The ultimate emergency measures to secure a NPP under an accidental condition with no designed power or water supply

In the recent nuclear catastrophe which occurred in Japan on March 11, 2011, several units of Fukushima conventional BWR experienced a total loss of power and water supply triggered by a heavy earthquake and a following Tsunami beyond design basis. In Fukushima accident it was observed that sea water was injected into reactors only after hydrogen explosion took place and it was considered a little too late to prevent core from damage. With regard to this fact, the Taiwan power company develops an ultimate measure to prevent reactor from encountering core damage, if either designed AC power or reactor water supply cannot be restored in time. This ultimate measure was named as DIVing plan, abbreviated from system depressurization, water injection and containment venting. Once any designed AC power or reactor water supply is made available, this DIVing plan will be activated to (1) depressurize reactor first, (2) inject any available water into reactor by any available power supply if this critical status cannot be restored in time, and (3) vent the containment if necessary to maintain containment integrity. In this paper the DIVing plan was simulated by RELAP5-3D to verify the concept of it and also to quantify the required raw water injection rate to prevent core from damage for both PWR and BWR plants in Taiwan, after the loss of passive cooling mechanism. Provided the passive cooling mechanism is lost within the first hour, for Chinshan BWR/4 and Kuosheng BWR/6 plants 1400 l/m (370 GPM) and 2441 l/m (645 GPM) raw water injection rate are, respectively, required and for Maanshan 3-loop PWR plant 2271 l/m (600 GPM) water injection rate is required, to prevent the PCT higher than 1088.6 K (1500 °F).