The Gaseous Diffusion Process

The Portsmouth Gaseous Diffusion Plant, built in 1953-1954, produces enriched uranium

hexafluoride (UF6) for commercial power reactors. In the past highly enriched uranium hexafluoride 235 was produced for the U.S. Navy. Enriched UF6 is material that contains the isotope U in assays (concentrations) greater than 0.711 weight percent. Commercial power plants currently use uranium enriched to the 3 to 5 percent range.

The plant is capable of producing a range of U235 assays from 0.2% to over 97%. In late 1991, the equipment that produced high assay uranium was taken off line and placed in long term shutdown. High assay material that was declared excess by the US Navy and Department of Energy was fed into the cascade and blended down to the assays used by commercial power plants. This refeed project was completed in July 1998. It is possible that other high assay material will be declared excess in the future and would possibly be blended down at PORTS. It is also possible that high assay production could be resumed in the future. The plant's certification under the Nuclear Regulatory Commission (NRC) limits the maximum assay to 10%.

Enrichment is accomplished using gaseous diffusion technology as the name implies. The gaseous diffusion cascade consists of many stages of equipment connected in series, i.e., in a cascade arrangement. Each stage consists of an electric motor, a compressor, and a converter which contains 235 a porous membrane through which the lighter U F6 diffuses at a slightly faster rate than the heavier 238 U F6. Separation takes place at a rate which is expressed as the square root of the ratio of the molecular weights of the materials being separated. For UF6, the degree of enrichment in each stage is about 1.004 (the square root of 352/349). Thus many stages of equipment are required.

The cascade contains over 4140 stages of equipment which are connected in series. At the current level of enrichment, 2760 stages are required, including purge cascades. Stages are grouped into cells, a cell being the smallest group of equipment that can be removed from service for maintenance. Cells are further grouped into units and units into buildings. Each cell contains bypass piping and inlet and outlet block valves to allow a cell to be taken off stream for maintenance or repair.

All of the equipment in a unit is the same size; there are five sizes of equipment which are designated (in order of decreasing size) as 33 (or 000), 31 (or 00), 29 (or 0), 27 and 25. The X-333 Building contains only one size of equipment (33 size) while the X-330 Building contains 31 and 29 size equipment and X-326 Building contains 27 and 25 size equipment. The largest equipment is at the bottom, i.e., the lowest enrichment, of the cascade and the smallest equipment is at the top. The largest equipment uses 3300 hp motors and the smallest uses 15 hp motors with several steps in between. The process piping which connects the various pieces of equipment ranges up to 42 inches in diameter. Virtually all connections in the cascade are welded to reduce the probability of leakage. Removing any major component besides the motor involves the use of cutting torches; the replacement equipment must be welded in place.

f:\starship\docs\cascade.wpd 1 The process begins with the arrival of natural assay UF6 from a fluorination plant or slightly enriched UF6 (currently 1.9%) from USEC's Paducah (KY) Gaseous Diffusion Plant. In accord with treaties and agreements made at the national level, USEC may also receive low enriched (LEU)

uranium from Russia. This material may be sold as is or it may be fed to the cascade. The UF6 is received in 10- or 14-ton cylinders which are heated in steam autoclaves in the X-342 or X-343 Feed

Vaporization Facilities to vaporize the UF6. The UF6 is fed to the cascade as a gas. Compressors drive the process gas (UF6) through the porous membrane in each stage. The enriched portion which passed through the porous membrane travels up the cascade while the depleted stream is returned to the intake of the compressor two stages below for recycling.

The process of compressing the gas creates large quantities of heat which must be removed. This is accomplished by means of a three stage cooling process. Each converter contains a cooler which is flooded with liquid Refrigerant-114 (R-114) which is vaporized due to the heat it absorbs from the process gas. The refrigerant then rises to a water-cooled condenser where it is condensed and runs back to the converter. All of the cooling systems are thermosyphon systems which contain no moving parts. The refrigerant is cooled in the condensers by recirculating cooling water which is pumped under pressure to large cooling towers where the heat is removed by air flowing upward through water falling through the cooling towers.

R-114 is also known as CFC-114 and Freon-114, Freon being a registered DuPont trademark for its original line of refrigerant products. The production of R-114, a Class I ozoned-depleting substance, has been banned since January 1, 1996, and is now available only as recycled material. The uranium enrichment plants have conducted extensive research into replacement coolants and have identified several potential replacements, three of which are under active consideration - perfluorobutane

(C4F10), perfluorocyclobutane (C4F8), and perfluorotetrahydrofuran, also called perfluoro-THF (C4F8O). All three substances have received USEPA approval under the Significant New Alternative Policy (SNAP). One of these substances may be introduced as supplies of R-114 are depleted. Current plans call for deploying the replacement coolant at the Paducah, KY plant and shipping R-114 from Paducah to PORTS. However, the replacement coolant may also be deployed at PORTS. Small amounts of the replacement coolant will be introduced into the cascade at PORTS

as impurities in the partially enriched UF6 received from Paducah for further enrichment.

