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Watanabe, Norio; Yonomoto, Taisuke; Tamaki, Hitoshi; Nakamura, Takehiko; Maruyama, Yu
Journal of Nuclear Science and Technology, 52(1), p.41 - 56, 2015/01
Times Cited Count：11 Percentile：67.3(Nuclear Science & Technology)On March 11, 2011, the Tohoku District-off the Pacific Ocean Earthquake and the subsequent tsunami resulted in the severe core damage at TEPCO's Fukushima Dai-ichi Nuclear Power Plant Units 1-3, involving hydrogen explosions at Units 1, 3, and 4 and the large release of radioactive materials to the environment. Four independent committees were established by the Japanese government, the Diet of Japan, the Rebuild Japan Initiative Foundation, and TEPCO to investigate the accident and published their respective reports. Also, the Nuclear and Industrial Safety Agency carried out an analysis of accident causes to obtain the lessons learned from the accident and made its report public. This article reviews the reports and clarifies the differences in their positions, from the technological point of view, focusing on the accident progression and causes. Moreover, the undiscussed issues are identified to provide insights useful for the near-term regulatory activities including accident investigation by the Nuclear Regulation Authority.
Kukita, Yutaka; Watanabe, Norio
JAEA-Technology 2014-036, 38 Pages, 2014/11
JAEA-Technology-2014-036.pdf:26.08MB
NAIIC emphasized the possibility of seismically-induced reactor coolant leakage and implied its causal connection to the accident, in particular at the Fukushima Daiichi Unit 1. This view of NAIIC has been addressed by the Accident Investigation Committee established by the Cabinet decision, NISA, and the Secretariat of NRA. Based on seismic response analyses, plant records and simulations, their reports uniformly note that seismically-induced leakage is unlikely to be a causal factor for the core damage though the possibility of insignificantly small leakage cannot be ruled out completely. Also refuted are some of the arguments made by NAIIC as grounds for suspecting safety-significant leakage. The present report re-examines the leak detection capability through the review of plant instruments and post-accident simulations, and adds some arguments in order to resolve the issue raised by NAIIC without technical ambiguity as far as possible. As well, the plant design uniqueness of Unit 1, the history of facility changes, the operating procedures and the actual operations are looked into to raise issues for further investigation.
Watanabe, Norio
JAEA-Review 2014-031, 18 Pages, 2014/08
JAEA-Review-2014-031.pdf:4.92MB
It has been recognized an important means to learn lessons from operating experience and to feed them back to the design, construction, operation and management of facilities. A lot of events involved similar occurrences which have been experienced in the past. These are referred to as precursors. In the present study, identified and discussed are the precursors to the accident at Fukushima Daiichi Nuclear Power Plant to obtain the generic lessons which should have been learned. As precursors to the Fukushima accident, six events are identified: massive internal flooding and loss of safety systems; prolonged station blackout involving loss of control room and loss of residual heat removal; external flooding involving loss of safety systems and multi units site issue; loss of offsite power with one of two emergency diesel generators inoperable; tsunami-induced flooding; common-mode loss of instrument power. Furthermore, the most notable near-miss to the Fukushima accident is discussed.
Watanabe, Norio; Yonomoto, Taisuke; Tamaki, Hitoshi; Nakamura, Takehiko; Maruyama, Yu
Nihon Genshiryoku Gakkai Wabun Rombunshi, 12(2), p.113 - 127, 2013/06
On March 11, 2011, the Tohoku District - off the Pacific Ocean Earthquake and the subsequent tsunami resulted in the severe core damage at the TEPCO's Fukushima Dai-ichi Nuclear Power Station Units 1-3, involving hydrogen explosions at Units 1, 3, and 4 and the large release of radioactive materials to the environment. The four independent committees were established by the Government, the Diet of Japan and the Rebuild Japan Initiative Foundation as well as TEPCO to investigate the accident and published their respective reports. Also, the Nuclear and Industrial Safety Agency carried out the analysis of accident causes to obtain the lessons learned from the accident and made its report public. This article reviews the reports and clarifies the differences in their positions, from the technological point of view, focusing on the accident progression and causes. As well, the undiscussed issues are identified to provide insights useful for the near-term regulatory activities including accident investigation by the Nuclear Regulation Authority.
Liu, Q.; Ishikawa, Jun; Maruyama, Yu; Watanabe, Norio
Journal of Nuclear Science and Technology, 49(5), p.479 - 485, 2012/05
Times Cited Count：3 Percentile：24.98(Nuclear Science & Technology)This paper presents a simple approach for estimating the temperature of the structures in the reactor pressure vessel (RPV) and the release rates of fission products (FPs) at the time of several months after the core melt accident at the Fukushima Daiichi Nuclear Power Plant. In this paper, basic concepts are firstly presented and then, a heat balance model is proposed to estimate the temperature of the uncovered reactor core and the upper structures in the RPV with the measured temperatures of the RPV outer wall. In addition, models for estimating the revaporization rate of cesium hydroxide (CsOH) inside the RPV and the leak rate of CsOH to the primary containment vessel are also presented. This approach is anticipated to be applicable to the Fukushima Daiichi #1, #2 and #3 Units.
