Effectiveness evaluation of the measures for improving resilience at ultra-high temperatures

Onoda, Yuichi; Nishino, Hiroyuki; Kurisaka, Kenichi; Yamano, Hidemasa

Proceedings of Probabilistic Safety Assessment and Management & Asian Symposium on Risk Assessment and Management (PSAM17 & ASRAM2024) (Internet), 10 Pages, 2024/10

We developed the measures for improving resilience of the sodium-cooled fast reactor structure using the failure mitigation technology and evaluated the effectiveness of the measures. To prevent core damage in the event of an accident progressing to an ultra-high temperature state, both measures to prevent overpressure in the reactor vessel and measures to cool the reactor core are required. As a core cooling measure, we developed a core cooling concept that promotes radiant heat transfer from the reactor vessel and cools the containment vessel outer surface by natural convection named Containment Vessel Auxiliary Cooling System (CVACS). We developed a method to use the reduction rate of core damage frequency as an indicator for effectiveness of the measures for improving resilience. The core damage frequency was evaluated by calculating the core cooling performance using CVACS, reflecting the results of structural analysis and human reliability analysis. By implementing measures for improving resilience in addition to existing measures, the core damage frequency of Japan loop-type sodium-cooled fast reactor caused by LOHRS has been reduced to about one-hundredth of the previous level.

Effectiveness evaluation methodology of the measures for improving resilience of nuclear structures against excessive earthquake

Kurisaka, Kenichi; Nishino, Hiroyuki; Yamano, Hidemasa

Proceedings of 30th International Conference on Nuclear Engineering (ICONE30) (Internet), 8 Pages, 2023/05

The objective of this study is to develop an effectiveness evaluation methodology of the measures for improving resilience of nuclear structures against excessive earthquake by applying the failure mitigation technology. This study regarded those measures for improving resilience of important structures, systems, and components for safety to enlarge their seismic safety margin. To evaluate effectiveness of those measures, seismic core damage frequency (CDF) is selected as an index. Reduction of CDF as an effectiveness index is quantified by applying seismic PRA technology. Accident sequences leading to loss of decay heat removal are significant contributor to seismic CDF of sodium-cooled fast reactors (SFRs), and those sequences result in core damage via ultra-high temperature condition. This study improved the methodology to evaluate not only the measures against shaking due to excessive earthquake but also the measures at the ultra-high temperature condition. To examine applicability of the improved methodology, a trial calculation was implemented with some assumptions for a loop-type SFR. Within the assumption, the measures for improving resilience were significantly effective for decreasing CDF in excessive earthquake up to several times of a design basis ground motion. Through the applicability examination, the methodology for the effectiveness evaluation was developed successfully.

Development plan of failure mitigation technologies for improving resilience of nuclear structures

Kasahara, Naoto*; Yamano, Hidemasa; Nakamura, Izumi*; Demachi, Kazuyuki*; Sato, Takuya*; Ichimiya, Masakazu*

Transactions of the 26th International Conference on Structural Mechanics in Reactor Technology (SMiRT-26) (Internet), 8 Pages, 2022/07

Utilizing fracture control, we are developing a technology to suppress the expansion of damage caused by an event that exceeds the design assumption. We made a plan to develop three issues; (1) Technology for mitigating failure consequence at extremely high temperatures, (2) Technology for mitigating failure consequence against excessive earthquakes, and (3) Methodology for improving reactor structure resilience.

Towards enhancing Fukushima environmental resilience

Miyahara, Kaname

Transactions of the American Nuclear Society, 117(1), p.51 - 52, 2017/10

This presentation highlights JAEA's challenges for contributing to recovering the previous life of residents and the development of resilient communities in Fukushima Prefecture based on considering needs of local people on the environmental restoration categorized by the state of evacuation orders and the lifting of such orders.

Extract a lesson from the Fukushima Daiichi Nuclear Power Plant Accident in the light of Safety-II; People perform an important role at the respond to a risk on an accident

Oba, Kyoko; Yoshizawa, Atsufumi*; Kitamura, Masaharu*

no journal, , 

This study introduces the necessity of stepping up the concept from Safety-I, risk removal type of safety, to the Safety-II, which aims to enhance system flexibility and resilience. In order to achieve Safety-II, the Fukushima Daiichi Nuclear Power Plant accident was investigated by using Resilience Engineering, which is the methodology going toward Safety-II. Focusing on responding, which is one of the four cornerstones of Resilience Engineering, workers in the Fukushima Daiichi Nuclear Power Plants executed flexible ideas to prevent catastrophic damage of the accident. Those responding were created by human with strong attitude in which few investigation reports mentioned. Those approaches show the importance of the Safety-II concept and Resilience Engineering methodology.

Leading and lagging indicators for safety of large-scale socio-technical systems

Kitamura, Masaharu*; Oba, Kyoko; Yoshizawa, Atsufumi*

no journal, , 

Socially constructed resilience by multiple organizations; The Case of Tokai No.2 Power Station

Oba, Kyoko; Yoshizawa, Atsufumi*; Kitamura, Masaharu*

no journal, , 

This paper focuses on the Tokai No.2 Nuclear Power Station, which was hit by earthquakes and subsequent tsunami in the Great East Japan Earthquake in 2011 but swiftly achieved cold shutdown. The earthquake struck the power station just before the scheduled completion of engineering work to raise the walls of the room housing a seawater intake pump. The fact that the work had been applied helped continuous operation of the seawater intake pump, a key piece of equipment for achieving cold shutdown. The power station followed its pre-defined procedure to bring its reactors to cold shutdown. Focusing on the background of the engineering work, which was not mentioned in past reports, this paper analyzes multiple organizations (main actors) based on the concept of Resilience Engineering to reveal how the collaboration between these organizations enhanced the power station's resilience, and considers the potential of such collaboration in boosting the resilience of our society.

Business continuity plan and resilience engineering; Consideration for enhancement of disaster prevention and mitigation based on case studies of Great East Japan Earthquake

Oba, Kyoko; Yoshizawa, Atsufumi*; Kitamura, Masaharu*

no journal, , 

At the time of the Great East Japan Earthquake, many socio-technical systems experienced significant damages from the earthquake and tsunami far beyond the preparedness for disasters. Therefore, necessity of Business Continuity Plan (BCP) has been recognized irrespective of domains. Case studies of various on-site responses related to this disaster were analyzed to extract lessons from BCP that is common to various systems. Specifically, in reference to the concept of Resilience Engineering that is focused for enhancing resilience of organizations (i.e. resilience and flexibility) in recent years, analysis was conducted with attention to the cases in which the concerned systems could restore or ensured the safety from disturbance. Lessons useful for disaster prevention and mitigation have been extracted successfully from activities conducted for preparing and responding to the earthquake-driven disturbances.

Experiences in Fukushima Dai-ichi Nuclear Power Plant in light of resilience engineering

Yoshizawa, Atsufumi*; Oba, Kyoko; Kitamura, Masaharu*

no journal, ,