Studies of evaluation basis accidents (EBA) and beyond evaluation basis accidents (BEBA) have been performed for the downsized weapons assembly/disassembly (A/D) operations. The studies postulated a set of accident scenarios that were representative of the risks and consequences for workers and the public from operations. Although not all potential accidents were addressed, those that were postulated have consequences and risks that are expected to envelop the consequences and risks of an operating facility.
The accident analyses in this PEIS have been closely coordinated with the Pantex Site-Wide EIS to ensure consistency. The Pantex Site-Wide EIS is a more detailed evaluation of the Pantex Plant (Pantex) operations than this PEIS. Consequently, if there are any differences between the two documents, this PEIS defers to the Pantex Site-Wide EIS as the more accurate analysis of potential impacts from accidents.
A range of hazardous conditions and potential accidents were reviewed as candidates for estimating the risks to workers and the public from operating this facility. Through a screening process, several evaluation basis and beyond evaluation basis accidents were selected for further definition and analysis. A brief description of each of the six accident scenarios and source terms is presented below. Table F.2.1.1-1 presents a summary of each accident scenario and source term. Further detail can be found in a topical report (HNUS 1996a).
Pantex Plant.
Pantex is located approximately 13.6 km (8.5 mi) from the northeast-southwest runway at Amarillo International Airport. The scenario involving aircraft impact considers an impact into a cell or bay, possibly causing a fire and subsequent detonation of high explosive (HE) with burning plutonium, or pit damage from debris. An assessment of the probability of aircraft impact into Pantex structures has been prepared for the Draft Environmental Impact Statement for the Continued Operation of the Pantex Plant and Associated Storage of Nuclear Weapons Components (DOE/EIS-0225D, March 1996). Based on existing information, aircraft impact into an assembly cell or bay buildings and the release of hazardous material is considered a credible but extremely unlikely event with an estimated probability in the range of 1x10-7 to 5x10-6/yr. For calculation purposes a value of 8x10-7/yr is assumed. A high-speed military aircraft or a large commercial aircraft crashing into a single facility could cause sufficient damage to release plutonium. The degree of damage incurred and any subsequent release of radioactive materials depends on the size and speed of the aircraft involved, among other factors. The impacts of an aircraft crash into a stockpile stewardship and management weapons A/D Facility are based on an analysis performed for the Pantex Site-Wide EIS of an aircraft crash into Zone 4 and Zone 12 facilities. Since stockpile stewardship and management facilities are only in Zone 12, the Pantex Site-Wide EIS impacts were scaled to 28 percent of the public risk, and 61 percent of the maximum offsite individual risk. For the noninvolved worker, the Pantex Site-Wide EIS estimates that a worker at 100 m (328 ft) will not survive the aircraft crash effects. For the
Stockpile Stewardship and Management PEIS
, the noninvolved worker is assumed to be at 1,000 m (3,281 ft) and survives the crash. The accident consequences and risks to the noninvolved worker and the maximally exposed individual are discussed in section F.2.1.2.
| Accident Scenario | Site | Accident Frequency (Per Year) | Total Material Released to Environment |
|---|---|---|---|
| 1. Aircraft impact and release | Pantex | 8x10-7 | 1 |
| NTS | <1x10-7 | Not applicable | |
| 2. Explosive dispersal of plutonium from high explosives detonation in cell or bay | Pantex | 5.7x10-6 | 62 g to 5,000 g plutonium2 metal |
| NTS | 5.7x10-6 | 96 g to 5,000 g plutonium2metal | |
| 3. Mechanical release due to pit drop or impact of forklift breaching pit cladding | Pantex | 7.8x10-3 | 6x10-5 g plutonium metal |
| NTS | 7.8x10-3 | 6x10-5 g plutonium metal | |
| 4. Inadvertent activation of explosive squib on tritium reservoir | Pantex | 0.02 | 1.8 g of tritium oxide and 18.2 g of elemental tritium |
| NTS | 0.02 | 1.8 g of tritium oxide and 18.2 g of elemental tritium | |
| 5. Operational fire-induced plutonium release | Pantex | 1x10-5 | 20 g plutonium oxide |
| NTS | 1x10-5 | 20 g plutonium oxide | |
| 6. Fire-induced release from tritium reservoirs in staging vault | Pantex | 4x10-7 | 600 g tritium oxide2 |
| NTS | 4x10-7 | 600 g tritium oxide2 |
Nevada Test Site. The probability of an aircraft impact into the downsized weapons A/D facilities is estimated at less than 10 -7 /yr and, in accordance with NEPA guidelines, does not have to be considered further.
