Aircraft accidents are a concern at Pantex Plant because of the volume of local air traffic, the proximity of Pantex Plant to flight paths into and from the Amarillo International Airport, and overflights. Even though the likelihood of an aircraft crash at Pantex Plant is small, a crash has the potential of releasing radioactive material from Pantex Plant facilities.
The number of annual air operations in the immediate vicinity of Pantex Plant is influenced by several factors. There is a regional air navigational aid, known as a Very High Frequency Omni-Directional Radio Range with Tactical Air Navigation (VORTAC), located within 8 kilometers (5 miles) of Pantex Plant. Because the air traffic in low-altitude and high-altitude air corridors is serviced by the VORTAC, it contributes to the air traffic in the vicinity of Pantex Plant. A significant number of military (primarily Air Force) aircraft conduct instrument approach and landing practice at the Amarillo International Airport. Furthermore, aerial application activities, such as crop dusting for several farm plots near Pantex Plant Site, add to the air traffic volume in the immediate vicinity of Pantex Plant.
The principal features of Pantex Plant are illustrated in Figure 184.108.40.206. With respect to aircraft accidents, the primary concern is with the 42 Steel Arch Construction (SAC) magazines and the 18 Modified Richmond magazines in Zone 4 West, and certain buildings in Zone 12. Figure 220.127.116.11 shows the layout of the 60 magazines in Zone 4 West (Pantex 1996a:3.1). Typically, no more than four persons work in a Zone 4 magazine. The Zone 4 Safety Analysis Report limits operations to seven personnel inside the magazine. Moreover, no more than five magazines (counting the A and B sides of the Modified Richmond magazines as separate magazines) can be open at any one time (DOE 1992b:8-21). The buildings of concern in Zone 12 are facilities containing nuclear weapons and nuclear weapon components. These include the bays and cells that represent nuclear explosive facilities, the special purpose buildings, and the Zone 12 staging facilities. A layout of Zone 12 South is shown in Figure 18.104.22.168.
The current VORTAC location relative to Pantex Plant is illustrated on Figure 22.214.171.124-1 (DOE 1995h:16). Because this location is nearly centered on a line between Pantex Plant and Runway 22, aircraft using the VORTAC intercept the final approach course from the beacon in the vicinity of Pantex Plant and pass over it in a straight line toward the runway. Aircraft using the airports Instrument Landing System (ILS) utilize the signals from the Back Course Localizer (BCL). This system guides the aircraft such that they fly over the northern portion of Zone 4. The BCL approach to Runway 22 is illustrated in Figure 126.96.36.199-2 (DOE 1995h:15).
There have been several previous assessments of the risk posed to Pantex Plant due to an aircraft crash. These analyses date back to a 1976 study conducted by Sandia National Laboratories. It should be noted that with the exception of the current analysis, all of the past studies conducted for Pantex Plant aircraft crash risk analyses have used the Solomon model with different data sets. A Safety Analysis Report (SAR) for Zone 4 was completed in 1993. The aircraft crash analysis from the Zone 4 SAR was incorporated into the Environmental Assessment for Zone 4, which was released in January 1994. This document resulted in a Finding of No Significant Impact (FONSI) for the interim storage of up to 12,000 pits in Zone 4.
At that time, the frequency of an aircraft crash into the storage bunkers, which could result in plutonium release, was reported to be 6.6 x 10-7, and thus termed "incredible". However, an Unreviewed Safety Question Determination (USQD) for the analysis contained in the Zone 4 SAR was issued in the spring of 1995. This determination questioned the validity of the aircraft overflight data used in the analysis. Additionally, the USQD found that the study used an incorrect application of the Solomon model. As part of the USQD, a corrected analysis was presented which gave a new probability of hitting a Zone 4 facility of approximately 2 x 10-5.
To obtain up-to-date aircraft overflight data for the study presented herein, DOE, with cooperation from the Federal Aviation Administration (FAA), installed a Radar Airspace Monitoring System (RAMS) at the Amarillo International Airport. This system collects data on the number and type of aircraft operations in the vicinity of Pantex Plant. These new data were used in this EIS to help evaluate the likelihood of an aircraft impact into Pantex Plant nuclear facilities. The new data are also being used to close out the USQD. The results of the past and current aircraft crash studies are presented in Table 188.8.131.52. As can be seen from these results, the trend for aircraft crash hit probability is in the low to mid 10-5 range.
