Operation Seanuts

Extracted from A History of the Management of Environmental Protection at Dounreay by GR Tyler, June 1998

In the summer of 1954, when design work for the construction of a chemical plant at Dounreay, which would cover the requirements of both Fast Reactor and E443 (Material Testing Reactors), commenced, the need for an effluent treatment plant was addressed.

It was agreed that the resulting low active effluent would need to be discharged to sea via a pipeline. At this time there was debate about the level of activity that it would be permissible to discharge to sea. Estimates at the time varied between a total activity of 1Ci per day up to 100Ci a day. At this stage nothing was known of the environmental processes, in the sea off the coast at Dounreay, that would govern the amount of activity it would be permissible to discharge to sea.

As a first step to determine those processes a project (Operation Seanuts) was put in hand in March 1955. A start had been made on the study of geology, zoology, fauna and flora, tides and winds of the coastal district. Moreover it was decided that in order to obtain reliable results on dispersion in the area a continuous discharge of fission products or other active material up to 100Ci per day was required. As a result proposals for the experiments were made to the chemical plant design committee in May 1955, and accepted.

The experiments were to consist of two parts. A nominal discharge of 10Ci per day of mixed fission products, obtained from the reprocessing of natural uranium fuel at Windscale, would be made at Dounreay to enable a comprehensive survey of the effects of such a discharge. Also, and on a larger scale, an inactive tracer should be used to determine the motion and rate of dispersion of the effluent in the neighbourhood of the discharge point.

The details of the proposed experiments were then detailed by W.L. Templeton, of the Windscale Research and Development Branch. They were to be as follows:

  • A background survey to be carried out on the shore against which the build-up of discharged activity would be assessed.
  • An experimental discharge of 10Ci per day to be made for 150 days combined with an activity survey of the shore to determine concentrating processes.
  • Discharges of the dye Amino-G-acid to be made in the immediate neighbourhood of the discharge point to determine the initial dilution, motion and rate of dispersal of the effluent.
  • Temperature/salinity measurements to be made of the sea between Strathy Point and Brims Ness to study the exchange of water between the bay and the main tidal stream.

Because spume was recognised as likely to be a major concentrating process, owing to its fine particle content, experiments were to be carried out after the discharges had started, on the deposition of spray and fine particles from the spume. As a precaution against possible contamination of the shore, it had been decided that the fission product discharges would start at 1Ci per day and build up to 10 Ci per day over a few weeks. Those experiments began in August 1955, using an outlet 140 feet below the low water mark, and some interim results, obtained up to October 31,1955, became available in January 1956. Those results showed that the dispersal of the effluent from the lower Dounreay Farm bay was not as great as expected owing to weak tidal streams and the presence of a rock barrier to the seaward of the outlet.

As a result it was recommended that sampling should continue until the middle of February. Also that two more discharges of Amino-G-acid should take place with the chemical being released from a boat outside the “rock barrier" in order to determine whether better dispersion took place there. The experiments continued, however, the chemical plants design committee concluded on the basis of the interim findings that the discharge point would have to be further out to sea or at a different point.

When further results, up to December 12, 1955, including the results of the dye discharges from the boat outside the rock barrier and information from floats released by the RN survey vessel HMS Shackleton from a position more than 400ft from the pipeline end where the sea depth was 45ft, were available, Templeton was able to make a positive recommendation.

This was to the effect that if the minimum amount of radioactivity to be discharged was to be 10 Ci per day then the outlet of the effluent pipeline should be situated at least 360 yards from high water mean of spring tides. As a result of the discussions which followed this recommendation it was agreed in March 1956 that the pipeline should discharge 2000ft beyond the water mark and should be laid by driving a tunnel under the sea and breaking through. However the committee asked that the experiments arranged (using floats and tracers), to confirm satisfactory dispersion at 2000ft be completed before completion of the vertical shaft that would need to be driven at the cliff to facilitate tunnelling.

