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Iwamoto, Osamu; Iwamoto, Nobuyuki; Kunieda, Satoshi; Minato, Futoshi; Nakayama, Shinsuke; Abe, Yutaka*; Tsubakihara, Kosuke*; Okumura, Shin*; Ishizuka, Chikako*; Yoshida, Tadashi*; et al.
Journal of Nuclear Science and Technology, 60(1), p.1 - 60, 2023/01
Times Cited Count：64 Percentile：99.99(Nuclear Science & Technology)Ito, Chikara; Ito, Keisuke; Ishikawa, Takashi; Yoshida, Akihiro; Sanada, Yukihisa; Torii, Tatsuo; Notomi, Akihiro*; Wakabayashi, Genichiro*; Miyazaki, Nobuyuki*
Hoshasen, 39(1), p.7 - 11, 2013/09
no abstracts in English
Sumino, Kozo; Kobayashi, Tetsuhiko; Isozaki, Kazunori; Yoshida, Akihiro
Nihon Hozen Gakkai Dai-7-Kai Gakujutsu Koenkai Yoshishu, p.255 - 257, 2010/07
In the experimental fast reactor Joyo, maintenance work was conducted based on the classification of safety importance over thirty years. Through the experience, it was confirmed that particular effort was not necessary for the maintenance of sodium cooling systems by controlling the coolant purity properly. Additionally, as a result of the technical review on aging for whole plant, significant aging phenomenon that is particular with sodium cooled fast reactor was not observed.
Aoyama, Takafumi; Sekine, Takashi; Maeda, Shigetaka; Yoshida, Akihiro; Maeda, Yukimoto; Suzuki, Soju; Takeda, Toshikazu*
Nuclear Engineering and Design, 237(4), p.353 - 368, 2007/02
Times Cited Count：17 Percentile：72.04(Nuclear Science & Technology)Many changes were made in the recent upgrade of the experimental fast reactor JOYO to the MK-III design. The core changes which were made to achieve a fourfold increase in irradiation capacity include the introduction of a second enrichment zone, an increase in core radius and a decrease in core height. Performance tests done at low power, during the rise to power, and at full power, which focus on the neutronics characteristics, are presented. These tests include the nuclear instrumentation system response, the approach to criticality and excess reactivity evaluation, control rod worth calibration, isothermal temperature coefficient evaluation, the calibration of the nuclear instrumentation system with reactor thermal power, and the burn-up reactivity coefficient evaluation. The measurements and comparisons with calculated predictions are shown. The design predictions are consistent with the performance test results, and all technical safety specifications are satisfied. The JOYO MK-III core will provide enhanced irradiation testing capability, as well as serve as a test bed for improving fast reactor operation, performance and safety. Through the performance test evaluation, the core characteristics of a small size sodium cooled fast reactor with a hard neutron spectrum are clarified.
Matsuba, Kenichi; Kawahara, Hirotaka; Ito, Chikara; Yoshida, Akihiro; Nakai, Satoru
UTNL-R-0453, p.12_1 - 12_10, 2006/03
no abstracts in English
Takamatsu, Misao; Kuroha, Takaya*; Yoshida, Akihiro
JNC TN9410 2004-005, 51 Pages, 2004/03
JNC-TN9410-2004-005.pdf:1.25MB
A study of passive safety test using JOYO has been carried out to demonstrate the inherent safety of sodium cooled fast reactors. In this study, emphasis was placed on the improvement of the accuracy of plant kinetics calculations. The Mimir-N2 analysis code, developed to analyze JOYO plant kinetics, was selected as the standard code for predicting plant behavior during transients. Mimir-N2 was Previously modified based on the data from plant characteristics and natural circulation tests during JOYO MK-II. Recently, the model of the core and the heat transport system of Mimir-N2 was upgraded to correspond to the modified heat transport system for MK-III. The MK-III performance test included manual reactor shutdown test and loss of power supply test etc. as transient tests. Although the sodium temperatures calculated by Mimir-N2 agreed well with the measurement results in the MK-III performance test, it was observed that the calculated sodium temperature descent rate at reactor vessel inlet and dump heat exchanger inlet etc. were slightly larger than measured. In order to further improve the accuracy of the calculation, the Mimir-N2 heat transport system models of the reactor vessel upper plenum, the hot leg of secondary heat transport system and the dump heat exchanger were modified based on the results of the MK-III performance test. As a result of the Mimir-N2 modification, the calculation results had improved agreement with the measurement results and it was confirmed that Mimir-N2 can accurately calculate plant behavior during transients such as reactor shutdown and loss of power supply.
