The Invisible Woman

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Complete Radionuclide List

This section provides additional detail on the characteristics and sources of the radionuclides most important for assessing radiological impacts on Department disposal operations.

C.2.1 Tritium

Tritium (³H) is a radioactive isotope of hydrogen. It has a half-life of 12.3 years and decays to helium-3 (³He) with the emission of a beta particle and no gamma ray. Tritium produces a very low-energy beta particle and is usually considered one of the least radiologically hazardous of the radionuclides. However, since it can replace normal hydrogen in chemical compounds essential for life, tritium poses a potential hazard that can be very mobile within the biological environment.

Light water reactors produce a small amount of tritium, primarily from ternary fission. Most tritium created in these reactors remains in the fuel rods. The major source of tritium in the DOE complex was the tritium production reactors. None of these reactors are currently producing, but a stockpile of tritium remains as part of the DOE mission. Presently, tritium is used in testing, component maintenance, and research applications.

The primary chemical waste forms of tritium from DOE activities are tritium gas and tritiated water, either as a liquid or vapor. Additionally, tritium waste forms generated from the thermonuclear weapons program (e.g., tritium production reactors) are lithium metal hydrides.

Tritium substitutes readily for ordinary hydrogen in water, and thus becomes part of the hydrological cycle. Through sandy soils, migration of tritium takes place at the same velocity as groundwater through sandy soils. However, the migration of tritium in groundwater is influenced by the soil type. Tritium migration is not slowed in sandy soils; but in clay soils, a small number of tritium atoms may exchange with ordinary hydrogen atoms in water molecules that are bound within the clay, thus slowing the migration.

The mechanisms of tritium gas uptake in vegetation are not well understood, but plants have the capability to oxidize tritium to form tritiated water. Many of the metabolic reactions that take place in living organisms are involved with the transfer of hydrogen. Any of these reactions can involve tritium instead of ordinary hydrogen. The oxygen and nitrogen atoms in organic molecules make it much easier for tritium to replace hydrogen associated with these groups than with hydrogen attached to carbon ato ms.

The biological half-life of tritium in the human body is about 10 to 12 days. The uptake of hydrogen in humans can occur through inhalation, ingestion, or absorption through the skin. The rate of inhalation is about two times the rate of absorption through the skin.

C.2.2 Cesium-137

Cesium-137 (¹³⁷Cs) is not a naturally occurring radionuclide. Its half-life is 30.2 years, and it emits one to two high-energy beta particles. Approximately 85 percent of all ¹³⁷Cs decays result in the emission of a 662 keV gamma ray. Due to the gamma ray energy of ¹³⁷Cs, it has been used to sterilize medical supplies and milk cartons, and irradiate food.

The primary means of producing ¹³⁷Cs is via nuclear fission. Industrial applications of ¹³⁷Cs include the production of plastic shrink tubing (irradiated plastic has the tendency to shrink after being heated); radiography to inspect metal castings and welds for flaws and material defects (e.g., cracks in steel pipes); radioactive measurement gauges for liquid or solid thicknesses (e.g., gauging of automobile sheet steel); treatment of sewage sludge to kill bacteria and viruses; and medical radiotherapy to kill cancerous tissue.

Chemically, cesium behaves like other alkali metals (lithium, sodium, potassium, etc.) and has the simplest of elemental chemistries (excepting the inert gases, such as helium). Cesium reacts with most other elements directly and reacts explosively with air and water. Therefore, metallic cesium must be handled in an inert atmosphere. Cesium reacts with most nonmetals to produce one or more binary compounds; it also forms numerous alloys and compounds with other metals, such as lead and tin. Various oxid es, sulfides, and similar compounds are readily hydrolyzed by water-forming cesium hydroxides. Cesium salts are generally characterized by high melting points, electrical conductivity of the melts, and high solubility in water.

