The Department of Energy’s Office of Enterprise Assessments (EA), in a June 24 report, identified some design and operational deficiencies with the criticality accident alarm system (CAAS) at the Y-12 National Security Complex in Oak Ridge, Tenn.
Fissile material operations at Y-12 pose the risk of a criticality accident, an uncontrolled nuclear reaction that could expose nearby facility personnel to radiation releases. The CAAS is meant to detect and offer immediate notification of these criticality accidents, initiating evacuation of workers from affected areas to locations away from high radiation hazards, EA said.
CAAS consists of radiation detectors, relay control circuitry, power supply, and annunciation devices, according to the report. The first two detect the criticality accident and signal to the annunciation devices to alert workers.
Y-12 currently has 51 CAAS detector systems in its inventory, with 36 deployed in the field and 15 maintained in a calibration lab.
The Office of Enterprise Assessments examined the CAAS in the site’s Buildings 9204-2E, 9212, 9215, and 9720-5. “Overall, the operability of CAAS is adequately being maintained and is verified through routine completion of surveillance testing requirements,” it found.
The report identified some deficiencies, including that the coverage area for the CAAS detectors installed in Building 9212 is not in compliance with operation limiting guidelines because of intervening shielding within the building, and that certain design requirements for some of the detectors have not been fully verified.
“Some areas that have thicker or more dense walls, such as vaults, can diminish effectiveness of detectors, so that aspect is factored into coverage areas,” CNS spokeswoman Ellen Boatner explained by email. “Y-12’s CAAS has a redundancy setup that ensures blanket coverage above and beyond the requirements of the national standard.”
Fissile material processing areas at Y-12 are given overlapping coverage by at least two CAAS stations at least 100 feet apart, the report said. “The radius of detector coverage for each station is at least 400 feet for nominally shielded areas and 100 feet for more heavily shielded areas,” it said.
EA found that the intervening shielding in Building 9212 was greater than the assumptions of the safety basis for the CAAS detectors installed in the building, meaning the safety basis assumptions are not being met.
The report said the component configuration baseline for all CAAS detectors “has not been established or maintained,” meaning the untested configuration creates uncertainty “that the CAAS will perform as expected and fulfill its assigned functional requirements as stated in the safety basis.”
It also found that previous system engineers at the site were not performing building walkdowns every three years as required “to verify that as-built conditions are properly documented.”
“The walkdowns of three buildings are more than two years overdue, and a walkdown report has not been issued for Building 9215,” according to the EA report. Walkdowns were done in half of the nuclear facilities last year, the report said, and the rest are scheduled for 2016.
EA determined that Y-12 managing and operating contractor Consolidated Nuclear Security’s (CNS) management of corrective maintenance for the CAAS system has fallen short of ensuring its reliability, since the system’s corrective maintenance backlog is growing. “The CNS target value for corrective maintenance backlog is two items,” EA said. “At the end of March 2016, 82 items were open, 65 of them were over 3 months old, 30 were over 6 months old, and the oldest was entered in January 2014.”
The EA did not identify any findings during its assessment.
According to Boatner, the deficiencies highlighted in the report are “based on questions about the methodology Y-12 uses to ensure the CAAS detectors’ ability to fully perform their functional requirements.”
“CNS has a strategy for CAAS replacement, which is supported by NPO,” she said. “Progress will be dependent on funding availability, but CNS and NPO understand the need to replace the aging system and are committed to getting things under way as soon as possible.”
