy should be finally determined by taking into account of the factors such as the cost of the accelerator and the beam current density on the beam window. As for the spallation target, eutectic Pb–Bi alloy was chosen out of several heavy metals, such as Hg and W, because of its good thermal property; the melting point of 398 K and the boiling point of 1943 K. Although Pb–Bi eutectic is comparatively corrosive to steel at the high temperature above 700 K, Russia has a lot of experience to use it as the coolant of reactors in submarines. Many countries including Japan have therefore started research and development to establish the technology for the usage of Pb–Bi as the spallation target. Nitride fuel has the advantage of accommodating various MA with a wide range of composition besides good thermal properties. Further it can support hard neutron spectrum suitable for effective transmutation of MA. For avoiding the production of hazardous 14 C, however, 15 N enriched nitrogen to 99.9% shall be used in the nitride fuel. In our reference design, tank-type structure is adopted. The inlet and the outlet temperatures of the primary Pb–Bi coolant are 603 and 703 K, respectively. Steam generators can be directly inserted in the reactor vessel because Pb–Bi is chemically compatible with water. The electric power is about 250 MW, which means the ADS can be a self-sustaining system provided the efficiency of the accelerator is more than 15%. From the result of the comparative study of ADS and fast reactor in advanced fuel cycle (OECD/NEA, 2002), efficiency of the accelerator is assumed to be 45%. In our reference design, efficiency is assumed to 30–40%. By using superconducting cavity by continuous wave operation, this value will be accomplished. To realize the ADS, JAERI has conducted the R&D in the fields of the proton accelerator, the Pb–Bi technology and the MA nitride fuel. Moreover, to demonstrate the feasibility of the ADS in the reactor physics aspects and target engineering aspects, a new experimental facility, the TEF is planned.
4. Fuel for MA transmutation The basic properties of the metallic and the nitride fuels with MA have been measured for about ten years
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(Minato et al., 2001). Through such studies, MA nitride has been chosen as the first candidate for the dedicated transmutation system because of its possible mutual solubility among the actinide mononitrides and its good thermal properties. As the R&D for the fuel fabrication, high-purity nitrides such as (Np, Pu)N, AmN and (Cm, Pu)N were synthesized by the carbo-thermic reduction method and their material properties have been measured. The irradiation test of such MA nitride fuel has not been performed yet, while (U, Pu)N fuel was irradiated in the experimental fast test reactor JOYO under the joint research with the Japan Nuclear Cycle Development Institute (JNC), and no failure of fuel pins was found as shown in Fig. 6 (Tanaka et al., 2002). As a reprocessing of the irradiated MA nitride fuel, pyrochemical process has been studied in JAERI. The pyrochemical process has several advantages over the wet process in treating such a dedicated fuel for transmutation including recycling feasibility of 15 N used in the nitride fuel. In the laboratory scale test, metallic Pu and Np were successfully recovered from non-irradiated PuN and NpN, respectively, by the molten-salt electrorefining technique.
5. Transmutation Experimental Facility (TEF) To study the basic characteristics of the ADS and to demonstrate its feasibility from viewpoints of the reactor physics and the spallation target engineering,
Fig. 6. Cross-section of (U, Pu)N fuel pin (40 GWd/t).
JAERI plans to build the TEF in the Tokai site under a framework of the J-PARC Project as illustrated in Fig. 7. TEF consists of two buildings: the transmutation physics experimental facility (TEF-P) and the ADS target test facility (TEF-T) as shown in Fig. 8. TEF-P is a zero-power critical facility where a low power proton beam is available to research the reactor physics and the controllability of the ADS. TEF-T is a material irradiation facility which can accept a maximum 600 MeV–200 kW proton beam into the spallation tar-
Fig. 7. Japan proton accelerator research complex (J-PARC).
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Fig. 8. Transmutation experimental facility (TEF).
get of Pb–Bi eutectic. The outline of TEF-P and TEF-T is presented hereafter (Oigawa et al., 2001). 5.1. Transmutation physics experimental facility (TEF-P) Several kinds of experiments to investigate neutronic performance of the ADS have been performed worldwide. Some of them are for the characteristics of the subcritical system such as MUSE program (Lebrat et al., 1999). MASURCA, a critical assembly for the fast reactor in France, is used with newly developed DT and DD neutron source. In Japan, subcritical experiments were just started at the fast critical assembly (FCA) by using a 252 Cf neutron source. Installation of DT neutron source to the FCA is also planned. Moreover, many experimental studies have been performed to the neutronics of the spallation neutron source with various target material such as lead, tungsten, mercury and uranium. These experiments for spallation target are not directly related to the ADS, but they are also useful to validate the neutronic characteristics of ADS. There has been, however, no experiment aiming at the research and the demonstration of the fast subcritical system combined with a spallation source. So the purpose of the TEF-P is divide roughly into three
subjects: (1) reactor physics aspects of the subcritical core driven by a spallation source, (2) demonstration of the controllability of the subcritical core including a power control by the proton beam power adjustment, and (3) investigation of the transmutation performance of the subcritical core using certain amount of MA and LLFP. The details of the experimental items are described later. The most serious problem to build a new nuclear facility is how to prepare the fuel, since tons of low-enriched uranium or plutonium are necessary to make the core critical or near-critical (e.g., keff = 0.95) in the fast neutron system. We expect to use the plate-type fuel of the FCA in JAERI/Tokai, or preferably to merge FCA into TEF-P. About two tons of metallic fuel of enriched uranium and plutonium will be available as well as natural and depleted uranium. Various simulation materials required simulating fast reactor and ADS such as lead and sodium for coolant, tungsten for solid target, ZrH for moderator, B4 C for absorber, and AlN for simulating nitride fuel will be prepared. TEF-P is therefore designed with referring to FCA; the horizontal table-split type critical assembly with a rectangular lattice matrix. Fig. 9 shows a conceptual view of the assembly. Proton beam was intro-
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Fig. 9. Conceptual view of TEF-P critical assembly.