The largest source of ¹³⁷Cs, and therefore the largest potential for waste material, is from nuclear reactors and the large inventory of ¹³⁷Cs stored in irradiated fuel. DOE also maintains a large inventory of ¹³⁷Cs as Special Case Waste in the form of sealed sources. These sources were designed to generate known amounts of gamma radiation for equipment and food sterilization, as well as other purposes. A small quantity of ¹³⁷Cs waste is also generated in research facilities. The primary waste forms that may contain ¹³⁷Cs, in addition to other fission products, include contaminated scrub water, decontamination solutions, demineralizers, contaminated clothing or gloves, contaminated tools and equipment, ion exchange resins, and filters.

The behavior of cesium in the environment is dictated by its chemical properties. Because of its high solubility, cesium generally moves with the ground water but is retained in clay soils. If cesium is not held in the soils, it can relocate through the root system of plants or through the leaves and stems by atmospheric deposition. Cesium-137 deposited on leaves is likely to penetrate into the plant more rapidly than cesium absorbed from the ground.

Absorption of cesium by humans takes place primarily through the digestive tract. Cesium, like potassium, enters body cells; however, cesium is bound more tightly than potassium. The biological half-life for cesium in humans depends on age, sex, and body mass. For adult humans, the biological half-life varies between 50 and 150 days, with a mean value of 101 days; for infants and children, the biological half-life ranges between 5 and 50 days.

C.2.3 Strontium-90

Strontium-90 (⁹⁰Sr) is not a naturally occurring radionuclide. It has a half-life of 29 years. Almost no gamma ray particles are released from the ⁹⁰Sr decay sequence. For example, 99.98 percent of all ⁹⁰Sr decays result in the emission of a 523 keV maximum-energy beta particle and a 2280 keV maximum-energy beta particle from ⁹⁰Y decay with no gamma ray. Chemically, strontium behaves like the other alkaline-earth metals (e.g., magnesium, calcium, and barium) a nd has a relatively simple chemistry. In a nuclear reactor fuel element, strontium preferentially forms a stable oxide. When released into the atmosphere, strontium oxide has a high affinity for water and will readily form a soluble hydroxide.

Strontium-90 exists because of human activities. Due to the high beta particle energies of ⁹⁰Sr (and its daughter ⁹⁰Y), it has been used in industrial applications to measure thicknesses of paper, plastic, rubber, and metal foils. It also has some medical applications such as treatment for some eye and skin diseases. Due to the low gamma ray activity of ⁹⁰Sr, it is not normally used as an irradiation source. The primary means of producing ⁹⁰Sr is via nuclear f ission, and the main source of ⁹⁰Sr is from fission product recovery.

Most of the ⁹⁰Sr that exists is trapped inside the spent UO₂ fuel in complex chemical compounds. Strontium-90 can be recovered from high-level radioactive waste streams for eventual separate disposal or use in industrial or medical applications. A large inventory of ⁹⁰Sr exists at Hanford. Some sealed sources used to generate known amounts of gamma radiation for thickness gauging and other purposes contain ⁹⁰S r. Strontium-90 is also used in some radioisotope thermoelectric generators.

The primary low-level waste streams produced at light water reactors include both wet and dry wastes, such as spent-ion exchange resins, filter sludges, filter cartridges, and compactible trash. Most of these wastes will contain small amounts of ⁹⁰Sr in the presence of other radioactive nuclides. Small amounts of radioactive waste containing ⁹⁰Sr are also generated in research facilities.

Since strontium typically is in a soluble form and chemically bonds less with surrounding soil and rock than many other radioactive species (for example ¹³⁷Cs), it tends to migrate further with the ground water. Strontium tends to percolate deeper into the soil due to the effects of leaching by soil moisture. This has the beneficial effect of reducing the probability that strontium will become airborne due to surface erosion, but it also means that strontium can more quickly migrate into an und erground water supply. Also because of its solubility, ⁹⁰Sr can be taken up by plants through the roots, which is the principal means by which strontium gets into the food chain. Absorption through the upper plant structures (leaves, stem) does not happen to an appreciable degree.

