Worst Case Credible Nuclear Transportation Accidents: Analysis for Urban and Rural Nevada

Transcription

1 Worst Case Credible Nuclear Transportation Accidents: Analysis for Urban and Rural Nevada Matthew Lamb and Marvin Resnikoff, Ph.D. Radioactive Waste Management Associates And Richard Moore, P.E. August 2001 Radioactive Waste Management Associates 526 W. 26 th Street #517 New York, NY 10001

2 Table of Contents Executive Summary...i Introduction Accident Locations and Potential Radionuclide Releases...4 Accident Locations...4 Release Estimates...5 Postulated Release Fractions and Inventory...9 Severity of the Accidents Being Considered in this Analysis Downwind Radioactive Particulate Concentrations Las Vegas Specific Accident...15 Individual Dose and Surface Contamination Estimates...15 Population Dose Estimates for Las Vegas Accidents...20 Contamination Inside Hotels: A Hypothetical Example...25 Las Vegas Emergency Response and Evacuation...27 Las Vegas Decontamination...40 Other Factors Affecting Cleanup Cost Estimates Rural Truck Accident: West Wendover, Nevada...49 General Characteristics of West Wendover, Nevada...49 Individual Dose and Surface Contamination Estimates...49 Population Density Estimate...52 Contamination Inside Hotels: A Hypothetical Example Rural Rail Accident: Carlin, Nevada...58 General Characteristics of the Carlin Tunnel Region...58 Individual Dose and Surface Contamination Estimates...59 Population Density Estimate...61 Population Dose Estimate...61 Possible Contamination of the Humboldt River...63 Conclusions...67 References...71 Appendices A. Discussion of Severe Accident Release Estimates A-1 B. Category 6 Accident Contamination Charts B-1 C. Alternative Population Density Calculation C-1 D. Detailed Population Dose Calculations D-1 E. Estimation of Indoor Air Concentration E-1

3 Nevada Spent Fuel Transportation Severe Accident Analysis Page i Executive Summary If the proposed Yucca Mountain waste repository opens, a large number of irradiated fuel and high-level waste shipments will converge in Nevada. According to the Department of Energy (DOE), there could be between 23,000 and 96,000 shipments to Yucca Mountain over four decades 1. Depending on a range of factors, such as the eventual transportation mode and any safety precautions that may be required, hundreds of accidents are expected nationwide. Some of these accidents could result in release of radioactive materials. As prior reports prepared by RWMA for the State of Nevada show 2, DOE has systematically underestimated the potential human health impacts from severe accidents and completely ignored their potential economic impacts. The cost of cleanup, evacuation and business loss resulting from a severe accident in a generic urban area can range from several billion to several hundred billion dollars. An accident in a rural area will have a different set of consequences, but has the potential to be as devastating as an accident in a more populated area. Except for population density, the previous analyses were location-specific. In contrast, this study estimates site-specific accident consequences for select urban and rural locations in the State of Nevada. These were chosen based on the locations of proposed and likely truck and rail transportation corridors en route to the geologic repository at Yucca Mountain. For the urban scenarios, representative truck and rail locations were chosen in Las Vegas, a potential crossroads for fuel traveling to the proposed facility. The rural truck accident location was chosen to be near the Utah-Nevada border along I-80, in the town of West Wendover. The chosen rural rail location is at the Carlin Tunnel along the Union Pacific and Southern Pacific railroads in western Elko County. This study estimated the nature and amount of radioactivity that could be released from a spent fuel shipping cask in the event of a serious accident, based on industry literature. From these release estimates, we estimated the extent of contamination and the consequences to individuals and collective populations associated with this contamination. Based on extensive discussions with local emergency personnel, this report also discusses the likely response by emergency personnel to an accident of this nature. Finally, the report lays out the decontamination technologies available and comments on their cost and effectiveness. Each cask that would be shipped to Yucca Mountain contains an enormous inventory of radioactive material. Casks are designed to withstand all credible highway and rail accidents. Even a small release in terms of the fraction of the entire inventory that is released, such as those considered in this report, can lead to major health and economic consequences. Our calculations assumed average, site-specific meteorological conditions and wind speeds. We used standard computer software, such as HOTSPOT and RISKIND, to model downwind air and surface particulate concentrations. We further assumed a severe impact would 1 U.S. Department of Energy, Draft Environmental Impact Statement for a Geologic Repository of Spent Nuclear Fuel and High-Level Radioactive Waste at Yucca Mountain, Nye County, Nevada. (DOE/EIS-0250D). pp. J Lamb, M and M Resnikoff, Consequence Assessment of Severe Nuclear Transportation Accident in an Urban Environment, Radioactive Waste Management Associates, 5 July 2000 Radioactive Waste Management Associates

