Energy Department officials described Friday’s incident at the sprawling facility whose combined lab cover some 1400 square kilometres in Western Idaho as a sodium fire that posed no danger to the public – but the accident was the second within a week.
Bellona nuclear physicist and executive director, Nils Bøhmer, who has visited the Idaho National Laboratory with other Bellona staff, said that aging equipment and facilities at the 62-year-old facility make it a subject of special concern for the environmental community.
The Energy Department said 10 other workers were evaluated on the site of the accident and later released, according to the Associated Press. Others at the complex were told to remain in their buildings as a precautionary measure, but later allowed to board buses home, the lab said.
Laboratory fire crews responded to the Materials and Fuel Complex. Officials say there’s no more evidence of a continued reaction or fire.
The lab said in a written statement that the sodium reaction resulted in a sudden pressure release that compromised system integrity and set off fire alarms in the vicinity.
The lab initially said that the unidentified employee, who works for the private Idaho Cleanup Project, was taken to Eastern Idaho Regional Medical Center in Idaho Falls for evaluation of burns.
In a later incident, the lab said the worker was sent home with”no physical evidence of any injury.” Hospital staff where the worker was taken would not comment on the workers condition, citing privacy laws.
On Tuesday, six workers were contaminated by low-level plutonium radiation and 10 others were exposed when a foot-long rectangular container of plutonium fuel inside the INL’s decommissioned Zero Power Physics Reactor (ZPPR) was opened during regular work to prepare it for shipment to another facility.
This latest incident involved a chemical reaction that occurred when sodium being stabilized for safer storage was exposed to moisture in the air, releasing hydrogen, project engineer Karen Moore told Reuters.
Such a reaction – which took place in a building adjacent to a decommissioned sodium-cooled experimental reactor – can range in magnitude from a flash to an explosion.
Accident not radiological
The INL was at pains to underscore that the accident was not radiological in nature and posed no danger to the public, and released a detailed statement on the incident on its website.
In its statement, the lab said emergency responders had reentered the control room of the building, which is owned and operated by the private Idaho Cleanup Project, after the sodium reaction, but not the boiler room itself.
The Idaho Cleanup Project is a private company contracted with the Energy Department to clean up waste at the site and workers there were involved in demolition and dismantlement activities, the lab said.
A recovery plan was under way along with a comprehensive investigation, the lab said.
Crews began treating the Sodium Boiler Building on Thursday by intentionally introducing a liquid into piping containing the metal to force a reaction and render the material safer to package and dispose, said the INL statement.
The Idaho Cleanup Project said in press release issued in March that sodium “can ignite on contact with air and react violently with water, producing hydrogen, making preparations and treatment a significant safety concern.”
Sodium was used as a coolant for the Experimental Breeder Reactor-II until the early 1990s, according to the lab.
When the reactor was shut down, the sodium coolant was drained; however, crews were tasked with removing residual sodium from the Sodium Boiler Building before demolishing the facility, the lab said.
Idaho National Lab accident history includes first US nuclear fatality
Some 6,000 employees and contractors work at the Idaho lab, which opened in 1949 as a national reactor testing station.
Last week’s exposure of 16 workers to plutonium was the most serious accident at the INL since 2007.
In that year, a worker was treated for minor burns and smoke inhalation from a small laboratory fire, though no radiation release was reported in connection with that incident.
In January 1961, the Idaho lab was the site of the only fatal nuclear accident in US history so far, killing 3, when an explosion occurred at the INL’s Stationary Low-Power Reactor Number One. A control rod for absorbing extra neutrons during nuclear reactions, was extracted too far, leading to a core meltdown and an explosion.
The reactor vessels jumped some three metres and concussion and blast killed all three military enlisted personnel working on the reactor. Because of severe radioactive contamination, all three men had to be buried in lead coffins.