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Activation analyses for the IFMIF-Liquid Breeder Validation Module (LBVM)
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Activation analyses for the IFMIF-Liquid Breeder Validation Module (LBVM) F. Mota ∗ , N. Casal, A. Mas, A. García, J. Molla, A. Ibarra. Laboratorio Nacional de Fusión por Confinamiento Magnético – CIEMAT, 28040 Madrid, Spain
h i g h l i g h t s • • • •
The objective of LBVM is to test functional materials related to liquid breeders for DEMO. An activation analysis has been performed for the whole LBVM of IFMIF. The results have been used to define the dismantling strategy of the module. Appear high radioactive and toxic radioisotopes such as Po210 and tritium.
a r t i c l e
i n f o
Article history: Received 31 July 2013 Received in revised form 17 March 2014 Accepted 20 March 2014 Available online xxx Keywords: IFMIF LBVM Activation Safety hazards Lithium–lead Liquid breeders
a b s t r a c t The Liquid Breeder Validation Module (LBVM) will be one of the medium flux irradiation modules of the International Fusion Materials Irradiation Facility (IFMIF) neutron source. The objective of this module – presently under design – is the test of functional materials related to liquid breeders for future nuclear fusion power reactors (DEMO). This paper aims to describe the activation analyses performed to estimate the radioactive inventory and the expected contact dose from the activated materials of the module following a 345 day irradiation period. These calculations supply valuable information for different aspects related to the design of the module, such as the safety evaluation and the waste management and disassembly plan. The neutron transport calculations have been performed using the McDeLicious code. The ACAB nuclear inventory code, with the activation nuclear libraries EAF-2007, has been used for the activation analyses. The main results point out that the contact dose of the LBVM materials is much higher than the hands-on-limits, as expected. Therefore, remote handling operations are requested for disassembling the module. It is important to remark that after 8 h decay time, the contact dose rate of the LBVM decreases 76% for the EUROFER steel components and 46% for the 316 LN components. Regarding the isotopic inventory, although the main activation comes from the module steel structures, the production of tritium and Po-210 in the lithium lead inside the experimental capsules deserved a careful analysis. © 2014 Elsevier B.V. All rights reserved.
1. Introduction Materials for future fusion reactors (DEMO) will be exposed to a particular hostile environment as a consequence of the intense radiation field created during the nuclear reaction. Therefore, the assessment of how this radiation may affect the physical properties of materials is fundamental for the nuclear fusion development. Hence, the main aim of the International Fusion Materials Irradiation Facility (IFMIF) [1] will be to provide an intense neutron source with adequate energy spectrum to irradiate candidate materials to
∗ Corresponding author. Tel.: +34 91 346 6578; fax: +34 91 346 6068. E-mail address: [email protected] (F. Mota).
test their suitability for use in a future nuclear fusion power reactor (DEMO). The main objective is to qualify materials with a high radiation resistant and low activation. The irradiation area of IFMIF is divided into three irradiation areas with high, medium and low neutron flux. The structural materials will be irradiated in the High Flux Test Module (HFTM) [1,2] since the irradiation parameters fit accurately with those of the most irradiated structural materials in a future nuclear fusion reactor. The medium flux irradiation area will be dedicated to hold several experiments to irradiate functional materials and other materials related to different breeder blanket concepts such as solid breeders (in the Tritium Release Test Module (TRTM)) [1,3], or liquid breeders (in the Liquid Breeder Validation Module (LBVM)) [4–6]. The LBVM will be focused on, as first approach, experiments
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Fig. 1. LBVM conceptual design.
related to the Helium Cooled Lithium Lead (HCLL) DEMO concept, which is based on liquid lithium–lead (PbLi) as breeder material. However, the possibility to tackle experiments related to other liquid breeder concepts could be assessed in the future. This paper is an analysis of the radioactive inventory and the expected activation gamma dose from the activated materials of the LBVM of IFMIF developed in the framework of the Engineering Validation and Engineering Design Activities (EVEDA) phase. These calculations supply valuable information for different aspects related to the design of the module, such as the safety evaluation and the waste management and disassembly plan.
an external diameter of 22 mm, an internal diameter of 20 mm and 80 mm height. The total inner volume of each cylindrical capsule is about 25 cm3 and it will contain about 15.7 cm3 of PbLi. The position of the capsules inside the irradiation module is such that the height of the PbLi volume will occupy the whole theoretical height of the beam footprint (50 mm) to maximize the irradiation volume. Fig. 1 shows a CAD drawing of the LBVM, where the main components have been identified. The detailed description of the module design can be found in the report [7].
2. LBVM
3.1. MCNP geometrical model
The present configuration of the LBVM (Fig. 1) consists basically on a stainless steel 316LN container capable of housing 16 cylindrical rigs. Each experimental rig will house one cylindrical experimental capsule partially filled with PbLi and the associated instrumentation. This assembly will rest on the Test Cell support structure by means of the Test Module Interface Head located in the upper part of the module and fixed to the container. The module will require helium cooling lines and helium purge lines (to sweep up the tritium produced in LiPb). These lines, welded to the container, will be connected to the Pipes and Cable Plugs of the Test Cell. The container is basically is a hollow T-shape structure built of stainless steel 316LN capable of housing 16 cylindrical rigs. The container also serves as common collector for the returning He cooling gas. A narrow (1 mm) gap between each rig and its correspondent compartment walls allows the helium cooling gas flow. The rig is the recipient built of SS316LN where the capsule is housed. The central part of the rig has the same shape than the capsule, but a narrow gap (2 mm) between the rig and the capsule allows the circulation of the purge gas. The lower part of each rig is a small diameter tube which is welded to the bottom part of the container and also to the entering purge gas line. The upper part of each rig is also a small diameter tube which is welded to the upper part of the container and also to the exit purge gas line. The capsules are closed recipients that contain the liquid breeder. Each rig will house one experimental cylindrical capsule built of EUROFER steel and partially filled with the liquid breeder (PbLi) and the associated instrumentation. The capsules will have
The model used for nuclear transport calculations is based on the md34 3D Test Cell geometrical reference model [8], including several modifications: (1) the horse shoe, present in the reference model, has been removed; (2) one extended version of the HFTM has been included; (3) in addition, the MCNP model of the LBVM has been introduced. For that, a simplified model of the LBVM CAD model was designed using CATIA/CAD code. Afterward, the MCAM code (developed by FDS Team, China [9]) was used to convert the LBVM CATIA/CAD model into the MCNP geometry. The neutronics model of the LBVM introduced in the Test Cell MCNP geometrical model is shown in Fig. 2. As it can be seen, it has been divided in six different sections from the top to the bottom for the activation calculations. These divisions have been done taking into account the neutron gradient in the vertical direction. The resulting sections have been named “upper” (number 1), “up” (number 2), “centre-up” (number 3), “center” (number 4), centre-down (number 5) and down (number 6) as represented in Fig. 2. In this figure the average neutron fluence rate calculated to each section is also shown. Several locations in the medium flux area of the Test Cell are possible for the LBVM [6,7]. The two more suitable ones are shown in Fig. 3. Although, the best location to reproduce the nuclear fusion irradiation conditions [6] corresponds to the configuration 2 (Fig. 3), the configuration 1 (Fig. 3) with the LBVM directly installed behind of the HFTM is also considered in case is necessary to increase the level of displacement damage in the module. Therefore, the configuration 1 has been used to study the safety issues, since the LBVM will suffer the most extreme irradiation conditions in this location.
