Proceedings of the 8th International Conference on Probabilistic Safety Assessment and Management May 14-18, 2006, New Orleans, Louisiana, USA OIL SPILL RISK ASSESSMENT FOR LOVIISA POWER PLANT PSAM-0388 Nici M. S. Bergroth/ Fortum Nuclear Services Ltd Kalle E. Jänkälä/Fortum Nuclear Services Ltd Sergey Ovsienko/State Oceanographic Institute ABSTRACT Preliminary oil risk estimates showed that oil transportations pose a significant core damage risk for Loviisa PWR located at the southern coast of Finland. Oil transportation has increased in the Gulf of Finland during the last few years and will further increase in the coming years enhancing the importance of this risk. Therefore, a more detailed assessment of oil spill impact frequencies has been performed for Loviisa nuclear power plant (NPP) taking into account hydrometeorological conditions, oil properties and leakage sizes as well as recent oil spill statistics. During cold shutdown states the loss of service water due to excessive sea vegetation or other clogging material in the sea is an essential risk contributor because the normal residual heat removal system and the emergency cooling systems are cooled by the same service water system. Oil of tankers and cargo-carrying ships as well as other potentially fouling cargo may clog the sea water cooling systems. Nevertheless, the crude oil transportations in the Gulf of Finland pose maybe the biggest threat. In the preliminary oil risk estimate for Loviisa NPP critical amount of oil was estimated to hit the plant with a frequency of 8 10-3 /year. This estimate was based on the frequency in the Gulf of Finland for oil spills of tens of thousands of tons and larger, which were assumed to hit the plant with certainty. The preliminary core damage frequency due to an oil spill was 5.4 10-8 /year during power and 8.6 10-6 at annual refueling outage. The new oil spill frequencies for the Gulf of Finland were estimated based on worldwide and Gulf of Finland oil spill statistics and seaborne crude oil transportations. In this study, oil spills 136.4 tons (equivalent to approx. 1000 barrels) were taken into consideration. A uniform oil spill probability distribution was assumed for the Gulf of Finland. Furthermore, no distinction was made between the different seasons and the probability of an oil spill. The assessment methodology of the oil impact probabilities is based on simulations of several oil spill scenarios with different intensities and durations in realistic weather and sea current conditions. Ten hypothetical spill points were selected on the main transportation route of the Gulf of Finland and five points on supplementary routes. For every spill point, different spill scenarios were studied ranging from 10 tons instantaneous spill to 144000 tons spill lasting ten days with 60 tons and 600 tons per hour spill intensities. For every spill scenario, trajectories were calculated representing space and time histories of the hypothetical spills starting from the selected spill points. Calculations were carried out for spills starting with ten minutes intervals for every day of a representative year excluding winter time when there is an ice deck on the sea. For every spill point 30240 trajectories were calculated. In the first stage of the calculations, preliminary dangerous scenarios were selected for further detailed calculations, in order to estimate the impact probabilities and average oil mass reaching the target areas. Impact probabilities were quantified for 10 µm and 50 µm thicknesses of oil in the target areas, based on sensitivity calculations, which showed that the probabilities are negligible for oil thicknesses of more than 100 µm. As a result, probabilities of oil impact in the target areas for each spill point and spill scenario within one to ten days of the spill were obtained. In order to cover the whole Gulf of Finland and thus, include the impact of oil spills occurring in areas beyond the calculated points, 24 additional hypothetical oil spill points were added to the main transportation route utilizing the data from the in detail calculated points. The final results were obtained by combining the determined oil spill frequencies and the impact probabilities within ten days from the 39 spill points. The results show that when oil spills 136.4 tons are considered the average frequency for 10 µm thick oil to appear in the cooling water intake area is 4 10-3 /year at power, when there is no ice deck on the sea, and slightly higher at annual refueling outage. However, for 50 µm thick oil the frequencies are over two times smaller. The estimates of the core damage frequencies seem to decrease with approximately 60% and 40% of the preliminary estimates for power and refueling outage, respectively. The effect of different variables on the result is presented in more detail in the paper. 1
