A simple 1-D model for activation of circulating fluids in nuclear reactors

This document presents a simple one-dimensional model of a nuclear reactor proposed for activation studies of circulating fluids under prolonged exposure at high neutron flux. The model can treat primary or secondary coolants. The coolant is assumed to flow through the core at constant speed, and it is recirculated through an outer loop. Such loop includes all the components of the reactor by means of equivalent lengths given by the flow passage area and the transit time. The model predicts the evolution of the coolant inventory along the circuit, which allows calculating activity and dose rates. Different solution methods are discussed, and the approximation of commutativity of the transmutation operators is successfully introduced to simplify both modeling and simulation. An example of an activation study with lead is presented to support the development program of new cleo LFR units.