A problem with the criticality alarm system at the nation’s primary storehouse for weapon-grade uranium brought a manager to the scene on a weekend in late April. The situation turned out to be concerning but not threatening.
The incident was revealed in a recently released activity report by Defense Nuclear Facilities Safety Board staff assigned to the Y-12 nuclear weapons plant in Oak Ridge, Tenn.
According to the report, the plant shift superintendent’s office at Y-12 “received an alarm indicating a problem” at the uranium storage facility on Saturday, April 23.
The superintendent contacted the shift manager who was on call for the Highly Enriched Uranium Facility – which was constructed at a cost of about $600 million and loaded with the stocks of fissionable materials around 2010-2011. After arriving at the scene and investigating the situation, the shift manager discovered that a CAAS (criticality accident alarm system) equipment cabinet had experienced a rise in temperature that was higher than the “alarm set point.”
The safety board report said Consolidated Nuclear Security, the government’s managing contractor at Y-12, had planned a number of on-site utility outages for that April weekend. However, the somewhat-reduced ventilation flow in the plant’s high-security uranium storehouse should not have created a problem because “the cooling ventilation for the room with the (alarm system’s equipment cabinet) remained operational,” the report said.
Additional reviews revealed that the temperature switch for the criticality alarm system had been inadvertently set to the same value as the temperature switch for the cabinet’s cooling fan. The DNFSB report also said it should be noted that the equipment cabinet’s cooling fan had been set to activate below what was considered the maximum operating temperature recommended by the vendor.
Still, there were issues that had to be addressed in a key area of the high-sensitivity facility.
“The fact-finding meeting for the event identified several apparent causes, including poor configuration control of the alarm set point, an inaccurate annual surveillance procedure, and poor conduct of operations,” the safety board report stated. “Technicians subsequently executed a corrected surveillance package to ensure proper operation of the CAAS.”
When asked how the situation was resolved, Y-12 spokeswoman Ellen Boatner said the temperature alarm was reset to the manufacturer’s specifications.
At one point during the April weekend, the shift manager at the uranium storage facility declared the alarm system to be “inoperable.” Once that was put into play, management had to establish a “limiting condition of operations” in order to compensate for the temporary loss of the criticality alarm system, the DNFSB said.
“The facility suspended fissile material handling operations,” Boatner said, acknowledging the response to the situation.
She said an investigation later showed there was no degradation of the alarm system due to the elevated temperature at the site, and the alarm system was restored to its “operable status.”
Steven Wyatt, a spokesman for the National Nuclear Security Administration’s Production Office, said fissile material operations were suspended from Saturday evening, April 23, when the issue was discovered, until Monday, April 25, when “auxiliary measures were put in place.”
Wyatt said corrective maintenance was completed on April 26, and the alarm system was returned to normal operations.
