Determination of Background Radioactivity at the WIPP and Comparison with Operational Data

H.C. Chiou and C.C. Jierree (Washington TRU Solutions L.L.C.)

The Waste Isolation Pilot Plant (WIPP) is a U. S. Department of Energy deep underground repository developed to demonstrate the safe and permanent disposal of transuranic (TRU) wastes from DOE defense programs. The WIPP received its first waste shipment on March 26, 1999, and has safely processed 3,290 shipments and disposed of 26,191 m3 TRU wastes as of January 26, 2005. Calculated annual doses to the public from 5 years of WIPP operations are evaluated against standards for the site. The calculated annual doses are consistently more than five orders of magnitudes below the standards, suggesting that the WIPP operation has not resulted in radiation exposure to the public. Comparison of repository release point composited data to composited data from seven environmental monitoring stations surrounding WIPP site (in service from before operations to the present) confirms no contribution to the radiological environment from WIPP operations. Because of this data comparison exercise, WIPP can interpret an effluent air filter measurement to determine if it falls within the upper boundary of background for the site, thus confirming that the activity did not come from the waste. A method is presented for normalizing radionuclide measurements to a common radiotoxic hazard index using plutonium-239 equivalent activity. This has allowed the development of a graded series of actions to take if radioactivity is ever detected above background levels.

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