In order to support the safe operation of the Krško Nuclear Power Plant (Westinghouse, 676
MW
e PWR), the seismotectonic structure of the Krško basin has been thoroughly investigated. As part of a ...wider study, a study on radon in soil gas was started in April 1999. Combined barasol detectors buried in six boreholes, two along the Orlica fault and four on either side of it, measure and record radon activity, temperature and pressure every 60
min. The results have been evaluated and the possibility of a correlation with seismic activity is discussed. Correlation between radon concentration and barometric pressure has been observed for all barasols. Preliminary results show that, at one location, the correlation coefficient between radon and barometric pressure changed sign before earthquakes.
The nuclear accident in Japanese plants in 2011 has initiated a quick response from the
countries utilizing a nuclear power. Krsko Nuclear Power Plant (NEK) was required by Slovenian
Nuclear Safety ...Administration (SNSA) to perform consequential actions to reduce the risk of severe
accidents and their consequences as low as feasible. NEK have analyzed the response to the severe
accidents, and based on the results of this analysis, proposed the measures to be implemented in the
shortest possible time.
In response to SNSA request NEK has developed the Safety Upgrade Program (SUP) which
contains a comprehensive set of measures for plant safety improvements. SUP Phase 1 has been
implemented during the Outage 2013.
This paper presents the work done on the evaluation of impact of plant modifications planned
for implementation in Phases 2 and 3 of NEK Safety Upgrade Program on the quantitative figure of
merit for the plant risk significance – total core damage frequency (CDF). A significance of the
most valuable measures in terms of contribution to the CDF reduction was determined and a new
fractional contribution of initiators categories was obtained.
The quantification of total CDF was made by employment of RiskSpectrum PSA code and
running a predefined set of analytical cases for all initiator categories covered by the scope of NEK
PSA model.
The basis for analysis was NEK’s most recent at-power PSA model which reflects the plant
status with plant modernization implemented in SUP Phase 1. The analysis was done in two steps.
In the first step plant modifications planned for SUP Phase 2 were addressed and in the second step
plant modernization measures and upgrades planned in SUP Phase 3 were modeled in addition to
those already modelled in the first step.
To improve the geologic model and test the approach, high-resolution seismic reflection methods were used in a re-evaluation study of earthquake hazard assessment at the Krško nuclear power plant ...(NPP) site. In a 13-km long profile recorded across the eastern part of the Krško basin (20-km long and 10-km wide), which is filled with up to 2 km of Neogene to Quaternary molasse sediments, the most prominent reflection was obtained from the top of the Badenian limestone, whereas the Mesozoic basement was less reflective. A syncline–anticline was interpreted that indicates a compressional tectonic style contrary to the prevailing hypothesis of a graben structure with normal border faults. In addition, very high-resolution shallow reflection profiling was performed at two locations close to the NPP for the detection of near-surface faults. Portable engineering seismic equipment was used for data acquisition to reduce costs and enable measurements in areas with difficult access. Geophone arrays were necessary for the suppression of strong ground roll and guided waves generated in the thick layer of dry gravel. Serious spatial aliasing of ground-coupled air-waves precludes
f-k filtering, necessitating the application of an internal mute. Two new subvertical normal faults with displacements of 50 and 80 m at the middle/upper Miocene interface were interpreted in the central part of the basin, while other faults, suggested by surface geological observations, were not confirmed. The further north of the two faults was traced in Pliocene–Quaternary deposits to a depth of 250 m. Reinterpretation of old analogue oil-exploration seismic profiles and gravity modelling has allowed the extension of results to a wider area. In the very high-resolution profile, recorded 0.5-km east of the NPP site, some discontinuities in reflections were established that were interpreted as faults. The possible vertical displacement at the sand (Pl, Q)/marl (Pl) interface is 7 m. The new structural-tectonic data obtained in the vicinity of the NPP requires essential changes to the model for earthquake hazard assessment.
