Pressure Vessel Fluence Calculations for the Hungarian VVER-440 Units for the Power Uprate and the Llifetime Extension

Abstract

Abstract.A major project was launched at Paks NPP, Hungary, to investigate the possibility of lifetime extension up to 60 years. At the same time, new fuel types with higher enrichment and containing pins with gadolinium have been introduced. Due to these plans, the radiation load of the pressure vessel was evaluated up to 60 years irradiation, taking into account the past and planned future cycles. The computational procedure, elaborated and validated earlier for the fast flux calculation in the pressure vessel was modified for the new fuel types. The neutron source at the core boundaries was taken from core design calculations and the neutron transport from the source to and through the pressure vessel was followed by Monte Carlo calculations. A number of calculations were performed to adequately follow the change of the neutron source. The paper details this procedure, the used Monte Carlo model, the influence of the different reloading schemes on the radiation load and the calculated results.

Reactor Dosimetry Aspects of the Service Life Extension of the Hungarian Paks NPP

“…The results have yielded a fast neutron fluence value of (2.6-3.6)10 20 cm −2 for the 50 years exposition of the RPVs of the NPP in the region of the neutron fluence rate maximum, strongly depending on the assumptions on the future core configurations. Calculations for irradiation periods longer than the extended 50 years service life have also been performed [9], and the results obtained were used in the PTS analysis.…”

“…The KARATE-MCNP code system was developed for this purpose (see in the next subsection) [1,2,9]. The results of the neutron transport calculations can then be compared with the corresponding experimental data, and applied further on in the dosimetry calculations (examples for the results of the neutron transport calculations can be found in the next subsection).…”