On the 11^th May 1967, Chapelcross Nuclear Power Station teetered on the edge of nuclear disaster. An operator on No.2 Reactor had discovered an unusual amount of radio-activity in the carbon dioxide gas (CO²) which circulated continuously between the pressure vessels and the heat exchangers. As a standard precaution, the reactor was immediately shut down until the anomaly could be investigated.

After depressurising the reactor, cameras were inserted into the offending fuel channel which showed a blockage caused by a melted Magnox can. With the gas unable to flow through the channel, a potentially catastrophic fire had ignited inside the reactor core.

As the can had deformed and melted, staff could not adopt the usual method of clearing the channel, meaning a special technique had to be devised.Willing volunteers were to enter behind a biological shield to fit a catch-pot under the defective fuel elements to ensure that no fragments from the melted can fell into the main reactor.

Senior members of staff members, Dr J.H. Martin the Manager of the Health, Physics and Safety department, Mr David MacDougall, the Deputy Superintendent and Mr L Clark volunteered to go into the reactor to complete the operation.  The manoeuvre had been carefully rehearsed and timed in a realistic model before being attempted. A special air chamber had been built around a duct into an air coolant cylinder where Dr Martin and Mr MacDougall entered wearing PVC suits. Their only link with outside was an air pipe, a radio communications cord and a nylon life line belted to their waists. The men commented, ‘the suits were clumsy to work in and we perspired a bit… we never thought about any danger… we did feel a little like Moon men’. Mr Clark was the sentry at the entrance to the duct whilst Dr Martin entered to make final measurements of radio-activity and Mr MacDougall ensured the catch-pot was in position.

Mr Tom Tuohy, the Managing Director of the United Kingdom Atomic Energy Association (UKAEA), congratulated the men who entered the reactor and called the operation ‘entirely successful.’ He also remarked that he did not consider the men were in grave danger going into the reactor as he would not have allowed the operation if there had been.

The UKAEA assured Annan locals that there was no danger of a radiation leak into the atmosphere. There had been a slight increase in radio-activity inside the reactor building however, because the radio-active materials decayed with a half-life of three hours, conditions were back to normal in 24 hours. Although the incident was very serious, a great deal of useful information was discovered through this stoppage. A new instrument was invented which would detect a serious break in a Magnox can within thirty-seconds and would shut down the reactor before the uranium reached its melting point.

In 1968, a year after the incident, Mr Tuohy highlighted that even though only three reactors were in operation, they were producing the same amount of electricity as they had in 1960 and were more productive than some other power plants. The breakdown of No.2 Reactor caused a loss of production which equated to a loss of £90,000 per month in electricity sales. This lasted for nearly two years only, coming back to power in 1969. Once back online, No.2 Reactor continued production until 2004 and was the last reactor to be shut down. Without the fearlessness of those willing to risk their safety to rectify the blockage, Chapelcross could have easily became as infamous as Chernobyl.