From a risk perspective, the hit and release probabilities (Table 184.108.40.206, Hit and Release Probability column) are the values of interest rather than the hit probabilities alone. Analyses of this type tend to be conservative in nature due to the inherent uncertainties. It is difficult to quantify these conservatisms and as a result, the hit and release probabilities for the Final EIS should be considered a conservative point estimate. The issue of conservatism is discussed in section 4.15.7.
Due to public concern regarding the risk of aircraft crash at Pantex Plant, the Secretary of Energy committed DOE officials to meet with the City of Amarillo, FAA, the U.S. Air Force, and other stakeholders to discuss alternative civilian and military flight patterns. An Overflight Working Group was formed to address ways to reduce the number of aircraft flying over Pantex Plant. Their recommendations are listed below (DOE 1995h:12, 13, 18).
· Develop a Memorandum of Understanding (MOU) between DOEs Amarillo Area Office and the local FAA facility. The MOU would permit:
Establishment of a telephone "hot line" between the Approach Control Facility and DOEs Amarillo Area Office Emergency Operations Center. Improved communication would permit the FAA to warn DOE of aircraft nearby with in-flight emergencies. This would allow the plant to modify activities vulnerable to aircraft crashes (completed).
Modified vectoring of approaching aircraft. When aircraft safety will not be affected, air controllers will avoid extended vectoring of aircraft over the plant boundaries (completed).
Use of discretionary holding patterns. When feasible, air controllers would offer a practice holding pattern away from plant boundaries when pilots request such practice (completed).
- Develop and implement a new Global Positioning System (GPS) non-precision approach that tracks around the plant's boundaries. This new navigation system was recently approved by FAA for use in all aircraft. As increasing numbers of aircraft become equipped with GPS, pilots will more frequently request this approach, which routes the aircraft away from plant boundaries (completed). A depiction of this approach is provided in Figure 220.127.116.11.
- Build an offset localizer approach with vertical guidance and distance measuring equipment, called an "Localizer Displaced Approach Glide Slope Approach." Because the Runway 22 BCL cannot be angled to the runway, this alternative is suggested. By adding a new antenna array at the end of Runway 22, aircraft equipped with instrument landing systems will be able to arrive along a path angled to the runway. This alternative will move aircraft tracks away from the nuclear materials stored in Zone 4. This new approach is illustrated in Figure 18.104.22.168.
- Install a GPS Ground Differential Station that would permit use of GPS precision minimums. FAA indicated that by building a GPS Ground Differential Station near the airfield, navigation accuracy of aircraft will be increased and glide-slope information can be added to the GPS approach mentioned above.
- Install a new enroute-approach navigation aid farther away from the plant (a new VORTAC). After installing this new VORTAC, the older VORTAC located midway between the airfield and the plant would be decommissioned. The new VORTAC station near the airport would permit the moving of existing FAA airways away from the plant. Existing VORTAC approaches that pass over the plant would be eliminated, and if warranted, FAA may elect to develop new approaches to the airport that are angled away from the plant.
- DOE has agreed to study new methods to fortify the areas where nuclear materials are handled or stored. Structures such as "Jersey Walls", fortified bunker entrances, and berms may be considered.
The Proposed Action would include the continued operation of Pantex Plant and the storage of up to 20,000 pits onsite. A quantitative assessment of the frequency (per year) that an aircraft crash could initiate an accidental release of plutonium at Pantex Plant was performed. Three terms were considered in the assessment:
- The frequency of an aircraft impacting the facility (hit probability).
- The potential of significantly damaging the building by scabbing or perforation, given the impact.
- The potential of a radioactive release, given significant building damage (release probability).
Figure 4.15.21 is a graphical representation of the three events that must occur to have a radioactive material release from a Pantex Plant facility due to an aircraft crash. The frequency of an aircraft impacting a facility was calculated using the Draft DOE Standard, Accident Analysis for Aircraft Crash into Hazardous Facilities (Draft DOE Standard) (DOE 1996g). It should be noted that this analysis is applicable to accidents only, not intentional acts of sabotage or terrorism.
