A Mathematical Model of Radiation-Induced Shape Change in Fuel Subassemblies of the BN-Type Reactor Core and Its Implementation in the ANSYS Software Package

Abstract

One of the main operability criteria for fuel subassemblies (FSAs) in sodium-cooled fast reactor cores, i.e., the criterion of tolerable shape change in the hexagonal wrapper tube, is formulated. The equations that enable one to investigate the kinetics of the stress-strain state of a three-dimensional body have been adapted to operating conditions of the FSAs. A mathematical model of radiation-induced shape change in ferritic-martensitic EP-450 grade steel is proposed. With regard to the proposed model and data on the radiation-induced shape change in other currently used and prospective BN reactor core structural materials, blocks for recording radiation-induced swelling and radiation-induced creep were developed for the ANSYS software package, which made it possible to utilize its potential in this area. The test case with the proposed models of the radiation-induced swelling and creep demonstrates that the developed blocks describe sufficiently well the radiation-induced shape change in the examined structural materials exposed to radiation. Calculation of the radiation-induced shape change in the FSA hexagonal wrapper tube has been performed at various radiation-induced swelling rates and radiation-induced creep moduli. The calculated results and the results of post-irradiation inspection of the FSA dimensions are compared. Recommendations for use of the proposed models designed to calculate and estimate the radiation-induced shape change and define the stress-strain state of the FSAs are made.