Increasing the accuracy of neutron load determination for VVER reactor components

The loss of ductility of the reactor pressure vessel (RPV) due to neutron irradiation and the possibly resulting brittle fracture of the vessel initiated by PTS is the most serious potential accident of VVER type reactors. In order to derive measures to reduce related risks a detailed knowledge of the neutron load is needed. Therefore, in the framework of the BMBF Reactor Safety Research Program (item 'Component Safety and Quality Assurance') a project was financed aiming at an increase of the reliability of the determination of the neutron load of VVER reactor components. This project complemented BMBF project 'Development of an improved methodology for the determination of the neutron load of the pressure vessel steel of VVER-1000 type reactors' (1/1996 - 12/1997). The intention was to support powerful research groups working in Russia in the field of reactor safety and to strengthen existing cooperation. Three research groups were involved, each consisting of two Russian scientists, working in three Russian research centres, namely the Scientific and Engineering Centre for Nuclear and Radiation Safety of Russian GOSATOMNADZOR (SEC NRS) Moscow, the Russian Research Centre 'Kurchatov Institute' (RRC) Moscow and the Institute of Physics and Power Enginering (IPPE) Obninsk. The objectives of the project were: - the further development and testing of neutron data bases for fluence calculations - providing reliable data for the evaluation of activation experiments at VVER reactors and formulation of the reactor models - assessment and further development of methods for verifying and adjusting the calculations by means of experiments - testing and further improvement of transport calculations with Russian data and codes-proposals for a safer operation of VVER reactors. In the following a short description of the obtained results will be presented. A detailed report is given. (orig.)