NEW FAST PULSED REACTOR, VIPER.

The design of a new, versatile fast pulsed reactor is described. The reactor is fuelled with uranium of medium enrichment in the form of metal rods set in a matrix block. The composition of the matrix block and the disposition of the fuel elements can be varied. The reactor is pulsed into the prompt critical condition by rapid insertion of a fuel rod and the subsequent nuclear transient is terminated by the inherent negative temperature coefficient of reactivity. The important new features of this reactor are that the Doppler effect in {sup 238}U provides a large part of the temperature coefficient and that the core composition can be changed so as to vary both the neutron lifetime and the Doppler effect. (author)