The Anatomy of Nuclear Waste by Ernest Goitein The low-level radioactive waste facility proposed for Ward Valley would accept power plant wastes as well as medical wastes. While medical wastes are short lived; power plant wastes are hazardous for thousands of years. Besides the fact that nuclear power is no longer economical, the problem of waste disposal for spent fuel and so called "low-level" waste has never been solved satisfactorily. This article explains where the nuclear power plant low-level wastes originate and defines some of the jargon The radioactive decontamination flush is cleaned up by resin absorption in demineralizers. These highly radioactive resins, containing corrosion products as well as the fission products and trans-uranics from the leaking fuel elements are called "low" level waste. There are several distinct sources of low-level radioactive waste from a nuclear power plant: Corrosion products. Water is circulated around the core of the reactor. Minute quantities of corrosion products suspended in that water pass through the reactor and absorb neutrons, changing into radioactive isotopes. This process is called "activation." A fraction of the water is circulated to a clean-up system where the corrosion products are removed by demineralizers (where contaminants are trapped in resin) and filters. The cleaned water is returned to the reactor system. Decontamination. Corrosion products plate out on piping and equipment. This creates a radioactive crust, or scale, that endangers repair or maintenance workers. To dissolve this coating of radioactive corrosion products a decontamination process is used during plant outages. Decontamination consists of a series of flushes alternating oxidizing mixtures (to loosen the scale) and chelating agents (to bind with and transport the loose scale). The radioactive decontamination flush is cleaned up by resin absorption in demineralizers. Defective fuel elements. The fuel consists of low-enriched uranium oxide (uo2) pellets in a thin zirconium cladding. Each fuel element has a diameter approximately the size of a pencil. As the core heats up, the fuel swells and stresses the thin cladding. This can result in pinhole leaks in some of the fuel elements. Transuranics -- elements such as neptunium. plutonium, americium and curium created when uranium absorbs neutrons -- and the fission products -- strontium, cesium, and iodine among them -- leak into the core coolant and are absorbed by the resins in the clean up system. These highly radioactive resins, containing the corrosion products as well as the fission products and trans-uranics from the leaking fuel elements are called low-level waste. They are hazardous for thousands of years, and are shipped to low level radioactive waste facilities. The demineralizer resins and filters, highly radioactive and inappropriately defined as low level waste, are then packaged, usually in carbon steel drums. These would be sent to Ward Valley. Decommissioning wastes. Once a nuclear power plant is permanently shut down, the decommissioning process begins. Under the "safe store" concept, the equipment is left undisturbed for 50 -- 100 years to allow radiation levels to decay, and make disassembly less hazardous. Many utilities have chosen not to wait. Major equipment, such as pressurizers, pumps, steam generators, evaporators, heat exchangers and even reactor vessel internals have been shipped to low-level waste facilities. The hazardous life of these components extends for thousands of years. Gaseous wastes. Radioactive gases are created by activation and by the fissioning process. These gases are normally compressed and stored for six months to allow for partial decay. They are then released to the "off-gas system," which filters out solid radioactive daughter products, such as strontium, barium and cesium. The gases are vented through a tall stack when the wind will disperse them. The filters are shipped to a low-level radioactive waste facility. Alternative storage concepts Low-level radioactive wastes, by nrc definition, include short lived medical wastes as well as power plant wastes hazardous for thousands of years. These different wastes should not be treated in the same way, or stored in the same facility. Medical and bio-technical waste streams, which have half lives of 90 days or less, and are therefore hazardous for less than 3--5 years, should be placed in a state of the art "storage-to-decay" facility. Such a facility could consist of a reinforced concrete structure with a leachate collection system, and capability to identify and repackage leaking containers. After five years' decay time these wastes are no longer radioactive and can be disposed of in landfills. Longer-lived utility wastes should remain stored on-site until a safe and responsible method is developed to deal with their danger. Utility wastes should never be placed in unlined trenches, as is current practice. All shallow-land burial sites have leaked and contaminated the surrounding area. After the shallow-land burial failures, European designs for power plant wastes have evolved concrete cells 60 ft x 70 ft x 30 ft high, protected from the weather by a movable structure, complete with a remotely operated crane, and leachate collection system. The location of a leaking container can be identified, and the container can be repackaged. It is essential that any radioactive waste facility for long lived power plant wastes be monitored (for detection and collection of leachate), retrievable (with the capability to repackage wastes) above-ground storage. Technical terms Roentgen -- the quantity of x-ray or gamma radiation that will produce 1 esu (electrostatic unit - a measurement of ionization) in 1 cm3 of air. Rad -- radiation absorbed dose. It is the quantity of radiation leading to the absorption of 100 ergs of energy per gram of irradiated material. rbe -- Relative Biological Effectiveness: a measure of comparing biological damage of ionizing radiation with that of x-rays of 200 kev energy. Rem -- roentgen equivalent man. Dose in rems = rbe 4 Dose in rads. Alpha radiation is much more damaging for the same rads than gamma radiation. 10 rads of alpha radiation equals 200 rems, whereas 10 rad of gamma radiation equals 10 rems. A millirem (mR) is a thousandth of a rem. Background radiation is in the order of 100--200 mR/yr. Sievert -- 100 rem. Sieverts are not as commonly used as rems, and perhaps have come into use to make the numbers appear less threatening. Curie -- a measure of radioactivity. It is defined as 37 billion disintegrations per second. Bequerel -- the basic unit of radioactivity in the meter- kilogram-second system. 1 Ci = 37 billion Bq Gamma radiation -- Part of the electromagnetic spectrum, with high energies and short wave lengths. This radiation readily penetrates matter. Shielding requires dense materials such as lead. Gamma radiation occurs in the decay of elements such as cobalt60 and cesium137 Beta radiation -- electrons discharged in the decay of some radioactive isotopes. Amount of shielding required depends on the energy level. Plastics usually provide good shielding. Alpha radiation -- the emission of the equivalent of the helium nucleus, consisting of 2 neutrons and 2 protons. Because of its weight an alpha particle will penetrate only a short distance -- a few inches -- in air, but are extremely biologically damaging if breathed in or ingested. Plutonium and all transuranics are alpha emitters. bwr -- a boiling water reactor. Steam is generated in the reactor vessel and piped to the turbine-generator to produce electricity. The turbine and all the auxiliary equipment become radioactive during operation, and extensive shielding is required. bwrs are the product of General Electric. pwr -- a pressurized water reactor. The hot water created in the reactor is pumped through steam generators where steam is produced. This steam, not radioactive, is used to generate electricity. More than 50% of nuclear plants in the US are of this design. The major problems have been with leaking tubes in the steam generators. This has resulted in outages and the very expensive replacement of steam generators. There is the potential for serious consequences from a s team generator tube rupture. pwrs are produced by Westinghouse, Combustion Engineering and Babcock & Wilcox. Half life -- The time when half the radioactivity has decayed. As a rule of thumb ten half lives to 20 half lives (a factor of 1000 to one million) are necessary to render the radioactivity harmless. Radioactive daughter products of the decay must also be considered since they can add considerably more time before a radioactive element becomes benign. Nano -- is a prefix for one billionth, 10-9 Pico -- is a prefix for one trillionth, 10-12 5000 cpm -- Five thousand counts per minute roughly corresponds to 1 mR/hr or 9 Rem/yr Maximum occupational exposure -- 5 Rem/yr Ernest Goitein, a professional engineer, has spent his career in power plant design and construction, with fourteen of those years as project engineer for three nuclear power plants. He is a board member of the ban Waste Coalition. -----------------