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A core design concept for multi-purpose research reactors
Nuclear Engineering and Design 252 (2012) 34–41
Contents lists available at SciVerse ScienceDirect
Nuclear Engineering and Design journal homepage: www.elsevier.com/locate/nucengdes
A core design concept for multi-purpose research reactors Chul Gyo Seo a,b , Nam Zin Cho a,∗ a b
Korea Advanced Institute of Science and Technology, 291 Daehak-ro, Yuseong-gu, Daejeon 305-701, Republic of Korea Korea Atomic Energy Research Institute, 1045 Daedeok-daero, Yuseong-gu, Daejeon 305-353, Republic of Korea
h i g h l i g h t s
We present a new design concept for multi-purpose research reactors of MTR-type fuel. Various in-core irradiation holes can be installed in the large core. In the compact core, high thermal flux can be achieved with a larger irradiation hole. Only a single type of fuel plate is used for the new core design.
a r t i c l e
i n f o
Article history: Received 10 November 2011 Received in revised form 20 June 2012 Accepted 27 June 2012
a b s t r a c t A new core design concept for multi-purpose research reactors is presented. New concept cores using material test reactor (MTR) type fuel are constructed with the edge trimmed in-core irradiation hole. Conventional research reactors have core configurations with a constant assembly pitch. Sizes of incore irradiation holes are limited to a multiple size of fuel assembly. The new concept enables a core configuration to have different sizes of in-core irradiation holes using the same size of fuel assembly. Two types of cores for multi-purpose research reactors are constructed and the performance results using MCNP calculation are compared. The new compact core for utilizing mainly beam tubes has a larger in-core irradiation hole and gives higher thermal neutron flux at the hole. The maximum thermal flux at the reflector region is almost the same. The new large core for utilizing in-core irradiation holes has small and large holes, while the conventional core has holes of the same size. The small hole is useful for high fast neutron flux and the large hole is useful for high thermal neutron flux. Compared to the conventional cores, the new cores use a smaller fuel assembly, which leads to enhanced safety at a high coolant speed for high power density. Two types of fuel plates are required for the conventional cores, but only one type of fuel plate will do for the new cores. This new design concept gives us several advantages and will be very useful for core design of multi-purpose research reactors. © 2012 Elsevier B.V. All rights reserved.
1. Introduction After the first criticality of Chicago Pile-1 on December 2, 1942, various research reactors have been developed and there are over 240 operational research reactors in the world (IAEA, 2010). Neutrons generated from research reactors are used for neutron scattering, neutron activation analysis, radiography, irradiation testing of materials and production of isotopes, etc. For most applications, higher neutron flux is always better. There are many practical constraints and difficulties for getting high neutron flux. A variety of fuels and cores have been developed to overcome the practical difficulties and satisfy their utilization purposes (Teruel and Rizwan-uddin, 2009). Especially, economic constraints pushed new reactors to be multi-purpose (Raina et al., 2006). New
∗ Corresponding author. Tel.: +82 42 350 3819; fax: +82 42 350 3810. E-mail address: [email protected] (N.Z. Cho). 0029-5493/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.nucengdes.2012.06.031
multi-purpose research reactors of over 10 MW power are listed in Table 1, in which no reactors are of the same type. In spite of different requirements, most reactors use material test reactor (MTR) type fuel. Reactor performance and operating costs strongly depend on fuel type. It is advantageous to owners if fuel is well-qualified for its performance and can be supplied by multiple vendors. A core of MTR-type fuel, in which fuel plates are arranged in a long rectangular box, is made up of regularly arranged plural fuel assemblies, control rods and irradiation holes. The overall core is a cylinder shape and surrounded by reflector. The core for isotope production and material test has fuel assemblies, control rods and irradiation holes in a rectangular lattice structure. Many irradiation holes make the core large and it can be classified into a “large core”. Other core concept was emerged for neutron scattering experiments. The experiments use thermal neutrons streaming out from beam tubes. The research reactors for neutron scattering have high thermal neutron flux in reflector region where beam tubes can be placed. To fulfill this requirement, a new design
C.G. Seo, N.Z. Cho / Nuclear Engineering and Design 252 (2012) 34–41
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Table 1 Multi-purpose research reactors in operation and under construction or planned with thermal power ≥10 MW after 1980. Country
Name
In operation Libya Indonesia Peru Japan Korea Algeria Egypt Germany Australia China
IRT-1 RSG-GAS RP-10 JRR-3 M HANARO ES-SALAM ETRR-2 FRM-II OPAL CARR
Under construction or planned RJH France India MPRR PALLAS Netherlands
Power (MW) 10 30 10 20 30 15 22 20 20 60 100 20 80
concept so called “inverse flux trap” was introduced at the design of the high flux beam reactor (HFBR) (Shapiro et al., 1983). Recently, this concept was utilized at the design of FRM-II called as “compact core” concept (Bönning and Von Der Hardt, 1987). This “compact core” concept which requires a high power density and a small core, deviates the FRM-II core from general design limits. The FRM-II core for an extreme performance uses a special fuel composed of involute fuel plates and highly enriched uranium of 93 w/o, while only low enriched uranium below 20 w/o is presently available in the world market. So, the latest multi-purpose research reactor, CARR, uses “compact core” concept and MTR-type fuel (Yuan and Kang, 1998). This paper presents a new design concept for multi-purpose research reactors of MTR-type fuel in Section 2. In Section 3, two types of cores are constructed to investigate characteristics of the new design concept. Comparison results for the two types of cores are given and discussed in Section 4. Finally, summary and conclusions are given in Section 5.
Fuel
Reflector
Criticality date
Tube type MTR type MTR type MTR type Rod type Rod type MTR type Involuted plate MTR type MTR type
Be Be Be, Graphite D2 O D2 O Graphite, D2 O D2 O D2 O D2 O D2 O
1981 1987 1988 1990 1991 1992 1997 2004 2006 2010
Curved plate MTR type MTR type
Be D2 O Be
Construction Planned Planned
2. New design concept This section introduces a new core design concept useful for design of a multi-purpose research reactor of MTR-type fuel. A new core design concept is to construct a core using edge trimmed irradiation hole. A conceptual drawing of the irradiation hole is given in Fig. 1. Edges of the irradiation hole are trimmed, unlike conventional irradiation holes which are rectangular boxes with a hole or holes. As the frame of the conventional irradiation hole is rectangular in shape, the space is not fully used for experimental facilities, which are of cylindrical shapes. The frame of the new irradiation hole becomes more compact by trimming superfluous parts. The four faces of the irradiation hole could be contacted with fuel assemblies, but the four corners of the irradiation hole should be contacted with other irradiation holes or guide tubes except fuel assembly. The coolant in a fuel assembly flows in a high speed, therefore structural integrity of the fuel is important. Fuel should be placed by face-to-face contact with other structures such as fuel
Fig. 1. Conceptual drawing of the edge trimmed irradiation hole.
