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Gunji, Satoshi; Araki, Shohei; Arakaki, Yu; Izawa, Kazuhiko; Suyama, Kenya
Proceedings of 12th International Conference on Nuclear Criticality Safety (ICNC2023) (Internet), 9 Pages, 2023/10
JAEA has been modifying a critical assembly called STACY from a solution system to a light-water moderated heterogeneous system to validate computation results of criticality characteristics of fuel debris generated in the accident at TEPCO's Fukushima Daiichi Nuclear Power Station. To experimentally simulate the composition and characteristics of fuel debris, we will prepare several grid plates which make particular neutron moderation conditions and a number of rod-shaped concrete and stainless-steel materials. Experiments to evaluate fuel debris's criticality characteristics are scheduled using these devices and materials. This series of STACY experiments are planned to measure the reactivity of fuel debris-simulated samples, measure the critical mass of core configurations containing structural materials such as concrete and stainless steels, and the change in critical mass when their arrangement becomes non-uniform. Furthermore, two divided cores experiments are scheduled that statically simulate fuel debris falling, and also scheduled that subcriticality measurement experiments with partially different neutron moderation conditions. The experimental plans have been considered taking into account some experimental constraints. This paper shows the schedule of these experiments, as well as the computation results of the optimized core configurations and expected results for each experiment.
Araki, Shohei; Gunji, Satoshi; Arakaki, Yu; Yoshikawa, Tomoki; Murakami, Takahiko; Kobayashi, Fuyumi; Izawa, Kazuhiko; Suyama, Kenya
Proceedings of 12th International Conference on Nuclear Criticality Safety (ICNC2023) (Internet), 8 Pages, 2023/10
New experiments simulating fuel debris in the new criticality assembly, STACY, are designed to contribute to the validation of criticality calculations for criticality control of the fuel debris in the Fukushima Daiichi Nuclear Power Plant accident. In the new STACY experiment, a two-region core consisting of a driver region and a test region was investigated in order to configure a debris-simulated core with under-moderation condition (lattice pitch 1.27-cm) having the constraint of available fuel rod number. The test region with a 1.27-cm lattice pitch is surrounded by the driver region, in which fuel rods are arranged in a checkerboard pattern on a 1.27-cm lattice plate, with a 1.80-cm lattice pitch. Neutron spectra and sensitivity were calculated by using MCNP6 and ENDF/B-VII. The core which has a 1717 test region with 373 fuel rods is the largest two-region core under the constraint. It was found that the core which has a 17
17 test region can simulate the neutron spectra of under-moderation condition in a 13
13 region inside the test region with the root-mean square percentage error of less than 5%. It was also confirmed that the sensitivity of
Si and
Ca (n,
) reactions when the concrete simulant, was loaded could be simulated.
Araki, Shohei; Gunji, Satoshi; Arakaki, Yu; Murakami, Takahiko; Yoshikawa, Tomoki; Hasegawa, Kenta; Tada, Yuta; Izawa, Kazuhiko; Suyama, Kenya
Proceedings of 4th Reactor Physics Asia Conference (RPHA2023) (Internet), 4 Pages, 2023/10
To conduct integrated thermal power measurements for the performance test of the modified STACY, we re-analyzed the experimental data measured in the solution fuel STACY using the activation method. We validated its feasibility under the limited number of activation detectors. The re-analyzed results of the activation method by using MVP and PHITS with JENDL-4.0 indicated that the effect of the difference of the position between activation detectors was small enough, and the results agreed with that of the fission product analysis within almost 10%. It is conceivable that the activation method could be adopted instead of the fission product analysis.
Xu, P. G.; Tomota, Yo*; Arakaki, Yu; Harjo, S.; Sueyoshi, Hitoshi*
Materials Characterization, 127, p.104 - 110, 2017/05
Times Cited Count:46 Percentile:92.84(Materials Science, Multidisciplinary)Tomimoto, Hiroshi; Kato, Yasushi; Owada, Hiroyuki; Sato, Nao; Shimazaki, Yosuke; Kozawa, Takayuki; Shinohara, Masanori; Hamamoto, Shimpei; Tochio, Daisuke; Nojiri, Naoki; et al.
