Feasibility analysis of aggressive cooldown in OPR-1000 nuclear power plants

• We examine the feasibility of aggressive cooldown, particularly in OPR-1000 plants.
• We review experimental and simulation results, EOPs, and time estimates.
• Aggressive cooldown is, in general, expected to be performed successfully.
• There is potential for failure to initiate aggressive cooldown in a timely manner.
• Investigation on allowing higher cooldown rate in OPR-1000 plants is recommended.

Aggressive cooldown is the action taken by main control room (MCR) operators to rapidly cool down and depressurize the reactor coolant system at the maximum allowed cooldown rate during a small break loss of coolant accident (SBLOCA) or a steam generator tube rupture accident with failure of high-pressure safety injection (HPSI) in a pressurized water reactor. We examined the feasibility of aggressive cooldown in OPR-1000 nuclear power plants by establishing success criteria based on experimental results and thermal–hydraulic code simulations, reviewing emergency operating procedures, and estimating the necessary time for MCR operators to initiate aggressive cooldown based on experimental results with licensed nuclear power plant operators. For an SBLOCA with a break size of 0.02 ft2 combined with total failure of HPSI, we found that aggressive cooldown can generally be performed successfully, but there is potential for failure to initiate aggressive cooldown in a timely manner. We discuss the potential effects of introducing the Ultimate Procedure on reducing the core damage potential. Detailed analysis and further discussion are necessary to reduce uncertainties associated with aggressive cooldown and its positive effect on the safety of nuclear power plants.