Science
By JULIE DUTTON

Cleaning the 'crud' out of Dresden-1

NOW IN ITS twentieth year of operation, Commonwealth Edison's Dresden-1 nuclear plant holds the longevity record for commercial power production from a light water reactor. Dresden-1 is also slated to be the nation's first commercial reactor to undergo decontamination (cleaning the reactor piping to remove radioactive deposits).

The cleanup is necessary to reduce radiation exposure to plant personnel performing maintenance and inspection duties. Of the four decontamination methods considered — mechanical cleaning, operational techniques, chemical cleaning and water flushing — chemical cleaning was selected because it promises the greatest possible reduction in radiation levels, has low corrosion rates and is a one-solution treatment. The chemical technique has been used in Canada, Germany and France without any significant problems.

The decontamination procedure will be conducted in several stages. After the reactor has been shut down, the fuel will be removed to a fuel storage pool on the plant site. The primary cooling system will then be drained, and decontamination apparatus consisting of temporary piping and other equipment will be installed. The apparatus will connect the reactor with a facility capable of processing the radioactive liquid that will result from the decontamination. After testing the equipment, 90,000 gallons of a chemical solvent will be injected and allowed to circulate for 100 hours. The solvent is supposed to clean the "crud" out of the reactor system by selectively dissolving the radioactive oxides. The solvent containing the radioactive "crud" will then be drained into shielded tanks, and the primary coolant system will be rinsed with demineralized water to flush out any residual solvent.

Com Ed initiated its $37.5 million laundering of Dresden-1 with a petition to the Nuclear Regulatory Commission (NRC) in December 1974. In 1975, permission was granted to proceed up to the actual implementation. Dresden-1 has been shut down since October 31, 1978, and is expected to return to service in June 1981. The shut down is not solely for decontamination, but also for "a lot of other modifications in parallel to cleaning," according to Jerry White, Dresden-1 engineer. Receiving particular attention is the update of safety features. Built under the safety criteria of the 1950's, Dresden-1 still safe, but Com Ed is implementing some unmandated safety measures because, "we think this is the prudent thing to do," said A. David Rossin, system nuclear research engineer at Commonwealth Edison.

The $37.5 million price tag on the Dresden project includes development work, engineering and construction of facilities. The U.S. Department of Energy contributed $8.25 million. The Electric Power Research Institute, a coalition of the electric utility industry, supplied about $4 million. Just what the consumers' tab will be is not certain. Rossin noted that the expenditure is part of the cost of the plant, to be absorbed over a number of years. He also pointed out that Dresden-1 is a very economical plant, so that if the decontamination gives it a new lease on life, it could represent a savings to users. According to the NRC, much of the $37.5 million represents a one-time research and development expenditure that would not enter into costs of future decontamination efforts at other nuclear plants. Presently there are no plans to flush any other nuclear facilities, but cost estimates for such procedures range from $1 million to $5 million.

Although the Dresden procedure is expected to provide useful information for future decontaminations, it has drawn criticism from those concerned with possible negative environmental effects. At issue is whether the Dresden decontamination warrants an environmental impact statement (EIS). Environmental activist Kay Drey and a consumer group, the Illinois Safe Energy Alliance, advocate such an assessment in light of the precedential nature of Dresden-1. Although the Illinois attorney general, the Council on Environmental Quality, and the Department of Energy are all reviewing the EIS issue, the ultimate decision rests with the NRC, which was expected to decide by mid-March. In a 1975 Safety Evaluation, the NRC has stated, "The [decontamination] system has been designed so that no chemical or radiological wastes will be released to the environment from the decontamination process .... Therefore, no adverse environmental impacts are anticipated due to the decontamination."

Paul O'Connor of the NRC pointed out that Dresden-1 does not fall within any of the nine specific actions requiring an environmental impact statement (as outlined in Title 10 of the U.S. Code of Federal Regulations), but the commission could mandate a statement under the tenth option: "any other action . . . significantly affecting the quality of human environment."

Attention has also been directed at the level of radiation to which workers will be exposed during the decontamination. Dresden's Jerry White said, "The procedure we have developed and plan to implement minimizes workers' exposure during decontamination and waste handling," O'Connor of the NRC noted that the exposures will be well within the 3 rems per quarter permitted under occupational standards, and that decontamination "does not tend to be... a high rate dose job."

Questions have also arisen over the decontamination wastes, which are considered low-level. The decontamination solvent, NS-1, which was developed by Dow Chemical, contains chelates, or chemical agents to bind the radioactive deposits. One study of wastes containing chelates buried at Oak Ridge National Laboratory indicated that chelates promote radionuclide migration into the environment. However, White said, "What they did at Oak Ridge we do not

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condone at all ... it was a unique situation." NRC's O'Connor agreed, pointing out that Oak Ridge had particular hydrological and geological features not found at Hanford, Wash., the designated burial site for the Dresden decontamination wastes. According to O'Connor, the water table was quite high at Oak Ridge so that water was actually coming into the burial pits. At Hanford, which is a desert site, the water level has been determined to be 300 feet below the burial site. Thus, the NRC spokesman said, there is "essentially no mechanism to cause material to move." A spokesman for the Council on Environmental Quality noted that the wastes will be at a separate burial area at Hanford to allow separate monitoring.

O'Connor also emphasized that Oak Ridge wastes were in liquid form, which will not be true of Dresden's. A vinyl ester resin solidification agent will be used to encapsulate the 3000-curie decontamination waste. The solidified waste will then be put in 55-gallon drums and shipped to Hanford.

A final concern with the Dresden project is the compatibility of the solvent and the reactor materials: Will NS-1 degrade the integrity of the reactor system, causing corrosion and leaks? According to White, there has already been extensive materials testing, and Com Ed does "not expect compatibility or corrosion problems." The NRC has required a comprehensive post-cleaning inspection to be conducted by Com Ed before Dresden-1 can resume operation. In a review of the Dresden proposal, the NRC concluded, "Dresden Nuclear Power Station Unit 1 could be subjected to the chemical cleaning without undue corrosion or other deleterious materials compatibility effects . . . and that the radiological safety program is adequate to assure that the health and safety of the public and the onsite personnel will not be endangered by the Dresden 1 decontamination program. "

This column will report policy developments concerning science and technology in Illinois. Support for this column is provided in part by a National Science Foundation grant to the Illinois Legislative Council Science Unit, where Julie Dutton is a science intern.

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