A newly released Department of Energy assessment of the criticality accident alarm system at the Y-12 nuclear weapons plant said the operation is “adequately” maintained, but the review team identified two “deficiencies” that raised uncertainty as to whether the system will fully function as planned.
A nuclear criticality accident is an uncontrolled nuclear chain reaction with release of dangerous levels of radiation. Such an accident is Y-12’s biggest fear because of the huge volume of fissionable material — highly enriched uranium — that is stored and processed at the Oak Ridge plant. The only criticality accident in Y-12 history occurred June 16, 1958, and eight workers were hospitalized with severe doses of radiation. (Accident scene is pictured, right.)
The new assessment was conducted earlier this year, and it included a review of the alarm components in four Y-12 facilities — Buildings 9212, Beta-2E, 9215 and 9720-5 — that are involved in the handling of enriched uranium.
The currently used suite of accident detectors at Y-12 were purchased and installed in the 1990s, according to the report.
“Overall, the operability of CAAS (criticality accident alarm system) is adequately being maintained and is verified through routine completion of surveillance testing requirements defined in (safety documents),” the report stated.
However, the DOE assessment team “identified two deficiencies that indicate that there is some amount of uncertainty in the CAAS detectors’ ability to perform its functional requirements specified in the safety basis.”
According to the DOE assessment report, the uncertainty was introduced when the detector design “was not adequately controlled” following modifications to the system since the initial testing.
Also, the “intervening shielding” in some Y-12 buildings is greater than what’s assumed in the safety documents that establish the area covered by the accident detectors.
The report specifically cited these two deficiencies:
— The coverage area for the installed criticality accident detectors in Building 9212 — the main processing center for bomb-grade uranium — is not in compliance because of the shielding inside 9212 and possibly some adjoining buildings.
— Some design requirements for certain detectors “have not been fully verified” and other issues have made it difficult to validate the system’s “safety function performance.”
The report said the assessment team also identified other deficiencies “with a lower level of significance.” Among those was that Consolidated Nuclear Security — the government’s managing contractor at Y-12 — has not adequately responded to issues related to a backlog of maintenance on the criticality accident alarm system. That backlog is reportedly growing.
The National Nuclear Security Administration, the semi-indepdendent part of DOE that oversees the nuclear weapons facilities, is reportedly working with CNS to promote improvements in the alarm system and ultimately replace the aging alarm system in some of the Y-12 buiildings.
The report said Y-12 currently has 51 criticality accident detector systems in its inventory. Thirty-six of those are deployed in the field, and 15 are maintained in Y-12’s criticality calibration laboratory “in various stages of readiness” for field deployment.
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