4 Nevada Spent Fuel Transportation Severe Accident Analysis Page ii lead to a ground level puff release of radioactive particulates. Our release estimates did consider the accident scenario involving fire-only conditions, which would result in a more protracted release of material and a higher effective release height. Near a transportation accident, this report estimates acute radiation doses due to inhalation of a passing radioactive cloud to be in the hundreds of rems close to the release location. This is a thousand times what a person receives from background radiation in a year. Thousands of people are likely to be in the downwind path. For example, this study estimated that over 138,000 persons would be affected by a severe rail accident releasing radioactive material in Las Vegas. Persons indoors would also be exposed. If ventilation systems were shut off, radioactive particulates would settle within hotels and other buildings, contaminating rugs, furniture, beds, and causing a radiation dose to those inside. Discussions with emergency personnel in Las Vegas and Clark County clearly indicate the accident would overwhelm local response capabilities. Before local emergency responders could accurately assess the problem, the radioactive plume would have already contaminated an extensive area. Radioactive particulates settling on roads and highways are likely to be spread by traffic, possibly contaminating distant locations and extending the area of contamination past that assumed in this study. This may result in the contamination of many more people than was estimated in this report. Given the high number of people exposed, local responders will be able to identify, let alone effectively quarantine, contaminated people. Thus, it will be extremely difficult to stop the spread of contamination. Initial decontamination efforts will probably be limited to emergency responders and people in the closest vicinity of the accidents. Decontamination of the affected population in general will be a massive effort. Evacuation will be difficult at best. Spontaneous evacuation by people in the contaminated area will probably occur in great numbers, making the targeted evacuations much more difficult to complete. At a minimum, the evacuation of highly contaminated areas would be necessary. For a rail accident, evacuation would have to be in a radius greater than one kilometer; this would represent a large number of people if the accident took place near the Las Vegas Strip. In the case of an accident in Las Vegas, consideration would have to be given to closing McCarren airport in order to prevent the migration of contaminated persons. Alternately, all passengers would have to be screened for contamination. This would require a huge amount of resources that could be better utilized dealing with the major issues. The incident would overwhelm the capability of the local medical community. Blood and urine samples of contaminated people should be taken to track the levels of contamination and exposure, but this would be very difficult given the number of contaminated and potentially contaminated individuals. Mental health resources would be overwhelmed as well. Unless radionuclides, particularly cesium, were removed from surfaces, remaining residents would be exposed for long time periods. Complete decontamination would be Radioactive Waste Management Associates

5 Nevada Spent Fuel Transportation Severe Accident Analysis Page iii prohibitively expensive and would also expose workers; a balance would take place between clean-up costs and long-term radiation exposures. In this report we chose the EPA s Protective Action Guide as a criteria for decontamination; assuming that a person should receive more than 5 rems over a 50-year period, including initial inhalation due to the passing cloud. If areas are decontaminated, we estimate between 6,000 and 41,000 latent cancer fatalities would result from exposure to radiation resulting from the rail accident in Las Vegas, depending on the risk model. If radioactive contaminants were remediated, there would be continuous direct gamma exposure to remaining residents. Further, this would result in a tremendous concomitant economic cost to the tourist industry. Social stigma costs are beyond the scope of this report. Using the economic model of RADTRAN 5, evacuation and decontamination costs could range to hundreds of billions of dollars. These potential costs greatly exceed the amount of insurance coverage held by nuclear utilities or the Department of Energy. This raises the question of how such an expensive endeavor would be financed. Government financing of clean-up would require an act of Congress, which would significantly delay remedial action. While the population densities are obviously lower in a rural area, an accident in West Wendover on I-80, or a rail accident near the Carlin tunnel, both in Northern Nevada, would also have serious consequences. I-80 is the main route into and out of West Wendover, as well as a major cross-country thoroughfare. An accident that spread radioactive contamination could cut off the exit and either leave cars trapped or have vehicles spread the contamination miles down the highway. This report calculates the accident consequences in West Wendover. A rail accident near the Carlin tunnel, in a canyon adjacent to the Humboldt River, would lead to contamination of the river bed and water for miles downstream and leading to accumulations in slowly moving sections of the river. Use of the river for recreation or drinking would be curtailed for years to come. This study shows the potentially disastrous consequences of an accident leading to the release of radioactive material from a spent fuel transportation cask. It also underscores the importance of preparation of emergency response for such an accident. Acknowledgement of the potential for disaster, even if the probabilities are high, is important in attempting to prepare for an unprecedented spent fuel transportation campaign. The tables below summarize the findings of this study. Table ES-1 presents a comparison of the Las Vegas accidents discussed in this study with the urban maximum reasonably foreseeable accident scenarios listed in the DEIS for the Yucca Mountain Facility. Table ES-2 presents a comparison of the rural accidents discussed in this study with the rural maximum reasonably foreseeable accident scenario listed in the DEIS for the Yucca Mountain Facility. The consequences estimated in this report are significantly higher than those estimated in the Yucca Mountain DEIS, primarily due to the assumption of a higher population density and an increased release fraction for cesium. Radioactive Waste Management Associates

6 Nevada Spent Fuel Transportation Severe Accident Analysis Page iv Table ES-1: Comparison of State of Nevada and Yucca Mountain EIS Consequence Assessments : Urban Accidents Urban Truck Accident Urban Rail Accident State of Nevada, Cat.5 a Acute (24-hour) Population Dose 846 (person-rem) b State of Nevada, Cat.6 a YM DEIS, Cat. 5 a YM DEIS, Cat. 6 a State of Nevada, Cat.5 a 26, , , ,931 12,771,207 29, , Expected Latent Cancer Fatalities c year Population Dose (personrem) b Expected Latent Cancer Fatalities c year Population Dose (person-rem) b Expected Latent Cancer Fatalities c 1,306 Dose to Maximally Exposed Individual (rem) d Area contaminated to greater than rem long-term dose (km 2 ) 6,386-40,868 State of Nevada, Cat.6 a YM DEIS, Cat. 5 a YM DEIS, Cat. 6 a 61, a. Release fractions are presented in Tables 1 and 2 of this report b. The Yucca Mountain DEIS assumed an urban population based on the average densities in successive 8-kilometer rings around the 21 largest cities in the continental U.S. The State of Nevada estimated the population of the Las Vegas MSA using data from the 2000 U.S. Census, and with the methodology explained in Section 3 of this report. c. The Expected Latent Cancer Fatalities, and the probability of increasing a latent cancer fatality, are in the Yucca Mountain DEIS assuming a value of LCFs per person-rem exposure. The State of Nevada presents a range of latent cancer fatalities based on the value of LCFs per person-rem exposure. See Section 3, under "Population Dose Estimates for Las Vegas Accidents." d. The Maximally Exposed Individual was assumed to be located 360 meters downwind of the release in the Yucca Mountain DEIS (pp. 6-31). For comparison, the State of Nevada made the same assumption. Radioactive Waste Management Associates

