HANFORD
Tank Farms
The principal function of the tank farms is the safe storage of byproduct material left over from plutonium extraction operations prior to permanent disposal. This byproduct material has no useful purpose and is stored in 177 underground storage tanks with capacities ranging from 500,000 gallons to 1,000,000 gallons (for a cumulative total of 55 million gallons). This waste material is composed of toxic chemicals that were used to remove fission products from irradiated reactor fuel. The more hazardous materials can be divided into four groups: (1) the high heat load tanks, where water must be added periodically to keep tank temperatures within allowable limits, (2) ferrocyanide tanks, which are explosive at certain elevated temperatures, (3) hydrogen generating tanks, and (4) tanks with organics that are flammable. Little is known about the exact chemical content of the tanks; as a result, tank characterization is a crucial, ongoing activity. Approximately 2,300 personnel support tank farm activities; about 700 are in the operations organization and are at the tank farms regularly.
The TWRS has 177 underground HLW storage tanks containing approximately 55 million gallons of caustic wastes. This waste accumulation is the result of more than 40 years of nuclear weapons and reactor-fuel- grade plutonium production. The wastes are stored in 149 single-shell tanks (SSTs) and 28 double-shell tanks (DSTs).
The waste stored in these tanks came from (1) plutonium and uranium recovery processes from irradiated fuel; (2) three radionuclide recovery processes from waste; and (3) miscellaneous sources (laboratories and reactor decontamination solutions). The wastes were concentrated and mixed together in order to minimize the number of storage tanks required. The tank contents vary between relatively homogeneous to highly heterogeneous mixtures of liquids, slurries, saltcakes, and sludges.
Knowledge of the waste material in specific tanks is poor and requires further evaluation (i.e. sampling). To date, an effective sampling program has not been designed and requires resolution of two issues. First, the required number of samples has not been established. Sample size impacts worker health and safety and the confidence level associated with sample results. Second, there have been problems in taking samples. The waste is highly radioactive and requires special precautions for personnel and handling of equipment and samples. Sampling equipment has not been readily available, and there have been problems fitting the equipment through the access holes (risers) in the tanks.
TWRS tanks contain about half the curies (250 of 500 million) of radioactivity and mass of hazardous chemicals found on the Hanford Site. The HLW is stored in 149 SSTs and 28 DSTs that are covered with about 10 feet of soil and gravel and located in groupings call "tank farms" in the 200 West and 200 East areas of the Site. The SSTs were built from 1943 to 1964 with a design life of approximately 30 years. The domes of the SSTs are made of concrete without a steel inner liner. The DSTs were built from 1968 to 1986 with a design life of approximately 50 years. The air space between the inner and outer shells is monitored for leaks.
The SSTs contain approximately 150 million curies of radioisotopes (mostly Cs-137 in saltcake and interstitial liquids, and Sr-90 in sludge). Of the older SSTs, 67 have leaked or are assumed to have leaked approximately 1 million gallons of wastes (containing approximately 1.2 million curies of radio-isotopes) into the ground.
A TWRS Single-Shell Tank Interim Stabilization Project is under way and is designed to minimize the amount of HLW leaked from SSTs through interim stabilization and intrusion prevention. Interim stabilization of SSTs is the removal of pumpable supernatant and interstitial liquid from SST systems into DST systems. Interim stabilization has been completed on 111 SSTs. The completion of SST interim stabilization is a TPA milestone. Intrusion prevention is the disconnecting and blanking or capping of pipelines from SST systems and installing barriers to avoid inadvertent liquid addition. Intrusion prevention is completed on the SSTs after interim stabilization. Interim stabilization and intrusion prevention will continue through fiscal year 2000, with an overall budget of over $60 million. Planned actions for fiscal years 1996 and 1997 include completion of a new cross-site transfer line (to be privatized) and pumping of 12 SSTs.
Photo Date: 17 April 1978
Photo Number: 303 058 001
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