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Journal Articles

Preliminary experiment in a graphite-moderated core to avoid full mock-up experiment for the future first commercial HTGR

Okita, Shoichiro; Fukaya, Yuji; Sakon, Atsushi*; Sano, Tadafumi*; Takahashi, Yoshiyuki*; Unesaki, Hironobu*

Proceedings of International Conference on Physics of Reactors 2022 (PHYSOR 2022) (Internet), 9 Pages, 2022/05

Journal Articles

Neutron capture and total cross-section measurements and resonance parameter analysis of niobium-93 below 400 eV

Endo, Shunsuke; Kimura, Atsushi; Nakamura, Shoji; Iwamoto, Osamu; Iwamoto, Nobuyuki; Rovira Leveroni, G.; Terada, Kazushi*; Meigo, Shinichiro; Toh, Yosuke; Segawa, Mariko; et al.

Journal of Nuclear Science and Technology, 59(3), p.318 - 333, 2022/03

Journal Articles

Numerical simulation of two-phase flow in fuel assemblies with a spacer grid using a mechanistically based method

Ono, Ayako; Yamashita, Susumu; Suzuki, Takayuki*; Yoshida, Hiroyuki

Proceedings of 19th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-19) (Internet), 16 Pages, 2022/03

JAEA is developing the methodology to predict the critical heat flux based on a mechanism in order to reduce the cost for full mock-up test. The evaluation method based on a mechanism is expected to be able to predict in the wide range of parameter under the unexpected conditions including the severe accident. In this study, the JUPITER code developed by JAEA is examined to apply for the two-phase flow simulation of LWR fuel assembly with the spacer grid. The benchmark data of single-phase flow in the bundle with the spacers by KAERI were used to validate the simulation result by JUPITER. Moreover, the single-phase flow simulation was conducted by another simulation method, STAR-CCM+, as a supplemental analysis to consider the effect of the different simulation methods. Finally, the two-phase flow simulation for the bundle with the spacer was conducted by JUPITER. The effect of the spacer with a vane on the bubble behavior is discussed.

Journal Articles

Experiments of melt jet-breakup for agglomerated debris formation using a metallic melt

Iwasawa, Yuzuru; Sugiyama, Tomoyuki; Abe, Yutaka*

Nuclear Engineering and Design, 386, p.111575_1 - 111575_17, 2022/01

Journal Articles

Design of a portable backup shutdown system for the high temperature gas cooled reactor

Hamamoto, Shimpei; Ho, H. Q.; Iigaki, Kazuhiko; Goto, Minoru; Shimazaki, Yosuke; Sawahata, Hiroaki; Ishitsuka, Etsuo

Nuclear Engineering and Design, 386, p.111564_1 - 111564_8, 2022/01

The experience of Fukushima Daiichi Nuclear Power Plant accident caused by the great earthquake that occurred in eastern Japan in 2011 showed the importance of preparing for the loss of function of the engineered safety features. Increasing the strength of equipment to prevent loss of function in an accident is effective, but the possibility of loss of function remains. Therefore, it is important to have an alternative to lost functions in order to put the accident under control early. Thus, this study designed an alternative shutdown system, namely a portable backup shutdown system (PBSS), to make countermeasures in the event of a loss of shutdown function more robust without impairing economic efficiency of the High Temperature Gas-cooled Reactor (HTGR). The PBSS is portable and capable of being installed manually so that it can operate in a total loss of off-site electricity. Various neutron absorber materials for the PBSS were also considered from the viewpoints of technical and cost-effective properties. As results of optimization, the boron nitride (BN) was selected as it shows a good neutronic property as well as a reasonable cost in comparison with other materials.

Journal Articles

Seismic classification of high temperature engineering test reactor

Ono, Masato; Shimizu, Atsushi; Ohashi, Hirofumi; Hamamoto, Shimpei; Inoi, Hiroyuki; Tokuhara, Kazumi*; Nomoto, Yasunobu*; Shimazaki, Yosuke; Iigaki, Kazuhiko; Shinozaki, Masayuki

Nuclear Engineering and Design, 386, p.111585_1 - 111585_9, 2022/01

In the late 1980s during the design stage, the seismic classification of the high temperature engineering test reactor (HTTR) was formulated. Owing to the lack of operation experiences of the HTTR to sufficiently understand the safety characteristics of high temperature gas cooled reactors (HTGR) at that time, the seismic classification of commercial light water reactors (LWR) was applied to HTTR. However, the subsequent operation experiences and test results using HTTR made it clear that the seismic classification of commercial LWR was somewhat too conservative for the HTGR. As a result, Class S facilities were downgraded compared to the commercial LWR. Moreover, the validity of the new seismic classification is confirmed. In June 2020, the Nuclear Regulatory Authority approved that the result of the seismic classification conformed to the standard rules of the reactor installation change.

