Study on Buckling Strength and Post Buckling Behaviors of Reactor Vessel Lower Heads

2021 ◽  
Author(s):  
Masato Murohara ◽  
Akira Yamazaki ◽  
Takuya Sato ◽  
Naoto Kasahara
Keyword(s):  
Structural Design ◽  
Nuclear Power ◽  
Reactor Vessel ◽  
Lessons Learned ◽  
Buckling Strength ◽  
Severe Accidents ◽  
Design Basis ◽  
Post Buckling ◽  
Fukushima Daiichi ◽  
Very High

Abstract As the lessons learned from the Fukushima Daiichi Nuclear Power Plant accident, the importance of controlling the behavior after a failure and mitigating consequences of a failure was recognized. Conventional reactor structural design has been aimed at preventing the occurrence of failure due to Design Basis Events (DBE). This study aims to improve the resilience of the reactor structure under Beyond Design Basis Events (BDBE), such as very high temperatures and excessive earthquakes during severe accidents, by mitigating the consequences after failure.

Post-Fukushima Research and Development Strategies and Priorities for Water Cooled Reactor Technology Development

2016 ◽  
Author(s):  
Katsumi Yamada ◽  
Abdallah Amri ◽  
Lyndon Bevington ◽  
Pal Vincze
Keyword(s):  
Research And Development ◽  
International Organizations ◽  
Nuclear Power ◽  
Power Plants ◽  
Development Strategies ◽  
Lessons Learned ◽  
Member States ◽  
North East ◽  
Severe Accidents ◽  
Fukushima Daiichi

The Great East Japan Earthquake and the subsequent tsunami on 11 March 2011 initiated accident conditions at several nuclear power plants (NPPs) on the north-east coast of Japan and developed into a severe accident at the Fukushima Daiichi NPP, which highlighted a number of nuclear safety issues. After the Fukushima Daiichi accident, new research and development (R&D) activities have been undertaken by many countries and international organizations relating to severe accidents at NPPs. The IAEA held, in cooperation with the OECD/NEA, the International Experts’ Meeting (IEM) on “Strengthening Research and Development Effectiveness in the Light of the Accident at the Fukushima Daiichi Nuclear Power Plant” at IAEA Headquarters in Vienna, Austria, 16–20 February 2015. The objective of the IEM was to facilitate the exchange of information on these R&D activities and to further strengthen international collaboration among Member States and international organizations. One of the main conclusions of the IEM was that the Fukushima Daiichi accident had not identified completely new phenomena to be addressed, but that the existing strategies and priorities for R&D should be reconsidered. Significant R&D activities had been already performed regarding severe accidents of water cooled reactors (WCRs) before the accident, and the information was very useful for predicting and understanding the accident progression. However, the Fukushima Daiichi accident highlighted several challenges that should be addressed by reconsidering R&D strategies and priorities. Following this IEM, the IAEA invited several consultants to IAEA Headquarters, Vienna, Austria, 12–14 May 2015, and held a meeting in order to discuss proposals on possible IAEA activities to facilitate international R&D collaboration in relation to severe accidents and how to effectively disseminate the information obtained at the IEM. The IAEA also held Technical Meeting (TM) on “Post-Fukushima Research and Development Strategies and Priorities” at IAEA Headquarters, Vienna, Austria, 15–18 December 2015. The objective of this meeting was to provide a platform for experts from Member States and international organizations to exchange perspectives and information on strategies and priorities for R&D regarding the Fukushima Daiichi accident and severe accidents in general. The experts discussed R&D topic areas that need further attention and the benefits of possible international cooperation. This paper discusses lessons learned from the Fukushima Daiichi accident based on the presentations and discussions at the meetings mentioned above, and identifies the needs for further R&D activities to develop WCR technologies to cope with Fukushima Daiichi-type accidents.

Safety Assurance for Boiling Water Reactors (BWRs) Beyond Design Basis

2012 ◽  
Author(s):  
Salomon Levy
Keyword(s):  
Heat Sink ◽  
Nuclear Power ◽  
Power Plants ◽  
Lessons Learned ◽  
Event Scale ◽  
Proper Actions ◽  
Safety Assurance ◽  
Available Water ◽  
Design Basis ◽  
Fukushima Daiichi