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C.G. Seo, N.Z. Cho / Nuclear Engineering and Design 252 (2012) 34–41
Fig. 2. Core configurations of the CARR core and a new core.
assembly, irradiation hole and guide tube of control rod. Any corners of core structures should not be contacted with fuel plate or side plate of fuel assembly. Other types of contacts with the irradiation hole are allowed to preferably maintain face-to-face contact with the fuel. We explain the new concept using the CARR core mentioned above. The CARR core by the conventional design concept is shown in the left side of Fig. 2, in which fuel assemblies are regularly arranged. The core consists of 16 standard fuel assemblies, 4 follower fuel assemblies, and one in-core irradiation hole. Fillers occupy the space between the peripheral fuel assemblies and the inner wall of the reflector tank. Two types of fuel plates in the core should be used for two types of fuel assemblies in a rectangular lattice structure. The new design concept can change the CARR core into a new core as shown in the right side of Fig. 2. The new core has an edge trimmed irradiation hole at the center of the core. All fuel assemblies in the core are placed by face-to-face contact with other structures. The size of the standard fuel is equivalent to the size of the follower fuel, therefore one type of fuel plate can be used in two fuel assemblies. 3. Core construction There are many types of research reactors depending on standards of classification. When we use beam tube as a criterion, the reactors are usually divided into two types. So, in this study two types of cores are constructed to investigate characteristics of the new design concept. The first type of core is a compact core for utilizing mainly beam tubes. The second type of core is a large core for isotope production and irradiation test of materials. The compact core has one in-core irradiation hole for multi-purpose utilization and consists of 20 fuel assemblies. The compact core uses heavy water as a reflector and moderated and cooled by light water. The large core consists of 5 in-core irradiation holes and 20 fuel assemblies. The large core is moderated and cooled by light water also, but uses beryllium as a reflector. The two cores are research reactors of closed tank type for high power density. The coolant flows
downward and driving mechanisms of control rods are located underneath the cores. The control rods are moving within their guide tubes. Each control rod consists of a follower fuel and its connected Hf absorber. 3.1. Compact core A compact core is surrounded by an annular heavy water tank to obtain a large irradiation volume. The tank is 150 cm high and 150 cm in diameter. A thick Zircaloy wall of 1.5 cm divides the core and the reflector. A space between the wall and the fuel assemblies is filled with Be fillers. The central in-core irradiation hole is loaded with a target made of Al alloy of 6.0 cm in diameter. A space surrounding the target within the irradiation hole is filled with water to booster thermal neutron flux at the target. Core A by the conventional design concept is modeled in detail using MCNP (MCNP, 2003) as shown in Fig. 3. The mesh tally overlapped with structures is used for calculating thermal neutron flux distribution. It is difficult to compare two cores directly because the new concept core uses one type of fuel assembly and the conventional core uses two types of fuel assemblies. The sizes of fuel assemblies are adjusted for a same reactor power and a same power density to compare the two cores at the same condition. Core B by the new design concept is constructed using one type of fuel assembly, 7.62 × 7.62 cm, shown in Fig. 4. The active length of the fuel is 60.0 cm and other basic parameters are the same as those of JRR-3M. The standard fuel of Core A is 7.85 × 7.85 cm and the follower fuel is 6.59 × 6.59 cm. The irradiation hole of Core B becomes large and thus the core is modified into Core B . While the irradiation holes of Core A and Core B have the same inner diameter, those of Core A and Core B’ have the same minimum thickness, 0.5 cm. Two cores have the same thickness for fuel plate, side plate, and guide tube as shown in Table 2. Other dimensions such as Hf thickness, thickness of Zircaloy wall, and diameter of housing vessel are the same for a comparison. Four control rods are commonly used for reactor control and a first shutdown system (FSS). A second shutdown system (SSS) could be realized by drainage of heavy water like the OPAL reactor
C.G. Seo, N.Z. Cho / Nuclear Engineering and Design 252 (2012) 34–41
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Fig. 3. Cross sectional view of MCNP model for Core A.
Table 2 Main parameters for Core A and Core B. Core A Reactor power (MW) Total uranium loading (kg) Fuel meat Uranium density (gU/cm3 ) Active length (cm)
Core B 40
38.41
38.25 U3 Si2 –Al 4.8 60
Fuel assembly type
Standard
Follower
Standard/follower
Fuel assembly size (cm) Number of plates Meat width (cm) Meat thickness (cm) Cladding thickness (cm) Thickness of side plate (cm) Coolant gap (cm) Guide tube size (cm) Thickness of guide tube (cm) Hf absorber size (cm) Thickness of Hf absorber (cm)
7.85 22 6.43 0.051 0.038 0.48 0.229
6.59 17 5.17 0.051 0.038 0.48 0.254
7.62 21 6.2 0.051 0.038 0.48 0.235 8.88 0.5 7.62 0.5
7.85 0.5 6.59 0.5
(Kim, 2006) or insertion of other shutdown rods into heavy water like the CARR reactor. The SSS for the compact core is omitted and is not modeled in this study. 3.2. Large core Both thermal and fast neutrons are important to utilization of a large core, while mainly thermal neutrons are used in the compact
core. Fast neutrons are required for material irradiation tests and thermal neutron flux should be high for isotope production and other irradiation tests. The reactors for irradiation tests become large to provide irradiation holes surrounded by fuel assemblies. Two large cores in Fig. 5 are constructed using 20 fuel assemblies as in the compact cores. The core of a 7 × 7 rectangular lattice has 45 channels which are positioned by fuel assemblies, control rods and irradiation holes. The cores could be loaded with more fuel assemblies or control rods. The right core of Fig. 5 is a new concept core with different in-core irradiation holes. The core is surrounded with a pressure vessel which has an outer diameter of 76 cm and a thickness of 2 cm. The outer region of the pressure vessel is surrounded with a Be block reflector of 20 cm in thickness and 100 cm in height. The outside of the Be reflector is filled with a pool water. Four control rods are connected with each magnetic clutch and moving by each stepping motor. Four control rods are commonly used for reactor control and FSS. Two shutdown rods driven by a hydraulic force are allocated for SSS. Large cores use the same fuel assemblies employed at Core A and Core B. Each large core has an in-core irradiation hole for fast neutron flux trap and 4 in-core irradiation holes for thermal neutron flux trap. Fig. 6 shows MCNP models for Fig. 5. The left core, Core C, is a conventional concept core and the right core, Core D, is a new concept core. The central irradiation hole has a minimized water gap for fast neutron irradiation and other irradiation holes have thick water gaps for thermalizing fission neutrons. All irradiation holes are loaded with Al alloy targets of 6.0 cm in diameter. The new design concept enables core to have different sizes of irradiation holes. Core E and Core F in Fig. 6 are constructed as examples.
