Ken Schwartz
CE397
Term Paper
Risk Characterization of Chemical Releases for a Potential Pit Conversion and MOX Fuel Fabrication Facility
Background
Pantex was started in 1945 as a plant to load conventional ammunition shells and bombs for the U.S. Army. In 1951, the Atomic Energy Commission (AEC) arranged to convert the plant to perform nuclear weapons operations. These operations include weapons assembly, disassembly, and stockpile surveillance, and require the handling, (but not processing), of plutonium, uranium, tritium, and a variety of non-radioactive hazardous and toxic chemicals. A list of current activities at Pantex is given in Table 1 below.
Pantex is located approximately 17 miles northeast of downtown Amarillo, Texas. Figure 1 shows the location of the Pantex site relative to the surrounding areas, and figure 2 shows the layout of the Pantex plant. The plant is situated on 14,900 acres of land, of which 9,100 acres belong to the Federal Government, and 5,800 acres belong to Texas Tech University. The plant is owned by the government and managed by the Department of Energy’s (DOE) Assistant Secretary for Defense Programs (DP). The plant is run by a contractor, the Mason & Hanger-Silas Mason company.
Table 1. Current Missions at Pantex
Mission |
Description |
Plutonium Storage |
Provide storage of pits from dismantled nuclear weapons |
High Explosive Components |
Manufacture for use in nuclear weapons |
Weapon Assembly |
Assemble new nuclear weapons for the stockpile |
Weapon Maintenance |
Retrofit, maintain, and repair stockpile weapons |
Quality Assurance |
Stockpile quality assurance testing and evaluation |
Weapon Disassembly |
Disassemble stockpile weapons as required |
Test/Training Programs |
Assemble nuclear weapon-like devices for training |
Weapons Dismantlement |
Dismantle nuclear weapons no longer required |
Development Support |
Provide support to design agencies as requested |
Environmental Management |
Environmental restoration and waste management activities |
Source:DOE/EIS-0229
Land Use
Pantex is located in Carson County, in the panhandle region of Texas. The region has a fairly flat topography, with numerous playa lakes. A playa lake, or basin, is a term describing numerous lakes in the region, usually less than 0.6 miles in diameter, that receive water runoff from the surrounding areas. Land that is not used exclusively by Pantex for operations is used by Texas Tech Agriculture Research for agricultural purposes. These consist of dry farming and livestock grazing. The land also contains one (1) residence approximately 3.7 miles southwest of the weapons fabrication facility.(DOE/EIS-0225)
Surrounding Pantex is private property used primarily as farmland (mostly dry) and grazing fields for cattle. The closest residences are approximately 157 ft from the western and northeastern boundaries(DOE/EIS-0225). There are eleven (11) residences within 0.3 miles of the Pantex boundaries(Hay-Wilson). Outside of the immediate boundaries, the regions of focus are Carson, Armstrong, Potter, and Randall counties(diagram). Figure 1 and 2 show Pantex and the surrounding counties. The land utilization and irrigation statistics are shown in figure 3, and tables 2 and 3.
Figure 1. Diagram of Pantex Facility
Figure 2. Diagram of Amarillo, Pantex, and the Surrounding Counties
Figure 3. Land Utilization Around the Pantex Plant
Table 2. Land Utilization in the Counties Surrounding Pantex (square kilometers)
Land Use |
Armstrong |
Carson |
Potter |
Randall |
Total(%) |
Agriculture |
789.7 |
1,290.1 |
241.4 |
1,425.5 |
3,697.0 (39.0%) |
Herb, Shrub, and Mixed Range |
1,565.9 |
986.3 |
1,963.2 |
781.7 |
5,297.1 (55.9%) |
Deciduous, Evergreen, and Mixed Forest |
0 |
0 |
0 |
0 |
0 (0%) |
Urban, Commercial |
15.8 |
60.9 |
131.1 |
61.4 |
268.8 (2.8%) |
Forested and other Wetland |
21.0 |
32.1 |
8.0 |
37.6 |
98.7 (1.0%) |
Surface Water Bodies |
16.6 |
20.7 |
30.8 |
10.4 |
78.5 (0.8%) |
Other(Barren) |
7.8 |
2.9 |
14.0 |
11.9 |
36.5 (0.4%) |
Subtotal |
2,367.3 |
2,392.9 |
2,388.5 |
2,328.4 |
9,477.1 (100%) |
Table 3. Irrigated Land Area (square miles) in Counties Surrounding Pantex
Armstrong |
Carson |
Potter |
Randall |
Total (%) |
|
Total Irrigated Land Area (percentage of total Agriculture) |
32.6 (4.4%) |
406.4 (31.5%) |
29.0 (12.%) |
135.5 (9.5%) |
603.7 (16%) |
Furrow and Flood Land Area (percentage of total irrigated) |
24.6 (75.3%) |
306.9 (75.5%) |
18.9 (65.1%) |
98.9 (73%) |
449.4 (74.4%) |
Sprinkler Land Area (percentage of total irrigated) |
8.0 (24.7%) |
99.5 (24.5%) |
10.1 (34.9%) |
36.5 (27%) |
154.4 (25.6%) |
The land utilization and irrigation information suggest that the movement of COC’s in sediment into surface water would originate primarily from land used for cattle grazing and secondly from irrigated farmlands. This is because the ranges are closer to open water sources than the farmland. However, a majority of the sediment, from runoff, would originate with the farmland because of its high erodability. The conclusion that can be drawn from this is that short-term chemical "challenging" of area surface water via sediments would be small.