Air traffic data (for 6.5 years of runway operations) for the Amarillo International Airport were obtained from the FAA and used in conjunction with approximately 12 months of RAMS data collected at the Amarillo International Airport Tower (PC 1996h). Air traffic data in the vicinity of the airport on an annual basis are summarized in Table 4.15.21. Projected building areas and aircraft crash frequency data were combined with the air traffic data to calculate the aircraft impact frequency for Zone 4 and Zone 12 buildings. The likelihood of any aircraft impacting a building in either Zone 4 West or Zone 12 is extremely unlikely (3.2 x 10-5 per year). The likelihood that any aircraft impacts a Zone 12 building is slightly greater than that of impacting a Zone 4 West magazine, primarily due to the fact that the total Zone 12 target area is slightly larger than that of Zone 4 West.
The potential of significant building damage given an aircraft impact is then determined. If an impact occurs, the potential of significant building damage is predicated upon structural analyses that consider the weight and speed of the impacting aircraft compared with the resiliency of the facility. The potential for significant building damage from crashes involving various classes of aircraft was evaluated using the structural evaluation approach presented in the Draft DOE Standard (DOE 1996g). Table 4.15.22 presents the building damage matrix for each aircraft class for specific facilities in Zone 4 West and Zone 12. Significant building damage is defined as either perforationwhen a missile (flying object) generated by an aircraft crash penetrates into a facilityor scabbingwhen an impact of an aircraft missile on a facility generates a secondary missile inside the facility.
Based on calculations using structural penetration equations provided in the Draft DOE Standard, and given the nature of the heavily reinforced, earth covered structures at Pantex Plant, only about 9 percent of the potential aircraft impacts in Zone 4 West result in significant building damage. Similarly, for Zone 12, approximately 17 percent of the potential aircraft impacts in Zone 12 result in significant building damage.
An aircraft impact into a Zone 12 building that causes significant damage may not necessarily lead to a release of radioactive material. Release of radioactive material is not reasonably foreseeable for nuclear explosive bays, cells, and special purpose facilities (frequency of occurrence is less than 10-6 per year). In addition, the radioactive materials inventory is much less than what would be found in Zone 4 West magazines. Consequently, the probability of a release in Zone 12 is approximately equal to that for Zone 4 West facilities.
A high explosive (HE) detonation in Zone 4 West is possible only in weapon magazines. However, if an aircraft crashes into a magazine and causes significant damage, it is unlikely that the magazine will contain weapons, since most of the storage magazines will be used for pit storage. For the 12,000-pit case, approximately 70 percent of the magazines will contain pits only, whereas for the 20,000-pit case, up to 100 percent of the Zone 4 West magazines could be occupied by pits only.
An aircraft crash that causes significant damage to a weapons magazine would not necessarily lead to an explosive plutonium release. The likelihood of an explosive release is dependent on numerous factors, including the type of explosive contained within weapons stored in the magazine (conventional or insensitive high explosives) and the nature of the crash and damage to the magazine (e.g., if there is a fire inside the magazine or a missile from the crash impacts a weapon).
For this analysis, it was conservatively assumed that significant building damage to a magazine containing HE (in weapons form) would lead to an explosive plutonium release involving the contents of the magazine. The likelihood of an HE detonation in a weapon magazine due to an aircraft impact is not reasonably foreseeable (frequency of occurrence is less than 10-6 per year). The aircraft crash analysis in this section and in appendix E focuses on release probability only. This probability is combined with other conditional probabilities and consequences to evaluate the risk due to aircraft crash at Pantex Plant. The consequences and risk associated with this event are discussed in section 4.14.2, Human Health.
An aircraft impact into a Zone 4 pit magazine may damage a large fraction of the pit containers, and an ensuing fire could result in a release of plutonium. An aircraft crash that causes significant damage to a pit storage magazine would not necessarily lead to a plutonium release. Pits are currently stored in ALR8 containers, which provide significant thermal and impact resistance. In the future, pits will be stored in a new container, the AT400A, that will provide additional thermal and impact protection. Appendix F provides a description of current and potential future pit containers.