Liu, Q.; Ishikawa, Jun; Maruyama, Yu; Watanabe, Norio
Journal of Nuclear Science and Technology, 49(5), p.486 - 495, 2012/05
Times Cited Count：0 Percentile：0.01(Nuclear Science & Technology)This work examines the feasibility of the method proposed in the preceding part of a two-part paper. The base case study shows that water injection via the core spray line is more effective to cool the uncovered core and to reduce the release of CsOH. Sensitivity study is conducted by introducing the dimensionless decay heat, which combines the effects of the ratio of the flooded core, the ratio of the slumped core and the leak ratio of the injected water on the steam generation rate associated with the forced convection cooling in the reactor pressure vessel (RPV). The results show that the temperatures of the uncovered core and the other structures increase with the dimensionless decay heat. So does the release rate of CsOH. The relationships of the measurable RPV wall temperature with the temperatures of the uncovered core and the other structures as well as the release characteristics of CsOH are also examined in this work.
Hirano, Masashi; Yonomoto, Taisuke; Ishigaki, Masahiro; Watanabe, Norio; Maruyama, Yu; Shibamoto, Yasuteru; Watanabe, Tadashi; Moriyama, Kiyofumi
Journal of Nuclear Science and Technology, 49(1), p.1 - 17, 2012/01
Times Cited Count：97 Percentile：91.67(Nuclear Science & Technology)An unprecedented earthquake and tsunami struck the Fukushima Dai-ichi Nuclear Power Plants on 11 March 2011. Although extensive efforts have been continuing on investigations into the causes and consequences of the accident, and the Japanese Government has presented a comprehensive report on the accident in the IAEA Ministerial Conference held in June 2011, there is still much to be clarified on what happened during the accident and why. This article aims at identifying what should be clarified further about the progression of the accident at Units 1-3 through the review and analysis of information released from Tokyo Electric Power Company and government authorities. It also discusses the safety issues raised by the accident based on the insights gained, in order to contribute to establishing a new framework that pursues continuous improvement toward the highest standards of safety that can reasonably be achieved.
Narumiya, Yoshiyuki*; Ohashi, Hirotada*; Miyata, Koichi*; Watanabe, Norio
Dai-13-Kai Nihon Jishin Kogaku Shimpojiumu Rombunshu (DVD-ROM), p.1159 - 1166, 2010/11
no abstracts in English
Ohashi, Hirotada*; Narumiya, Yoshiyuki*; Miyata, Koichi*; Watanabe, Norio
Nihon Genshiryoku Gakkai-Shi ATOMO
, 52(11), p.732 - 736, 2010/11
no abstracts in English
Ohashi, Hirotada*; Narumiya, Yoshiyuki*; Miyata, Koichi*; Watanabe, Norio
Anzen Kogaku Shimpojiumu 2010 Koen Yokoshu, p.110 - 113, 2010/07
no abstracts in English
Kimura, Masanori; Watanabe, Norio; Homma, Toshimitsu
JAEA-Review 2010-021, 54 Pages, 2010/06
JAEA-Review-2010-021.pdf:1.01MB
International Atomic Energy Agency (IAEA) emphasizes the importance of emergency planning and requires the development of emergency response to implement effectively protective measures in IAEA Safety requirement GS-R-2. In the United States of America (USA), Nuclear Regulatory Commission (NRC) requires licensees, as a condition of licensing, the development of emergency planning including emergency classification and Emergency Action Levels (EALs) scheme. In order to consider incorporating emergency classification and EALs scheme into emergency preparedness and response in Japan, we surveyed the EALs scheme in the USA. This report provides the outline of EALs guideline, NEI99-01 "Methodology for Development of Emergency Action Levels", developed by Nuclear Energy Institute (NEI) and the brief descriptions on 8 accidents where an emergency was declared in the USA. As well, the findings from the survey are summarized.
Sato, Takeshi; Watanabe, Norio; Yoshida, Kazuo
JAEA-Technology 2009-028, 29 Pages, 2009/05
JAEA-Technology-2009-028.pdf:2.66MB
The importance to make use of lessons learned and knowledge from accidents and troubles in safety management of nuclear research facilities is recognized widely. By the root cause analysis of accidents and troubles, lessons learned and knowledge have been arrived about safety management of facilities. The root cause analysis has been performed for accidents and troubles generated at nuclear research facilities in Japan Atomic Energy Agency (JAEA) from about 1990. Because the analysis is performed for various facilities, anyone have been used the analysis method of possible of utilize. On this account the analysis method has been developed and adopted an existing analysis method. This report introduces the analysis method that has been used for the root cause analysis of these accidents and troubles. Furthermore, this report apply a generally well known JCO Criticality Accident to each analysis method as an example and explain on the direction for uses.
