Nuclear Regulatory Commission inspectors have returned to the National Institute of Standards and Technology (NIST) laboratory at Boulder, Colo., to continue inspections aimed at determining the circumstances and safety consequences associated with a plutonium contamination event which occurred on June 9.

Elmo Collins, administrator of the NRC Region IV office in Arlington, Texas, said an expanded NRC Special Inspection Team arrived at the laboratory on Monday, June 30, to continue NRC review efforts which began on June 11. NIST, an NRC licensee, had reported to the NRC on June 10 that a plutonium source used as a reference standard had ruptured on June 9, resulting in the contamination of at least two workers, contamination of the laboratory, and an apparent unplanned discharge of some of the material into the facility's sanitary sewage system when a worker washed his hands.

"The expanded inspection activities are necessary to independently confirm on-site radiological conditions and to verify the adequacy of NIST actions which have been taken or are planned," Collins said. "The team has not identified any conditions which pose a health threat to the public or the environment, and the NRC inspection team is continuing its investigation."

Collins also said the NRC today issued a Confirmatory Action Letter to NIST formalizing actions that NIST has committed to take in response to the incident. He said that the letter specifies that the NIST Boulder facility will not use NRC-licensed radioactive materials until the NRC is satisfied that procedures and training are adequate. The letter also specifies that NIST complete a thorough radiation dose assessment for all individuals potentially exposed to plutonium and provide the results to the NRC in writing and that NIST finalize its evaluation of the amount of plutonium which may have been released into the sanitary sewage system and report the results to the NRC. NIST written plans to decontaminate the facility must be submitted to the NRC for approval before use. Copies of the NRC Event Reports issued June 11 and June 20 are available from the NRC Web site at www.nrc.gov/reading-rm/adams.html. The accession numbers are ML081630377 and ML 081720574. Copies of the NRC Confirmation of Action Letter issued July 2 may be obtained from the same Web site under accession number ML081840441.