Analysis of regularly perturbed lattices and reaction rate distributions from TIC experiments for X7 lattices

Abstract

Temporary International Collective (TIC) was established in 1972 by an agreement among seven countries, namely, Bulgaria, Czechoslovakia, Germany, Hungary, Poland, Romania and Union of Soviet Socialist Republics. The main objective of TIC was to provide the experimental data for the reactor physics analysis of water cooled and water moderated power reactors (WWER). Extensive experimental work for different core configurations was carried out by TIC countries to investigate the physics behavior of WWER lattices and the results were published in TIC volumes. In this paper, TIC experiments on regularly perturbed cores have been analyzed as part of the validation of indigenous computer codes, EXCEL, TRIHEX-FA and HEXPIN developed at Light Water Reactors Physics Section, B.A.R.C. The few group homogenized parameters of assembly cell or individual lattice cells were obtained by the hexagonal lattice burn-up code EXCEL and the core diffusion calculations were then performed using hexagonal assembly geometric code TRIHEX-FA and the pin-by-pin diffusion code HEXPIN. A transport-diffusion theory correction to the absorber cell cross section by a diffusion iterative technique (DIT) was used to iteratively adjust the absorber cell cross sections such that the transport leakage into the absorber cell is reproduced by diffusion theory. Neutron-nuclear multi-group cross-section libraries in WIMS/D format in 69/172 energy groups have been released by IAEA at the conclusion of WIMS library update project (WLUP). In the present study we have used libraries based on ENDF/B-6, ENDF/B-7, JEFF3.1 and JENDL3.2 evaluated nuclear datasets. Except ENDF/B-6, the trends of the k eff from the remaining three libraries were found to be similar. JEFF3.1 data is being used for most of the design computations of LWR projects in India. Therefore, HEXPIN simulations were performed using the cross section library based on JEFF3.1 data. The calculated results are presented in two categories. In category-1, the calculated k eff values using TRIHEX-FA and HEXPIN are presented for the TIC experiments on Xn lattices. In our earlier work, we have reported that there is a need to perform 3-D core computations for leakage calculations. The improvements in k eff values by using core calculation tools, TRIHEX-FA and HEXPIN, are presented in this paper by comparing the results with zero dimensional buckling model of EXCEL. In category-2, calculated reaction rate distributions for different activation foils are compared with the measured reaction rate distributions from the TIC experiments. Reaction rate distributions have been calculated using cross section library based on JEFF3.1 data.