Abstract
The service life of the Hungarian Paks Nuclear Power Plant (NPP) will be extended from the originally planned 30 years to 50 years. To improve the reliability of the results obtained in frame of the old reactor pressure vessel (RPV) surveillance programme, new methods have been developed, and based on them, the old exposition data have been re-evaluated for all the four reactor units. At the same time, a new RPV surveillance programme has been developed and introduced, and long term irradiations have been performed to determine the radiation damage of the surveillance specimens due to the high fast neutron exposition. Neutron transport calculations have been performed with a validated neutron transport code system to determine the fast neutron exposition of the RPVs during the extended service life. The cavity dosimetry is in the introductory phase. This paper presents the new developments in the field of the RPV surveillance dosimetry and summarises the results obtained. According to the results the service life of the NPP can safely be extended for the planned 50 years.
Highlights
The Paks Nuclear Power Plant (NPP) comprises four VVER-440/213 type reactor units with an original nominal thermal power of 1375 MW
The application of the cavity dosimetry can supply valuable information: experimental data obtained from the measurement and evaluation of the activities of the neutron monitors irradiated in the cavity can be used to determine the fast neutron exposition of the outer wall of the reactor pressure vessel (RPV) in several important geometrical positions, and for the validation of the neutron transport calculations
Averaging the neutron fluence rates in the region of their maximum value resulted in a significant reduction in the uncertainty of the fast neutron exposition of the RPV specimens
Summary
The Paks Nuclear Power Plant (NPP) comprises four VVER-440/213 type reactor units with an original nominal thermal power of 1375 MW. A new RPV surveillance programme was developed in a way that the irradiation results should show the exposure of the RPV after the planned extended service life with a better reliability than before This type of RPV surveillance irradiations have been performed in all the four reactor units. Neutron transport calculations were performed based on the new reactor core configuration to be used during the extended service life, and the fast neutron exposure of the RPV was estimated over the planned 50 years service life of the NPP. This paper presents the developed new methods and reactor dosimetry results and, due to the efforts listed above, indications on the fast neutron exposure of the RPV during the extended service life of the NPP. The pressurized thermal shock (PTS) analysis performed to determine the lifetime of the RPVs is based on these reactor dosimetry results
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