Regional Hydrology
There are no streams or rivers on or near the Pantex plant. All water needs for the facility are obtained from groundwater(DOE/EIS-0225D). There are five (5) playa lakes on the DOE site; playas 1-3 are located on the grounds of the Pantex plant, and playas 4 and 5 are on the region leased by Texas Tech University. The Pantex Wastewater Treatment Facility discharges into playa 1. Playas 1, 2, and 4 receive stormwater runoff and condensed cooling water from buildings. Stormwater runoff from the burning ground flows into playa 3(DOE/EIS-0225). Water quality of playas 1, 2, and 3, Pantex Lake, and the Bushland playa are monitored for comparative purposes. The only major source of surface water in the surrounding area is the Canadian River, which flows eastward into Lake Meredith. Lake Meredith is located approximately 27 kilometers north of the Pantex plant(Risk Char.). Lake Meredith is a man-made reservoir which is used to supply drinking water to much of the Panhandle population. None of the runoff from the Pantex facility drains into Lake Meredith(Risk Char.).
There are two primary sources of groundwater for Pantex and the surrounding area: the Ogallala Aquifer and the Dockum Group Aquifer. In addition, numerous "perched" aquifers exist beneath the Pantex site. The Ogallala Aquifer ranges in thickness from less than a foot, to 1,300 feet, with an average of 200 feet, and stretches
Figure 4. Thickness of Ogallala Aquifer beneath Pantex Region
from the Texas Panhandle to South Dakota. A thickness map is shown on figure 4. In the region near Amarillo, the Ogallala lies under most of the region, with the exception of the Canadian River Valley. The gradient generally runs northwest to southeast, but in the region around Pantex, it runs from the southwest to the northeast. Figure 5 shows a gradient and elevation map of the Ogallala in the surrounding area, and figure 6 shows the same for the Pantex site(Ground Water). The Ogallala can be considered fresh (<1000 mg/L total dissolved solids).
Figure 5 Gradient Map of the Ogallala Aquifer (Blue)
Figure 6. Gradient Map of Ogallala Aquifer at Pantex (DOE/EIS-0225D)
The Dockum Group Aquifer runs beneath the Ogallala, and ranges from fresh to briny(< 3000 mg/L total dissolved solids). The characteristics of the Dockum Group beneath Pantex is not completely understood. The portion of the Dockum that underlies Potter, Carson, Armstrong, and Randall counties is apparently acceptable for many uses(Risk Char). There are a few water wells that tap into it, but it is used primarily for domestic and livestock purposes, and has little economic importance in the Pantex area.
Currently, the water supplying the city of Amarillo, not including industry, originates 35% from groundwater, and 65% from Lake Meredith. The water, used from Lake Meredith, is supplied by the Canadian River Municipal Water Authority (CRMWA), to 11 cities and towns in the area. Water usage and source is shown in table 4 (Risk Char). The Ogallala is capable of yielding, in excess of, 1,060 gal/min, or 554.8 million gal/yr (DOE/EIS-0225D). Recharge rates are estimated at 0.02 to 4.1 cm/yr (DOE/EIS-0225D).
