- Email: [email protected]
Comparison of the transportation risks for the spent fuel in Korea for different transportation scenarios
Annals of Nuclear Energy 38 (2011) 535–539
Contents lists available at ScienceDirect
Annals of Nuclear Energy journal homepage: www.elsevier.com/locate/anucene
Comparison of the transportation risks for the spent fuel in Korea for different transportation scenarios Jongtae Jeong ⇑, D.K. Cho, H.J. Choi, J.W. Choi Korea Atomic Energy Research Institute, 150-1 Dukjin-Dong, 1045 Daedeokdaero, Yuseong, Daejeon, Republic of Korea
a r t i c l e
i n f o
Article history: Received 16 May 2008 Accepted 11 September 2010 Available online 20 October 2010 Keywords: Transportation risk Spent fuel Transportation scenarios Casks Transportation means Population risk
a b s t r a c t According to the long term management strategy for spent fuels in Korea, they will be transported from the spent fuel pools in each nuclear power plant to the central interim storage facility (CISF) which is to start operation in 2016. At the start of the operation of the final repository (FR), by the year 2065, transport will then take place between the CISF and the FR. Therefore, we have to determine the safe and economical logistics for the transportation of these spent fuels by considering their transportation risks and costs. In this study, we developed four transportation scenarios for a maritime transportation by considering the type of transportation casks and transport means in order to suggest safe and economical transportation logistics for the spent fuels in Korea. And, we estimated and compared the transportation risks for these four transportation scenarios. Also, we estimated and compared the transportation risks resulting from accidents during the transportation of PWR and PHWR spent fuels by road trailers from the CISF and the FR. From the results of this study, we found that risks resulting from accidents during the transportation of the spent fuels have a very low radiological risk activity with a manageable safety and health consequences. The results of this study can be used as basic data for the development of safe and economical logistics for a transportation of the spent fuels in Korea by considering the transportation costs for the four scenarios which will be needed in the near future. Ó 2010 Elsevier Ltd. All rights reserved.
1. Introduction At present, a total of 20 units of nuclear power plants (NPP) are in operation in Korea, sharing about 40% of the total production of electricity. These 20 units of NPPs are located at four different sites (Kori, Wolsong, Yonggwang, and Ulchin). In addition to these 20 units of NPPs, we have four more units that are currently under construction. Upon the completion of these units, the share of nuclear power generation will be increased to 46.1% by 2015. Such an active nuclear energy program, however, has inevitably resulted in producing significant quantities of low-and intermediate-level waste and spent nuclear fuel. The amount of spent nuclear fuel is also sharply increasing. As shown in Fig. 1, the cumulative amount was about 7960 ton in 2005, and we expect it to increase up to 19,000 ton by 2020. We expect the total amount of SF from the existing and planned NPPs during their life time to be about 36,000 tU (Choi et al., 2007). The spent fuel is stored in temporary storage pools at plant sites. However, all the storage pools are expected to reach their full capacity in a couple of years. To resolve this insufficient storage capacity at each plant site, we have expanded their capacity by a ⇑ Corresponding author. Tel.: +82 42 868 2718; fax: +82 42 868 8198. E-mail address: [email protected] (J. Jeong). 0306-4549/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.anucene.2010.09.030
re-racking and transshipment as a short-term solution. Ulchin units 1 and 2 have also expanded their storage capacity by adopting high-density storage racks, while Yonggwang unit 1 is also undertaking a transshipment of its spent fuel to its neighboring units 3 and 4. Also, we have a plan to construct and operate a centralized interim storage facility (CISF), which is to start its operation in 2016. And the final repository (FR) will start its operation in 2065. At present, the sites for the CISF and FR are assumed to be located near the Wolsong nuclear power plant site where four CANDU type pressurized heavy water reactors are being operated. And the site for the FR is assumed to be located within 30 km from the site for the CISF. Before the operation of the CISF and the FR starts, we have to prepare a suitable logistics system for the transportation of the spent fuel from each site to the CISF and between the CISF and the FR by considering the necessary safety and costs. The most important factor for the preparation of a suitable logistics system for the transportation of the spent fuel is its safety. Therefore, the objective of this study is to estimate and compare the safety level resulting from accidents during the transportation of the spent fuel for various transport scenarios by considering the type of transportation casks and transport means in order to suggest a safe and economical transportation logistics system for the spent fuels in Korea.
536
J. Jeong et al. / Annals of Nuclear Energy 38 (2011) 535–539 Table 1 Radionuclide inventory for a reference spent fuel assemblies. Radionuclide
Fig. 1. The amount of spent fuel in Korea.