Fig. 4. Cross sectional views of MCNP models for Core B and Core B .
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Fig. 5. Core configurations of a conventional large core and a new large core.
Fig. 6. Cross sectional views of MCNP models for Core C and Core D.
Fig. 7. Cross sectional views of MCNP models for Core E and Core F.
C.G. Seo, N.Z. Cho / Nuclear Engineering and Design 252 (2012) 34–41
Core E has the same size of irradiation holes, which is larger than the size of the fuel assembly. Core F has a large central hole and four small irradiation holes (Fig. 7).
Table 3 Reactivity worths for core models at several core conditions [%k/k].
Core A Core B Core B
4. Results and discussion The calculated results are obtained using MCNP version 5 which uses the standard libraries at room temperature based on ENDF/BVI. All cores are loaded with fresh fuel assemblies without burnable poison. Control rods are inserted about 1/3 for evaluating real neutron flux. This position is assumed to be at an equilibrium xenon state of begin of cycle (BOC). The reactor powers are assumed to be 40 MW which is a lower power density than that of the CARR. The average heat flux of the reactors is 1.28 MW/m2 , while the CARR core without in-core irradiation hole has an average heat flux of 1.39 MW/m2 . The presented neutron flux is a calculated neutron flux of 40 MW power multiplied by the effective multiplication factor. The fast neutron flux is defined as neutron flux with neutron energy above 0.1 MeV and the thermal neutron flux is below 0.625 eV. Mesh tally of 2 × 2 × 5 cm is used to calculate neutron flux distribution. The neutron flux of a target is a maximum neutron flux among fluxes evaluated at segments of 5 cm length. All MCNP calculations were carried out at ‘KCODE mode’. Each case was simulated with 500 active cycles of 100,000 particles per cycle. Prior to the reactivity calculation, a criticality at each core condition was calculated. The reactivity worth for two cases was defined as ‘reactivity worth [%k/k] = (1/k Case1 − 1/k Case2 ) × 100’. The statistical error is small enough, in which the reactivity worth is about 0.01%k/k and power distribution is below 0.1% and the maximum neutron flux is below 0.5%. 4.1. Compact core A compact core is used for mainly utilizing beam tubes, but the calculation models do not have beam tubes for a comparison. The calculated reactivity worths at several control rods’ positions are listed in Table 3. The core excess reactivity is enough as a reactor and the control rods have a sufficient reactivity worth to shut down the reactor safely. The excess reactivity of Core A is a little bit large because Core A has smaller guide tubes made of Al alloy. Core B modified from Core B spends 0.73%k/k for a higher thermal neutron flux. The guide tube of Core A is 7.85 × 7.85 cm and that
39
Excess
All rods 1/3 in
All rods in
(N-1) rods in
21.50 21.27 20.54
3.93 4.34 4.37
30.02 38.75 38.28
17.50 20.39 20.09
of Core B is 8.88 × 8.88 cm. The thickness of guide tubes is 0.5 cm for both. The size of follower fuel and Hf absorber makes a difference for reactivity worths of control rods. The new concept core has a large rod worth and could use other weakly absorbing material instead of Hf. Core B replaced by stainless steel has total rod worth of 15.63%k/k. Control rods made of stainless steel could be selected at the new concept core according to its fuel management strategy. The peak position of thermal neutron flux is formed at −10 cm below the core center. At this axial position, radial profile of thermal neutron flux is plotted at Fig. 8. On the basis of Core A, thermal neutron flux is almost the same at the reflector region, but shows a big difference at the irradiation hole. The new design concept provides not only a high thermal neutron flux but also a large irradiation volume. An overall volume of the hole increases by 56.5% and an effective volume for targets increases by 78.0%. The new concept utilizes effectively a space of the irradiation hole by trimming the edges. The core by the new concept can adjust the size of the irradiation hole by adjusting the thickness of the guide tube. Large irradiation hole can provide a large difference from the viewpoint of utilization of experimental facility. Thick water layer of Core B is replaced with a pressure boundary made of Zircaloy and targets can be loaded or unloaded on power state. It is also possible to install a test loop of high temperature and pressure requiring a large irradiation hole. A high reactor power is required in order to obtain a high thermal neutron flux, but the power is one of main constraints. The compact core concept provides a higher neutron flux at the same power level. The following equation explains this concept well (Difilippo et al., 1986): ˚th ∝
2/3
P P P 2/3 = P 1/3 = A V V
= P 1/3 ¯ 2/3 .
(1)
This argument shows that power density is more important than reactor power for high neutron flux. It is required to increase power
Fig. 8. Radial profile of thermal neutron flux in each core.
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Table 4 Reactivity worths for core models at several core conditions [%k/k].
Core C Core D Core E Core F
Table 5 Comparison of maximum neutron fluxes for core models.
Excess
All rods 1/3 in
All rods in
FSS (N-1) status
SSS
22.40 22.34 22.34 22.44
3.07 3.46 3.45 3.49
17.04 20.30 20.23 20.29
8.50 9.28 9.22 9.28
10.98 13.23 13.99 13.40
Position of irradiation hole
density as much as possible. High power density makes flow velocity fast for fuel cooling, and consequently structural integrity of fuel assembly becomes more important. Flow velocity should be below a criterion so called critical flow velocity Vc for maintaining structural integrity of fuel assembly. The critical flow velocity is defined as the minimum flow velocity to buckling collapse of one or more fuel plates. The velocity is related with the following parameters (Miller, 1958):
Center
Down
Left
Right
Up
Core C
3.52E+14a 6.72E+14b 1.69E+15c
4.26E+14 5.29E+14 1.53E+15
4.08E+14 5.12E+14 1.47E+15
4.06E+14 5.13E+14 1.47E+15
4.22E+14 5.32E+14 1.53E+15
Core D
3.55E+14 6.75E+14 1.70E+15
4.93E+14 4.60E+14 1.54E+15
4.71E+14 4.47E+14 1.47E+15
4.72E+14 4.75E+14 1.46E+15
4.91E+14 4.96E+14 1.53E+15
Core E
3.81E+14 6.51E+14 1.73E+15
4.64E+14 4.97E+14 1.54E+15
4.37E+14 4.78E+14 1.47E+15
4.37E+14 4.97E+14 1.54E+15
4.62E+14 4.78E+14 1.47E+15
Core F
4.15E+14 6.26E+14 1.77E+15
3.95E+14 5.45E+14 1.51E+15
3.80E+14 5.24E+14 1.46E+15
3.79E+14 5.16E+14 1.44E+15
3.93E+14 5.33E+14 1.50E+15
a b
Vc ∝
(Pt )
3/2
(Cg )
(Pw )2
1/2
,
c
(2)
where Pt = plate thickness, Cg = coolant gap, Pw = plate width. The size of fuel assembly should be small for high power density which requires high flow velocity. The largest plate width in the conventional core is 6.89 cm while the new core uses plate width of 6.66 cm. According to Eq. (2), the critical flow velocity in the new core increases by 6.5%. Thus, the new concept provides stronger structural integrity of the fuel assembly. 4.2. Large core For evaluation of a large core, Core D by the new concept is compared on the basis of Core C by the conventional concept. Core E and Core F by the new concept are compared also. Reactivity worths of core models at several core conditions are calculated and tabulated in Table 4. Core excess reactivities are almost the same but reactivity worths of control rods are considerably different. Reactivity worths of SSS are larger than reactivity worths of FSS for evaluating a shutdown margin by the “n-1” concept. If the reactivity worth of FSS is not large enough for its safe shutdown, additional control
Thermal. Fast. Total neutron flux.