INTRODUCTION Preliminary oil risk estimates showed that oil transportations in the Gulf of Finland pose a significant core damage risk for Loviisa nuclear power plant (NPP) located at the southern coast of Finland. The Loviisa NPP consists of two 510 MWe VVER-440 (PWR) reactors commissioned in 1977 and 1981. The crude oil transportations in the Gulf of Finland have increased substantially during the last few years and will further increase in the coming years enhancing the importance of this risk. Therefore, a more detailed assessment of oil spill impact frequencies has been performed for Loviisa NPP taking into account real hydrometeorological conditions, oil properties and different leakage sizes as well as recent oil spill statistics. This assessment methodology and the results will be presented in this paper. During cold shutdown states the loss of service water due to excessive sea vegetation or other clogging material in the sea is an essential risk contributor because the normal residual heat removal system and the emergency cooling systems are cooled by the same service water system. During hot states alternative cooling means are available by blowing steam into the atmosphere with the backup emergency feed water system. The backup residual heat removal system, which was recently built, utilizes as default the service water system of the other unit. It is also possible to change the intake of the service water systems to the cooling water discharge channel. Oil of tankers and cargo-carrying ships as well as other potentially fouling cargo may clog the sea water cooling systems and endanger the alternative service water intake route on the discharge side. The crude oil transportations in the Gulf of Finland pose maybe the biggest threat with the possibility of a large discharge of tens of thousands of tons of cargo oil into the sea following an accident. The risk of oil impact at the Loviisa NPP subsequent to an oil accident in the Gulf of Finland depends primarily on how far from the plant the accident occurs and how big the oil spill is. Weather, wind and sea currents may, however, have a decisive effect, varying rather significantly with the season and the location of the spill. Oil combating both directly at the open sea as well as in the immediate proximity of the power plant has an influence also. However, the effectiveness of oil combating is uncertain, as it may vary rather much depending on the location and size of the spill as well as on the prevailing weather conditions. PRELIMINARY OIL RISK ASSESSMENT AND BACKGROUND In the preliminary oil risk estimate for Loviisa NPP critical amount of oil was estimated to hit the plant with a frequency of 8 10-3 /year. This estimate was directly based on the frequency of oil spills of tens of thousands of tons and larger in the Gulf of Finland. Oil spills of this magnitude were assumed to hit the plant with certainty if occurred anywhere in the Gulf of Finland. The frequency was rather roughly estimated based on worldwide data on very large oil accidents during the past 25 years and seaborne oil transportations in the world and in the Gulf of Finland in recent years. For Loviisa NPP, the preliminary core damage frequency due to an oil accident in the Gulf of Finland was 5.4 10-8 /year during power and 8.6 10-6 at annual refueling outage. During refueling outage the oil risk is quite considerable standing for nearly 17% of the total core damage frequency of low power and non-power states. As only very large oil spills were taken into consideration in the preliminary assessment one of the main objectives of this work was to make the oil risk assessment noticeably more comprehensive by including smaller spills. By widening the scope of the evaluation to include also smaller spills, new and more detailed oil spill frequencies were required for spills of different sizes in the Gulf of Finland. Furthermore, the assumption made in the preliminary study concerning the conditional impact probability of the large spills could with certainty not be applied to smaller spills. Consequently, a detailed analysis of oil impact probabilities at the Loviisa NPP for spills of different sizes in the Gulf of Finland comprises a major part of this work. The impact probability evaluation was considered to be the most important improvement of the oil risk assessment, not only in view of the smaller spills, but the impact probabilities of the large spills were also expected to drop from the earlier assumption. The methodology and results of these two key parts of the oil risk assessment will be presented in detail in the following chapters. The new updated oil risk assessment for the Loviisa NPP, which was performed by combining the results from the oil spill frequency estimation and the oil impact evaluation, as well as the obtained final results, will be presented and discussed briefly thereafter. OIL SPILL FREQUENCY ESTIMATION A rather extensive review on risk factors of the ship traffic in the Gulf of Finland was published in 2002 by Helsinki University of Technology and the Technical Research Centre of Finland (VTT) [1]. In Finland, data on ship accidents has been collected systematically since 1979 and a good listing and presentation of the time coverage of 2
