Severe accident management in Nordic Boiling Water Reactors (BWRs) is achieved by quenching and cooling core debris ejected by the reactor vessel into a deep pool of water. However steam explosions can occur as a result of contact of hot corium particles with volatile coolant, challenging containment structures. Through a systematic ROAAM+ analysis it has been shown that the formation of coolable debris bed requires sufficiently deep pool of water in the cavity, which, unfortunately also significantly increases steam explosion loads. The present study focuses on analyzing steam explosions during severe accidents initiated by loss of coolant accident (LOCA) and station blackout (SBO) in Nordic BWRs using a framework based on dynamic coupling of MELCOR and TEXAS-V codes developed earlier. The analysis aims to assess if time evolution of the accident progression can limit possible conditions for the FCI and steam explosion, and then study the consequences in the cavity, particularly with concrete interactions and failure of the cavity basemat. 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 95th percentile approaching 1 due to its low fragility limit of 6kPa.s, making failure likely in most scenarios. Mode of debris ejection seems to have a minor influence on the non-reinforced hatch door failure. Based on these unmitigated, conservative calculations, source term releases to the environment are large (at least two orders of magnitude above regulatory limits), with about half of the release as contaminated water. Results from these simulations enhance our understanding of the accident evolution on the steam explosion risks specific to Nordic BWRs and support improvements in accident management and containment design. The full model simulations will also be used in developing efficient and fast running dynamic surrogate models.