rods or some restriction on fuel management will be required. As shown in Table 4, the new design concept provides larger reactivity worth of FSS. To compare neutron fluxes of large cores, maximum neutron fluxes at targets within irradiation holes are divided into thermal and fast neutron fluxes. Fig. 9 shows power distribution and neutron flux simultaneously for Core C and Core D. In principle, the fast neutron flux at the central holes of Core D should be high but are almost the same for low assembly powers within guide tubes. Thermal neutron fluxes at other irradiation holes of Core D are high about 15%. Core D has high thermal and fast flux holes at the same core. Table 5 shows a comparison of neutron fluxes for other reactors. Core E has the irradiation holes of the same size like Core C, but the thermal fluxes of Core E are high by about 7–9%. If the central hole of Core F is replaced with the same hole like Core B , the maximum thermal flux is estimated to be 8.33 × 1014 n cm−2 s−1 . If the maximum thermal flux is most important, Core F is the best core model.
Fig. 9. Relative power distribution and maximum fast and thermal neutron fluxes at targets for Core C and Core D.
C.G. Seo, N.Z. Cho / Nuclear Engineering and Design 252 (2012) 34–41
5. Summary and conclusions In recent years, most of the new multi-purpose research reactors use MTR-type fuel. The reactors have core configurations with a constant assembly pitch. Sizes of in-core irradiation holes are limited to a multiple size of fuel assembly. Since the frame of the irradiation hole is rectangular in shape, the space is not fully used for the cylindrical facilities. This paper introduces a new core design concept capable of overcoming the limitations of the conventional reactors. A new core design concept is to construct a core using edge trimmed irradiation holes. The new concept enables a core configuration to have different sizes of in-core irradiation holes using the same size of fuel assembly. The research reactors can be categorized into two types: compact core and large core. The two types of cores are constructed to investigate characteristics of the concept. The detail models are set up and the results are analyzed. The compact core by the new design concept provides following characteristics:
41
possibility that the core has only one type of fuel assembly without division into standard fuel and follower fuel. One type of fuel assembly is advantageous to reduce development and qualification costs, fuel management, fuel costs, and so on. This paper uses high power reactors of high power density, but the new concept is not limited to high power reactors. Maximum neutron flux level is more important at low power reactors, in which the large irradiation hole by the new concept can provide the required high neutron flux easily. Thus, the new design concept provides different characteristics and would be helpful to design new multi-purpose research reactors. This work does not provide depletion effects for investigating characteristics of the new design concept at the same condition. As the total uranium loadings of the core models are almost the same, the characteristics of the new concept will be maintained with burnup. The detailed analyses including the thermal hydraulics analysis and structural analysis would be required in a future study to implement the new concept at a real reactor construction. References
- The thermal neutron fluxes are almost the same at the reflector region. - The thermal neutron flux at the irradiation hole is very high. - An effective volume of the irradiation hole increases by 78.0%. - The control rod worth is very large such that other weakly absorbing material could be used. - Shapes of the irradiation hole and the core become close to cylinders. As for the large core, the concept provides following characteristics: - The cores with different sizes of irradiation holes can be constructed. - Both high fast and thermal neutron fluxes are available at the same core. - The large control rod worth can be useful for fuel management. - The irradiation hole close to a cylinder in shape provides a large effective volume for experimental devices. The cores by the new concept are loaded with smaller fuel assemblies which provide safety advantage for high power density. The new concept core uses fuel plates of the same size, that is, convenient for fuel manufacturing. The new concept provides a
Bönning, K., Von Der Hardt, P., 1987. Physics and safety of advanced research reactors. Nucl. Instrum. Methods Phys. Res. A260, 239–246. Difilippo, F.C., et al., 1986. A preliminary reactor design for the Center for Neutron Research. Nucl. Instrum. Methods Phys. Res. A249, 59–65. IAEA, 2010. Available via web at http://www.iaea.org/worldatom/rrdb/. Kim, S., 2006. The OPAL (open pool Australian light-water) reactor in Australia. Nucl. Eng. Technol. 38 (5), 443–448. MCNP, 2003. MCNP-A General Monte Carlo N-Particle Transport Code, Version 5. LA-CP-03-0245, Los Alamos National Laboratory. Miller, D.R., 1958. Critical Flow Velocities for Collapse of Reactor Parallel-Plate Fuel Assemblies, KAPL-M-DRM-13. Knolls Atomic Power Lab., Schenectady, NY. Raina, V.K., Sasidhaöran, K., Sengupta, S., Singh, T., 2006. Multi purpose research reactor. Nucl. Eng. Des. 236, 770–783. Shapiro, S., Rorer, D.C., Kuper, H. (Eds.), 1983. HFBR Handbook. BNL-24182. Brookhaven National Laboratory. Teruel, F., Rizwan-uddin, 2009. An innovative research reactor design. Nucl. Eng. Des. 239, 395–407. Yuan, L., Kang, Y., 1998. Problems concerned in fuel design of CARR. In: 1998 International Meeting on Reduced Enrichment for Research and Test Reactors, Sao Paulo, Brazil. Chul Gyo Seo (BS, nuclear engineering, Hanyang University, Korea, 1991; MS, nuclear engineering, Korea Advanced Institute of Science and Technology (KAIST), 1999) is a principal researcher at Korea Atomic Energy Research Institute (KAERI). His interests include nuclear reactor core physics. Nam Zin Cho (BS, nuclear engineering, Seoul National University, Korea, 1971; MS, 1976 and PhD, 1980, nuclear engineering, University of California, Berkeley, USA) is a professor at Korea Advanced Institute of Science and Technology (KAIST). His interests include nuclear reactor physics and analysis.
