Indo - UK: Premature, Oscillation-Induced Critical Heat Flux ("Premature OICHF")

Water is an excellent coolant for nuclear reactors, but steam is a very poor one. The ability to predict with confidence, but without excessive conservatism, the point at which cooling by water will turn into cooling by just steam is absolutely vital. The the rate of transfer of heat at which this transition occurs is known as the "critical heat flux" (CHF).

Predicting the circumstances under which CHF would occur (and then making sure that reactor operating conditions stay well away from them) is a very large part of the thermal hydraulic design of water cooled reactors.

There are some, unusual, circumstances in which the flows inside a nuclear reactor can become unsteady and cyclical, with flow-rates rising and falling with time. Under the circumstances, predicting the critical heat flux not surprisingly becomes rather more complicated and difficult.

This project is attempting to build a computer model which will predict when critical heat flux occurs in the presence of cyclical flows. The second strand of this project is to conduct experiments in which a test section is exposed to a cyclical flow, and the occurrence or not of critical heat flux is observed. The model we develop will then be tested and refined against these measurements.

A validated, general-purpose tool for predicting critical heat flux under conditions of oscillatory flow will be a useful additional capability available to reactor designers and safety analysts.

Nuclear power worldwide is a very important source of electricity, and it is a source upon which it looks probable that increased reliance will be placed in future, as concerns about the burning of fossil fuel and so on increase.

All nuclear plants need to be carefully designed to ensure that they remain properly cooled during both normal and under fault conditions. For a water-cooled plant, this means cooled by liquid water, as opposed to by steam. A better ability to predict the transition from water cooling to steam cooling will allow better design decisions to be made, and allow more reliable selection of setpoints, and thermal and power limits, and so on.

This will have significant economic benefits to the plant builder and operator, and ultimately to the consumer as it will prevent the costs of the plant being higher than they would otherwise be, and thus will similarly be reflected to it in electricity prices being less high than they might have been otherwise.