JAEA Reports

Measurement methods for the radioactive source distribution inside reactor buildings using a one-dimensional optical fiber radiation sensor (Contract research); FY2020 Nuclear Energy Science & Technology and Human Resource Development Project

Collaborative Laboratories for Advanced Decommissioning Science; Nagoya University*

JAEA-Review 2021-033, 55 Pages, 2021/12

JAEA-Review-2021-033.pdf:2.9MB

The Collaborative Laboratories for Advanced Decommissioning Science (CLADS), Japan Atomic Energy Agency (JAEA), had been conducting the Nuclear Energy Science & Technology and Human Resource Development Project (hereafter referred to "the Project") in FY2020. The Project aims to contribute to solving problems in the nuclear energy field represented by the decommissioning of the Fukushima Daiichi Nuclear Power Station, Tokyo Electric Power Company Holdings, Inc. (TEPCO). For this purpose, intelligence was collected from all over the world, and basic research and human resource development were promoted by closely integrating/collaborating knowledge and experiences in various fields beyond the barrier of conventional organizations and research fields. The sponsor of the Project was moved from the Ministry of Education, Culture, Sports, Science and Technology to JAEA since the newly adopted proposals in FY2018. On this occasion, JAEA constructed a new research system where JAEA-academia collaboration is reinforced and medium-to-long term research/development and human resource development contributing to the decommissioning are stably and consecutively implemented. Among the adopted proposals in FY2019, this report summarizes the research results of the "Measurement methods for the radioactive source distribution inside reactor buildings using a one-dimensional optical fiber radiation sensor" conducted in FY2020. We are developing a one-dimensional optical fiber radiation sensor that can estimate the radioactive source distribution "along lines" instead of "at points". To improve the conventional time-of-flight optical fiber radiation sensor for the application under high dose rate environment, basic evaluation tests were conducted using various optical fibers with different diameters and materials. We found the usefulness of quartz optical fiber as a one-dimensional radiation sensor with high position resolution. We also conducted the study of a newly-developed

Journal Articles

Toward mechanistic evaluation of critical heat flux in nuclear reactors, 2; Recent studies and future challenges toward mechanistic and reliable CHF evaluation

Okawa, Tomio*; Mori, Shoji*; Liu, W.*; Ose, Yasuo*; Yoshida, Hiroyuki; Ono, Ayako

Nihon Genshiryoku Gakkai-Shi ATOMO$$Sigma$$, 63(12), p.820 - 824, 2021/12

The evaluation method of the critical heat flux based on the mechanism is needed for the efficient design and development of fuel in reactors and the appropriate safety evaluation. In this paper, the current researches relating to the mechanism of the critical heat flux are reviewed, and the issue to be considered in the future are discussed.

JAEA Reports

Operation, test, research and development of the High Temperature Engineering Test Reactor (HTTR) (FY2019)

Department of HTTR

JAEA-Review 2021-017, 81 Pages, 2021/11

JAEA-Review-2021-017.pdf:2.53MB

The High Temperature Engineering Test Reactor (HTTR) is the first High-Temperature Gas cooled Reactor (HTGR) constructed in Japan at the Oarai Research and Development Institute of the Japan Atomic Energy Agency with 30MW in thermal power and 950$$^{circ}$$C of outlet coolant temperature. The purpose of the HTTR is to establish and upgrade basic technologies for HTGRs. The HTTR has accumulated a lot of experience of HTGRs' operation and maintenance up to the present time throughout rated power operations, safety demonstration tests, long-term high temperature operations and demonstration tests relevant to HTGRs' R&Ds. In the fiscal year 2019, we continued to make effort to restart operations of the HTTR that stopped since the 2011 off the Pacific coast of Tohoku Earthquake. It is necessary for the HTTR reoperation to prove conformity with the new regulatory requirements for research reactors enacted in December 2013. So we might cope with government agency to pass the inspection of application document for the HTTR licensing. This report summarizes the activities carried out in the fiscal year 2019, which were the situation of the new regulatory requirements screening of the HTTR, the operation and maintenance of the HTTR, R&Ds relevant to commercial-scale HTGRs, the international cooperation on HTGRs and so on.

