Resonance Calculation Based on Equivalent Geometry Method for Complex Geometry Fuel

Abstract

There are various geometric fuels in reactors, including cylindrical fuel such as SPERT test reactor, plate fuel such as JRR3 research reactor, annular fuel such as Xi’an Pulse Reactor, and other geometric fuel such as advanced test reactor, etc. Many researchers made efforts for the resonance calculation of these geometric kinds of fuels and several methods were proposed, such as the equivalence theory, the ultrafine group method, the subgroup method, and the globallocal method. At the beginning of the equivalence theory and the ultrafine group method, only cylindrical fuels and plate fuels are supported. Thus, some improvements were proposed in the following years, such as trinomial rational approximation for the equivalence theory and the MOC (method of characteristics) based ultrafine group method. However, these methods have some accuracy and efficiency problems. As for the subgroup method, although arbitrary geometry fuel can be treated since the subgroup fixed source equation can be solved by the MOC, the geometry processing capability of the subgroup method is limited by the resonance integral table. As for the uniformity problembased resonance integral table, the accuracy is not enough. While for the nonuniformity problembased resonance integral table, the arbitrary geometric ability will be lost. For the globallocal method, only cylindrical fuel and plate fuel can be solved. Thus, in this paper, based on the globallocal coupling strategy, a resonance calculation method based on the equivalent geometry method for complex geometric fuels was proposed. First, for the isolated system of complex geometry fuel, based on the conservation of escape probability, an equivalent onedimensional (1D) cylindrical (or plate) fuel model of the complex geometry fuel was established. Secondly, based on the conservation of the collision probability of the fuel to the outer structure material, the equivalent size of the fuel outer structure material was obtained. Then, based on the Dancoff factor conservation of the complex geometry fuel, the equivalent moderator of 1D cylindrical (or plate) fuel model was established. And finally, for the equivalent 1D cylindrical (or plate) model, the pseudoresonantnuclide subgroup method was used to calculate the selfshielding crosssection. The method was applied to the resonance calculation of noncylindrical geometry fuel. As for the pin cases and assembly cases, the deviation of the microscopic absorption section is less than 320%, and the deviation of the eigenvalue is less than 150 pcm. The power deviation is less than 0128%. Compared with the MOCbased pseudoresonantnuclide subgroup resonance calculation method, under the comparable calculation accuracy, the calculation efficiency increases by more than two orders of magnitude. For the core level case, the eigenvalue difference is 338 pcm, the maximum deviation of assembly power is 1182%. The results show geometry flexibility, high accuracy, and high efficiency of this method.

Keywords

• equivalent geometry method
• resonance calculation
• necp-x
• complex geometry fuel