The Scottish National Party energy spokeswoman, Nicola Sturgeon, said that the party had received a letter from a former employee at the Caithness nuclear reprocessing plant which highlights "disturbing" breaches of safety.
In one incident in the early Sixties, the letter alleged that NAK (liquid sodium and potassium used as a coolant in the fast reactor) was dumped in the sea by shooting it through the air from a hose. It claimed that NAK may also have been dumped in the waste shaft, probably as a contaminant of fast-reactor fuel rods.
The letter added: "The explosion in the shaft in 1977 may have been caused by NAK. If NAK was put in the shaft then it was an act of criminal folly because the shaft leaks continuously and is therefore full of water, and NAK and water explode on contact. The action of dumping NAK or materials containing NAK in a water-filled shaft defies belief and is an act of gross stupidity."
Staff at Dounreay yesterday confirmed that they were investigating the allegations concerning NAK and would respond "shortly".
At a news conference in Edinburgh, Ms Sturgeon said: "The unstable nature of the so-called high active waste shaft - in reality simply a hole in the ground - is of great concern and the possibility that NAK was dumped in the sea in the Sixties is a new piece of information that must be thoroughly investigated.
"We are calling for an independent technical investigation into all past and present activities at Dounreay and believe that this can only credibly be carried out by a European or international agency.
"At the same time, on the basis of what we already know, the situation is serious enough to warrant a police investigation into the breaches of public safety that have taken place over the years."
A spokesman for Dounreay said: "Allegations relating to the Sixties' operations on NAK are being thoroughly investigated and we will be responding shortly.
"On the issue of the waste shaft, which stores only low- to intermediate- level waste and was licensed to do so by the Government, we would point out the following: The shaft is in the short- to medium-term safe and we are taking every step to make sure this remains the case; the shaft is monitored at all times.
"We share the SNP's view that this is a priority and we have publicly stated several times we are now looking towards achieving a long-term and permanent solution to this issue by assessing two key options: in- situ confinement or retrieval. We will make our recommendations to the Government as soon as is practically possible."Reuse content