Scenario 2: Explosive dispersal of plutonium from HE detonation in cell or bay. The combined probability of an explosive dispersal of plutonium in a bay (7x10-7/yr) or cell (5x10-6/yr) is 5.7x10 -6 /yr. This value is conservatively based on 2,000 weapons operations per year. The anticipated number of weapons operations per year is 300 for the downsize A/D mission at Pantex.
Scenario 2.1: Explosive dispersal of plutonium from high explosives detonation in an assembly bay. Explosive dispersal of a plutonium pit would be the greatest when HE is in direct contact with the pit during an explosion or fire. The explosion would blow off the roof and doors of the bay; thus, no material would be retained inside the structure. As a result, it is assumed that all of the respirable plutonium would be released into the environment.
Pantex Plant. For the purposes of this analysis, the release of respirable plutonium from a Pantex assembly bay is assumed to be 5,000 grams (g) (176 ounces [oz]). The probability of this accident is 7x10-7/yr.
Nevada Test Site. For the purposes of this analysis, the release of respirable plutonium from a Nevada Test Site (NTS) assembly bay is assumed to be 5,000 g (176 oz). The probability of this accident is 7x10-7 /yr.
Scenario 2.2: Explosive dispersal of plutonium from high explosives detonation in an assembly cell assuming no roof collapse. A detonation of less than 45 kilograms (kg) (100 pounds [lb]) (130 lb trinitrotoluene [TNT] equivalent) of HE is estimated to be the amount of HE that would not cause the roof of a gravel gertie cell at Pantex or NTS to at least partially collapse. The explosion, which would cause greater than atmospheric pressures, would exist in the cell for approximately 1 minute. Since the roof does not collapse, a large fraction of the plutonium would be retained by the intact structures. In the case of large detonations causing the cell roof to collapse, the estimated release and consequences are bounded by the case in which the roof does not collapse.
Pantex Plant. The calculated respirable release from a Pantex assembly cell for this scenario is estimated to be 62 g (2.2 oz) of plutonium. The probability of this accident is 5x10-6/yr.
Nevada Test Site. The total respirable release from the NTS assembly cell for this scenario is estimated to be 96 g (3.4 oz) of plutonium. The probability of this accident is 5x10-6/yr.
Scenario 3: Mechanical release due to dropping a pit and breaching the cladding. For the purposes of this analysis, a pit is generically defined as a 6.5-kg (14-lb) spherical shell clad in thin metal alloy. Operational scenarios that have the potential to release small quantities of plutonium include dropping a pit onto the floor, cracking the external cladding because of disassembly stress, hitting a pit with other equipment, pulling out a pit tube during A/D, and breaching a container and pit with a forklift. A pit drop accident is used to characterize the category of events leading to violation of pit integrity.
An event of this nature has occurred at Pantex, where a weapon cladding was cracked, resulting in localized contamination around the pit. In this instance, the airborne contamination was insufficient to actuate the radiation alarm, and the worker dose was less than 0.1 rem.
Pantex Plant. The probability of a pit drop or forklift impact accident with a small plutonium release to a cell or bay at Pantex is 7.8x10 -3 /yr. The total release to the environment is estimated to be 6x10-5 g of plutonium. Nevada Test Site. The probability of a pit drop or forklift impact accident with a small plutonium release to a cell or bay at NTS is 7.8x10 -3 /yr. The total release to the environment is estimated to be 6x10 -5 g of plutonium.
Scenario 4: Inadvertent activation of explosive squib on tritium reservoir. During assembly or disassembly of a nuclear explosive, conditions could be encountered in which an electro-explosive device is accidentally fired and releases tritium from a reservoir. There have been two events (one at a weapons complex and one at a military installation) in which a squib was inadvertently actuated, releasing tritium from a reservoir. Since the events occurred, added precautions have been implemented. For this scenario, the squib valve must fire, releasing tritium from the reservoir, and the stem tube must be breached or disconnected from the pit (the latter is a normal step of disassembly).
For the purposes of this analysis, a reservoir is assumed to contain 20 g (0.7 oz) of elemental tritium. The entire amount of this tritium is assumed to be released in gaseous form. (Only hydrogen tritide is considered in assessing of worker dose, because only about 1 percent of hydrogen tritide is converted to tritium oxide after 1 hour.) All elemental tritium is 100 percent respirable. The amount of tritium which becomes airborne in the cell or bay is thus 20 g (0.7 oz). Upon detecting tritium, the exhaust fans will continue to operate and exhaust tritium to the atmosphere. The potential offsite doses from the tritium release would depend on the extent of tritium oxidation, which is estimated to be 9 percent as a bounding limit.