Table 4. Water Usage and Sources in the Amarillo Area (Risk Characterization, 1998)
Municipal Water Supplied, 1000 L/yr |
Total Allocation, CRWMA |
|||||
City/Town |
Wells Ground-water |
Surface Water CRWMA |
Total |
Percent Surface Water |
L/yr |
Percent Used |
Amarillo |
26,789,359 |
36,512,284 |
57.68 |
37,665,294 |
96.94 |
|
Borger |
3,282,103 |
3,324,477 |
50.32 |
5,639,934 |
58.95 |
|
Brownsfield |
696,906 |
1,446,800 |
67.49 |
2,234,021 |
64.76 |
|
Lamesa |
670,306 |
1,964,250 |
74.56 |
2,214,708 |
88.69 |
|
Levelland |
656,636 |
1,946,360 |
74.77 |
2,835,724 |
68.64 |
|
Lubbock |
19,217,457 |
36,511,266 |
65.52 |
37,665,294 |
96.94 |
|
O’Donnell |
0 |
177,063 |
100.00 |
282,554 |
62.67 |
|
Pampa |
1,832,753 |
3,299,509 |
64.29 |
7,280,384 |
45.32 |
|
Plainview |
2,954,620 |
3,667,625 |
55.38 |
3,751,487 |
97.76 |
|
Slaton |
92,807 |
846,466 |
90.12 |
1,601,827 |
52.84 |
|
Tahoka |
207,357 |
400,905 |
65.91 |
467,540 |
85.75 |
|
Total, L |
56,400,304 |
90,099,985 |
|
101,638,768 |
||
Total, m3 |
1,295 |
2,068 |
|
2,333 |
The uppermost sediments of the stratigraphy under the Pantex site consist of the Black Water Draw Formation. This consists of approximately 50 feet of windblown sand, clay, and silt. Directly beneath the Black Water Formation is a thin bed known as the "Caprock", which is characteristic of the Ogallala Formation. The Caprock is made up of a caliche bed formed during several hundred thousands years over a very stable landscape. Beneath the Caprock is the Ogallala Formation. The Ogallala is comprised of three (3) zones: the unsaturated, fine-grained, and saturated zones. The unsaturated zone, or Upper Ogallala, consists of approximately 200 feet of silt and sand(CE394K). Beneath this is a relatively thin zone of fine-grained material. This material produces a barrier to the flow of infiltrating water, causing it to "perch". This form discontinuous pools of water, known as perched aquifers. Below this region exists the saturated zone, in which the drinking water aquifer resides. The saturated zone ranges in depths from 350 to 425 feet below the surface of Pantex(Ground Water). A 3-dimensional representation, and a simplified 2-dimensional cross-section of the strata is shown in charts 7 and 8 (Hay-Wilson). Chart 9 shows a computer generated diagram of the Ogallala, perched aquifers, and playa lakes beneath Pantex based on well data from the University of Texas Bureau of Economic Geology(Ground Water). Properties of the aquifers were measured in wells. The average horizontal hydraulic conductivity is K=9.3 ft/day, and the transmissivity T=2200 ft2/day for the Ogallala Aquifer. The properties of the perched aquifers are K= 30 ft/day, and T = 300 ft2/day(Hay-Wilson).
Figure 7. 3-Dimensional Stratigraphic Cross-Section beneath the Pantex Plant
Figure 8. 2-Dimensional Simplified Stratagraphic Cross-Section beneath the Pantex Plant
Figure 9. Computer Generated Diagram of Groundwater Beneath Pantex
Meterological Properties
Pantex is located on the Southern High Plains of the Texas Panhandle. The topography ranges from flat to gently rolling plains. There are no unique geological landforms. Figure 10 shows the distribution of wind at Amarillo in 1991. The measurements were taken at a height of 10 m at the Amarillo National Weather Service Station(ANWSS). The average annual wind-speed is 6.0 m/s prevailing in the south to southwest direction. The data collected by the ANWSS for 1991 indicates that unstable conditions occur ~14 % of the time, neutral conditions about 64%, and stable conditions about 22 % of the time.
Figure 10. Mean Wind Speeds and Direction Frequencies for Amarillo (10 m)
Average temperatures in the location of Amarillo range from –5.7 C in January, to 32.8 C in July, with a mean of 13.8 C. The average annual precipitation is 49.7 cm. Figure 11 shows the average rainfall in the Amarillo area.