duced horizontally from the center of the fixed half assembly. In the experiment with the proton beam, keff , of the critical assembly will be kept less than 0.98. One proton with energy of 600 MeV produces about 15 neutrons by the spallation reaction with heavy metal target such as lead. The 10 W proton beam corresponds to the source strength of 1.5 × 1012 neutrons/s, which is strong enough to measure the power distribution at the deep subcritical state such as keff = 0.90. In the conceptual design of the facility, the shielding property for high energy neutrons is calculated. About 2 m thickness of concrete shield is necessary even when the core is surrounded by about 1m of lead reflector. Safety aspect of the facility is also extensively studied. The prompt critical accident can be terminated without fuel melting by the reactor scram system with multiplicity and variety. The unexpected introduction of the 10 W beam into the critical state also can be terminated safely with the reactor scram. Using this TEF-P facility, many experimental studies are planned. The research and development (R&D) to be carried out at TEF-P is described below. As for the neutronics in the subcritical system, power distribution, keff , effective neutron source strength, and neutron spectrum are measured by
changing parametrically the subcriticality and the spallation source position. The material of the target will also be altered with Pb, Pb–Bi, W, and so on. The reactivity worth is also measured for the case of the coolant void and the intrusion of the coolant into the beam duct. It is desirable to make the core critical in order to ensure the quality of experimental data of the subcriticality and the reactivity worth. As for the demonstration of the hybrid system, feedback control of the reactor power is examined by adjusting the beam intensity. Operating procedures at the beam trip and the re-start are also examined. As for the transmutation characteristics of MA and LLFP, fission chambers and activation foils are used to measure the transmutation rates. The cross section data of MA and LLFP for high energy region (up to several hundreds MeV) can be measured by the time-of-flight (TOF) technique with the proton beam of about 1ns pulse width. Several kinds of MA and LLFP samples are also prepared to measure their reactivity worth, which is important for the integral validation of cross section data. Ultimate target of the facility is to install a partial mock-up region of MA nitride fuel with air cooling to measure the physics parameters of the transmutation system. The central rectangular region (28 cm×28 cm) will be replaced with a hexagonal subassembly which
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can partially load the pin-type MA fuel around the spallation target. The distinguished points of TEF-P in comparison with existing experimental facilities can be summarized as follows: (1) both the high energy proton beam and the nuclear fuel are available, (2) the maximum neutron source intensity of about 1012 n/s is strong enough to perform precise measurements even in the deep subcritical state (e.g., keff = 0.90), and, is low enough to easily access to the assembly after the irradiation, (3) wide range of pulse width (1 ns–0.5 ms) can be available by the laser charge exchange technique described later, (4) MA and LLFP can be used as a shape of foil, sample and fuel by installing an appropriate shielding and a remote handling devise. 5.2. ADS target test facility (TEF-T) JAERI proposes the ADS using a Pb–Bi for both spallation target and coolant of the fuel region. Pb–Bi is one of the alternative options of the coolant of the fast system and it also has a function of liquid spallation target simultaneously in the ADS. There are, however, many technical issues to use Pb–Bi. To solve them, several R&D programs are proposed. Material irradiation experiment in stagnant Pb–Bi environment has been performed at the SINQ facility in Paul Scheller Institute (PSI), Switzerland. MEGAPIE project (Bauer et al., 2001) is also planned at PSI to
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demonstrate feasibility of Pb–Bi target by using the existing accelerator facilities. According to the limitation of existing equipment of the facility and machine time, experimental data obtained from these programs are limited. Fig. 10 illustrates the experimental condition of these experiments and required parameter range for ADS design. As shown in the figure, more experimental data, these must be taken parametrically and systematically, are required to perform the detailed design of the ADS. TEF-T aims at preparation of the database required for ADS design. Another important component for ADS is a beam window. Beam window forms a boundary between an accelerator and a subcritical core. Beam window suffers heavy irradiation of proton and spallation neutron, mechanical stress caused by the pressure difference between the accelerator and flowing Pb–Bi target, thermal stress arising from heat deposition of high energy particles and beam transients (startup, shutdown and beam trip) and chemical interaction with Pb–Bi. It is important to prepare the database to estimate a lifetime of the beam window. So that, the experiments to obtain the design database for beam window are also the important mission of TEF-T. Some technical subjects must be investigated for the high-power spallation target system, e.g., the purification system for spallation products and the polonium, remote handling device for the Pb–Bi system, and so on. Hence, non-radioactive tests described later have been performed at JAERI.
Fig. 10. Irradiation data to be taken in Pb–Bi environment.
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TEF-T mainly consists of a Pb–Bi spallation target, a Pb–Bi cooling system (primary loop), a helium gas cooling system (secondary loop) and an access cell to handle irradiation test pieces. Pb–Bi is filled into a cylindrical vessel made by type 316 stainless steel. An effective size of the vessel is about 15 cm diameter and 60 cm long. Several kinds of target are planned and designed according to the objective of the experiment. One of the target vessels is designed to irradiate ten or more irradiation samples in the flowing Pb–Bi environment. A primary Pb–Bi loop is designed to allow Pb–Bi flow with 2 m/s of a maximum velocity and 450 ◦ C of maximum temperature. Though we selected a type 316 stainless steel as a structural material of the target vessel, other candidate materials can be used according to the result of corrosion test in Pb–Bi loop. Target vessel is mounted on a movable trolley and is to be withdrawn to the access cell after the irradiation. The access cell has functions to replace target vessel, to clean up residual Pb–Bi to reduce exposure dose by the spallation products, and to pick up irradiated material test pieces remotely. The primary cooling devices are also located in the access cell to make a path of the loop short and improve maintainability. A preliminary analysis of the Pb–Bi target neutronics was performed. Pb–Bi (45%Pb–55%Bi) is filled in a cylindrical vessel made by type 316 stainless steel. Average Pb–Bi temperature is assumed to 400 ◦ C. Thickness of the vessel is set to 1 mm. A sample holder for the irradiation samples, which are to be installed in the target, is not considered at this analysis. ATRAS code system was used for the analysis. The cutoff energy of the spallation calculation for proton and neutron were set at 20 MeV. A transport analysis of the neutrons below the cutoff energy was done by P3 –S8 approximation. Figure 11 shows a two-dimensional R–Z analysis model. Figure 12 indicates axial distributions of the annual displacement per atom (DPA) of type 316 stainless steel at various radial positions. A radiation dose over 10 DPA is observed at the depth from 3 to 14 cm. The figure indicates that the Pb–Bi target of TEF-T has enough performance to irradiate samples at ADS operating condition by adjusting the beam profile. A preliminary estimation of the beam window lifetime was also performed. Parameters to determine the heat deposition distribution are the same as those of
Fig. 11. Two-dimensional analysis model of TEF-T spallation target.
previous neutronics analysis. A temperature distribution and a flow vector of the Pb–Bi were delivered by the preliminary thermal-hydraulic analysis. From the result, average servicing temperature of 400 ◦ C and average flow speed of 0.7 m/s were obtained while the maximum temperature of the beam window was kept less than 600 ◦ C. Based on the temperature distribution of the beam window, structure analysis was performed. The maximum stress in the beam window that occurs at transient period such as beam on/off or beam trip is about 95 N/mm2 . From the stress analysis result, lifetime of the window is estimated about 4000 h and the maximum cycle of beam on/off (including beam trip) is also estimated as about 104 times. Detailed thermal and structural analysis is now underway. In the viewpoint of engineering application of Pb–Bi, there are many key issues, which should be solved before the construction of TEF-T. They
Fig. 12. Axial DPA distribution of 316SS irradiation sample.
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Fig. 13. Material corrosion test device.
Fig. 14. Liquid Pb–Bi loop.
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are materials problems and handling techniques of flowing Pb–Bi. To control these technical issues, JAERI performs two experimental studies with the material corrosion test device and the liquid Pb–Bi loop. A material corrosion test device, which shown in Fig. 13, can perform a corrosion test of structural materials in stagnant eutectic Pb–Bi. A first corrosion test in stagnant Pb–Bi has done with various materials (2.25Cr–Mo steel, F82H, Mod. 9Cr–1Mo steel, 14Cr–16Ni–2Mo steel, type 410 and 430 stainless steel, pure iron and pure molybdenum) at 550 ◦ C. Oxide films formed on the surface of the materials during the corrosion test for 500–3000 h in oxide-saturated/controlled Pb–Bi. It was found that the thickness of the oxide films tends to decrease with the chromium content in the steels. It is also observed that the oxygen films on 2.25Cr–Mo steel, F82H, Mod.9Cr–1Mo steel and 14Cr–16Ni–2Mo steel is consist of two layers, Fe oxide and Cr–Fe oxide. A temperature of Pb–Bi spallation target in TEF-T ranges around 450 ◦ C maximally in the flowing condition at a speed about 1 m/s. Constructed liquid Pb–Bi loop illustrated in Fig. 14 has operated to simulate the designed spallation target condition. An electromagnetic pump and an electromagnetic flow meter are equipped to validate a potential application of Pb–Bi to TEF. Tube type specimen made of type 316 austenitic stainless steel is installed in the flowing line. The loop has been operated over 9000 h at the argon gas environment. During the operation, maximum temperature, temperature difference and flow rate of the Pb–Bi is set to 450, and 50–100 ◦ C and 5 l/min, respectively. Test section of the loop was
inspected every 3000 h with different operation condition. About 100 m of corrosion was observed at the first operation with type 316 stainless steel sample.
