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Re: [cdn-nucl-l] Calder Hall and Chapelcross closures
In a message dated 2/7/04 2:31:51 pm, email@example.com writes:
The Guardian article also did not explain why these old small Magnox units continued to operate, whereas the newer larger units at Berkley, Bradwell, Hunterston "A", Hinkley and Trawsfyydd where all shutdown years ago. Was it something technical about Chapel Cross and Callder Hall, like lower gas temperatures, or was it because they also produced another valuable product ?
Neil, many thanks for pointing out the inaccuracies in the Guardian Article (although it's a national paper and is not the same as the Manchester Guardian). Unfortunately it just illustrates how little effort is made in this particular paper to check the facts before publication.
To answer your question (see above) there is no one single reason why the larger commercial plants were closed while the older 1st generation plants remained open. One of the reasons was that all of the original 8 reactors were very similar and based on very basic technology and were significantly over engineered. Each of the 2nd generation Magnox plants were unique one of a kind designs, a key failure of the UK nuclear Power programme. It was meant to produce a competitive nuclear industry in the UK and involved at least 3 different consortia. Canada sensibly abandoned plans to try and produce a competitive private nuclear industry very early on (after NPD-1 I think). Throughout the llife of the commercial plants this has meant that most major plant problems were unique to each site (2 reactors) and the cost resolving these could not be spread across multiple reactors/sites unlike any issue from the Calder/Chapelcross plants.
The following is a summary of what I can recall about the closure of each of the commercial plants.
Berkley was the first to close and I believe that this was due to problems with the fuel route for irradiated fuel. The UK Regulator (the Nuclear Installations Inspectorate) required major upgrade to the irradiated fuel route at Berkley and the CEGB (Central Electricity Generating Board) decided that the costs of the upgrade could not be recovered during the remaining planned operational life of the plant.
Bradwell, I'm not sure about. If I recall correctly it completed some 38 years of operation and was not planned to operate for much longer anyway. There is another issue which has/will continue to affect the operational lifetimes of the Magnox Power Plants in the UK and this is the operation of the Magnox reprocessing plant at Sellafiled. This is to close in 2012 and by that time all the irradiated Magnox fuel will have to be processed. This has led to much earlier closure dates for Oldbury and Wylfa in particular, and the timing of various plant closure will have been modified to meet this target. At shutdown for example there were approximately 72,000 irradiated fuel element remaining in the reactors at Hinkley Point A.
Hunterston A was closed following the introduction into service of the large AGR at Torness. I'm not aware of any technical issue which forced the closure of Hunterston A, it was simply that the SSEB (South of Scotland Electricity Board) had a large surplus of generating capacity. I believe that the two AGR power plants in Scotland (Torness and Hunterston B) can supply 40% of Scotlands Electricity needs. The SSEB did look into returning Hunterston A into service as the UKs electricity market was moving towards a privatised, competitive market but I understand that the plant wasn't condition properly when it was shut down and would have required as a minimum new boilers/steam generators. (Hmmm, plant not laid up properly at shutdown, does this story seem familiar?)
Hinkley A (as there is a B station which was one of the first AGRs to become operational in the UK) was shutdown because of issue with the safety case for the steel reactor pressure vessel (with the exception of the last two plants, Wylfa and Oldbury, all of the Magnox stations had steel pressure vessels). Work was being undertaken to address both the RPV safety case and also a separate issue with some significant welds on the boilers when BNFL Magnox decided to close the plant. The reason put forward was the cost of revising the RPV safety case. In the UK the regulatory framework is based upon some very broad principles, but it isn't very prescriptive unlike for example the US regulatory system. As a result it can be very difficult to estimate the time and costs involved in making a case to the regulator on significant issues. It's not simply a case that you have a clearly defined standard to meet and you can employ specialist contractors to do the necessary ASME (or other) type tests and you have a pass fail criteria. In the UK you can spend an awful lot of time and money producing case for consideration by the regulator which the regulator can/will then ask for a lot of additional information or new justification before the accept the case that has been made and issue a new license to operate. Incidentally it was this same issue of unknown cost that stopped further work on different fuel (Magrox, slightly enriched uranium fuel in a stainless steel clad) that would have allowed Wylfa and Oldbury to continue operating after the closure of the magnox reprocessing plant in 2012.
Trawsfynydd was also effected by issues with it's steel pressure vessel. These were more pronounced at Trawsfynydd because this plant had the highest neutron flux and therefore the greatest amount of embrittlement within the RPV. This issue was identified when it was shutdown in 1990/91? when during a routine maintenance outage steel samples were recovered from within the core and analysed. These showed that the neutron 'ageing' was greater than thought. A lot of work was undertaken at the time to remove pipework in the top sections of the boilers (although this would have meant less generating capacity) to increase the temperature of the gas returning to the reactor and return the vessel temperature to point within the ductile range for the steel. The plant had other issues and was not planned to operate beyond 30 years anyway. As a result it was decided that it was uneconomic to continue with the remaining modifications and safety case. Being a cynic, my personal view was that Trawsfyndd was sacrificed to provide information on RPV damage to justify the continued operation of the remaining steel RPV plants. After shutdown work continued for at least two years to remove sections of the RPV using robots for further analysis.
One final point neither Calder Hall or Chapelcross has been used in recent years to produce weapons grade plutonium, I can say for sure but UK stocks of warheads/free fall bombs have been static for more than two decades, the new trident fleets warheads were essentially recycled Polaris ones. However the reason Chapelcross continued to operate after Calder Hall was because it had a facility for the production of tritium for a UK government agency.