Reactor Shut-Down Device, Progress Report For Period Ending November 30, 1952

This report describes work done at N.A.A. on devising a safety shut-down device for reactors. Specifications require the device to be capable of quickly shutting down a reactor if the neutron flux exceeds a prescribed level and to be self-contained, reliable, and inaccessible to sabotage or bomb damage. The triggering device should be as independent of electrical and mechanical circuitry as possible. That is, the chain of action between the flux increase and the introduction of poison should be minimised. Such a device would be of particular value for high power reactors as a means of reducing the "safe limits" requirements of these reactors. At present the device is visualized as consisting of a reactor poison whose introduction into the reactor by gas pressure would be triggered directly by an increased neutron flux.