JAEA-Technology 2009-025, 29 Pages, 2009/06
The first driver fuel of the HTTR (High Temperature Engineering test Reactor) was loaded in 1998 and the HTTR reached first criticality state in the same year. The HTTR has been operated using the first driver fuel for a decade. In Fuel elements assembling, 4770 of fuel rods which consist of 12 kinds of enrichment uranium are loaded into 150 fuel graphite blocks for HTTR second driver fuel elements. Measures of prevention of fuel rod miss loading, are employed in fuel design. Additionally, precaution of fuel handling on assembling are considered. Reception of fuel rods, assembling of fuel elements and storage of second driver fuels in the fresh fuel storage rack in the HTTR were started since June, 2008. Assembling, storage and pre-service inspection were divided into three parts. The second driver fuel assembling was completed in September, 2008. This report describes concerns of fuel handling on assembling and storage work for the HTTR fuel elements.
Yamazaki, Kazunori; Kameyama, Yasuhiko; Inoi, Hiroyuki; Arakaki, Etsushi; Shinozaki, Masayuki; Ota, Yukimaru
JAEA-Testing 2008-002, 52 Pages, 2008/03
The High Temperature Engineering Test Reactor (HTTR) has the Gaseous Radwaste Treatment System (GRTS). This system appropriately collects all potentially radioactive gases discharged from the plant. After the gases are decayed with the Decay tank and decreased with the Filtering system, the gases are discharged into the atmosphere under monitoring. This system is maintained every year for keeping the performance. The maintenance is very important. Furthermore, the maintenance is profitable for designing a new High Temperature Gas cooled Reactor. This report describes the newly developed, maintenance items and improvements of the GRTS.
Kameyama, Yasuhiko; Watanabe, Shuji; Inoi, Hiroyuki; Shimizu, Yasunori; Arakaki, Etsushi; Shinozaki, Masayuki; Ota, Yukimaru
JAEA-Testing 2008-001, 63 Pages, 2008/03
The High Temperature Engineering Test Reactor (HTTR) has the Auxiliary Component Cooling Water System (ACCWS) and the General Cooling Water System (GCWS). ACCWS supplies the cooling water to the many facilities those are necessary to operate and cool the reactor. GCWS supplies the cooling water to the many facilities those are necessary to operate and cool the reactor in normal circumstances. Two kinds of the cooling water are cooled with the Cooling Tower. Each facility has the circulation pump, the cooling tower, the piping, the valve, the strainer and the injection system of the chemical solution. And these two facilities are operating all the year. This report describes maintenance items, improvements and management of the ACCWS and the GCWS.
Hamamoto, Shimpei; Iigaki, Kazuhiko; Shimizu, Atsushi; Sawahata, Hiroaki; Kondo, Makoto; Oyama, Sunao; Kawano, Shuichi; Kobayashi, Shoichi; Kawamoto, Taiki; Suzuki, Hisashi; et al.
JAEA-Technology 2006-030, 58 Pages, 2006/03
During normal operation of High Temperature engineering Test Reactor (HTTR) in Japan Atomic Energy Agency (JAEA), the reactivity is controlled by the Control Rods (CRs) system which consists of 32 CRs (16 pairs) and 16 Control Rod Drive Mechanisms (CRDMs). The CR system is located in stand-pipes accompanied by the Reserved Shutdown System (RSS). In the unlikely event that the CRs fail to be inserted, the RSS is provided to insert BC/C pellets into the core. The RSS shall be designed so that the reactor should be held subcriticality from any operation condition by dropping in the pellets. The RSS consists of B
C/C pellets, hoppers which contain the pellets, electric plug, driving mechanisms, guide tubes and so on. In accidents when the CRs cannot be inserted, an electric plug is pulled out by a motor and the absorber pellets fall into the core by gravity. A trouble, malfunction of one RSS out of sixteen, occurred during a series of the pre-start up checks of HTTR on February 21, 2005. We investigated the cause of the RSS trouble and took countermeasures to prevent the issue. As the result of investigation, the cause of the trouble was attributed to the following reason: In the motor inside, The Oil of grease of the multiplying gear flowed down from a gap of the oil seal which has been deformed and was mixed with abrasion powder of brake disk. Therefore the adhesive mixture prevented a motor from rotating.
Araki, Shohei; Arakaki, Yu; Maekawa, Tomoyuki; Murakami, Takahiko; Hasegawa, Kenta; Yoshikawa, Tomoki; Tada, Yuta; Kamikawa, Yutaka; Sumiya, Masato; Seki, Masakazu; et al.
no journal, ,
In the TEPCO's Fukushima Daiichi Nuclear Power Plant accident, fuel debris was formed by fuel melting and mixing with in-core structures. Although the detailed properties of the fuel debris are still unknown, it is thought to contain materials such as iron and concrete. Then, in order to understand the criticality characteristics of fuel debris, JAEA is conducting a comprehensive numerical analysis assuming the composition of fuel debris containing concrete and iron. However, integral experimental data including these materials are scarce, and the validation of the analytical results has not been fully investigated. Thus, JAEA modified the criticality facility STACY in order to obtain experimental data that will contribute to the validation. This report describes the outline and status of the modified-STACY, and the plan is also presented.