2. Modelling and assumptions Although there are different operation timeframes of the nuclear power plant sites, we consider only the amount of the spent fuel assemblies stored at the Yonggwang nuclear power plant site as a reference spent fuel for a pressurized water reactor for a maritime transportation. Total 17,000 spent fuel assemblies are expected to be transported from the Yonggwang nuclear power plant site to the CISF site by the year 2075 which is equivalent to 7200 tU. During this study, we will consider 1 day to unload completely a cask at a final destination, and 1 day to prepare it for a return transport. The transit time by sea will be 24 h. For the case of a PWR, two types of fuel assemblies, i.e., Vantage 5H and Korea Standard Fuel Assembly (KSFA), are being operated at the Yonggwang nuclear power plants. However, we selected the Vantage 5H fuel assembly as a reference fuel assembly to be transported to the CISF site because most of the spent fuels stored at the spent fuel storage pool are Vantage 5H fuel assemblies (Choi et al., 2007). The radionuclide inventory of a reference fuel assembly was calculated by using the ORIGEN-ARP code (Gauld et al., 2004). During the calculation of the radionuclide inventory of a reference fuel assembly, we assumed that the initial enrichment of uranium was 4.5 wt.% and the discharge burnup was 45GWD/ MTU. We used a nuclear reaction library obtained by using the SAS2 module in the SCALE5 code package (Gauld and Hermann, 2005). Also, we assumed that the cooling time was 7 years to obtain conservative results. The calculated radionuclide inventories based on these assumptions are summarized in Table 1. The radionuclide inventory of a reference fuel assembly for CANDU reactors was also calculated by using the ORIGEN-ARP code. During the calculation of the radionuclide inventory of a reference fuel assembly, we assumed that the initial enrichment of uranium was 0.71 wt.% and the discharge burnup was 7.5GWD/ MTU, and a built-in CANDU cross section library was used. Also, we assumed that the cooling time was 7 years to obtain conservative results. The calculated radionuclide inventories based on these assumptions are also summarized in Table 1. We considered two types of transport casks for the transportation of PWR spent fuels. One is based on an existing TN international concept, the TN-24, capable of carrying 24 spent fuel assemblies, and the other is the KN-12 cask being used in Korea. For the case of PHWR spent fuels, we consider the Advanced Kor-
H-3 Mn-54 Fe-55 Co-58 Co-60 Kr-85 Sr-89 Sr-90 Y-90 Y-91 Zr-95 Nb-95 Ru-103 Rh-103m Rh-106 Ru-106 Sn-123 Sb-125 Te-125m Te-127 Te-129 Te-129m I-129 Cs-134 Cs-137
Inventory (Ci/MTU) PWR
PHWR
6.22E+02 8.05E-03 1.70E+00 4.23E-10 6.07E+01 7.45E+03 4.92E-10 8.58E+04 8.58E+04 7.73E-08 1.52E-06 3.34E-06 4.21E-14 4.20E-14 5.72E+03 5.72E+03 7.10E-04 1.71E+03 4.17E+02 1.36E-03 5.12E-19 7.99E-19 4.31E-02 2.15E+04 1.24E+05
2.52E+02 1.93E-03 1.58E+00 1.54E-10 3.09E+01 1.36E+03 3.65E-10 1.46E+04 1.46E+04 5.62E-08 1.05E-06 2.32E-06 2.81E-14 2.80E-14 1.72E+03 1.72E+03 4.26E-04 4.20E+02 1.03E+02 8.10E-04 3.68E-19 5.74E-19 7.76E-03 1.21E+03 2.15E+04
Radionuclide
Ba-137m Ce-141 Ce-144 Pr-144 Pr-144m Pm-147 Pm-148m Sm-151 Eu-154 Eu-155 U-232 U-233 U-234 U-235 U-236 U-238 Pu-238 Pu-239 Pu-240 Pu-241 Am-241 Am-242m Cm-242 Am-243 Cm-244
Inventory (Ci/MTU) PWR
PHWR
1.17E+05 3.39E-18 2.49E+03 2.49E+03 3.49E+01 3.00E+04 6.98E-15 5.03E+02 5.62E+03 1.40E+03 3.80E-02 3.99E-05 1.22E+00 1.75E-02 3.53E-01 3.12E-01 4.85E+03 3.78E+02 6.10E+02 1.25E+05 1.86E+03 1.26E+01 1.18E+01 4.04E+01 4.64E+03
2.03E+04 2.35E-18 1.00E+03 1.00E+03 1.40E+01 1.11E+04 1.26E-15 6.50E+01 3.38E+02 2.11E+02 1.24E-04 8.44E-07 1.72E-03 4.78E-03 4.82E-02 3.31E-01 7.14E+01 1.59E+02 2.27E+02 1.80E+04 2.47E+02 3.17E-01 2.91E-01 5.36E-01 1.14E+01
ean Disposal Cask (AKDC)-CANDU casks which are being developed in Korea. The AKDC-CANDU is capable of carrying 420 bundles of PHWR spent fuel which is now in operation in Wolsong nuclear power plants in Korea. Detailed specifications of these casks are given in Table 2. For the maritime transportation, we considered two types of ships, the INF-2 and INF-3 ships. The INF-2 ships are certified to carry irradiated nuclear fuel or high-level radioactive wastes with an aggregate activity of less than 2 106 TBq, and they are also certified to carry plutonium with an aggregate activity less than 2 105 TBq. The number of transported casks per INF-2 ship will depend on the cask activities. INF-3 ships are certified to carry irradiated nuclear fuel or high-level radioactive wastes, and certified to carry plutonium with no restriction on the aggregate activity of the materials. For the road transportation between the CISF and the FR, we assumed that road trailers, identical as those used in France between nuclear power plants and the reprocessing plant could be operated in Korea. These vehicles are specifically designed to transport a spent fuels cask. They are composed of a tractor and an 8 or 9 axle’s trailer, on which a transport frame is mounted. A tarpaulin which will help thermal flow circulation will cover the cask during transportation. Also, the design of the transport frame will be adapted to each transport cask. We also assumed that the ground itinerary between the CISF and the FR should be chosen in accordance with the design of the road transport, specifically regarding the bridges and tunnels to be crossed. We estimated the transportation risks by using the RADTRAN5 code (Neuhauser et al., 2000). It is a computer code for an analysis of the consequences and risks of a radioactive material transportation. It can be used for the estimation of risks associated with an incident-free transportation of a radioactive material and with accidents that might occur during transportation. According to the definition of the US Department of Transportation, incidentfree (or normal) transportation is a transportation during which no accident, packaging, or handling abnormality or malevolent attack occurs. All the accidents that might occur during transportation can be considered in the transportation risk assessment by
537
J. Jeong et al. / Annals of Nuclear Energy 38 (2011) 535–539 Table 2 Specifications of transport casks. Cask
