Studies of hydrogen assisted failures initiating at the cladding outer surface of high burn-up fuel using a modified Ring Tensile Technique

Conference · Sun Jul 01 04:00:00 EDT 2007

OSTI ID:21229282

Alvarez-Holston, A M; Lysell, G; Grigoriev, V ^[1]

---

1. Studsvik Nuclear, 61182 Nykoeping (Sweden)

A testing technique to study outside-in failures of high burnup fuel cladding has been developed within SCIP (Studsvik Cladding Integrity Program). The technique is used to study time independent crack initiation as well as time dependent crack propagation such as delayed hydride cracking (DHC). One of the main purposes of the study is to get a better understanding of the operating mechanisms behind through wall failures that initiate at the cladding outer surface and propagate in a radial/axial direction sometimes causing long axial splits during power ramp testing. The results show that sharp incipient cracks can form in a hydride dense rim at the outer surface of BWR and PWR claddings at operating temperatures and at hoop stresses well below the yield stress of the bulk material once the hydrogen concentration locally exceeds about 9000 wppm H. Incipient cracks formed in the hydride dense rim of BWR cladding propagated through wall after 112 minutes at 400 MPa when tested at 250 deg. C. SEM examinations of the fracture surface and cross section showed typical features of delayed hydride cracking (DHC). At 300 deg. C, DHC was initiated but the crack arrested in the interior and through wall failure occurred by ductile rupture of the remaining ligament at 575 MPa. In high burnup PWR cladding tested at 385 deg. C, incipient cracks formed in the hydride rim. However, in this case the crack did not propagated by DHC. Instead through wall failure occurred by shear instability at 500 MPa. The results support the idea that there is an upper temperature limit above which DHC will not occur in zirconium cladding. The first results from the modified ring tensile testing are in good agreement with previous results from ramp testing and thereby indicate that the testing technique can be used to predict failure mechanisms induced during ramp testing. (authors)

• Research Organization: American Nuclear Society, 555 North Kensington Avenue, La Grange Park, IL 60526 (United States)
• OSTI ID: 21229282
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
42 ENGINEERING
BWR TYPE REACTORS
CLADDING
CRACK PROPAGATION
CRACKS
FRACTURES
HYDRIDES
HYDROGEN
NUCLEAR FUELS
PRESSURE RANGE MEGA PA 100-1000
PWR TYPE REACTORS
RUPTURES
SCANNING ELECTRON MICROSCOPY
STRESSES
TESTING
ZIRCONIUM