Objectif
A procedure for retrospective dosimetry will be developed which can be applied by most laboratories, which have a physical as well as a chemical laboratory. The method will not depend of the type of steel neither the length of the cooling time. The neutron fluence will be determined measuring the activity induced in small amounts of the structural materials for which the fluence has to be known. The material has to be made available in the form of small chips or scrapings. The determination of the neutron fluence will be mainly focussed on the reaction93Nb (n,n' )93Nbrn.Chemical treatment will be needed to remove the disturbing 60Co from the scraped material and to set the 93Nbm apart. The type of treatment and the accuracy, which can be realised, will strongly depend on the type of material the cooling time and whether materials are present as substantial amount or as trace element.
PROJECTS ACTUAL OUTCOME (in terms of technical achievements or if appropriate task per task) The most important conclusion is that retrospective dosimetry is a useful tool to determine the neutron fluence at locations inside a Nuclear Power Plant e.g. at the welds of a Reactor Pressure Vessel without any other neutron monitors. Procedures are available to remove the 60Co activity. The most important condition for success is the presence of sufficient niobium in the material. For cladding materials, typical for VVERs containing 8 mg Nb/g, accuracy better than 5% can be achieved. At least 50 mg Nb/g in a sample of 100 mg is required to achieve an accuracy of 10 %. The chemistry can be performed in normally equipped radiochemical laboratories. Availability of ICP-MS equipment or a nuclear reactor with counting equipment close to the reactor is needed and may be beyond the scope of some laboratories.