different Finnish sources on ship accidents can be found in reference [1]. However, most of these sources include only accidents occurred in Finnish territorial waters and they can not, thus, be used for the oil spill frequency estimation in general for the Gulf of Finland. Some risk estimates for the Gulf of Finland have been presented in previously published works in connection with risk estimates done for the whole Baltic Sea area [2-4]. However, these works are based on old data without the information on the rapid development oil transportations in the Gulf of Finland which exists today. Most importantly, nevertheless, the spill frequencies in these works were considered to be presented much too coarsely for spills of different sizes to be suitable for this work. One fundamental objective of this work was, therefore, to obtain new detailed spill frequencies for spills of different sizes in the Gulf of Finland based on recent statistics. For this work, accident statistics for the Gulf of Finland was compiled from data obtained from the Finnish Environment Institute (SYKE), Helsinki Commission (HELCOM) [5-8] and the Maritime Accident Response Information System for the Baltic Sea (MARIS) [9]. Most of these sources covered the entire Baltic Sea area. The initial idea was to estimate the oil spill frequencies for spills of different sizes in the Gulf of Finland based on Gulf of Finland oil spill statistics. However, the statistics revealed that very few oil spills of somewhat significant size have occurred in the Gulf of Finland since 1969. Most of the oil spills occurred in the Gulf of Finland can in this context generally be considered as extremely small and they are, hence, outside the scope of this study. Accordingly, the data on oil accidents in the Gulf of Finland proved to be unsuitable for a wide-ranging statistical analysis on oil spill frequencies for spills of different sizes. Although slightly better, the situation did not change remarkably when oil spill statistics for the whole Baltic Sea area were examined. Therefore, the oil spill frequencies for spills of different sizes were in this study estimated for the Gulf of Finland based on worldwide statistics on oil accidents, although worldwide statistics probably do not represent very well directly the general situation in the Gulf of Finland. The data on worldwide oil accidents is, however, composed of an adequate amount of incidents for a detailed statistical analysis. World oil accident data Data on worldwide oil accidents can be found in numerous sources. The various statistics are, however, problematic in light of their contents and the way they are presented. The main problems are that the reporting criteria of the different statistics are usually very different and the time coverage often differs significantly. In addition, most of the statistics are, unfortunately, presented only for very coarse spill size categories without any information on individual accidents and a detailed processing of the data is, thus, not possible. The data on worldwide oil accidents used for this work was compiled from two sources [10-13] with appropriate reporting threshold and most importantly a sufficient detailed level of information on individual accidents. The TAG tanker spill database [10] includes oil accidents fulfilling the following criteria: the source of the spill is a tanker or a barge with a petroleum product as cargo, the spill must be at least 136.4 tons (1000 barrels) in size and the spill must be accidental, acts of war are not included. Both cargo and fuel spills of petroleum carriers are included. The time span covered in the TAG database is 1974-1997 with, however, no data entered for years 1991 and 1992. For this work, barges were excluded from the data because they are not representative for the Gulf of Finland. The TAG data was supplemented with data from Oil Spill Intelligence Report (OSIR) [11-13] for the time period 1998 - August 2004. In order to meet the same level of detail as in the TAG database, the data was apart from years 1998 and 1999 collected from the weekly published newsletter [11]. For years 1998 and 1999 detailed OSIR compilations on world oil accidents were used [12, 13]. OSIR is believed to be the most comprehensive source for oil accidents in the world. Apart from excluding barges, the same criteria used in the TAG database were applied when data was collected from the different OSIR sources. In order to assess the quality of the data collected for this study, the data was compared with data on world oil spills 136.4 tons for oil tankers and combined carriers covering years 1993-2003 obtained from the International Tanker Owners Pollution Federation Limited (ITOPF). As seen in Figure 1, the collected data is in general rather well compatible with the ITOPF data, despite some small differences. World seaborne oil transportations In addition to worldwide oil accident statistics, data on world seaborne oil transportations were essential for the oil spill frequency estimation. Data on world seaborne oil transportations was needed, in order to express the estimated oil spill frequencies per million tons of oil transported, and thus, obtain frequencies usable for the Gulf of Finland. Heavy oils, especially crude oil, were considered to comprise the most vital threat to the heat removal of 3
