Effective Dose Calculation in the VVER-440 Reactor Maintenance Area
28th Symposium of AER on VVER Reactor Physics and Reactor Safety (2018, Olomouc, Czechia)
Reactor physics experiments and code validation (benchmarks)
Abstract
A nuclear reactor is a prolific source of potentially dangerous nuclear radiation. This radiation is unavoidable, since most of the radiation released originates with the fission process itself. In addition to the energetic neutrons, gamma rays are emitted simultaneously with the fission event. To enable personnel to work in the vicinity of an operating reactor, it is necessary to absorb the nuclear radiation released in a thick shield surrounding the core. Even for regions where human access in not permitted during reactor operation, the shielding may be necessary to limit the activation and possible destruction of construction materials or electronic devices. To fulfill the present needs in the Slovak nuclear industry detailed and precise KENO 3D model of the VVER-440/V213 reactor has been developed for criticality, shielding and detector response calculations. This paper investigates several modelling issues associated with VVER-440 criticality and shielding calculations using the SCALE computational system. The model was partially validated by the criticality calculation of the real operational conditions reached on the 310th effective day in Slovak NPP Jaslovské Bohunice unit 4 during cycle 30. Special attention was given to the methodology applied to the determination of the fuel isotopic vectors modelled in one-sixth symmetry core configuration based on which the decay gamma and spontaneous fission neutron source was determined. In case of the effective dose calculation the CADIS-FW variance reduction technique was utilized to decrease statistical uncertainties to acceptable values. To demonstrate the capabilities of the SCALE system and the developed VVER-440 model, two point detectors were placed just behind the dry shielding and one was placed at the outer side of the door leads into the room A004.