Godiva Device

Godiva Device

The Lady Godiva device was an unshielded, pulsed nuclear reactor originally situated at the Los Alamos National Laboratory (LANL), New Mexico, U.S. It was one of a number of criticality devices within Technical Area 18 (TA-18). Specifically, it was used to produce bursts of neutrons and gamma rays for irradiating test samples, and inspired development of Godiva-like reactors. Physicist Otto Frisch remembered the Los Alamos team called an earlier unshielded uranium-235 assembly in 1944 "Lady Godiva".

The radiation source within the Godiva device was a fissile metallic mass (usually highly enriched 235U), about 30 cm in diameter. This was located at the top of a two-metre-high metal tower. The burst of radiation was produced when a piston of fissile material was quickly inserted and extracted from a cavity within the larger fissile mass. During the time these two masses were combined, they formed a critical mass and a nuclear chain reaction was briefly sustained.

Godiva's design was inspired from a self terminating property discovered when incorrectly experimenting with the Jemima device in 1952. Jemima operated by remotely lifting one stack of enriched uranium-235 disks up towards another, fixed, stack. On 18 April 1952, due to a miscalculation, Jemima was assembled with too many disks; this caused an excursion of 1.5 x 1016 fissions—an automatic scram—but no damage.

On 3 February 1954 and 12 February 1957, accidental criticality excursions occurred causing damage to the device, but fortunately only insignificant exposures to personnel. This original Godiva device, known as Lady Godiva, was irreparable after the second accident and was replaced by the Godiva II.