Improving the safety of the high temperature gas-cooled reactor "HTTR" based on Japan's new regulatory requirements

Hamamoto, Shimpei; Shimizu, Atsushi; Inoi, Hiroyuki; Tochio, Daisuke; Homma, Fumitaka; Sawahata, Hiroaki; Sekita, Kenji; Watanabe, Shuji; Furusawa, Takayuki; Iigaki, Kazuhiko; et al.

Nuclear Engineering and Design, 388, p.111642_1 - 111642_11, 2022/03

https://doi.org/10.1016/j.nucengdes.2021.111642

Following the Fukushima Daiichi Nuclear Power Plant accident in 2011, the Japan Atomic Energy Agency adapted High-Temperature engineering Test Reactor (HTTR) to meet the new regulatory requirements that began in December 2013. The safety and seismic classifications of the existing structures, systems, and components were discussed to reflect insights regarding High Temperature Gas-cooled Reactors (HTGRs) that were acquired through various HTTR safety tests. Structures, systems, and components that are subject to protection have been defined, and countermeasures to manage internal and external hazards that affect safety functions have been strengthened. Additionally, measures are in place to control accidents that may cause large amounts of radioactive material to be released, as a beyond design based accident. The Nuclear Regulatory Commission rigorously and appropriately reviewed this approach for compliance with the new regulatory requirements. After nine amendments, the application to modify the HTTR's installation license that was submitted in November 2014 was approved in June 2020. This response shows that facilities can reasonably be designed to meet the enhanced regulatory requirements, if they reflect the characteristics of HTGRs. We believe that we have established a reference for future development of HTGR.

Temperature coefficient measurement test of HTTR; Burn-up characteristic of temperature coefficients at reactor power 30 kW and 9 MW

Ono, Masato; Goto, Minoru; Shinohara, Masanori; Nojiri, Naoki; Tochio, Daisuke; Shimazaki, Yosuke; Yanagi, Shunki

JAEA-Technology 2013-001, 35 Pages, 2013/03

JAEA-Technology-2013-001.pdf:6.04MB

The temperature coefficient measurements of the HTTR have been carried out. In the beginning of the operation, temperature coefficients at the reactor power of 30 kW and 9 MW were obtained through 1999 to 2000. The operation days of the HTTR fuel reached 375 Effective Full Power Days (EFPD), which is over a half of design operation days (660 EFPD). The temperature coefficient measurements were conducted at the same power levels of 30 kW and 9 MW to evaluate burnup effect. Also, to measure temperature coefficient in high accuracy, technique of core temperature control and technique of core temperature homogenization were established.

Handling of HTTR second driver fuel elements in assembling and storage working

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

JAEA-Technology-2009-025.pdf:21.78MB

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.

Contribution to improvement of HTGR technology by using HTTR operation data

Nakagawa, Shigeaki; Tochio, Daisuke; Shinohara, Masanori; Nojiri, Naoki; Nishihara, Tetsuo; Goto, Minoru; Takamatsu, Kuniyoshi

Proceedings of 2009 International Congress on Advances in Nuclear Power Plants (ICAPP '09) (CD-ROM), p.9476_1 - 9476_6, 2009/05

Ultrasonic test results for the reactor pressure vessel of the HTTR; Longitudinal welding line of bottom dome

Nojiri, Naoki; Owada, Hiroyuki; Kato, Yasushi

JAEA-Technology 2008-045, 38 Pages, 2008/06

JAEA-Technology-2008-045.pdf:6.95MB

This paper describes the inspection method, the measured area, etc. of the ultrasonic test of the in-service inspection (ISI) for welding lines of the reactor pressure vessel of the HTTR and the inspection results of the longitudinal welding line of the bottom dome. The pre-service inspection (PSI) results for estimation of occurrence and progression of defects to compare the ISI results is described also.

Present status of HTTR and its operational experience

Iyoku, Tatsuo; Nojiri, Naoki; Tochio, Daisuke; Mizushima, Toshihiko; Tachibana, Yukio; Fujimoto, Nozomu

Proceedings of 15th International Conference on Nuclear Engineering (ICONE-15) (CD-ROM), 8 Pages, 2007/04

A HTGR is particularly attractive because of its capability of producing high temperature helium gas and its inherent safety characteristics. Hence, the HTTR wasconstructed at the Oarai Research Establishment of the Japan Atomic Energy Agency. The HTTR achieved the full power of 30MW and reactor outlet coolant temperature of about 850C on December 7, 2001. After several operation cycles, the HTTR achieved the reactor outlet coolant temperature of 950C on April 19, 2004. It is the highest coolant temperature outside reactor pressure vessel in the world. Extensive tests are planned in the HTTR and a process heat application system will be coupled to the HTTR, where hydrogen will be produced directly from the nuclear energy.