Absorption of strontium by humans takes place primarily through the gastrointestinal tract. Once in the body, up to 95 percent of ⁹⁰Sr is eventually excreted within a few weeks. The remaining fraction is fixed within the skeletal structures, preferentially in the areas of bone growth. Health hazards include the possibility of bone cancer. Strontium enters the body and can replace calcium atoms within the bone. The effective half-life of ⁹⁰Sr that remains in the skeletal structures is about 18 years (including both decay and biological/chemical processes).

C.2.4 Uranium

Natural uranium chiefly contains three isotopes of uranium; uranium-234 (²³⁴U), uranium-235 (²³⁵U), and uranium-238 (²³⁸U). Uranium-234 is a member of the ²³⁸U decay chain and usually found in equilibrium with its ²³⁸U parent. The amount of ²³⁸U in natural uranium is more than 99 percent, but the ²³⁵U, present at 0.72 percent in natural uranium, is most radioactive and important in nuclear weapons and nuclear reactors. Enri ching uranium, a process by which the percentage of ²³⁵U is increased in relation to the other uranium radionuclides, makes it useful in nuclear weapons and nuclear reactors. Uranium-234 has a half-life of 2.5 x 10⁵ yr and exists as 0.0057 percent of natural uranium. Uranium-230 (²³⁰U) is also a member of the ²³⁸U decay chain but has a short half-life of only 20.8 days.

Uranium-238 has a half-life of 4.47 x 10⁹ years. This radionuclide decays by alpha particle emission to ²³⁴Th. A series of 14 alpha and beta transitions results in the stable ²⁰⁶Pb nuclide. Moderately high-energy alpha particles, low-energy x-rays, and low-energy beta particles are emitted during this series of transitions.

The presence of uranium can be very significant in assessing the long-term performance of a LLW disposal facility due to the quantity, radiotoxicity, and mobility of its daughter products, which include isotopes of radium and radon.

Uranium is very reactive and forms compounds with many other elements, such as the halides, oxygen, and hydrogen. The ability of soil to adsorb uranium out of the ground water depends on a number of factors, including pH and the presence or absence of complexing agents. In the presence of low pH soil conditions, uranium is very soluble and tends to remain in the ground water rather than being adsorbed by the soil.

The principal radiological hazard associated with uranium is due to the relatively high-energy alpha particles its radionuclides and daughters emit. Since these alpha particles do not penetrate materials easily, external exposure to uranium does not pose a high risk. The principal risk is due to either inhalation or ingestion. Inhalation occurs either from release of volatile uranium compound or from suspension of volatile uranium-laden aerosols. Ingestion can occur when the uranium is introduced into water for consumption or the food chain by plant uptake. When uranium is either ingested or inhaled, it is removed from the body with a biological half-life varying between 6 and 5,000 days, depending on which organ has become contaminated. Uranium tends to concentrate in the kidneys and the bones. Additionally, if inhaled, the lungs can receive a dose.

C.2.5 Plutonium

Plutonium is an element produced in nuclear reactors by neutron irradiation of uranium. Neutron capture converts uranium-238 (²³⁸U) into neptunium-239 (²³⁹Np) which transforms, in a matter of days, into plutonium 239 (²³⁹Pu). Absorption of more neutrons and other nuclear reactions generate the other isotopes of plutonium, such as plutonium-238 (²³⁸PU), plutonium-240 (²⁴⁰Pu), plutonium-241 (²⁴¹Pu), and plutonium-242 (²⁴²Pu). All isotopes of plutonium are radioactive.

Plutonium-239 is fissile (i.e., fissionable by neutrons), and thus able to sustain a nuclear chain reaction. This property made ²³⁹Pu a suitable material for nuclear warheads. Plutonium was produced in special reactors at Hanford and SRS. No plutonium for weapons has been produced since 1988.

