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Yamada, Fumiaki; Mori, Takero
no journal, ,
The core cooling by the nature circulation was effective, that evaluated the form of the circulation root of various coolant in the failure of forced circulation of main heat transport system which was an accident sequence of loss of heat removal system more than design basis accident of the FBR from plant dynamics characteristic analysis.
Kurisaka, Kenichi; Nishino, Hiroyuki; Sotsu, Masutake
no journal, ,
In the sodium-cooled fast reactor, we proposed redundant and independent safety measures to prevent loss of heat removal against failure of the design-based-accident countermeasures. By considering those safety measures, we implemented deterministic evaluation of their effectiveness and probabilistic study on reduction of the occurrence frequency of loss-of-heat-removal. As a result, we obtained prospect to prevent loss-of-heat-removal with robust measures.
Onoda, Yuichi; Nishino, Hiroyuki; Kurisaka, Kenichi; Yamano, Hidemasa; Demachi, Kazuyuki*
no journal, ,
In order to evaluate the effectiveness of the measures for improving resilience at ultra-high temperatures, a concept of evaluation focusing on core damage frequency was proposed. Assuming loss of heat removal systems event after reactor shutdown which may result in core damage in sodium-cooled fast reactors, the measures for improving resilience which enable to recover the safety functions at ultra-high temperatures are identified: one is to retain the primary coolant using failure mitigation technology, and the other is to add a heat removal system that can be used under ultra-high temperature conditions. The core damage frequencies were calculated preliminarily and their reduction effect was estimated by comparing them before and after the introduction of the measures for improving resilience.
Kurisaka, Kenichi; Nishino, Hiroyuki; Yamano, Hidemasa
no journal, ,
This study aims to evaluate the effectiveness of the measures for improving resilience against excessive earthquake. Loss of heat removal systems (LORHS) after reactor shutdown is focused on. Implementation of those measures could prevent the seismic-induced LOHRS itself or core damage due to ultra-high temperature condition resulting from LOHRS. Based on this, we developed the methodology that the effectiveness is evaluated by the reduction of core damage frequency. As an example, its applicability to sodium-cooled fast reactors was examined.
Onoda, Yuichi; Kurisaka, Kenichi; Yamano, Hidemasa
no journal, ,
We invented an effectiveness evaluation method of the measures for improving resilience by quantifying the event tree focusing on the accident sequence that leads to an ultra-high temperature state due to loss of heat removal systems in a sodium-cooled fast reactor and by evaluating the reduction rate of core damage frequency before and after the introduction of measures for improving resilience. If the conditional success probability of measures for improving resilience is tentatively set to 0.81, the reduction rate of core damage frequency for all accident sequences leading to loss of heat removal systems becomes 19%. By taking measures to improve resilience, the core damage frequency can be reduced to the order of 1.0
10
(1/reactor year).
Onoda, Yuichi; Kurisaka, Kenichi; Yamano, Hidemasa
no journal, ,
Focusing on the accident sequence leading to ultra-high temperatures due to loss of heat removal systems, the effectiveness of the measures for improving reactor structural resilience was preliminarily evaluated for next-generation sodium-cooled fast reactors. Focusing on countermeasures to promote heat dissipation from the reactor vessel, the cooling performance of these measures was preliminarily evaluated. In addition, we examined the uncertainty of accident progression and the success or failure of the measures for improving resilience, and preliminarily evaluated the branch probability of the event tree. As a result, it was confirmed that the reduction rate of the core damage frequency due to the assumed countermeasures can be quantified.