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Cladding Evaluation in the Yucca Mountain Repository Performance Assessment

Published online by Cambridge University Press:  10 February 2011

Eric R. Siegmann ,
J. Kevin McCoy  and
Robert Howard
Eric R. Siegmann
Affiliation:
Duke Engineering and Services, eric_siegmann@ymp.gov(all) 1211 Town Center Drive, Las Vegas, NV 89144
J. Kevin McCoy
Affiliation:
Framatome Technologies(all) 1211 Town Center Drive, Las Vegas, NV 89144
Robert Howard
Affiliation:
TRW Environmental Safety Systems, (all) 1211 Town Center Drive, Las Vegas, NV 89144
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Abstract

The Yucca Mountain Project (YMP) 1998 Total System Performance Assessment Viability Assessment (TSPA-VA) analyzed the degradation of Zircaloy clad commercial fuel rods and the resulting exposure of the fuel in the event of a waste package failure. The cladding degradation mechanisms considered were damage before emplacement, mechanical failure from drift collapse, localized corrosion, general corrosion, delayed hydride cracking (DHC), hydride reorientation, creep rupture, and stress corrosion cracking (SCC). The potential for further cladding degradation due to cladding rupture as a result of fuel oxidation was also considered in the modeling effort. These models have been improved for use in future TSPAs.

The current cladding degradation model divides the analysis into two phases, cladding failure (perforation) and cladding unzipping (crack propagation caused by the expansion of UO2 fuel after reaction with water). Cladding failure occurs during reactor operation, from creep strain failure during high temperature periods in dry storage or in the early periods in the repository, or localized corrosion. After a Waste Package (WP) containing spent nuclear fuel in the repository fails, moisture is assumed to enter the waste package and the failed cladding starts to unzip (tear open) from the formation of secondary uranium phases. This slowly exposes the fuel. In addition, the inventory of fission products located in the gap between the cladding and fuel pellet is rapidly released. The cladding model limits the amount of fuel that is exposed to moisture and becomes available for dissolution. As a result, the doses to the affected population are reduced (factor of 20 to 50 in TSPA-VA) from the case where cladding is not considered.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 608: Symposium QQ – Scientific Basis for Nuclear Waste Management XXIII , 1999 , 3
Copyright
Copyright © Materials Research Society 2000

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References

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