6. High intensity proton accelerator development As mentioned in the previous section, the proton accelerator for the ADS should have the power of more than 20 MW, which is ten times higher than the currently existing accelerator. The most crucial issue to achieve such high power is how the beam loss can be reduced to the acceptable level. Moreover, very high efficiency should be achieved to assure the self-sustainability for electricity of the whole system. Taking into account of these conditions, the superconducting linear accelerator (SC-LINAC) is regarded as the most promising choice. The SC-LINAC consists of a series of “cryomodules”, which contain two units of superconducting cavities made of high-purity niobium as shown in Fig. 15. The development of the SC-LINAC has been carried out stepwise in JAERI. As the first step, a single-cell cavity was fabricated and tested, and the maximum surface peak field of 51 MV/m was achieved. A five-cell cavity was then fabricated and tested so that the maximum surface peak field of 40 MV/m was recorded (Ouchi, 2002). As the next step, two units of nine-cell cavities was fabricated and mounted in a cryomodule to demonstrate the good performance as a total system. The demonstration will start from 2004. In addition to above mentioned development, JAERI has started the J-PARC Project as already shown in
Fig. 15. Schematic view of 9-cell cryomodule.
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Fig. 16. Roadmap toward the realization of ADS.
Fig. 7. As the first phase of this project, a proton LINAC with 0.33 mA × 400 MeV and two proton synchrotrons with 0.33 mA × 3 GeV and 0.015 mA × 50 GeV, respectively, are under construction. Through the experience of the construction of a 400 MeV linear accelerator, we can accumulate the technology for the low energy part of LINAC. In the second phase of this project, SC-LINAC will be constructed to upgrade the proton energy from 400 to 600 MeV. Then the 600 MeV proton beam will be introduced into the Transmutation Experimental Facility.
7. Conclusion The roadmap to realize the ADS is illustrated in Fig. 16. After the basic R&D mentioned above and the experiments in the TEF, an experimental ADS with thermal power of 80 MW is considered to become necessary in late 2010s to demonstrate the feasibility of the ADS from engineering aspects. The experimental ADS will be operated by MOX fuel at first and the fuel will be gradually altered to MA nitride fuel which will be supplied from the fuel fabrication pilot plant. The demonstration of the MA transmutation will be completed by 2030, including the reprocessing of the nitride fuel irradiated in the experimental ADS. The ADS is the innovative and flexible nuclear system to incinerate the long-lived nuclear waste. It is also considered to be used for energy production and for 233 U production from 232 Th. The ADS is, there-
fore suitable for many kinds of scenarios for nuclear power development. This fact means that the ADS can be deployed in many nations and hence its research and development can be effectively promoted by international collaborations. Especially, we would like to propose the TEF project as an international collaboration.
Acknowledgements A part of this work was funded by the Ministry of Education, Culture, Sports, Science and Technology (MEXT) of Japan.
References Alcouffe, R.E., Brinkley, F.W., Marr, D.R., O’Dell, R.D., 1990. Users Guide for TWODANT: A Code Package for Two-Dimensional, Diffusion-Accelerated, Neutral-Particle Transport. LA-10049-M. Bauer, G.S., Salvatores, M., Heusener, G., 2001. MEGAPIE, a 1 MW pilot experiment for a liquid metal spallation target. In: Proceedings of the Fifteenth Meeting of the International Collaboration on Advanced Neutron Sources, ICANS-XV, Tsukuba, Japan, 6–9 November, 2000, JAERI-Conf 2001-002 (KEK Proceedings 2000-22), vol. II, p. 1146. CCC-459, 1980. BOLD VENTURE IV. A Reactor Analysis Code System, Version IV. CCC-545, 1990. SCALE-4 A Modular Code System for Performing Standardized Computer Analysis for Licensing Evaluation.
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Kim Y., Park, W.S., Hill, R.N., Taiwo T.A., Yang, W.S., 2002. An investigation of subcriticality level in accelerator-driven system. In: Proceedings of International Conference on the New Frontiers of Nuclear Technology: Reactor Physics, Safety and High-Performance Computing, PHYSOR 2002. Lebrat, J.F., Soule, R., Martini, M., 1999. Experimental Investigation of Multiplying Subcritical Media in Presence of an External Source Operating in Pulsed or Continuous Mode: the MUSE-3 Experiment. In: Proceedings of the Third International Conference on Accelerator Driven Transmutation Technologies and Applications, ADTTA99, 7–11 June, 1999, Prague, Czech Republic. Minato, K., Arai, Y., Akabori, M., Nakajima, K., 2001. Research on Nitride Fuel for Transmutation of Minor Actinides. ANS Topical Meeting, AccApp/ADTTA 2001, 11–15 November, 2001, Reno, USA. Nakagawa, T., Shibata, K., Chiba, S., Fukahori, T., Nakajima, Y., Kikuchi, Y., Kawano, T., Kanda, Y., Ohsawa, T., Matsunobu, H., Kawai, M., Zukeran, A., Watanabe, T., Igarashi, S., Kosako, K., Asami, T., 1995. Japanese evaluated nuclear data library version-3 revision-2: JENDL-3.2. J. Nucl. Sci. Technol. 32, 1259. O’Dell, R.D., 1977. Standard Interface Files and Procedures for Reactor Physics Codes, Version IV. LA-6941-MS. OECD/NEA, 2002. Accelerator-Driven Systems (ADS) and Fast Reactors (FR) in Advanced Nuclear Fuel Cycles—A Comparative Study. Oigawa, H., Sasa, T., Ikeda, Y., Kikuchi, K., Maekawa, F., Meigo, S., Kasugai, Y., Tsujimoto, K., Nishihara, K., Konno, C., Kai, T., Takano, H., Yamane, T., 2001. Conceptual Design of Transmutation Experimental Facility. International
Conference on Back-End of the Fuel Cycle, GLOBAL2001, 10–13 September, 2001, Paris, France. Ouchi, N., 2002. R&D status of superconducting proton LINAC and KEK/JAERI high intensity proton accelerator project. In: Proceedings of the Third International Workshop on the Utilization and Reliability of High Power Proton Accelerators, HPPA2002, 12–16 May, 2002, Santa Fe, USA. Sasa, T., Tsujimoto, K., Takizuka, T., Takano, H., 1999. Accelerator-driven Transmutation Reactor Analysis Code System—ATRAS. JAERI-Data/Code 99-007. Takada, H., Yoshizawa, N., Kosako, K., Ishibashi, K., 1998. An Upgrade Version of the Nucleon Meson Transport Code: NMTC/JAERI97. JAERI-Data/Code 98-005. Takano, H., Nishihara, K., Tsujimoto, K., Sasa, T., Oigawa, H., Takizuka, T., 2000. Transmutation of long-lived radioactive waste based on double-strata concept. Progress Nucl. Energy 37, 371. Tanaka, K., Maeda, K., Koyama, S., 2002. Post Irradiation Examination of Uranium–Plutonium Mixed Nitride Fuels for Fast Reactor—Destructive Examination of Nitride Fuel. JNC TN9400 2002-001. The Joint Project Team of JAERI and KEK, 1999. The Joint Project for High-Intensity Proton Accelerators. JAERI-Tech 99-056 (KEK Report 99-4, JHF-99-3). Tsujimoto, K., Sasa, T., Nishihara, K., Takizuka, T., Takano, H., 2000. Accelerator-driven system for transmutation of high-level waste. Progress Nucl. Energy 37, 339. Tsujimoto, K., Sasa, T., Nishihara, K., Oigawa, H., Takano, H., 2004. Neutronics Design for Lead-Bismuth Cooled AcceleratorDriven System for Transmutation of Minor Actinide. J. Nucl. Sci. Technol. 41, 21.
