The 'Equivalent Plutonium' Concept and its Application to Synergetic Fuel Cycles Calculation

Abstract

The advanced fuel cycles are seen as very interesting alternatives to improve the utilization of Uranium resources in the middle term. Among them, the synergetic cycles between different type of reactors, particularly PWR and CANDU are seen as very promising. In the frame of the Argentinean-Brazilian cooperation agreement, a neutronic and economical study was done on a Tandem cycle between the Brazilian Pressurized Water Reactor Angra-I, and the Argentinean CANDU reactor Embalse. The first calculations showed very interesting results regarding the obtainable savings in natural resources, the cost of the fuel cycle, and the lower quantity of wastes to be disposed. To perform the initial calculations, two methods were mainly used: standard calculation codes, which use discrete ordinates or collision probabilities method to solve the neutronics of the cell, or an algorithm that from now on we will call EQUIVALENT PLUTONIUM. The present work describes the concept in which the algorithm is based, the obtention of the coefficients needed for its determination, and, as an example, the results obtained applying the algorithm to two particular cases of Tandem cycles: CANDU MOX fuel fabricated from PWR fuel, diluted with natural uranium, and with depleted uranium. The obtained results are compared with calculations performed with WIMS code. It was verified that the methodology which makes use of the concepts of equivalent plutonium simplifies a lot bum-up and blending ratio calculations for preliminary fuel cycle analysis, giving results with very good approximation. (approximately 5%) and in a very simple way.