Contents lists available at SciVerse ScienceDirect
Nuclear Engineering and Design journal homepage: www.elsevier.com/locate/nucengdes
A core design concept for multi-purpose research reactors Chul Gyo Seo a,b , Nam Zin Cho a,∗ a b
Korea Advanced Institute of Science and Technology, 291 Daehak-ro, Yuseong-gu, Daejeon 305-701, Republic of Korea Korea Atomic Energy Research Institute, 1045 Daedeok-daero, Yuseong-gu, Daejeon 305-353, Republic of Korea
h i g h l i g h t s
We present a new design concept for multi-purpose research reactors of MTR-type fuel. Various in-core irradiation holes can be installed in the large core. In the compact core, high thermal flux can be achieved with a larger irradiation hole. Only a single type of fuel plate is used for the new core design.
a r t i c l e
i n f o
Article history: Received 10 November 2011 Received in revised form 20 June 2012 Accepted 27 June 2012
a b s t r a c t A new core design concept for multi-purpose research reactors is presented. New concept cores using material test reactor (MTR) type fuel are constructed with the edge trimmed in-core irradiation hole. Conventional research reactors have core configurations with a constant assembly pitch. Sizes of incore irradiation holes are limited to a multiple size of fuel assembly. The new concept enables a core configuration to have different sizes of in-core irradiation holes using the same size of fuel assembly. Two types of cores for multi-purpose research reactors are constructed and the performance results using MCNP calculation are compared. The new compact core for utilizing mainly beam tubes has a larger in-core irradiation hole and gives higher thermal neutron flux at the hole. The maximum thermal flux at the reflector region is almost the same. The new large core for utilizing in-core irradiation holes has small and large holes, while the conventional core has holes of the same size. The small hole is useful for high fast neutron flux and the large hole is useful for high thermal neutron flux. Compared to the conventional cores, the new cores use a smaller fuel assembly, which leads to enhanced safety at a high coolant speed for high power density. Two types of fuel plates are required for the conventional cores, but only one type of fuel plate will do for the new cores. This new design concept gives us several advantages and will be very useful for core design of multi-purpose research reactors. © 2012 Elsevier B.V. All rights reserved.
1. Introduction After the first criticality of Chicago Pile-1 on December 2, 1942, various research reactors have been developed and there are over 240 operational research reactors in the world (IAEA, 2010). Neutrons generated from research reactors are used for neutron scattering, neutron activation analysis, radiography, irradiation testing of materials and production of isotopes, etc. For most applications, higher neutron flux is always better. There are many practical constraints and difficulties for getting high neutron flux. A variety of fuels and cores have been developed to overcome the practical difficulties and satisfy their utilization purposes (Teruel and Rizwan-uddin, 2009). Especially, economic constraints pushed new reactors to be multi-purpose (Raina et al., 2006). New
∗ Corresponding author. Tel.: +82 42 350 3819; fax: +82 42 350 3810. E-mail address: [email protected] (N.Z. Cho). 0029-5493/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.nucengdes.2012.06.031
multi-purpose research reactors of over 10 MW power are listed in Table 1, in which no reactors are of the same type. In spite of different requirements, most reactors use material test reactor (MTR) type fuel. Reactor performance and operating costs strongly depend on fuel type. It is advantageous to owners if fuel is well-qualified for its performance and can be supplied by multiple vendors. A core of MTR-type fuel, in which fuel plates are arranged in a long rectangular box, is made up of regularly arranged plural fuel assemblies, control rods and irradiation holes. The overall core is a cylinder shape and surrounded by reflector. The core for isotope production and material test has fuel assemblies, control rods and irradiation holes in a rectangular lattice structure. Many irradiation holes make the core large and it can be classified into a “large core”. Other core concept was emerged for neutron scattering experiments. The experiments use thermal neutrons streaming out from beam tubes. The research reactors for neutron scattering have high thermal neutron flux in reflector region where beam tubes can be placed. To fulfill this requirement, a new design
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Table 1 Multi-purpose research reactors in operation and under construction or planned with thermal power ≥10 MW after 1980. Country
Name
In operation Libya Indonesia Peru Japan Korea Algeria Egypt Germany Australia China
IRT-1 RSG-GAS RP-10 JRR-3 M HANARO ES-SALAM ETRR-2 FRM-II OPAL CARR
Under construction or planned RJH France India MPRR PALLAS Netherlands
Power (MW) 10 30 10 20 30 15 22 20 20 60 100 20 80
concept so called “inverse flux trap” was introduced at the design of the high flux beam reactor (HFBR) (Shapiro et al., 1983). Recently, this concept was utilized at the design of FRM-II called as “compact core” concept (Bönning and Von Der Hardt, 1987). This “compact core” concept which requires a high power density and a small core, deviates the FRM-II core from general design limits. The FRM-II core for an extreme performance uses a special fuel composed of involute fuel plates and highly enriched uranium of 93 w/o, while only low enriched uranium below 20 w/o is presently available in the world market. So, the latest multi-purpose research reactor, CARR, uses “compact core” concept and MTR-type fuel (Yuan and Kang, 1998). This paper presents a new design concept for multi-purpose research reactors of MTR-type fuel in Section 2. In Section 3, two types of cores are constructed to investigate characteristics of the new design concept. Comparison results for the two types of cores are given and discussed in Section 4. Finally, summary and conclusions are given in Section 5.
Fuel
Reflector
Criticality date
Tube type MTR type MTR type MTR type Rod type Rod type MTR type Involuted plate MTR type MTR type
Be Be Be, Graphite D2 O D2 O Graphite, D2 O D2 O D2 O D2 O D2 O
1981 1987 1988 1990 1991 1992 1997 2004 2006 2010
Curved plate MTR type MTR type
Be D2 O Be
Construction Planned Planned
2. New design concept This section introduces a new core design concept useful for design of a multi-purpose research reactor of MTR-type fuel. A new core design concept is to construct a core using edge trimmed irradiation hole. A conceptual drawing of the irradiation hole is given in Fig. 1. Edges of the irradiation hole are trimmed, unlike conventional irradiation holes which are rectangular boxes with a hole or holes. As the frame of the conventional irradiation hole is rectangular in shape, the space is not fully used for experimental facilities, which are of cylindrical shapes. The frame of the new irradiation hole becomes more compact by trimming superfluous parts. The four faces of the irradiation hole could be contacted with fuel assemblies, but the four corners of the irradiation hole should be contacted with other irradiation holes or guide tubes except fuel assembly. The coolant in a fuel assembly flows in a high speed, therefore structural integrity of the fuel is important. Fuel should be placed by face-to-face contact with other structures such as fuel
Fig. 1. Conceptual drawing of the edge trimmed irradiation hole.