TN-24
KN-12
AKDC-CANDU
Loaded weight (tons) Dimensions (m)
125.6 Diameter: 2.935 Length: 7.013 24 Spent fuel assemblies Licensed and operated (in France) – IAEA 1996
83 Diameter: 1.942 Length: 4.809 12 Spent fuel assemblies Licensed and operated (in Korea)
24 Diameter: 1.22 Length: 3.66 420 Bundles of PHWR spent fuel Being developed (in Korea)
Capacity Status
using the RADTRAN5 code. And all major modes of commercial transport may be analyzed with RADTRAN5: highway, rail, barge, ship, cargo air, and passenger air. The RADTRAN5 component models and their interrelationships are shown in Fig. 2. For the maritime transportation, we considered three accidents, that is, a collision, a fire, and a foundering and sinking. The accident occurrence probabilities for these three accidents were derived from results of the IAEA Coordinated Research Project (Sprung and Ammerman, 2003). They gathered and examined accident data in order to develop accident frequencies for ship accidents. Fifteen years of ship accident data covering the years 1979–1993 were gathered and examined. In order to obtain the ship accident frequencies, we used the ship accident frequencies suggested by them and the actual distance between the Yonggwand site and the CISF site, which is approximately 650 km. Then we obtained the accident frequencies, which are 6.22 10 7 accidents/km for a collision, 6.59 10 8 accidents/km for a fire, and 4.78 10 7 accidents/km for a foundering and sinking accident. For the road transportation, we considered two accidents, that is, an impact and a fire. The accident occurrence frequency of these accidents was obtained by using the accident data covering the years 2000–2005 in Korea and the annual average travel distance of all kinds of cars. Then we obtained the accident frequencies, which are 9.52 10 7 accidents/km for an impact and 5.70 10 8 accidents/km for a fire. We classified the radionuclides into five groups, i.e., inert gas, iodine, cesium, ruthenium, and particulates. The release fractions for these five radionuclide groups were derived from the results of the Modal Study cask regions (Fischer et al., 1987). The NRC Modal Study designated several discrete cask response regions and assigned release fractions for each radionuclide group for these five radionuclide groups. We selected the highest value of the release fractions in order to obtain conservative results. Other parameters that enter the calculational process, such as shielding factors, a deposition velocity, an aerosol fraction, and a respirable
fraction were derived from the DOE Handbook on a Transportation Risk Assessment (Chen et al., 2002). 3. Transportation scenarios We assumed that the CISF site was located near the Wolsong nuclear power plant site. Both the Yonggwang and Wolsong nuclear power plant sites are located near the coastline. Therefore, we considered only a maritime transportation between Yonggwang nuclear power plant and the CISF. The distance between these two sites is approximately 650 km. If we assume that the first phase of the transport between the Yoggwang site and CISF will start in 2016, and it will last 25 years, 472 fuel assemblies will transported per year. The TN-24 cask can contain 24 fuels assemblies. Consequently the equivalent of 20 TN-24 casks needs to be transferred. With an INF-2 ship four maritime journeys are needed per year. Indeed only five transport casks can be loaded per ship because of strict regulations concerning an irradiated material’s activity. With the INF-3 ship a maritime journey is needed once a year, thanks to the absence of restrictions concerning an irradiated material’s activity. Therefore, 20 casks can be loaded in the same vessel. The scenario with KN-12 cask is close to the TN-24 cask scenario. The first transfer between Yonggwang site and CISF will start in 2016 and will last 25 years. 5000 tU are to be transported. It means that 472 assemblies (200 tU) will be transferred per year. The KN-12 cask contains 12 fuels assemblies. Consequently the equivalent of 40 KN-12 casks needs to be transferred. With the INF-2 ship four maritime journeys are needed per year. A maximum of 10 transport casks can be loaded per ship because of strict regulations concerning irradiated materials activity. With the INF3 ship one maritime journey per year is needed per year. In this case, 40 KN-12 casks have to be loaded in the same vessel. The four transportation scenarios for the maritime transportation by considering the capacity of the casks and the ships are summarized in Table 3.
Fig. 2. RADTRAN5 component models and their interrelationship.
538
J. Jeong et al. / Annals of Nuclear Energy 38 (2011) 535–539
Table 3 Maritime transportation scenarios. Scenario
1 2 3 4
Table 5 Expected values of population risk for road transport (Person-Sv).
Transportation cask
Ship
TN-24 TN-24 KN-12 KN-12
INF-2 INF-3 INF-2 INF-3
No. of fuel transportation cask
Number of maritime journeys
5 20 10 40
4 1 4 1
For the transportation of spent fuels between the CISF and the FR, we considered road transportation by using road trailers. According to the operational timeframe of the storage sites, that is, the CISF and the FR, 17,000 spent fuels assemblies are expected to be evacuated from the Yonggawang site by 2975 which is equivalent to 7200 tU. During 30 years, a flow rate of 240 tU per year is suggested, which leads to an equivalent of 24 TN-24 casks and 47 KN-12 cask transfers per year. Only one cask can be loaded per trailer, so 24 round trips per year for the TN-24 cask and 47 round trips per year for the KN-12 cask will be necessary. During the lifetime of the four CANDU type reactors being operated at the Wolsong site, the total amount of spent fuels to be generated was estimated as 780,000 bundles. According to the generic concept of the final repository for spent fuels in Korea, the spent fuel bundles of CANDU type reactor are assumed to be transported to the final repository over 25 years. If we assume that the five AKDC-CANDU casks were transported per trailer, 370 round trips per year will be necessary. Also, we assumed that the final repository would be constructed and operated within 30 km from the CISF.
