Determination of required delay time following reactor shutdown prior to actuation of LOFT ECCS Bypass

The results of calculations are presented for the decay time required prior to LOFT ECCS shutdown bypass actuation following a reactor shutdown. These calculations are based on a LOCA occurring during hot shutdown which would void the core. Based on an operator response time of 20 minutes to manually establish ECC flow, the reactor decay time was calculated to prevent the fuel cladding temperature from exceeding 1100/sup 0/F. Results show that 211 hours are required following normal reactor shutdown from 55 MW reactor power before ECCS shutdown bypass actuation can be allowed if the reactor is not in cold shutdown condition. One hundred (100) seconds are required following a LOCE before ECCS shutdown bypass actuation can be allowed.