Improved gap conductance model for the TRAC code. [PWR]

The purpose of the present work, as indicated earlier, is to improve the present constant fuel clad spacing in TRAC-P1A without significantly increasing the computer costs. It is realized that the simple model proposed may not be accurate enough for some cases, but for the initial calculations made the DELTAR model improves the predictions over the constant ..delta..r results of TRAC-P1A and the additional computing costs are negligible.