§ Mr. D. E. Thomas
asked the Secretary of State for the Environment if, pursuant to the answer of 25 January, Official Report, column 556, he will explain why (a) plutonium-240 is included in the plutonium-239 figure, (b) plutonium-242 has never been analysed separately and (c) how his Department judges or estimates the mass of the plutonium discharged to sea from the Sellafield Windscale plant in the light of the lack of these separate analyses.
§ Mr. Waldegrave
The analytical technique employed cannot distinguish between plutonium-240 and plutonium-239 which in any case have similar radio toxicities. Plutonium-242 has never been analysed separately since the quantities involved are negligible being less than one-thousandth part of the sum of plutonium-239 and plutonium-240. My Department is concerned primarily with the radiological effects of discharges which are related to radioactivity rather than mass. If necessary, the mass of plutonium discharged can be calculated from the known relationship between the radioactivity, which is measured, and mass. In the case of the mixture of plutonium-239 and plutonium-240, a ratio of the two may be calculated for this purpose using the principles of nuclear physics.