4. Results and discussion Risks for the spent fuel transportation arise from both conventional vehicular accidents and exposures to an ionizing radiation under both normal and accident conditions. Transportation risk includes health and safety risks that arise from the exposures to workers and members of the public to radiation from shipments of radioactive wastes (NRSB, 2006). The health effect risks arise from exposures to people who travel, work, or live near transportation routes and transportation workers themselves to radiation from radioactive waste packages. The incident-free results for the in-transit population exposure in person-Sv are in the range of 1.69 10 5 and 4.23 10 6 for all the accidents considered in this study. According to the results summarized in Table 4, the expected values for the population risk in person-Sv for the maritime transportation are in the range of 1.74 10 8 and 2.20 10 8 for a collision accident, 1.85 10 9 and 2.35 10 9 for a fire accident, 1.34 10 8 and 1.70 10 8 for a foundering and sinking accident. All these values for the population risks in person-Sv are low radiological risk activities with manageable safety and health consequences. Although the amount of transportation casks per year is the same for the four scenarios, the population risk for the case of using the INF-2 ship shows a higher value than that for the case
Table 4 Expected values of population risk for maritime transport (Person-Sv). Accident scenario
Collision
Fire
Foundering and sinking
1 2 3 4
2.20E-08 1.74E-08 2.19E-08 1.75E-08
2.34E-09 1.85E-09 2.35E-09 1.85E-09
1.69E-08 1.34E-08 1.70E-08 1.34E-08
Accident cask
Collision
Fire
TN-24 KN-12 AKDC-CANDU
9.77E-07 1.16E-06 1.07E-04
5.85E-08 6.93E-08 6.41E-06
of using the INF-3 ship. This may be attributed to the fact that the INF-3 ship can carry more transportation casks per journey than the INF-2 ship because the INF-3 ships are certified to carry plutonium with no restriction on the aggregate activity of the materials. Therefore, we have to reduce the number of journeys per year in order to reduce the population risks resulting from the accidents during the maritime transportation of spent fuels. And the results expressed as a population risk show the same value if we use the same transportation ship with the same amount of transportation casks. Among the three accidents considered in this study during the maritime transportation, the population risk for the fire accident shows the minimum value of the population risk because the occurrence probability of the fire accident is the lowest and we use the same value for the release fraction. The population risks resulting from the accidents during the road transportation are summarized in Table 5. As in the case of the maritime transportation, the population risk for the fire accident shows a lower value than that for the impact accident because the occurrence probability of the fire accident is lower than that of the impact accident and we use the same value for the release fraction. Between the two transportation casks for the PWR spent fuels, the population risk for the case of using the TN-24 cask shows a lower value than that for the case of using the KN-12 cask for the accidents, an impact and a fire. This is attributed to the fact the number of round trips per year for the case of using the TN-24 cask is nearly half of that for the case of using the KN-12 cask. Therefore, the number of round trips per year for the road transportation of spent fuels is an important factor for the population risks resulting from the accidents during a transportation as in the case of a maritime transportation. Therefore, the population risks resulting from the accidents during the road transportation of spent fuels for the case of using the AKDC-CANDU shows the largest value of the population risk because the number of round trips per year is much higher than that for the case of TN-24 and KN-12.
5. Summary and conclusion According to the long term management strategy for spent fuels in Korea, they will be transported from the spent fuel pools in each nuclear power plant to the central interim storage facility (CISF). Also, transport activities will take place between the CISF and the final repository (FR), which will start its operation by the year 2065. Therefore, we have to determine the safe and economical logistics for the transportation of these spent fuels by considering their transportation risks and costs. We developed four maritime transportation scenarios by considering the type of transportation casks and transport means in order to suggest a safe and economical transportation logistics system for the spent fuels in Korea. For these four transportation scenarios, we estimated and compared the transportation risks resulting from accidents during a transportation from a nuclear power plant site to a centralized interim storage facility by using the RADTRAN5 program. We considered three accidents for the case of maritime transport, that is, a collision, a fire, and a foundering and sinking accident. And we developed the road transport scenarios by considering different transport casks for the PWR and PHWR spent fuels between the CISF and
J. Jeong et al. / Annals of Nuclear Energy 38 (2011) 535–539
FR. We considered the accidents for the road transport, that is, an impact and a fire. The expected values for the population risk in person-Sv for both a maritime and road transport are low radiological risk activities with manageable safety and health consequences. According to the results for both the maritime and road transport, the number of journeys per year was found to be a very important factor if we transport the same number of transport casks for the spent fuels. Therefore, we have to reduce the number of journeys per year in order to reduce the population risks resulting from the accidents during a maritime transportation of the spent fuels. And the population risk shows the same value if we use the same transportation ship with the same amount of transportation casks. Among the accidents considered in this study during the maritime and road transportations, the population risks for the fire accident shows a minimum value of the population risk because the occurrence probability of the fire accident is the lowest and we use the same value for the release fraction. The results of this study can be used as basic data for the development of a safe and economical logistics system for a transportation of the spent fuels in Korea by considering the transportation costs for the four scenarios which will be needed in the near future.
539
Acknowledgement This project has been carried out under the Nuclear R&D Program by Ministry of Science and Technology in Korea. References Chen, S.Y. et al., 2002. A Resource Handbook on DOE Transportation Risk Assessment. DOE/EM/NTP/HB-01. Choi, J.W. et al., 2007. High-level Radwaste Disposal Technology Development. KAERI/RR-2765/2006. Fischer, L.E. et al., 1987. Shipping Container Response to Severe Highway and Railway Accident Conditions, NUREG/CR-4829, UCID-20733. Gauld, I.C., Hermann, O.W., 2005. SAS2: A Coupled One-dimensional Depletion and Shielding Analysis Module. ORNL/TM-2005/39. Version 5, vol. I, Oak Ridge National Laboratory. Gauld, I.C., Bpwman, S.M., Leal, L.C. et al., 2004. ORIGEN-ARP: Automatic Rapid Processing for Spent Fuel Depletion, Decay, and Source Term Analysis. NUREG/ CR-0200, Oak Ridge National Laboratory. Neuhauser, K.S., Kanipe, F.L., Weiner, R.F., 2000. RADTRAN5 Technical Manual. Sandia National Laboratory, SAND2000-1256. Nuclear and Radiation Studies Board (NRSB), 2006. Going the Distance? The Safe Transport of Spent Fuel and High-level Radioactive Wastes in the United States. National Academic Press. Sprung, J., Ammerman, D., 2003. Methods for the Assessment of Risk in the Sea Transport of Radioactive Material. IAEA-CN-101/60.