Research and development on accelerator-driven transmutation system at JAERI Toshinobu Sasa∗ , Hiroyuki Oigawa, Kazufumi Tsujimoto, Kenji Nishihara, Kenji Kikuchi, Yuji Kurata, Shigeru Saito, Masatoshi Futakawa, Makoto Umeno, Nobuo Ouchi, Yasuo Arai, Kazuo Minato, Hideki Takano Japan Atomic Energy Research Institute, 2-4, Shirakata-Shirane, Tokai, Ibaraki 319-1195, Japan Received 8 May 2003; received in revised form 3 October 2003; accepted 25 November 2003
Abstract Japan Atomic Energy Research Institute carries out research and development on accelerator-driven system (ADS) to transmute minor actinides and long-lived fission products in high-level radioactive waste. The system is composed of high intensity proton accelerator, lead-bismuth spallation target and lead-bismuth cooled subcritical core with nitride fuel. About 2500 kg of minor actinide is loaded into the subcritical core. Annual transmutation amount using this system is 250 kg with 800 MW of thermal output. This transmutation amount corresponds to the amount of minor actinides produced from 10 units of 1GWe power reactors annually. A superconducting linear accelerator with the beam power of 20–30 MW is connected to drive the subcritical core. To maximize the transmutation efficiency, the nitride fuel without uranium, such as (Np, Am, Pu)N, is selected. The nitride fuel irradiated in the ADS is reprocessed by pyrochemical process followed by the re-fabrication of nitride fuel. Many research and development activities are under way and planned in the fields of subcritical core design, spallation target technology, lead-bismuth handling technology, accelerator development, and minor actinide fuel development. Especially, to study and evaluate the feasibility of the ADS from physics and engineering aspects, the transmutation experimental facility (TEF) is proposed under a framework of the High-Intensity Proton Accelerator Project. © 2004 Elsevier B.V. All rights reserved.
1. Introduction In 1988, the Japan Atomic Energy Commission launched a long term R&D program named Options Making Extra Gains from Actinides and fission products (OMEGA) for partitioning and transmutation of long-lived radioactive nuclides. In the OMEGA program, Japan Atomic Energy Research Institute (JAERI) has proposed a double-strata fuel cycle con∗ Corresponding author. Tel.: +81-29-282-6436; fax: +82-29-282-6438. E-mail address: [email protected] (T. Sasa).
cept (Takano et al., 2000) which consists of two fuel cycles; current commercial fuel cycle and dedicated fuel cycle for the transmutation of minor actinides (MA) and long lived fission products (LLFP). By the double-strata fuel cycle that illustrated in Fig. 1, no significant modification is required to the current fuel cycle, and long-lived nuclides are confined into the second-strata small cycle that is optimized to the transmutation of MA and LLFP. JAERI proposes an accelerator-driven system (ADS) for the effective transmutation of MA and LLFP. When the fuel is mainly composed of MA, a delayed neutron fraction, which influences the safety operation of crit-
0029-5493/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.nucengdes.2003.11.033
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In this paper, research and development (R&D) on the ADS at JAERI is reviewed and future plans are also presented.
2. Code development for ADS neutronic performance analysis
Fig. 1. Double strata fuel cycle concept.
ical reactor, becomes lower than that of conventional nuclear reactors. In the case of ADS, the delayed neutron fraction does not directly affect the operation in comparison with a critical reactor because of the subcriticality of the system. There also exists a wide margin of reactivity to install various compositions of MA that are related to the burn-up profile and the types of spent fuel. JAERI proposes a lead–bismuth (Pb–Bi) target/coolant system as a primary candidate of the ADS (Tsujimoto et al., 2000). A proton beam of 1.5 GeV–20 MW is injected and the system is designed to generate 800 MW of thermal power. To realize the ADS, there are many technical subjects; the neutronics of the subcritical core driven by spallation neutrons, the engineering application of the high power spallation target, the development and the operation of the intense proton accelerator, MA nitride fuel fabrication and so on. To solve these technical issues relevant to the ADS development, construction of the transmutation experimental facility (TEF) is planned under the Japan Proton Accelerator Research Complex (J-PARC) Project that is directed by JAERI and High Energy Accelerator Research Organization (KEK) (The Joint Project Team of JAERI and KEK, 1999).
The incident particle of ADS is a proton with energy around 1 GeV and reactions in spallation target mainly occur in the energy range above 100 MeV. Reactions in such high energy region are different from those considered in conventional reactor analysis. On the other hand, in the fuel surrounding the target, most of reactions occur below several tens MeV. For the design study of ADS, calculations in the wide energy range from electron volt or kilo electron volt up to giga electron volt must be performed to analyze specific neutronics parameters such as spallation neutron yield from the spallation target, spatial and energy distribution of the spallation neutrons, heat deposition distribution, time evolution of the isotope composition of the fuel and the subcriticality of the core, particle flux and power density distribution in the subcritical core, decay heat of the spallation target and fuel, coolant void reactivity, Doppler coefficient and so on. To analyze these parameters, an analysis code system named “Accelerator-driven Transmutation Reactor Analysis code System (ATRAS)” to analyze the neutronics and burn-up properties of ADS was developed (Sasa et al., 1999). ATRAS is an integrated code system that performs the following analyses: • spallation, evaporation and high energy fission reactions in high energy region; • proton, neutron and pion transport in high energy region; • neutron reactions and transport in low energy region; and • core burn-up in low energy region. The structure of the ATRAS is illustrated in Fig. 2. Analysis codes included in ATRAS are connected to each other through CCCC format binary file (O’Dell, 1977). In ATRAS, hadronic cascade processes that occur in the energy range from MeV to GeV are calculated with the NMTC/JAERI97 (Takada et al., 1998).
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Fig. 2. Structure of the ATRAS code system.
