Antun Schaller and Damir Subašic
Hazardous Waste Management Agency (APO)
Zagreb, Croatia

Croatia, as the co-owner of the Nuclear Power Plant Krško (NPP Krško), has an active participation in the search for solution of a safe and environmentally acceptable final disposal of low- and intermediate waste (L/ILW) produced in the power plant, as well as the waste expected to be generated during the power plant decommissioning. The decision on the country (Croatia or Slovenia) which will finally repose radioactive waste, has not been yet brought but both countries are under obligation to run concurrent preparations and actions preceding construction of the L/ILW repository. Besides NPP Krško, there are also some minor quantities of radioactive waste that have been generated from various nuclear applications - medicine, industry, research institutes, radioactive lightning protectors, ionising smoke detectors, etc. - in Croatia itself. Due to such a situation, the National policy on radioactive waste disposal was developed in Croatia a few years ago, although it has not yet been formally adopted as an official document. The siting of radwaste repository represents presently the key element of waste disposal policy in Croatia. Namely, no further progress cannot be expected if no candidate sites are promoted by the National Physical Plan as suitable for further detailed field-investigations which would result in selection of the final (i.e. most suitable) L/ILW repository site. Through additional evaluation of potential sites, 4 preferred sites were finally selected in 1996 as candidate sites to be included into the Physical plan of Croatia. All of them were supposed to be subjected to detailed field investigations and other necessary researches. However, two of them were rejected during the Parliament debate in July 1997, so that only two sites remained presently as candidates for the repository siting. The final candidate sites are expected to be announced - if any - until the end of 1997, simultaneously with promotion of the new Physical plan of Croatia. The inclusion of candidate sites for L/ILW repository into the Physical plan in 1997 is necessary to confirm the final repository site in 2002 and start of operation in 2007, as it has previously been agreed.

The necessity of construction of low- and intermediate level radioactive waste (L/ILW) repository in Croatia is derived from the fact that we are dealing with two main sources of radioactive waste materials. The first group of sources is referring to wastes generating in the Republic of Croatia itself, and the second one includes radioactive waste originating from operation of the Krško Nuclear Power Plant (Krško NPP). Although the plant is situated in the neighbouring Republic of Slovenia, it represents the joint venture facility of both Slovenia and Croatia. Therefore, Croatia is obliged to find appropriate solution to dispose a half of all radioactive waste generated during the lifetime of the NPP.

Radioactive waste in Croatia originates mostly from a few nuclear applications: medicine, industry, agriculture and scientific researches. In addition to this, there are about 60,000 ionising smoke detectors and 380 ionising lightning protectors in the country. However, total amount of radioactive waste which has been generated in Croatia so far is not more than 52 m³, and its estimated gross activity is 2.3 x 10¹² Bq. The waste is composed by radionuclides like ^152,154Eu, used in ionising lightning protectors; ²⁴¹Am, installed in ionising smoke detectors; ¹⁹² Ir, ⁹⁰ Sr, ⁸⁵Kr and some others, applied in measurement and processing techniques in industry; ¹³⁷Cs and ⁶⁰Co used in medicine, etc. The wastes are being temporary stored in two storage facilities at scientific institutes "Ruder Boškovi}" and the Institute for Medical Research and Occupational Health in Zagreb.

The Krško NPP is apparently the greatest producer of all radioactive waste expected to be disposed in Croatia. Since the plant started operation in 1982, some 2,000 m³ of LLW/ILW with total activity of about 3.6 x 10¹³ Bq have been generated there so far. It is realistic to expect some 8,500 m³ of LLW/ILW to be generated in the lifetime of the NPP. After rough estimates, the total activity of LLW/ILW generated during the plant lifetime, could reach some 1.5 x 10¹⁴ Bq. In addition, some 11,000-12,000 m³ of decommissioning waste is expected to be produced in the plant until the end of its operation. This type of waste is supposed to be composed of 53 % LLW, 36% ILW and 11 % high-level waste. The prevailing radionuclide, ⁶⁰Co, is "responsible" for about 90 % of total activity of decommissioning waste. Anyhow, we expect about 10,000-11,000 m³ of L/ILW generated in the lifetime of the Krško NPP, which will require to be disposed in Croatia.

There are two repository design options considering to be optionally applied in Croatia: either near-surface engineered burial, or subsurface disposal in tunnels.