the power plant. In this work, the main interest was, therefore, in world seaborne crude oil transportations, for which data was found in annual reviews published by BP and Fearnley AS [14, 15]. Review period The collected data on world oil accidents and seaborne crude oil transportations showed that the estimated oil spill frequencies would evidently change noticeably depending on the considered time period. The number of occurred oil spills in the world has decreased dramatically since the seventies and the positive development is still continuing steadily. The world seaborne crude oil transportations have, on the other hand, increased steadily since the middle of the eighties. The development of world oil accidents 136.4 tons and seaborne crude oil transportations are shown in Figure 1. Based on the clear trends seen in Figure 1, the oil spill frequencies were in this study estimated by taking into consideration data from the period 1993 - August 2004. Although clearly conservative in view of the most recent statistics, the chosen review period represents the current situation somewhat realistically. TAG & OSIR ITOPF Seaborn crude oil movements Fearnleys & BP 70 2000 60 50 40 30 20 10 1800 1600 1400 1200 1000 800 600 400 200 million tons 0 0 1974 1977 1980 1983 1986 1989 1992 1995 1998 2001 2004 Figure 1. World oil spills 136.4 tons and seaborne crude oil movements 1974 - August 2004 Spill frequencies for spills of different sizes Frequency estimations for oil spills of different sizes per million tons crude oil transported were obtained by fitting a function to data processed from the detailed oil accident statistics for spills of different sizes. Cumulative data was used, i.e. the frequency estimation obtained for a given spill size is for spills equal and larger than the given spill size. The resulting function valid roughly for spill sizes 136.4-200000 tons is presented in Eq. 1 f = 10 5 (0,0507 log( x) 0,9669 log( x) + 7,0895 log( x) 25,095 log( x) + 42,520 log( x) 29,808) Where, f = Oil spill frequency per million tons crude oil transported x = Spill size 4 A very good fit to the data was obtained with the above defined function. One of the biggest advantages of the regression analysis was that the frequencies of very large oil spills could be estimated, although none had been recorded during the chosen review period. Because of the general trend of oil spills of different sizes during the 3 2 Eq. 1 4
review period, the frequencies for the very large spills are, however, slightly overestimated. This conclusion is based on a comparison of data from different review periods. Statistical data and obtained oil spill frequency estimates are presented for some spill sizes for comparison in Table 1. Table 1. Comparison of statistical data and oil spill frequency estimates Spill size [t] data [/a] estimate [/a] data [/million t.] estimate [/million t.] 150000 0 0.041 0 2.60E-05 100000 0 0.085 0 5.37E-05 75000 0.172 0.138 1.08E-04 8.68E-05 50000 0.259 0.254 1.63E-04 1.60E-04 10000 1.121 1.180 7.05E-04 7.42E-04 1000 3.362 3.281 2.12E-03 2.06E-03 500 4.914 4.874 3.09E-03 3.07E-03 136,4 8.879 8.667 5.59E-03 5.45E-03 Gulf of Finland Recent oil transportation and terminal development in the Gulf of Finland are presented in detail in the work of Hänninen and Rytkönen [16]. Data on oil transportations in the Gulf of Finland including year 2004 and an updated estimate for year 2010 was obtained from VTT. Based on these figures, the oil transportations in the Gulf of Finland in 2005 were estimated to 118 million tons, compared to 43 million tons in 2000. Although the obtained figures include all oil products, they were in this study assumed to present crude oil transportations. Furthermore, as the worldwide oil accident statistics include in general the whole transportation route, half of the oil accidents per million tons of crude oil transported via the Gulf of Finland were assumed to occur in the Gulf of Finland. As a result, the oil spill frequency for spills 136.4 tons estimated for the Gulf of Finland for year 2005 is approximately 0.32/year. However, based on Gulf of Finland statistics, the actual occurrence rate in the Gulf of Finland during the chosen review period is nearly two times smaller, including all types of ships. The results obtained based on the world data were, therefore, scaled according to the Gulf of Finland statistics. OIL IMPACT PROBABILITY ASSESSMENT The assessment of oil impact probabilities at the Loviisa NPP for spills of different sizes in the Gulf of Finland was based on mathematical modeling of several oil spill scenarios with different intensities and durations in realistic weather and sea current conditions, following a statistical analysis of the results. The behavior of oil