Implementation of a Post-Dryout Model in the ASSERT Subchannel Code

Abstract

This paper describes the implementation of a method in the ASSERT code for calculating post-dryout temperatures. In current subchannel codes, including ASSERT, the CHF calculation is done explicitly following the evaluation of flow and enthalpy distributions across a bundle; hence post-dryout effects cannot be simulated. ASSERT has been modified such that CHF calculations are performed during the solution. The new procedure evaluates the CHF conditions and flags those subchannels and locations where post-CHF conditions are present. This permits use of the appropriate wall shear and wall/vapour heat- transfer model for the evaluation of subchannel pressure and sheath temperatures. A preliminary validation of the post-dryout version of ASSERT was performed by comparing a few selected U-1 post-dryout runs against the predictions. The results look promising.