Sensitivity Studies of the Effect of Cladding Degradation on TSPA Results


The Commercial Spent Nuclear Fuel (CSNF) cladding directly influences the dose by reducing the release rate of radionuclides compared to bare fuel. A cladding degradation model was introduced in the Total System Performance Assessment - Viability Assessment (TSPA-VA) and has evolved into the TSPA-SR (Sight Recommendation), Rev 00 and most recently the Supplemental Science and Performance Analyses (SSPA) models. TSPAs are large computer models that predict how the radionuclides might escape through the various barriers and migrate through the different geological regions and predict the dose to the critical population. The major components in the cladding degradation model are initial cladding failure, creep, stress corrosion cracking (SCC), localized corrosion, mechanical failures (due to seismic events and rock overburden) and cladding unzipping. In the bare fuel case, the dose is controlled by the failure rate of the waste packages (WPs), the solubility limits for certain radionuclides, and the rate of diffusion of the radionuclides through the cracks in the WPs. The cladding degradation model involves two steps, perforation followed by unzipping. Sensitivity studies have shown that cladding limits dose primarily by preventing dissolution of the UO2 fuel (when the cladding is not perforated). If all the cladding is assumed to be perforated and cladding unzipping occurs, the peak dose would be within 4% of that of bare fuel. The UO2 dissolution rate (the driving mechanism for cladding unzipping) is sufficiently rapid that assuming instant dissolution increases the dose by only 12% from the base case. In the current cladding degradation model, cladding accounts for a reduction in dose for the first 100,000 years of a factor of 16 when compared with bare fuel. This is because of the low initial cladding failure rate (2.1% including SCC and creep) and few failures from localized corrosion (late WP breach and limited water entering the WPs). Failure of the cladding by rock overburden accounts for an increasing trend in dose at times greater than 100,500 years. This mechanism increases the peak dose and delays the peak from approximately 200,000 to 300,000 years. In conclusion, the cladding degradation model, mostly through preventing water from contacting the UO2, reduces the dose predicted in the TSPA analysis.

This is a preview of subscription content, access via your institution.


  1. 1.

    Siegmann, E. R., J. K. McCoy, R. Howard. “Cladding Evaluation in the Yucca Mountain Repository Performance Assessment,” Mat. Res. Soc. Symp. Proc. Vol. 608, pp. 3–9, 2000.

    Google Scholar 

  2. 2.

    CRWMS M&O 1998. “Waste form Degradation, Radionuclide Mobilization, and Transport Through the Engineered Barrier System.” Chapter 6 of Total System Performance Assessment-Viability Assessment (TSPA-VA) Analyses Technical Basis Document. B00000000-01717-4301-00006 REV 01. Las Vegas, Nevada: Civilian Radioactive Waste Management System Management &Operation (CRWMS M&O).

    Google Scholar 

  3. 3.

    Siegmann, E. R. (2000) Clad Degradation - Summary and Abstraction. ANL-WISMD-000007 REV 00 ICN 01. Las Vegas, Nevada: CRWMS M&O.

    Google Scholar 

  4. 4.

    Total System Performance for the Site Recommendation. TDR-WIS-PA-000001 Las Vegas, NV: (CRWMS M&O) 2000.

    Google Scholar 

  5. 5.

    FY 01 Supplemental Science and Performance Analysis. TDR-MGR-MD-000007 REV 00 Las Vegas, NV: (CRWMS M&O) 2001

    Google Scholar 

  6. 6.

    Siegmann, E. R. and P. Macheret, R. Howard. “Evaluating Cladding Creep during Dry Storage and Repository Placement,” Mat. Res. Soc. Symp. Proc. Vol. 713, to be published.

  7. 7.

    Edsinger, K. 2000. “A Review of Fuel Degradation in BWRs.” Light Water Reactor Fuel Performance Conference, Park City Utah, April 9-14, 2000. La Grange Park, Illinois: American Nuclear Society.

    Google Scholar 

  8. 8.

    Armijo, J. S. 1994. “Performance of Failed BWR Fuel.” Proceedings, 1994 Internationalcal Meeting on Light Water Reactor Fuel Performance, West Palm Beach, Florida, April 17-21, 1994. La Grange Park, Illinois: American Nuclear Society.

    Google Scholar 

Download references

Author information



Corresponding author

Correspondence to Eric Siegmann.

Rights and permissions

Reprints and Permissions

About this article

Cite this article

Siegmann, E., Devonec, E. Sensitivity Studies of the Effect of Cladding Degradation on TSPA Results. MRS Online Proceedings Library 713, 1159 (2001).

Download citation