Whether perforation of a pit magazine would result in damage to pit containers is uncertain. In this analysis, it is assumed that 25 percent of the pit containers in a magazine contribute to a release (DOE 1994w:App I). Spilled aircraft fuel is likely to cause a fire in a crash that results in perforation of a storage magazine, and for this analysis it is conservatively assumed that a fire occurs 100 percent of the time. Whether or not this fire involves the contents of the magazine is also uncertain. In this analysis, it is assumed that it does. The likelihood of impact depends on the number of pit magazines in use. For the Proposed Action, the maximum number of pits stored will be 20,000. The likelihood of an aircraft impact causing a release is extremely unlikely (frequency of occurrence is less than or equal to 10-4 per year, but greater than or equal to 10-6 per year).
The risk and consequences of aircraft impacts at Pantex Plant are discussed in section 22.214.171.124, Impacts of Continued Operations. The risk to the public from aircraft impact dispersal accidents is low relative to other risks. A person in the vicinity of Pantex Plant has an approximately 4.3 x 10-12 increase in fatal cancer risk from potential aircraft crash plutonium dispersal accidents compared with a baseline annual fatal cancer risk of 1.7 x 10-3.
The likelihood of an aircraft impacting either a weapon magazine or a Zone 12 building is the same as discussed under the Proposed Action.
The likelihood of an aircraft impacting a Zone 4 pit magazine depends on the number of pit magazines in use. For the No Action Alternative, the maximum number of pits stored at Pantex Plant will be 12,000, which would require all 18 Modified Richmond and 18 SAC magazines. This reduces the likelihood of an aircraft impacting a pit magazine and causing a release by 44 percent from the Proposed Action, such that it is not reasonably foreseeable. The reason for this disproportional reduction is the preferential storage of pits in Modified Richmond magazines, which are less vulnerable to aircraft impacts than SAC magazines. For the 12,000-pit case it is assumed that the remaining 24 SAC magazines contain weapons. The release frequency for weapons magazines is also not reasonably foreseeable (6.8 x 10-7).
The likelihood of an aircraft impacting either a weapon magazine or a Zone 12 building is the same as discussed under the Proposed Action.
As previously stated, the likelihood of an aircraft impacting a Zone 4 pit magazine depends on the number of pit magazines in use. The maximum number of pits stored at Pantex Plant under the Pit Storage Relocation Alternative would be 12,000. As discussed under the No Action Alternative, the relocation of 8,000 pits reduces the likelihood of an aircraft impacting a pit magazine and causing a release by 44 percent from the Proposed Action, such that it is not reasonably foreseeable. Relocating 20,000 pits to another site will ultimately reduce the Pantex Plant pit inventory to zero. This would reduce the likelihood of a release from an aircraft impacting a pit magazine at Pantex Plant to zero.
The cumulative impacts presented here include impacts of the continued operations at Pantex Plant combined with impacts associated with activities described in the WM PEIS, SSM PEIS, and S&D PEIS. Since the Pantex Plant EIS Proposed Action and the SSM PEIS No Action Alternative represent a continuum of operations, the impacts associated with any new mission or facility that could be implemented at Pantex Plant are discussed in the context of that continuum. The impacts from the WM PEIS program are combined with those of the Pantex Plant EIS Proposed Action. The impacts from the S&D PEIS are combined with those of the SSM PEIS No Action Alternative. A detailed discussion of this methodology is presented in section 4.2.
Since the DOE programs have not identified exact locations of buildings where plutonium would be resident, it is not possible to quantitatively determine the impacts from these three programs. Therefore, a qualitative assessment was done comparing the three programs to the existing facilities in use.
126.96.36.199 Impacts of Alternatives in the Waste Management Programmatic Environmental Impact Statement
The WM PEIS is only concerned with plutonium as transuranic (TRU) waste. Under normal operations Pantex Plant does not produce TRU waste. Actions in the WM PEIS would not affect the locations of plutonium (both in pits and weapons) in Zone 4 or 12. Therefore, there would be no change in the aircraft accident probability from WM PEIS actions.
