Development of simple success criteria regarding alternative water injection for emergency response to long-term station blackout of BWR

This paper discusses the conditions regarding the alternative water injection which prevents core damage under long-term station blackout of a Boiling Water Reactor (BWR). A BWR-5 model plant was analyzed by RELAP5/SCDAP mod3.5 by changing six parameters regarding the accident scenario and alternative water injection. It was found that preventing core damage was almost equivalent to preventing cladding rupture. When the temperature of fuel rod reaches the region where cladding creep rupture occurs, oxidation and heatup of Zircaloy begin to accelerate each other as a result of increased surface area by that cladding rupture. By summarizing the results of sensitivity analyses, the discriminants for calculating an index of core condition and their threshold values for preventing core damage were proposed. Such information prepared for each BWR plant would be useful in the actual emergent condition where the measurements of core parameters are unavailable.