Maeda, Yukimoto; Aoyama, Takafumi; Yoshida, Akihiro; Sekine, Takashi; Ariyoshi, Masahiko; Ito, Chikara; Masaaki, Nemoto; Murakami, Takanori; Isozaki, Kazunori; Hoshiba, Hideaki; et al.
JNC TN9410 2003-011, 197 Pages, 2004/03
JNC-TN9410-2003-011.pdf:10.26MB
MK-III performance tests began in June 2003 to fully characterize the upgraded core and heat transfer system. Then, the last pre-use inspection was finished in November 2003.This report summarize the result of each performance test.
Takamatsu, Misao; Kuroha, Takaya*; Yoshida, Akihiro
JNC TN9400 2003-012, 38 Pages, 2003/03
JNC-TN9400-2003-012.pdf:2.03MB
A study of passive safety test using Joyo has been carried out to demonstrate the inherent safety of sodium cooled fast reactor. In this study, emphasis was placed on the improvement on feedback reactivity calculation accuracy. Especially, the core bowing reactivity has been one of the main targets of this study because it can be designed to provide negative reactivity in the event of power excursion. The core bowing reactivity was calculated by "MERBA" (MEchanical behavior and Reactivity shift caused by core Bowing Analysis code system for Joyo)" which had been developed for Joyo MK-II core. Through the operation of MK-II core, measured power reactivity coefficient shows a power dependency on reactor thermal power, which is considered to be caused by core bowing effect. In order to investigate the mechanism of this phenomenon, the measured power dependency on power reactivity coefficient were compared with the calculation by "MERBA". It was confirmed that the power dependency on the power reactivity coefficient of the MK-II core could be explained by a core bowing reactivity. In the upgraded MK-III core, neutron flux, the coolant temperature difference between reactor inlet and outlet, etc. will be changed and these may effect on the core bowing reactivity. Therefore, the core bowing reactivity of MK-III performance tests core was evaluated using "MERBA" which was modified to analyze MK-III core. As a result of "MERBA" calculation, the core bowing behavior of MK-III performance tests core was almost similar to MK-II core; the fuel subassembly was initially bent toward the core center at zero power, because the middle spacer pad of fuel subassembly was suppressed by reflectors which have rather large permanent distortion. During the thermal power increase, the fuel subassembly was bent to outward and the negative reactivity was inserted by the fuel movement to outward.
; Maeda, Yukimoto; Suzuki, Soju; Hara, Hiroshi
Russian Forum for Sci. and Tech. FAST NEUTRON REAC, 0 Pages, 2003/00
The experimental fast reactor JOYO attained its initial criticality in 1977 with the MK-I breeder core. In 1982, JOYO was modified to the MK-II irradiation core and finished its operation in 2000. Throughout the successful operation of MK-I and MK-II core, the net operation time has exceeded 60,000 hours, and experience on the operation, maintenance and core/fuel management of a fast reactor plant has been accumulated. Furthermore the MK-III modification program is underway to improve the irradiation capability of JOYO. When the MK-III core is started, it will support irradiation tests in feasibility studies for fast reactor and related fuel cycle research and development in Japan.
