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Journal Articles

Investigation on dust captured by quintuple filters installed upstream of primary gas circulators in HTTR

Inaba, Yoshitomo; Hamamoto, Shimpei; Furusawa, Takayuki; Saikusa, Akio; Sakaba, Nariaki

Journal of Nuclear Science and Technology, 51(11-12), p.1373 - 1386, 2014/11

https://doi.org/10.1080/00223131.2014.946978

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

A main objective to install filters upstream of primary gas circulators in the high temperature engineering test reactor (HTTR), besides having a primary helium purification system, is the reduction and removal of circulating dust in the primary circuit. A problem encountered with the filters during the initial operations of the HTTR was that the differential pressure across the filters had increased excessively over the duration of the operations so that the differential pressure would be expected to exceed the limit value regulated in the HTTR operation manual. It was speculated that either the carbon traced back chemical reactions, the debris from mechanical contacts or both of these sources might be captured by the filters. Then, the filters were replaced and inspected to identify the cause of the increase of the filter differential pressure. As a result, it was found that the increase is caused by clogging of the filters by the dust traced back to the physical contact of the piston rings of the gas circulators equipped in the primary helium purification system. Hence, prismatic block-type very high temperature reactors (VHTRs) do not continuously supply carbon dust from the cores in operation.

Journal Articles

Helium leak and chemical impurities control technology in HTTR

Tochio, Daisuke; Shimizu, Atsushi; Hamamoto, Shimpei; Sakaba, Nariaki

Journal of Nuclear Science and Technology, 51(11-12), p.1407 - 1412, 2014/11

https://doi.org/10.1080/00223131.2014.921126

Times Cited Count：5 Percentile：36.96(Nuclear Science & Technology)

Japan Atomic Energy Agency (JAEA) has designed and developed High Temperature Gas-cooled Reactor (HTGR) hydrogen cogeneration system named GTHTR300C. The helium gas is used as the primary coolant in HTGR. The helium gas is easy to leak, and the primary helium leakage should be controlled tightly from the viewpoint of preventing the release of radioactive materials to the environment. Moreover from the viewpoint of preventing the oxidization of graphite and metallic material, the helium coolant chemistry should be controlled tightly. The primary helium leakage and the helium coolant chemistry during the operation is the major factor in the HTGR for commercialization of HTGR system. This paper shows the design concept and the obtained operational experience on the primary helium leakage control and primary helium impurity control in the HTTR. Moreover the future plan to obtain the operational experience on these controls for commercialization of HTGR system is shown.

Journal Articles

Control method of purification system of helium coolant for suppressing decarburization of heat-resistant alloy used in very high temperature gas cooling reactors

Hamamoto, Shimpei; Sakaba, Nariaki; Takeda, Yoichi*

Nihon Genshiryoku Gakkai Wabun Rombunshi, 9(2), p.174 - 182, 2010/09

https://doi.org/10.3327/taesj.J08.058

Chemistry control is important for the helium coolant of High Temperature Gas-cooled Reactors (HTGRs). Decarburizing atmosphere reduced creep rupture strength of the heat resistant alloy using for the heat exchanger. This paper describes active control of impurities concentration using existing helium purification system which consists of helium heater, Cupper oxide bed (CuOT), Molecular sieve bed, Cold Charcoal bed and each bypass line. Analysis showed that efficiency control of CuOT is effective in an improvement of decarburizing atmosphere. This effect is based on that H $_{2}$ which is not removed cause the increase in carbon monoxide effective in formation of carburizing atmosphere by water-gas-shift reaction.

Journal Articles

Helium chemistry for very high temperature reactors

Sakaba, Nariaki; Hamamoto, Shimpei; Takeda, Yoichi*

Journal of Nuclear Science and Technology, 47(3), p.269 - 277, 2010/03

https://doi.org/10.3327/jnst.47.269

Times Cited Count：7 Percentile：45.04(Nuclear Science & Technology)

Lifetime extension of high-temperature equipment such as the intermediate heat exchanger of high-temperature gas-cooled reactors (HTGRs) is important from the economical point of view. Since the replacing cost will cause the increasing of the running cost, it is important to reduce replacing times of the high-cost primary equipment during assumed reactor lifetime. In the past, helium chemistry has been controlled by the passive chemistry control technology in which chemical impurity in the coolant helium is removed as low concentration as possible, as does Japan's HTTR. Although the lifetime of high-temperature equipment almost depends upon the chemistry conditions in the coolant helium, it is necessary to establish an active chemistry control technology to maintain adequate chemical conditions. In this study, carbon deposition which could occur at the surface of the heat transfer tubes of the intermediate heat exchanger and decarburization of the high-temperature material of Hastelloy XR used at the heat transfer tubes were evaluated by referring the actual chemistry data obtained by the HTTR. The chemical equilibrium study contributed to clarify the algorism of the chemistry behaviours to be controlled. The created algorism is planned to be added to the instrumentation system of the helium purification systems. In addition, the chemical composition to be maintained during the reactor operation was proposed by evaluating not only core graphite oxidation but also carbon deposition and decarburization. It was identified when the chemical composition could not keep adequately, injection of 10 ppm carbon monoxide could effectively control the chemical composition to the designated stable area where the high-temperature materials could keep their structural integrity beyond the assumed duration. The proposed active chemistry control technology is expected to contribute economically to the purification systems of the future very high-temperature reactors.

JAEA Reports

Test plan using the HTTR for commercialization of GTHTR300C

Tachibana, Yukio; Nishihara, Tetsuo; Sakaba, Nariaki; Ohashi, Hirofumi; Sato, Hiroyuki; Ueta, Shohei; Aihara, Jun; Goto, Minoru; Sumita, Junya; Shibata, Taiju; et al.

