A fire in part of Dounreay’s Prototype Fast Reactor (PFR) facility last month led to an “unauthorised release” of radioactivity into the environment.
Dounreay Site Restoration Limited (DSRL) said “procedural non-compliances and behavioural practices” by staff led to the incident on 7 October.
DSRL said trace amounts of tritium were released and did not pose a risk to the public.
No-one at the plant was hurt in the early morning incident.
The Caithness site’s fire brigade extinguished the blaze in the PFR’s sodium tank farm within 30 minutes.
What is tritium?
Tritium is a radioactive isotope of the element hydrogen.
It is produced naturally in the Earth’s upper atmosphere, but is also produced by nuclear weapons explosions and commercially in civilian reactors.
According to the US Environmental Protection Agency, tritium is used to illuminate exit signs in buildings, aircraft gauges and dials on wristwatches.
The Scottish Environment Protect Agency allows DSRL to discharge specified amounts of a gaseous waste called krypton-85 into the atmosphere.
Kr-85 is found in some types of light bulbs.
Levels of the gas increased in 2012 compared to 2011 due to work to decommission Dounreay’s fast reactor and prototype fast reactor.
Since then, radioactivity in the environment around Dounreay has been found in low and ever decreasing concentrations, according DSRL.
The reactor ceased operating in 1994 and is more than halfway through a process of being decommissioned.
More than 1,500 tonnes of sodium, a material used when the reactor was in operation, has been safely destroyed so far.
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