Optimization of the initial fuel loading of the Indian PHWR with thorium bundles for achieving full power

Abstract

When attempting initial power flattening with thorium bundles, the placement of the bundles should take into account not only the need for power flattening, but also the fact that sharp flux depressions caused by the presence of thorium can alter the reactivity worth of shutdown systems. Since the safety assessment of the reactor is made under the assumption of certain shutdown worths, it is important that these worths are not disturbed by the fuel loading. We describe here a method by which this problem is tackled. The thorium loading that was worked out using this method was found to satisfy all the desired criteria of full power, and no loss of worth of the two independent shutdown systems. This loading has been used in the Indian PHWR at Kakrapar, the KAPS-1, which went critical on 3 September 1992.