Abstract
The paper analyzes the approaches to improve the efficiency of blackout accident management taking into account the lessons of the great accident at Fukushima Daiichi NPP in 2011. It is found that the afterheat removal passive systems by natural circulation through steam generators cannot provide conditions for adequate safety functions to remove heat from the reactor and maintain the required feedwater level in the steam generator during blackout accidents and multiple failures of safety-related systems. The application of alternative approaches using auxiliary feedwater steam generator driven pumps requires additional experiment-calculated operability / reliability qualification for a blackout accident and multiple failures of NPP safety-related systems. However, implementation of alternative SDEFP system requires in-depth qualification for the conditions of blackout accidents. Safety systems of passive heat removal from the steam generator (adequately to active safety electrical systems) cannot ensure safety functions on control of required feedwater level in the steam generator and heat removal from the reactor core during blackout accidents (at least 72 hours) and multifailure accidents. The system of the steam generator driven emergency feedwater pump can be the alternative solution to ensure safety functions on heat removal through the steam generator during blackout accidents. Additional study of efficiency of steam driven pumps at the experimental facilities that meet real-life criteria of hydrodynamic similarity is a necessary condition for implementation of system of the steam driven emergency feedwater pump. Application of an integrated approach to manage blackout accidents is reasonable. At the initial stage of accident with relatively high steam pressure in the steam generator it is required supply of feedwater by the steam driven emergency pump
Highlights
Many researches and scientific and technical reports covers the analysis of the reasons, consequences and lessons of great accident at Fukushima-Daiichi NPP in 2011: TEPCO/operating organization, IAEA experts [1], stress tests of National safety regulatory inspectorates/commissions of the leading nuclear states, the largest design and production companies of nuclear power, independent scientific researches etc
At the initial moment of accident, at Units 1, 2 and 3 BWRs were automatically stopped by earthquake recording signal
To fulfil safety functions on keeping required level of feedwater in steam generator (SG) and heat removal from the reactor during blackout accidents, it is need to develop and implement alternative systems based on the adequacy principle of passive and design active safety systems
Summary
Many researches and scientific and technical reports covers the analysis of the reasons, consequences and lessons of great accident at Fukushima-Daiichi NPP in 2011: TEPCO/operating organization, IAEA experts [1], stress tests of National safety regulatory inspectorates/commissions of the leading nuclear states, the largest design and production companies of nuclear power, independent scientific researches etc. Actual Fukushima lessons concerning blackout accidents the followings: – PSS have to fulfil safety functions for a long time, adequately to ASS; – PSS have to meet requirements for seismic stability and other external extreme events, as well as the main NPP equipment. The work [6] determines accident of a double ended rupture of main steam lines in case of feedwater non-isolation of SG as the worst conditions for increasing pressure and temperature of the containment steam-gas environment In case of such non-isolation the required level of boiler water in SG is keep by emergency and/or auxiliary feedwater pumps (EFWP/AFWP). To fulfil safety functions on keeping required level of feedwater in SG and heat removal from the reactor during blackout accidents, it is need to develop and implement alternative systems based on the adequacy principle of passive and design active safety systems
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