Figure 11. Temperature Range and Average Cumulative Rainfall in Amarillo
Potential Missions at Pantex
With the end of the cold war, the role of thermonuclear warheads has diminished. As such, the United States has declared 38.2 metric tons (MT) of plutonium to be surplus to national security needs. Much of this plutonium is in the form of hollow plutonium spheres, called pits. The goal of disposition of the surplus plutonium is to minimize the risk that the material could fall into the hands of unauthorized parties, and to minimize the risk of reintroduction into nuclear arsenals. A potential option being analyzed is the conversion of the material into Mixed-Oxide Fuel (MOX). The MOX fuel would then be used by commercial light water nuclear power generating reactors. After use in a nuclear reactor, the fuel becomes saturated with fission by-products, and the plutonium cannot be re-processed for weapons development(Risk Char).
In order to complete this goal, the plutonium metal must first be converted into plutonium dioxide powder. This powder will be combined with uranium dioxide powder, pressed into ceramic pellets, and made into fuel rods. Two distinct facilities would be required to complete this process. The first would convert the metal into a powder, and the second would convert the powder into MOX fuel(Risk Char).
The procedure currently proposed for the conversion, from a metal into an oxide form, is the Advanced Recovery and Integrated Extraction System (ARIES). The plutonium will enter this process in the form of plutonium pits. A pit is a spherical shell of plutonium, surrounded by a beryllium or stainless-steel cladding, and depending on the weapon type that it came out of, may have a variety of other attached components. These other components will be removed and sent to other parts of the plant for handling. The remaining pit will be bisected, the plutonium will be removed from the cladding and converted into an oxide. This oxide will undergo gallium removal, then be canned, tagged, decontaminated, and assayed for record(LA-13178). This facility will be designed to put out 35 metric tons of plutonium, in a dioxide powder form, within a 10 year operational period. The facility will also be designed to process 45 metric tons of plutonium, to allow that ~30% of the plutonium may not meet quality standards. A flowchart of the ARIES process is shown in figure 12.
Figure 12. Flow Diagram of the ARIES Process
The second step in the conversion process is the production of MOX fuel rods. This entails combining the plutonium dioxide with depleted or natural uranium dioxide, and using this mixture to fabricate ceramic fuel pellets. A column of pellets is loaded into zircaloy cladding to form fuel rods. These fuel rods will then be combined with enriched uranium dioxide to form fuel bundles. The fuel bundles will be used as reactor fuel in either boiling water reactors (BWR) or pressurized water reactors (PWR), which could use enrichments ranging from 3 wt% to 7 wt%. The fabrication capacity of the MOX fabrication facility will vary depending upon the final fuel design, the number of reactors employed, the loading pattern, and the cycle length. However, the largest facility envisioned has a fabrication capacity of 100 MT of MOX fuel. This is the nominal facility selected for this study. The 100 tonne facility will combine approximately 99 MT of UO2 with the 3.5 MT of PuO2 obtained each year from the ARIES process. This process is seen in figure 13.
Figure 13. Flow Diagram of MOX Fabrication
During operation of these facilities, chemicals are required for processing, and maintainance and cleaning. A list of these chemicals, and quantities are given below.