3. Computational methodology
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Cu, and the INPE-FZK [16] evaluation for 6 Li and 7 Li [17] have been used in the present analysis. The radioactive isotopic inventory and the expected contact ␥dose from the activated materials of the LBVM were calculated using the nuclear inventory code ACAB. This code was designed by UNED University to perform both activation and transmutation calculations for nuclear applications [18]. For this calculation the activation data library chosen was EAF-2007 [19]. For both neutron transport and activation calculations three materials have been taken into account as main make-up of the LBVM. The materials considered are SS316LN for container, EUROFER for experimental capsules and lithium–lead eutectic alloy (Pb–15 Li) as liquid breeder inside the experimental capsule. The chemical composition of the SS316LN, EUROFER and lithium–lead eutectic alloy considered for the calculations is shown in Table 1. In addition, the composition of the dry air is also presented in the table since, in order to propagate the decay gamma sources, the LBVM is considered isolated in the space with dry air as the atmosphere surrounding the module to emulate the possible environment of the test facility hot cell. The activation results have been calculated for each of sections in which the model has been divided (Fig. 2). In addition, the equivalent absorbed ␥-dose to water surrounded the LBVM has been calculate for evaluate the effect of the decay photon sources in remote handling equipment to establish the dismantling strategy. The procedure to calculate both the materials activation and the maps of gamma absorbed doses is the following:
Fig. 2. Vertical section of the LBVM MCNP geometry. The LBVM is divided in six parts for the activation calculations.
3.2. Neutron transport and nuclear isotopic inventory calculations The neutron transport calculations have been performed by means of McDelicious code [10,11]. This code was developed by FZK (Forchungszentrum Karlsruhe, Germany) as an enhancement to the MCNP5 code [12], to reproduce the neutron source n+ 6,7 Li of IFMIF [13]. The nuclear data library FENDL-3/SLIB release 2 [14] has been used in the neutron transport calculations. However, FENDL-3/SLIB contains nuclear data of a few nuclides evaluated only for neutron energies up to 20 MeV. Thus, the LA150n [15] library for 1 H and
• Neutron transport calculations were developed by means of the McDelicious code in the MCNP 3D model of Test Cell, configuration 1, to obtain the averaged neutron spectra on each section of the model (Fig. 2). The volume considered to calculate the average neutron spectrum is defined by the horizontal area corresponding to the 4 central rigs of the front row of the LBVM (dotted line, Fig. 4) and the whole height of each section of the LBVM. In this way, the neutron spectrum obtained will determine an upper bound of the radiation level suffered by each section of the LBVM, i.e. a conservative activation calculation has been considered. • Once the neutron spectrum of each LBVM section has been calculated, the ACAB code has been used to calculate the isotopic inventory and decay photon sources generated on each section and for each relevant material. The ACABAN code, developed by neutronics team of the Fusion National Laboratory (CIEMAT), has been used to analyze the output files of the ACAB code. Both, the isotopic inventory and the decay photon sources have been calculated assuming 345 days of full power of neutron irradiations and,
Fig. 3. Test cell configurations suitable to irradiated the LBVM [6]. Configuration 1: the LBVM is located just behind the HFTM; Configuration 2: the shifter plate is located behind the HFTM and the LBVM behind the NSS module. The configuration chosen to the activation calculations is the configuration 1. HFTM, High Flux Test Module; NSS, Neutron Spectral Shifter; LBVM, Liquid Breeder Validation Module; TRTM, Tritium Release Test Module; LFTM, Low Flux Test Module.
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Table 1 Chemical composition of SS316LN, EUROFER and eutectic Pb–15 Li alloy with impurities (wt %) and dry air (at %).
Fe C Mn Ni Cr Mo N P S Si Cu Ta Ti B Nb Co Al O K Bi V Zr Ag Cd Sn Sb Ba Tb W Ir Pb As
SS316LN [20] (wt%) (7.93 g/cm3 )
EUROFER [21] (wt%) (7.87 g/cm3 )
PbLi [22] (wt%) (9.6 g/cm3 )
64.688 0.03 1.8 12.25 17.5 2.5 0.07 0.025 0.01 0.5 0.3 0.01 0.1 0.001 0.1 0.05 0.05 0.002 0.0005 0.0008 0.004 0.002 0.0002 0.0002 0.002 0.0005 0.0005 0.0005 0.001 0.0005 0.0008 0.0005
88.982 0.105 0.400 0.005 9.001 0.005 0.030 0.005 0.005 0.050 0.005 0.070 0.010 0.001 0.001 0.005 0.010 0.010
Li Na Fe Ni Sn Ta Bi Pb
Dry air (at %) (1.325E−3 g/cm3 ) 0.597 0.027 0.003 0.001 0.056 0.002 0.005 99.309
C N O Ar
0.01 68.69 30.12 1.17
0.200
1.100
in addition, the sources was calculated at 24 h after the shutdown. The project team of the IFMIF-EVEDA project has estimated that the annual campaigns will be about 345 days irradiation plus 20 days of maintenance per year. • In order to propagate the decay photon sources, a second MCNP geometry model is defined. The geometrical model of the LBVM is the same than the used in the neutron transport calculation, but it is taken out of the test cell (emulating a maintenance operation) and placed isolated in the space, in order to obtain the gamma absorbed dose map (24 h after shutdown) surrounding to the LBVM. Then, the decay photon sources calculated in each section and for each material evaluated are emitted randomly from the different points inside of each section. The emission points are defined taking into account the locations of the different materials and the emission is isotropy in each point. 4. Radioactivity and contact ␥-dose results Fig. 5(a) and (b) shows the evolution with time of the specific activity (radioactivity per kg) and the contact ␥-dose rate (time decay curves) as a function of mass for PbLi, SS316LN and EUROFER
for each LBVM section. As the experimental capsules are located in section 4, and they are made up of Eurofer and partially filled with PbLi, the activation of these materials has been only calculated in this section. However, the activation of the SS316LN steel is calculated in every section, since both the container is made up of SS316LN. The time decay curves characterize the activation behaviour of the considered LBVM sections and for the different materials assessed. It is possible to see that the decay curves corresponding to section 4 for both kind of steels have a similar behaviour during the first year after the shutdown, but in the period from 1 year to 100 year the specific activity of EUROFER steel drops up to two orders of magnitude more than the one of SS316LN. In addition, it must be take into account that the amount of EUROFER in LBVM section 4 is 0.75 kg while the amount of the SS316 is 2.32 kg, therefore the data corresponding to section 4 should be multiplied by these values to obtain the total specific activity in the centre of the LBVM. In the rest of the module (the other LBVM sections) the activity per kg is lower but the amount of steel will be higher. Therefore, although, the activation of the section 1 is the lowest, its specific activity is not negligible (Fig. 5).