188.8.131.52 Impacts of Alternatives in the Stockpile Stewardship and Management Programmatic Environmental Impact Statement
The SSM PEIS includes three alternatives that apply to Pantex Plant: No Action, Downsize Existing Capability, and Relocate Capability. Although the No Action Alternative does not account for the time plutonium is at risk, there would be a reduction in the risk from an aircraft crash because of the reduction in operations. Under the downsizing alternative, there would be a consolidation of facilities and a commensurate reduction in the risk from an aircraft crash due to the fewer number of target facilities. Under the relocation alternative, the risk from an aircraft crash into assembly, disassembly, and HE fabrication facilities would be reduced to zero.
184.108.40.206 Impacts of Alternatives in the Storage and Disposition of Weapons Usable Fissile Materials Programmatic Environmental Impact Statement
If any of the three storage alternatives (Upgrade Facilities at Multiple Sites, Consolidate Plutonium in One Facility, or Collocate Plutonium and Highly Enriched Uranium in Two Facilities) were implemented, there would be a change in the aircraft crash probability. Since the result of any of these alternatives would be to remove all pits (plutonium not in weapons) from Zone 4, this would reduce the aircraft crash induced release probability. If the Upgrade Alternative is selected, all plutonium pits would be moved to existing buildings 1266 and 1282. This would reduce the aircraft accident probability almost proportionally to the number of Modified Richmond and SAC magazines no longer used in Zone 4. The aircraft crash probability in Zone 4 would be only for those magazines where nuclear weapons are staged. The impact of additional plutonium in Zone 12 would be minimal because buildings 1266 and 1282 are adjacent to buildings 1241 and 1242.
The Consolidation Alternative has two options at Pantex Plant: (1) to build a new facility and modify existing facilities in Zone 12 South or (2) build a new facility in Zone 12 South. Under the first option, there would be a reduction in the aircraft accident probability due to a reduction in the plutonium inventory in Zone 4 and a minimal increase in Zone 12 South as discussed in the Upgrade Alternative. The new facility in Zone 12 South would have a smaller total area (true, shadow, and skid) compared to the pit storage magazines no longer used in Zone 4. There would be an increase in the hit probability for Zone 12 because of the addition of a new facility, but overall, the aircraft accident probability would be reduced. The impacts from the second option, building a new facility, or from the Collocation Alternative, would be similar to the Upgrade Alternative since material would be moved from Zone 4 to Zone 12 South.
The final S&D PEIS will include an alternative that is a refinement of these storage alternatives. As discussed in sections 1.4 and 1.7.3 of this volume, the final S&D PEIS will include an alternative under which pits from Rocky Flats Environmental Technology Site (RFETS) could be transferred to Pantex Plant for storage in Zone 4 as early as 1997. The impacts of this alternative are fully accounted for in this EIS because the pits from RFETS could not cause the total number of pits stored in Zone 4 to exceed the storage limit of 20,000 pits analyzed under the Proposed Action. Furthermore, RFETS pits that could come to Pantex Plant would have the same characteristics, as analyzed in the S&D PEIS, as pits currently or previously stored at Pantex Plant. However, the receipt of pits from RFETS would require additional repackaging activities prior to storing them in Zone 4 (see section 4.12 5.3). Appendix Q of the S&D PEIS indicates that these repackaging and intrasite transportation activities could result in less than 10-2 additional latent cancer fatalities. Impacts from the disposition alternatives are not assessed since the S&D PEIS will select a technology and strategy, not a site for disposition.
Potential mitigation measures either reduce the frequency of an aircraft impact or reduce the probability that the aircraft impact causes a release due to significant building damage, fire, and/or HE detonation. Results from this study indicate that a large fraction of the risk associated with aircraft crash in Zone 12 comes from older facilities that are not heavily reinforced or earth covered. Recommendations of the Overflight Working Group are presented in section 220.127.116.11. DOE has committed to implement the risk reduction measures proposed by the overflight working group. It is estimated that implementation of the MOU, the offset localizer, relocation of the VORTAC, and 65 percent use of the GPS would result in an 82 percent cumulative risk reduction (DOE 1995h:22). This 82 percent reduction was estimated using the Solomon Model. Fortification of areas and structures in which nuclear materials are handled and stored could further reduce the impact of aircraft accidents.
