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Geophysical research in the surroundings of Krsko NPP

 
Geophysical research in the surroundings of Krsko NPP

Description

Summary

Since earthquakes are considered to be one of the most important risk for all NPPs, the Slovenian Nuclear Safety Administration (SNSA) initiated a multi-year programme of scientific investigations of the Krsko basin and its surroundings: from Geologic Investigation to the final Evaluation of Seismic Safety of the Structural Elements of Krsko NPP.

The present project concerns only one of the intermediate points of the overall program and is confined to the Geophysical Investigation. This phase is particularly important because, by using modern technologies of high resolution multichannel reflection seismic, it is possible to obtain, at different scales, an improved and highly resolved image of the subsurface structures that need to be evaluated in order to assess the potential seismic hazard of the area.

The Krsko (south-eastern
Slovenia
) Nuclear Power Plant (NPP) is located in a Neogene sedimentary basin filled with more than 1000 m of Neogene to Quaternary sediments. The Krsko basin is part of the Sava folds situated at the western rim of the Pannonian basin at the junction of the
Southern Alps, Dinarides and Pannonian basin.

Recent investigations show that this area exhibit characteristics of all these geotectonic units (GOSAR, 1996 and references therein): basement (Mesozoic) rocks are deformed in NW-SE direction, Neogene sediments in NE-SW while Quaternary beds are characterised by E-W oriented compressional structures. This area is characterised by increased heat-flow density and seismic activity, compared with the neighbouring areas. The 5.7 magnitude seismic event that occurred in 1917 near Brezice is an important indicator of the activity of this area.

A complementary aspect considered as well concerns the transfer of technology to the Local Beneficiary and Subcontractor, in order to enable them to perform similar work on their own in the future. The local partners have acquired substantial experience in modern methods of investigation used (regarding the management of complex equipment and the use of comprehensive industrial seismic processing and interpretation packages accomplishing the high industrial standards available in oil companies and geophysical service companies). This transfer of knowledge and the joint work effort made by the Partners and the Local Experts and Subcontractors, contributed to a great consensus on the technical methodology used and to the establishment of a strong relationship. The Partners and the Local Experts intend to use the jointly developed technique to address similar projects in other areas

The network of seismic profiles recorded in this research project revealed structural elements of the Krsko basin with fine detail never seen before. This wealth of new information has implications well beyond the central targets of the project. The discussion in the report at hand focuses on the central targets, all detail relevant for the investigation has been included; however, further evaluation and analysis of the data are being considered.

The interpretation of structural elements in the surroundings of Krsko NPP down to depths of 2 km showed that no major seismogenie features intersect the site of the Nuclear Power Plant. Two lineaments have been identified that are of sufficient size to warrant further inspection. No fault traces were found close to or at the surface, indicating undisturbed Neogene sediments.

First and foremost the feature present around CDP 1300 on line KK-03-99 reaching from the Mesozoic hard rocks up towards the surface must be considered a potential hazard. It may be part of the Artice flexure zone. Its continuation towards greater depths is uncertain, as the survey geometry does not allow sufficient resolution at these levels.

It is recommended to improve the seismological network and to include a high-quality station in this area such that the detection of small tremors and local earthquakes and the determination of their hypocentres become possible. Seismic monitoring of this area is considered essential.

The second feature present at the northern end of line KK-02-99 and potentially linked to the Orlica fault system is less pronounced. Seismic monitoring of this area should be accomplished with the modernisation and refinement of the seismological network.


Beneficiary Organization Details

Krsko NPP (Solovenia):
http://www.nek.si

Project Aims

Since earthquakes are considered to be one of the most important risk for all NPPs, the Slovenian Nuclear Safety Administration (SNSA) initiated a multi-year programme of scientific investigations of the Krško basin and its surroundings: from Geologic Investigation to the final Evaluation of Seismic Safety of the Structural Elements of Krško NPP.

The present project concerned only one of the intermediate points of the overall program and was confined to the Geophysical Investigation. This phase was particularly important because, by using modern technologies of high resolution multichannel reflection seismic, it proved possible to obtain, at different scales, an improved and highly resolved image of the subsurface structures that need to be evaluated in order to assess the potential seismic hazard of the area. The project consisted in particular, in performing a 40 km square loop reflective seismic profiling around the Krusko site in order to:

  • Obtain a good subsurface information about geological and tectonic features;
  • Locate the faults cutting through the bedrock and the sediments;
  • Define the position of the faults on the surface as a accurately as possible.

Project Results

The project was completed according to the specified Terms of Reference. A comprehensive project report, containing all the results from the seismic profiling was submitted to the beneficiary organization.

A complementary aspect considered as well concerned the transfer of technology to the Local Beneficiary and Subcontractor, in order to enable them to perform similar work on their own in the future. The local partners have acquired substantial experience in modern methods of investigation used (regarding the management of complex equipment and the use of comprehensive industrial seismic processing and interpretation packages accomplishing the high industrial standards available in oil companies and geophysical service companies). This transfer of knowledge and the joint work effort made by the Partners and the Local Experts and subcontractors, contributed to a great consensus on the technical methodology used and to the establishment of a strong relationship. The Partners and the Local Experts were intending to use the jointly developed technique to address similar projects in other areas.

Further Project Results

a) Further information on the project results could be sought from the beneficiary organization.
b) Project Executive summary is available at: http://www.gov.si/ursjv/en/index.php


General Information

Title: 
Geophysical research in the surroundings of Krsko NPP
Programme: 
PHARE
Budget year: 
1995
Countries: 
Slovenia
Types of activities: 
On Site Assistance
NPP: 
Krsko
Installation types: 
PWR
Duration (months): 
189
Contractors: 
EPTISA
OGS
University of Leoben
Sub-contractors: 
The Institute for Geology, Geotechnics and Geophysics (IGGG), Slovenia
Status: 
Completed
Old reference: 
PH1.08/95
Effective contract date: 
09/09/1999
Closure date: 
01/09/2000