用過核燃料乾式中期貯存中護套材料之壽命預估

Life Time Prediction of Spent Fuel Cladding Using Computer Code DATING

本報告乃利用現有的DATING程式對中期貯存中，用過燃料護套最主要的劣化機制——潛變變形和潛變破裂，做定量的模擬。DATING程式利用現在的數個對於鋯合金的潛變變形和潛變破裂機制，並且將變溫和變應力的中期貯存的環境簡化成可以代入上述機制的條件，利用損傷累積法，進而求出護套材料的壽命預估值。反之，對於已知的中期貯存年限，DTAING程式可反推出在一初始應力下，護套所需要求的初始溫度。1985年，美國原子委員會NRC針對護套的潛變性質而要求於鈍氣充填下軟式貯存時營運情形來決定，有鑑於此，我國在執行或訂定中期貯存之相關法規時DATING程式所提供的研究方法與結果將可做為一項操作規範的重要參考。

The DATING computer code was used in this study to quantitatively simulate the major degradation mechanism-creep deformation and fracture of zircaloy cladding of spent fuel during interim dry storage. Formulating the mechanisms of creep and the change of cladding temperature and stress, the DATING code applies linear damage accumulation method to predict the integrity of the cladding material. On the other hand, for a known storage period, DATING code can be used to calculate the maximum allowable temperature limit at a beginning stress for dry storage of spent fuel cladding. In 1985, the U.S. Nuclear Regulatory Commission (NRC) developed an independent model to calculate allowable temperature limits for inert gas cask storage, which is being used on a case-by-case basis for each cask vendor application. The model accounts for variations In fuel design, burnup level, spent fuel age, and storage cask design. DATING Code is one of the computer code developed to meet the regulation of NRC. The licensing of dry storage will begin to processed by AECROC by 1995. The methodology of DATING code and the results calculated from this code can be employed as an important reference in licensing the dry storage of spent fuel.