Trawsfynydd Lake (Hansard, 4 July 1991)

§ Mr. Frank Cook
To ask the Secretary of State for Wales (1) if he will identify the means and routes by which radioactivity has entered Trawsfynydd lake, giving comparable information for other bodies of water that are not directly connected with discharges from the Trawsfynydd nuclear power station, and account for the presence of natural radioactivity, past fall-out from Chernobyl and other nuclear-related incidents that have resulted in airborne radioactive matter entering Trawsfynydd lake; and if he will make a statement;
(2) if he will provide the results of any analysis undertaken by or reported to his office on the increased radiation dose, whole body and internal organs, received by the most exposed members of the public as a result of the water level of Trawsfynydd lake being lowered for investigation repairs to the dam serving to contain the waters of the lake; and if he will make a statement;
(3) if he will provide the level of radioactivity currently in situ in the sediments of lake Trawsfynydd, and the proportions of the overall radioactive inventory contributed by each principal radionuclide specie, stating how each radionuclide specie is distributed across the lake bottom and through the sediment; and if he will make a statement.

§ Mr. Nicholas Bennett
[holding answer 28 June 1991]: The directorate of fisheries research of the Ministry of Agriculture, Fisheries and Food monitors regularly the levels of any radioactivity found in environmental materials taken from Lake Trawsfynydd. Measurements 193W are also made in other lakes. The results are published in the annual reports of monitoring of radioactivity in surface and coastal waters of the British Isles. Copies of the report are available in the Library of the House.
The regular monitoring reports include analysis of the measurements in terms of both internal and external radiation doses. There is no evidence of any increase of dose to members of the public which is attributable to the lowering of the water level in the lake.
Radioactive nuclides are regularly monitored in Lake Trawsfynydd sediments and the results published in the annual reports. More detailed investigations into the radionuclide content of sediment profiles are currently being undertaken by the Ministry of Agriculture, Fisheries and Food and the results will be published.

§ Mr. Frank Cook
To ask the Secretary of State for Wales what consideration his Department has given to the radiological consequenced to individual members of the public of allowing the Trawsfynydd lake to be completely drained and/or abandons when the present nuclear power station located on its shores ceases to function; what conclusions he has reached in terms of the most exposed individual of the public; and if he will make a statement.

§ Mr. Nicholas Bennett
[holding answer 28 June 1991]: When Trawsfynydd power station is to be decommissioned, full account will be taken of potential radiation exposure to members of the public from such operations. However, the presence of the recently refurbished Maentwrog hydroelectric power station will ensure the need to maintain the lake for many years to come.

§ Mr. Frank Cook
To ask the Secretary of State for Wales if he will give the period for which the level of the lake was lowered in order to facilitate investigation and repairs to the dam containing the waters of Trawsfynydd lake, and state by how much, on average, the level of the lake was lowered and by what extent in area lake bottom sediments were exposed; and if he will make a statement.

§ Mr. Nicholas Bennett
[holding answer 28 June 1991]: I understand from Nuclear Electric that Trawsfynydd lake level was lowered in December 1986 from a nominal 194W maximum of 650 ft above mean sea level—AMSL—to a nominal maximum of 642 ft AMSL to aid investigative work on the main dam structure. The level rose during early 1987 but was again reduced to 644 ft AMSL nominal maximum in May 1987 to relieve pressure on the clam structure until the new dam is completed, which is expected to be later this year.
When the lake's maximum level is lowered, areas of the lake shore which are normally covered by water, except during the summer months, are uncovered for longer periods. The size of these exposed areas varies from one part of the lake to another, depending on the slope of the shore at any point.

§ Mr. Frank Cook
To ask the Secretary of State for Wales which organisation is to be responsible for maintaining Trawsfynydd lake at the desired levels and in good repair in future years; for how long the lake will have to be maintained full and in good repair if any undesirable radiation exposure to any member of the public is to be avoided; and if he will make a statement.

§ Mr. Nicholas Bennett
[holding answer 28 June 1991]: Nuclear Electric owns the lake and is responsible for maintaining it at the required level. I understand that the primary purpose of the lake is to provide water for the Maentwrog hydro-electric scheme.
If at any time the draining of the lake is proposed, a full assessment of any potential radiological consequences will be made beforehand so that all necessary measures can be taken, including those required to ensure public safety.

§ Mr. Frank Cook
To ask the Secretary of State for Wales if water run off from Trawsfynydd lake enters any source of potable water supplies.

§ Mr. Nicholas Bennett
[holding answer 28 June 1991]: There are no licensed potable water abstractions from Trawsfynydd lake or the Afon Prysor into which it discharges. However, records are not kept of single abstractions of less than 5 cu m or of abstractions by adjoining land owners which are permitted without licence.