; Yoshida, Akihiro; Aoyama, Takafumi; Maeda, Yukimoto
Saikuru Kiko Giho, (21), p.5 - 25, 2003/00
A Joyo upgrade program named MK-III program was started to develop future FBR in 1987. The main objectives of this program are increasing the capability as an irradiation test bed core and developing innovative FBR technologies.In order to modify the irradiation capability, the core and plant modification program which consists of increasing the neutron flux density of the core, modification of the cooling system, modification of the plant availability factor and upgrading irradiation technologies were decided based on the result s of survey calculations. The licensing work completed in 1995, and all the modification work completed in 2003. JOYO will start rated power operation along with several irradiation tests in 2004. Also the installation and demonstration program of innovative technologies such as Self-actuated shut down system for demonstration FBR and double-walled steam generator for future FBR were investigated.
; Yoshida, Akihiro; Aoyama, Takafumi; Maeda, Yukimoto
Saikuru Kiko Giho, (21), p.17 - 25, 2003/00
Design works on the MK-III upgrading core were carried out and detailed core specification was determined from a viewpoint of increasing a fast neutron flux and a capacity for irradiation rigs. Based on the results of nuclear, thermal hydraulic calculation and shielding calculation, it was confirmed that the MK-III core shows expected core performance along with the integrity of the whole core.
; ;
JNC TN9410 2002-002, 81 Pages, 2002/03
JNC-TN9410-2002-002.pdf:2.41MB
The experimental fast reactor "JOYO" is being upgraded to the MK-III core to improve its irradiation capability. At present, the MOX fuel is fabricated using 18% enriched uranium. However, due to the JCO accident, 18% enriched uranil nitrate is not available in Japan. So, the uranium enrichment of MOX fuel will decrease starting with the third fuel manufacturing campaign in 2010. The nuclear and thermal design of JOYO MK-III next generation core started in 2001. We examined the criticality, linear heat rate and other parameters for two fuel compositions with a 60cm core height. About 31% plutonium content is required to keep the core reactivity as much as the present MK-III core when using plutonium with 63% fissile plutonium ratio. In case of usig reprocessing plutonium only for the MK-III inner driver fuel from the ATR Fugen, which has less fissile plutonium ratio about 50%, plutonium content needs to increase about 32.6%. Neutron flux decreased about 5
7% from the present MK-III score mainly due to the increase of core height, but exceeded the MK-II core. The control rod worth, the absolute value of Doppler coefficient and power coefficient are larger than the MK-III stcore. The absolute value of the sodium void reactivity decreased but remained negative. These calculations confirmed the safety of each core configuration. Safety analyses were also carried out and it was confirmed that maximum fuel temperature during the transient event and the post accident public radiation dose are almost same as those of the MK-III core.
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JNC TN9410 2002-001, 47 Pages, 2002/03
JNC-TN9410-2002-001.pdf:13.56MB
A study on the inherent safety test at the Experimental Fast Reactor Joyo has been performed to demonstrate the inherent safety of fast breeder reactors. In this study, emphasis was placed on the improvement on the feedback reactivity calculation accuracy. The investigation work for core bowing calculation has been continued because it is expected to cause negative feedback reactivity that would improve the passive safety of a fast breeder reactor. The core bowing behavior in JOYO has been analyzed by the system which consists of the MK-II core management code system MAGI, the interface code TETRAS and the core bowing calculation code BEACON. As it was supposed that the coolant flow inside of the reactor vessel might effects on wrapper tube temperature, detailed coolant flow was calculated by single-phase multi-dimensional therml-hydraulic analysis code AQUA. (1)As a result of the AQUA calculation, it was made clear that the coolant flow effect on the coolant temperature was negligible in fuel region. (2)The coolant temperature at the outlet of reflectors adjacent to a fuel subassembly are affected by the coolant flow that comes from the outlet of reflectors in the 6 th and the 7 th row. It decreases the outlet temperature of the reflectors in the 5 th row in AQUA calculation. (3)High temperature coolant flow exists in neighbor of the outlet of reflectors in the 810 throw. As a result, coolant temperature calculated by AQUA are higher in 3040
C than that calculated by TETRAS. It was made clear that the coolant flow inside of the reactor vessel had no effect on driver fuel bowing, which was the dominant factor of the core bowing reactivity. On the other hand, in reflectors region, it affects the wrapper tube temperature, which determine the irreversible swelling and creep. Essentially, in order to verify the feedback reactivity effect caused by the core bowing, it is desired to measure the mechanical behavior of the subassemblies under ...
