In vessel detection of delayed neutron emitters from clad failure in sodium cooled nuclear reactors: Information treatment

• The formalism of hypothesis testing is applied to the detection of abnormal situations in a reactor vessel.
• Clad failure monitoring in breeder reactors is taken as an example.
• False alarms are addressed by a bayesian approach.
• Operating several independent detectors at the same location is shown to be very effective.

With appropriate techniques, the information brought by the in-vessel instrumentation of nuclear reactors may betray rather subtle departures from normal state indicating an abnormal situation at early stages, to improve both safety and availability. This paper takes the case of the detection of delayed neutrons released by a clad failure in sodium-cooled fast neutron reactors as an illustrative application of hypothesis testing. Two methods are discussed, seeking either for a counting excess of for a departure from stationarity, yielding similar results. The question of false alarms is addressed by a Bayesian approach that takes into account the prior probability of failure. The use of several identical sensors is shown to be effective.