Journal Articles

Comparisons between passive RCCSS on degree of passive safety features against accidental conditions and methodology to determine structural thickness of scaled-down heat removal test facilities

Takamatsu, Kuniyoshi; Matsumoto, Tatsuya*; Liu, W.*; Morita, Koji*

Annals of Nuclear Energy, 162, p.108512_1 - 108512_10, 2021/11

 Times Cited Count:0 Percentile:0.01(Nuclear Science & Technology)

The objectives of this study are as follows: to understand the characteristics, degree of passive safety features for heat removal were compared for RCCSs based on atmospheric radiation and based on atmospheric natural circulation under the same conditions. Next, simulations on accidental conditions, such as increasing average heat-transfer coefficient via natural convection due to natural disasters, were performed with STAR-CCM+, and methodology to control the amount of heat removal was discussed. As a result, a new RCCS based on atmospheric radiation is recommended because of the excellent degree of passive safety features/conditions, and the amount of heat removal by heat transfer surfaces which can be controlled. Finally, methodology to determine structural thickness of scaled-down heat removal test facilities for reproducing natural convection and radiation was developed, and experimental methods by using pressurized and decompressed chambers was also proposed.

Journal Articles

Stoichiometry between humate unit molecules and metal ions in supramolecular assembly induced by Cu$$^{2+}$$ and Tb$$^{3+}$$ measured by gel electrophoresis techniques

Nakano, Sumika*; Marumo, Kazuki*; Kazami, Rintaro*; Saito, Takumi*; Haraga, Tomoko; Tasaki-Handa, Yuiko*; Saito, Shingo*

Environmental Science & Technology, 55(22), p.15172 - 15180, 2021/11

Humic acid (HA) can strongly complex with metal ions to form a supramolecular assembly via coordination binding. However, determining the supramolecular size distribution and stoichiometry between small HA unit molecules constituting HA supramolecule and metal ions has proven to be challenging. Here, we investigated the changes in the size distributions of HAs induced by Cu$$^{2+}$$ and Tb$$^{3+}$$ ions using a unique polyacrylamide gel electrophoresis (PAGE) for the separation and quantification of HA complexes and metal ions bound, followed by UV-Vis spectroscopy and EEM-PARAFAC. It was found that the supramolecular behaviors of Cu$$^{2+}$$ and Tb$$^{3+}$$ complexes with HA collected from peat and deep groundwater (HHA) differed. Our results suggest that this supramolecular stoichiometry is related to the abundance of sulfur atoms in the elemental composition of HHA. Our results provide new insights into HA supramolecules formed via metal complexation.

Journal Articles

Study on chemical form of tritium in coolant helium of high temperature gas-cooled reactor with tritium production device

Hamamoto, Shimpei; Ishitsuka, Etsuo; Nakagawa, Shigeaki; Goto, Minoru; Matsuura, Hideaki*; Katayama, Kazunari*; Otsuka, Teppei*; Tobita, Kenji*

Proceedings of 2021 International Congress on Advances in Nuclear Power Plants (ICAPP 2021) (USB Flash Drive), 5 Pages, 2021/10

Impurity concentrations of hydrogen and hydride in the coolant were investigated in detail for the HTTR, a block type high-temperature gas reactor owned by Japan. As a result, it was found that CH$$_{4}$$ was 1/10 of H$$_{2}$$ concentration, which was under the conventional detection limit. If the ratio of H$$_{2}$$ to CH$$_{4}$$ in the coolant is the same as the ratio of HT to CH$$_{3}$$T, the CH$$_{3}$$T has a larger dose conversion factor, and this compositional ratio is an important finding for the optimal dose evaluation. Further investigation of the origin of CH$$_{4}$$ suggested that CH$$_{4}$$ was produced as a result of a thermal equilibrium reaction rather than being released as an impurity from the core.

JAEA Reports

Report of summer holiday practical training 2020; Feasibility study on nuclear battery using HTTR core; Feasibility study for nuclear design, 3

Ishitsuka, Etsuo; Mitsui, Wataru*; Yamamoto, Yudai*; Nakagawa, Kyoichi*; Ho, H. Q.; Ishii, Toshiaki; Hamamoto, Shimpei; Nagasumi, Satoru; Takamatsu, Kuniyoshi; Kenzhina, I.*; et al.

JAEA-Technology 2021-016, 16 Pages, 2021/09

JAEA-Technology-2021-016.pdf:1.8MB

As a summer holiday practical training 2020, the feasibility study for nuclear design of a nuclear battery using HTTR core was carried out, and the downsizing of reactor core were studied by the MVP-BURN. As a result, it is clear that a 1.6 m radius reactor core, containing 54 (18$$times$$3 layers) fuel blocks with 20% enrichment of $$^{235}$$U, and BeO neutron reflector, could operate continuously for 30 years with thermal power of 5 MW. Number of fuel blocks of this compact core is 36% of the HTTR core. As a next step, the further downsizing of core by changing materials of the fuel block will be studied.

