A Numerical Simulation of Radiation Chemistry for Controlling the Oxidising Environment in Water-Cooled Nuclear Power Reactors

Dorota Swiatla-Wojcik

doi:10.3390/app12030947

Abstract

Maintaining the integrity of materials of light-water nuclear power reactors requires the development of effective methods to control and minimise the corrosive environment associated with the radiolysis of a coolant. In this study, the behaviour of the oxidising environment is simulated using a hybrid method. The hybrid method has advantages in that the production of radiolytic species under exposure of the coolant to ionising radiation is simulated while providing material and charge balances. Steady-state concentrations of stable and transient oxidising agents are calculated as a function of radiation composition and dose rate by numerical integration of the system of kinetic equations describing radiation chemistry of neutral water, the alkaline solution, and the hydrogenated systems at 300 °C. The importance of the reactions and equilibria constituting the radiolysis scheme of the coolant is assessed. The influence of the presence of a base and the injected H2 on the yield of key reactions responsible for the formation of the main oxidants H2O2 and O2 are discussed. Simulation indicated the synergic effect of H2 gas and base added to the coolant on diminishment of the steady-state concentration of oxidants.

Highlights

Light-water reactors (LWRs), categorised into boiling-water reactors (BWRs) and pressurised-water reactors (PWRs), are the most widespread type of nuclear power reactors [1]
The cooling water operates at high pressure and temperature conditions (7–7.5 MPa, 285 ◦ C in BWRs and ca. 15.5 MPa, 315 ◦ C in PWRs) and is exposed to intense fluxes of gamma rays and fast neutrons [2]
The concept of the hybrid method is to combine diffusion–kinetic calculation for the radiolytic species initially clustered in radiation tracks and kinetic calculation of reactants homogenously distributed in the bulk solvent

Summary

Introduction

Light-water reactors (LWRs), categorised into boiling-water reactors (BWRs) and pressurised-water reactors (PWRs), are the most widespread type of nuclear power reactors [1]. The cooling water operates at high pressure and temperature conditions The stable oxidants (H2 O2 and O2 ) create a corrosive environment contributing significantly to stress corrosion cracking of the structural materials [1,2,4,5,6]. The harmful effect of oxidants is strengthened by the low acidity (low pH) of water at the operating temperatures. To minimise the concentration of dissolved oxidants and increase pH, the chemicals such as H2 , hydrazine (N2 H4 ), ammonia (NH3 ), lithium hydroxide (LiOH) are added to the coolant [1]. A quantitative understanding of how these additives change a corrosive environment in the nuclear core is still insufficient but essential to control stress corrosion cracking and maintain the integrity of materials in reactor circuits. It is important to estimate critical hydrogen concentration

Methods

Results

Discussion

Conclusion