Numerical Computation of Fission-Product Poisoning Build-up and Burn-up Rate in a Finite Cylindrical Nuclear Reactor Core

Mathew Ademola Jayeola,Ayodeji Olalekan Salau,Adebimpe Amos Amosun,Musbaudeen Kewulere Fasasi,Babatunde Michael Ojo

doi:10.30516/bilgesci.397197

Mathew Ademola Jayeola, Ayodeji Olalekan Salau + Show 3 more

Open Access

https://doi.org/10.30516/bilgesci.397197

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Abstract

All fission products are classified as reactor poisons because they absorb neutrons to some extent, most of which buildup slowly as the fuel burns up and eventually constitutes a long term reactivity effect in the core. Amidst the numerous fission fragments produced per fission, the presence of Xenon-135 and Samarium-149 has the greatest effect on a reactor core multiplication factor because of their large absorption cross-sections. In this study, we present a modified one-group time independent neutron diffusion equation using the method of Eigen functions and also provided an algorithm to calculate the temperature variations of the neutron fluxes. The solution obtained from the diffusion equation was used to determine the initial thermal neutron flux needed for the reactor startup. The four basic fission-product poisoning buildup and burn-up rate equations were solved using direct integration method and constant flux approximation over a particular time interval. Furthermore, a computer algorithm called Java code for Fission-Product Poisioning Build-up and Burn-up (Jac-FPPB) code was designed to calculate the temperature variations of the neutron fluxes, fission -isotopes cross sections and the atom concentrations of the fission products over a given time interval. The result from Jac-FPPB code showed that the neutron fluxes and neutron energies increase as the temperature of the fuel increases. In addition, the computed atom concentrations of each fission isotopes at any given time interval showed that the isotopes increasingly build up steadily at the initial time interval and rises to a constant level where the buildup rate of the isotopes approximately equals its burn up rate. This study concluded that the designed algorithm (JaC-FPBB code) proved efficient as it could compute the build-up and burn-up rates for the two important fission fragments in a nuclear reactor core. The code is easily accessible and could serve as a tool for the development of nuclear energy in developing countries, especially Nigeria.

Highlights

All nuclear reactors operate on the principle of nuclear fission (Marcum and Spinrad, 2013)
As the fission chain reaction continues, many fission fragments popularly called nuclear reactor poisons buildup in the reactor core
The temperature variations of the neutron flux and neutron energy in the reactor core as well as the computed crosssections for, Xenon-135 and Samarium-149 needed for their respective atom concentration computations were presented

Summary

Introduction

All nuclear reactors operate on the principle of nuclear fission (Marcum and Spinrad, 2013) This is the process in which a heavy atomic nucleus splits into two smaller fragments (Fermi, 1940). The emitted neutrons may cause new fissions which in turn yield more neutrons, and so forth Such self-sustaining series of fissions constitutes a fission chain reaction. As the fission chain reaction continues, many fission fragments popularly called nuclear reactor poisons buildup in the reactor core. Some of these poisonings Xenon-135 and Samarium149 have large absorption cross sections for thermal neutrons, thereby constituting significant threat to the normal operation of the reactor system

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