JAEA Reports

HTTR burnup characteristic analysis with detailed axial burning region using MVP-BURN

Ikeda, Reiji*; Ho, H. Q.; Nagasumi, Satoru; Ishii, Toshiaki; Hamamoto, Shimpei; Nakano, Yumi*; Ishitsuka, Etsuo; Fujimoto, Nozomu*

JAEA-Technology 2021-015, 32 Pages, 2021/09

JAEA-Technology-2021-015.pdf:2.74MB

Burnup calculation of the HTTR considering temperature distribution and detailed burning regions was carried out using MVP-BURN code. The results show that the difference in k$$_{rm eff}$$, as well as the difference in average density of some main isotopes, is insignificant between the cases of uniform temperature and detailed temperature distribution. However, the difference in local density is noticeable, being 6% and 8% for $$^{235}$$U and $$^{239}$$Pu, respectively, and even 30% for the burnable poison $$^{10}$$B. Regarding the division of burning regions to more detail, the change of k$$_{rm eff}$$ is also small of 0.6%$$Delta$$k/k or less. The small burning region gives a detailed distribution of isotopes such as $$^{235}$$U, $$^{239}$$Pu, and $$^{10}$$B. As a result, the effect of graphite reflector and the burnup behavior could be evaluated more clearly compared with the previous study.

JAEA Reports

Impact assessment for internal flooding in HTTR (High temperature engineering test reactor)

Tochio, Daisuke; Nagasumi, Satoru; Inoi, Hiroyuki; Hamamoto, Shimpei; Ono, Masato; Kobayashi, Shoichi; Uesaka, Takahiro; Watanabe, Shuji; Saito, Kenji

JAEA-Technology 2021-014, 80 Pages, 2021/09

JAEA-Technology-2021-014.pdf:5.87MB

In response to the new regulatory standards established in response to the accident at TEPCO's Fukushima Daiichi Nuclear Power Station in March 2011, measures and impact assessments related to internal flooding at HTTR were carried out. In assessing the impact, considering the characteristics of the high-temperature gas-cooled reactor, flooding due to assumed damage to piping and equipment, flooding due to water discharge from the system installed to prevent the spread of fire, and flooding due to damage to piping and equipment due to an earthquake. The effects of submersion, flooding, and flooding due to steam were evaluated for each of them. The impact of the overflow of liquids containing radioactive materials outside the radiation-controlled area was also evaluated. As a result, it was confirmed that flooding generated at HTTR does not affect the safety function of the reactor facility by taking measures.

Journal Articles

A Pseudo-material method for graphite with arbitrary porosities in Monte Carlo criticality calculations

Okita, Shoichiro; Nagaya, Yasunobu; Fukaya, Yuji

Journal of Nuclear Science and Technology, 58(9), p.992 - 998, 2021/09

 Times Cited Count:0 Percentile:0.01(Nuclear Science & Technology)

Journal Articles

Nuclear data processing code FRENDY; A Verification with HTTR criticality benchmark experiments

Fujimoto, Nozomu*; Tada, Kenichi; Ho, H. Q.; Hamamoto, Shimpei; Nagasumi, Satoru; Ishitsuka, Etsuo

Annals of Nuclear Energy, 158, p.108270_1 - 108270_8, 2021/08

 Times Cited Count:0 Percentile:0.01(Nuclear Science & Technology)

Journal Articles

Concepts and basic designs of various nuclear fuels, 5; Fuels for high temperature gas-cooled reactor and molten salt reactor

Ueta, Shohei; Sasaki, Koei; Arita, Yuji*

Nihon Genshiryoku Gakkai-Shi ATOMO$$Sigma$$, 63(8), p.615 - 620, 2021/08

no abstracts in English

Journal Articles

Thermal-hydraulics to risk assessment; Roles of thermal-hydraulics simulation to risk assessment

Maruyama, Yu; Yoshida, Kazuo

Nihon Genshiryoku Gakkai-Shi ATOMO$$Sigma$$, 63(7), p.517 - 522, 2021/07

no abstracts in English

JAEA Reports

Mesh effect around burnable poison rod of cell model for HTTR fuel block

Fujimoto, Nozomu*; Fukuda, Kodai*; Honda, Yuki*; Tochio, Daisuke; Ho, H. Q.; Nagasumi, Satoru; Ishii, Toshiaki; Hamamoto, Shimpei; Nakano, Yumi*; Ishitsuka, Etsuo

JAEA-Technology 2021-008, 23 Pages, 2021/06

JAEA-Technology-2021-008.pdf:2.62MB

The effect of mesh division around the burnable poison rod on the burnup calculation of the HTTR core was investigated using the SRAC code system. As a result, the mesh division inside the burnable poison rod does not have a large effect on the burnup calculation, and the effective multiplication factor is closer to the measured value than the conventional calculation by dividing the graphite region around the burnable poison rod into a mesh. It became clear that the mesh division of the graphite region around the burnable poison rod is important for more appropriately evaluating the burnup behavior of the HTTR core..

1651 (Records 1-20 displayed on this page)