The basic regulation is the "Law on Ionising Radiation Protection and Special Safety Actions in Nuclear Energy Implementation" [ 1] , issued in 1984. From this law, 17 regulations and codes of practice have been subsequently derived. Documents which require to be emphasised here due to their particular importance in the field of site selection and radioactive waste repository construction and operation, are "Code of Practice on Conditions of Locating, Construction, Start-up and Operation of Nuclear Facilities"[ 2] , "Code of Practice on Standard Format of Safety Report and Other Documentation Needed for Safety of Nuclear Facilities" [ 3] , as well as "Code of Practice on Methods of Collecting, Account, Processing, Storing, Final Disposal and Release of Radioactive Waste Substances in the Environment" [ 4] . These regulations went into effect according to the "Law on Taking Over the Federal Laws in the Field of Health Protection, Applied in the Republic of Croatia as Republic Laws" [ 5] . It should be additionally mentioned that a new "Law on radiation protection" has been already drafted and is expected to be finalised and approved in a couple of months.

The national regulatory body competent for radioactive waste management, as well as ionising radiation protection issues at all, has not been established in Croatia as a single institution covering all related issues. It consists of sections at two separated governmental entities: the Ministry of Health and the Ministry of Economy. Sanitary Inspectorate, as a section of the Ministry of Health, is the competent national authority for ionising radiation protection. The Ministry of Economy, i.e. Department of Nuclear Safety, is competent for issues covering Croatian involvement in the operation of the Krško NPP.

The global concept of the Radioactive Waste Repository Project in Croatia consists of several interfering main task groups. Besides site selection, it also comprises licensing, technology & design development, safety assessment, economic evaluation, transportation analysis and waste characterisation. The whole project is supported by particular activities related to development of legislation and regulatory body re-organisation. Since there is an urgent economic need to ensure additional energy sources in Croatia, the site selection of both thermo-electric and nuclear power plants is incorporated into the same program.

The site selection includes two stages: the first, site survey stage (Fig. 1), terminating with inclusion of preferred (i.e. final candidate) sites into the Regional Planing Act of Croatia; and the second, site evaluation stage, aiming to define the final repository site through field investigations and other necessary actions at finally chosen preferred sites. Selection of waste repository was performed by multiple criteria analysis, based on 10 exclusionary and 28 comparative criteria. All criteria applied were published in the official gazette of Croatia "Narodne novine", No. 78/1992.

Presently, the first part of site selection, i.e. site survey stage is about to be finalised. It included the actions that are extremely sensitive since defining of site selection methodology and criteria, as well as achieving political and public acceptance for repository siting, had to be done before preferred (i.e. candidate sites) were identified and included into the Regional Planning Act of Croatia being, thus, available for further field investigations. The activities were performed in two phases: (1) regional analysis and selection of potential areas; and (2) selection of preferred sites (Fig. 1).

Regional analysis was based on assessment of whole territory of Croatia using chosen exclusionary criteria ("exclusionary screening"). Areas which did not meet requirements of at least one of these criteria, were eliminated. Remaining areas were designed as potential areas for further analyses. Regional analysis was based on appropriate information derived from topographic and other thematic maps of Croatia in the scale 1:300,000.

In selection of preferred sites all previously selected potential areas were checked again by exclusionary criteria, but now evaluated on the basis of more detailed data and in larger scale maps (1:100,000). Comparative criteria were then applied to both potential areas and potential sites in order to identify potential sites and preferred sites, respectively.

Complete process of site selection beginning with development of methodology and site selection criteria up to proposal of a few preferred sites, was performed in the period 1988-1997. According to preliminary agreement achieved by the Governments of Slovenia and Croatia in 1996, confirmation of the final repository sites in both countries is expected to be done in 2002 and start of operation in 2007 (Tab. I).

Site selection process started with definition of methodology and exclusionary criteria for the global reconnaissance of Croatia (56,538 km² in size) in order to find out potential areas. By exclusionary screening 7 potential areas have been selected. After comparative criteria had been defined, potential areas were subjected to more detailed evaluation and 34 potential sites lying within potential areas themselves, were identified. Through comparison of potential sites and their internal characterisation, 4 preferred sites were found out. These, preferred (or candidate) sites were expected to be included in the Regional Planning Act of Croatia until the end of 1997. However, two of them were rejected by a political decision in the Parliament debate in July 1997.

After inclusion in Regional Planning Act, the sites are foreseen to be subjected to detailed on-site investigations and additional surveying as it was previously planned. These explorations are expected to define: (1) the most suitable preferred site out of 2-3 investigated sites, and (2) the exact microlocation (some 20 hectares) for exact repository site.