Safety assurance of nuclear power plants cannot be achieved with highly inaccurate design bases coupled with extended operation beyond them as was the case at Fukushima Daiichi Units 1, 2, and 3. They resulted in core melts and radioactivity releases to the environment at the highest level 7 on the International Nuclear Event Scale (INES). The inexplicable low tsunami design basis used at Fukushima has been blamed for most of the extensive flooding and damages at the plants which led to a station blackout (SBO). But “the regulatory guidelines which stated that SBOs need not be considered played a large and negative role in the three core melts that transpired” (1). There were many other relevant Japan regulatory inadequacies which contributed to the severity of the events and they are covered in Section I titled Incorrect Design Basis and Inadequate Regulations. They are preceded by a short Introduction listing previous evaluations of the Fukushima Daiichi accident and providing a summary description of its immediate consequences. Section II covers Fukushima Daiichi Inadequate Operations during Beyond Design Basis Events, including failure to properly operate the isolation condenser (IC) and to recognize the limitations of the reactor core isolation cooling (RCIC). The IC and RCIC were installed to provide short term cooling during BWR SBO followed by injection of firewater to take the reactors to cold shutdown. The three Fukushima core melts could have been avoided by increasing focus upon depressurizing the reactors and using the installed fire water systems which were lined up to operate within one to three hours after the earthquake. They would have been able to add any kind of available water to the three depressurized reactors and take them to and keep them at cold shutdown conditions. Instead, Unit 1decided to shutdown IC for unexplained reasons while Units 2 and 3 chose to delay water addition to their depressurized reactors while RCIC was presumed to be working. Japan operators, management, and regulators may not have taken enough into account that, due to the tsunami failure of the plant ultimate heat sink, after IC stops working and RCIC is no longer certain to be available, the result is that: (1) the containment water is the only heat sink left to absorb the reactor decay heat transported there by the RCIC and reactor relief valves; (2) only a limited number of hours is available to inject any kind of other available water into the depressurized reactors; (3) high containment pressure is to be avoided as well as the ensuing difficulties to vent it; and (4) incorrect reactor water level data should not be relied upon to discourage proper actions as happened at all three Fukushima Daiichi Units. This broad statement is justified in much more details in Section II. Section III takes advantage of all the lessons learned at Fukushima to achieve Safety Assurance Beyond Design Basis. It includes all the necessary elements to avoid and limit future core melts. Most important of all is to have nuclear power plant personnel and management “exhibit very strong safety culture (and safety assurance beyond design basis), believe in them and to live them” as they prevail in US according to M.J. Virgilio, Deputy Executive Director of US NRC (2).

Identification of Non-Safety Systems to Withstand Beyond Design Basis Events

2012 ◽  
Author(s):  
James Nygaard ◽  
Ping Wan ◽  
Desmond Chan ◽  
Sara Barrientos
Keyword(s):  
Nuclear Power ◽  
Power Plants ◽  
Nuclear Power Plants ◽  
Systems Approach ◽  
Lessons Learned ◽  
Initial Assessment ◽  
Stress Tests ◽  
Multiple Systems ◽  
Design Basis ◽  
Fukushima Daiichi

As an aftermath of the natural disasters affecting the Fukushima Daiichi nuclear power plants in Japan, there has been great attention to provide assurance of safety of nuclear power plants around the world. Accordingly, many countries are requiring “stress tests” for their plants to assess the ability to withstand disaster scenarios for which they were not originally designed. Additional efforts are underway to capture lessons learned related to the operation of critical or major systems. Each operator and each country’s regulatory authority may be at different levels of completion for these activities. However, effects on non-safety related or peripheral systems have not been specifically addressed as standalone items or in an integrated systems approach. This paper seeks to produce an initial assessment of vulnerable systems, structures or components of non-safety related areas that may become critical to the safe operation of a nuclear plant or to the first steps to maintain stability of the plant during a postulated beyond design basis event. The same assessment is valid for events of significant magnitude, or for events affecting the entire site or region, even if a plant’s design basis is not exceeded. The initial assessment is based on widespread events, such as at the Fukushima Daiichi station, with focus on large nuclear power reactors. Certain peripheral plant systems support plant operators and staff or emergency responders such as by affording communication or physical access to plant areas. Other peripheral systems support plant operation or recovery, for example provision of diverse power supply or cooling means. Passive components common to multiple systems such as cables and piping are also assessed. Once vulnerable systems, structures or components are identified, various modifications or mitigation approaches will be discussed.

