Accident Lessons at the Fukushima-Daiichi NPP for the Safety of the Nuclear Power Industry in Ukraine

Abstract

The main causes of destructive steam and gas explosions with catastrophic environmental consequences during the accidents at Fukushima-Daiichi NPP were the loss of tightness of the passive safety systems of the reactor residual fuel removal safety system and the critical residual heat removal function in the spent nuclear fuel holding tank . The main lesson of the Fukushima accident for the environmental safety of Ukraine's nuclear power industry is the need to anticipate the possibility of unlikely emergency events with catastrophic environmental consequences. Such unlikely events include: flooding of the nuclear power plant site, complete long-term blackout, steam-gas destructive explosions, joint action of external extreme phenomena. Based on this, the following lessons of the Fukushima accident were formulated for the nuclear power industry of Ukraine regarding unlikely emergency events with catastrophic environmental consequences: lesson 1 - the need for reliable isolation of diesel generator rooms from external extreme events; lesson 2 - the need to improve strategies and methods of managing accidents with complete long-term blackout and lesson 3 - the need to determine the conditions of steam-gas explosions. The lessons of the Fukushima accident and the known results of the analysis of explosive conditions in nuclear power plants with WWER determine the need to improve methods for modeling the conditions and consequences of steam and gas explosions at the dynamic stages of emergency processes.The lessons of the Fukushima accident and the results of the calculated modeling of accidents with complete long-term power outages of nuclear power plants with WWER determine the need to improve strategies and ways to prevent and manage accidents with complete long-term power outages.A promising approach is the integrated use of additional passive safety systems to ensure the function of feeding steam generators with turbopumps (area for high pressures) and natural circulation (area for low pressures).