Those experiments confirmed that dilution and dispersion at the 2000 ft mark were satisfactory and said to be at least a good as those at Windscale. In the meantime, Templeton had summarised the results of all the experiments so far as the basis for discussion between UKAEA and the Department of the Secretary of State for Scotland. The previously reported results on the discharges of aged mixed fission products and Amino-G-acid had shown that despite the limitations of the discharge point the levels of activity in biological samples and sand from along the coast at Dounreay, were well below maximum permissible concentrations whilst the levels found in fish, lobsters and crab did not differ greatly from background.

However it was acknowledged that a period of discharge of at least a year would be required to be certain that no concentrations were taking place by organisms in the area. Moreover, attention was drawn to relatively high levels of activity deposited on sand from the stable spume produced during rough weather, although that activity tended to reduce to the original level after two or three tides with no spume being produced.

Templeton also gave details of additional experiments. Bottom soundings had been taken and tidal streams measured by HMS Shackleton and by the UKAEA. An attempt had been made to determine the turnover of water between the bay bounded by Brim's Ness and Strathy Point and the main Pentland Firth stream by the taking of salinity samples and the measuring of temperatures at a number of points over the area in the period August 1955 to January 1956. Additionally, a habit survey was carried out to obtain information on commercial fishing and the collection of marine organisms in the immediate area.

The bottom survey had indicated that the experimental pipe outlet was in 26ft of water at high water, and was bounded 150ft to the seaward by a rock barrier, the peaks of which were 15ft below the surface at high water. At low water spring tides the rock barrier was just visible. The tidal stream work had shown that over the experimental outlet there was little or no movement of water. At a point a further 550ft seaward, with no wind (the worst conditions) there was a 0.2 knot easterly moving flood tide with a 0.1 knot westerly moving ebb tide.

As far as the temperature and salinity measurements were concerned, Dr Tait of the Scottish Home Department's marine laboratory thought that the results might not be inconsistent with conservation of the waters of the bay, apart from storms. However he suggested that more observations should be taken including some near the bottom for better interpretation of the water movement. [These further measurements were, in the event, not made until after discharges commenced. However they did allow Dr Tait to conclude that they were not consistent with the notion of no bottom flow, but that rather the water in the bay was, in the absence of strong winds, turned over in a period of about 3 weeks. In winds over force 5 (21 knots) a rapid turnover of a few days only was experienced.

The chemical dye experiments had shown that compared to the initial dilution of only 1E2 at the shore opposite the outlet when discharged from the experimental pipeline, initial dilutions at a point 1800ft from the shore in calm conditions were at least 2E4 with further dilution to 1E5 during the westerly movement. In rough sea conditions with northerly winds up to 35 mph slightly increased dilutions were shown on the westerly movement. During a discharge in a north west wind of Force 4, dilutions of 1E8 were detected on the shore.

As a result of his experiments Templeton concluded that by moving the pipeline outlet to the new position, 1800 ft. from the high water mark the experimental discharge rate of 10 Ci a day could be increased by a factor of 100. However, in line
with the usual policy of the AEA to increase the discharge rate of radioactive effluent into the sea by gradual steps, he recommended that an authorisation from the Secretary of State for Scotland should be sought to discharge 100 Ci a day at the new position.

Following the cessation of the discharges at the beginning of January 1956, a comprehensive pre-operational background survey in the area commenced in June 1956. This survey involved land sampling of roots, soil and vegetation from 40 points, gamma and beta measurements and air sampling and sea and shore monitoring and sampling. Initially at some points near to the coast readings in excess of background were found, up to 2x background, which it was thought were possibly owing to activity blown on to the land in spray during the experimental discharges of fission products. These levels had reverted to background when repeat surveys were carried out in September 1956.

By May 1957 the fourth sampling cycle of this background survey was underway and arrangements were being made to sample sheep’s thyroids and analyse them for I131. The following month sampling of vegetation for gamma spectrometry analysis for fission products and milk analysis for I131 and Sr90 commenced. After analysis at Dounreay the sheep’s thyroids were being sent on for check analysis at the MAFF Laboratory at Weybridge.

The pre-operational survey programme was rounded off with the taking of special seaweed samples from the Orkney Islands and the sampling of fish obtained from the market at Scrabster. The results of the pre-operational district gamma radiation survey were reported by Stott and Escott who concluded that in the period 1956-60 there had been no increase in background radiation in the vicinity of Dounreay.

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