Scottish CND     Safety of Trident

9. CHRONOLOGICAL ASSESMENT

Materials Production

Britain has had facilities to produce weapons grade plutonium at Windscale from 1950 to 1957, at Calder Hall since 1956 and at Chapelcross since 1958. Weapons grade plutonium could also be produced at other magnox reactors. Plutonium produced in the earlier years, which was not used in bombs exploded in nuclear tests, will have been recycled for use in future weapons. Some Trident warheads will contain plutonium produced in the 1950s and 1960s and other warheads will contain plutonium produced more recently. Likewise the HEU used in Trident nuclear weapons will be from a stockpile which includes recently enriched HEU as well as some enriched many years ago. The HEU for submarine reactors will be enriched several years before the fuel core is loaded - however as the requirement is spread over a 28 year period from 1988 to 2016 only a fraction of the enrichment work may have been completed so far.

Weapons Production

There are two indications of the warhead production capacity.

a. It was originally planned to produce all the nuclear warheads for Trident in the A90 facility at Aldermaston within 8 to 10 years. Assuming a stockpile target of 400 warheads this suggests that A90 would have a production capacity of between 40 and 50 warhead pits per year. The A45 facility has a production capacity less than half that of A45 - "the rate within the current facilities is under half the initial rate for the new facilities". This suggest that A45 could produce 20 to 25 warhead per year.

b. The production programme was altered and it was decided to produce all the warheads for HMS Vanguard and a proportion of the warheads for HMS Victorious in A45. The first Trident warhead pit was produced from A45 in December 1988. At the time it was assumed that A45 would be replaced by A90 during 1992, which implies that it was planned to produce around 100 in A45 during a 4 year period. This suggest that A45 could produce around 25 warheads per year.

Combining these two approaches, it would appear that A45 has a production capacity of around 25 warheads per year and A90 of around 50 warheads per year. There will be a gap of several months between pit production and when the warhead is completely assembled.

Nuclear Weapons Transport

If each vehicle carries 2 Trident warheads then 50 vehicle movements would be required to deliver warheads whose pits were produced in A45 between 1989 and the end of 1992. All nuclear weapons convoys visiting the Trident area from July 1992 to August 1996 have been recorded. Taking account of the need to rotate Chevaline warheads the number of vehicles delivering Trident warheads was around 100, which could have been carrying around 200 warheads. Delivery of the warheads which have still to be built, around 300, would require a further 50 vehicle movements.

Naval Reactor life cycles

Each PWR 2 reactor is due to be refuelled either once or twice, ie to be use up either 2 or 3 cores. The prototype at Dounreay was the first reactor to be made critical around 1988, followed by HMS Vanguard in 1992, HMS Victorious in 1993 and HMS Vigilant in 1995. The reactor on HMS Vengeance will be made critical around 1997.

The fuel core in a reactor is irradiated when it is made critical for the first time and it remains irradiated after the submarine has been defuelled and for many years to come. So the total number of irradiated fuel cores will rise steadily throughout the period Trident is in service. These irradiated fuel cores represent one of the main hazards of the system.

Scottish CND     Safety of Trident