Plutonium-240 is more radioactive and generates more heat than ²³⁹Pu. In addition to ²³⁹Pu, weapons grade plutonium contains up to 6 percent ²⁴⁰Pu; fuel-grade plutonium used in breeder reactors contains up to 18 percent ²⁴⁰Pu; and reactor grade plutonium from power-producing reactors contains up to 24 percent ²⁴⁰Pu. Plutonium-238 is intensely radioactive and generates significant quantities of heat. It is used to make general purpose heat sources and radioisotope thermoelectric generators to produce electricity in spacecraft.

All plutonium isotopes except ²⁴¹Pu emit alpha particles as the principal form of radiation. Plutonium isotopes also emit small amounts of gamma and neutron radiation. Plutonium-241 decays into americium-241 (²⁴¹Am), which is a much stronger source of gamma radiation.

Plutonium is usually stored as metal or as powdered oxide. Plutonium metal, the form used in nuclear weapons, will corrode to the oxide form if exposed to air or moisture. Other processes involving plutonium include purification in strong acids, ion exchange, and physical state conversion. Because of these processes, the forms of plutonium found in the DOE complex include metal, oxide, solutions, and scrap/residues.

Most data on plant uptake of plutonium have shown that the majority of plutonium found in native plants and agricultural crops comes from surface deposition rather than soil-plant absorption via the roots. Plutonium concentrations are dependant on plant species, plant age, vegetation type, soil pH, positive ion exchange capability, mineral and organic composition, the plutonium chemical form, and duration of the contamination. Root absorption of plutonium, when present in soil, does occur; however, transl ocation to the aboveground portions of the plant is limited to less than 0.01percent of the total plutonium concentration in the soil.

Inhalation of plutonium delivers significant internal radiation doses to the body. Absorption of plutonium via ingestion delivers a much lower internal dose than inhalation. When plutonium enters the body, its biological behavior is determined by its physical and chemical characteristics. Very small plutonium particles are complexed in the blood and deposited in the liver and on bone surfaces. These d eposits are metabolized very slowly, with biological elimination half-lives of about 50 to 100 years.

C.2.6 Carbon-14

Carbon-14 (¹⁴C) is a long-lived radionuclide with a half-life of 5,730 years. When ¹⁴C undergoes radioactive decay, the nucleus emits a single beta particle with an energy of 0.156 MeV. There are no radionuclides that decay to form ¹⁴C; therefore, it has no parent. The ¹⁴C radionuclide is naturally produced in the upper atmosphere by the reaction of neutrons of cosmic ray origin with nitrogen, oxygen, and carbon.

Carbon-14 is also produced in nuclear reactors as a result of absorption of neutrons by nitrogen, carbon, or oxygen present as components of air, coolant, moderator, structural materials, fuel, or impurities. Additionally, ¹⁴C is produced for preparation of labeled materials used in medical or biological tracer research.

Because of neutron activation of nitrogen-14, an impurity found in non-fuel reactor components, the activated metals waste stream from nuclear reactors contains a substantial amount of ¹⁴C. Additional ¹⁴C produced in the coolant may add to the contamination of other waste streams including ion exchange resins, concentrated liquids, filter sludge, cartridge filters, and trash.

The chemistry of carbon is quite complex and involves both oxidation-reduction and nonoxidation-reduction reactions. The predominant forms of ¹⁴C available for transport at a LLW disposal site are carbon dioxide (¹⁴CO₂), methane (¹⁴CH₄), carbonate ion (¹⁴CO₃^-2), bicarbonate ion (H¹⁴CO₃^-), and elemental carbon in activated metals.

The main forms of ¹⁴C of concern for ground water transport are bicarbonate and carbonate. Bicarbonate is produced during the dissolution of calcium carbonate into water with a pH of 6.5 to 9, or in the dissolving of carbon dioxide. These two categories encompass essentially all of the ¹⁴C activity in the waste disposal site available for ground-water transport. Ground-water sources should not be contaminated by activated metals with ¹⁴C. The ¹⁴C found in these metals is expected to remain in the disposal site because ¹⁴C atoms are dispersed throughout the metal matrix; most of the metals are corrosion resistant (stainless steel); the corrosion products are, in general, insoluble in either freshwater or seawater; and the carbon is in its elemental form and thus unavailable for microbial activity.