; Yogo, Shizuhide
Proceedings of 9th International Conference on Nuclear Engineering (ICONE-9) (CD-ROM), (487), 492 Pages, 2001/04
The experimental fast reactor Joyo finished its operation as an irradiation core in June, 2000. Throughout the operation of MK-I (breeder core)and MK-II (irradiation core),the net operation time has exceeded 60,000 hours. During these operations there were no fuel failures or serious plant problems. The MK-III modification program will improve irradiation capability to demonstrate advanced technologies for commercial Fast Breeder Reactor (FBR). When the MK-III core is complete, it will support irradiation tests in feasibility studies for reactor for reactor and related fuel cycle research and development in Japan.
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JNC TN9440 2001-003, 52 Pages, 2001/03
JNC-TN9440-2001-003.pdf:1.39MB
The MK-III core upgrade program is now in progress for the Experimental Fast Reactor JOY0. The objective of this program is to increase irradiation capability for irradiation tests. Performance tests for the new core were planed and operation schedule was developed during 2000. A total of 27 MK-III core and plant performance tests will be carried out between September. 2002 and January. 2003.
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JNC TN9410 2001-013, 45 Pages, 2001/03
JNC-TN9410-2001-013.pdf:3.67MB
The Joyo experimental fast reactor is being upgraded with MK-III core to improve the irradiation capability. The initial MK-III core fuel being manufactured with MOX powder with equal parts of uranium and plutonium. The uranium has 18% 
U enrichment with uranil nitrate. Due to the JCO accident, uranil nitrate is not available in Japan. The first two fuel campaigns for the MK-III core will use JNC plutonium processed in France so the fuel composition will match the initial fuel. However, this plutonium is limited and future plutonium imports have many unresolved problems and may not be available for MK-III fueling. Assuming that the 3
fuel campaign in 2010 will use MOX from reprocessing plant as an alternate, a core and thermal design of Joyo MK-III next generation core has started. The MOX powder extracted from the reprocessing plant will decrease the U enrichment of fabricated fuel pellets. To reach criticality with this fuel, the active core height and plutonium content of fuel should be increased. With 20% enriched uranium, the core design requires 34% plutonium content and 55cm fuel height. With 5% enriched uranium for LWR, the core design requires 37% plutonium content and 60cm fuel height. Neutron flux decreases with increasing core height and increases with increased plutonium content so the two effects can cancel each other out and the maximum fast neutron flux is as high as that of MK-III standard core. While the effect on control rod characteristics due to increasing the fuel height is small, the decrease of effective delayed neutron ratio 
eff causes increased control rod reactivity described in the cent of unit. The absolute values of Doppler coefficient and power coefficient increase. The absolute value of sodium void reactivity decreases but it is still negative. The maximum fuel temperature meets the thermal design standard value based on the decreased fuel melting point due to the increased plutonium content.