Araki, Shohei; Izawa, Kazuhiko; Gunji, Satoshi; Arakaki, Yu; Suyama, Kenya
no journal, ,
JAEA has been modifying the Static Experiment Critical Facility (STACY) to study the criticality characteristics of fuel debris. The concrete rod consists of a clad tube (9.5-mm od, 7.5-mm id, 1495-mm length) and a concrete simulant. It can be installed inthe core for fuel debris experiments. This report presents the status of the test production of a concrete rod.
Arakaki, Yu; Izawa, Kazuhiko; Gunji, Satoshi; Araki, Shohei; Suyama, Kenya
no journal, ,
JAEA has been modifying the Static Experiment Critical Facility (STACY) to experimentally study on the criticality characteristics of fuel debris. Although arbitrary detectors or activation samples can be placed in the core of STACY, they must be contained in sheath tubes (insertion tubes) that have been approved by the regulatory authorities. This report presents the status of the design study of the insertion tube for the experiments in the modified STACY.
Yoshikawa, Tomoki; Araki, Shohei; Arakaki, Yu; Izawa, Kazuhiko; Gunji, Satoshi; Suyama, Kenya
no journal, ,
In order to clarify the criticality characteristics of fuel debris, we plan experiments in the Static Experiment Critical Facility (STACY) by using concrete and steel simulating the structural materials of the core of the Fukushima Daiichi Nuclear Power Plant. In order to carry out the experiments, it is necessary to obtain a construction permit for the core with the debris structural material simulant mentioned above. In this presentation, we present the analysis results and the feasible core configuration for obtaining the certification from the regulatory body.
Araki, Shohei; Murakami, Takahiko; Kamikawa, Yutaka; Arakaki, Yu; Tada, Yuta; Aizawa, Eiju; Ishii, Junichi; Seki, Masakazu; Izawa, Kazuhiko; Gunji, Satoshi
no journal, ,
We conducted thermal power measurements and thermal power calibration for a performance test in the modified STACY. The activation method was adopted in the thermal power measurements. The core for the measurements consisted of 253 fuel rods and a sample driver. The gold foils used for the activation foil method were installed in the sample driver. The operation was carried out twice, at 20-W and 50-W. The neutron flux in the core and the response of the gold foil were calculated using MVP and PHITS, respectively, with JENDL-5 as the nuclear data. In each measurement, the integrated power was 4.2-Wh and 8.9-Wh, respectively. The indicated power with default setting was found to be about 50% higher than the evaluated value.
Hasegawa, Kenta; Arakaki, Yu; Murakami, Takahiko; Sumiya, Masato; Aizawa, Eiju; Seki, Masakazu; Ishii, Junichi; Araki, Shohei; Izawa, Kazuhiko; Gunji, Satoshi
no journal, ,
no abstracts in English
Araki, Shohei; Gunji, Satoshi; Yoshikawa, Tomoki; Arakaki, Yu; Izawa, Kazuhiko; Suyama, Kenya
no journal, ,
The first criticality of the statistical criticality assembly called "STACY", which JAEA has been modifying, is scheduled for 2024. After the first criticality, experiments using debris structure material rods are being prepared. At the spring 2023 annual meeting, we presented the results of a study on the core characteristics of the experimental core under the condition of using 900 fuel rods. However, it is requested to consider the core configuration with 400 fuel rods due to the fuel procurement. In this study, we reanalyzed the core with 400 fuel rods and confirmed that the core characteristics are included in that of the previous presentation.
Gunji, Satoshi; Araki, Shohei; Arakaki, Yu; Izawa, Kazuhiko
no journal, ,
In the experiment to evaluate the criticality characteristics of fuel debris using STACY, rod-shaped simulants will be made of mortar composition to simulate the concrete assumed to be contained in the fuel debris. For that cases, it is necessary to evaluate the effect of composition-related uncertainties on critical experiments. In this study we performed computations in which the contents of water, silica, and lime, which are the main components of the simulants, were perturbed, and the effect on the critical water level was investigated. As a result, it was confirmed that there was no significant effect within the manufacturing tolerance of the simulants.