On 23 February, the US and UK carried out a ‘sub-critical’ nuclear test at the Nevada underground testing site.
The test, conducted by Los Alamos National Laboratory and the Atomic Weapons Establishment (AWE) Aldermaston, took place in a laboratory of horizontal tunnels about 290 metres underground. It was the first since May 2004, the ninth under the Bush administration, and the second carried out with Britain since a joint test in February 2002.
In a sub-critical test, less fissile material is used in a device than would be needed for a critical mass – the necessary amount for a self-sustaining nuclear fission chain reaction. It therefore does not break the terms of the Comprehensive Test Ban Treaty (CTBT).
Stewardship – or designs for new weapons?
The tests are officially part of the US Stockpile Stewardship Programme, originally set up in 1993 to “ensure the safety and reliability of the existing nuclear warhead stockpile" – to examine the effects of ageing of components and the fissile material, which affects the weapon's explosive yield and also its safety in storage. Existing Cold-War warhead designs produced compact, high-yield weapons that needed to be tested regularly and were not designed for long life in a post-testing era.
Sub-critical tests assess the behaviour of the plutonium in the weapon as it is strongly shocked by forces produced by the chemical high explosives that trigger the chain reaction. However, they could also be used to verify designs for adapted or new weapons. They also reflect increased participation of UK personnel at US nuclear laboratories and Britain’s increased interest in tests. This coincides with the impending decision whether to replace the UK’s Trident missile and warheads.
As the CTBT forbids exploding a weapon to test it, US nuclear laboratories and AWE also use giant lasers to simulate the very high temperatures and densities reached during the phases of a warhead’s operation, and supercomputers to carry out modelling of warhead processes and properties.
The UK works closely on design and maintenance of its nuclear warheads with the three main US nuclear weapons laboratories. The UK Trident warhead is closely based on the US Trident W76 warhead and was tested at the Nevada test site.
A £150 million refurbishment programme is under way at AWE Aldermaston, with £1.2 billion slated for a new hydrodynamics research facility, supercomputer and giant laser. An upgraded AWE could be suitably equipped for operations beyond the stewardship programme, such as a replacement for Trident.
New designs through the back door
As part of the overall US stewardship programme, Rep. Congressman David Hobson created the US Reliable Replacement Warhead (RRW) programme to allow only existing weapons to be renovated, rather than developing new designs that would need underground testing. Hobson’s subcommittee have ruled against funding several controversial nuclear weapons initiatives to adapt old weapons or create new ones. The RRW was therefore set up as a compromise to maintain stewardship only, while keeping the nuclear weapons laboratories occupied in challenging research and engineering problems.
But, according to NIS nuclear consultant Andy Oppenheimer, the RRW allows for complete upgrades of warhead components, including the nuclear explosive. The test data could be used to guide development of new warhead designs, most notably a replacement for Trident.
Gradually, therefore, RRW concepts could be applied to warhead development to meet new strategic requirements – pre-emptive destruction of bunkers – and that the entire current stockpile would eventually be replaced with a new generation of warheads. A US Department of Energy Advisory Board task force recommended in July 2005 that a new version of the RRW be initiated that would incorporate new design concepts.
Many scientists believe that sub-critical tests and sophisticated simulation methods cannot supply the ultimate proof afforded in the past by nuclear tests. The Bush administration refuses to re-submit the CTBT to Congress for ratification and has long been seeking to reduce the amount of time required to prepare a site for a full nuclear weapon test from its current level of two to three years.
Although the tests are claimed to be for stewardship only, in conducting them the US and UK governments are sending out the wrong message – ‘do as we say, not as we do’ – to countries accused of nuclear proliferation, most notably Iran and North Korea. This message will be amplified if future tests are carried out and new weapons emerge.