Godiva device

Experimenters produced bursts of gamma rays and neutrons by assembling Godiva I's three parts and dropping a burst rod through the centre. This image shows it in the safe, scrammed, state.

The Lady Godiva device[1] was an unshielded, pulsed nuclear reactor[2] 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".[3]

The radiation source within the Godiva device was a fissile metallic mass (usually highly enriched 235U),[4] 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.[2]

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.[1]

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.[1]

Godiva II

A cylindrical wire cage encloses the spherical uranium mass at the top of this image of Godiva II.

Godiva II was constructed inside a concrete building with 20-inch-thick (510 mm) walls and 8-inch-thick (200 mm) roof in a canyon a quarter-mile away from the control room.[5]

In 1959, Los Alamos agreed to make Godiva II available to DOD contractors free of charge for 2 days each month, acknowledging its unique facility for radiation tests.[6]

Godiva's success in creating intense bursts spurred development of similar pulsed reactors, which also suffered accidental excursions, for example: 28 May 1965 at the 1965 White Sands Missile Range (parts were thrown 15 feet);[7] and 6 September 1968 at the Aberdeen Proving Ground (middle melted, disks warped and bolts stretched).[8]

In December 2002, the U.S. Department of Energy announced it was to move its TA-18 testing equipment including the Godiva burst machine from the LANL to the Device Assembly Facility (DAF) at the Nevada Test Site (NTS).[2][9]

See also

Notes

  1. 1 2 3 McLaughlin et al. pages 78, 80-83. "Jemima ... apparent self terminating property of this excursion stimulated study with Lady Godiva,46,47,48"
  2. 1 2 3 Garcia page 1
  3. ↑ Frisch, Otto Robert (1980). What Little I Remember. Cambridge University Press. pp. 161–162. ISBN 9780521280105. an unusual assembly ... no reflecting material ... For obvious reasons we called it the Lady Godiva assembly.
  4. ↑ McLaughlin et al. page 109, "93%"
  5. ↑ Engelke pages 3-4
  6. ↑ Zipprich, L.J.
  7. ↑ McLaughlin et al. page 86, "Unreflected uranium–molybdenum metal fast burst reactor"
  8. ↑ Kazi et al., "center third of the safety block was melted"
  9. ↑ U.S. Department of Energy page 1

References

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