Workers at the Hanford Site on Wednesday resumed stabilizing the second PUREX Plant radioactive waste storage tunnel with concrete-like grout to prevent its possible collapse.
The project was suspended for several days after an Oct. 26 incident in which steam was spotted coming from a small building attached to the tunnel, leading to a precautionary take-cover order for more than 500 workers in the 200 East Area at the center of the Department of Energy property in Washington state.
The four-hour order was lifted after crews were sent into the area near the tunnel wearing protective clothing and filtered-air respirators. They started generators to power lights and cameras installed earlier in the tunnel and checked for any spread of radioactive contamination. None was found.
The cameras showed steam in the tunnel as the latest thin grout layer cured, generating heat and moisture. Some of the steam escaped the tunnel at the building at the end closest to the PUREX Plant and was visible in the cold air of the early morning, according to DOE.
Water vapor was not expected to be coming from the building after an exhaust system with HEPA filters was installed before grouting began on the 1,700-foot tunnel, the department said.
The building had been sealed after being used to lift large shield doors to allow 28 railcars loaded with obsolete and failed equipment highly contaminated with radioactive waste to be pushed into the tunnel from 1964 to 1996.
Over the weekend, Hanford workers patched the shield door housing. Early in the week they inspected other parts of the tunnel, including its original, deactivated ventilation system, to make sure there would be no more steam leaks.
The Energy Department said the take-cover order was precautionary due to the potential for personnel to be exposed to hazards, although there was no immediate evidence of a release of radioactive materials. “We hope that public confidence in a situation like Friday’s would be increased by the fact that we act conservatively to protect people until we know whether or not there is a danger,” DOE said in a statement.
An emergency was not declared and the Emergency Operations Center in Richland was not activated, as occurred in the partial collapse of the older of the two Hanford tunnels in May 2017. Monitoring detected no radioactive particles in the collapse of the first tunnel, after dirt mounded above it fell in on the radioactive waste it contained. The first tunnel holds eight railcars loaded with contaminated equipment. It was filled with grout last year.
The second tunnel was also found to be at risk of collapse. Grouting began in October.
The Energy Department is required to submit a report within 15 days to the Washington state Department of Ecology, a Hanford regulator, outlining what occurred last week and assessing whether there will be any effect on the ongoing work. The Energy Department notified the state agency immediately the morning of Oct. 26 that work had been halted after the steam was seen and kept state officials informed until it confirmed no release of contamination, said Ecology spokesman Randy Bradbury.
The Washington state Department of Health is reviewing DOE’s air monitoring data and asking follow-up questions. It also set up air monitoring equipment along the tunnel for the duration of the grouting operation, including the area where the steam escaped, said John Martell, manager of the Radioactive Air Emissions Section of the Health Department’s Office of Radiation Protection. He expects to have data within a couple weeks showing whether Department of Health monitors detected any airborne contamination.