Neutronics calculations of HTTR with several nuclear data libraries

Goto, Minoru; Nojiri, Naoki; Shimakawa, Satoshi

Journal of Nuclear Science and Technology, 43(10), p.1237 - 1244, 2006/10

https://doi.org/10.3327/jnst.43.1237

Benchmark calculations for several HTTR core conditions were performed with four cross-section sets which were generated from JENDL-3.3, JENDL-3.2, ENDF/B-6.8 and JEFF-3.0 using a continuous energy Monte Carlo code MVP. The core conditions were an annular form core at room temperature and a full core with cylindrical form at room temperature and at full power operation. Study of k discrepancies caused by difference of the nuclear data libraries and identification of nuclide which gives large effects on the k discrepancies were carried out. Comparison of the k between calculations and experiments was also carried out. As the results, for each HTTR core conditions, JENDL-3.3 gives the k agreement with the experiments within 1.5%k, JENDL-3.2 gives the k agreement within 1.7%k, and ENDF/B-6.8 and JEFF-3.0 give k agreement within 1.8%k. There is little k discrepancy between ENDF/B-6.8 and JEFF-3.0. The discrepancy between JENDL-3.3 and JENDL-3.2 is caused by difference of U-235 data and has temperature dependency. The k discrepancy between JENDL-3.3 and ENDF/B-6.8 or JEFF-3.0 is caused by difference of graphite data.

Burnup characteristics of burnable poison and core characteristics of HTTR

Fujimoto, Nozomu; Nojiri, Naoki

JAEA-Technology 2005-008, 45 Pages, 2006/01

JAEA-Technology-2005-008.pdf:1.9MB

The HTTR uses burnable poison to compensate the change in reactivity with burnup. The burnable poison is a rod type and the change in effective absorption cross section become large due to its shape. Therefore, change in effective cross section of burnable poison due to burnup, temperature, fuel enrichment, etc. are evaluated and the core calculation model for burnup calculation. Using the model, burnup calculations are carried out and compared with results of experiments and other code. It become clear that the model shows reasonable results.

Annular core experiments in HTTR's start-up core physics tests

Fujimoto, Nozomu; Yamashita, Kiyonobu*; Nojiri, Naoki; Takeuchi, Mitsuo; Fujisaki, Shingo; Nakano, Masaaki*

Nuclear Science and Engineering, 150(3), p.310 - 321, 2005/07

https://doi.org/10.13182/NSE03-79

Annular cores were formed in startup-core-physics tests of the High Temperature Engineering Test Reactor (HTTR) to obtain experimental data for verification of calculation codes. The first criticality, control rod positions at critical conditions, neutron flux distribution, excess reactivity etc. were measured as representative data. These data were evaluated with Monte Carlo code MVP that can consider the heterogeneity of coated fuel particles (CFP) distributed randomly in fuel compacts directly. It was made clear that the heterogeneity effect of CFP on reactivity for annular cores is smaller than that for fully-loaded cores. Measured and calculated effective multiplication factors (k) were agreed with differences less than 1%k. Measured neutron flux distributions agreed with calculated results. The revising method was applied for evaluation of excess reactivity to exclude negative shadowing effect of control rods. The revised and calculated excess reactivity agreed with differences less than 1%k/k.

DELIGHT-8; One dimensional fuel cell burnup analysis code for High Temperature Gas-cooled Reactor (HTGR) (Joint research)

Nojiri, Naoki; Fujimoto, Nozomu; Mori, Tomoaki; Obata, Hiroyuki*

JAERI-Data/Code 2004-012, 65 Pages, 2004/10

JAERI-Data-Code-2004-012.pdf:7.77MB

DELIGHT code is a fuel cell burnup analysis code which can produce the group constants necessary for High Temperature Gas-cooled Reactors (HTGR) core analyses. Collision probability method is used to the lattice calculation. The lattice calculation model is a cylinder type fuel or a ball type fuel of the HTGR. This code characterizes the burnup calculation considering the double heterogeneity caused by coated fuel particles of the HTGR fuel. DELIGHT code has updated its nuclear data library to the latest JENDL-3.3 data, and included new burnup chain models in order to calculate high burnup HTGR cores. The material regions of the periphery burnable poisons (BPs) were divided into details in order to improve calculation accuracy of the BP lattice calculation. This report presents the revised points of the DELIGHT-8 and can be used as user's manual.