The plant's process coolant systems contain approximately 6.5 million pounds of R-114. Some of this refrigerant leaks to atmosphere and some leaks into the process gas where it is an impurity. Due to its low molecular weight, it moves to the top of the cascade where it accumulates in a "bubble" behind air, nitrogen, and other light gases. The accumulation of excessive amounts of refrigerant in the bubble degrades cascade performance. In order to more efficiently purge the refrigerant from the cascade, a side stream device called the Freon® Degrader is located within the Top Purge Cascade. Gas from the refrigerant bubble is shunted to an electrically heated furnace into which fluorine gas is introduced. The resulting reaction breaks the R-114 (MW = 171) into several lighter molecular weight substances, mostly carbon tetrafluoride (MW = 88) in order to more easily purge it from the cascade. The degradation products are returned to the top purge cascade. The Freon® Degrader may or may not be used depending on operating conditions.

2 After processing, the product (enriched uranium) and tails (depleted uranium) are withdrawn from the cascade into 10-ton and 14-ton cylinders respectively and allowed to solidify. Product withdrawal occurs in the X-333 Low Assay Withdrawal Area (LAW) or the X-326 Extended Range Product Withdrawal Area (ERP). Tails withdrawal occurs in the X-330 Tails Withdrawal Area (Tails). The product cylinders are then taken to the X-344 Toll Enrichment Facility where they are again heated and sampled to verify the enrichment and determine customer charges. The product is then transferred into 2.5 ton customer cylinders. The customer cylinders are placed into protective overpacks and shipped to either the customer or a fuel fabrication plant.

Several ancillary processes are associated with the gaseous diffusion cascade; without them, the cascade would not be able to operate. These are the cold recovery systems, the building wet air evacuation systems, the seal exhaust systems, and the purge cascades. Each of these systems has a vent to atmosphere and each has a continuous stack sampler which operates continuously any time the source is in operation. These systems will be discussed in the following sections. Table 1 lists the radiological vents from the gaseous diffusion cascade.

Table 1. Gaseous Diffusion Cascade Vents

OEPA Source Name PORTS Source Stack ID

P458 X-326 Top Purge Vent (X-326-P-2799) P459 X-326 Side Purge Vent (X-326-P-2798) P460 X-330 Cold Recovery/Building Wet Air Evacuation (X-330-P-272) P461 X-333 Cold Recovery Vent (X-333-P-852) P462 X-333 Building Wet Air Evacuation Vent (X-333-P-856) P424 X-333 Seal Exhaust System Area 1 (X-333-A-851) P425 X-330 Seal Exhaust System Area 2 (X-330-A-262) P426 X-330 Seal Exhaust System Area 3 (X-330-A-279) P427 X-326 Seal Exhaust System Area 4 (X-326-A-512) P465 X-326 Seal Exhaust System Area 5 (formerly P428) (X-326-A-528) P429 X-326 Seal Exhaust System Area 6 (X-326-A-540)

3 Top and Side Purge Cascades

The Top and Side Purge Cascades are an integral part of the gaseous diffusion cascade; it would not operate properly without them. The UF6 process gas contains small amounts of other gases which were either deliberately or inadvertently introduced. Wet atmospheric air continuously leaks into the cascade past the compressor seals and through cracks and pinholes that sometimes develop.

UF6 reacts with the moisture in the air to form gaseous hydrogen fluoride (HF) and uranyl fluoride (UO2F2) which is solid at operating temperatures. This material settles out and degrades cascade efficiency. It also poses a uranium accountability problem as the material appears to be lost. A third concern is the possibility of a nuclear criticality incident if the material is allowed to collect in the process equipment. In order to recover this uranium, fluorine and/or chlorine trifluoride are introduced to remove these uranium deposits. Nitrogen and oxygen from the inleaked air are also present. The process coolant, R-114, also leaks into the cascade. Nitrogen and/or dry air are used to provide a buffer between the cascade and the atmosphere. Some of the buffer gases also leaks into the cascade. Due to the much lower molecular weights of these substances, they flow rapidly to the top cells of the cascade where they block the upflow of UF6 process gas unless they are removed.

The purge cascades perform this function. Ten cells at the very top of the cascade form the purge cascades, with five cells belonging to each the Side and Top Purge Cascades. The two purge cascades are operated in series, the Side Purge being first in line. These cascades remove most of the light gases and vent them to the atmosphere through a system of activated alumina traps. Some of the light gases are recycled to balance pressures in the cascade.

Both of the purge cascades are vented through four inch lines by air jet eductors. Each vent has a continuous vent sampler located after the air jet which pull an isokinetic sample of the stack gas through a pair of activated alumina traps which are referred to as the primary and secondary traps. The primary traps are changed and analyzed weekly and the secondary traps are changed and analyzed quarterly.

