Burnup and power generation distribution near pellet surface of high burnup LWR fuel

In the case of a LWR fuel, plutonium is produced more at the pellet surface than the center, and burnup and power generation rate at the surface becomes higher than the pellet average value. This phenomenon is called surface effect. Since the surface effect has much influence on the fuel performance evaluation, we made out a simple calculation model for surface effect by fitting the results of ANRB code, a detailed burnup distribution calculation code. Putting this simple model into the fuel performance evaluation code, it is shown that the fuel center temperature and the FP gas release rate are remarkably reduced with the consideration of the surface effect. It is considered that the accuracy of fuel performance evaluation at high burnup is able to be promoted utilizing this surface effect simple calculation model. (author)