Subcritical nuclear tests remain useful for maintaining the U.S. nuclear weapons stockpile in the absence of nuclear explosive testing, the JASON defense advisory panel affirmed in a letter report last year. But “a gap exists in the current US capability to carry out and diagnose such experiments,” the panel said.
Subcritical experiments simulate aspects of nuclear explosions using chemical explosives. But since a subcritical mass of plutonium (or a surrogate material) is used, no actual nuclear explosion occurs.
The main purpose of subcritical experiments is to identify and decrease uncertainties in weapon performance. “For all weapons in the current stockpile, at the present time margins are adequate and uncertainties are within margins, both for normal operation and for nuclear safety should accidents occur,” the JASON panel said. “However, future aging of these weapons and their remanufacture may increase uncertainties, and JASON finds that scaled [subcritical] experiments in Pu [plutonium] may significantly reduce uncertainties that may arise in the future.”
But “JASON finds that x-ray radiography is needed to diagnose subcritical experiments in Pu… and that the US currently lacks adequate radiography at U1a [the nuclear complex in Nevada] for this purpose.”
The JASON letter report was prepared for the National Nuclear Safety Administration at the direction of Congress. A copy was released by NNSA last week under the Freedom of Information Act.
See Enhanced Capabilities for Subcritical Experiments, JSR-16-Task-011, October 7, 2016.