JAEA-Technology 2009-063, 155 Pages, 2010/02

JAEA-Technology-2009-063.pdf:17.27MB

This report describes full scope of the feasible future test plan mainly using the HTTR. The test items cover fuel performance and radionuclide transport, core physics, reactor thermal hydraulics and plant dynamics, and reactor operations, maintenance, control, etc. The test results will be utilized for realization of Japan's commercial Very High Temperature Reactor (VHTR) system, GTHTR300C.

Journal Articles

Active chemistry control for coolant helium applying high-temperature gas-cooled reactors

Sakaba, Nariaki; Hamamoto, Shimpei; Takeda, Yoichi*

Proceedings of 4th International Topical Meeting on High Temperature Reactor Technology (HTR 2008) (CD-ROM), 7 Pages, 2008/09

Lifetime extension of high-temperature materials utilized, for instance, at the heat transfer tubes of the intermediate heat exchanger of high-temperature gas-cooled reactors is important because high-cost primary equipment will be continued its operation during reactor lifetime without replacing. Since lifetime of high-temperature materials almost depends upon the chemistry conditions in the coolant helium, it is necessary to establish an active chemistry control methods. This technology can maintain adequate chemical conditions during reactor operation. In the past, helium chemistry has been controlled by the passive chemistry control technology in which chemical impurity in the coolant helium removes as low concentration as possible, as does Japan's first high-temperature gas-cooled reactor HTTR. In this study, carbon deposition which could be occurred at the surface of the heat transfer tube and decarburization of the high-temperature material of Hastelloy XR were evaluated by referring the chemistry data obtained by the HTTR. In addition, the chemical composition to be maintained during the reactor operation in order to keep the structural integrity and thermal efficiency of the heat transfer tube was proposed by evaluating not only core graphite oxidation, but also carbon deposition and decarburization. It was also identified when the chemical composition could not keep adequately, injection of 10 ppm carbon monoxide could effectively control the chemical composition to the designated stable area where the high-temperature materials can keep their structural integrity beyond the assumed duration. The proposed active chemistry control technology is expected to contribute economically to the purification systems of the future very high-temperature reactors.

Journal Articles

R&D of lifetime extension for primary materials by active chemistry control for coolant helium; A Study of chemical equilibrium in the HTGR core

Sakaba, Nariaki; Hamamoto, Shimpei; Takeda, Yoichi*

Transactions of the American Nuclear Society, 97(1), p.678 - 680, 2007/11

Inherent safety advantages of the helium gas cooled reactors over other types of reactors depend importantly on the chemical stability of the actual helium coolant gas itself. Although helium being an inert gas does not react with fuel and components, chemical impurities which exist in the actual helium coolant can react with the surface of high-temperature materials such as the heat transfer tubes of the intermediate heat exchanger. The chemical effect of the impurities strongly influences to shorten the lifetime of the high-temperature materials. The dominant chemical reactions occurring in the core have not previously identified due to the complicated effects of not only high temperatures but also radioactivity during power operation of the helium gas cooled reactors. As such the methodology to control the high-temperature material lifetime has not been established because of the lack of knowledge and active control of the carbon activity and partial pressure of the oxygen which determine the creep fatigue of the high-temperature materials. The present study of the chemical equilibriums in the HTGR core is an initial effort to establish the lifetime extension methodology. The study examines the effects of high temperature and irradiation on the chemical equilibriums in the core by using an analytical code and basing on the chemical impurity data obtained in the HTTR operations.

Journal Articles

R&D of lifetime extension for primary materials by active chemistry control for coolant helium; Corrosion tests of heat resistant alloy

Takeda, Yoichi*; Hamamoto, Shimpei; Sakaba, Nariaki

Transactions of the American Nuclear Society, 97(1), P. 677, 2007/11

Ni-base heat-resistant alloys are used for the structural components in gas cooled reactors and exposed to high-temperature helium gas environment. The degradation issues of the material like oxidation and creep are primary concern for the plant operation and further development of the alloys to be used in Very High-Temperature Reactor (VHTR) and Gas-Cooled Fast Reactor (GFR). In this investigation, corrosion testing facility was fabricated in order to investigate oxidation behavior of heat resistant alloys in high-temperature helium environments.

Journal Articles

Structural integrity assessments of helium components in the primary cooling system during the safety demonstration test using the HTTR

Sakaba, Nariaki; Tachibana, Yukio; Nakagawa, Shigeaki; Hamamoto, Shimpei

Transactions of 18th International Conference on Structural Mechanics in Reactor Technology (SMiRT-18), p.4499 - 4511, 2005/08

Safety demonstration tests using the HTTR are now underway in order to verify the inherent safety features and to improve the safety design and evaluation technologies for HTGRs, as well as to contribute to research and development for the VHTR, which is one of the Generation IV reactor candidates. The coolant flow reduction test by running down gas circulators, which is one of the safety demonstration tests, is a simulation test of anticipated transients without scram. During the coolant flow reduction test, temperature of the high-temperature helium components and chemistry in the primary circuit are changed rapidly. This paper describes the structural integrity assessments of helium components, e.g. helium pipes, heat exchangers, during the coolant flow reduction test. From the result of this evaluation, it was found that the helium components were kept their structural integrity during temperature and chemistry transient condition in the coolant flow reduction test from the reactor power at 30%. It was also confirmed by this assessment that the coolant flow reduction test will be able to perform with its enough safety margins from the reactor power at 100%.

Journal Articles