Fig. 4. Cross section of the LBVM taken at the middle plane of the experimental capsules.
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PbLi
Radioactivity [Bq/Kg]
1.E+14
1.E+12
1.E+10
Total H3 PB 201 PB 203 PB207M HG 203 Po 210 TL 202 PB 202
1.E+08
Fig. 6. Total Radio activity density and the partial radioactivity density of the main radioisotopes that provide the dominant contribution after 345 days of full power year irradiation in PbLi.
Fig. 5. Evolution with time of the (a) radioactivity and (b) the contact ␥-dose rate for PbLi, SS316LN and EUROFER for each LBVM section assessed.
In this paper, since the safety hazards related with the activation of the different kind of steels is being addressed in the study of others components more irradiated in IFMIF, e.g. the HFTM or back plate [23,24], we will focus on the study of the safety hazards associated with the activation of the characteristic element of this module, i.e. the PbLi breeder. In addition, the values of the contact ␥-dose rate and specific activity for SS316LN steel in LBVM, in
the most extreme irradiation area (section 4), fall between those expected for HFTM and TRTM [25]. Furthermore, as observed in Fig. 5(a) and (b), we can note that although the activity of the PbLi is almost keeping constant during the first 100 years, similar to behaviour of the both stainless steels assessed, the contact ␥-dose decreases quickly in the same time period. That behaviour is due to the kind of radioactive decays of the radioisotopes generated by the neutron irradiation. To explain this issue, the radioisotopes that provide the dominant contribution to the specific activity and the contact ␥-dose for PbLi are presented in Tables 2 and 3, respectively. It should be stressed, however, that the results depend significantly on assumed impurities. It is characteristic that the radioisotopes which contribute most to the specific activity are not the same than those that contribute most to the contact ␥-dose rate. In addition, Fig. 6 shows the time decay curves of the specific activity and for some of the most important radioisotopes. From Fig. 6 and both Tables 2 and 3 is obtained that the activity of the PbLi will decreases one order of magnitude in the first seconds after shutdown, mainly because of the decay of the Pb-207M.
Table 2 List of radioisotopes that provide the dominant contribution in percentage (higher than 0.1% of contribution) to the radioactivity (Bq/kg) for PbLi. Isotopes
Shutdown
8h
1 day
30 days
1 year
H 3 (T½ = 12.32 y) HE 6 (T½ = 806.7 ms) NA 22(T½ = 2.60 y) SN117M (T½ = 13.76 d) SN119M (T½ = 293.1 d) SN123 (T½ = 129.2 d) TA182 (T½ = 114.43 d) HG203 (T½ = 46.595 d) HG205 (T½ = 5.14 m) TL200 (T½ = 26.1 h) TL201 (T½ = 72.912 h) TL202 (T½ = 12.23 d) TL204 (T½ = 3.78 y) TL206 (T½ = 4.2 m) TL207 (T½ = 4.77 m) TL207M (T½ = 1.33 s) TL208 (T½ = 3.053 m) PB200 (T½ = 21.5 h) PB201 (T½ = 9.33 h) PB202M (T½ = 3.53 h) PB203 (T½ = 51.92 h) PB203M (T½ = 6.21 s) PB204M (T½ = 1.14 h) PB207M (T½ = 0.806 s) PB209 (T½ = 3.253 h) Radioactivity (Bq/kg)
2.69 0.47 X X X X X 0.1 0.17 X 0.2 X X 0.94 0.86 0.46 0.33 X 0.19 0.3 5.28 2.64 4.86 79.81 0.28 1.32083E+14
32.68 X X 0.43 0.24 X X 1.27 X 0.36 2.34 0.77 0.48 X X X X 0.27 1.25 0.77 57.67 X 0.43 X 0.61 1.0875E+13
38.09 X X 0.49 0.28 X X 1.46 X 0.36 2.46 0.86 0.56 X X X X 0.19 0.45 X 54.28 X X X X 9.3313E+12
94.13 X 0.13 0.28 0.64 0.21 0.14 2.36 X X X 0.41 1.37 X X X X X X X X X X X X 3.7594E+12
98.08 X 0.12 X 0.32 X X X X X X X 1.27 X X X X X X X X X X X X 3.426E+12
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Table 3 List of radioisotopes that provide the dominant contribution in percentage (higher than 0.1% of contribution) to the shutdown contact ␥-dose (Sv/h) for PbLi. Isotopes
Shutdown
8h
1 day
30 days
1 year
NA 22 (T½ = 2.6027 y) NA 24 (T½ = 14.951 h) MN 54 (T½ = 312.12 d) CO 56 (T½ = 77.283 d) CO 58 (T½ = 70.86 d) CO60 (T½ = 1925.28 d) NI 57(T½ = 35.6 d) IN113M (T½ = 99.476 m) SN117M (T½ = 13.76 d) SN123 (T½ = 129.2 d) SB125 (T½ = 2.7586 y) TA182 (T½ = 114.43 d) HG203 (T½ = 46.595 d) TL200 (T½ = 26.1 h) TL202 (T½ = 12.23 d) TL207M (T½ = 1.33 s) TL208 (T½ = 3.053 m) PB200 (T½ = 21.5 h) PB201 (T½ = 9.33 h) PB202M (T½ = 3.53 h) PB203 (T½ = 51.92 h) PB203M (T½ = 6.21 s) PB204M (T½ = 1.14 h) PB207M (T½ = 0.806 s) BI205 (T½ = 15.31 d) BI206 (T½ = 6.243 d) BI207 (T½ = 32.9 y) Contact dose rate (Sv/h)
X X X X X X X X X X X X X X X 0.35 1.1 X X 0.39 0.16 1.38 7.17 89.2 X X X 33,230
1.78 0.72 X X 0.42 X X X X X X 1.41 0.58 7.06 2.91 X X X 10.51 21.96 37.56 X 13.94 X 0.48 X X 123.7
3.65 0.7 0.2 0.13 0.86 X 0.11 X X X X 2.87 1.18 12.35 5.74 X X 0.11 6.61 2.01 62.06 X X X 0.11 0.91 X 60.46
39.42 X 2.07 1.09 7.18 0.28 X 0.47 0.19 0.23 0.11 26.65 8.45 X 12.29 X X X X X X X X X 0.34 0.4 0.62 5.475
83.79 X 2.67 0.15 0.74 0.67 X 0.17 X 0.1 0.24 9.55 0.16 X X X X X X X X X X X X X 1.65 2.017
After that, up to 1 day radioactive decay, the largest contribution to the specific activity is due to both tritium and Pb-203. Afterward, tritium (3.3E12 Bq/kg) will dominate the activation in PbLi up to 1000 years. Nevertheless, it should be noted that part of this tritium will be continuously removed during irradiation by the purge gas system of the LBVM towards the tritium measuring station. In addition, it must be reminded that the tritium radioactive decay is produced by -emission; therefore, it does not contribute to the contact ␥-dose rate. However, the safety hazards associated with the tritium are due to the fact that it is difficult to control because of its high capacity to diffuse through the materials and for its high radioactive toxicity by inhalation or ingestion. Tritium will be emitted in the LBVM in its molecular form T2 . These molecules dissociate and recombine in contact with the atmosphere and form different compounds (e.g. HT, DT, HTO, DTO, etc.). Following the guidelines recommendations [26], the tritium should be considered as tritiated water (DTO, HTO, etc.) for the dose impact and the worker and for design consideration. Regarding Table 3 is obtained that, after one day decay, the radioisotope that contributes most to the contact ␥-dose rate is Na-22, in spite of its low concentration, Table 2. Hence, due to a combination of these factors mentioned above, the contact ␥-dose rate