Contents lists available at ScienceDirect
Annals of Nuclear Energy journal homepage: www.elsevier.com/locate/anucene
Comparison of the transportation risks for the spent fuel in Korea for different transportation scenarios Jongtae Jeong ⇑, D.K. Cho, H.J. Choi, J.W. Choi Korea Atomic Energy Research Institute, 150-1 Dukjin-Dong, 1045 Daedeokdaero, Yuseong, Daejeon, Republic of Korea
a r t i c l e
i n f o
Article history: Received 16 May 2008 Accepted 11 September 2010 Available online 20 October 2010 Keywords: Transportation risk Spent fuel Transportation scenarios Casks Transportation means Population risk
a b s t r a c t According to the long term management strategy for spent fuels in Korea, they will be transported from the spent fuel pools in each nuclear power plant to the central interim storage facility (CISF) which is to start operation in 2016. At the start of the operation of the final repository (FR), by the year 2065, transport will then take place between the CISF and the FR. Therefore, we have to determine the safe and economical logistics for the transportation of these spent fuels by considering their transportation risks and costs. In this study, we developed four transportation scenarios for a maritime transportation by considering the type of transportation casks and transport means in order to suggest safe and economical transportation logistics for the spent fuels in Korea. And, we estimated and compared the transportation risks for these four transportation scenarios. Also, we estimated and compared the transportation risks resulting from accidents during the transportation of PWR and PHWR spent fuels by road trailers from the CISF and the FR. From the results of this study, we found that risks resulting from accidents during the transportation of the spent fuels have a very low radiological risk activity with a manageable safety and health consequences. The results of this study can be used as basic data for the development of safe and economical logistics for a transportation of the spent fuels in Korea by considering the transportation costs for the four scenarios which will be needed in the near future. Ó 2010 Elsevier Ltd. All rights reserved.
1. Introduction At present, a total of 20 units of nuclear power plants (NPP) are in operation in Korea, sharing about 40% of the total production of electricity. These 20 units of NPPs are located at four different sites (Kori, Wolsong, Yonggwang, and Ulchin). In addition to these 20 units of NPPs, we have four more units that are currently under construction. Upon the completion of these units, the share of nuclear power generation will be increased to 46.1% by 2015. Such an active nuclear energy program, however, has inevitably resulted in producing significant quantities of low-and intermediate-level waste and spent nuclear fuel. The amount of spent nuclear fuel is also sharply increasing. As shown in Fig. 1, the cumulative amount was about 7960 ton in 2005, and we expect it to increase up to 19,000 ton by 2020. We expect the total amount of SF from the existing and planned NPPs during their life time to be about 36,000 tU (Choi et al., 2007). The spent fuel is stored in temporary storage pools at plant sites. However, all the storage pools are expected to reach their full capacity in a couple of years. To resolve this insufficient storage capacity at each plant site, we have expanded their capacity by a ⇑ Corresponding author. Tel.: +82 42 868 2718; fax: +82 42 868 8198. E-mail address: [email protected] (J. Jeong). 0306-4549/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.anucene.2010.09.030
re-racking and transshipment as a short-term solution. Ulchin units 1 and 2 have also expanded their storage capacity by adopting high-density storage racks, while Yonggwang unit 1 is also undertaking a transshipment of its spent fuel to its neighboring units 3 and 4. Also, we have a plan to construct and operate a centralized interim storage facility (CISF), which is to start its operation in 2016. And the final repository (FR) will start its operation in 2065. At present, the sites for the CISF and FR are assumed to be located near the Wolsong nuclear power plant site where four CANDU type pressurized heavy water reactors are being operated. And the site for the FR is assumed to be located within 30 km from the site for the CISF. Before the operation of the CISF and the FR starts, we have to prepare a suitable logistics system for the transportation of the spent fuel from each site to the CISF and between the CISF and the FR by considering the necessary safety and costs. The most important factor for the preparation of a suitable logistics system for the transportation of the spent fuel is its safety. Therefore, the objective of this study is to estimate and compare the safety level resulting from accidents during the transportation of the spent fuel for various transport scenarios by considering the type of transportation casks and transport means in order to suggest a safe and economical transportation logistics system for the spent fuels in Korea.
536
J. Jeong et al. / Annals of Nuclear Energy 38 (2011) 535–539 Table 1 Radionuclide inventory for a reference spent fuel assemblies. Radionuclide
Fig. 1. The amount of spent fuel in Korea.