The vent lines exit the south end of the building and ascend to the top of a 50-meter tower. Top Purge is vented through a single pipe. At the base of the tower, the Side Purge vent line splits into three pipes to reduce the velocity of the gas stream. All four pipes are four inches in diameter and are tipped with five inch corrosion resistant pipe at the very top of the tower. The four pipes form a square pattern about five feet on a side.

In order for the cascade to operate properly, the two purge cascades must always be in operation. To allow for routine maintenance and equipment failure, the cascade contains a third air jet, the Emergency Jet (E-Jet) which is connected to both the Top and Side Purge Cascade vent lines through block valves. E-Jet contains an isokinetic stack sampler identical to those on the Top and Side Purge vents so that all emissions from the two purge cascades will be monitored. The vent line from E-Jet

4 feeds into the Side Purge vent line at the base of the tower. Side Purge is normally valved into E-Jet to provide extra capacity.

E-Jet does not have a separate exit point. It simply provides an alternate route for the vent streams through a stack sampler to an existing vent such that all emissions from the purge cascades are monitored. The sample traps for the Emergency Jet are changed and analyzed weekly for the primary trap and quarterly for the secondary trap, the same as the Purge Cascade Samplers.

The four pipes should be viewed as a single emission point due to their proximity to each other and the fact that the emissions originated from the same source - two purge cascades connected in series. For modeling under 40 CFR 61 subpart H, the emissions recorded by all three samplers are added together.

Cold Recovery and Building Wet Air Evacuation Systems

As with any equipment, failures will occur. Two ancillary systems have been built into the cascade to facilitate repair and maintenance. Cold recovery systems are used to reduce UF6 concentrations to safe levels prior to opening equipment to the atmosphere. This is done for both worker protection and environmental protection. Cold recovery systems consist of several refrigerated vessels which freeze and trap UF6 from the gas passing through them, reducing the concentration to about 300 ppm. Chemical traps containing sodium fluoride subsequently reduce the UF6 concentration to less than 10 ppm.

Wet air evacuation systems remove wet air from the equipment following repair to prevent it from reacting with the process gas. Both cold recovery and wet air evacuation systems use air jet eductors to draw the air through chemical traps filled with activated alumina and/or sodium fluoride which

effectively reduce the concentration of UF6 to less than 10 ppm. The cold recovery and building wet air evacuation systems are intermittent systems, operating only when needed. Each vent is continuously sampled by an isokinetic sampler while its respective system is in use.

In the X-333 Building, the Cold Recovery and Building Wet Air Evacuation Systems have separate vents. In the X-330 Building, they share a common vent. The X-326 building is not equipped with wet air evacuation or cold recovery system equipment; the contaminated air is returned to the cascade where it will accumulate in the top cells to be processed by the purge cascades.

When equipment is to be removed from service for maintenance or repair, the cell is taken off line

and the UF6 process gas is evacuated back to the cascade. It is then purged with dry air to remove residual UF6 from the equipment before the system is opened to the atmosphere. The contaminated air is then processed through the appropriate cold recovery system (X-333 or X-330 Cold Recovery)

to remove the entrained UF6 before the air is vented to atmosphere.

Once maintenance is complete, the cell is tested to insure that it is leak tight. The moist air in the cell is then removed using the building wet air evacuation system or cold recovery system depending

5 on the concentration of UF6 in the gas. In the X-326 Building this material is returned to the cascade.

Before maintenance, the cell will often be treated with chlorine trifluoride or fluorine to remove any uranium deposits that may have formed as a result of the equipment failure or air inleakage. The

resulting mixtures are also processed through one of the cold recovery systems to remove any UF6 before the material is vented to atmosphere. Again, in the X-326 Building, this material must be disposed of by feeding it to the cascade. The material collects in the top cells where it is removed and processed through one of the purge cascades before it is vented to atmosphere.

Seal Exhaust Systems

The Seal Exhaust Systems are ancillary systems to the gaseous diffusion cascade which is the main process equipment. The seal exhaust systems do not produce a product nor do they have a true process input. They operate continuously since the cascade is never shut down. Their purpose is to help optimize the operation of the cascade by preventing wet air from leaking into the process gas stream. These systems are additional vents from the cascade.

Enrichment takes place in the gaseous diffusion cascade which is a series of 4140 stages of equipment. Under the current 10 percent assay limitation, a maximum of about 2760 stages will be on stream. Each stage contains a compressor which is driven by an external motor. Each

compressor has two seals, one on each end of its shaft, to seal the process gas (UF6) in and moist air out. UF6 reacts instantly with water to form uranyl fluoride (UO2F2) and hydrogen fluoride (HF); cascade performance would be seriously degraded if significant quantities of wet air were allowed

to come in contact with the UF6. The seal cavities are purged with dry air at a low flow rate. The system also has the capability of using dry nitrogen or a mixture of dry air and dry nitrogen. Each seal is connected by piping to a header which is connected to a vacuum pump station.