Carbon distributes itself quickly among the major environmental components—the atmosphere, the biosphere, and surface waters. Transfer among these components takes place over a period of a few years. Carbon-14 is easily transferred during biological processes and soil-plant interactions that involve carbon compounds.

The metabolism and kinetics of ¹⁴C in the human body follow those of ordinary carbon. A fraction of carbon introduced into the body is retained as protein, fat, carbohydrates, and other materials. The remainder of ingested carbon is excreted unchanged or is metabolized to CO₂, urea, or other metabolites. Inhaled ¹⁴CO₂ rapidly equilibriates with the air in the lung and enters many organic components of body tissue. The ingestion pathway is the primary route for ¹⁴C incorporation. The corresponding biological half-life of ¹⁴C is approximately 40 days.

C.2.7 Technetium-99

Technetium-99 (⁹⁹Tc) is a long-lived radionuclide with a half-life of 213,000 years. When it undergoes radioactive decay, its nucleus emits a single beta particle with a maximum energy of 0.293 MeV. The decay of ⁹⁹Tc forms stable ruthenium-99 (⁹⁹Ru). Oxidation-reduction reactions dominate the chemistry of ⁹⁹Tc. The two most common forms of technetium are the pertechnetate ion (TcO) and technetium dioxide (TcO₂).

Uranium and plutonium undergoing thermal fission in nuclear reactors produce most of the ⁹⁹Tc that exists as waste. This waste comes in several forms, including ion exchange resins, filter sludge, cartridge filters, and decommissioning waste. Some ⁹⁹Tc is present at certain fuel cycle facilities (such as enrichment facilities) because of the recycling of spent reactor fuel that took place within the DOE complex. Several nuclear power plant waste streams that may contain ⁹⁹Tc are usually mixed with concrete to create a solid waste form. Some ⁹⁹Tc waste is also generated through medical, industrial, and academic research.

The high solubility of pertechnetate allows it to move quite rapidly in ground-water systems. The migration rate of pertechnetate is expected to be very close to the velocity of ground water unless it is reduced to a less soluble form. The pertechnetate ion is not volatile; its airborne escape from a LLW disposal facility into the atmosphere is not a concern.

The main route of entry of ⁹⁹Tc into the human body is by ingestion. Once in the body, ⁹⁹Tc localizes in the thyroid gland and the gastrointestinal tract. Within 10 hours, it redistributes to the stomach and organs with excretory functions, such as the kidneys and salivary glands. The time required for the body to eliminate one-half of an amount of ⁹⁹Tc by regular processes of excretion is approximately 60 hours. Very l ittle ⁹⁹Tc is assimilated by the muscle or the brain. Hair, however, retains ⁹⁹Tc for long periods of time after a dose and can be a good indicator of ⁹⁹Tc contamination.

C.3 Processes That Generate LLW

This section describes the major DOE missions that have and are creating LLW within the complex.

C.3.1 Nuclear Fuel Cycle

Nuclear fuel cycle wastes contain the isotopes of uranium, ²³⁵U and ²³⁸U, and small amounts of their daughter products. They are produced in the early steps of the fuel cycle, at the conversion facilities, at the enrichment facilities, and at the fuel fabrication facilities.

The gaseous diffusion uranium enrichment complex produces waste where small amounts of uranium are contained in liquids from equipment cleanup that is routed to settling ponds where it precipitates as sludge.

Fabrication of fuel produces LLW in the form of dry solids of CaF₂ containing low concentrations of enriched uranium and other low-activity waste. Other uranium-bearing waste are in the forms of liquids and sludges.

C.3.2 Centrifugation

Centrifugation is a treatment process that removes suspended solids from LLW streams. In a centrifuge, the rapid rotation of a perforated basket or bowl containing the waste stream causes the solids to separate from the liquids by centrifugal action. The liquids are forced out through the basket wall, and the solids collect and are removed by mechanical action or sprays. Centrifuges are used to dewater resins and filter sludges and to concentrate dilute sludges.

