Fuel management method using power mapping and optimization theory for CANDU reactors

Abstract

An important task in operating a nuclear reactor is the design of a reloading pattern or refueling sequence for each fuel cycle. Light water reactors are usually batch-refueled, while the refueling is performed daily in a Canada deuterium uranium (CANDU) reactor. For an on-power refueling reactor like CANDU, it is important to incorporate the exact core status into the fuel management so that enough operating margin is reserved. In this study, a new optimal fuel management method is developed for a CANDU 600 MWe (CANDU-6) reactor. At first, an efficient power mapping method has been developed, which provides an accurate core status of an operating CANDU reactor. Secondly, an optimum refueling channel selection method has been developed by an optimization theory. For the power mapping method, the measured detector readings are used as boundary conditions of the diffusion theory calculation with the Kalman filtering (DIKAL) method. First, the measured detector readings are transformed into the measured mesh flux through an appropriate approximation. Then, the difference between the calculated and measured mesh flux is filtered out by Kalman filtering technique, in which the measured mesh flux is used as an internal boundary condition of the diffusion equation. The performance of the DIKAL method was assessed for various core states and applied to the calculation of power and flux distribution in the CANDU 6 reactor. Sensitivity studies have shown that DIKAL method is insensitive to the detector random and systematic errors. It is also shown that the DIKAL approach is more accurate compared with the flux synthesis approach currently being used in CANDU 6 reactors. An optimal refueling simulation method (OPTIMA), practically applicable to a CANDU 6 reactor, has also been developed. The objective of the optimization is to reproduce the reference core performance during refueling simulation, while satisfying the operation limits of channel and bundle powers. The opt...