7 Nevada Spent Fuel Transportation Severe Accident Analysis Page v Table ES-2: Comparison of State of Nevada and Yucca Mountain EIS Consequence Assessments : Rural Accidents Rural Truck Accident Rural Rail Accident State of Nevada, Cat.5 a Acute (24-hour) Population Dose 799 (person-rem) b Expected Latent Cancer Fatalities c year Population Dose (person- 27,886 rem) b Expected Latent Cancer Fatalities c year Population Dose 388,326 (person-rem) b State of Nevada, Cat.6 a YM DEIS, Cat. 5 a YM DEIS, Cat. 6 a State of Nevada, Cat.5 a , ,859 State of Nevada, Cat.6 a YM DEIS, Cat. 5 a YM DEIS, Cat. 6 a Expected Latent 194- Cancer Fatalities c ,243 Dose to Maximally Exposed Individual (rem) d Area contaminated to greater than rem long-term dose (km 2 ) a. Release fractions are presented in Tables 1 and 2 of this report b. The Yucca Mountain DEIS assumed a rural population based on national averages for a representative rail route. The State of Nevada estimated the rural truck population based on West Wendover, Nevada, and the rural rail population based on Elko, Nevada. See Sections 4 and 5 of this report. c. The Expected Latent Cancer Fatalities, and the probability of increasing a latent cancer fatality, are in the Yucca Mountain DEIS assuming a value of LCFs per person-rem exposure. The State of Nevada presents a range of latent cancer fatalities based on the value of LCFs per person-rem exposure. d. The Maximally Exposed Individual was assumed to be located 360 meters downwind of the release in the Yucca Mountain DEIS (pp. 6-31). For comparison, the State of Nevada made the same assumption. Radioactive Waste Management Associates

8 Nevada Spent Fuel Transportation Severe Accident Analysis Page 1 Introduction If the proposed Yucca Mountain waste repository opens, a large number of irradiated fuel and high-level waste shipments will converge in Nevada. According to the Department of Energy (DOE), there could be between 23,000 and 96,000 shipments to Yucca Mountain over four decades 3. Depending on a range of factors, such as the eventual transportation mode and any safety precautions that may be required, hundreds of accidents are expected nationwide. Some of these accidents could result in release of radioactive materials. DOE has estimated that a maximum reasonably foreseeable truck or rail accident could release enough radioactive materials to cause 4 to 31 latent cancer fatalities. DOE estimates the probability of such accidents at 1.4 to 1.9 in 10 million per year. 4 RWMA has previously evaluated DOE's accident consequence estimates. As prior reports prepared for the State of Nevada show 5, DOE has systematically underestimated the likely human health impacts of severe accident. Moreover, DOE has completely ignored the potential economic impacts of severe accidents. The cost of cleanup, evacuation and business loss resulting from a severe accident in a generic urban area can range from several billion to several hundred billion dollars. An accident in a rural area will have a different set of consequences, but has the potential to be as devastating as an accident in a more populated area. Except for population density, the previous analyses were location-specific. Assuming average weather conditions, average population density and a selected accident severity, the health effects and economic consequences were using standard computer models, such RADTRAN4 6 and RISKIND 7 and their associated economic models. The accidents assumed in the previous analyses were the maximum reasonably foreseeable accident scenario for rail and truck shipments as defined by the Department of Energy (DOE) in the draft Environmental Impact Statement (EIS) 8 for the proposed geologic repository at Yucca Mountain, Nevada. Our previous studies did investigate specific accident locations or specific details about evacuation and decontamination following an accident. This study estimates site-specific accident consequences for select urban and rural locations in the State of Nevada. These were chosen based on the locations of proposed and likely truck and rail transportation corridors en route to the geologic repository at Yucca Mountain. For the urban scenarios, representative truck and rail locations were chosen in Las Vegas, a potential crossroads for fuel traveling to the proposed facility. The rural truck accident location was chosen to be near the Utah-Nevada border along I-80, in the town of West 3 U.S. Department of Energy, Draft Environmental Impact Statement for a Geologic Repository of Spent Nuclear Fuel and High-Level Radioactive Waste at Yucca Mountain, Nye County, Nevada. (DOE/EIS-0250D). pp. J Ibid., pp to Lamb, M and M Resnikoff, Consequence Assessment of Severe Nuclear Transportation Accident in an Urban Environment, Radioactive Waste Management Associates, 5 July Neuhauser and Kanipe, User s Guide for RADTRAN 4. SAND , Sandia National Laboratories. 7 Yuan et al, RISKIND: A Computer Program for Calculating Radiological Consequences and Health Risks from Transportation of Spent Nuclear Fuel. ANL/EAD-1. Argonne National Laboratory. 8 U.S. Department of Energy, Draft Environmental Impact Statement for a Geologic Repository of Spent Nuclear Fuel and High-Level Radioactive Waste at Yucca Mountain, Nye County, Nevada. (DOE/EIS-0250D). Radioactive Waste Management Associates

