A paperwork mistake caused a deadline to check some Hanford waste tanks for the buildup of flammable gas to be missed for more than eight months.
Regulations require that the underground radioactive waste tanks in groups called the A, BY and C Tank Farms be sampled every 365 days for flammable gases, said John Britton, spokesman for Washington River Protection Solutions.
The Department of Energy contractor realized Dec. 21 that sampling had been missed in late March for the C Farm tanks, in early May for the A Farm tanks and in mid July for the BY Farm tanks.
Sampling was done the next day with no serious problem discovered.
DOE takes any violation seriously, it said in a statement. It is reviewing the quality of its contractor's data management and compliance with required procedures.
The problem occurred when an incorrect date was entered on a spreadsheet used to track sampling, Britton said.
The three tank farms include two dozen single-shell tanks that still hold radioactive waste. Hydrogen gas can be produced as materials in the waste break down.
However, the highest risk of flammable gas generation is in Hanford's double-shell tanks, some of which have more recently generated radioactive waste and some of which are high heat tanks. They are actively ventilated with exhausters and monitored more frequently.
In September 2012, the Defense Nuclear Facility Safety Board called for faster action to make improvements in ventilation systems for Hanford's 28 double-shell tanks. It said that a significant flammable gas accident would have considerable radiological consequences, endanger personnel, contaminate portions of the tank farms and seriously disrupt the waste cleanup mission.
DOE responded by instituting an improved testing and monitoring system for double-shell tanks ventilation.
Single-shell tanks, with their lower risk of flammable gas buildup, use a passive ventilation system.
Washington River Protection Solutions has changed is procedures for single-shell tanks since the monitoring lapse was discovered, Britton said.
Although there was not an immediate safety issue, not following the schedule for monitoring the single-shell tanks for flammable gas buildup was an unacceptable lapse in conduct of operations, he said.
"It's a very serious error and we're aggressively taking actions to remedy the issue," he said.