2. Modelling and assumptions Although there are different operation timeframes of the nuclear power plant sites, we consider only the amount of the spent fuel assemblies stored at the Yonggwang nuclear power plant site as a reference spent fuel for a pressurized water reactor for a maritime transportation. Total 17,000 spent fuel assemblies are expected to be transported from the Yonggwang nuclear power plant site to the CISF site by the year 2075 which is equivalent to 7200 tU. During this study, we will consider 1 day to unload completely a cask at a final destination, and 1 day to prepare it for a return transport. The transit time by sea will be 24 h. For the case of a PWR, two types of fuel assemblies, i.e., Vantage 5H and Korea Standard Fuel Assembly (KSFA), are being operated at the Yonggwang nuclear power plants. However, we selected the Vantage 5H fuel assembly as a reference fuel assembly to be transported to the CISF site because most of the spent fuels stored at the spent fuel storage pool are Vantage 5H fuel assemblies (Choi et al., 2007). The radionuclide inventory of a reference fuel assembly was calculated by using the ORIGEN-ARP code (Gauld et al., 2004). During the calculation of the radionuclide inventory of a reference fuel assembly, we assumed that the initial enrichment of uranium was 4.5 wt.% and the discharge burnup was 45GWD/ MTU. We used a nuclear reaction library obtained by using the SAS2 module in the SCALE5 code package (Gauld and Hermann, 2005). Also, we assumed that the cooling time was 7 years to obtain conservative results. The calculated radionuclide inventories based on these assumptions are summarized in Table 1. The radionuclide inventory of a reference fuel assembly for CANDU reactors was also calculated by using the ORIGEN-ARP code. During the calculation of the radionuclide inventory of a reference fuel assembly, we assumed that the initial enrichment of uranium was 0.71 wt.% and the discharge burnup was 7.5GWD/ MTU, and a built-in CANDU cross section library was used. Also, we assumed that the cooling time was 7 years to obtain conservative results. The calculated radionuclide inventories based on these assumptions are also summarized in Table 1. We considered two types of transport casks for the transportation of PWR spent fuels. One is based on an existing TN international concept, the TN-24, capable of carrying 24 spent fuel assemblies, and the other is the KN-12 cask being used in Korea. For the case of PHWR spent fuels, we consider the Advanced Kor-
H-3 Mn-54 Fe-55 Co-58 Co-60 Kr-85 Sr-89 Sr-90 Y-90 Y-91 Zr-95 Nb-95 Ru-103 Rh-103m Rh-106 Ru-106 Sn-123 Sb-125 Te-125m Te-127 Te-129 Te-129m I-129 Cs-134 Cs-137
Inventory (Ci/MTU) PWR
PHWR
6.22E+02 8.05E-03 1.70E+00 4.23E-10 6.07E+01 7.45E+03 4.92E-10 8.58E+04 8.58E+04 7.73E-08 1.52E-06 3.34E-06 4.21E-14 4.20E-14 5.72E+03 5.72E+03 7.10E-04 1.71E+03 4.17E+02 1.36E-03 5.12E-19 7.99E-19 4.31E-02 2.15E+04 1.24E+05
2.52E+02 1.93E-03 1.58E+00 1.54E-10 3.09E+01 1.36E+03 3.65E-10 1.46E+04 1.46E+04 5.62E-08 1.05E-06 2.32E-06 2.81E-14 2.80E-14 1.72E+03 1.72E+03 4.26E-04 4.20E+02 1.03E+02 8.10E-04 3.68E-19 5.74E-19 7.76E-03 1.21E+03 2.15E+04
Radionuclide
Ba-137m Ce-141 Ce-144 Pr-144 Pr-144m Pm-147 Pm-148m Sm-151 Eu-154 Eu-155 U-232 U-233 U-234 U-235 U-236 U-238 Pu-238 Pu-239 Pu-240 Pu-241 Am-241 Am-242m Cm-242 Am-243 Cm-244
Inventory (Ci/MTU) PWR
PHWR
1.17E+05 3.39E-18 2.49E+03 2.49E+03 3.49E+01 3.00E+04 6.98E-15 5.03E+02 5.62E+03 1.40E+03 3.80E-02 3.99E-05 1.22E+00 1.75E-02 3.53E-01 3.12E-01 4.85E+03 3.78E+02 6.10E+02 1.25E+05 1.86E+03 1.26E+01 1.18E+01 4.04E+01 4.64E+03
2.03E+04 2.35E-18 1.00E+03 1.00E+03 1.40E+01 1.11E+04 1.26E-15 6.50E+01 3.38E+02 2.11E+02 1.24E-04 8.44E-07 1.72E-03 4.78E-03 4.82E-02 3.31E-01 7.14E+01 1.59E+02 2.27E+02 1.80E+04 2.47E+02 3.17E-01 2.91E-01 5.36E-01 1.14E+01
ean Disposal Cask (AKDC)-CANDU casks which are being developed in Korea. The AKDC-CANDU is capable of carrying 420 bundles of PHWR spent fuel which is now in operation in Wolsong nuclear power plants in Korea. Detailed specifications of these casks are given in Table 2. For the maritime transportation, we considered two types of ships, the INF-2 and INF-3 ships. The INF-2 ships are certified to carry irradiated nuclear fuel or high-level radioactive wastes with an aggregate activity of less than 2 106 TBq, and they are also certified to carry plutonium with an aggregate activity less than 2 105 TBq. The number of transported casks per INF-2 ship will depend on the cask activities. INF-3 ships are certified to carry irradiated nuclear fuel or high-level radioactive wastes, and certified to carry plutonium with no restriction on the aggregate activity of the materials. For the road transportation between the CISF and the FR, we assumed that road trailers, identical as those used in France between nuclear power plants and the reprocessing plant could be operated in Korea. These vehicles are specifically designed to transport a spent fuels cask. They are composed of a tractor and an 8 or 9 axle’s trailer, on which a transport frame is mounted. A tarpaulin which will help thermal flow circulation will cover the cask during transportation. Also, the design of the transport frame will be adapted to each transport cask. We also assumed that the ground itinerary between the CISF and the FR should be chosen in accordance with the design of the road transport, specifically regarding the bridges and tunnels to be crossed. We estimated the transportation risks by using the RADTRAN5 code (Neuhauser et al., 2000). It is a computer code for an analysis of the consequences and risks of a radioactive material transportation. It can be used for the estimation of risks associated with an incident-free transportation of a radioactive material and with accidents that might occur during transportation. According to the definition of the US Department of Transportation, incidentfree (or normal) transportation is a transportation during which no accident, packaging, or handling abnormality or malevolent attack occurs. All the accidents that might occur during transportation can be considered in the transportation risk assessment by
537
J. Jeong et al. / Annals of Nuclear Energy 38 (2011) 535–539 Table 2 Specifications of transport casks. Cask