C.3.3 Decontamination and Decommissioning

Decommissioning nuclear facilities at the end of their useful life will produce large volumes of LLW, much of it as contaminated concrete and metal vessels and piping. Decommissioning waste will generally contain the same isotopes as produced during facility operation. Depending on the type of facility and its previous operations, waste streams from the decommissioning may include activated metal, activated concrete, contaminated metal, contaminated concrete, dry solid waste (trash), spent resins, filter cartridges, and evaporator bottoms.

Decontamination technologies involve the removal of deposited radioactivity from contaminated equipment and other solid waste forms by physical and/or chemical methods. They are used at contaminated sites to clean these surfaces so as to restore structures and equipment to a condition to be reused or, prior to demolition, to reduce the potential for demolition waste to be radioactive. Decontamination activities usually involve the use of four processes—physical decontamination, chemical decontaminati on, electropolishing, and ultrasonic cleaning.

C.3.4 Remediation

The remediation of radiologically contaminated sites, including buildings, storage piles, equipment, and underlying soils, can be broadly divided into two categories: (1) the decommissioning of nuclear facilities, which may involve the removal of contaminated equipment and structural components and the decontamination of building and equipment surfaces to remove radioactivity; and (2) the cleanup and stabilization of sites that may contain radioactive contamination in buildings, equipment, waste storage pil es, and underlying soil. In some instances, the contamination may be detectable as elevated radionuclide levels in ground water, surface water, or airborne pathways.

C.3.5 Waste Water Treatment

Liquid wastes can be treated to remove contaminants and thus permit the treated liquid to be disposed, or to concentrate the liquid (and contaminants) and reduce the volume to be disposed. Liquids in the form of contaminated ground water or leachate can be pumped to the surface for treatment or can be treated in situ. Generally, the treatment of liquids or semisolids will produce an effluent that can be discharged and a residual sludge or liquid in which the radioactive constituents are concentrate d. The processes that follow are often used at radiologically contaminated sites for treatment of waste liquids:

• Chemical precipitation, or separation can be used to remove soluble metals from contaminated ground water or impounded liquids.

• Ion exchange techniques can be used to remove inorganic salts from a liquid waste stream.

• Evaporation can be used to reduce the volume of radioactive liquids and to remove water from a solution.

• Filtration technology can be used to remove suspended solids from a solution by forcing the liquid phase through a porous membrane and collecting the solid phase on the filter medium.

• Activated carbon adsorption is a physical treatment that can be used to remove complex mixtures of organic contaminants from leachate or ground water.

C.3.6 Stabilization

Stabilization systems are used to immobilize inorganic waste within an inert matrix. Solidification is required for liquid wastes to achieve regulatory limits on water in packages. It is also used for the stabilization of semisolid and solid wastes. There are a number of binder materials commercially available, the selection of which will be dictated by the characteristics of the waste and the relative economics of the competing techniques. Although most waste and soil from a remediated site are shipped offsite or stored in unpackaged bulk form or packaged essentially water free and not stabilized, there are situations in which liquid and/or semisolid wastes will require stabilization and packaging prior to shipment.

Among the available binder materials, cement has the longest record of experience and is applicable to a wide range of waste compositions. The cement is either used as a binder by itself or mixed with a material such as fly ash or cement kiln dust. The waste stream is slurried into this mixture and allowed to set, creating a volume typically twice that of the original waste volume. Thermoplastic binding using asphalt is a competing technique that, although generally more expensive than cementation, provi des certain improvements in leaching characteristics and greater volume reduction factors.

C.3.7 Dewatering

Dewatering is a liquid removal technique using concentration technologies that are particularly applicable to treatment of semisolids. In dewatering, either pumping and/or gravitational drainage is used to remove the water from a semisolid. A commonly employed approach for treating ion exchange resins, called "in-container dewatering," involves the use of multiple filter elements placed in a disposable container and connected to a pump.