Design of Severe Accident Management Systems for Beyond Design Basis External Hazards at Paks NPP

2016 ◽  
Author(s):  
Tamás János Katona ◽  
András Vilimi
Keyword(s):  
Power Plant ◽  
Nuclear Power Plant ◽  
Nuclear Power ◽  
Severe Accident ◽  
Management Systems ◽  
Basic Question ◽  
Severe Accidents ◽  
Design Basis ◽  
Accident Management ◽  
External Events

Paks Nuclear Power Plant identified the post-Fukushima actions for mitigation and management of severe accidents caused by external events that include updating of some hazard assessments, evaluation of capacity / margins of existing severe accident management facilities, and construction of some mew systems and facilities. In all cases, the basic question was, what level of margin has to be ensured above design basis external hazard effects, and what level of or hazard has to be taken for the design. Paks Nuclear Power Plant developed certain an applicable in the practice concept for the qualification of already implemented and design the new post-Fukushima measures that is outlined in the paper. The concept and practice is presented on several examples.

Risk Communication in the Food Field

2014 ◽  
Vol 9 (sp) ◽  
pp. 598-602
Author(s):  
Hideaki Karaki ◽  
Keyword(s):  
Power Plant ◽  
Risk Communication ◽  
Nuclear Power ◽  
Lessons Learned ◽  
Agricultural Products ◽  
Accurate Information ◽  
Contaminated Food ◽  
Fukushima Daiichi ◽  
The Government ◽  
The U.S

The first BSE case in Japan was found in 2001. The BSE risk in Japan was small and the measures taken by the government successfully prevented the spread of BSE. However, because consumers did not have accurate information, they did not trust the government and refused to consume beef. Based on the lessons learned, the government enacted the Food Safety Basic Act in 2003, and risk communication in the food field was started. In 2003, the first BSE case was found in the U.S. that were supplying nearly one third of the beef consumed in Japan, and the government banned beef import from the U.S. The BSE risk in the U.S. was also small and it was possible to resume imports of beef after the appropriate measures. Despite the government efforts of risk communication, consumers rejected the resumption of imports. In 2011, food was contaminated with radioactive substances discharged from the Fukushima Daiichi nuclear power plant. Although government eliminated the contaminated food from the market, some consumers rejected all of the agricultural products of the Fukushima region, again a failure of risk communication. Here, the current situation and problems of the risk communication in Japan will be described.

Performance degradation of candidate accident-tolerant cladding under corrosive environment

2017 ◽  
Vol 35 (3) ◽  
pp. 129-140 ◽  
Author(s):  
Fumihisa Nagase ◽  
Kan Sakamoto ◽  
Shinichiro Yamashita
Keyword(s):  
Nuclear Power ◽  
Fission Products ◽  
Zirconium Alloys ◽  
Performance Degradation ◽  
Lessons Learned ◽  
Light Water Reactor ◽  
Fuel Cladding ◽  
Power Station ◽  
Light Water ◽  
Fukushima Daiichi

AbstractLight-water reactor (LWR) fuel cladding shall retain the performance as the barrier for nuclear fuel materials and fission products in high-pressure and high-temperature coolant under irradiation conditions for long periods. The cladding also has to withstand temperature increase and severe loading under accidental conditions. As lessons learned from the accident at the Fukushima Daiichi nuclear power station, advanced cladding materials are being developed to enhance accident tolerance compared to conventional zirconium alloys. The present paper reviews the progress of the development and summarizes the subjects to be solved for enhanced accident-tolerant fuel cladding, focusing on performance degradation under various corrosive environmental conditions that should be considered in designing the LWR fuel.

Countermeasures Derived From the Lessons of the Fukushima Daiichi Nuclear Power Plant Accident

2013 ◽  
Author(s):  
Tadashi Narabayashi
Keyword(s):  
Power Plant ◽  
Nuclear Power Plant ◽  
Pacific Ocean ◽  
Electric Power ◽  
Nuclear Power ◽  
Safety Evaluation ◽  
Lessons Learned ◽  
The Other ◽  
Nuclear Accidents ◽  
Fukushima Daiichi

On March 11, 2011, Tokyo Electric Power Company’s Fukushima Daiichi Nuclear Power Plant (NPP) was hit by a tsunami caused by the Tohoku-Pacific Ocean Earthquake, resulting in nuclear accidents in Units #1 to #4. With the aim of improving the safety of NPPs worldwide, we summarize the lessons that have been learned following a thorough analysis of the event and make specific proposals for improving the safety of such facilities. The author has been involved in investigating the causes of the accidents and developing countermeasures for other NPPs in Japan as a member of the Committee for the Investigation of Nuclear Safety of the Atomic Energy Society of Japan [1], an advisory meeting member of NISA with regard to technical lessons learned from the Fukushima Daiichi NPP accidents, and a Safety Evaluation Member of NISA for the other NPPs in Japan [2].

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