NMTC/JAERI97 calculates hadronic cascade processes, such as a intra-nuclear cascade process, an evaporation process and a high energy fission process. An isobar model and a pre-equilibrium model can also be considered. A high energy fission model, nucleon–nucleon reaction cross sections and level density parameters were revised and applied to the NMTC/JAERI97. When neutrons produced from hadronic cascade processes are slowed down below a cut-off energy, that can be arbitrary defined by user, they are scored into a neutron history file. The position, direction, energy and importance of the cut-off neutrons are recorded. The FSOURCE code was developed to create a fixed neutron source file for a succeeding neutron transport analysis by the deterministic method. FSOURCE generates the spatial, energy and angular distributions of the cut-off neutrons from the history file. The angular distribution of the cut-off neutrons is expressed in the form of a Legendre polynomial. The number of energy groups and the order of the Legendre polynomial can be arbitrary specified by user. To transport the neutrons below cutoff energy, the two-dimensional discrete ordinate transport code TWODANT (Alcouffe et al., 1990) is prepared. It is difficult to solve fixed neutron source problem with
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fissile material by Monte Carlo method. Source neutrons are multiplied as a function of neutron multiplication factor and this requires very long computation time to obtain the results. Therefore, for the calculation models containing fissile material, a deterministic analysis code TWODANT is selected and included into ATRAS. One unique function of ATRAS is its capability of burn-up analysis for accelerator-driven systems. It is important to determine the burn-up characteristics of ADS transmutor, since it specifies the efficiency of transmutation. And it should be ensured that the burn-up reactivity change does not cause the core to become critical. The BURNER code, the burn-up calculation module in the VENTURE (CCC-459, 1980) code system, is included into ATRAS. When the user uses BURNER together with TWODANT, it is possible to obtain the burn-up characteristics by using the energy spectrum and flux distribution taking account of the spallation neutron source. In the BURNER code, the user can easily modify the burn-up and decay chain of the nuclides and apply the latest data to the analysis. The program CHFUEL was developed to simulate the fuel exchange at the end of the burn-up cycle. The neutron group cross section set for the ATRAS code system was prepared from the JENDL-3.2 (Nakagawa et al., 1995) cross section library. About 150 nuclides that are necessary to analyze the JAERIproposed ADS were selected from the JENDL-3.2 library. Higher actinides such as Bk and Cf, long-lived fission products and lanthanides that would mix with MA in a dry reprocessing process were also included. Average cross sections of fission products were prepared as a lumped fission product. These lumped fission product cross sections are used to consider the nuclides which are not explicitly considered in the burn-up chain. Nuclides required for the analysis of the systems using 232 Th–233 U fuel were also prepared. The effective cross sections for the deterministic neutron transport and burn-up calculation in the low energy region are prepared by the CSAS module in the SCALE-4 (CCC-545, 1990) code system. Heterogeneity of the fuel pin configuration and correction of the self-shielding factor can be considered to construct the effective cross section files. A utility program MKISO was prepared to convert the effective microscopic cross-section file from the SCALE standard AMPX format to the CCCC format.
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To obtain the neutronics and burn-up characteristics of ADS, several calculation codes in ATRAS are used. To facilitate the data input, we developed a pre-processing program named “ATRAS driver” and included it into ATRAS. The user needs to specify the calculation model only once into the input data file of the ATRAS driver. Then, the ATRAS driver creates input data files for the calculation codes used in the analysis. Parameters those are required for the heterogeneous cell calculation and the analysis by TWODANT can be specified into the input data file of the ATRAS driver. The ATRAS code system adopts the CCCC format binary files to save disk space and access time, but these files are unreadable for the user. Furthermore, some calculation results like the neutron energy spectrum are listed in separate files from the hadronic cascade code and neutron transport code. A post-processing program “ATRAS utility” was created to read the binary files and calculate the results such as a particle energy spectrum from high energy region to low energy region, reaction rates and actinide inventories at each burn-up step. The decay heat and the radiotoxicity of residual MA in the spent fuel can also be analyzed by the ATRAS utility.
3. ADS transmutation plant design The reference ADS design proposed by JAERI (Tsujimoto et al., 2000) is the 800 MWth fast subcritical core fueled with MA nitride, cooled by Pb–Bi eutectic and driven by the spallation neutron source using Pb–Bi target and proton accelerator as shown in Fig. 3. About 250 kg of MA can be burned annually by fission reactions, which corresponds to the amount of MA produced in 10 Units of LWRs whose burn-up is 33,000 MWD/t. The current reference design of the subcritical core consists of one fuel zone. It is convenient to manage the spent fuel and fuel reloading. However, it also gives rather higher power peaking value than that of multi fuel zone core. To reduce the peaking factor especially for the radial one, two approaches were examined. First method is separation of fuel section into two zones by changing Pu mixing ratio. Another way is location of Pb–Bi buffer zone between the spallation target section and the fuel section. Fig. 4 shows a
Fig. 3. Conceptual design of ADS (800 MWth).
comparison of radial power density distribution at the beginning of first cycle. From the further analysis results, latest core configuration illustrated in Fig. 5 is arranged (Tsujimoto et al., 2004).
Fig. 4. Comparison of radial power distribution.
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Fig. 5. Subcritical core configuration.
In this reference design, maximum value of the effective multiplication factor, keff , is set at 0.95. To achieve the above mentioned thermal power with this keff , a high-power proton beam, at least 22 MW, is required. Moreover, taking account of the burn-up reactivity swing, keff will be deteriorated to 0.93, where a proton beam of about 30 MW is necessary. The adequate subcritical level of the ADS must be defined by considering several reactivity factors (Kim et al., 2002), such as system cool down from operation temperature to refueling temperature, unusual coolant temperature rise and coolant intrusion into beam duct, and uncertainties caused from measurement and calculation. Based on our reference design of ADS, sum of the estimated reactivity factors were determined about 2.5% k/k. It means that the initial keff of our proposed ADS can increase from 0.95 to 0.97. The re-arrangement of the system parameters is in progress. To supply a powerful proton beam, a superconducting linear accelerator should be developed. Considering the energy efficiency of a neutron source, the specification of the proton beam, 1.5 GeV × 15–20 mA,
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is temporally chosen, though the acceleration energy should be finally determined by taking into account of the factors such as the cost of the accelerator and the beam current density on the beam window. As for the spallation target, eutectic Pb–Bi alloy was chosen out of several heavy metals, such as Hg and W, because of its good thermal property; the melting point of 398 K and the boiling point of 1943 K. Although Pb–Bi eutectic is comparatively corrosive to steel at the high temperature above 700 K, Russia has a lot of experience to use it as the coolant of reactors in submarines. Many countries including Japan have therefore started research and development to establish the technology for the usage of Pb–Bi as the spallation target. Nitride fuel has the advantage of accommodating various MA with a wide range of composition besides good thermal properties. Further it can support hard neutron spectrum suitable for effective transmutation of MA. For avoiding the production of hazardous 14 C, however, 15 N enriched nitrogen to 99.9% shall be used in the nitride fuel. In our reference design, tank-type structure is adopted. The inlet and the outlet temperatures of the primary Pb–Bi coolant are 603 and 703 K, respectively. Steam generators can be directly inserted in the reactor vessel because Pb–Bi is chemically compatible with water. The electric power is about 250 MW, which means the ADS can be a self-sustaining system provided the efficiency of the accelerator is more than 15%. From the result of the comparative study of ADS and fast reactor in advanced fuel cycle (OECD/NEA, 2002), efficiency of the accelerator is assumed to be 45%. In our reference design, efficiency is assumed to 30–40%. By using superconducting cavity by continuous wave operation, this value will be accomplished. To realize the ADS, JAERI has conducted the R&D in the fields of the proton accelerator, the Pb–Bi technology and the MA nitride fuel. Moreover, to demonstrate the feasibility of the ADS in the reactor physics aspects and target engineering aspects, a new experimental facility, the TEF is planned.