Pantex Plant. The probability of inadvertent squib activation during operations in an assembly cell or bay is 0.02/yr. The total release is estimated to be 1.8 g (0.06 oz) of tritium oxide and 18.2 g (0.6 oz) of elemental tritium.
Nevada Test Site. The probability of inadvertent squib activation during operations in an assembly cell or bay is estimated to be the same as at Pantex with the same total release of 1.8 g (0.06 oz) of tritium oxide and 18.2 g (0.6 oz) of elemental tritium.
Scenario 5: Operational fire-induced plutonium dispersal. The metal-clad plutonium pits are designed to maintain their integrity for certain temperature levels but are not intended to function as barriers against release. The facilities (assembly cells or bays) that can have plutonium pits outside of their containers would likely remain intact in a fire not associated with an explosion. A bounding scenario for fire-induced plutonium dispersal assumes the radioactive material limit in a cell or bay is dispersed by fire with no containment.
Pantex Site. The probability of an operational fire-induced plutonium dispersal is 1x10 -5 /yr. The total material released is 20 g (0.7 oz) of plutonium oxide.
Nevada Test Site. The operational fire at Pantex is assumed to occur at NTS with the same frequency and release as at Pantex.
Scenario 6: Fire-induced release from tritium reservoirs in staging vault. In this scenario, an earthquake is assumed to cause a fire in the vault where in-process tritium reservoirs are stored. The fire causes 100 percent of the tritium reservoirs in the vault to fail, releasing its entire contents. In addition, it is assumed that the elemental tritium is completely oxidized by the fire.
Pantex Plant. The probability of a release of tritium from the Pantex A/D staging area is 4x10 -7 /yr. For the purposes of this analysis, the release is assumed to be 600 g (21 oz) of tritium oxide.
Nevada Test Site. It is assumed that this scenario at Pantex would be applicable at NTS. Therefore, the accident probability is 4x10 -7 /yr. For the purposes of this analysis, the release is assumed to be 600 g (21 oz) of tritium oxide.
Tables F.2.1.2-1 and F.2.1.2-2 list the set of accidents selected to represent consequences and risks to workers and the public from accidental releases of radioactive materials during operations at Pantex and NTS, respectively. For each accident, the table identifies the frequency of occurrence and the consequences to a hypothetical worker located 1,000 m (3,281 ft) from the accident, a hypothetical individual located at the nearest site boundary, and the public out to a distance of 80 km (50 mi). The risks of cancer fatality for the worker, the individual at the site boundary, and the public for the composite set of accidents are also shown.
| Noninvolved Worker at 1,000 Meters | Maximum Offsite Individual | Population to 80 Kilometers | |||||||
|---|---|---|---|---|---|---|---|---|---|
| Accident Scenario | Dose (rem) | Probability of Cancer Fatality3 | Dose (rem) | Probability of Cancer Fatalitya | Dose (person-rem) | Cancer Fatalities | Accident Frequency (per year) | ||
| 1. Aircraft impact and release 4 | 23 | 9.2x10-3 | 23 | 0.012 | 2.8x10 3 | 1.4 | 8.0x10 -7 | ||
| 2. Explosive dispersal of plutonium in cell or bay | 16.9 | 6.8x10 -3 | 12.9 | 6.5x10 -3 | 3.8x10 3 | 1.9 | 5.7x10 -6 | ||
| 3. Mechanical release from impact breach of pit cladding | 3.2x10 -6 | 1.3x10 -9 | 2.4x10 -6 | 1.2x10 -9 | 6.5x10 -4 | 3.2x10 -7 | 7.8x10 -3 | ||
| 4. Inadvertent activation of explosive squib on tritium reservoir | 9.7x10 -4 | 3.9x10 -7 | 7.4x10 -4 | 3.7x10 -7 | 0.20 | 9.9x10 -5 | 0.02 | ||
| 5. Operational fire-induced plutonium release | 0.52 | 2.1x10 -4 | 0.40 | 2.0x10 -4 | 107 | 0.054 | 1.0x10 -5 | ||
| 6. Fire-induced release from tritium reservoirs in staging vault4 | 0.31 | 1.2x10 -4 | 0.24 | 1.2x10 -4 | 66 | 0.033 | 4.0x10 -7 | ||
| Impacts for Composite Set of EBAs and BEBAs5 | |||||||||
