Four defunct Hanford nuclear reactors have had their steel doors welded shut again after passing inspections to make sure they remain safe and secure.
They were dimly lit, grimy and overall a little eerie inside, based on the description of Ken Niles, nuclear safety administrator for the Oregon Department of Energy, who toured H Reactor while it was opened up.
“Unlike B Reactor, it was not all dressed up for visitors,” he said.
The plan for eight of Hanford’s nine reactors once used to produce weapons plutonium is to tear them down to little more than their radioactive cores and seal them up for 75 years to let their radiation decay to more manageable levels. The exception is B Reactor, the world’s first production scale reactor, which is being preserved as part of the new Manhattan Project National Historical Park.
The first reactor to be sealed up, or “cocooned,” was C Reactor in 1998. The recent inspection was its third in the 17 years since then. It was the second inspection for D and H Reactors, and the first for N Reactor, which was cocooned just three years ago.
“I wasn’t quite sure what to expect,” Niles said.
The group allowed into H Reactor was told to stick close together. They spent much of their time on the stairs, going downstairs to below grade and then climbing stairs to above the reactor block.
They held onto hand rails that had gone grimy, and a radiation control technician checked their hands to make sure they had picked up no radioactive contamination.
Workers for Hanford contractor Mission Support Alliance were on the tour, looking for any items that could be scavenged for use or display to the public at B Reactor.
The reactor face looked similar to that of B Reactor, with 2,004 horizontal, capped tubes where uranium fuel was inserted into the 35-foot tall graphite block. Above the core is a mechanical area about 80 feet high where vertical safety rods hung, ready to be dropped to rapidly shut down a reaction in an emergency.
While B Reactor’s control room looks much as it did when it began operating in 1944 — with hundreds of gauges, dials and switches — much of the H Reactor control room has been torn out, Niles said.
One worker who evidently helped with the cocooning of H Reactor left a bit of graffiti behind, a stick figure and the date 7-22-05. Much of the equipment was marked with tags from when they were taken out of operation. H Reactor produced plutonium for the nation’s nuclear weapons program from 1949 to 1965.
As the tour stood looking at the rear face of the reactor, they heard a faint wailing. It took a moment to realize it was a previously scheduled test of emergency sirens at the Columbia River.
Bat guano and spider webs were found during the inspections all the reactors, and two or three live bats were seen in H and C Reactors, said Rick Moren, director of long-term stewardship for Mission Support Alliance. But those were the only signs of life in the reactors.
Overall, inspectors found pretty much what they expected in all four reactors, he said.
They performed an assessment of the original concrete structures of the reactor and the metal roofs and metal siding added at the tops of the reactors, finding no signs of deterioration. They already knew there were some small gaps in the cocoon siding, where the bats may be getting in, and sealing those up will be considered.
Instruments that provide remote information about the temperature and possible moisture inside the reactor were checked for signs of wear. No precipitation has infiltrated the reactor, based on the even distribution of dust on the floor, Moren said.
A radiological survey of the exterior and interior confirmed that radiation above background levels was confined to the reactor core or other areas where it had been previously identified.
The reactors had the welds ground away on their doors two weeks before the inspections to allow them to air out and for air samples to be collected to make sure they were clear of contaminants. Radon is a concern in the sealed up reactors.
The Department of Energy is legally required to have the six reactors that have been cocooned so far inspected every five years.
However, Hanford regulators have agreed to let DOE vary the inspection dates to allow reactors to be put on a schedule to be inspected together every five years as an efficiency and cost-savings measure, said Keith Grindstaff, manager of the DOE Long-Term Stewardship Program.
By inspecting all the reactors together this year about $100,000 may be saved, Moren said.
Planning for the inspections and training of an inspection crew was done jointly. A large range of specialists, including in industrial, biological and radiological safety and controls, are involved in the work.
Moving the equipment and construction trailers on site for the inspections and them demobilizing them also was done together.
Inspections of DR and F Reactor also have been done in recent years. All six will remain welded closed now until their next planned joint inspections in 2020.