decreases quickly, Fig. 5(b), while the specific activity is almost kept constant during the first 100 years, Fig. 5(a). Although the amount of Po-210 produced in the PbLi is small (less than 0.1% of the total amount of specific activity), its production must be evaluated in detail. Po-210 belongs one of the groups of radioisotopes of highest hazard [27]. It is an extremely toxic and radioactive volatile metal ␣-emitter with half-life of 138.39 days. Its limit of annual intake for the public is only 1E4 Bq and its specific dose 4.56E−14 Sv/Bq [28,29]. It is especially important when the LBVM capsules are being opened in the Test Facility Hot Cells after irradiation, since the Po-210 gas will be released. As an average, in the experimental capsules, 5.3E7 Bq/kg of Po-210 will be expected after one year of irradiation. Another important radioisotope because of its potential for release at high temperatures is the Hg-203. Hg-203 is a –␥ emitter which specific dose is 5.43E−16 Sv/Bq and the annual limit on
annual intake 9.14E6 Bq. Therefore it should be taking into consideration for the handling of the capsule. 5. Gamma dose map around the module In order to establish the dismantling strategy minimizing the damage to the Remote Handling equipment, the absorbed ␥doses rate in water have been calculated around the whole LBVM and around one experimental PbLi capsule. The vertical absorbed gamma dose map in water after 345 days of full power irradiation and after 24 h of decay time around the LBVM is shown in Fig. 7. Furthermore, the horizontal map around one of the most irradiated experimental capsules is shown in Fig. 8 (corresponding to a capsule in the first row of rigs and in the centre of the beam footprint). In both case, dry air atmosphere around the module have been considered to emulate the possible environment of the Test Facility hot cell.
Fig. 7. Gamma absorbed dose rate to water of the whole LBVM (vertical cut, across LBVM centre) after 345 days of full power irradiation and 24 h decay time.
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important to remember that will appear highly radioactive and toxic radioisotopes such as Po210 and tritium. The absorbed gamma dose rate to water around the entire module has been calculated. Values from 30 up to 300 Gy/h to a distance of 0.5–1 m from the most irradiated area of LBVM have been obtained. These values exceed the radiation resistance of some RH equipment. However, the absorbed ␥-dose rate map generated by an experimental capsule decreases three orders of magnitude with respect to the one induced by the whole module. Therefore, the results have been used to define the dismantling strategy of the module in order to minimize the damage to the RH equipment [7].
Acknowledgment This work has been funded by the MINECO Ministry under projects AIC10-A-000441 and AIC-A-2011-0654. Fig. 8. Gamma absorbed dose rate to water of one capsule (horizontal cut, across the capsule mid plane) after 345 days of full power irradiation and 24 h decay time.
References In Fig. 7, it can be seen that the maximum doses in the LBVM correspond to the most irradiated area of the module, with gamma dose rates that could exceed the radiation resistance of the Remote Handling (RH) equipment. Therefore, the disassembly strategy has been developed in such a way to avoid, as much as possible, the manipulation of the central part of the module. However, Fig. 8 shows how the absorbed ␥-dose rate map generated by an experimental capsule decreases three orders of magnitude with respect to the one induced by the whole module, Fig. 7. Then, the rigs will be extracted from the top of the module and each rig cut (in the central area for extracting the capsule) independently to minimize the radiation to the RH equipment. The foreseen disassembly process is summarized in the LBVM maintenance plan (Appendix 10 of Ref. [7]).
6. Conclusions An activation analysis has been performed for the whole LBVM of IFMIF employing the nuclear inventory code (ACAB code), with the activation nuclear data libraries EAF-2007. The ACABAN code, developed by neutronics team of the Fusion National Laboratory (CIEMAT), was used to analyze the output files of the ACAB code. The neutron spectra were obtained from the neutron transport calculation using McDeLicious code with the configuration 1 of the 3D geometrical model of the IFMIF Test Cell, Fig. 3. The values of the contact ␥-dose rate and specific activity for SS316LN steel in LBVM, in the location with the most extreme irradiation conditions (configuration 1), falls between those expected for HFTM and TRTM [25]. At the central part of the LBVM, after 8 h decay time, the contact ␥-dose rate decreases a 76% for EUROFER steel (capsules) and 46% for the SS316LN steel (rigs, container wall). In addition, after one year decay, the contact ␥-dose rate has still a values close to 1000 Sv/h, while, in the upper areas of the LBVM, a value close to 10 Sv/h is expected. This is as a consequence of the intense neutron gradients appearing when we go far away from the experimental irradiation area, due to the directionality of the IFMIF neutron source. Regarding the activation of the breeder blanket material studied, PbLi, we can conclude that the contact ␥-dose rate, after the shutdown, presents similar values to those obtained for stainless steels (EUROFER and SS316LN), but after 30 days decay, those values decrease up to 5.47 Sv/h and after one year decay up to 2.01 Sv/h. Although the contact ␥-dose rate decreases quickly, it is
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Contents lists available at ScienceDirect
Fusion Engineering and Design journal homepage: www.elsevier.com/locate/fusengdes
Activation analyses for the IFMIF-Liquid Breeder Validation Module (LBVM) F. Mota ∗ , N. Casal, A. Mas, A. García, J. Molla, A. Ibarra. Laboratorio Nacional de Fusión por Confinamiento Magnético – CIEMAT, 28040 Madrid, Spain
h i g h l i g h t s • • • •
The objective of LBVM is to test functional materials related to liquid breeders for DEMO. An activation analysis has been performed for the whole LBVM of IFMIF. The results have been used to define the dismantling strategy of the module. Appear high radioactive and toxic radioisotopes such as Po210 and tritium.