In order to minimize emissions, the inlet line to each vacuum pump passes through chemical traps which contain alumina granules. The alumina removes gaseous and particulate uranium compounds, technetium compounds, compounds of uranium daughters and transuranics, and gaseous fluorides. Under routine operating conditions, the alumina traps remove these substances down to a residual level of less than one part per million regardless of the influent concentration. Under abnormal conditions, the traps function effectively until breakthrough occurs after which they are totally ineffective. Should this occur, those pumps would be shut down and other pumps started. Adequate warning of abnormal operation should be given by the on-line space recorders (ionization chambers) and other operations instrumentation. Table 2 gives information on the six Seal Exhaust Stations.

6 Table 2. Seal Exhaust Stations

Max. No. of Number Number of Number of Location Stages in of Seals Vacuum Traps/ Operation Serviced Pumps Pump

X-333 Area 1 640 1280 10 1 X-330 Area 2 600 1200 4 3 X-330 Area 3 500 1000 12 3 X-326 Area 4 960 1920 32 3 X-326 Area 5 960 1920 24 3 X-326 Area 6 480 960 24 3 ------Total 4140 8280 106 16

All of the equipment in Area 5 and in parts of Areas 4 and 6 has been shut down and buffered with dry air. A maximum of 1456 stages will be on stream unless material with an assay higher than 5 percent is produced, in which case more stages will be required. The purpose of the seal exhaust system is to maintain a low flow of purge gases through the seal, thereby preventing wet air from

infiltrating into the cascade. Inevitably, a small amount of process gas (UF6) leaks past the seals and is exhausted with the purge gas. The gas stream passes through alumina traps in front of the vacuum pumps and oil demisters following the pumps. Normally only two to six pumps are in operation at a time except in Area 2 where one or two will be on stream.

Continuous Emissions Monitors

Radiation monitors were installed on the purge cascade vents, the cold recovery vents and the seal exhaust vents when they were built. The original monitors, called space recorders, were simple ionization chambers which are still in use. In addition, 5-liter gas bulb samples were (and still are) taken periodically to verify the radiation monitors. A continuous vent monitoring system was developed in house and installed on the outlet of each of the three purge jets, the two cold recovery vents, X-333 building evacuation vent, the six seal exhaust vents, and the X-344 Toll Transfer Facility Gulper System. The continuous vent monitor is an isokinetic sampling system which continuously extracts a flow-proportional portion of the gas stream and passes it through two activated alumina traps in series. On most samplers, the primary trap is removed and analyzed weekly if the source was operated during that week. The secondary trap is changed and analyzed quarterly. The total vent flow and the sample flow are measured and recorded when the traps are changed. The alumina is then removed and analyzed to determine the amount of each constituent collected over the sampling period. The continuous vent monitors analyze airborne discharges to quantify the amount of uranium, technetium, and fluorides released to the atmosphere for environmental and accountability purposes. In addition to the continuous vent monitor sample flow,

7 the total vent flow is measured by a flow sensor probe installed in the vent header close to the sampling point.

Radiological Emissions

The gaseous diffusion cascade is designed to contain the UF6 process gas; control devices further reduce emissions levels. Nevertheless, very small quantities of UF6 and other radioactive materials present in the raw material are emitted. At full production levels, the plant would process approximately 58 million pounds of UF6 per year. Emissions of uranium from all the cascade vents combined are typically 20 to 25 pounds per year. Thus less than 0.0001 percent of the material which is processed is emitted. Technetium, a man-made element resulting from nuclear fission, was introduced into the uranium fuel cycle when spent reactor fuel was reprocessed (from the 1950s until the 1970s). Minor amounts of technetium and uranium decay products such as thorium and neptunium are emitted along with the uranium.

Typical process input data for the gaseous diffusion process are given in Table 3 and typical emissions data for all process combined are given in Table 4. Typical radionuclide emissions for each process vent are given in attachments to the specific vents in the Title V application itself. These data are based on stack sampling data for CY 1993 when the plant's calculated dose to the public was at its highest level ever (for process emissions only), mostly due to emissions of Tc99 resulting from the cleanup of high assay uranium process equipment. It must be stressed that these emissions are such a small percentage of the feed material that they may vary up to several orders of magnitude at a given vent. Predicting vent-specific emission levels is virtually impossible since most emissions of radioactive materials are due to process upsets.

