The prediction problems of VVER fuel element cladding failure theory

Abstract

tA method for forecasting of VVER fuel element (FE) cladding failure due to accumulation of deformationdamage parameter, taking into account the fuel assembly (FA) loading history and the damage parameterdistribution among FEs included in the FA, has been developed. Using the concept of conservative FEgroups, it is shown that the safety limit for damage parameter is exceeded for some FA rearrangement,though the limits for circumferential and equivalent stresses are not reached. This new result contradictsthe wide-spread idea that the damage parameter value plays a minor role when estimating the limitingstate of cladding. The necessary condition of rearrangement algorithm admissibility and the criterion forminimization of the probability of cladding failure due to damage parameter accumulation have beenderived, for using in automated systems controlling the cladding tightness.