a r t i c l e
i n f o
Article history: Received 31 July 2013 Received in revised form 17 March 2014 Accepted 20 March 2014 Available online xxx Keywords: IFMIF LBVM Activation Safety hazards Lithium–lead Liquid breeders
a b s t r a c t The Liquid Breeder Validation Module (LBVM) will be one of the medium flux irradiation modules of the International Fusion Materials Irradiation Facility (IFMIF) neutron source. The objective of this module – presently under design – is the test of functional materials related to liquid breeders for future nuclear fusion power reactors (DEMO). This paper aims to describe the activation analyses performed to estimate the radioactive inventory and the expected contact dose from the activated materials of the module following a 345 day irradiation period. These calculations supply valuable information for different aspects related to the design of the module, such as the safety evaluation and the waste management and disassembly plan. The neutron transport calculations have been performed using the McDeLicious code. The ACAB nuclear inventory code, with the activation nuclear libraries EAF-2007, has been used for the activation analyses. The main results point out that the contact dose of the LBVM materials is much higher than the hands-on-limits, as expected. Therefore, remote handling operations are requested for disassembling the module. It is important to remark that after 8 h decay time, the contact dose rate of the LBVM decreases 76% for the EUROFER steel components and 46% for the 316 LN components. Regarding the isotopic inventory, although the main activation comes from the module steel structures, the production of tritium and Po-210 in the lithium lead inside the experimental capsules deserved a careful analysis. © 2014 Elsevier B.V. All rights reserved.
1. Introduction Materials for future fusion reactors (DEMO) will be exposed to a particular hostile environment as a consequence of the intense radiation field created during the nuclear reaction. Therefore, the assessment of how this radiation may affect the physical properties of materials is fundamental for the nuclear fusion development. Hence, the main aim of the International Fusion Materials Irradiation Facility (IFMIF) [1] will be to provide an intense neutron source with adequate energy spectrum to irradiate candidate materials to
∗ Corresponding author. Tel.: +34 91 346 6578; fax: +34 91 346 6068. E-mail address: [email protected] (F. Mota).
test their suitability for use in a future nuclear fusion power reactor (DEMO). The main objective is to qualify materials with a high radiation resistant and low activation. The irradiation area of IFMIF is divided into three irradiation areas with high, medium and low neutron flux. The structural materials will be irradiated in the High Flux Test Module (HFTM) [1,2] since the irradiation parameters fit accurately with those of the most irradiated structural materials in a future nuclear fusion reactor. The medium flux irradiation area will be dedicated to hold several experiments to irradiate functional materials and other materials related to different breeder blanket concepts such as solid breeders (in the Tritium Release Test Module (TRTM)) [1,3], or liquid breeders (in the Liquid Breeder Validation Module (LBVM)) [4–6]. The LBVM will be focused on, as first approach, experiments
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Fig. 1. LBVM conceptual design.
related to the Helium Cooled Lithium Lead (HCLL) DEMO concept, which is based on liquid lithium–lead (PbLi) as breeder material. However, the possibility to tackle experiments related to other liquid breeder concepts could be assessed in the future. This paper is an analysis of the radioactive inventory and the expected activation gamma dose from the activated materials of the LBVM of IFMIF developed in the framework of the Engineering Validation and Engineering Design Activities (EVEDA) phase. These calculations supply valuable information for different aspects related to the design of the module, such as the safety evaluation and the waste management and disassembly plan.
an external diameter of 22 mm, an internal diameter of 20 mm and 80 mm height. The total inner volume of each cylindrical capsule is about 25 cm3 and it will contain about 15.7 cm3 of PbLi. The position of the capsules inside the irradiation module is such that the height of the PbLi volume will occupy the whole theoretical height of the beam footprint (50 mm) to maximize the irradiation volume. Fig. 1 shows a CAD drawing of the LBVM, where the main components have been identified. The detailed description of the module design can be found in the report [7].
2. LBVM
3.1. MCNP geometrical model
The present configuration of the LBVM (Fig. 1) consists basically on a stainless steel 316LN container capable of housing 16 cylindrical rigs. Each experimental rig will house one cylindrical experimental capsule partially filled with PbLi and the associated instrumentation. This assembly will rest on the Test Cell support structure by means of the Test Module Interface Head located in the upper part of the module and fixed to the container. The module will require helium cooling lines and helium purge lines (to sweep up the tritium produced in LiPb). These lines, welded to the container, will be connected to the Pipes and Cable Plugs of the Test Cell. The container is basically is a hollow T-shape structure built of stainless steel 316LN capable of housing 16 cylindrical rigs. The container also serves as common collector for the returning He cooling gas. A narrow (1 mm) gap between each rig and its correspondent compartment walls allows the helium cooling gas flow. The rig is the recipient built of SS316LN where the capsule is housed. The central part of the rig has the same shape than the capsule, but a narrow gap (2 mm) between the rig and the capsule allows the circulation of the purge gas. The lower part of each rig is a small diameter tube which is welded to the bottom part of the container and also to the entering purge gas line. The upper part of each rig is also a small diameter tube which is welded to the upper part of the container and also to the exit purge gas line. The capsules are closed recipients that contain the liquid breeder. Each rig will house one experimental cylindrical capsule built of EUROFER steel and partially filled with the liquid breeder (PbLi) and the associated instrumentation. The capsules will have
The model used for nuclear transport calculations is based on the md34 3D Test Cell geometrical reference model [8], including several modifications: (1) the horse shoe, present in the reference model, has been removed; (2) one extended version of the HFTM has been included; (3) in addition, the MCNP model of the LBVM has been introduced. For that, a simplified model of the LBVM CAD model was designed using CATIA/CAD code. Afterward, the MCAM code (developed by FDS Team, China [9]) was used to convert the LBVM CATIA/CAD model into the MCNP geometry. The neutronics model of the LBVM introduced in the Test Cell MCNP geometrical model is shown in Fig. 2. As it can be seen, it has been divided in six different sections from the top to the bottom for the activation calculations. These divisions have been done taking into account the neutron gradient in the vertical direction. The resulting sections have been named “upper” (number 1), “up” (number 2), “centre-up” (number 3), “center” (number 4), centre-down (number 5) and down (number 6) as represented in Fig. 2. In this figure the average neutron fluence rate calculated to each section is also shown. Several locations in the medium flux area of the Test Cell are possible for the LBVM [6,7]. The two more suitable ones are shown in Fig. 3. Although, the best location to reproduce the nuclear fusion irradiation conditions [6] corresponds to the configuration 2 (Fig. 3), the configuration 1 (Fig. 3) with the LBVM directly installed behind of the HFTM is also considered in case is necessary to increase the level of displacement damage in the module. Therefore, the configuration 1 has been used to study the safety issues, since the LBVM will suffer the most extreme irradiation conditions in this location.