4. Fuel for MA transmutation The basic properties of the metallic and the nitride fuels with MA have been measured for about ten years
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(Minato et al., 2001). Through such studies, MA nitride has been chosen as the first candidate for the dedicated transmutation system because of its possible mutual solubility among the actinide mononitrides and its good thermal properties. As the R&D for the fuel fabrication, high-purity nitrides such as (Np, Pu)N, AmN and (Cm, Pu)N were synthesized by the carbo-thermic reduction method and their material properties have been measured. The irradiation test of such MA nitride fuel has not been performed yet, while (U, Pu)N fuel was irradiated in the experimental fast test reactor JOYO under the joint research with the Japan Nuclear Cycle Development Institute (JNC), and no failure of fuel pins was found as shown in Fig. 6 (Tanaka et al., 2002). As a reprocessing of the irradiated MA nitride fuel, pyrochemical process has been studied in JAERI. The pyrochemical process has several advantages over the wet process in treating such a dedicated fuel for transmutation including recycling feasibility of 15 N used in the nitride fuel. In the laboratory scale test, metallic Pu and Np were successfully recovered from non-irradiated PuN and NpN, respectively, by the molten-salt electrorefining technique.
5. Transmutation Experimental Facility (TEF) To study the basic characteristics of the ADS and to demonstrate its feasibility from viewpoints of the reactor physics and the spallation target engineering,
Fig. 6. Cross-section of (U, Pu)N fuel pin (40 GWd/t).
JAERI plans to build the TEF in the Tokai site under a framework of the J-PARC Project as illustrated in Fig. 7. TEF consists of two buildings: the transmutation physics experimental facility (TEF-P) and the ADS target test facility (TEF-T) as shown in Fig. 8. TEF-P is a zero-power critical facility where a low power proton beam is available to research the reactor physics and the controllability of the ADS. TEF-T is a material irradiation facility which can accept a maximum 600 MeV–200 kW proton beam into the spallation tar-
Fig. 7. Japan proton accelerator research complex (J-PARC).
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Fig. 8. Transmutation experimental facility (TEF).
get of Pb–Bi eutectic. The outline of TEF-P and TEF-T is presented hereafter (Oigawa et al., 2001). 5.1. Transmutation physics experimental facility (TEF-P) Several kinds of experiments to investigate neutronic performance of the ADS have been performed worldwide. Some of them are for the characteristics of the subcritical system such as MUSE program (Lebrat et al., 1999). MASURCA, a critical assembly for the fast reactor in France, is used with newly developed DT and DD neutron source. In Japan, subcritical experiments were just started at the fast critical assembly (FCA) by using a 252 Cf neutron source. Installation of DT neutron source to the FCA is also planned. Moreover, many experimental studies have been performed to the neutronics of the spallation neutron source with various target material such as lead, tungsten, mercury and uranium. These experiments for spallation target are not directly related to the ADS, but they are also useful to validate the neutronic characteristics of ADS. There has been, however, no experiment aiming at the research and the demonstration of the fast subcritical system combined with a spallation source. So the purpose of the TEF-P is divide roughly into three
subjects: (1) reactor physics aspects of the subcritical core driven by a spallation source, (2) demonstration of the controllability of the subcritical core including a power control by the proton beam power adjustment, and (3) investigation of the transmutation performance of the subcritical core using certain amount of MA and LLFP. The details of the experimental items are described later. The most serious problem to build a new nuclear facility is how to prepare the fuel, since tons of low-enriched uranium or plutonium are necessary to make the core critical or near-critical (e.g., keff = 0.95) in the fast neutron system. We expect to use the plate-type fuel of the FCA in JAERI/Tokai, or preferably to merge FCA into TEF-P. About two tons of metallic fuel of enriched uranium and plutonium will be available as well as natural and depleted uranium. Various simulation materials required simulating fast reactor and ADS such as lead and sodium for coolant, tungsten for solid target, ZrH for moderator, B4 C for absorber, and AlN for simulating nitride fuel will be prepared. TEF-P is therefore designed with referring to FCA; the horizontal table-split type critical assembly with a rectangular lattice matrix. Fig. 9 shows a conceptual view of the assembly. Proton beam was intro-
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Fig. 9. Conceptual view of TEF-P critical assembly.
duced horizontally from the center of the fixed half assembly. In the experiment with the proton beam, keff , of the critical assembly will be kept less than 0.98. One proton with energy of 600 MeV produces about 15 neutrons by the spallation reaction with heavy metal target such as lead. The 10 W proton beam corresponds to the source strength of 1.5 × 1012 neutrons/s, which is strong enough to measure the power distribution at the deep subcritical state such as keff = 0.90. In the conceptual design of the facility, the shielding property for high energy neutrons is calculated. About 2 m thickness of concrete shield is necessary even when the core is surrounded by about 1m of lead reflector. Safety aspect of the facility is also extensively studied. The prompt critical accident can be terminated without fuel melting by the reactor scram system with multiplicity and variety. The unexpected introduction of the 10 W beam into the critical state also can be terminated safely with the reactor scram. Using this TEF-P facility, many experimental studies are planned. The research and development (R&D) to be carried out at TEF-P is described below. As for the neutronics in the subcritical system, power distribution, keff , effective neutron source strength, and neutron spectrum are measured by
changing parametrically the subcriticality and the spallation source position. The material of the target will also be altered with Pb, Pb–Bi, W, and so on. The reactivity worth is also measured for the case of the coolant void and the intrusion of the coolant into the beam duct. It is desirable to make the core critical in order to ensure the quality of experimental data of the subcriticality and the reactivity worth. As for the demonstration of the hybrid system, feedback control of the reactor power is examined by adjusting the beam intensity. Operating procedures at the beam trip and the re-start are also examined. As for the transmutation characteristics of MA and LLFP, fission chambers and activation foils are used to measure the transmutation rates. The cross section data of MA and LLFP for high energy region (up to several hundreds MeV) can be measured by the time-of-flight (TOF) technique with the proton beam of about 1ns pulse width. Several kinds of MA and LLFP samples are also prepared to measure their reactivity worth, which is important for the integral validation of cross section data. Ultimate target of the facility is to install a partial mock-up region of MA nitride fuel with air cooling to measure the physics parameters of the transmutation system. The central rectangular region (28 cm×28 cm) will be replaced with a hexagonal subassembly which
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can partially load the pin-type MA fuel around the spallation target. The distinguished points of TEF-P in comparison with existing experimental facilities can be summarized as follows: (1) both the high energy proton beam and the nuclear fuel are available, (2) the maximum neutron source intensity of about 1012 n/s is strong enough to perform precise measurements even in the deep subcritical state (e.g., keff = 0.90), and, is low enough to easily access to the assembly after the irradiation, (3) wide range of pulse width (1 ns–0.5 ms) can be available by the laser charge exchange technique described later, (4) MA and LLFP can be used as a shape of foil, sample and fuel by installing an appropriate shielding and a remote handling devise. 5.2. ADS target test facility (TEF-T) JAERI proposes the ADS using a Pb–Bi for both spallation target and coolant of the fuel region. Pb–Bi is one of the alternative options of the coolant of the fast system and it also has a function of liquid spallation target simultaneously in the ADS. There are, however, many technical issues to use Pb–Bi. To solve them, several R&D programs are proposed. Material irradiation experiment in stagnant Pb–Bi environment has been performed at the SINQ facility in Paul Scheller Institute (PSI), Switzerland. MEGAPIE project (Bauer et al., 2001) is also planned at PSI to
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demonstrate feasibility of Pb–Bi target by using the existing accelerator facilities. According to the limitation of existing equipment of the facility and machine time, experimental data obtained from these programs are limited. Fig. 10 illustrates the experimental condition of these experiments and required parameter range for ADS design. As shown in the figure, more experimental data, these must be taken parametrically and systematically, are required to perform the detailed design of the ADS. TEF-T aims at preparation of the database required for ADS design. Another important component for ADS is a beam window. Beam window forms a boundary between an accelerator and a subcritical core. Beam window suffers heavy irradiation of proton and spallation neutron, mechanical stress caused by the pressure difference between the accelerator and flowing Pb–Bi target, thermal stress arising from heat deposition of high energy particles and beam transients (startup, shutdown and beam trip) and chemical interaction with Pb–Bi. It is important to prepare the database to estimate a lifetime of the beam window. So that, the experiments to obtain the design database for beam window are also the important mission of TEF-T. Some technical subjects must be investigated for the high-power spallation target system, e.g., the purification system for spallation products and the polonium, remote handling device for the Pb–Bi system, and so on. Hence, non-radioactive tests described later have been performed at JAERI.