8 Table 3. Estimated Maximum Hourly Material Input to the Gaseous Diffusion Process

Material Use Amount Lb/hr

Uranium Hexafluoride Process Gas 6,598 R-114 Primary Coolant 5.4 Nitrogen Buffer Gas 75 Air Buffer Gas 110 Air Motive Gas for Vent Jets 17,959 Fluorine Uranium Deposit Removal 19.6 Chlorine trifluoride Uranium Deposit Removal 1.8

Notes:

1. The amounts given above are averages over several years when plant operations were near design levels but should not be construed as absolute maximum values as they are not tied directly to operating levels.

2. R-114 is not deliberately introduced into the process gas stream; it is used as the process coolant in closed loop thermosyphon cooling systems. However, substantial quantities of R-114 are lost through leakage to the atmosphere (80%), the cascade (10%) and the recirculating cooling water (RCW) systems (10%). The amount given in the table represents the average amount added annually to replace losses to the cooling systems. Losses represent approximately 6.2 percent of the amount of coolant contained in the cascade.

9 Table 4. Typical Emissions Data for the Gaseous Diffusion Cascade*

Chemical Amount

Average Maximum

lb/hr TPY lb/hr TPY

Uranium 2.0 E-3 8.78 E-3 4 3.2 E-1 Technetium-99 2.4 E-4 1.05 E-3 2.2 E-1 1.1 E-2 Hydrogen Fluoride 16.38 19.32 18.55 21.42 R-114 41.16 180.28 500 400 Arsenic 8.0 E-4 3.0 E-3 9.7 E-2 1.0 E-2 * For all process vents combined. Explanations for the above emissions can be found at the end of this document.

The USEPA has established a plant-wide emission limit of 10 millirem per year effective dose equivalent (EDE) to the most exposed member of the public resulting from operations at DOE facilities (40 CFR 61.92). This is a very conservative limit considering that a worker may be exposed to 5 rem per year, a level 500 times as high as the limit to the public. Exposure to the public in the United States from natural sources amounts to approximately 300 mrem per year and radiation from man-made sources adds another 60 mrem per year. Thus, the exposure to the public from activities at PORTS is insignificant in comparison. PORTS believes that it would be appropriate for the OEPA to adopt the USEPA facility-wide limit rather than attempting to set vent-specific limits for PORTS. PORTS requests that vent-specific emission limits not be imposed by the OEPA and that the USEPA limit of 10 mrem/yr for the entire facility be adopted by the OEPA.

The dose to the public is calculated by first determining total plant emissions for each different radionuclide emitted during the year. These quantities are then input into a USEPA-mandated computer model (CAP88 or CAP88-PC) along with the annual meteorological data. The model then calculates the expected concentration of each radionuclide at the plant perimeter in each of the 16 compass points. Finally, the model calculates the dose from each radionuclide to its respective target organ (bone, lung, etc.) and sums the results to give the total effective dose equivalent.

Each facility owned or operated by DOE submits an annual report to USEPA in accordance with 40 CFR 61.94 showing its radiological emissions and dose assessment. Emissions from PORTS have always resulted in an effective dose equivalent (EDE) well below the 10 mrem/yr limit. To date, the maximum EDE from PORTS has been 1.69 mrem per year in 1998 due to a fire in

10 the X-326 Process Building on December 9, 1998. The EDE is typically approximately 0.13 mrem/yr. Copies of the annual NESHAP report are furnished to the Ohio EPA. Table 5 gives the annual EDE for 1993-1998.

Table 5. Annual Dose Assessment to Members of the Public

Year EDE mrem/yr

1993 0.91 1994 0.06 1995 0.13 1996 0.14 1997 0.12 1998 1.69

Notes:

1. EDE values through 1995 are for total plant operations; a single report and dose assessment was prepared for the site. Since 1996, values are for USEC operations only; separate reports and dose assessments are now prepared per USEPA guidance.

2. The majority of the dose in 1993 (at least 0.8 mrem) was due to the release of technetium from the X- 326 Process Building during the shutdown, cleanup, and mothballing of the high assay production facilities. Long-dormant technetium deposits were disturbed and quickly overwhelmed the control traps, resulting in unusually large emissions of technetium.

3. The dose from normal operations in 1998 was 0.12 mrem. The remainder, 1.57 mrem was due to a fire in the X-326 Process Building. Much of the uranium that was released during the fire was converted from fluorides (Class Y) to oxides (Class D); the technetium was converted from Class D to Class W; and the uranium daughters were converted from Class W to Class Y. The longer retention times in the body resulted in much larger EDEs than would have resulted from these same losses during normal operations.

Nonradiological Emissions

Several nonradiological substances are emitted from the gaseous diffusion cascade and/or from several ancillary processes associated with the cascade. These ancillary processes include the X-342 Fluorine Generation Facility and the X-705 Pellet Dryer. Several non-radiological substances are emitted by these sources, either directly from the source or indirectly from the cascade. These emissions include HF, R-114 coolant, and arsenic which was inadvertently introduced to the enrichment process in years past. Each of these substances will be discussed individually in the following sections.