In accordance with the above mentioned, it is necessary to clarify involved basic terminology referring to selected areas i.e. sites: potential areas represent larger areas (100-600 km²), characterised by acceptable insulation properties; potential sites are smaller homogeneous areas (10-20 km²), derived from potential areas, which are favourable for siting radioactive waste repository, and, finally, preferred sites are small areas (8-15 km²), highly acceptable for the repository siting and therefore convenient to be included into the Regional Planning Act of Croatia [ 6] .

It is to add that site selection methodology, criteria applied and results of each selection phase have been positively assessed by IAEA expert missions in 1991, 1995 and 1997 [ 7] .

There were 10 exclusionary criteria applied in the first phase of the site selection process, i.e. in regional analysis of whole territory of Croatia, aiming to reject all areas which have not met requirements defined by any of the involved criteria. The criteria were referring to three basic principles for repository siting: safety, acceptability and cost-benefit ratio. The following criteria were applied:

1. Meteorology and hydrology - Risk of flooding: All natural floodplain areas (assessed in respect to return periods of 1,000 years) are excluded, disregarding whether they are protected or not.
2. Geology and seismology - Seismotectonics: Areas with maximum potential earthquake intensity equal to or higher than IX MCS, are excluded.
3. Geology and seismology - Neotectonics: Zones characterised by known active faults, are excluded.
4. Geology and seismology - Lithology and geomorphology: Areas characterised by increased erosion rate due to lithology (i.e. prevailing rock types) and/or relief dynamics, as well as areas composed of rocks which are unstable under natural conditions (e.g. which are not resistant to weathering etc.) and after performed civil-engineering works, are excluded (for shallow land disposal). Areas characterised by land-sliding and rock-falling are excluded if it is estimated that these processes could pose a hazard to repository structures (for disposal in tunnels).
5. Hydrogeology - Protection of water-bearing layers: Areas containing protected sources of drinking water are excluded. In order to preserve groundwater from possible radioactive pollution, disposal facility can not be situated within an area characterised by significant water-bearing layers of any type.
6. Demography - Population density: Areas characterised by population density of 80 inhabitants per square kilometre (i.e. the average population density value in Croatia) or more within a 20 km radius around the facility site, are excluded.
7. Present and planned land use types - Special purposes: Areas designated for special purposes, including their protected zones, are excluded.
8. Present and planned land use - Mining, i.e. exploitation of ores and minerals: Areas in zones of present of planned mining including exploitation of minerals, gas, oil, coal etc., are excluded.
9. Environmental protection - Protection of natural heritage: National parks, natural parks and other naturally specific areas of common interest, are excluded.
10. Environmental protection - Protection of cultural heritage: Areas containing monuments of cultural heritage which are registered in the List of World Cultural and Natural Heritage, as well as those which are of an extraordinary national importance, are excluded.

After the rejected areas had been "overlapped" by every single exclusionary criterion involved, there remained a few "blank" zones suitable for waste disposal. As indicated in the same map, there were 7 potential areas found out in these suitable zones: Petrova gora, Trgovska gora - Zrinska gora, Moslavacka gora, Bilogora, Papuk-Krndija, Psunj and Pozeškagora. All of them, excluding the hilly region of Bilogora, represent horst-mountains, composed of solid rocks (granite, amphibolite, gneiss, schists).

Proposed parameters and criteria, applied in the site identification, selection and comparison of potential sites, were defined by a special team of experts, composed of specialists from different fields of interest (from geology to sociology). Comparative criteria were generally presented as requirements for achieving a certain goal or a desired state. These goals can be defined as desirable conditions, and - if a desirable condition can not be achieved - the criteria should describe the degree of acceptability (i.e. in what extent the solution approaches to desirable conditions). Four "aspects" of comparative criteria have been developed to cover all needed aspects needed for comparative site evaluation:

1. Criteria related to engineering aspects show whether the engineering requirements for acceptable radioactive waste disposal are satisfied. With regard to this comparative criteria group, sites requiring simple and less expensive engineering solutions are preferred.
2. Safety-related criteria examine whether the safety requirements for construction and/or operation of the facility are met. Emphasis is placed on evaluation of physical properties of an area which could have negative effects on the facility safety.
3. Criteria referring to environmental impact and acceptability in the closer site area show whether the safety requirements concerning the impact of the facility on the immediate environment, are met. Emphasis is placed on environmental impact of the facility during its regular operation as well as in the cases of possible accidents.
4. Criteria related to acceptability of the facility site in the broader area assess possible impact of the radioactive waste disposal facility on the broader area. Emphasis is placed on analysis of present and planned land use types, as well as on degree of social acceptance regarding possible changes in the value of the area.