Fig. 10. Irradiation data to be taken in Pb–Bi environment.
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TEF-T mainly consists of a Pb–Bi spallation target, a Pb–Bi cooling system (primary loop), a helium gas cooling system (secondary loop) and an access cell to handle irradiation test pieces. Pb–Bi is filled into a cylindrical vessel made by type 316 stainless steel. An effective size of the vessel is about 15 cm diameter and 60 cm long. Several kinds of target are planned and designed according to the objective of the experiment. One of the target vessels is designed to irradiate ten or more irradiation samples in the flowing Pb–Bi environment. A primary Pb–Bi loop is designed to allow Pb–Bi flow with 2 m/s of a maximum velocity and 450 ◦ C of maximum temperature. Though we selected a type 316 stainless steel as a structural material of the target vessel, other candidate materials can be used according to the result of corrosion test in Pb–Bi loop. Target vessel is mounted on a movable trolley and is to be withdrawn to the access cell after the irradiation. The access cell has functions to replace target vessel, to clean up residual Pb–Bi to reduce exposure dose by the spallation products, and to pick up irradiated material test pieces remotely. The primary cooling devices are also located in the access cell to make a path of the loop short and improve maintainability. A preliminary analysis of the Pb–Bi target neutronics was performed. Pb–Bi (45%Pb–55%Bi) is filled in a cylindrical vessel made by type 316 stainless steel. Average Pb–Bi temperature is assumed to 400 ◦ C. Thickness of the vessel is set to 1 mm. A sample holder for the irradiation samples, which are to be installed in the target, is not considered at this analysis. ATRAS code system was used for the analysis. The cutoff energy of the spallation calculation for proton and neutron were set at 20 MeV. A transport analysis of the neutrons below the cutoff energy was done by P3 –S8 approximation. Figure 11 shows a two-dimensional R–Z analysis model. Figure 12 indicates axial distributions of the annual displacement per atom (DPA) of type 316 stainless steel at various radial positions. A radiation dose over 10 DPA is observed at the depth from 3 to 14 cm. The figure indicates that the Pb–Bi target of TEF-T has enough performance to irradiate samples at ADS operating condition by adjusting the beam profile. A preliminary estimation of the beam window lifetime was also performed. Parameters to determine the heat deposition distribution are the same as those of
Fig. 11. Two-dimensional analysis model of TEF-T spallation target.
previous neutronics analysis. A temperature distribution and a flow vector of the Pb–Bi were delivered by the preliminary thermal-hydraulic analysis. From the result, average servicing temperature of 400 ◦ C and average flow speed of 0.7 m/s were obtained while the maximum temperature of the beam window was kept less than 600 ◦ C. Based on the temperature distribution of the beam window, structure analysis was performed. The maximum stress in the beam window that occurs at transient period such as beam on/off or beam trip is about 95 N/mm2 . From the stress analysis result, lifetime of the window is estimated about 4000 h and the maximum cycle of beam on/off (including beam trip) is also estimated as about 104 times. Detailed thermal and structural analysis is now underway. In the viewpoint of engineering application of Pb–Bi, there are many key issues, which should be solved before the construction of TEF-T. They
Fig. 12. Axial DPA distribution of 316SS irradiation sample.
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Fig. 13. Material corrosion test device.
Fig. 14. Liquid Pb–Bi loop.
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are materials problems and handling techniques of flowing Pb–Bi. To control these technical issues, JAERI performs two experimental studies with the material corrosion test device and the liquid Pb–Bi loop. A material corrosion test device, which shown in Fig. 13, can perform a corrosion test of structural materials in stagnant eutectic Pb–Bi. A first corrosion test in stagnant Pb–Bi has done with various materials (2.25Cr–Mo steel, F82H, Mod. 9Cr–1Mo steel, 14Cr–16Ni–2Mo steel, type 410 and 430 stainless steel, pure iron and pure molybdenum) at 550 ◦ C. Oxide films formed on the surface of the materials during the corrosion test for 500–3000 h in oxide-saturated/controlled Pb–Bi. It was found that the thickness of the oxide films tends to decrease with the chromium content in the steels. It is also observed that the oxygen films on 2.25Cr–Mo steel, F82H, Mod.9Cr–1Mo steel and 14Cr–16Ni–2Mo steel is consist of two layers, Fe oxide and Cr–Fe oxide. A temperature of Pb–Bi spallation target in TEF-T ranges around 450 ◦ C maximally in the flowing condition at a speed about 1 m/s. Constructed liquid Pb–Bi loop illustrated in Fig. 14 has operated to simulate the designed spallation target condition. An electromagnetic pump and an electromagnetic flow meter are equipped to validate a potential application of Pb–Bi to TEF. Tube type specimen made of type 316 austenitic stainless steel is installed in the flowing line. The loop has been operated over 9000 h at the argon gas environment. During the operation, maximum temperature, temperature difference and flow rate of the Pb–Bi is set to 450, and 50–100 ◦ C and 5 l/min, respectively. Test section of the loop was
inspected every 3000 h with different operation condition. About 100 m of corrosion was observed at the first operation with type 316 stainless steel sample.