11 Hydrogen Fluoride

Hydrogen fluoride (HF) is the major hazardous emission from the cascade. HF comes from two

sources in the cascade — 1) the reaction of UF6 with water to form uranyl fluoride and hydrogen fluoride and 2) the reaction of cell treatment gases (fluorine and chlorine trifluoride) with water which also releases hydrogen fluoride. These reactions will occur in the process piping if enough moisture leaks into the system; otherwise, they will occur in the atmosphere after the gases are released.

Hydrogen fluoride is also emitted from two ancillary processes — the X-705 Sodium Fluoride Pellet Dryer and the X-342 Fluorine Generation Facility. Although not a part of the gaseous diffusion process, the X-705 Pellet Dryer produces sodium fluoride pellets for use in chemical traps on the process vents. The pellet dryer is an electrically heated oven in which sodium bifluoride pellets are heated to form sodium fluoride pellets. One to two 400-pound batches are processed monthly; each batch yields 271 pounds of sodium fluoride pellets and 129 pounds of hydrogen fluoride which is vented to the atmosphere. Annual emissions of HF would be a maximum of 3096 pounds and an average of 1548 pounds based on historical data. The X-342 Fluorine Generation Facility converts HF to fluorine gas by means of an electrochemical process. The fluorine is used primarily to remove uranium deposits from the process equipment. Table 6 gives emission rates of HF from these processes.

Table 6. Hydrogen Fluoride Emissions

Year Cascade Pellet Fluorine Total Dryer Generation lb/yr lb/yr lb/yr lb/yr tons/yr

1994 19,426 516 9,787 29,729 14.86 1995 15,478 1,935 9,367 26,780 13.39 1996 5,821 1,161 2,221 9,203 4.60 1997 6,660 774 1,479 8,913 4.46 1998 11,338 0 2,465 13,803 6.90 1999 10,121 129 986 11,236 5.62

12 Arsenic

Low levels of arsenic are emitted. Arsenic was inadvertently introduced into the nuclear fuel cycle several years ago when fluorine containing arsenic as an impurity was used to fluorinate the uranium. The arsenic became trapped in the process and is emitted slowly but continuously. Emissions of arsenic are in the range of 20 pounds per year.

Refrigerant-114 (R-114)

R-114 is currently used as the process coolant. Some of the R-114 is lost due to leaks in the system caused by mechanical failure, corrosion and erosion of the coolers and piping, other accidental causes, and, on occasion, by human error. Since 1993, losses have averaged approximately 180 tons per year under normal operating conditions. The possibility for higher emissions exists. Under ideal circumstances there would be no R-114 emissions; however, small leaks are always present and large releases occur periodically due to equipment failure. Table 7 gives R-114 release data.

Table 7. R-114 Losses

Year R-114 Released Lbs

1993 344,000 1994 370,000 1995 300,000 1996 320,000 1997 360,000 1998 390,000 1999 440,000

PORTS has a program in place to reduce the loss of R-114 from the cascade. This involves early identification of small leaks, watching for increasing leak rates, and assigning a high priority to the “top ten” leakers. Methods for making “in situ” repairs have been developed and other methods are under study. “In situ” repairs are made on systems with small leak rates while the equipment is still on line but those with large leak rates must be repaired by physically removing the equipment from the process.

Historically, approximately ten percent of the overall R-114 emissions leak into the cascade while ten percent go to the Recirculating Cooling Water System (RCW), and eighty percent is

13 emitted directly to the atmosphere. These percentages vary from year to year but are representative of historical emissions pathways. Assuming losses of 200 tons per year (slightly higher than recent losses), 20 tons go to the cascade, 20 tons go to the RCW, and 160 tons go directly to the atmosphere. R-114 losses amount to about six percent of the total refrigerant contained in the cascade (6.5 million pounds). This is well within the USEPA allowable annual leak rate of 35 percent for industrial process cooling systems.

R-114 enters the process gas stream through leaks in the cooling systems. Due to the molecular

weight of the R-114, it collects in a "bubble" between the UF6 process gas and the light gases being purged. To help eliminate the refrigerant, the process gas may be passed through a side- stream treatment called the Freon® Degrader. This system is a closed loop in the Top Purge Cascade. The degrader electrically heats the process gas and injects fluorine to convert the R-114 into five components of lower molecular weight. Ninety percent of the R-114 entering the degrader becomes carbon tetrafluoride; the remaining ten percent is equally comprised of hexafluoroethane, chloropentafluoroethane, chlorofluoroethane, and dichlorodifluoromethane (R-12). The Freon® Degrader may or may not be used depending on the quantity of R-114 that has collected at the top of the cascade. Emissions due to the Freon® Degrader are given in Table 8.

