DETECTION OF UNDECLARED ACTIVITIES IN RESEARCH REACTORS

In accordance with the Nuclear Non-Proliferation Treaty and the Treaty Establishing the European Atomic Energy Community safeguards inspections are performed in nuclear facilities by the IAEA and the EURATOM Safeguards Directorate. The inspection methods are permanently improved. Therefore, a Core Inventory Verifier (CIVR) is being developed as an indirect method for the verification of the core inventory and to check the declared operation of research reactors. Changes in the configuration (material composition, quantity and/or geometry) in the core itself or in its surroundings should have an influence on neutron energy spectra and consequently, they should be detectable by suitable methods of neutron spectrometry, e.g. with the ‘Core Inventory Verifier’. Among others, the presence of additional amounts of breeding material such as U-238 and Th-232 in the blanket of the reactor is of special interest. Neutron spectra information taken during safeguards inspections could be compared to previously defined standard values for the assembly. For routine inspections the experimental methods must be safely and easily applicable in shorttime measurements with adequate and simple data evaluation by inspectors without special experience in physical details of the method. In the present paper results of differential fast neutron spectrum measurements will be shown which have been gained by means of proton recoil spectrometry. The experiments were carried out at the zero power reactor AKR of the Technical University of Dresden in a horizontal irradiation channel facing the surface of the core. The measurements are compared to MCNP-4B spectra calculations. The influence of changes in the materials in the surroundings of the detector position is demonstrated and the possibility for detection of undeclared activities with the CIVR method is discussed.