3. Computational methodology
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Cu, and the INPE-FZK [16] evaluation for 6 Li and 7 Li [17] have been used in the present analysis. The radioactive isotopic inventory and the expected contact ␥dose from the activated materials of the LBVM were calculated using the nuclear inventory code ACAB. This code was designed by UNED University to perform both activation and transmutation calculations for nuclear applications [18]. For this calculation the activation data library chosen was EAF-2007 [19]. For both neutron transport and activation calculations three materials have been taken into account as main make-up of the LBVM. The materials considered are SS316LN for container, EUROFER for experimental capsules and lithium–lead eutectic alloy (Pb–15 Li) as liquid breeder inside the experimental capsule. The chemical composition of the SS316LN, EUROFER and lithium–lead eutectic alloy considered for the calculations is shown in Table 1. In addition, the composition of the dry air is also presented in the table since, in order to propagate the decay gamma sources, the LBVM is considered isolated in the space with dry air as the atmosphere surrounding the module to emulate the possible environment of the test facility hot cell. The activation results have been calculated for each of sections in which the model has been divided (Fig. 2). In addition, the equivalent absorbed ␥-dose to water surrounded the LBVM has been calculate for evaluate the effect of the decay photon sources in remote handling equipment to establish the dismantling strategy. The procedure to calculate both the materials activation and the maps of gamma absorbed doses is the following:
Fig. 2. Vertical section of the LBVM MCNP geometry. The LBVM is divided in six parts for the activation calculations.
3.2. Neutron transport and nuclear isotopic inventory calculations The neutron transport calculations have been performed by means of McDelicious code [10,11]. This code was developed by FZK (Forchungszentrum Karlsruhe, Germany) as an enhancement to the MCNP5 code [12], to reproduce the neutron source n+ 6,7 Li of IFMIF [13]. The nuclear data library FENDL-3/SLIB release 2 [14] has been used in the neutron transport calculations. However, FENDL-3/SLIB contains nuclear data of a few nuclides evaluated only for neutron energies up to 20 MeV. Thus, the LA150n [15] library for 1 H and
• Neutron transport calculations were developed by means of the McDelicious code in the MCNP 3D model of Test Cell, configuration 1, to obtain the averaged neutron spectra on each section of the model (Fig. 2). The volume considered to calculate the average neutron spectrum is defined by the horizontal area corresponding to the 4 central rigs of the front row of the LBVM (dotted line, Fig. 4) and the whole height of each section of the LBVM. In this way, the neutron spectrum obtained will determine an upper bound of the radiation level suffered by each section of the LBVM, i.e. a conservative activation calculation has been considered. • Once the neutron spectrum of each LBVM section has been calculated, the ACAB code has been used to calculate the isotopic inventory and decay photon sources generated on each section and for each relevant material. The ACABAN code, developed by neutronics team of the Fusion National Laboratory (CIEMAT), has been used to analyze the output files of the ACAB code. Both, the isotopic inventory and the decay photon sources have been calculated assuming 345 days of full power of neutron irradiations and,
Fig. 3. Test cell configurations suitable to irradiated the LBVM [6]. Configuration 1: the LBVM is located just behind the HFTM; Configuration 2: the shifter plate is located behind the HFTM and the LBVM behind the NSS module. The configuration chosen to the activation calculations is the configuration 1. HFTM, High Flux Test Module; NSS, Neutron Spectral Shifter; LBVM, Liquid Breeder Validation Module; TRTM, Tritium Release Test Module; LFTM, Low Flux Test Module.
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Table 1 Chemical composition of SS316LN, EUROFER and eutectic Pb–15 Li alloy with impurities (wt %) and dry air (at %).
Fe C Mn Ni Cr Mo N P S Si Cu Ta Ti B Nb Co Al O K Bi V Zr Ag Cd Sn Sb Ba Tb W Ir Pb As
SS316LN [20] (wt%) (7.93 g/cm3 )
EUROFER [21] (wt%) (7.87 g/cm3 )
PbLi [22] (wt%) (9.6 g/cm3 )
64.688 0.03 1.8 12.25 17.5 2.5 0.07 0.025 0.01 0.5 0.3 0.01 0.1 0.001 0.1 0.05 0.05 0.002 0.0005 0.0008 0.004 0.002 0.0002 0.0002 0.002 0.0005 0.0005 0.0005 0.001 0.0005 0.0008 0.0005
88.982 0.105 0.400 0.005 9.001 0.005 0.030 0.005 0.005 0.050 0.005 0.070 0.010 0.001 0.001 0.005 0.010 0.010
Li Na Fe Ni Sn Ta Bi Pb
Dry air (at %) (1.325E−3 g/cm3 ) 0.597 0.027 0.003 0.001 0.056 0.002 0.005 99.309
C N O Ar
0.01 68.69 30.12 1.17
0.200
1.100
in addition, the sources was calculated at 24 h after the shutdown. The project team of the IFMIF-EVEDA project has estimated that the annual campaigns will be about 345 days irradiation plus 20 days of maintenance per year. • In order to propagate the decay photon sources, a second MCNP geometry model is defined. The geometrical model of the LBVM is the same than the used in the neutron transport calculation, but it is taken out of the test cell (emulating a maintenance operation) and placed isolated in the space, in order to obtain the gamma absorbed dose map (24 h after shutdown) surrounding to the LBVM. Then, the decay photon sources calculated in each section and for each material evaluated are emitted randomly from the different points inside of each section. The emission points are defined taking into account the locations of the different materials and the emission is isotropy in each point. 4. Radioactivity and contact ␥-dose results Fig. 5(a) and (b) shows the evolution with time of the specific activity (radioactivity per kg) and the contact ␥-dose rate (time decay curves) as a function of mass for PbLi, SS316LN and EUROFER
for each LBVM section. As the experimental capsules are located in section 4, and they are made up of Eurofer and partially filled with PbLi, the activation of these materials has been only calculated in this section. However, the activation of the SS316LN steel is calculated in every section, since both the container is made up of SS316LN. The time decay curves characterize the activation behaviour of the considered LBVM sections and for the different materials assessed. It is possible to see that the decay curves corresponding to section 4 for both kind of steels have a similar behaviour during the first year after the shutdown, but in the period from 1 year to 100 year the specific activity of EUROFER steel drops up to two orders of magnitude more than the one of SS316LN. In addition, it must be take into account that the amount of EUROFER in LBVM section 4 is 0.75 kg while the amount of the SS316 is 2.32 kg, therefore the data corresponding to section 4 should be multiplied by these values to obtain the total specific activity in the centre of the LBVM. In the rest of the module (the other LBVM sections) the activity per kg is lower but the amount of steel will be higher. Therefore, although, the activation of the section 1 is the lowest, its specific activity is not negligible (Fig. 5).
