Boiling water reactor (BWR) utilities in Japan began to consider the d
evelopment of a mechanistic model to describe the critical heat transf
er conditions in the BWR fuel subchannel. Such a mechanistic model wil
l not only decrease the necessity of tests, but will also help by remo
ving some overly conservative safety margins in thermal hydraulics. Wi
th the use of a postdry-out heat transfer correlation, new acceptance
criteria may be applicable to evaluate the fuel integrity. Mechanistic
subchannel analysis models will certainly back up this approach. This
model will also be applicable to the analysis of large-size fuel bund
les and examination of corrosion behavior.