9 Nevada Spent Fuel Transportation Severe Accident Analysis Page 2 Wendover. The chosen rural rail location is at the Carlin Tunnel along the Union Pacific and Southern Pacific railroads in western Elko County. The Las Vegas urban area is an interesting choice for a location-specific accident scenario because it has very unusual, if unique, economic and demographic characteristics. Potential highway and rail routes to Yucca Mountain traverse the downtown Las Vegas area known worldwide for its large casinos and resort hotels. High population densities are seen at each of the major hotels. A large hotel could contain as many as 10,000 guests and 2,000 employees 9. Many hotels and casinos are less than one-half mile from a potential shipping route, and some hotel properties are physically adjacent to proposed routes to Yucca Mountain. Las Vegas is one of the premiere tourist destinations in the country, attracting nearly 36 million visitors in the year 2000, filling approximately 125,000 hotel rooms 10. In the event of a radioactive release, evacuation would be difficult, owing to the highly transient population, the fact that many visitors would have access to a vehicle, and the concentration of people in a relatively small area. The total time an area remains evacuated may be lengthy while cleanup proceeds. As the center of Nevada s most important industry, any accident resulting in the closure of large casinos, even if temporarily, will have cascading effects on the economic wellbeing of residents, local governments and the State. Other aspects of Las Vegas unique nature make calculation of health effects very difficult. It can be ascertained at this point whether, for example, a large hotel downwind from a radioactive release would be able to shut off its ventilation system in time to prevent contaminated air from entering the building. If the ventilation system were shut off too late, it would have the effect of trapping radioactive material inside the hotel. On the other hand, given sufficient time to shut off the air intakes to a hotel, the immediate consequences of a release could be reduced. This report addresses these issues. The rural areas we investigate also exhibit characteristics that could result in very severe radiological accident impacts. The evacuation routes are limited, in some cases limited to one highway. Blockage of an entire direction of evacuation due to a radioactive release would significantly inhibit migration. Water supplies may be close to highways and railroads, creating the possibility of contamination of drinking water. Emergency response capabilities are very limited, compared to urban centers. In addition, the highway and railway characteristics in rural areas may present conditions that allow greater release of radioactive materials, such as increased travel speeds, steep grades and bare rock surfaces. In this study, specific analyses of severe, yet credible highway and rail accidents at specific locations within the State of Nevada are undertaken. Because of the uncertainty in the mode of transportation to be ultimately used, as well as the vast demographic and geographic differences among likely transportation corridors in Nevada, this study will provide separate consequence assessments for 4 accident scenarios: A severe truck accident and a severe rail accident involving the transportation of spent nuclear fuel through the metropolitan area of Las Vegas, a severe truck accident in the town of West Wendover, near the Nevada-Utah border, and a severe rail accident at the Carlin Tunnel, near the city of Carlin along the Union Pacific and Southern Pacific railroads. At the heart of this study will be an estimation of the breadth and 9 The MGM Grand Hotel has 5,034 rooms. Assuming 2 persons per room, it could contain 10,000 guests at full occupancy. According to the Las Vegas Sun (8/13/2000, Casinos Compete for Job Hopping Workers, the MGM Grand has 8,000 employees. This study assumes 25% of these employees are working at any given time. 10 Las Vegas Convention and Visitors Authority 2000 Executive Summary. Radioactive Waste Management Associates

10 Nevada Spent Fuel Transportation Severe Accident Analysis Page 3 depth of contamination under each scenario and an evaluation of the real ability and cost to evacuate and decontaminate the exposed areas. These evaluations will necessarily focus on different factors for the rural and urban areas. We first must assess what is a credible accident at the specific chosen locations. In Las Vegas, population densities might be high at specific potential accident locations, but vehicle speeds may be low. That is, at certain locations, a potential accident might be sufficiently severe to lead to a release of radioactive particulates. Or, high impact accidents may be possible at specific locations, but the population density may be low. In Section 1, we discuss the specific locations we considered for potential accidents, and the type of accidents that are credible at those locations. For each of these accidents, we discuss the radionuclide inventory that may be released. In Section 2, we discuss the downwind radioactive particulate and gas concentrations in air and surface concentrations of particulates. This information is used to estimate the potential inhalation exposures to individuals outside and within buildings, and the direct gamma dose rates due to deposited radionuclides. The information is also used to determine potential remediation alternatives and economic costs. In Section 3 we discuss the specific situation in Las Vegas for truck and train accidents. We estimate the population density in the tourist areas of Las Vegas, and the health impact to visitors outside and within hotels. We also estimate the surface concentrations inside and outside hotels and the effort and cost to decontaminate horizontal (streets, sidewalks) and vertical (side of buildings) surfaces. This section also investigates the ability to evacuate residents and visitors. In Section 4, we discuss the specific situation for truck and train accidents in rural areas of Northern Nevada. Radioactive Waste Management Associates

11 Nevada Spent Fuel Transportation Severe Accident Analysis Page 4 1. Accident Locations and Potential Radionuclide Releases Accident Locations Together with Robert Halstead, Nevada Nuclear Waste Projects Office, we investigated potential accident locations in greater Las Vegas and in select rural areas in northern Nevada. The chosen locations provide a range of potential severe accident scenarios, from the highdensity areas along the Las Vegas Strip to the relatively remote areas near the Carlin Tunnel. The decision to perform a consequence assessment for an accident occurring at a specific location was made in order to provide a hypothetical exercise with which to estimate damages and test the capacity of emergency response. Obviously, it is impossible to predict the precise location of an accident, its severity, and the meteorological conditions at the time of the accident. However, it is instructive to provide a hypothetical scenario as a representative possibility of what could happen if there is a severe accident at various points in Nevada. Because we are suggesting that an accident will happen at the locations chosen, analysis of specific entities, such as potential indoor building contamination, is treated generically. For example, a representative hotel is modeled to estimate what the consequences could be in the event of an accident. Keeping in mind that the chosen locations are intended to be representative, and that this study is in no way predicting the location of accidents, we investigate the following scenarios: Clark County/Las Vegas Potential Accident Locations Truck: A. The chosen location is at the interchange of Interstates I-80 and I-15 in Las Vegas, referred to as the spaghetti bowl. More specifically, the scenario will involve a truck traveling on I-15 going into the spaghetti bowl. Speeds at this location can approach 70 miles per hour, and there is the possibility of a severe crash into a bridge abutment, a fall from an elevated highway structure, and/or collision with other vehicles hauling gasoline or other hazardous materials. Wind data from the McCarran International Airport is employed to obtain an average wind direction, speed, and stability category (see Figure 1). Rail: B. The chosen location is on a stretch of the Union Pacific rail line between Flamingo Avenue and Spring Mountain Road. Along this stretch, the UP goes underneath I-15, and at one point is approximately 20 feet from the parking lot of a hotel. Potential accident scenarios include derailment of a runaway train and/or collision with a train hauling explosive or flammable materials. There is a petroleum pipeline running alongside the railroad tracks at this point, creating the possibility for a severe thermal environment in the event of an accident. The same meteorological data which is used in the truck accident scenario is also employed here. Rural Counties/Potential Accident Locations Radioactive Waste Management Associates

