Severe accident management in Nordic Boiling Water Reactors aims to achieve termination of the accident progression by quenching and cooling core melt released from the vessel into a deep pool of water beneath the reactor. However, steam explosion that can occur upon contact of hot corium with the volatile coolant might represent a challenge to containment integrity. The present study focuses on analyzing steam explosions during severe accidents initiated by LOCA and SBO in Nordic BWRs using a framework based on coupling of MELCOR and TEXAS-V codes. MELCOR provides detailed thermal-hydraulic and fission product behavior modeling, while TEXAS specializes in simulating fuel-coolant interactions and steam explosion dynamics. The analysis of explosion impulse CDFs and failure probabilities obtained for selected transient analyses highlights that the non-reinforced hatch door has the highest failure probability with 95 th percentile approaching 1 due to its low fragility limit of 6kPa.s, making failure likely in most scenarios. Reinforcing the hatch door reduces failure probabilities, particularly in LOCA-IDEJ1 and SBO-IDEJ0 scenarios. The coupled MELCOR-TEXAS model enables a detailed examination of both pressure loads on containment structures, and the effect of containment failure on the release of fission products in transient scenarios.
Acharya et al. (Sun,) studied this question.