Study of Coolant Activation and Dose Rates with Flow Rate and Power Perturbations in Pool-Type Research Reactors

Abstract

A computer code using the multigroup diffusion theory based LEOPARD and ODMUG programs has been developed to calculate the activity in the coolant leaving the core of a pool-type research reactor. Using this code, the dose rates at various locations along the coolant path with varying coolant flow rate and reactor power perturbations are determined. A flow rate decrease from 1000 to 145 m³/h is considered. The results indicate that a flow rate decrease leads to an increase in the coolant outlet temperature, which affects the neutron group constants and hence the group fluxes. The activity in the coolant leaving the core increases with flow rate decrease. However, at the inlet of the holdup tank, the total dose rate first increases, then passes through a maximum at ∼500 m³/h, and finally decreases with flow rate decrease. The activity at the outlet of the holdup tank is mainly due to ²⁴Na and ⁵⁶Mn, and it increases by ∼2% when the flow rate decreases from 1000 to 145 m³/h. In an accidental power rise at constant flow rate, the activity in the coolant increases, and the dose rates at all the points along the coolant path show a slight nonlinear rise as the reactor power density increases.