TN-24
KN-12
AKDC-CANDU
Loaded weight (tons) Dimensions (m)
125.6 Diameter: 2.935 Length: 7.013 24 Spent fuel assemblies Licensed and operated (in France) – IAEA 1996
83 Diameter: 1.942 Length: 4.809 12 Spent fuel assemblies Licensed and operated (in Korea)
24 Diameter: 1.22 Length: 3.66 420 Bundles of PHWR spent fuel Being developed (in Korea)
Capacity Status
using the RADTRAN5 code. And all major modes of commercial transport may be analyzed with RADTRAN5: highway, rail, barge, ship, cargo air, and passenger air. The RADTRAN5 component models and their interrelationships are shown in Fig. 2. For the maritime transportation, we considered three accidents, that is, a collision, a fire, and a foundering and sinking. The accident occurrence probabilities for these three accidents were derived from results of the IAEA Coordinated Research Project (Sprung and Ammerman, 2003). They gathered and examined accident data in order to develop accident frequencies for ship accidents. Fifteen years of ship accident data covering the years 1979–1993 were gathered and examined. In order to obtain the ship accident frequencies, we used the ship accident frequencies suggested by them and the actual distance between the Yonggwand site and the CISF site, which is approximately 650 km. Then we obtained the accident frequencies, which are 6.22 10 7 accidents/km for a collision, 6.59 10 8 accidents/km for a fire, and 4.78 10 7 accidents/km for a foundering and sinking accident. For the road transportation, we considered two accidents, that is, an impact and a fire. The accident occurrence frequency of these accidents was obtained by using the accident data covering the years 2000–2005 in Korea and the annual average travel distance of all kinds of cars. Then we obtained the accident frequencies, which are 9.52 10 7 accidents/km for an impact and 5.70 10 8 accidents/km for a fire. We classified the radionuclides into five groups, i.e., inert gas, iodine, cesium, ruthenium, and particulates. The release fractions for these five radionuclide groups were derived from the results of the Modal Study cask regions (Fischer et al., 1987). The NRC Modal Study designated several discrete cask response regions and assigned release fractions for each radionuclide group for these five radionuclide groups. We selected the highest value of the release fractions in order to obtain conservative results. Other parameters that enter the calculational process, such as shielding factors, a deposition velocity, an aerosol fraction, and a respirable
fraction were derived from the DOE Handbook on a Transportation Risk Assessment (Chen et al., 2002). 3. Transportation scenarios We assumed that the CISF site was located near the Wolsong nuclear power plant site. Both the Yonggwang and Wolsong nuclear power plant sites are located near the coastline. Therefore, we considered only a maritime transportation between Yonggwang nuclear power plant and the CISF. The distance between these two sites is approximately 650 km. If we assume that the first phase of the transport between the Yoggwang site and CISF will start in 2016, and it will last 25 years, 472 fuel assemblies will transported per year. The TN-24 cask can contain 24 fuels assemblies. Consequently the equivalent of 20 TN-24 casks needs to be transferred. With an INF-2 ship four maritime journeys are needed per year. Indeed only five transport casks can be loaded per ship because of strict regulations concerning an irradiated material’s activity. With the INF-3 ship a maritime journey is needed once a year, thanks to the absence of restrictions concerning an irradiated material’s activity. Therefore, 20 casks can be loaded in the same vessel. The scenario with KN-12 cask is close to the TN-24 cask scenario. The first transfer between Yonggwang site and CISF will start in 2016 and will last 25 years. 5000 tU are to be transported. It means that 472 assemblies (200 tU) will be transferred per year. The KN-12 cask contains 12 fuels assemblies. Consequently the equivalent of 40 KN-12 casks needs to be transferred. With the INF-2 ship four maritime journeys are needed per year. A maximum of 10 transport casks can be loaded per ship because of strict regulations concerning irradiated materials activity. With the INF3 ship one maritime journey per year is needed per year. In this case, 40 KN-12 casks have to be loaded in the same vessel. The four transportation scenarios for the maritime transportation by considering the capacity of the casks and the ships are summarized in Table 3.
Fig. 2. RADTRAN5 component models and their interrelationship.
538
J. Jeong et al. / Annals of Nuclear Energy 38 (2011) 535–539
Table 3 Maritime transportation scenarios. Scenario
1 2 3 4
Table 5 Expected values of population risk for road transport (Person-Sv).
Transportation cask
Ship
TN-24 TN-24 KN-12 KN-12
INF-2 INF-3 INF-2 INF-3
No. of fuel transportation cask
Number of maritime journeys
5 20 10 40
4 1 4 1
For the transportation of spent fuels between the CISF and the FR, we considered road transportation by using road trailers. According to the operational timeframe of the storage sites, that is, the CISF and the FR, 17,000 spent fuels assemblies are expected to be evacuated from the Yonggawang site by 2975 which is equivalent to 7200 tU. During 30 years, a flow rate of 240 tU per year is suggested, which leads to an equivalent of 24 TN-24 casks and 47 KN-12 cask transfers per year. Only one cask can be loaded per trailer, so 24 round trips per year for the TN-24 cask and 47 round trips per year for the KN-12 cask will be necessary. During the lifetime of the four CANDU type reactors being operated at the Wolsong site, the total amount of spent fuels to be generated was estimated as 780,000 bundles. According to the generic concept of the final repository for spent fuels in Korea, the spent fuel bundles of CANDU type reactor are assumed to be transported to the final repository over 25 years. If we assume that the five AKDC-CANDU casks were transported per trailer, 370 round trips per year will be necessary. Also, we assumed that the final repository would be constructed and operated within 30 km from the CISF.
