Review of retrospective dosimetry and their application to experimental reactors

Knowledge of neutron induced embrittlement of reactor vessel or experimental devices is a key issue for the operating time management of material test nuclear reactors, in particular pressurized water reactors.Experimental determination of the thermal and fast neutron fluences or dpa (displacement per atoms) is often technically impossible with the standard dosimetry techniques. The retrospective dosimetry technique can enable this fluence evaluation by measuring the activity of a sample taken from the chosen device for a radio-isotope which concentration is representative of the neutron fluence received. This technique, which makes possible the neutron fluence measurement at any accessible location in the reactor, implies to precisely know the initial concentration of the parent isotope. Sample collection can be done either “in vivo”, if the amount of withdrawn material is small enough not to damage the device, or “post mortem” for destructive measurements. Based on existing retrospective dosimetry experiments conducted in various reactor facilities, a presentation of the method is performed. Then, possible benefits brought by its use on research reactors, such as the future JHR reactor facility (CEA Cadarache centerFrance), are discussed in the fields of operating life survey of the reactor and the experimental devices, experimental sample instrumentation and decommissioning operations.