; *
JNC TN9400 2001-051, 38 Pages, 2001/03
JNC-TN9400-2001-051.pdf:3.46MB
The study on the passive safety test by using the Experimental Fast Reactor Joyo was performed to demonstrate the inherent safety of fast breeder reactors. An analysis code: Mimir-N2, which has been developed to analyze Joyo plant kinetics, was selected as a standard code for this study. In order to increase the reliability of the calculation, Mimir-N2 code was adjusted based on the data obtained through several plant characteristics tests carried out in Joyo. Throughout an operational data obtained in Joyo, it is supposed that the burn-up dependency observed on the power reactivity coefficient might be coming fiom the reactivity shift caused by a depression of a thermal expansion of fuel pellet. Based on the relationship between the measured power reactivity coefficient and the core averaged burn-up, the burn-up dependency mentioned above was estimated and introduced to Mimir-N2. As a result, calculated core and plant dynamics during the step reactivity response test, such as the response of the power range neutron monitor and the coolant temperature at the core inlet / outlet, corresponded with the measured value, Especially, it was confirmed that Mimir-N2 can simulate the perturbation caused by the thermal expansion of the core support plate. In addition, Mimir-N2 was modified to be enable to take into account for the core bowing reactivity, which is calculated by the core bowing reactivity analysis system developed for Joyo. The preliminary analysis of the plant dynamics during the ATWS events in MK-III core were carried out by using modified Mimir-N2. As a result, it was confirmed that the core bowing reactivity should not be neglected because it sometimes shows positive feedback characteristics.
; ; Aoyama, Takafumi
JNC TN9400 2001-033, 45 Pages, 2001/01
JNC-TN9400-2001-033.pdf:7.55MB
Fission Products (FPs) were not considered in conventional fast reactor shielding analyses that were predominantly developed in clean core experiments like the JASPER program. However, in power reactors with high burn-up, the accumulation of FP affects the neutron balance so it cannot be neglected in the neutron flux calculation. In this study, the lumped group constants of FP nuclides were computed based on the JENDL-3.2 nuclear data library and these were compiled to the JSD-J2 set. Using the constants, the effect of the FP nuclides on shielding calculation was evaluated in the JOYO experimental fast reactor. Generation and depletion for nearly 880 FP nuclides can be computed with the ORIGEN2 burn-up calculation. The calculation uses the specification and material contents of the JOYO Mk-II driver as an example of fast reactor MOX fuel. About 99.8% of the total FP neutron absorption comes from 165 major nuclides. The cross section data for these nuclides are stored in the JENDL-3.2 library. The contributions of other FP nuclides were found to be negligible so the calculation used only these 165 FP nuclides. The lumped group constants for the FP nuclides were generated as follows. The 100 group infinite dilution cross section of each individua1 FP nuclide was computed with the NJOY-94 code. The energy group structure is the same as the JSD-J2 set and the scattering anisotropy is considered up to P3 components of Legendre expansion. Atomic number densities of FP nuclides generated from U, 
U, 
Pu and 
Pu were independently computed by ORIGEN2 as a function of fuel burn-up. The lumped FP constants were then obtained by averaging the infinite dilution cross sections with the atomic number densities based on the assumption that one fission produces one lumped FP. To verify the calculated lumped FP constants, the absorption microscopic cross section data were compared with the JFS-3-J3.2 group constants used for the fast reactor ...
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JNC TN9410 2001-009, 26 Pages, 2000/12
JNC-TN9410-2001-009.pdf:2.22MB
The study on the passive safety test in the Experimental Fast Reactor Joyo has becn performed to demonstrate the inherent safety of fast breeder reactors. In this study, emphasis was placed on the improvement of the accuracy of the feedback reactivity analysis. If the core bowing reactivity which is one of the feedback reactivity can be negative in core designing, the inherent safety of fast breeder reactors is expected to be improved. Then the core bowing reactivity evaluation technique is being improved. Through the core characteristics measurements in Joyo, a power dependency was observed on the power reactivity coefficient. The reason of the phenomenon was supposed to be a core bowing reactivity. Therefore, the power reactivity coefficient was measured by the step response measurement test and measured values were analyzed on the hypothesis that power dependency of the power reactivity is caused by core bowing reactivity. The core bowing displacement has been calculated by "BEACON". considering the refueling and irradiation history of each operation cycle in Joyo. The core bowing reactivity has been calculated by "ARCHCOM" based on the results of "BEACON". The core bowing reactivity of each reactor power was calculated and compared with the measured power dependency of the power reactivity coefficient. The calculated value agreed with measured one within the factor 0.6 to 2.0. As aresult, the core bowing behavior can explain the power dependency which is observed on the power reactivity coefficient in Joyo.
