Overview of reactor pressure vessel cladding

Abstract

Licence extension of NPPs requires a new safety analysis of the plant covering the extended operating life. One of the most important safety considerations is the integrity of the RPV (Reactor Pressure Vessels). The RPV material suffers several ageing-related effects during operating service: neutron (and gamma) irradiation embrittlement, thermal ageing, low-cycle fatigue, thermal fatigue and corrosion. Generally, the most severe effects are irradiation and the thermal embrittlement of the RPV belt near the fuel core zone, which is often referred to as the beltline. Nearly all operating RPVs are covered inside with a stainless steel layer called RPV cladding. The RPV cladding generally made by welding results in very rough grain size and its mechanical and thermal properties are different from the RPV base material, causing high residual stresses. The thickness of RPV cladding is 2?10 mm. Since the RPV cladding was previously considered only as an anticorrosive layer the mechanical properties and the role in the RPV integrity were not properly studied. In this review, the existing relevant informations on RPV cladding properties are summarised.