spills at sea is strongly dependent on the location of the accident, oil properties, local hydrometeorological conditions, regime and volume of leakage. Practically every oil spill, especially big spills, is individual. Hence, the most reasonable way to analyze the problem is to simulate the fate of numerous hypothetical oil spills. The problem is very singular because the areas of interest, which in this study are the cooling water intake and discharge areas of the NPP, are rather small and located closely to the coastline. In addition, the geometry of the surrounding areas is very complicated due to many islands. Methodology of modeling Hydrometeorological data representing typical conditions in a synoptic sense in the Gulf of Finland from the point of view of atmospheric circulation and ice conditions was used for the oil spill calculations. Meteorological data for the chosen period 1.6.1993-1.7.1994 was provided with three hour time steps by Helsinki University. For circulation modeling the 3D baroclinic model with free surface and variable vertical turbulent viscosity coefficient was used. The calculations were performed with five nautical miles mesh with 105 times 145 cells. The mathematical models and computational methods used in the oil spill calculations are not presented in this paper. Detailed information on these subjects can be found in reference [17]. Ten hypothetical oil spill points were selected on the main transportation route of the Gulf of Finland and five additional points on supplementary routes closer to the Loviisa NPP. The target areas and the distribution of the hypothetical spill points in the Gulf of Finland are shown in Figure 2. In the figure, zone 1 represents the cooling water intake area and zone 2 the cooling water discharge area, which is included in the analysis because the feed of the service water system can in extremis alternatively be taken from the cooling water discharge area. 5
In order to obtain specific impact probability estimates both for power operation and refueling outage, the different seasons of the year were processed separately. Calculations for winter season were not carried out in this study as there is an ice deck on the sea. Based on the hydrometeorological data, batch (instantaneous) oil spill scenarios representing a space-time history of the hypothetical spill development were defined with ten minutes intervals. Such a small interval may appear too detailed, but it strongly decreases the scatter of the calculated probabilities. In this study, the movement and behavior of the batch spills were calculated for ten days because sensitivity calculations indicated that the impact probabilities increased only little after seven days. Figure 2. Target areas and hypothetical oil spill points The spill duration is as a rule a much more valuable parameter from the point of view of impact probability than the amount of oil spilled. The calculated batch spill scenarios served as a base for subsequent calculations of leak (prolonged) spill scenarios, lasting from one to ten days. Specifically, each leak scenario was represented as a series of consequent batch spills. The number of batch spill scenarios used in order to calculate the leak scenarios within the limit of a season was limited by the time history of the calculated batch spill scenarios and the maximum duration of the considered leak spills. For every spill point 10080 batch scenarios were calculated for each ice free season. With 15 spill points, in total 4989600 spill scenarios were taken into account, i.e. 453600 batch scenarios and 4536000 leak scenarios. Based on the first set of calculations, preliminary dangerous spill scenarios were selected for more detailed calculations. Scenarios, which penetrated within ten kilometers radius of the Loviisa NPP, were chosen and simulated once again in the second stage. However, in the second stage the differentiation of the batch spill sizes was entered. Two batch spill sizes were considered, 10 and 100 tons, resulting in 60 and 600 tons per hour spill intensities. Consequently, impact probabilities were in this study evaluated for spills ranging from 10 tons instantaneous spill to 144000 tons spill lasting ten days. Furthermore, in order to simulate the spatial configuration of the basic batch spills, the batch spills were reproduced in the second stage as a set of 30 spillets (1/30 part of 6
