Radioactive Waste

Over the entire period of operation slightly radioactive effluent had been run down a drain pipe and allowed to soak into the soil. This effluent was diluted with brine from the distillation plant to keep it below the maximum permissible concentration set by the AEC. But the radioactive contaminants from the effluent were being re-concentrated in the soil by the soil itself acting as an ion-exchange column. Partway through the life of the reactor someone realized that this was happening and the drainpipe was extended to prevent the concentration becoming too high in any one place. The Naval Nuclear Power Unit decided that this did not necessarily constitute a violation of the Antarctic Treaty, which bans disposing of radioactive waste, because the treaty did not define the term radioactive waste. But just to be on the safe side they promised to shift any soil that had radioactivity in excess of the standards set domestically by either the Soviet Union or the United States.

Removal Plan

A fascinating document called "Removal plan for the PM-3A nuclear power plant," prepared by the Naval Nuclear Power Unit, described the apparently very thorough safety precautions that would be involved. Building interiors would be washed, for example, to remove possible contamination, and then painted to seal in any contamination that might have survived the washing.

The removal plan also disclosed that leaks had taken place. In the 11 years of operation there had been three occasions when cracks had appeared in the containment vessels. These were welded up, but not before they had allowed an undisclosed amount of shield water to soak into the backfill. Neutrons passing through the tanks had further activated the backfill.

Polar Research

The Navy settled for dismantling the reactor at a predicted cost of $800,000, and reverting to diesel generators. The Secretary of the U.S. National Academy of Sciences committee on polar research says Nukey Poo was shut down because of "numerous malfunctions and its pollution potential." On the other hand, the New Zealand government's Department of Scientific and industrial Research, Antarctic Division, says the reasons were "purely economic." Dismantling Nukey Poo was scheduled to be a three-year operation. Many of the components were highly radioactive and this made dismantling much slower than the original assembly. 

Investigations

Subsequent investigations seemed to show that moisture had not caused the cracking; but a detailed inspection was never undertaken at McMurdo. It was calculated that detailed inspection and repair of the source of dampness in the insulation canning would cost $1.5 minion and take two to three years. If the inspection showed there were cracks, then the pressure vessel would have to be replaced and the cost would go up to $2 million. Despite remote operating procedures it was calculated that over 35 persons would receive "significant" doses of radiation during this process. To build a new plant altogether would be prohibitively expensive (up to $35 million), and would take six years.

Loss of Coolant Accident

This would have been the first case of a loss-of-coolant accident leading to a core meltdown, the bogey that haunts this type of reactor. It could have happened at McMurdo, but fortunately the possibility was forestalled by "routine inspection." All pressurized and boiling water nuclear power stations today are fitted with emergency core cooling systems which are intended to prevent a loss-of-coolant developing into a core meltdown. Some critics say that when the crunch comes, the emergency core cooling systems won't work. But this would have been an academic point at McMurdo, as the reactor was not fitted with any emergency core cooling systems at all.

Speculation in New Zealand

This aroused some speculation in New Zealand that a nuclear spill had taken place, but an article in the U.S. Antarctic Journal described how the reactor had simply been shut down after routine inspection revealed wet insulation around some pipes. Chloride had been found in the dampness and it was feared that this might have initiated chloride stress corrosion cracking in primary piping or in the reactor pressure vessel. Such cracking could have led to the vessel or a pipe bursting, allowing all the primary coolant water to escape. The reactor core would drastically overheat and possibly melt its way down through the containment vessel and cause disastrous dispersal of radioactivity.

Final Shutdown

The final shutdown for Nukey Poo came earlier than expected however. The reactor stopped generating shortly before the opening of the 1972-73 season, in September 1972. No announcement about the shutdown was made until the end of the season, when it was said in late February that "a fault" had caused the shutdown. According to the Deepfreeze commander it had been touch and go getting enough substitute diesel fuel into McMurdo that summer and for a while complete evacuation was being considered. At the opening of the following season, it was announced that the reactor was shut down for good, and that it would be dismantled and shipped back.