12 Nevada Spent Fuel Transportation Severe Accident Analysis Page 5 Truck: C. The chosen location of the severe rural truck accident is on I-80 near the Utah/Nevada border, at the West Wendover exit. Due to the relatively remote nature of this location, trucks can be expected to travel at fairly high speeds, giving the possibility of a severe impact scenario. Westbound trucks have been observed traveling 55 to 65 mph at this location, and eastbound trucks have been observed traveling at 65 to 75 mph. The short distance and absence of dividers between the east- and westbound lanes creates the possibility for high-speed, head-on collisions 11. Rocky outcroppings along the westbound highway wayside create the possibility of an impact collision onto a hard surface. Wind data was obtained from the Wendover Air Field in Utah, very close to the potential accident location. Because of the geography near the location (salt flats to the east and mountains to the west), the most likely wind direction is out of the east. Figure 2 presents the wind rose used to obtain average meteorological conditions for this location. Rail: D. The chosen location of the severe rural rail accident is on the Union Pacific and Southern Pacific lines that run near I-80 in Elko County at the entrance to the Carlin Tunnel. This accident location has been chosen because it is upwind of farming areas, a major river, and the City of Elko. An accident at this location would also likely cause the closure of I-80. Hazardous materials are routinely shipped along this route, including tanker shipments of propane to a terminal at Beowawe. In the event of a derailment involving cars containing flammable materials, the tunnel creates the possibility of a long-duration fire. Wind data was obtained from the Elko Airport in Elko, approximately 20 miles to the northeast of the proposed accident location. Figure 3 presents the wind rose used to obtain average meteorological conditions for this location. Release Estimates The question of how much radioactivity may be released in an accident of a given severity is a contentious one. Currently, there are no plans to physically test to destruction the transportation casks likely to be used for the transcontinental spent fuel shipping campaign to the proposed facility at Yucca Mountain. Instead, several studies have been conducted by the Nuclear Regulatory Commission or its contractors to estimate cask response to accident conditions using computer modeling. Different studies have focused on different criteria for correlating accident severity with cask damage. For example, one NRC-contracted research team correlated cask damage with strain to the inner cask wall 12, while a more recent study by Sandia National Laboratory primarily focused on the bolts and seal in the lid region of the cask. 13 For this study, we have elected to use the cask response estimates derived by the Modal Study 11 Personal Communication with Robert Halstead, Nevada Nuclear Waste Projects Office, 8/29/ Fischer, LE, et al, Shipping Container Response to Severe Highway and Rail Accident Conditions: Main Report (Technical Report), Lawrence Livermore National Laboratory, NUREG/CR-4829-v1-v2, February Referred to as The Modal Study in this report. 13 Sprung, JL et al, Reexamination of Spent Fuel Shipping Risks Estimates, Sandia National Laboratories, NUREG/CR-6672, March 2000 Radioactive Waste Management Associates

13 Nevada Spent Fuel Transportation Severe Accident Analysis Page 6 with certain modifications to account for information obtained since its publication. The Sandia study, referred to as NUREG/CR-6672, was used in this report for reasons discussed below and in Appendix A, even though the focus on the bolts is considered an improvement over the Modal Study. The more recent NRC-sanctioned cask response study, NUREG/CR-6672, contains certain flaws which result in a non-conservative estimation of container response to severe stresses. In its peer review of NUREG/CR-6672, Lawrence Livermore National Laboratory (LLNL), the researchers for the Modal Study, have raised valid criticisms regarding the modeling of the bolt and seal area of the lid which are critical to the size opening during an accident and the amount of radioactivity released. In particular, when predicting strain on the seal regions and the bolts, NUREG/CR-6672 did explicitly model the grooved region between the cask lid and the lid well. Rather, it estimated the deformation at a location near where the O-rings would be located. 14 Further, the modeling assumed that the cask wall and lid are much stiffer than the closure bolts, and the opening displacements are the result of displacement discontinuities between the cask body and lid, and are greatly affected by bolt clamping force. 15 We agree with LLNL that the model of the bolt region is overconstrained and underpredicts the size of the potential opening under stress. Underpredicting the size of the caskto-environment leak opening has cascading effects on the estimation of releases in the event of an accident. A more detailed discussion of our criticisms of NUREG/CR-6672 appears in Appendix A. The Modal Study release estimates were therefore used, with important modifications to account for information obtained since its publication. These modifications are discussed below, according to the three barriers that must be breached for a radioactive release to the environment to occur. Fuel Matrix When fuel is heated in reactors, a percentage of volatile radionuclides, such as cesium, will migrate out of the fuel matrix under the influence of temperature gradients and concentrate in the fuel-clad gap. 16 This gap cesium inventory is directly related to the release fraction in the event of an accident because it can be released in the event of any cladding breach. In fact, virtually all of the cesium released from the fuel in the event of a spent fuel shipping accident will be this gap cesium. For the fuel matrix, the Modal Study assumes 0.3% of the cask inventory of cesium will be present between the cladding and the fuel pellet. 17 However, for reasons discussed in Appendix A, we believe that the estimate made by Gray et al (9.9% gap cesium inventory) is on more solid experimental ground. Assuming the cesium release fraction is directly proportional to the gap inventory, we intend to increase the release fraction posited in the Modal Study by a factor of 33. For particulates and gases, other release fractions apply, as discussed below. 14 NUREG/CR-6672, pg ibid. 16 Gray and Wilson, Spent Fuel Dissolution Studies, FY1994 to Pacific Northwest Laboratories. PNL-10540, The Modal Study uses the results of experiments recorded in : SAND , Sanders et al. A Method for Determining the Spent Fuel Contribution to Transport Cask Containment Requirements. Sandia National Laboratories. Radioactive Waste Management Associates

