WWER RPV Dosimetry Benchmarking in LR-0 Reactor. Recent Activity

摘要

The main activities of WWER dosimetry arise from necessity of solution of the following actual problems: - reliable assessment of reactor pressure vessel embrittlement for WWER-440 and WWER-1000 reactors, -prolongation of the RPV lifetime for WWER-440s beyond designed terms. The improvement of the reactor pressure vessel (RPV) dosimetry in WWER type reactors leads to the multifactor approach taking into account not only the fast neutron fluence. The increase of the precision of the description of the mixed photon and neutron radiation field needs careful benchmarking to eliminate the probable biases. Three models (mock-ups) of WWER type reactors assembled in the LR-0 experimental reactor in NRI (Rez, Czech Republic) were qualified for benchmarking of RPV dosimetry in the frame of a European Project REDOS. Radial full-scale mock-ups, which copy geometry and material composition of the core periphery, reactor internals, RPV, and biological shielding, represent the engineering benchmarks. The mock-ups are azimuthally (60 degrees) and axially (1.25 m fuel active length) shortened. The mock-ups were designed with respect to possibility to provide the best guess of the space-energy distribution of fast neutrons for the RPV monitoring system, thus the operational density of moderator was simulated in downcomer by insertion of an air layer (displacer).