Thermal-hydraulic analysis of loss-of-cooling accident in spent fuel pool of Bushehr NPP using the RELAP5 and MELCOR

Following the Fukushima Daiichi accident, the simulation of accidents related to the Spent Fuel Pool (SFP) became more important due to the high content of long-lived radionuclides, and lack of the protection by the pressure vessel despite its low decay heat. Therefore, the loss-of-cooling accident in the SFP of the Bushehr NPP was first simulated in this paper. The RELAP5 (as the Best Estimate code) and MELCOR (as a Severe Accident code) codes were used for simulation of the loss-of-cooling accident. The decay heat power calculation was performed by the ORIGEN code. The nodalization of SFP was done by using the Final Safety Analysis Report (FSAR) of Bushehr NPP. Different phenomena such as increasing water temperature in the pool, water boiling and decreasing of pool water level, spent fuel uncovering, increasing fuel temperature and the onset of fuel melting, hydrogen production, and release of radio-nuclides were observed and investigated. The steady-state results were validated by Bushehr NPP operating data. Verification of transient and accident results was performed by code-to-code (RELAP5 & MELCOR) comparison approach and Bushehr NPP data, the results showed that a good agreement together.