Table 8. Emissions Created by Freon® Degrader** (When in use)

Chemical Amount Average Maximum R-114 Emission Rate @20 tpy @40 tpy lb/hr TPY lb/hr TPY

Carbon Tetrafluoride 4.11 18 8.22 36 Hexafluoroethane 0.11 0.5 0.23 1 Chloropentafluoroethane 0.11 0.5 0.23 1 Chlorofluoroethane 0.11 0.5 0.23 1 Dichlorodifluoromethane 0.11 0.5 0.23 1

** Average R-114 emissions are 200 TPY. Approximately 10% (20 tpy) leaks into the Cascade and passes through the Freon® Degrader if it is in use. If not, it goes to atmosphere. Approximately 10% more (20 tpy) leaks into the Recirculating Cooling Water System (RCW) and is vented through the cooling towers. The remaining 80% (180 TPY) escapes directly to the atmosphere. The Freon® Degrader is a closed component of the Cascade;it does not have an external vent. Degradation products from the Freon® Degrader are returned to the Top Purge Cascade and are vented through the Top Purge Cascade Vent. The Freon® Degrader is not shown on the Cascade Diagram; only vents to atmosphere are shown.

14 Ambient Air Concentrations of Hydrogen Fluoride

Argonne National Laboratory modeled emissions from the Gaseous Diffusion Cascade for inclusion in an environmental impact statement for PORTS using the ISC model. Hydrogen fluoride emissions were modeled with an input of 11 tons per year and using composite meteorological data for the years 1985-1990. The maximum ground level concentration was 0.355 :g/m3 along the East Perimeter of the Plant. PORTS scaled the Argonne concentration value to reflect a level of 21.42 tons per year (the maximum anticipated release of HF) and arrived at a value of 0.691 :g/m3.

PORTS used the much more conservative USEPA SCREEN model to determine the ambient air concentration of hydrogen fluoride from plant operations. The estimated concentration for the estimated maximum emissions of 21.42 tons of HF is 14.06 :g/m3. PORTS used the OEPA REVIEW OF NEW SOURCES OF AIR TOXIC EMISSIONS OPTION A to determine the Maximum Acceptable Ground-Level Concentration (MAGLC) under the Ohio Air Toxics Policy by using the MAGLC formula: (TLV/10*8/X*5/Y) = 4(TLV/XY). PORTS used the 1994 ACGIH Handbook of Threshold Limit Values (TLV) to obtain a ceiling value of 2.6 mg/m3 for hydrogen fluoride (the HF value was listed as F-). PORTS then calculated the HF concentrations (HF values can obtained by multiplying F- values by a factor of 1.05. The conversion factor is obtained by dividing the molecular weight of the HF by the molecular weight of F-. The molecular weight of HF = 20, F- = 19, therefore the conversion factor is 20/19 = 1.05).

The MAGCL was then calculated for three different scenarios. The first scenario was the TLV/42 which yielded a maximum allowable HF concentration of 65.16 :g/m3. The second scenario, TLV/75, yielded a maximum allowable HF concentration of 36.49 :g/m3. The final scenario, TLV/100, yielded a maximum allowable HF concentration of 27.36 :g/m3. The TLV/100 has been proposed as a new MAGCL level by the OEPA, however it has not been adopted. The HF concentration at PORTS for the maximum emissions level is 51 percent of the MAGLC for the TLV/100 scenario and 22 percent of the MAGCL for the TLV/42 scenario. Thus, the ambient air concentrations due to plant emissions should be well below the levels allowed by any of the MAGLC scenarios.

Calculation Methodology

R-114

The Maximum tons per year (TPY) is derived from the estimated losses through all pathways, Direct leaks to the atmoshpere, through the RCW system, and to atmosphere through the diffusion cascade (400 ton per year).

15 The Maximum pound per hour (lb/hr) was calculated from an accidental release of 16,239 lb which occurred in a forty-eighty hour period. This yielded a rate of 338 lb/hr. For assurance due to the possibility of larger releases the number was raised to 500 lb/hr.

The Average tons per year (TPY) was determined by averaging the R-114 emissions from 1993 through 1999; the average was 180.28 tons per year.

The Average pounds per hour (lb/hr) was calculated by using the average number of pounds per year divided by the number of hours in a year, the average pounds per hour is 41.16.

360,571 lb/yr divided by 8,760 hrs (365 days X 24 hrs/day) equals 41.16 lb/hr.

Uranium, Technetium, and Other Radionuclides

The primary hazard from the radionuclides present at PORTS is the ionizing radiation emitted by the substance, not the chemical hazard. In order to determine the effects of radionuclides on the body, it is necessary to examine the quantity and type of radiation emitted. The quantity of each radionuclide emitted from a source, expressed in Curies, is referred to as the source term. The source term that is used to calculate the EDE includes all releases from the plant site, including routine emissions (whether stack or fugitive, monitored or unmonitored) and emissions from incidents, accidents, fires, and natural disasters.