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Fig. 2. Core configurations of the CARR core and a new core.
assembly, irradiation hole and guide tube of control rod. Any corners of core structures should not be contacted with fuel plate or side plate of fuel assembly. Other types of contacts with the irradiation hole are allowed to preferably maintain face-to-face contact with the fuel. We explain the new concept using the CARR core mentioned above. The CARR core by the conventional design concept is shown in the left side of Fig. 2, in which fuel assemblies are regularly arranged. The core consists of 16 standard fuel assemblies, 4 follower fuel assemblies, and one in-core irradiation hole. Fillers occupy the space between the peripheral fuel assemblies and the inner wall of the reflector tank. Two types of fuel plates in the core should be used for two types of fuel assemblies in a rectangular lattice structure. The new design concept can change the CARR core into a new core as shown in the right side of Fig. 2. The new core has an edge trimmed irradiation hole at the center of the core. All fuel assemblies in the core are placed by face-to-face contact with other structures. The size of the standard fuel is equivalent to the size of the follower fuel, therefore one type of fuel plate can be used in two fuel assemblies. 3. Core construction There are many types of research reactors depending on standards of classification. When we use beam tube as a criterion, the reactors are usually divided into two types. So, in this study two types of cores are constructed to investigate characteristics of the new design concept. The first type of core is a compact core for utilizing mainly beam tubes. The second type of core is a large core for isotope production and irradiation test of materials. The compact core has one in-core irradiation hole for multi-purpose utilization and consists of 20 fuel assemblies. The compact core uses heavy water as a reflector and moderated and cooled by light water. The large core consists of 5 in-core irradiation holes and 20 fuel assemblies. The large core is moderated and cooled by light water also, but uses beryllium as a reflector. The two cores are research reactors of closed tank type for high power density. The coolant flows
downward and driving mechanisms of control rods are located underneath the cores. The control rods are moving within their guide tubes. Each control rod consists of a follower fuel and its connected Hf absorber. 3.1. Compact core A compact core is surrounded by an annular heavy water tank to obtain a large irradiation volume. The tank is 150 cm high and 150 cm in diameter. A thick Zircaloy wall of 1.5 cm divides the core and the reflector. A space between the wall and the fuel assemblies is filled with Be fillers. The central in-core irradiation hole is loaded with a target made of Al alloy of 6.0 cm in diameter. A space surrounding the target within the irradiation hole is filled with water to booster thermal neutron flux at the target. Core A by the conventional design concept is modeled in detail using MCNP (MCNP, 2003) as shown in Fig. 3. The mesh tally overlapped with structures is used for calculating thermal neutron flux distribution. It is difficult to compare two cores directly because the new concept core uses one type of fuel assembly and the conventional core uses two types of fuel assemblies. The sizes of fuel assemblies are adjusted for a same reactor power and a same power density to compare the two cores at the same condition. Core B by the new design concept is constructed using one type of fuel assembly, 7.62 × 7.62 cm, shown in Fig. 4. The active length of the fuel is 60.0 cm and other basic parameters are the same as those of JRR-3M. The standard fuel of Core A is 7.85 × 7.85 cm and the follower fuel is 6.59 × 6.59 cm. The irradiation hole of Core B becomes large and thus the core is modified into Core B . While the irradiation holes of Core A and Core B have the same inner diameter, those of Core A and Core B’ have the same minimum thickness, 0.5 cm. Two cores have the same thickness for fuel plate, side plate, and guide tube as shown in Table 2. Other dimensions such as Hf thickness, thickness of Zircaloy wall, and diameter of housing vessel are the same for a comparison. Four control rods are commonly used for reactor control and a first shutdown system (FSS). A second shutdown system (SSS) could be realized by drainage of heavy water like the OPAL reactor
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Fig. 3. Cross sectional view of MCNP model for Core A.
Table 2 Main parameters for Core A and Core B. Core A Reactor power (MW) Total uranium loading (kg) Fuel meat Uranium density (gU/cm3 ) Active length (cm)
Core B 40
38.41
38.25 U3 Si2 –Al 4.8 60
Fuel assembly type
Standard
Follower
Standard/follower
Fuel assembly size (cm) Number of plates Meat width (cm) Meat thickness (cm) Cladding thickness (cm) Thickness of side plate (cm) Coolant gap (cm) Guide tube size (cm) Thickness of guide tube (cm) Hf absorber size (cm) Thickness of Hf absorber (cm)
7.85 22 6.43 0.051 0.038 0.48 0.229
6.59 17 5.17 0.051 0.038 0.48 0.254
7.62 21 6.2 0.051 0.038 0.48 0.235 8.88 0.5 7.62 0.5
7.85 0.5 6.59 0.5
(Kim, 2006) or insertion of other shutdown rods into heavy water like the CARR reactor. The SSS for the compact core is omitted and is not modeled in this study. 3.2. Large core Both thermal and fast neutrons are important to utilization of a large core, while mainly thermal neutrons are used in the compact
core. Fast neutrons are required for material irradiation tests and thermal neutron flux should be high for isotope production and other irradiation tests. The reactors for irradiation tests become large to provide irradiation holes surrounded by fuel assemblies. Two large cores in Fig. 5 are constructed using 20 fuel assemblies as in the compact cores. The core of a 7 × 7 rectangular lattice has 45 channels which are positioned by fuel assemblies, control rods and irradiation holes. The cores could be loaded with more fuel assemblies or control rods. The right core of Fig. 5 is a new concept core with different in-core irradiation holes. The core is surrounded with a pressure vessel which has an outer diameter of 76 cm and a thickness of 2 cm. The outer region of the pressure vessel is surrounded with a Be block reflector of 20 cm in thickness and 100 cm in height. The outside of the Be reflector is filled with a pool water. Four control rods are connected with each magnetic clutch and moving by each stepping motor. Four control rods are commonly used for reactor control and FSS. Two shutdown rods driven by a hydraulic force are allocated for SSS. Large cores use the same fuel assemblies employed at Core A and Core B. Each large core has an in-core irradiation hole for fast neutron flux trap and 4 in-core irradiation holes for thermal neutron flux trap. Fig. 6 shows MCNP models for Fig. 5. The left core, Core C, is a conventional concept core and the right core, Core D, is a new concept core. The central irradiation hole has a minimized water gap for fast neutron irradiation and other irradiation holes have thick water gaps for thermalizing fission neutrons. All irradiation holes are loaded with Al alloy targets of 6.0 cm in diameter. The new design concept enables core to have different sizes of irradiation holes. Core E and Core F in Fig. 6 are constructed as examples.