Potential sites were compared by weighted criteria. In this phase it is necessary to choose the most appropriate method of site evaluation and comparison. There are several techniques and methods in world practice. On the basis of experiences acquired in Croatia and Slovenia in the field during last few years, the multiple criteria analysis has been chosen as the most effective. In particular, the method PROMETHEE (i.e. "Preference Ranking Organisation Method for Enrichment Evaluations"), created by J.P. Brans and P. Vincke, has been applied in our case. The method represents a computerised analysis of multiple criteria technique and decision-making methods. Thus, the objectivity of site selection process and assessment has been successfully achieved. The method is based on application of numerous criteria in order to express inter-relations among alternatives, indicating so the group of "better" solutions. The relative significance of every single criterion is expressed by assigning to it a corresponding weighting factor. The values of weighting factors have been defined by applying the rating method, and are based on decisions of the expert team. After discussion, members of the expert team proposed weighting factors for all comparative criteria. As result, a special expert co-ordinating group adopted the final list of weighting factors, arranged by 6 subject i.e. thematic groups and 4 aspects (Tab. II).

It gets obvious that the expert team found out the criteria aspect C ("Environmental impact and acceptability in the closer site area") as the most important: share of total weighting factor value of this aspect is even 52.5 % . These criteria group is followed by the criteria group B ("Safety related aspects") having the share 30.0 %. The acceptability of broader site area (aspect D) is expressed by share of total weighting factor 9.5 %, since it is assumed that L/ILW repository will have almost no impact on the broader site area. Finally, the importance of engineering aspects was estimated to be only 8 % because the L/ILW repository is not expected to require considerable civil-engineering interventions.

Evaluation of 7 potential areas by the above discussed comparative criteria led firstly to identification of 97 potential sites within the areas. These sites were thereafter subjected to additional evaluation on the maps in scales 1:300,000 and 1:100,000, and analysed by the PROMETHEE computer code. As result, 47 potential sites out of previously chosen 97, were assessed as more perspective. These sites were subdued to evaluation based on maps in scale 1:25,000. By assessing basic lithological and hydrogeological features as well as risk of flooding, some of sites were subsequently rejected, so that 34 potential sites finally remained as more suitable. Their distribution by the potential areas is as follows:

After a more detailed comparative analysis by the code PROMETHEE had been done, there were chosen 4 preferred sites out of 34 potential sites involved. The size of preferred sites vary from 8-15 km² and are somewhat smaller that potential sites themselves. In addition, a few microlocations have been subsequently selected within each of proposed preferred sites. The following preferred sites (with respective size) have been proposed:

1. THE LEGISLATION OF THE REPUBLIC OF CROATIA, "Law on Ionising Radiation Protection and Special Safety Actions in Nuclear Energy Implementation", Official Gazette "Slu`beni list", No. 62, Zagreb, Croatia (1984).
2. THE LEGISLATION OF THE REPUBLIC OF CROATIA, "Code of Practice on Conditions of Locating, Construction, Start-up and Operation of Nuclear Facilities", Official Gazette "Slu`beni list", No. 52, Zagreb, Croatia (1988).
3. THE LEGISLATION OF THE REPUBLIC OF CROATIA, "Code of Practice on Standard Format of Safety Report and Other Documentation Needed for Safety of Nuclear Facilities", Official Gazette "Slu`beni list", No. 68, Zagreb, Croatia (1988).
4. THE LEGISLATION OF THE REPUBLIC OF CROATIA, "Code of Practice on Methods of Collecting, Account, Processing, Storing, Final Disposal and Release of Radioactive Waste Substances in the Environment", Official Gazette "Slu`beni list", No. 40, Zagreb, Croatia (1986).
5. THE LEGISLATION OF THE REPUBLIC OF CROATIA, "Law on Taking Over the Federal Laws in the Field of Health Protection, Applied in the Republic of Croatia as Republic Laws", Official Gazette "Narodne novine", No. 53, Zagreb, Croatia (1991).
6. "Site Survey Stage of the Siting Process for Low- and Intermediate Level Radioactive Waste Disposal Facility", The Institute for Urban Planning of Croatia, Zagreb, Croatia (1991).
7. "The Mission Report", Radioactive Waste Management Advisory Program (WAMAP), IAEA, Vienna, Austria (1991).
8. "Review Repository Site Selection Criteria", End of Mission Report, Nuclear Power Programme Support, Department of Technical Co-Operation, IAEA, Vienna, Austria (1995).
9. "Evaluation of Low and Intermediate Level Waste Repository Design", End of Mission Report, Nuclear Power Programme Support, Department of Technical Co-Operation, IAEA, Vienna, Austria (1997).

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