Thermo mechanical behaviour of fresh zircaloy-4 under LOCA conditions

International audienceDuring a Loss of Coolant Accident in a Pressurized Water Reactor, a break on the reactor primary circuit leads to the quick water depressurization from 155 to almost 1 bar. The fast temperature g of the fuel cladding from 320°C to 1200°C induces filling gas pressure increase. Thus, the pressure difference between the inner and outer tube surfaces grows, leading to important hoop stresses. Simultaneously, steam environment affects the creep behaviour of the cladding by oxidation and hydriding. Hydriding has several noticeable effects [1] on the creep behaviour of Zircaloy-4, creep rate decrease, embrittlement and shift of phase transition temperatures (α→ α + β, α + β → β) towards lower temperature.A custom experimental setup is used to study the macroscopic secondary creep behaviour of as-received and hydrided zircaloy-4 (cladding material) under a representative thermo-mechanical loading. The experimental matrix focuses on the following ranges, temperature between 700°C and 800°C (the phase transformation temperature of as-fabricated material is about 820°C), hoop stress in a range of 20 - 75 MPa and hydrogen content between 0 and 650 ppm. Experimental setup, post-treatment and preliminary results are here presented on as-received zircaloy-4 (Zr - 1,3 Sn - 0,2 Fe - 0,1 Cr)