Table 5. Annual Chemical Usage for the ARIES plant
Chemical, Gas, or Compound |
Estimated Annual Consumption |
Chlorine |
62 m3 |
Helium |
4800 m3 |
P-10 |
0.55 m3 |
Sulfuric Acid |
470 kg |
Phosphoric Acid |
240 kg |
Hydrazine |
0.9 kg |
Oils and Lubricants |
1600 kg |
Cleaning Solvent |
140 kg |
Polyphosphate |
70 kg |
Inorganic Phosphate |
27 kg |
Organic Phosphate |
21 kg |
Polyelectrolyte |
240 kg |
Liquid Nitrogen |
1100 kg |
Aluminum Sulfate |
16 kg |
Betonite |
480 kg |
Table 6. Yearly Ion Exchange Balance
Resource |
Mass (kg) |
HNO3 (nitric acid) |
2713 |
HF (hydroflouric acid) |
23 |
Al(NO3)3 9H2O (aluminum nitrate nanohydrate) |
146 |
H2O2 (hydrogen peroxide) |
498 |
NH2OH (hydroxyl amine) |
1444 |
C2H2O4 (oxalate) |
1274 |
O2 (oxygen) |
1171 |
H2) (water) |
7763 |
Resin |
13 |
Wastes |
Mass (kg) |
TRU waste (0.5 wt% Am) |
162 |
Mixed Waste (resin) |
13 |
Effluent (water) |
7763 |
O2 |
235 |
CO2 |
1932 |
NO2 |
1006 |
NO |
656 |
Table 7. Annual Chemical Requirements for MOX Fabrication Facility
Chemical |
Annual Consumption |
Process and Non-Process Chemicals |
|
Oxygen |
Negligible |
Argon |
256 kg (146 m3) |
Nitrogen |
18 kg (0.02 m3) |
Helium |
16 kg (0.09 m3) |
Hydrogen |
3066 kg |
- Service Laboratorya |
|
-H2SO4 |
50 lbs |
-HNO3 |
25 lbs |
-HCl |
15 lbs |
- Lab Scrubbera |
|
-NaNO3 |
3100 lbs |
-NaOH |
500 lbs |
- Blendinga |
|
-Poly Ethylene Glycol |
700 lbs |
- Pressinga |
|
-Zinc Stearate |
700 lbs |
- Cooling Tower Blowdowna |
|
-Orthophosphate |
600 lbs |
Cellulosicsb (paper, rags, wipes) |
50 lbs |
Hydraulic Fluidb (lubricants) |
48 lbs |
Polymethyl metacrylateb (glovebox window) |
226 lbs |
Polyvinyl chlorideb (wrapping, covers) |
8 lbs |
Alcoholb |
2 lbs |
In order to identify the potential level of risk associated with these quantities of chemicals, a risk based evaluation will be performed. This will back-calculate what the initial concentrations of a chemical or chemicals would have to be in order for a person to receive a risk-based exposure limit. In order to perform this evaluation, the potential receptors and exposure pathways must be identified. These are identified in table 8.
Table 8. Potential receptors, exposure mediums, and exposure pathways at Pantex
Receptor |
Exposure Medium |
Exposure Pathway |
On-site |
||
Workers at Pantex |
soil |
Contact |
Inhalation |
||
Ingestion |
||
groundwater |
Ingestion |
|
Off-site |
||
Adult |
groundwater |
Ingestion |
Child |
||
air |
Volatilization to air |
|
These exposure pathways were chosen because they will deliver the highest potential exposure. If the RBEL’s for these pathways are above the maximum possible exposures, then there is no need for further analysis. The models for these exposures are from the Texas Risk Reduction Program (TRRP). An example of a calculation for a carcinogenic are as follows:
Worker exposure from soil:
Total RBEL (soil) =
[mg/kg] [mg/kg] [mg/kg] [(mg/m3-air)/(mg/kg-soil)][(mg/m3-air)/(mg/kg-soil)]
The following table defines the variables used in the previous equations:
Table 9. Variable definitions and values used for TCE
Variable |
Definition |
Value |
Source |
RL |
Cancer Risk Level |
10-5 |
Default |
BW |
Body Weight(kg) |
70 |
Default |
AT |
Averaging Time (yr) |
70 |
TRRP |
Sfo |
Oral Slope Factor (mg/kg× day) |
1.1*10-2 |
TCE |
EF |
Exposure Frequency (days/yr) |
250 |
TRRP |
ED |
Exposure Duration (yr) |
25 |
TRRP |
Irs |
Soil Ingestion Rate (mg/day) |
100 |
TRRP(comm.) |
SFd |
Dermal Slope Factor (mg/kg× day) |
||
SA |
Skin Surface Area (cm2) |
3300 |
TRRP(adult) |
AF |
Soil to Skin Adherence Factor (mg/cm2× event) |
0.12 |
TRRP(adult) |
ABSd |
Dermal Absorption Fraction |
0 |
TCE |
URF |
Inhalation Unit Risk Factor |
1.7*10-6 |
TCE |
r s |
Soil Bulk Density (g-soil/cm3-soil) |
0.39 |
Risk Char. |
Ds |
Thickness of affected surface zone (cm) |
60 |
Default |
Q/C |
Inverse of mean concentration in air at center of affected soil area ((g/m2-s)/(kg/m3)) |
(68.81) 120. |
(0.5 acre area) .002 acre area approx. |
t |
Averaging time for vapor flux (s) |
7.8*108 |
Default commercial |
V |
Fraction of vegetable coverage |
0 |
None present |
Um |
Mean annual windspeed (m/s) |
6.0 |
DOE/EIS-0225 |
Ut |
Equivalent threshold value of windspeed (m/s) |
6.6 |
DOE/EIS-0225 |
F(x) |
Function dependant on Ut/Um |
0.224 |
Default |
This yields a PCL of 260 mg TCE/kg of soil. Since this number is based upon the assumption that the spill is 10 meters x 3 meters x 0.6 meters (depth), this results in a spill of 12*103 grams of TCE. The assumptions for the size of the spill is based upon a single spill, as the containers are closed and sealed until needed inside the building.