| Expected consequences6 | 2.0x10-6 | 2.0x10 -6 | 5.2x10 -4 | ||||||
| Expected risk (per year) | 5.6x10 -8 | 5.6x10 -8 | 1.5x10 -5 | ||||||
| Impacts for Composite Set of EBAs | |||||||||
| Expected consequences6 | 1.7x10-6 | 1.7x10-6 | 4.8x10 -4 | ||||||
| Expected risk (per year) | 4.8x10 -8 | 4.6x10 -8 | 1.3x10 -5 | ||||||
| Impacts for Composite Set of BEBAs | |||||||||
| Expected consequences6 | 6.2x10-3 | 8.0x10-3 | 0.94 | ||||||
| Expected risk (per year) | 7.4x10-9 | 9.7x10-9 | 1.1x10-6 | ||||||
| Noninvolved Worker at 1,000 Meters | Maximum Offsite Individual | Population to 80 Kilometers | |||||||
|---|---|---|---|---|---|---|---|---|---|
| Accident Scenario | Dose (rem) | Probability of Cancer Fatality7 | Dose (rem) | Probability of Cancer Fatality | Dose (person-rem) | Cancer Fatalities | Accident Frequency (per year) | ||
| 1. Aircraft impact and release | 8 | 8 | 8 | 8 | 8 | 8 | 8 | ||
| 2. Explosive dispersal of plutonium in cell or bay | 26.1 | 0.01 | 2.3 | 1.1x10 -3 | 361 | 0.18 | 5.7x10 -6 | ||
| 3. Mechanical release from impact breach of pit cladding | 4.7x10 -6 | 1.9x10 -9 | 4.0x10 -7 | 2.0x10 -10 | 5.4x10 -5 | 2.7x10 -8 | 7.8x10 -3 | ||
| 4. Inadvertent activation of explosive squib on tritium reservoir | 1.4x10 -3 | 5.7x10 -7 | 1.2x10 -4 | 6.2x10 -8 | 0.016 | 8.1x10 -6 | 0.02 | ||
| 5. Operational fire-induced plutonium release | 0.77 | 3.1x10 -4 | 0.066 | 3.3x10 -5 | 8.9 | 4.4x10 -3 | 1.0x10 -5 | ||
| 6. Fire-induced release from tritium reservoirs in staging vault9 | 0.42 | 1.7x10 -4 | 0.038 | 1.9x10 -5 | 5.6 | 2.8x10 -3 | 4.0x10 -7 | ||
| Impacts of Composite Set of EBAs and BEBAs10 | |||||||||
| Expected consequences11 | 2.7x10 -6 | 2.9x10 -7 | 4.4x10 -5 | ||||||
| Expected risk (per year) | 7.4x10 -8 | 8.1x10 -9 | 1.2x10 -6 | ||||||
| Impacts for Composite Set of EBAs | |||||||||
| Expected consequences11 | 2.7x10-6 | 2.9x10-7 | 4.4x10-5 | ||||||
| Expected risk (per year) | 7.4x10 -8 | 8.1x10 -9 | 1.2x10-6 | ||||||
| Impacts for Composite Set of BEBAs | |||||||||
| Expected consequences11 | 1.7x10-4 | 1.9x10-5 | 2.8x10 -3 | ||||||
| Expected risk (per year) | 6.7x10-11 | 7.7x10-12 | 1.1x10-9 | ||||||
1 For the aircraft crash accident, the Stockpile Stewardship and Management PEIS impacts are based on a percentage of the risks described in the Pantex Site-Wide Draft EIS. See the discussion under Scenario 1 in this section for additional details.
2 The maximum amount of material is a hypothetical amount chosen for the purposes of this analysis. HNUS 1996a.
3 Probability (increased likelihood) of cancer fatality to a hypothetical member of the public located at the site boundary or a worker located at 1,000 m (3,281 ft) from the accident as a result of exposure to the indicated dose if the accident occurred.
4 A beyond evaluation basis accident (BEBA). All other listed accidents are evaluation basis accidents (EBA).
5 For the offsite population of 285,409, the average probability of cancer fatality/risk of cancer fatality (per year) for the composite set of accidents is 1.8x10-9/5.3x10-11.
6 Result of exposure to the indicated dose if the accident occurs. All values are mean values. Model results.
7 Probability (increased likelihood) of cancer fatality to a hypothetical member of the public located at the site boundary or to a worker located 1,000 m (3,281 ft) from the accident as a result of exposure to the indicated dose if the accident occurred.
8 Not applicable. The probability of an aircraft crash is estimated to be lower than 10 -7 /yr.
9 A beyond evaluation basis accident (BEBA). All other listed accidents are evaluation basis accidents (EBA).
10 For the offsite population of 18,517, the average probability of cancer fatality/risk of cancer fatality (per year) for the composite set of accidents is 2.4x10-9/6.5x10-11.
11 Result of exposure to the indicated dose if the accident occurs. All values are mean values. Model results.