batch spill), with the initial position depending on the particular size of the batch spill. Thus, leak spill scenarios lasting ten days were simulated by the movement of 43200 spillets. In the second stage, the impact probabilities and the average oil mass reaching the target areas were estimated based on the trajectories of the spillets penetrating the designated target areas shown in Figure 2. If even one spillet of a spill scenario reaches the specific target area, the scenario is dangerous. Consequently, the impact probabilities are not dependent on the number of spillets that penetrate the target area. The number of spillets was used in order to evaluate the extent of impact, i.e. the amount of oil reaching the target area. However, the impact intensity is not exclusively determined by the oil mass. The oil thickness, including implicitly the oil slick area, is an important parameter. Sensitivity calculations showed that the impact probabilities in the target areas are negligible for oil thicknesses of more than 100 µm. In this study, the impact probabilities were, therefore, quantified for 10 µm and 50 µm oil thicknesses. As a result, impact probabilities within one to ten days of the spill were obtained for each target area for 10 µm and 50 µm oil thicknesses, for each season, spill point and scenario. UPDATED OIL RISK ESTIMATES The oil risk assessment was performed by combining the results from the oil spill frequency estimation and the oil impact evaluation. However, for this purpose, the obtained oil impact probabilities were processed, in order to obtain estimates for the whole year including the entire Gulf of Finland. In order to cover the whole Gulf of Finland, 24 additional hypothetical oil spill points were added to the main transportation route with the same distance between points as for the calculated points to include the impact of oil spills occurring in areas beyond the calculated points. The impact probabilities for the additional points were conservatively assumed to decrease in succession to two-thirds of the impact probability of the previous point. A schematic representation of the area of Gulf of Finland that is covered by the original 15 points and the 24 additional points placed on the main transportation route is shown in Figure 3. 61,00 Harbours Loviisa NPP Main transportation route covered by all points Original points on main transportation route Original points on supplementary routes Kotka Lat_N 60,00 Helsinki Hanko 25,28; 59,85 27,00; 59,99 27,76; 60,20 29,20; 60,13 St. Petersburg 30,25; 59,93 22,68; 59,56 Tallin 59,00 22,00 23,00 24,00 25,00 26,00 27,00 28,00 29,00 30,00 31,00 Long_E Figure 3. Covered areas of the Gulf of Finland In the oil risk assessment, average impact probabilities within ten days from the 39 spill points were used. The whole year was taken into consideration for power operation, where as only summer was considered for refueling outage. The impact probability during winter was in this study assumed to be zero. Average impact probabilities for Loviisa NPP within ten days for the whole year for spills of different sizes, i.e. spill durations, with a spill intensity of 60 tons per hour are shown in Figure 4. The effect of the additional points is, despite the conservative assumption of the impact probabilities of these points, rather significant, decreasing the 7
average impact probabilities with approximately 60%. Regression analysis was performed on all data sets presented in Figure 4 for both 60 and 600 tons per hour spill intensities, in order to obtain functions compatible to be used together with the function for the spill frequencies for spills of different sizes. The five hypothetical oil spill points situated on the supplementary routes increase the average impact probabilities rather decisively, due to their closeness to the Loviisa NPP. When considered all 39 points, the five points on the supplementary routes increase the average impact probabilities with approximately 35% compared to the average impact probabilities from the 34 points on the main transportation route. Impact probability 0,10 0,05 Zone1 (10 mikrons) Zone2 (10 mikrons) Zone1 (50 mikrons) Zone2 (50 mikrons) 0,00 60 1440 2880 4320 5760 7200 8640 10080 11520 12960 14400 Spill Size [tons] Figure 4. Average impact probabilities within ten days for spills of different sizes with 60 tons per hour spill intensity In this study, the oil risk assessment was performed for oil spills 136.4 tons with the last considered spill size category 150000 tons. For spills in the range 136.4-14400 tons average impact probabilities for 60 and 600 tons per hour spill intensities were used. Accident statistics show that the accidents in the Gulf of Finland are rather unevenly distributed. No correlation between the accident distribution and occurred oil spills can, however, be seen. Therefore, a uniform oil spill probability distribution was assumed for the main transportation route and the supplementary routes representing the whole Gulf of Finland. Furthermore, no distinction was made between the different seasons and the probability of an oil spill. Final Results The results show that when oil spills 136.4 tons are considered the average frequency for 10 µm thick oil to appear in the cooling water intake area is 4.0 10-3 /year during power and 4.7 10-3 /year during refueling outage. For the cooling water discharge area the corresponding numbers are slightly smaller: 3.7 10-3 /year and 4.2 10-3 /year, respectively. For 50 µm thick oil the frequencies are in general roughly two times smaller. Considering spills 136.4 tons and 10 µm, the core damage frequency due to an oil spill at refueling outage decreases to approximately 5 