14 Nevada Spent Fuel Transportation Severe Accident Analysis Page 7 In addition, the Modal Study does adequately consider CRUD spallation in the event of an accident. In our analysis, we assume an independent estimate for this source term, using the procedure outlined in the RISKIND User s Manual 18. Rod Cladding Breach A rod cladding breach could be caused by an impact or internal rod pressure due to high temperature. We discuss impact and fuel temperature breaches separately. Impact Contrary to the discussion in the Topical Safety Analysis Report for the HI-STAR transportation cask 19 and physical intuition, the Modal Study assumes the rods are most susceptible to breach in an end-on impact 20. Figure 8-3 in the Modal Study presents the researchers assumption that 3% of fuel rods break at a strain of 0.2% on the cask inner shell, that is, acceleration < 40g. 10% are assumed to break in under 2% strain (>40g), and all rods are assumed to break for the most severe category, loads >100g. The analysis presented in the Holtec Topical Safety Analysis Report, conversely, assumes that a sideways impact > 63g is sufficient to shatter the cladding. All impact accidents we consider here have a deceleration greater than 63g. Therefore, we assume that 100% of the cladding is shattered by impact under the accident conditions considered. Burst Rupture For a burst rupture due to high temperature and internal pressure, the Modal Study assumes no breach for mid-thickness temperatures less than 650 o F, and 100% breach for temperatures greater than 650 o F. 21 For temperatures greater than 400 o F, fuel oxidation can occur under aerobic conditions, and UO 2 oxidizes to U 3 O 8. Oxidation releases additional amounts of cesium and creates particulates. We discuss the potential fire duration necessary to cause burst rupture below. Cask Opening The Modal Study assumes all radioactive material released from a fuel rod into the cask cavity is released if a leak path exists in the containment cask, and it further assumes a leak path exists for any accident with maximum strain > 0.2% or lead mid-thickness temperature > 500 o F. 22 Under the accident classification scheme adopted by the Yucca Mountain draft EIS, the temperature of the mid-lead thickness of a cask must exceed 650 o F for a Category 4 accident. For a Category 5 accident, impact must produce strain > 2%. Both Category 4 and 5 accidents 18 Yuan et al. RISKIND-A Computer Program for Calculating Radiological Consequences and Health Risks from Transportation of Spent Nuclear Fuel. Argonne National Laboratories, ANL/EAD-1, Topical Safety Analysis Report for the HI-STAR 100 Cask System. Holtec Report No. HI , Modal Study, pg Modal Study, pg Modal Study, pg Radioactive Waste Management Associates

15 Nevada Spent Fuel Transportation Severe Accident Analysis Page 8 lead to identical cesium releases, according to the Modal Study, and both event types are considered plausible in the Las Vegas area and in the chosen locations of the rural accidents. Thermal Severity: Potential for Seal Failure The potential thermal severity of a given accident is a strong function of the location and circumstances surrounding it. The presence of a large source of flammable material is necessary to sustain a fire, since the spent fuel casks themselves are combustible. Collision with a rail tanker carrying flammable material, or the rupture of a petroleum or gas pipeline located near the crash site, are possible fuel sources for a long-duration fire. Of the accident locations chosen, the Las Vegas scenarios are located near potential sources of flammable material; therefore a hightemperature fire is a possibility. For the rural scenarios, the possibility that the rail could carry combustible material creates the possibility for a high-temperature, long-duration fire. The potential accident in West Wendover is less likely to be accompanied by a high-temperature fire, although this possibility can be ruled out. West Wendover is a major gasoline refueling site, so it is common for gasoline tankers to be near the site of the hypothetical accident. An accident could result in a fire raising the temperature of a steel-depleted uranium-steel cask above the temperatures causing seal degradation. The Modal Study considers seal degradation to begin at 500 o F. However, the seals used in current-generation casks differ from those modeled by the Modal Study. NUREG/CR-6672 presents temperature profiles for steel-du-steel cask subjected to long-duration engulfing fires of 800 o C and 1000 o C 23. Interpolating from this profile (1000 o C fire, the flame temperature of diesel fuel), we estimate that a steel-du-steel cask subjected to a 1000 o C engulfing fire would heat to 500 o F in approximately 25 minutes (41 minutes for an 800 o C fire). The above temperature limits are applicable to the GA-4 truck cask since the bolted closure uses a pair of ethylene propylene gaskets 24. These gaskets operate properly below 400 o F. A study performed by M. Greiner of the University of Nevada calculates the time to reach 400 o F based on fire temperature and cask condition. Since the impact limiter protects the cask seal region, the duration will depend on whether the cask is intact or the impact limiter is missing. According to this study, the time for the seal area to reach 400 o F is 2 hours for an intact cask in a 1000 o C fire, and only 0.4 hrs without the impact limiter. A fire of sufficient strength and duration necessary to degrade cask seals is considered plausible in all of the scenarios examined here. Thermal Severity: Potential for Cladding Failure Aher significant temperature criterion is the temperature required for fuel cladding to degrade. Greiner chooses 1100 o F. For an intact GA-4 truck cask, the cladding temperature would reach 1100 o F in 3 hours in a 1000 o C fire. Without a neutron shield, the time would be 0.9 hours. According to NUREG/CR-6672, a typical experimental pool fire with fuel from one tanker truck can last 60 minutes 25. Thus, fires resulting in casks exceeding 1100 o F are fairly 23 NUREG/CR-6672, Table Greiner, M, Spent Nuclear Fuel Shipping Cask Performance in Severe Accident Fires: Performance Envelope Analysis, Fire Environment Modeling and Full-Scale Physical Testing, U of Nevada, July 20, NUREG/CR-6672, pg. 6-6 Radioactive Waste Management Associates