Fig. 4. Cross sectional views of MCNP models for Core B and Core B .
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Fig. 5. Core configurations of a conventional large core and a new large core.
Fig. 6. Cross sectional views of MCNP models for Core C and Core D.
Fig. 7. Cross sectional views of MCNP models for Core E and Core F.
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Core E has the same size of irradiation holes, which is larger than the size of the fuel assembly. Core F has a large central hole and four small irradiation holes (Fig. 7).
Table 3 Reactivity worths for core models at several core conditions [%k/k].
Core A Core B Core B
4. Results and discussion The calculated results are obtained using MCNP version 5 which uses the standard libraries at room temperature based on ENDF/BVI. All cores are loaded with fresh fuel assemblies without burnable poison. Control rods are inserted about 1/3 for evaluating real neutron flux. This position is assumed to be at an equilibrium xenon state of begin of cycle (BOC). The reactor powers are assumed to be 40 MW which is a lower power density than that of the CARR. The average heat flux of the reactors is 1.28 MW/m2 , while the CARR core without in-core irradiation hole has an average heat flux of 1.39 MW/m2 . The presented neutron flux is a calculated neutron flux of 40 MW power multiplied by the effective multiplication factor. The fast neutron flux is defined as neutron flux with neutron energy above 0.1 MeV and the thermal neutron flux is below 0.625 eV. Mesh tally of 2 × 2 × 5 cm is used to calculate neutron flux distribution. The neutron flux of a target is a maximum neutron flux among fluxes evaluated at segments of 5 cm length. All MCNP calculations were carried out at ‘KCODE mode’. Each case was simulated with 500 active cycles of 100,000 particles per cycle. Prior to the reactivity calculation, a criticality at each core condition was calculated. The reactivity worth for two cases was defined as ‘reactivity worth [%k/k] = (1/k Case1 − 1/k Case2 ) × 100’. The statistical error is small enough, in which the reactivity worth is about 0.01%k/k and power distribution is below 0.1% and the maximum neutron flux is below 0.5%. 4.1. Compact core A compact core is used for mainly utilizing beam tubes, but the calculation models do not have beam tubes for a comparison. The calculated reactivity worths at several control rods’ positions are listed in Table 3. The core excess reactivity is enough as a reactor and the control rods have a sufficient reactivity worth to shut down the reactor safely. The excess reactivity of Core A is a little bit large because Core A has smaller guide tubes made of Al alloy. Core B modified from Core B spends 0.73%k/k for a higher thermal neutron flux. The guide tube of Core A is 7.85 × 7.85 cm and that
39
Excess
All rods 1/3 in
All rods in
(N-1) rods in
21.50 21.27 20.54
3.93 4.34 4.37
30.02 38.75 38.28
17.50 20.39 20.09
of Core B is 8.88 × 8.88 cm. The thickness of guide tubes is 0.5 cm for both. The size of follower fuel and Hf absorber makes a difference for reactivity worths of control rods. The new concept core has a large rod worth and could use other weakly absorbing material instead of Hf. Core B replaced by stainless steel has total rod worth of 15.63%k/k. Control rods made of stainless steel could be selected at the new concept core according to its fuel management strategy. The peak position of thermal neutron flux is formed at −10 cm below the core center. At this axial position, radial profile of thermal neutron flux is plotted at Fig. 8. On the basis of Core A, thermal neutron flux is almost the same at the reflector region, but shows a big difference at the irradiation hole. The new design concept provides not only a high thermal neutron flux but also a large irradiation volume. An overall volume of the hole increases by 56.5% and an effective volume for targets increases by 78.0%. The new concept utilizes effectively a space of the irradiation hole by trimming the edges. The core by the new concept can adjust the size of the irradiation hole by adjusting the thickness of the guide tube. Large irradiation hole can provide a large difference from the viewpoint of utilization of experimental facility. Thick water layer of Core B is replaced with a pressure boundary made of Zircaloy and targets can be loaded or unloaded on power state. It is also possible to install a test loop of high temperature and pressure requiring a large irradiation hole. A high reactor power is required in order to obtain a high thermal neutron flux, but the power is one of main constraints. The compact core concept provides a higher neutron flux at the same power level. The following equation explains this concept well (Difilippo et al., 1986): ˚th ∝
2/3
P P P 2/3 = P 1/3 = A V V
= P 1/3 ¯ 2/3 .
(1)
This argument shows that power density is more important than reactor power for high neutron flux. It is required to increase power
Fig. 8. Radial profile of thermal neutron flux in each core.
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Table 4 Reactivity worths for core models at several core conditions [%k/k].
Core C Core D Core E Core F
Table 5 Comparison of maximum neutron fluxes for core models.
Excess
All rods 1/3 in
All rods in
FSS (N-1) status
SSS
22.40 22.34 22.34 22.44
3.07 3.46 3.45 3.49
17.04 20.30 20.23 20.29
8.50 9.28 9.22 9.28
10.98 13.23 13.99 13.40
Position of irradiation hole
density as much as possible. High power density makes flow velocity fast for fuel cooling, and consequently structural integrity of fuel assembly becomes more important. Flow velocity should be below a criterion so called critical flow velocity Vc for maintaining structural integrity of fuel assembly. The critical flow velocity is defined as the minimum flow velocity to buckling collapse of one or more fuel plates. The velocity is related with the following parameters (Miller, 1958):
Center
Down
Left
Right
Up
Core C
3.52E+14a 6.72E+14b 1.69E+15c
4.26E+14 5.29E+14 1.53E+15
4.08E+14 5.12E+14 1.47E+15
4.06E+14 5.13E+14 1.47E+15
4.22E+14 5.32E+14 1.53E+15
Core D
3.55E+14 6.75E+14 1.70E+15
4.93E+14 4.60E+14 1.54E+15
4.71E+14 4.47E+14 1.47E+15
4.72E+14 4.75E+14 1.46E+15
4.91E+14 4.96E+14 1.53E+15
Core E
3.81E+14 6.51E+14 1.73E+15
4.64E+14 4.97E+14 1.54E+15
4.37E+14 4.78E+14 1.47E+15
4.37E+14 4.97E+14 1.54E+15
4.62E+14 4.78E+14 1.47E+15
Core F
4.15E+14 6.26E+14 1.77E+15
3.95E+14 5.45E+14 1.51E+15
3.80E+14 5.24E+14 1.46E+15
3.79E+14 5.16E+14 1.44E+15
3.93E+14 5.33E+14 1.50E+15
a b
Vc ∝
(Pt )
3/2
(Cg )
(Pw )2
1/2
,
c
(2)
where Pt = plate thickness, Cg = coolant gap, Pw = plate width. The size of fuel assembly should be small for high power density which requires high flow velocity. The largest plate width in the conventional core is 6.89 cm while the new core uses plate width of 6.66 cm. According to Eq. (2), the critical flow velocity in the new core increases by 6.5%. Thus, the new concept provides stronger structural integrity of the fuel assembly. 4.2. Large core For evaluation of a large core, Core D by the new concept is compared on the basis of Core C by the conventional concept. Core E and Core F by the new concept are compared also. Reactivity worths of core models at several core conditions are calculated and tabulated in Table 4. Core excess reactivities are almost the same but reactivity worths of control rods are considerably different. Reactivity worths of SSS are larger than reactivity worths of FSS for evaluating a shutdown margin by the “n-1” concept. If the reactivity worth of FSS is not large enough for its safe shutdown, additional control
Thermal. Fast. Total neutron flux.