Ingestion of class-1 or 2 groundwater from soil leachate:
[mg/kg]
[mg/L]
[(mg/L-H2O)/(mg/kg-soil)]
[cm/yr]
[cm/yr]
Kd=foc*Koc
Table 10. Variable Definitions and values used for TCE
Variable |
Definition |
Value |
Source |
Irw |
Water ingestion rate(L/day) |
2. |
TRRP |
q ws |
Volumetric water content in vadose zone soils [(cm3-H2)/(cm3-soil)] |
0.46 |
Calculated |
Kd |
Soil-water partition coefficient [(cm3-wat)/g-soil)] |
1.86 |
TCE |
H |
Henry’s Law constant |
4.0 |
TCE |
q as |
Volumetric air content [(cm3-air)/(cm3-soil)] |
0.28 |
Risk Char. |
L1 |
Thickness of affected surface (cm) |
60 |
Default |
L2 |
Depth to groundwater table (cm) |
10,400 |
Min depth on site |
Ugw |
Groundwater velocity (cm/yr) |
0.017 |
Calculated |
d gw |
Groundwater mixing zone thickness (cm) |
1,520 |
Min thickness |
If |
Net infiltration rate of water through soil (cm/yr) |
2.22 |
Calculated |
W |
Width of source parallel to groundwater flow direction (cm) |
1000 |
Assumption |
q r |
Irredusable water content in vadose zone soil |
0.1 |
Risk Char. |
Ks |
Saturated hydraulic conductivity (cm/hr) |
1.31 |
Risk Char. |
l |
Soil parameter that characterizes range of pore sizes within soil |
0.48 |
Risk Char. |
G |
Highest recharge rate (cm/yr) |
4.1 |
DOE/EIS-0225 |
I |
Hydraulic gradient |
.0051 |
Calculated |
q T |
Total soil porosity |
0.74 |
Calculated |
foc |
Organic carbon fraction |
0.01 |
Approx. |
Koc |
Organic carbon partition coefficient |
186. |
TCE |
n |
Porosity |
0.39 |
Risk Char. |
x |
Distance down gradient of source |
3500 |
Dist to wells |
a x |
Longitudinal groundwater dispersivity (m) |
35 |
x*.01 |
a y |
Traverse groundwater dispersivity(m) |
11.7 |
.33*a x |
a z |
Vertical groundwater dispersivity(m) |
1.75 |
0.05*a x |
l i |
First-Order degradation rate (1/day) |
0 |
No decay |
Sw |
Source width (cm) |
300 |
Hypothetical |
Sd |
Source depth (cm) |
60 |
Hypothetical |
This results in a calculated RBEL of 1.3 mg/L. If a well was dug into the Ogallala aquifer close to zone 4, the concentration of TCE in the soil would have to be 56 mg/kg ( No drinking water wells are located in zone 4). If the well was dug close to the northeast boundary of Pantex (the approximate location of some of Amarillo’s and Pantex’s water wells), the concentration would have to be 3.0 * 106 mg/kg soil. As ingestion from groundwater would be the pathway of highest exposure for a child, the calculated PCL for a child drinking from the same well water is 29 * 103 mg/kg.
In order to analyze the RBEL of a COC due to inhalation at an off-site location, we will use the following:
d air = 2.15*s z
Table 11. Variable Definitions and values used for TCE
Variable |
Description |
Value |
Source |
Q |
Air Volumetric Flow Rate (m3/s) |
117.46 |
Calculation |
t |
Averaging time for vapor flux(s) |
7.8*108 |
Def. Comm. |
s y |
Traverse air dispersion coefficient(m) |
120.5 |
F class Briggs |
s z |
Vertical air dispersion coefficient(m) |
27.32 |
F class Briggs |
d air |
Ambient air mixing zone height(m) |
58.73 |
Calculation |
A |
Cross-sectional area of emission source (m2) |
9 |
Calculation |
Uair |
Wind speed (m/s) |
1 |
F class |
L |
Length of air emission source parallel to wind direction (m) |
10 |
Assumption |
Values used for a residence 3.5 km from source. To obtain maximum, an F class stability is used.with a wind speed of 1 m/s along a line from source to residence. y = 0.