The USEPA limit for radionuclide emissions from DOE facilities is 10 mrem per year effective dose equivalent (EDE). To date, the maximum EDE due to emissions from PORTS has been 1.69 mrem per year in 1998 due to a fire in the X-326 Process Building on December 9, 1998. At current uranium assay levels (5 percent) and emission rates, 10 mrem would be equivalent to almost 7,700 curies (1490 kg or 3278 lbs) of uranium plus 25,700 curies (1,500 kg or 3300 lb) of technetium. PORTS emissions are far below the extremely conservative 10 mrem/yr limit established by the EPA.

The EDE is highly dependent on the radionuclide mix in plant emissions and upon the meteorological conditions during the year. The radionuclide mix depends upon where in the process the emissions occur. The lighter isotopes (234U, 235U, 236U, and 99Tc) migrate to the top of the cascade and the 238U migrates to the bottom of the cascade. 234U emits over 18,000 times as much alpha radiation as 238U; 235U and 236U fall in between. Once emitted, the radioactive materials are dispersed by the wind; the ultimate distribution depends on the meteorological conditions, particularly the wind speed and direction. Due to variability in meteorological conditions, primarily wind speed and direction, the location of the maximum EDE varies from year to year.

Therefore, it is impossible to determine maximum emissions rates in terms of pounds per hour or tons per year (or even Curies) which would cause an EDE of 10 mrem/yr which is an extremely conservative limit in the first place. In order to determine the EDE, total plant emissions (in grams) of each radionuclide are first determined. The total curies of each radionuclide are then

16 determined by multiplying the quantity in grams of each radionuclide by the specific activity (in curies per gram) for that radionuclide. These data are then input into the CAP88 model along with the annual meteorological data file, average annual temperature, and annual rainfall.

CAP88 first determines the concentration (in curies) of each radionuclide at each receptor location in each of the 16 compass points. Next, the effect of each radionuclide on specific target organs (i.e., uranium to bone) is determined in terms of dose (mrem/yr). The individual doses are then summed and the result is the EDE to the individual. The largest dose to any individual is the EDE.

17 Arsenic

All Arsenic values were calculated from samples obtained from 8/18/93 through 3/30/94.

The Maximum tons per year (TPY) was determined by obtaining the average pound per year value which was extrapolated from the above mentioned sampling period. The average value was multiplied by a factor of 3 to obtain an assumed maximum value expressed in tons per year.

6.616376 lbs/yr multiplied by 3 equals 19.84913 lbs/yr divided by 2000 lbs/ton equals 0.010 tons per year.

The Maximum pounds per hour (lb/hr) was determined by assuming that the largest weekly emissions were emitted in a one hour period 0.097 lb/hr.

The Average tons per year (TPY) was determined by summing the results of all vents which showed an emission plus the established limit of detection for the remaining vents for all weeks converted to tons per year.

The Average pounds per hour (lb/hr) was determined by summing the results of all vents which showed an emission plus the established limit of detection for the remaining vents for all weeks expressed in pounds per hour.

Hydrogen Fluoride

HF from the Cascade

Hydrogen fluoride emissions from the cascade were based on measured vent emissions.

HF from the X-705 Pellet Dryer

Emissions from the X-705 Pellet Dryer were based on the stoichoimetry and process rates. Each batch uses 400 pounds of sodium bifluoride pellets. The equation for the process is as follows:

NaHF2 + heat ö NaF + HF amu 62 ö 42 + 20 lbs 400 ö 271 + 129

Annual emissions = 129 lb/batch x batches/yr

18 HF from the Fluorine Generation Process

Emissions from the Fluorine Generation Process were based on HF feed rates and fluorine production rates. Each cylinder of HF weighs 850 pounds and normal usage is one to two cylinders per month.

It is known from experience that the actual yield is only approximately 71 percent of the HF fed to the fluorine generators as opposed to 95 percent theoretical yield. The Fluorine Generation Facility contains four fluorine generators which employ a molten potassium fluoride (KF) salt which is saturated with hydrogen fluoride. The HF is electrolytically converted to hydrogen and fluorine, the hydrogen being vented. Only one of the generators is normally on line. The off- line generators are kept hot to prevent the KF salt from solidifying and ruining the generator. There is a slow, steady loss of HF from the off-line generators which is periodically replaced. This accounts for much of the missing 24 percent that should have been converted to fluorine. Five percent of the original mass of the HF is hydrogen.

The equation for the process is as follows:

2HF ö H2 + F2 amu 20 x 2 ö (1 x 2) + (19 x 2) 40 ö 2 + 38 lbs 850 ö 42.5 + 807.5 (theoretical yield) 850 x 0.71 ö 603.5 (71% is observed yield)

Annual emissions = cyl/yr x 850 lb/cyl x 0.71 yield

19