rods or some restriction on fuel management will be required. As shown in Table 4, the new design concept provides larger reactivity worth of FSS. To compare neutron fluxes of large cores, maximum neutron fluxes at targets within irradiation holes are divided into thermal and fast neutron fluxes. Fig. 9 shows power distribution and neutron flux simultaneously for Core C and Core D. In principle, the fast neutron flux at the central holes of Core D should be high but are almost the same for low assembly powers within guide tubes. Thermal neutron fluxes at other irradiation holes of Core D are high about 15%. Core D has high thermal and fast flux holes at the same core. Table 5 shows a comparison of neutron fluxes for other reactors. Core E has the irradiation holes of the same size like Core C, but the thermal fluxes of Core E are high by about 7–9%. If the central hole of Core F is replaced with the same hole like Core B , the maximum thermal flux is estimated to be 8.33 × 1014 n cm−2 s−1 . If the maximum thermal flux is most important, Core F is the best core model.
Fig. 9. Relative power distribution and maximum fast and thermal neutron fluxes at targets for Core C and Core D.
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5. Summary and conclusions In recent years, most of the new multi-purpose research reactors use MTR-type fuel. The reactors have core configurations with a constant assembly pitch. Sizes of in-core irradiation holes are limited to a multiple size of fuel assembly. Since the frame of the irradiation hole is rectangular in shape, the space is not fully used for the cylindrical facilities. This paper introduces a new core design concept capable of overcoming the limitations of the conventional reactors. A new core design concept is to construct a core using edge trimmed irradiation holes. The new concept enables a core configuration to have different sizes of in-core irradiation holes using the same size of fuel assembly. The research reactors can be categorized into two types: compact core and large core. The two types of cores are constructed to investigate characteristics of the concept. The detail models are set up and the results are analyzed. The compact core by the new design concept provides following characteristics:
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possibility that the core has only one type of fuel assembly without division into standard fuel and follower fuel. One type of fuel assembly is advantageous to reduce development and qualification costs, fuel management, fuel costs, and so on. This paper uses high power reactors of high power density, but the new concept is not limited to high power reactors. Maximum neutron flux level is more important at low power reactors, in which the large irradiation hole by the new concept can provide the required high neutron flux easily. Thus, the new design concept provides different characteristics and would be helpful to design new multi-purpose research reactors. This work does not provide depletion effects for investigating characteristics of the new design concept at the same condition. As the total uranium loadings of the core models are almost the same, the characteristics of the new concept will be maintained with burnup. The detailed analyses including the thermal hydraulics analysis and structural analysis would be required in a future study to implement the new concept at a real reactor construction. References
- The thermal neutron fluxes are almost the same at the reflector region. - The thermal neutron flux at the irradiation hole is very high. - An effective volume of the irradiation hole increases by 78.0%. - The control rod worth is very large such that other weakly absorbing material could be used. - Shapes of the irradiation hole and the core become close to cylinders. As for the large core, the concept provides following characteristics: - The cores with different sizes of irradiation holes can be constructed. - Both high fast and thermal neutron fluxes are available at the same core. - The large control rod worth can be useful for fuel management. - The irradiation hole close to a cylinder in shape provides a large effective volume for experimental devices. The cores by the new concept are loaded with smaller fuel assemblies which provide safety advantage for high power density. The new concept core uses fuel plates of the same size, that is, convenient for fuel manufacturing. The new concept provides a
Bönning, K., Von Der Hardt, P., 1987. Physics and safety of advanced research reactors. Nucl. Instrum. Methods Phys. Res. A260, 239–246. Difilippo, F.C., et al., 1986. A preliminary reactor design for the Center for Neutron Research. Nucl. Instrum. Methods Phys. Res. A249, 59–65. IAEA, 2010. Available via web at http://www.iaea.org/worldatom/rrdb/. Kim, S., 2006. The OPAL (open pool Australian light-water) reactor in Australia. Nucl. Eng. Technol. 38 (5), 443–448. MCNP, 2003. MCNP-A General Monte Carlo N-Particle Transport Code, Version 5. LA-CP-03-0245, Los Alamos National Laboratory. Miller, D.R., 1958. Critical Flow Velocities for Collapse of Reactor Parallel-Plate Fuel Assemblies, KAPL-M-DRM-13. Knolls Atomic Power Lab., Schenectady, NY. Raina, V.K., Sasidhaöran, K., Sengupta, S., Singh, T., 2006. Multi purpose research reactor. Nucl. Eng. Des. 236, 770–783. Shapiro, S., Rorer, D.C., Kuper, H. (Eds.), 1983. HFBR Handbook. BNL-24182. Brookhaven National Laboratory. Teruel, F., Rizwan-uddin, 2009. An innovative research reactor design. Nucl. Eng. Des. 239, 395–407. Yuan, L., Kang, Y., 1998. Problems concerned in fuel design of CARR. In: 1998 International Meeting on Reduced Enrichment for Research and Test Reactors, Sao Paulo, Brazil. Chul Gyo Seo (BS, nuclear engineering, Hanyang University, Korea, 1991; MS, nuclear engineering, Korea Advanced Institute of Science and Technology (KAIST), 1999) is a principal researcher at Korea Atomic Energy Research Institute (KAERI). His interests include nuclear reactor core physics. Nam Zin Cho (BS, nuclear engineering, Seoul National University, Korea, 1971; MS, 1976 and PhD, 1980, nuclear engineering, University of California, Berkeley, USA) is a professor at Korea Advanced Institute of Science and Technology (KAIST). His interests include nuclear reactor physics and analysis.