HC Deb 28 January 1987 vol 109 cc296-7W
Mr. D. E. Thomas

asked the Secretary of State for Wales further to his reply to the hon. Member for Meirionnydd Nant Conwy on 15 January, Official Report, columns 282–3, containing tables of public radiation doses, if he can explain why the dose in 1985 was lower than in 1975; whether the dose in 1986 is expected to be lower than in 1985; and if he will make a statement.

Mr. Mark Robinson

The differences in dose to the critical group between 1975 and 1985 reflects the greater proportion of hatchery reared rainbow trout now caught and consumed by anglers compared with 10 years ago, when the lake stock was predominantly the brown trout variety. As levels of radioactivity in fish in the lake are derived from the power station's liquid effluent, rainbow trout have a lower concentration compared with brown trout owing to their different feeding habits. Shorter residence time is also a factor.

It is too early to assess the dose to the critical group for 1986 since all the analytical data are not yet available. The results will be published later this year in the MAFF report "Radioactivity in Surface and Coastal Waters of the British Isles 1986", copies of which will be placed in the Library of the House.

Mr. D. E. Thomas

asked the Secretary of State for Wales, further to his reply to the hon. Member for Meirionnydd Nant Conwy on 15 January, Official Report, column 283, concerning changes expected to take place concerning maximum exposure to radiation of members of the public, what proportion of the maximum exposure in each recent year is attributable to discharges made in preceding years; what calculations have been made on the likely maximum exposure in each of the three years following a cessation of all discharges, in the case that this was to occur immediately; and if he will make a statement.

Mr. Mark Robinson

Critical group exposure to radiation from consumption of fish from Lake Trawsfynydd includes an element attributable to past discharges from the power station. In the case of radiocaesium, the principal type of activity in terms of dose to the critical group, research has shown a time lag from discharge to uptake in fish of about three to six months. In the event of all discharges ceasing concentrations in fish would decline accordingly.