10-6, which is approximately 11% of the total core damage frequency estimate at refueling outage. CONCLUSIONS The methodology used for an in depth assessment of the oil risk for the Loviisa NPP has been presented in this paper. New detailed oil spill frequencies for spills of different sizes 136.4 tons in the Gulf of Finland were obtained based on worldwide and Gulf of Finland oil spill statistics and oil transportations. Mathematical modeling of oil spills was performed with data representing typical conditions in the Gulf of Finland for several oil spill scenarios in order to obtain conditional oil impact probabilities for the Loviisa NPP for spills of different sizes. Although working with a very intricate problem with numerous variables affecting the results, a much more comprehensive and detailed oil risk assessment was successfully performed for the Loviisa NPP. However, the presented results are rather conservative and various issues can be improved in the future. In the current work, the effect of oil combating has, for example, not been taken into account. It is believed, that this topic will require the most work in the future, as it is in a decisive position concerning the impact probability. In the Loviisa NPP probabilistic safety assessment model oil combating has been taken into consideration separately. Currently oil combating is roughly assumed to prevent oil from reaching the power plant with the probability of 0.9. 8
Although impact probabilities for the Loviisa NPP are considered negligible during winter, this subject should be investigated more thoroughly. Furthermore, the probability distributions of oil accidents in the Gulf of Finland can be assessed in more detail. Finally, the probability of simultaneous impact in the cooling water intake and discharge needs further analysis. REFERENCES [1] Hänninen, S., Nyman, T., Rytkönen, J. Sonninen, S., Jalonen, R., Palonen, A. and Riska, K., 2002, Suomenlahden meriliikenteen riskitekijät. Esiselvitys, VTT Tutkimusraportti BVAL34-021198, Espoo, Finland. Available online at http://www.mintc.fi/www/sivut/dokumentit/liikenne/merenkulku/meririski.pdf * [2] Magnusson, K. and Forsman, B., 1996, Transportation of oils in the Baltic Sea Area 1995, HELCOM, SSPA Maritime Consulting AB, Report 7596-1, 26.4.1996. [3] Magnusson, K., 1998, Oil Handling in the Baltic Sea Area, 1996-2001, HELCOM, SSPA Maritime Consulting AB, Report 7935-2, 29.4.1998. [4] COWI, 1998, Baltic Sea Environmental study, TACIS Research Report, 1-5, Tacis services DG IA, European Commission, 1998. [5] HELCOM, 2001, Compilation on Ship Accidents in the Baltic Sea Area 1989-1999; Final Report, Helsinki Commission - Baltic Marine Environment Protection Commission, HELCOM, HELCOM SEA 2/2001. Available online www.helcom.fi/stc/files/maps/accidents/accidents1989to1999.pdf * [6] HELCOM, 2002, Compilation on Ship Accidents in the Baltic Sea Area in 2000, 2001, HELCOM SEA 5/2002. Available online at www.helcom.fi/stc/files/maps/accidents/accidents2000to2001.pdf * [7] HELCOM, 2003, Compilation on Ship Accidents in the Baltic Sea Area 2002. HELCOM RESPONSE 3/2003. Available online at http://www.helcom.fi/stc/files/maps/accidents/accidents2002.pdf * [8] HELCOM, 2004, Compilation on Ship Accidents in the Baltic Sea Area 2003. HELCOM RESPONSE 5/2005. Available online at http://www.helcom.fi/stc/files/maps/accidents/accidents2003.pdf * [9] MARIS, 2004, Maritime Accident Response Information System - MARIS, Baltic Marine Environment Protection Commission, HELCOM. Available online at http://www.helcom.fi/gis/maris/en_gb/main/ * [10] TAG, 2001, Tanker Spill Database - TAG, Environmental Technology Center, Canada. Available online at http://www.etc-cte.ec.gc.ca/databases/tankerspills/default.aspx * [11] OSIR, 2000-2004, Oil Spill Intelligence Report, newsletter, Aspen Publishers Inc. formerly published by Cutter Information Corp. Available online at http://online.aspenpubs.com/oil/lpext.dll?f=templates&fn=main-h.htm * [12] OSIR, 1999, International Oil Spill Statistics: 1998, Aspen Publishers Inc. formerly published by Cutter Information Corp. Available online at http://online.aspenpubs.com/oil/lpext.dll?f=templates&fn=main-h.htm * [13] DeCola, E., 2000, International Oil Spill Statistics: 1999, OSIR, Cutter Information Corp. [14] BP, 2005, BP Statistical Review of World Energy 2005. Available online at http://www.bp.com/statisticalreview * [15] Fearnley AS, 2001, Fearnleys Review 2000, Fearnresearch, ISSN 0801-4086. Available online at http://www.fearnresearch.com/asset/61/1/61_1.pdf * 9
[16] Hänninen, S., Rytkönen, J., 2004, Oil transportation and terminal development in the Gulf of Finland, VTT Industrial Systems, Espoo, 141 p. + app. 6 p. VTT Publications 547, ISBN 951-38-6412-X; 951-38-6413-8. Available online at http://www.vtt.fi/inf/pdf/publications/2004/p547.pdf * [17] Ovsienko, S., 2002, An updated assessment of the risk for oil spills in the Baltic Sea area, HELCOM. Available online at http://www.helcom.fi/stc/files/shipping/riskforoilspillsreport2002.pdf * Referred to on 9.12.2005 10