Using these values, the RBEL for TCE at a house 3.5 km from zone 4 at Pantex is 0.24 mg/m3, which calculates into a PCL of 4.2*1016 mg/kg in soil. This number is exceptionally high due to the low volatility of TCE compared to the quantity needed to exceed the RBEL.
Based on the previous calculations, it is observed that the exposure pathway that requires the lowest concentration of TCE in the soil is the exposure to a worker on-site from a combination of soil inhalation, ingestion, and dermal contact. In order for a dose from inhalation off-site, or exposure by ingestion of well-water, to exceed regulated values, it would require orders of magnitude more of a chemical to be spilled. The protective concentration level of TCE in the soil was found to be 260 mg/kg. For the volume of soil being looked at, this means that 12.4*103 g of TCE would have to be spilled. It is important to recognize that this number was based upon a small localized single-occurrence accidental spill. The reason these assumptions were made is that, with few exceptions, the chemicals will not be handled outside of the containment buildings. In addition, because these chemicals are being handled in relatively small quantities, the amount of chemical spilled in an accident would be small. The PCL’s for TCE that were calculated shows that a spill at a new facility at Pantex would most probably not exceed TRRP guidelines. Calculated values for the PCL from soil exposure of other chemicals under consideration are shown in table 12.
Table 12. Calculated values for TCE and tetrachloroethylene for worker exposure
Chemical |
Dose to worker from soil |
Dose to a worker from a well |
||
PCL (mg/kgsoil) |
Amount of chemical required to exceed PCL (g) |
PCL (mg/kgsoil) |
Amount of chemical required to exceed PCL (g) |
|
Trichloroethylene (TCE) |
260 |
12.4*103 |
2.6*106 |
1.4*108 |
Tetrachloroethylene |
55 |
2.6*103 |
1.6*106 |
7.6*107 |
Conclusions
The results for the inhalation off-site show that further study would be almost pointless. The quantities that would be required are greater than the amounts that would be present at both facilities during their entire operating period. The quantity needed to exceed the PCL for ingestion from groundwater is also too large of an amount to focus on, provided groundwater drinking wells are kept out of zone 4. If drinking water wells are drilled close to the facility, the quantity that would have to be spilled is still highly improbable, but the possibility exists. The only transport pathway and receptor that may require further study is the dose to a worker at Pantex from a large spill. The quantities required are still very large, but due to the high number of variables and the number of assumptions made in the calculations, the possibility exists for exceedence of the PCL.
Works Cited
Amarillo National Research Center for Plutonium (ANRCP), 1998. "Risk Characterization of Potential Missions at the Pantex Plant," March 1998.
(DOE 1996c) U.S. Department of Energy. "Storage and Disposition of Weapons-Usable Fissile Materials Final Programmatic Environmental Impact Statement." Washington, D.C.: U.S. Department of Energy, DOE/EIS-0229; 1996.
Harman, Dr. Wyatte L., Srinivasan, Dr. Raghavan. "Site Characterization by Major Land Uses and Preliminary Implications for Agricultural Sedimentation, Pantex." Texas Agricultural Experiment Station, Temple, Texas July 25, 1997.
Hay-Wilson, Leslie, "Background Data Analysis for Risk Characterization at the Pantex Plant." University of Texas at Austin, November 30, 1996.
Los Alamos National Laboratory, (LANL) 1997. "Pit Disassembly and Conversion Facility, Environmental Impact Statement Draft Data Response – Pantex Plant," Los Alamos National Laboratory, July 29, 1997.
(PX DOE 1996b) "Draft Environmental Impact Statement for the Continued Operation of the Pantex Plant and Associated Storage of Nuclear Weapon Components Volume I – Main Report." DOE/EIS-0225D, U.S. Department of Energy, Washington, D.C. March 1996.
Texas National Resource Conservation Commission (TNRCC), 1996. "Texas Risk Reduction Program – Draft Version," December 16, 1996.