[en] This report gives details of changes in model which have been, or are about to be, implemented in the UK version of RELAP III. The changes embrace features representing steam slip ratio, momentum flux terms including change of area, frictional pressure drop interaction with discharge conditions, options for discharge models, the Smith slip ratio and two-phase multiplier, modifications to dryout and rewetting criteria, bubble rise in a horizontal steam drum, pipework heat and radiation cooling, spray cooling under stagnant conditions, determination of steady state conditions, and inclusion of a slave pin calculation. Most of these features are already programmed, those on which work is continuing being indicated in the test. (author)