Clad Degradation- Summary and Abstraction for LA

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The purpose of this model report is to develop the summary cladding degradation abstraction that will be used in the Total System Performance Assessment for the License Application (TSPA-LA). Most civilian commercial nuclear fuel is encased in Zircaloy cladding. The model addressed in this report is intended to describe the postulated condition of commercial Zircaloy-clad fuel as a function of postclosure time after it is placed in the repository. Earlier total system performance assessments analyzed the waste form as exposed UO{sub 2}, which was available for degradation at the intrinsic dissolution rate. Water in the waste package quickly became saturated ... continued below

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58 pages

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Stahl, D. October 1, 2004.

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Description

The purpose of this model report is to develop the summary cladding degradation abstraction that will be used in the Total System Performance Assessment for the License Application (TSPA-LA). Most civilian commercial nuclear fuel is encased in Zircaloy cladding. The model addressed in this report is intended to describe the postulated condition of commercial Zircaloy-clad fuel as a function of postclosure time after it is placed in the repository. Earlier total system performance assessments analyzed the waste form as exposed UO{sub 2}, which was available for degradation at the intrinsic dissolution rate. Water in the waste package quickly became saturated with many of the radionuclides, limiting their release rate. In the total system performance assessments for the Viability Assessment and the Site Recommendation, cladding was analyzed as part of the waste form, limiting the amount of fuel available at any time for degradation. The current model is divided into two stages. The first considers predisposal rod failures (most of which occur during reactor operation and associated activities) and postdisposal mechanical failure (from static loading of rocks) as mechanisms for perforating the cladding. Other fuel failure mechanisms including those caused by handling or transportation have been screened out (excluded) or are treated elsewhere. All stainless-steel-clad fuel, which makes up a small percentage of the overall amount of fuel to be stored, is modeled as failed upon placement in the waste packages. The second stage of the degradation model is the splitting of the cladding from the reaction of water or moist air and UO{sub 2}. The splitting has been observed to be rapid in comparison to the total system performance assessment time steps and is modeled to be instantaneous. After the cladding splits, the rind buildup inside the cladding widens the split, increasing the diffusion area from the fuel rind to the waste package interior. This model report summarizes the component models, developed for the two stages noted above, that are used as inputs to TSPA-LA. The model concludes that less than two percent of the fuel, including all of the stainless-steel clad fuel, received at the repository is failed (perforated) upon receipt at the repository. All failed fuel is assumed to axially split upon waste package failure exposing the fuel to oxidation from the in-package environment. TSPA-LA then calculates the release of radionuclides from the exposed volume of oxidized fuel.

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58 pages

Notes

INIS; OSTI as DE00837708

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  • Other Information: PBD: 1 Oct 2004

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  • Report No.: ANL-WIS-MD-000021, REV 01
  • Grant Number: AC28-01RW12101
  • DOI: 10.2172/837708 | External Link
  • Office of Scientific & Technical Information Report Number: 837708
  • Archival Resource Key: ark:/67531/metadc782534

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  • October 1, 2004

Added to The UNT Digital Library

  • Dec. 3, 2015, 9:30 a.m.

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  • March 11, 2016, 4:30 p.m.

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Stahl, D. Clad Degradation- Summary and Abstraction for LA, report, October 1, 2004; Las Vegas, Nevada. (digital.library.unt.edu/ark:/67531/metadc782534/: accessed August 19, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.