Fracture of Zircaloy-4 cladding tubes with or without hydride blisters in uniaxial to plane strain conditions with standard and optimized expansion due to compression tests

Abstract

test, which induces a near uniaxial loading, were proposed and developed to reach higher biaxiality ratios (ratio between mechanical quantities in axial and in circumferential direction). The first optimization, named HB-EDC for High-Biaxiality EDC, allowed to reach transverse plane strain conditions. The second optimization, named VHB-EDC for Very High Biaxiality EDC, was designed to reach higher loading biaxiality ratios. These optimized EDC tests were performed * Tel.: +33 1 69 08 39 43; e-mail: arthur.hellouin-de-menibus@cea.fr 1 at 25 • C, 350 • C and 480 • C on unirradiated hydrided Cold Worked Stress Relieved (CWSR) Zircaloy-4 samples. First, samples unhydrided or uniformly hydrided up to 1130 wppm were tested. Secondly, samples hydrided at 310 wppm with a hydride blister were tested. A large ductility reduction is induced by the increase in biaxiality level in absence of a hydride blister or with small blisters (<50 µm deep). The fracture strain decreases quickly with the blister depth at 25 • C, but more progressively at higher temperature. An equation that quantifies the fracture strain reduction with the blister depth is proposed. Eventually, one of the tests developed in the present study, the HB-EDC test, was proven to be a good compromise between the test complexity and the stress state reached. It is a good candidate to characterize the mechanical behaviour of irradiated cladding.

Thermomechanical loading applied on the cladding tube during the pellet cladding mechanical interaction phase of a rapid reactivity initiated accident

“…The stress biaxiality is between 0.6 and 0.95. Efforts are currently underway to develop easy-to-use testing techniques on cladding tubes that cover such loading biaxiality levels [22,12,23].…”

“…Sugiyama et al [3] results indicated that 60% and 85% of the cladding section was at a temperature lower than 350°C and 480°C respectively at cladding fracture. In laboratory tests that aimed at studying RIA conditions should therefore take into account the temperature level as it affects the material mechanical and thermal behavior [7] and the fracture process [10][11][12], the quantity of dissolved hydrides [13] and the extent of the irradiation recovery [14]. The temperature gradient in the cladding wall is likely one of the thermomechanical loading conditions that is most difficult to reproduce experimentally.…”

Mechanical Properties of Zircaloy-4 Cladding Tube by Advanced Expansion due to Compression (A-EDC) Test

“…Meanwhile, some slight disparities can still be observed. 6,[22][23][24][25][26] Experimentally, the A-EDC test can achieve a stable uniaxial tension condition in the hoop direction throughout the test. For the other tests, some of them are unable to derive stress-strain relation by experiments.…”

A model to describe the mechanical behavior and the ductile failure of hydrided Zircaloy-4 fuel claddings between 25 °C and 480 °C

“…Full-scale in-pile experiments performed in the NSRR or the CABRI reactors [4,5] have shown that, in the case of Zircaloy-4 cladding, the fuel rod can withstand a lower level of deposited energy during the RIA transient when it has a very high burnup, due in particular to hydrogen-induced cladding embrittlement. The mechanical properties of the cladding material depend among other things on hydrogen content, temperature and stress/strain state [3,6,7,8,9].…”

“…Most of the tests currently available reproduce only approximately these features [3,8], which are quite difficult to generate out-of-pile, although some efforts were and are still made to manage it [8,9,14,15,16]. Generally, corrective factors are applied in order to take into account the differences in mechanical loading (biaxiality and strain rate in particular) between separate-effect tests and the actual conditions [12,16].…”