16 Nevada Spent Fuel Transportation Severe Accident Analysis Page 9 rare, needing a significant source of very high-burning fuel. For our analysis, we consider the possibility of a post-accident thermal environment to cause cask cladding to degrade to be small. It should be ed, however, that the proximity of petroleum and gas pipelines to the Las Vegas rail accident location suggests that this type of accident would be possible at this location. Structural Severity According to the Modal Study, Category 5 accidents produce greater than a 2% strain on the cask inner wall, and Category 6 accidents produce strain greater than 30%. The Modal Study estimated that a 2% strain on the cask inner wall could occur in an end-on impact with an unyielding target at a velocity of 46 mph 26. For a truck cask, a 30% strain on the cask inner wall could occur in an end-on impact with an unyielding target at a velocity of 76 mph 27. A 2% strain assuming a side impact with a train sill (or similar immovable object such as a bridge abutment) could occur at a speed of 20 mph 28. For a rail cask, the minimum side impact speed would be 27 mph. A 30% strain due to side impact would occur at 105 mph (train) or 150 mph (truck). In our opinion, the accident speeds required to produce a 2% strain are plausible in Las Vegas and in rural counties. The category 6 accidents, requiring substantial stresses and thermal loads, were considered by the Department of Energy in its analysis of the maximum reasonably foreseeable accident scenario. For comparison, we will also provide an analysis of this type of accident. Postulated Release Fractions and Inventory To estimate the release fractions to be used in this study, we take the results from the Modal Study accidents corresponding to severity category 5 as used in the Yucca Mountain DEIS, correcting for the additional cesium believed to be in the fuel-cladding gap. Table 1 summarizes differences between the assumptions in this report and those made for the Yucca Mountain DEIS. Table 2 presents the release fractions used in this report, along with a comparison to those used in the Yucca Mountain DEIS. Table 3 presents the amount of material released under the various scenarios listed in Table Modal Study, pg ibid. 28 Modal Study, Table 6.3 Radioactive Waste Management Associates

17 Nevada Spent Fuel Transportation Severe Accident Analysis Page 10 Table 1: Comparison of accident scenarios used in this study with those used in the Yucca Mountain DEIS Yucca Mountain DEIS Maximum Reasonably Foreseeable accident scenario based on probability Risk and Consequence Assessments performed Estimated consequences for severity category 6 truck and accidents in urban locations and a severity category 6 truck accident in a rural location 26 year-cooled PWR fuel having a burnup of 39,560 MWD/MTU assumed 0.3% of cesium inventory assumed in Fuel- Clad Gap Meteorological conditions based on national averages CRUD inventory explicitly modeled This Study No estimate of probability Consequence Assessment only Estimated consequences for severity category 5 and 6 truck and rail accidents in urban and rural locations 5 year-cooled PWR fuel having a burnup of 39,560 MWD/MTU assumed 9.9% of cesium inventory assumed in Fuel-Clad gap Site-specific meteorological averages used Assumes that all CRUD is released to environment in the event of a rod failure No discussion of economic impacts Economic impacts, including cost of decontamination and evacuation, discussed Table 2: Comparison of Various Release Fractions for Severe Spent Fuel Transportation Accidents Release Fractions Category 5 Category 6 Radionuclide YMEIS State of Nevada* YMEIS State of Nevada* Class Inert gas 3.90E E E E-01 Iodine 4.30E E E E-02 Cesium 2.00E E E E-02 Ruthenium 4.80E E E E-04 Particulates 2.00E E E E-05 CRUD 1.00E E E E+00 *For these accidents, the Cesium release fractions are increased by a factor of 33 to account for the results of Gray et al regarding gap cesium inventory. Radioactive Waste Management Associates

18 Nevada Spent Fuel Transportation Severe Accident Analysis Page 11 Table 3: Release Estimates for Various Accident Severities Radionuclide Class Gas I Cs Ru Part. CRUD Truck Inventory * (Rail Inventory) 1.38E+04 (8.26E+04) 0.00E+00 (0.00E+00) 2.64E+05 (1.58E+06) 6.32E+04 (3.8E+05) 8.25E+05 (4.96E+06) 8.71E+03 (5.23E+04) Category 5 Truck Accident YMEIS State of Nevada Amount Released, Curies Category 6 Truck Accident YMEIS State of Nevada Category 5 Rail Accident YMEIS State of Nevada Category 6 Rail Accident YMEIS State of Nevada 5.39E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E+1 *Spent Fuel Inventory Assumes 5-year cooled PWR fuel having a burnup of 40,000 MWD/MTU. Truck casks are assumed to hold 4 PWR assemblies, and rail casks are assumed to hold 24 assemblies. It is important to e the decision to use 5-year cooled fuel for both the truck and rail accident scenarios. Currently, there are no licensed rail casks that are capable of shipping 5-year cooled fuel, and there are no casks in development to do so. However, it can be predicted whether such casks will be produced before fuel begins shipping to Yucca Mountain. Further, the recent issuance of a supplement to the Yucca Mountain DEIS 29 implies an abandonment of its oldest fuel first policy, proposing either the blending of hotter and cooler commercial spent nuclear fuel assemblies, the cooling of hotter fuel within an open, vented repository, or use of above-ground storage at the repository to cool fuel. To do any of these, hotter fuel will have to be shipped to the repository compared with the assumptions in the Yucca Mountain DEIS and the oldest fuel first policy. This results in the need for shipment of recently-discharged assemblies. For comparison, we used the RISKIND computer code to predict the release amounts and acute dose estimates for the Category 5 rail accident scenario. Assuming 10-year instead of 5- year cooled fuel results in a decrease in the acute dose by approximately 30%, and a decrease in the 50-year long-term dose by approximately 20%. Severity of the Accidents Being Considered in this Analysis In developing a consequence assessment of specific accidents occurring at specific locations, the usual probabilistic approaches to determining the maximum reasonably foreseeable accident scenario are irrelevant. It is impossible to predict the exact location and severity of any 29 U.S. Department of Energy, May Supplement to the Draft Environmental Impact Statement for a Geologic Repository for the Disposal of Spent Nuclear Fuel and High-Level Radioactive Waste at Yucca Mountain, Nye County, Nevada. DOE/EIS-0250D- S. Radioactive Waste Management Associates

