Implementation of CO2 and PbLi as working fluids in RELAP5/MOD3.3 towards accident analysis of COOL blanket for CFETR

•The RELAP5/MOD3.3 is modified with the implementation of the PbLi and CO2 as working fluids and verified.•The modified RELAP5/MOD3.3 is applied to the COOL blanket outboard segment for preliminary accident analyses.•Thermal hydraulic requirements can be satisfied according to steady state and plasma pulse operation simulation of the COOL blanket.•The COOL blanket can endure 20% of plasma heat flux excursion during MARFE event.•Safety requirements of COOL blanket can be generally fulfilled during LOFA with different assumptions and then mitigation measures are suggested accordingly.