it depends on the what kind of explosion you are trying to look into.

The explosion usually occurs mainly due to hydrogen build-up if the excess heat is not removed via the cooling water. You need to model the process of dissociation of H20 into H2+02 and then estimate the pressure developed inside the dome of the plant. Suppose this pressure exceeds the yield limit of the material. You may assume it has failed. i.e. (exploded, cracked). This is a fundamental approach that you can build on by adding complexities at later stages.