19 Nevada Spent Fuel Transportation Severe Accident Analysis Page 12 accident, making discussions about the probability of the exact accidents described in this study moot. For example, in its draft Environmental Impact Statement for the proposed geologic repository at Yucca Mountain, the Department of Energy classified the maximum reasonably foreseeable accident to be the most severe accident having an annual probability of occurrence of at least 1 in 10 million per year 30, this probability being based on accident rates, meteorology, and certain route characteristics (such as the frequency of time spent in an urban environment throughout the shipping campaign). While we differ with DOE s probability analysis 31, this is an issue addressed in this report. For our analysis, we rely on the determination of whether a given accident is credible at the chosen locations. Because we can predict the exact conditions at the time of the hypothetical accident for each site, we have used a variety of average statistics, such as wind conditions and population densities. Therefore, our analysis does assess such worst conditions scenarios as a severe accident in Las Vegas during the peak visitor season, opting instead to present an average population density based on yearly statistics. For each accident scenario, we provide two separate consequence assessments: a category 5 and category 6 accident. The category 6 accident scenario is considered by the DOE to be most severe accident that could credibly happen en route to the Yucca Mountain Repository. For the specific accident locations chosen in this study, we concentrate on the category 5 accident scenarios, after judging them to be the most credible severe accidents (see our section entitled Release Estimates, above). Therefore, the accidents postulated in this report are worstcase scenarios in the sense that one could imagine a worse situation from happening. Rather, they are severe, yet credible, accidents, with the understanding that they are meant to be representative of the types of severe accidents that could happen in different areas of Nevada and the country. 30 YM DEIS at J See, e.g., Nevada Agency for Nuclear Projects, February, State of Nevada Comments on the U.S. Department of Energy s Draft Environmental Impact Statement for a Geologic Repository for the Disposal of Spent Nuclear Fuel and High-Level Radioactive Waste at Yucca Mountain, Nye County, Nevada. Part 3, Specific Comments. pp Radioactive Waste Management Associates

20 Nevada Spent Fuel Transportation Severe Accident Analysis Page Downwind Radioactive Particulate Concentrations Based on the release estimates made in the previous section, we next estimate the downwind air and surface concentrations of radioactive particulates and gases resulting from the hypothetical accident scenarios. In a severe truck or rail accident, radioactive particulates and gases would be released and wafted downwind. People downwind and outdoors would then inhale these particulates and receive a radiation dose. Depending on the actions taken by emergency response officials and building personnel, persons inside buildings may or may receive a radiation dose due to inhaling particulates from the passing radiation cloud. If ventilation systems remain open during the passage of the radioactive cloud, we also calculate the inhalation doses and surface contamination within a large building or hotel. Particulates would settle on the ground, plants and surface streams. Gamma radiation emanating from the ground (groundshine) would also give rise to a radiation dose, the amount depending on the ground concentrations and the length of time a person remains in the contaminated area. In this study, we calculate the estimated air and ground deposition concentrations resulting from the release of spent nuclear fuel particulates and radioactive gas resulting from the four accident scenarios described above. From the air concentrations, we estimate the amount of radioactivity inhaled and the potential radioactive dose. From the ground concentrations, we determine the direct gamma exposure (groundshine) and discuss the nature and extent of the surface contamination. It must be ed that the behavior of the plume following the release of radioactive material will differ depending on the presence or absence of a hot thermal environment. For our analysis, we have essentially assumed a ground-level puff release with a moderate effective release height. A high-temperature fire would raise the effective release height, thereby reducing the contamination near the accident scene but spreading it out over a larger area. A fire-only accident (without a collision) would lead to continued volatilization of cesium and a more gradual release of radioactivity than assumed in our calculations, which considered an instantaneous release. Two computer programs, RISKIND 32 and HotSpot 33, were used to develop contaminant plumes for the four accident scenarios. RISKIND was developed at Argonne National Laboratories and designed to estimate the risks and consequences of spent fuel shipping accidents. HotSpot was developed at Lawrence Livermore National Laboratories and is used to estimate levels of airborne radioactivity and radioactive contamination following an accident. Both use standard Gaussian plume dispersion equations to estimate airborne concentrations and ground deposition of radionuclides. The spent nuclear fuel inventory obtained from RISKIND was used to develop the spent fuel inventory for use in both computer simulations. HotSpot is useful because the meteorology (wind speed, stability class, and direction) can be inputted and the program will develop contaminant plumes that can then be imported into GIS software and displayed on maps of Las Vegas and northern Nevada. The meteorological conditions used were inferred from data collected from the closest available center. For the Las 32. Yuan et al. RISKIND-A Computer Program for Calculating Radiological Consequences and Health Risks from Transportation of Spent Nuclear Fuel. Argonne National Laboratories, ANL/EAD-1, Hotspot Health Physics Code, Version Lawrence Livermore National Laboratory. Steven G. Homann, contact. Radioactive Waste Management Associates