C.3.8 Accelerator Targets

Accelerator targets are used to produce radionuclides through direct interaction with charged particle beams or indirectly through the interaction of induced radionuclides and other materials.

C.3.9 Weapons Production

Production reactors use high-enriched uranium (HEU) as a fuel to provide fission neutrons for capture by depleted uranium (DU). Uranium-238 captures the neutron to form ²³⁹U, which decays to ²³⁹Pu. If the target material is left in the process too long, an increased amount of ^240,241Pu will be formed. Production reactors also produce tritium. The ²³⁵U fission produces neutrons that are captured by a lithium-6 target, resulting in an alpha emission and tritium (³H). Other major isotopes produced in a production reactor include ²³⁸Pu, ²³⁷Np, ²⁵²Cf, ²⁴¹Am, ⁶⁰Co, ¹³⁷Cs, and ⁸⁵Kr.

There are various reprocessing methods to recover special nuclear materials from irradiated fuel and targets; the method used depends on the material the fuel is made from. All these methods, however, use some form of the Purex process. Purex is a solvent extraction system that uses tributyl phosphate to separate the materials in the fuel into transuranic elements, uranium, plutonium, and fission products. The fission products fraction contains the waste elements, and they are highly radioactive. These liquid wastes are evaporated and stored in underground tanks until decay heat has been reduced sufficiently for preparation for ultimate disposal.

C.3.10 Ion Exchange

Ion exchange is a process involving the selective removal of contaminants from liquids through the reversible interchange of similarly charged ions between an electrolyte solution and a solid phase. The contaminants are accumulated on to the exchange medium, which is typically a resin. Ion exchangers are either of the cation or anion type. A further categorization is between separate-bed systems (demineralizers) consisting of either cation or anion resins, and the mixed-bed system consisting of a station ary bed containing fixed anion and cation resins. The mixed-bed systems have been the predominant ion exchange choice for treatment of liquid wastes.

C.3.11 Nuclear Reactors

Control of radioactive materials in a power reactor is generally achieved by removing material from process streams, concentrating it in a relatively small volume, and disposing of that volume as LLW. Small amounts of radioactive material are present in the coolant of a power reactor from fuel leakage as well as from system corrosion products and impurities in the coolant that have been activated by neutron bombardment. The radioactive waste treatment systems are designed to remove these materials on an o ngoing basis through filtration and ion exchange resins in both the primary system and secondary, or auxiliary, systems that treat liquids with which the primary coolant may have come in contact.

Some of the LLW generated during the operation of a nuclear reactor include:

• ion exchange resins;

• filters that remove particulates from liquids or from air;

• concentrated liquids resulting from evaporative processes;

• dry active waste, which is a term generally applied to a wide variety of waste products such as cleaning materials, glass, filters, concrete, miscellaneous wood, and metals;

• nonfuel reactor components, such as fuel channels, control rods, and in-core instrumentation; and

• decontamination wastes.

C.3.12 Research Facilities

Some DOE facilities use radioactive materials in research and employ a variety of radioisotopes and material forms to achieve their purposes. Several waste streams are generated as a result of research and development activities: liquid scintillation vials, other organic and inorganic liquids, biological wastes, and trash. Accelerator targets and sealed sources are also produced. Certain research and development activities concerned with the fuel cycle processes or weapons production will generate waste streams similar to those processes.

C.3.13 Isotope Production

Processes that result in the generation of LLW include the production and distribution of radioisotopes for medical, academic, or industrial use; manufacture of materials containing radioisotopes; and the use of radioisotopes for research and testing and in gauges and instrumentation. Several distinct waste streams vary in the concentration of activity, isotopes contained, and volumes produced. Isotope production is achieved through irradiation of fuel and targets in a reactor, and the separation and puri fication of the resulting products. LLW generated from medical isotope production includes solidified aqueous liquids and trash produced in the separation, cleanup, and shipping of the radioisotopes.