Effect of process variables on texture and creep of pressurised heavy water reactor pressure tubes

Abstract

Zr-2.5 wt%Nb pressure tubes are used for coolant channels of Pressurised Heavy Water Reactors (PHWRs). These pressure tubes are lifetime components of the reactor and have to sustain extremely harsh conditions of temperature, pressure and neutron irradiation during service. One of the major life limiting factors for pressure tubes is diametral creep. This causes dilation of the pressure tube leading to flow bypass and inefficient heat removal from fuel bundles. This underscores the importance of producing pressure tubes with higher creep resistance. The primary metallurgical parameters controlling the creep strength of Zr-2.5Nb pressure tubes are texture, microstructure, grain size, dislocation density and alloying additions. This includes the strengthening of beta phase due to niobium enrichment. Heat treated Zr-2.5Nb pressure tubes have been reported to have the highest creep strength. This paper briefly discusses the effects of various processing parameters on the microstructure and texture of pressure tubes, which enhance their creep resistance.