Fig. 4. Cross section of the LBVM taken at the middle plane of the experimental capsules.
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PbLi
Radioactivity [Bq/Kg]
1.E+14
1.E+12
1.E+10
Total H3 PB 201 PB 203 PB207M HG 203 Po 210 TL 202 PB 202
1.E+08
Fig. 6. Total Radio activity density and the partial radioactivity density of the main radioisotopes that provide the dominant contribution after 345 days of full power year irradiation in PbLi.
Fig. 5. Evolution with time of the (a) radioactivity and (b) the contact ␥-dose rate for PbLi, SS316LN and EUROFER for each LBVM section assessed.
In this paper, since the safety hazards related with the activation of the different kind of steels is being addressed in the study of others components more irradiated in IFMIF, e.g. the HFTM or back plate [23,24], we will focus on the study of the safety hazards associated with the activation of the characteristic element of this module, i.e. the PbLi breeder. In addition, the values of the contact ␥-dose rate and specific activity for SS316LN steel in LBVM, in
the most extreme irradiation area (section 4), fall between those expected for HFTM and TRTM [25]. Furthermore, as observed in Fig. 5(a) and (b), we can note that although the activity of the PbLi is almost keeping constant during the first 100 years, similar to behaviour of the both stainless steels assessed, the contact ␥-dose decreases quickly in the same time period. That behaviour is due to the kind of radioactive decays of the radioisotopes generated by the neutron irradiation. To explain this issue, the radioisotopes that provide the dominant contribution to the specific activity and the contact ␥-dose for PbLi are presented in Tables 2 and 3, respectively. It should be stressed, however, that the results depend significantly on assumed impurities. It is characteristic that the radioisotopes which contribute most to the specific activity are not the same than those that contribute most to the contact ␥-dose rate. In addition, Fig. 6 shows the time decay curves of the specific activity and for some of the most important radioisotopes. From Fig. 6 and both Tables 2 and 3 is obtained that the activity of the PbLi will decreases one order of magnitude in the first seconds after shutdown, mainly because of the decay of the Pb-207M.
Table 2 List of radioisotopes that provide the dominant contribution in percentage (higher than 0.1% of contribution) to the radioactivity (Bq/kg) for PbLi. Isotopes
Shutdown
8h
1 day
30 days
1 year
H 3 (T½ = 12.32 y) HE 6 (T½ = 806.7 ms) NA 22(T½ = 2.60 y) SN117M (T½ = 13.76 d) SN119M (T½ = 293.1 d) SN123 (T½ = 129.2 d) TA182 (T½ = 114.43 d) HG203 (T½ = 46.595 d) HG205 (T½ = 5.14 m) TL200 (T½ = 26.1 h) TL201 (T½ = 72.912 h) TL202 (T½ = 12.23 d) TL204 (T½ = 3.78 y) TL206 (T½ = 4.2 m) TL207 (T½ = 4.77 m) TL207M (T½ = 1.33 s) TL208 (T½ = 3.053 m) PB200 (T½ = 21.5 h) PB201 (T½ = 9.33 h) PB202M (T½ = 3.53 h) PB203 (T½ = 51.92 h) PB203M (T½ = 6.21 s) PB204M (T½ = 1.14 h) PB207M (T½ = 0.806 s) PB209 (T½ = 3.253 h) Radioactivity (Bq/kg)
2.69 0.47 X X X X X 0.1 0.17 X 0.2 X X 0.94 0.86 0.46 0.33 X 0.19 0.3 5.28 2.64 4.86 79.81 0.28 1.32083E+14
32.68 X X 0.43 0.24 X X 1.27 X 0.36 2.34 0.77 0.48 X X X X 0.27 1.25 0.77 57.67 X 0.43 X 0.61 1.0875E+13
38.09 X X 0.49 0.28 X X 1.46 X 0.36 2.46 0.86 0.56 X X X X 0.19 0.45 X 54.28 X X X X 9.3313E+12
94.13 X 0.13 0.28 0.64 0.21 0.14 2.36 X X X 0.41 1.37 X X X X X X X X X X X X 3.7594E+12
98.08 X 0.12 X 0.32 X X X X X X X 1.27 X X X X X X X X X X X X 3.426E+12
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Table 3 List of radioisotopes that provide the dominant contribution in percentage (higher than 0.1% of contribution) to the shutdown contact ␥-dose (Sv/h) for PbLi. Isotopes
Shutdown
8h
1 day
30 days
1 year
NA 22 (T½ = 2.6027 y) NA 24 (T½ = 14.951 h) MN 54 (T½ = 312.12 d) CO 56 (T½ = 77.283 d) CO 58 (T½ = 70.86 d) CO60 (T½ = 1925.28 d) NI 57(T½ = 35.6 d) IN113M (T½ = 99.476 m) SN117M (T½ = 13.76 d) SN123 (T½ = 129.2 d) SB125 (T½ = 2.7586 y) TA182 (T½ = 114.43 d) HG203 (T½ = 46.595 d) TL200 (T½ = 26.1 h) TL202 (T½ = 12.23 d) TL207M (T½ = 1.33 s) TL208 (T½ = 3.053 m) PB200 (T½ = 21.5 h) PB201 (T½ = 9.33 h) PB202M (T½ = 3.53 h) PB203 (T½ = 51.92 h) PB203M (T½ = 6.21 s) PB204M (T½ = 1.14 h) PB207M (T½ = 0.806 s) BI205 (T½ = 15.31 d) BI206 (T½ = 6.243 d) BI207 (T½ = 32.9 y) Contact dose rate (Sv/h)
X X X X X X X X X X X X X X X 0.35 1.1 X X 0.39 0.16 1.38 7.17 89.2 X X X 33,230
1.78 0.72 X X 0.42 X X X X X X 1.41 0.58 7.06 2.91 X X X 10.51 21.96 37.56 X 13.94 X 0.48 X X 123.7
3.65 0.7 0.2 0.13 0.86 X 0.11 X X X X 2.87 1.18 12.35 5.74 X X 0.11 6.61 2.01 62.06 X X X 0.11 0.91 X 60.46
39.42 X 2.07 1.09 7.18 0.28 X 0.47 0.19 0.23 0.11 26.65 8.45 X 12.29 X X X X X X X X X 0.34 0.4 0.62 5.475
83.79 X 2.67 0.15 0.74 0.67 X 0.17 X 0.1 0.24 9.55 0.16 X X X X X X X X X X X X X 1.65 2.017
After that, up to 1 day radioactive decay, the largest contribution to the specific activity is due to both tritium and Pb-203. Afterward, tritium (3.3E12 Bq/kg) will dominate the activation in PbLi up to 1000 years. Nevertheless, it should be noted that part of this tritium will be continuously removed during irradiation by the purge gas system of the LBVM towards the tritium measuring station. In addition, it must be reminded that the tritium radioactive decay is produced by -emission; therefore, it does not contribute to the contact ␥-dose rate. However, the safety hazards associated with the tritium are due to the fact that it is difficult to control because of its high capacity to diffuse through the materials and for its high radioactive toxicity by inhalation or ingestion. Tritium will be emitted in the LBVM in its molecular form T2 . These molecules dissociate and recombine in contact with the atmosphere and form different compounds (e.g. HT, DT, HTO, DTO, etc.). Following the guidelines recommendations [26], the tritium should be considered as tritiated water (DTO, HTO, etc.) for the dose impact and the worker and for design consideration. Regarding Table 3 is obtained that, after one day decay, the radioisotope that contributes most to the contact ␥-dose rate is Na-22, in spite of its low concentration, Table 2. Hence, due to a combination of these factors mentioned above, the contact ␥-dose rate decreases quickly, Fig. 5(b), while the specific activity is almost kept constant during the first 100 years, Fig. 5(a). Although the amount of Po-210 produced in the PbLi is small (less than 0.1% of the total amount of specific activity), its production must be evaluated in detail. Po-210 belongs one of the groups of radioisotopes of highest hazard [27]. It is an extremely toxic and radioactive volatile metal ␣-emitter with half-life of 138.39 days. Its limit of annual intake for the public is only 1E4 Bq and its specific dose 4.56E−14 Sv/Bq [28,29]. It is especially important when the LBVM capsules are being opened in the Test Facility Hot Cells after irradiation, since the Po-210 gas will be released. As an average, in the experimental capsules, 5.3E7 Bq/kg of Po-210 will be expected after one year of irradiation. Another important radioisotope because of its potential for release at high temperatures is the Hg-203. Hg-203 is a –␥ emitter which specific dose is 5.43E−16 Sv/Bq and the annual limit on
annual intake 9.14E6 Bq. Therefore it should be taking into consideration for the handling of the capsule. 5. Gamma dose map around the module In order to establish the dismantling strategy minimizing the damage to the Remote Handling equipment, the absorbed ␥doses rate in water have been calculated around the whole LBVM and around one experimental PbLi capsule. The vertical absorbed gamma dose map in water after 345 days of full power irradiation and after 24 h of decay time around the LBVM is shown in Fig. 7. Furthermore, the horizontal map around one of the most irradiated experimental capsules is shown in Fig. 8 (corresponding to a capsule in the first row of rigs and in the centre of the beam footprint). In both case, dry air atmosphere around the module have been considered to emulate the possible environment of the Test Facility hot cell.
Fig. 7. Gamma absorbed dose rate to water of the whole LBVM (vertical cut, across LBVM centre) after 345 days of full power irradiation and 24 h decay time.
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important to remember that will appear highly radioactive and toxic radioisotopes such as Po210 and tritium. The absorbed gamma dose rate to water around the entire module has been calculated. Values from 30 up to 300 Gy/h to a distance of 0.5–1 m from the most irradiated area of LBVM have been obtained. These values exceed the radiation resistance of some RH equipment. However, the absorbed ␥-dose rate map generated by an experimental capsule decreases three orders of magnitude with respect to the one induced by the whole module. Therefore, the results have been used to define the dismantling strategy of the module in order to minimize the damage to the RH equipment [7].
Acknowledgment This work has been funded by the MINECO Ministry under projects AIC10-A-000441 and AIC-A-2011-0654. Fig. 8. Gamma absorbed dose rate to water of one capsule (horizontal cut, across the capsule mid plane) after 345 days of full power irradiation and 24 h decay time.
References In Fig. 7, it can be seen that the maximum doses in the LBVM correspond to the most irradiated area of the module, with gamma dose rates that could exceed the radiation resistance of the Remote Handling (RH) equipment. Therefore, the disassembly strategy has been developed in such a way to avoid, as much as possible, the manipulation of the central part of the module. However, Fig. 8 shows how the absorbed ␥-dose rate map generated by an experimental capsule decreases three orders of magnitude with respect to the one induced by the whole module, Fig. 7. Then, the rigs will be extracted from the top of the module and each rig cut (in the central area for extracting the capsule) independently to minimize the radiation to the RH equipment. The foreseen disassembly process is summarized in the LBVM maintenance plan (Appendix 10 of Ref. [7]).
6. Conclusions An activation analysis has been performed for the whole LBVM of IFMIF employing the nuclear inventory code (ACAB code), with the activation nuclear data libraries EAF-2007. The ACABAN code, developed by neutronics team of the Fusion National Laboratory (CIEMAT), was used to analyze the output files of the ACAB code. The neutron spectra were obtained from the neutron transport calculation using McDeLicious code with the configuration 1 of the 3D geometrical model of the IFMIF Test Cell, Fig. 3. The values of the contact ␥-dose rate and specific activity for SS316LN steel in LBVM, in the location with the most extreme irradiation conditions (configuration 1), falls between those expected for HFTM and TRTM [25]. At the central part of the LBVM, after 8 h decay time, the contact ␥-dose rate decreases a 76% for EUROFER steel (capsules) and 46% for the SS316LN steel (rigs, container wall). In addition, after one year decay, the contact ␥-dose rate has still a values close to 1000 Sv/h, while, in the upper areas of the LBVM, a value close to 10 Sv/h is expected. This is as a consequence of the intense neutron gradients appearing when we go far away from the experimental irradiation area, due to the directionality of the IFMIF neutron source. Regarding the activation of the breeder blanket material studied, PbLi, we can conclude that the contact ␥-dose rate, after the shutdown, presents similar values to those obtained for stainless steels (EUROFER and SS316LN), but after 30 days decay, those values decrease up to 5.47 Sv/h and after one year decay up to 2.01 Sv/h. Although the contact ␥-dose rate decreases quickly, it is
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