There are many conservatisms included in the Pantex Plant aircraft accident analysis that, if reduced or removed, have the potential to lower the probabilities of an aircraft crash incident substantially. This section presents some of these conservatisms and explains their effect on the aircraft crash risk to the Pantex Plant.
The Draft DOE Standard was created as a tool to be applied to all DOE sites where hazardous materials exist (DOE 1996g). As a result, it was written in a generic form without much site-specific detail. The Pantex Plant is unique in that it is situated close to an international airport. Because of this proximity, and the weapons operations conducted at Pantex Plant, the public has expressed concern regarding aircraft overflying the plant and crashing into nuclear facilities. DOE, in cooperation with the FAA, has responded to these concerns by attempting to reduce Pantex Plant overflights with the mitigation measures discussed in sections 18.104.22.168 and 4.15.6. When fully completed, these measures will reduce the number of aircraft overflying the Pantex Plant and the risk of an aircraft crash.
However, the Draft DOE Standard, as written, does not allow for consideration of these measures in the risk calculation. For the purposes of this analysis, it is assumed that all aircraft are on approach to the airport on the BCL, which intersects Zone 4 West. Even with the mitigation measures in place to move aircraft away from the current BCL, RAMS data indicate that aircraft do not typically fly this route. RAMS data also indicate high-altitude aircraft flying on defined airways, which is not recognized in the DOE Standards non-airport methodology.
In the event of an aircraft crash, the assumption used in the aircraft accident methodology is that a skidding aircraft will hit a facility with the same velocity that it had when it began the skid. This results in a highly conservative impact velocity since no credit is taken for drag, friction, or other factors that would reasonably be expected to contribute to a reduction in velocity. Additionally, the impact angles given are conservative when applied to facility roof impacts, because at these angles, it is quite possible that the potential penetrating missiles from the aircraft would simply ricochet off the facility. Pantex Plant has some structures in Zone 12 that are considered structurally "super stout." No credit is taken for these "super stout" facilities in the analysis.
Other conservatisms in the analysis include the assumption that the entire aircraft engine is the penetrating missile of concern. This is conservative since most of the fan shroud would be expected to tear away after striking a facility, leaving the engine shaft as the secondary penetrator. For the purposes of this analysis, it is also assumed that any facility authorized to contain nuclear explosives is occupied by nuclear explosives 24-hours a day, seven days a week (conservative because none of the authorized facilities contain nuclear explosives on a continual basis), and that the probability of an explosion after an accident resulting in a plutonium release is 1. This assumption is conservative because all impacts would not be expected to cause scabbing or perforation sufficient to cause an explosion and there is no consideration given as to whether high explosives are sensitive or insensitive.
Release assumptions are also considered to be highly conservative for several reasons. Potential impacts that could cause a wall or roof to fail, or a collapse of the whole facility, take no credit for the fact that the overburden would likely suppress any fire and prevent dispersal of materials. Further, no credit was taken for the filtration effects provided by earth covers on bays, cells, and Zone 4 West magazines.
A release of plutonium (from a magazine, for example) due to a fire would require sufficient fuel inside the facility to create a fire that would consume (completely surround) the plutonium container for at least 30 minutes. A sustained fire is unlikely since the assumed penetrators (engines) do not carry sufficient quantities of fuel to produce a sustained fire (fuel is typically contained in the wings of the aircraft). Further, there is a high probability that a skidding aircraft, which represents the majority of the risk, would dispense its fuel contents prior to facility impact.
The analysis takes no credit for the protection provided by the pit container (AL-R8) or the ability of the pits to withstand a fire. Pits, by themselves, have some degree of resiliency to fire, and the AL-R8 containers currently being used were previously certified as type B containers (i.e., were designed to withstand an all-consuming 30-minute fire and various drop and puncture tests). The analysis also assumes that 25 percent of the containers in a magazine would be torn open and their contents released as a result of the fire. Given the size of the penetrator (engine), it is unlikely that 25 percent of pit containers would be involved in an aircraft crash or that a sustained fire could occur.
Considering these many conservative assumptions, which could not be quantified, the actual risk associated with aircraft crash is probably much less than the point estimates presented in this document. Similarly, the actual radiological doses resulting from the aircraft accident scenarios are expected to be much less than those presented in section 4.14, Human Health.
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