6. High intensity proton accelerator development As mentioned in the previous section, the proton accelerator for the ADS should have the power of more than 20 MW, which is ten times higher than the currently existing accelerator. The most crucial issue to achieve such high power is how the beam loss can be reduced to the acceptable level. Moreover, very high efficiency should be achieved to assure the self-sustainability for electricity of the whole system. Taking into account of these conditions, the superconducting linear accelerator (SC-LINAC) is regarded as the most promising choice. The SC-LINAC consists of a series of “cryomodules”, which contain two units of superconducting cavities made of high-purity niobium as shown in Fig. 15. The development of the SC-LINAC has been carried out stepwise in JAERI. As the first step, a single-cell cavity was fabricated and tested, and the maximum surface peak field of 51 MV/m was achieved. A five-cell cavity was then fabricated and tested so that the maximum surface peak field of 40 MV/m was recorded (Ouchi, 2002). As the next step, two units of nine-cell cavities was fabricated and mounted in a cryomodule to demonstrate the good performance as a total system. The demonstration will start from 2004. In addition to above mentioned development, JAERI has started the J-PARC Project as already shown in
Fig. 15. Schematic view of 9-cell cryomodule.
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Fig. 16. Roadmap toward the realization of ADS.
Fig. 7. As the first phase of this project, a proton LINAC with 0.33 mA × 400 MeV and two proton synchrotrons with 0.33 mA × 3 GeV and 0.015 mA × 50 GeV, respectively, are under construction. Through the experience of the construction of a 400 MeV linear accelerator, we can accumulate the technology for the low energy part of LINAC. In the second phase of this project, SC-LINAC will be constructed to upgrade the proton energy from 400 to 600 MeV. Then the 600 MeV proton beam will be introduced into the Transmutation Experimental Facility.
7. Conclusion The roadmap to realize the ADS is illustrated in Fig. 16. After the basic R&D mentioned above and the experiments in the TEF, an experimental ADS with thermal power of 80 MW is considered to become necessary in late 2010s to demonstrate the feasibility of the ADS from engineering aspects. The experimental ADS will be operated by MOX fuel at first and the fuel will be gradually altered to MA nitride fuel which will be supplied from the fuel fabrication pilot plant. The demonstration of the MA transmutation will be completed by 2030, including the reprocessing of the nitride fuel irradiated in the experimental ADS. The ADS is the innovative and flexible nuclear system to incinerate the long-lived nuclear waste. It is also considered to be used for energy production and for 233 U production from 232 Th. The ADS is, there-
fore suitable for many kinds of scenarios for nuclear power development. This fact means that the ADS can be deployed in many nations and hence its research and development can be effectively promoted by international collaborations. Especially, we would like to propose the TEF project as an international collaboration.
Acknowledgements A part of this work was funded by the Ministry of Education, Culture, Sports, Science and Technology (MEXT) of Japan.
References Alcouffe, R.E., Brinkley, F.W., Marr, D.R., O’Dell, R.D., 1990. Users Guide for TWODANT: A Code Package for Two-Dimensional, Diffusion-Accelerated, Neutral-Particle Transport. LA-10049-M. Bauer, G.S., Salvatores, M., Heusener, G., 2001. MEGAPIE, a 1 MW pilot experiment for a liquid metal spallation target. In: Proceedings of the Fifteenth Meeting of the International Collaboration on Advanced Neutron Sources, ICANS-XV, Tsukuba, Japan, 6–9 November, 2000, JAERI-Conf 2001-002 (KEK Proceedings 2000-22), vol. II, p. 1146. CCC-459, 1980. BOLD VENTURE IV. A Reactor Analysis Code System, Version IV. CCC-545, 1990. SCALE-4 A Modular Code System for Performing Standardized Computer Analysis for Licensing Evaluation.
222
T. Sasa et al. / Nuclear Engineering and Design 230 (2004) 209–222
Kim Y., Park, W.S., Hill, R.N., Taiwo T.A., Yang, W.S., 2002. An investigation of subcriticality level in accelerator-driven system. In: Proceedings of International Conference on the New Frontiers of Nuclear Technology: Reactor Physics, Safety and High-Performance Computing, PHYSOR 2002. Lebrat, J.F., Soule, R., Martini, M., 1999. Experimental Investigation of Multiplying Subcritical Media in Presence of an External Source Operating in Pulsed or Continuous Mode: the MUSE-3 Experiment. In: Proceedings of the Third International Conference on Accelerator Driven Transmutation Technologies and Applications, ADTTA99, 7–11 June, 1999, Prague, Czech Republic. Minato, K., Arai, Y., Akabori, M., Nakajima, K., 2001. Research on Nitride Fuel for Transmutation of Minor Actinides. ANS Topical Meeting, AccApp/ADTTA 2001, 11–15 November, 2001, Reno, USA. Nakagawa, T., Shibata, K., Chiba, S., Fukahori, T., Nakajima, Y., Kikuchi, Y., Kawano, T., Kanda, Y., Ohsawa, T., Matsunobu, H., Kawai, M., Zukeran, A., Watanabe, T., Igarashi, S., Kosako, K., Asami, T., 1995. Japanese evaluated nuclear data library version-3 revision-2: JENDL-3.2. J. Nucl. Sci. Technol. 32, 1259. O’Dell, R.D., 1977. Standard Interface Files and Procedures for Reactor Physics Codes, Version IV. LA-6941-MS. OECD/NEA, 2002. Accelerator-Driven Systems (ADS) and Fast Reactors (FR) in Advanced Nuclear Fuel Cycles—A Comparative Study. Oigawa, H., Sasa, T., Ikeda, Y., Kikuchi, K., Maekawa, F., Meigo, S., Kasugai, Y., Tsujimoto, K., Nishihara, K., Konno, C., Kai, T., Takano, H., Yamane, T., 2001. Conceptual Design of Transmutation Experimental Facility. International
Conference on Back-End of the Fuel Cycle, GLOBAL2001, 10–13 September, 2001, Paris, France. Ouchi, N., 2002. R&D status of superconducting proton LINAC and KEK/JAERI high intensity proton accelerator project. In: Proceedings of the Third International Workshop on the Utilization and Reliability of High Power Proton Accelerators, HPPA2002, 12–16 May, 2002, Santa Fe, USA. Sasa, T., Tsujimoto, K., Takizuka, T., Takano, H., 1999. Accelerator-driven Transmutation Reactor Analysis Code System—ATRAS. JAERI-Data/Code 99-007. Takada, H., Yoshizawa, N., Kosako, K., Ishibashi, K., 1998. An Upgrade Version of the Nucleon Meson Transport Code: NMTC/JAERI97. JAERI-Data/Code 98-005. Takano, H., Nishihara, K., Tsujimoto, K., Sasa, T., Oigawa, H., Takizuka, T., 2000. Transmutation of long-lived radioactive waste based on double-strata concept. Progress Nucl. Energy 37, 371. Tanaka, K., Maeda, K., Koyama, S., 2002. Post Irradiation Examination of Uranium–Plutonium Mixed Nitride Fuels for Fast Reactor—Destructive Examination of Nitride Fuel. JNC TN9400 2002-001. The Joint Project Team of JAERI and KEK, 1999. The Joint Project for High-Intensity Proton Accelerators. JAERI-Tech 99-056 (KEK Report 99-4, JHF-99-3). Tsujimoto, K., Sasa, T., Nishihara, K., Takizuka, T., Takano, H., 2000. Accelerator-driven system for transmutation of high-level waste. Progress Nucl. Energy 37, 339. Tsujimoto, K., Sasa, T., Nishihara, K., Oigawa, H., Takano, H., 2004. Neutronics Design for Lead-Bismuth Cooled AcceleratorDriven System for Transmutation of Minor Actinide. J. Nucl. Sci. Technol. 41, 21.