Fuel Element Sheath Strains at High Powers and Burnups: Rationalizing the Reference Bundle Overpower Envelope

Abstract

A methodology is derived and described for calculating a revised 'Reference Design Bundle Overpower' envelope to a bundle burnup of 450 MW.h/kg U. This envelope is based on the criterion that average diametral sheath strains, measured at the pellet mid-plane positions, should not exceed 0.4 %. The algorithm for calculating strains is based on normalisation of measured strains, to allow for the effects of fuel density, power and burnup.