4. Results and discussion Risks for the spent fuel transportation arise from both conventional vehicular accidents and exposures to an ionizing radiation under both normal and accident conditions. Transportation risk includes health and safety risks that arise from the exposures to workers and members of the public to radiation from shipments of radioactive wastes (NRSB, 2006). The health effect risks arise from exposures to people who travel, work, or live near transportation routes and transportation workers themselves to radiation from radioactive waste packages. The incident-free results for the in-transit population exposure in person-Sv are in the range of 1.69 10 5 and 4.23 10 6 for all the accidents considered in this study. According to the results summarized in Table 4, the expected values for the population risk in person-Sv for the maritime transportation are in the range of 1.74 10 8 and 2.20 10 8 for a collision accident, 1.85 10 9 and 2.35 10 9 for a fire accident, 1.34 10 8 and 1.70 10 8 for a foundering and sinking accident. All these values for the population risks in person-Sv are low radiological risk activities with manageable safety and health consequences. Although the amount of transportation casks per year is the same for the four scenarios, the population risk for the case of using the INF-2 ship shows a higher value than that for the case
Table 4 Expected values of population risk for maritime transport (Person-Sv). Accident scenario
Collision
Fire
Foundering and sinking
1 2 3 4
2.20E-08 1.74E-08 2.19E-08 1.75E-08
2.34E-09 1.85E-09 2.35E-09 1.85E-09
1.69E-08 1.34E-08 1.70E-08 1.34E-08
Accident cask
Collision
Fire
TN-24 KN-12 AKDC-CANDU
9.77E-07 1.16E-06 1.07E-04
5.85E-08 6.93E-08 6.41E-06
of using the INF-3 ship. This may be attributed to the fact that the INF-3 ship can carry more transportation casks per journey than the INF-2 ship because the INF-3 ships are certified to carry plutonium with no restriction on the aggregate activity of the materials. Therefore, we have to reduce the number of journeys per year in order to reduce the population risks resulting from the accidents during the maritime transportation of spent fuels. And the results expressed as a population risk show the same value if we use the same transportation ship with the same amount of transportation casks. Among the three accidents considered in this study during the maritime transportation, the population risk for the fire accident shows the minimum value of the population risk because the occurrence probability of the fire accident is the lowest and we use the same value for the release fraction. The population risks resulting from the accidents during the road transportation are summarized in Table 5. As in the case of the maritime transportation, the population risk for the fire accident shows a lower value than that for the impact accident because the occurrence probability of the fire accident is lower than that of the impact accident and we use the same value for the release fraction. Between the two transportation casks for the PWR spent fuels, the population risk for the case of using the TN-24 cask shows a lower value than that for the case of using the KN-12 cask for the accidents, an impact and a fire. This is attributed to the fact the number of round trips per year for the case of using the TN-24 cask is nearly half of that for the case of using the KN-12 cask. Therefore, the number of round trips per year for the road transportation of spent fuels is an important factor for the population risks resulting from the accidents during a transportation as in the case of a maritime transportation. Therefore, the population risks resulting from the accidents during the road transportation of spent fuels for the case of using the AKDC-CANDU shows the largest value of the population risk because the number of round trips per year is much higher than that for the case of TN-24 and KN-12.
5. Summary and conclusion According to the long term management strategy for spent fuels in Korea, they will be transported from the spent fuel pools in each nuclear power plant to the central interim storage facility (CISF). Also, transport activities will take place between the CISF and the final repository (FR), which will start its operation by the year 2065. Therefore, we have to determine the safe and economical logistics for the transportation of these spent fuels by considering their transportation risks and costs. We developed four maritime transportation scenarios by considering the type of transportation casks and transport means in order to suggest a safe and economical transportation logistics system for the spent fuels in Korea. For these four transportation scenarios, we estimated and compared the transportation risks resulting from accidents during a transportation from a nuclear power plant site to a centralized interim storage facility by using the RADTRAN5 program. We considered three accidents for the case of maritime transport, that is, a collision, a fire, and a foundering and sinking accident. And we developed the road transport scenarios by considering different transport casks for the PWR and PHWR spent fuels between the CISF and
J. Jeong et al. / Annals of Nuclear Energy 38 (2011) 535–539
FR. We considered the accidents for the road transport, that is, an impact and a fire. The expected values for the population risk in person-Sv for both a maritime and road transport are low radiological risk activities with manageable safety and health consequences. According to the results for both the maritime and road transport, the number of journeys per year was found to be a very important factor if we transport the same number of transport casks for the spent fuels. Therefore, we have to reduce the number of journeys per year in order to reduce the population risks resulting from the accidents during a maritime transportation of the spent fuels. And the population risk shows the same value if we use the same transportation ship with the same amount of transportation casks. Among the accidents considered in this study during the maritime and road transportations, the population risks for the fire accident shows a minimum value of the population risk because the occurrence probability of the fire accident is the lowest and we use the same value for the release fraction. The results of this study can be used as basic data for the development of a safe and economical logistics system for a transportation of the spent fuels in Korea by considering the transportation costs for the four scenarios which will be needed in the near future.
539
Acknowledgement This project has been carried out under the Nuclear R&D Program by Ministry of Science and Technology in Korea. References Chen, S.Y. et al., 2002. A Resource Handbook on DOE Transportation Risk Assessment. DOE/EM/NTP/HB-01. Choi, J.W. et al., 2007. High-level Radwaste Disposal Technology Development. KAERI/RR-2765/2006. Fischer, L.E. et al., 1987. Shipping Container Response to Severe Highway and Railway Accident Conditions, NUREG/CR-4829, UCID-20733. Gauld, I.C., Hermann, O.W., 2005. SAS2: A Coupled One-dimensional Depletion and Shielding Analysis Module. ORNL/TM-2005/39. Version 5, vol. I, Oak Ridge National Laboratory. Gauld, I.C., Bpwman, S.M., Leal, L.C. et al., 2004. ORIGEN-ARP: Automatic Rapid Processing for Spent Fuel Depletion, Decay, and Source Term Analysis. NUREG/ CR-0200, Oak Ridge National Laboratory. Neuhauser, K.S., Kanipe, F.L., Weiner, R.F., 2000. RADTRAN5 Technical Manual. Sandia National Laboratory, SAND2000-1256. Nuclear and Radiation Studies Board (NRSB), 2006. Going the Distance? The Safe Transport of Spent Fuel and High-level Radioactive Wastes in the United States. National Academic Press. Sprung, J., Ammerman, D., 2003. Methods for the Assessment of Risk in the Sea Transport of Radioactive Material. IAEA-CN-101/60.