Watanabe, Norio
Kasai, 58(2), p.11 - 16, 2008/04
no abstracts in English
Watanabe, Norio
Nihon Genshiryoku Gakkai Wabun Rombunshi, 7(1), p.74 - 84, 2008/03
Since the beginning of 1980's, in the United States, there have been many licensee event reports (LERs) involving setpoint drift in safety or relief valves. The NRC has issued a lot of generic communications on this issue and the industry has made its efforts to resolve the issue. The NRC staff recently highlighted that over 70 LERs involved instances where these valves failed to meet the allowed setpoint tolerance from 2001 through August 2006. In this study, we analyzed the U.S. experience with setpoint drift in safety relief valves (SRVs) at BWRs, pressurizer safety valves (PSVs) and main steam safety valves (MSSVs) at PWRs by reviewing the LERs from 2000 to 2006 and examined the trend. It is found that for SRVs and MSSVs, the disc-seat bonding is a dominant cause of setpoint drifting high and has a tendency to result in relatively large deviation of setpoint. For PSVs, the deviation of setpoint is generally small although the causes are not specified in many instances.
Watanabe, Norio
JAEA-Review 2007-043, 132 Pages, 2007/12
JAEA-Review-2007-043.pdf:5.28MB
Since the beginning of 1980's, in the United States, there have been many reports involving setpoint drift of the safety or safety/relief valves. The United States Nuclear Regulatory Commission (NRC) has issued the generic communications on this issue and the industry has made their efforts to identify the causes and to take corrective actions. However, the NRC staff found that from 2001 through August 2006, over 70 licensee event reports (LERs) involved instances where safety or safety/relief valves failed to meet the allowed lift setpoint tolerance and issued the Information Notice 2006-24 in 2006 to alert licensees of operating experience insights associated with the safety and safety/relief valves exceeding the lift setpoint tolerance. This report provides the description on the historical NRC's responses to safety and safety/relief valve issues including setpoint drift and analyzes the trends of the ninety-four events, reported as LERs, involving setpoint drift at U. S. nuclear power plants during the years from 2000 to 2006.
Watanabe, Norio
Genshiryoku Handobukku, p.1189 - 1197, 2007/11
This paper is prepared as part of the pablication, named "Nuclear Handbook", on a request of its Editorial Board and provides the summaries, causes and lessons learned of the nuclear accidents that occurred at Three Mile Island Nuclear Power Plant Unit 2 (TMI-2), Chernobyl Nuclear Power Plant Unit 4, and JCO Nuclear Fuel Fabrication Facility.
Watanabe, Norio
JAEA-Review 2006-041, 43 Pages, 2007/02
JAEA-Review-2006-041.pdf:3.08MB
The Japan Atomic Energy Agency is carrying out the cooperative activity by providing specialized educational and training staff and making our facilities available for the graduate school of engineering in The University of Tokyo as part of developing human resources in nuclear technology. This report is prepared as a textbook for the lecture in the graduate school of engineering in The University of Tokyo and provides the outlines of procedures and analysis approach to the probabilistic safety assessment (PSA) for nuclear power plants, in particular, the level 1 PSA (evaluation of core damage frequency) with examples shown.
Watanabe, Norio
JAEA-Review 2006-040, 60 Pages, 2007/02
JAEA-Review-2006-040.pdf:5.41MB
The Japan Atomic Energy Agency is carrying out the cooperative activity by providing specialized educational and training staff and making our facilities available for the graduate school of engineering in The University of Tokyo as part of developing human resources in nuclear technology. This report is prepared as a textbook for the lecture in the graduate school of engineering in The University of Tokyo and provides the outlines of activities on the analysis of nuclear and radiological events and analysis methods as well as the summaries of major incidents and accidents that occurred.
Ishikawa, Jun; Muramatsu, Ken; Watanabe, Norio
Nihon Genshiryoku Gakkai Wabun Rombunshi, 5(4), p.305 - 315, 2006/12
The probabilistic safety assessment(PSA) results can be used for decision making in various areas including risk informed regulation, accident management, off-site emergency planning, and safety goal. Since there exist uncertainties in PSA results, uncertainty evaluation is one of the most important issues in PSA. This paper describes an approach to evaluation of uncertainties in source terms. We proposed a procedure of uncertainty evaluation for source terms by the use of severe accident analysis code THALES2 and applied this procedure to the evaluation of source terms for BWR-5/Mark-II plant. Source terms analysis was performed with THALES2 for containment overpressure failure scenarios involving core damage. From this analysis, uncertainty information of source terms, such as the timing of fission products (FPs) release to the environment and released fraction of FPs. As well, the dominant parameters for individual scenarios were identified: containment failure pressure, in-vessel and/or ex-vessel FP release rate, deposition of aerosols in the containment and reactor building.
Takahara, Shogo; Watanabe, Norio
Nihon Genshiryoku Gakkai Wabun Rombunshi, 5(4), p.282 - 291, 2006/12
no abstracts in English
