It is desired to accurately predict creep strains in zirconium claddings, subjected to cases such as sudden load drops or reversals, using the BISON fuel performance code. It has been experimentally proven that primary creep reinitializes at sudden load drops and reversals, which is different than normal operating conditions, where stresses increase gradually. A new visco-elastic primary creep model is added to BISON, which is capable of handling situations of load drops or reversals. The model is coupled with secondary creep models namely Hayes-Hoppe and Limback-Anderson, available in BISON to make predictions on cladding creep strains. The results are compared to Halden in-pile experiments IFA-585 and IFA-699. Based on the comparison, it is recommended to use the visco-elastic primary creep model coupled with Hayes-Hoppe secondary model for consistency and performance.

期望使用BISON燃料性能代码来准确预测锆包层中的蠕变应变，该应变会受到诸如突然的负荷下降或反转的情况的影响。实验已经证明，主蠕变会在突然的载荷下降和逆转时重新初始化，这与应力逐渐增加的正常运行条件不同。BISON添加了新的粘弹性主蠕变模型，该模型能够处理载荷下降或反转的情况。该模型与BISON中的次级蠕变模型Hayes-Hoppe和Limback-Anderson结合使用，可以对包层蠕变应变进行预测。将结果与Halden桩内实验IFA-585和IFA-699进行比较。根据比较，