asked the Secretary of State for Energy what breeding or conversion ratios have been achieved by the Dounreay experimental and prototype reactors.

The UKAEA informs me that the Dounreay fast reactor is an experimental reactor and that the prototype fast reactor, in addition to generating electricity, is equipped to carry out experimental work on fast reactor fuel and other technology. In consequence their breeding ratios are only unity or slightly less; but calculations, which are being confirmed by current experiments, indicate that were the prototype fast reactor to be fuelled with normal core and breeder elements a breeding ratio of about 1·2 would be achieved.