OPERATION MONITORING FOR OUT-OF-USE REACTORS WITH PASSIVE DETECTORS

There is an increasing number of research reactors which are temporarily or permanently out of use, but not yet decommissioned. Facilities which still have a critical fuel core load require measures for operation monitoring to make sure that they will not be used for undeclared activities between inspections. The basic safeguards relevant questions, which have to be answered, are: Has the alleged shut-down reactor been put into operation? If yes, than: At which time? How long? With which power? The target group for the described method of operation monitoring with passive detectors are medium and large research reactors. Different methods for operation monitoring have been developed up to now. Surveillance and sealing of control rod drive mechanism, pumps and valves or measurement of cooling water temperature seem to be appropriate measures to prevent and to lock clandestine reactor start-ups. But also these measures can be bypassed. Therefore a clear operation monitoring requires a permanent neutron monitoring of the core over the whole inspection period. Operation monitoring on the basis of neutron measurements can be performed using the reactor instrumentation and data recording (power history) by the operator or an independent safeguards monitor with data transfer for remote surveillance. Typically such devices are equipped with active neutron detectors. Breakdown of detector power supply or malfunction of electronics jeopardize the monitoring goals and have to be carefully considered in the choice of method and equipment for operation monitoring with active detectors (OMA). As alternative or additional back-up method the operation monitoring with passive detectors (OMP) is proposed. The OMP methodology is outlined and the advantages and limitations are discussed. OMP is considered as a special application of reactor-physical methods in safeguards [1].