(Juny 15, 2005) Cumbrians Opposed to a Radioactive Environment (CORE) has learned that the 83 cubic meter of liquor that leaked into THORP's Feed Clarification Cell over a nine-month period was comprised of dissolved fuel from Holland and Switzerland as well as from Germany. In parallel with removing the leaked liquor from the Cell floor, British Nuclear Group has been identifying options for re-starting THORP using just one (in stead of two) Accountancy tank.
(632.5706) CORE - Given that British Nuclear Group's Board of Investigation report, published on 26 May, confirms that liquor had been leaking into the Cell from July 2004 to April 2005 - and that at least three separate reprocessing 'campaigns' had been undertaken during this period (Dodewaard, Beznau and Unterweser respectively) - observers will not be surprised to learn that the fuel from more than one European customer was involved. British Energy's AGR fuel may also be involved, having been reprocessed prior to the Dutch fuel.
The BNG Board of Investigation report infers that, from July 2004, the leak rate increased with time until mid-January this year when the pipe work feeding Accountancy Tank B suffered a complete fracture as a result of fatigue stresses. German fuel, reprocessed after the complete fracture of the pipe, is therefore likely to form a majority of the leaked 83 cubic meters, with Swiss, Dutch and possibly UK AGR fuel in lesser amounts. No explanation has yet been provided by BNG as to how this cocktail of fuel, not only from different countries but also from different reactor types (BWR, PWR and possibly AGR fuel) can be properly processed in terms of separating out individual customers' products (plutonium and uranium) in line with the customer contracts and requirements. The liquor also contains dissolved steelwork from the support framework around the tank.
In parallel with removing the leaked liquor from the Cell floor, BNG has been identifying options for re-starting THORP. The Nuclear Decommissioning Authority (NDA) under the Freedom of Information Act (FoI) released details of these options to CORE. The information has revealed, via a BNG update on 24 May, that the company has selected - 'as the most appropriate' option - the re-start of THORP with the use of Accountancy Tank A only, thus permanently isolating the fractured pipe work and Tank B which it fed. In use, Tank A will be used as a pumping tank only with accountancy of the dissolved fuel being carried out in a downstream buffer storage tank.
Though a detailed investigation will be carried out into the reliability/safety of the pipe work now intended to be used, BNG has said that it consists of a different and more flexible pipe-run than that which fractured at Accountancy Tank B. No detail is given as to how liquor accountancy can be carried out in the future in a buffer tank under the selected option, nor of the undoubted reduction to THORP's throughput rate as a result of having to operate on one tank instead of two.
BNG's Board of Investigation (BoI) report, together with information received from the NDA under the Freedom of Information Act, reveals a catalogue of human and design errors that contributed to the leak. The most significant are highlighted below.
- BNG has blamed the 'new plant' culture, which pervades THORP operatives from managers down who believed "material losses on this scale could not conceivably be due to a leak; there had to be an error in the paperwork" (BNG BoI).
- Despite previous accidents in the plant, the 'new plant' culture has continued and lessons not been learned. "Given the history of such events so far, it seems likely that there will remain a significant chance of further plant failures occurring in the future (CORE emphasis) even with the comprehensive implementation of the recommendations of this report". (BNG BoI)
- The accountancy tanks were designed to move vertically (to allow weighing) and provision made for restraint to lateral movement of the tanks during agitation or seismic events. It is now known that the restraints were never fitted and that modifications were made to the steelwork supporting the tanks allowing greater potential for lateral movement. This movement led to the stress fracture of the 40mm pipe where it joined the tank. (BNG FoI)
- "These stresses arose as a result of modifying the design and not maintaining the intent i.e. restraining vessel movement" (BNG BoI)
- The pipe work leading to the Accountancy Tank had exceeded its theoretical life expectancy given the level of vibration observed in the video of the tank operation. (NDA FoI - BNG THORP Feed Clarification Cell Update 24 May 2005)
- There is evidence to suggest that the accountancy tanks have recently been agitated for longer periods than required to take homogenous samples. (BNG BoI)
- Despite the requirement to regularly sample and measure liquor levels on the Cell floor "the operations staff did not act appropriately to 'off normal' conditions in either the level instrumentation or the sampling process". (BNG BoI)
- Operators were not alerted by the Cell's sump alarms. "There is a significant history of erratic alarm operation associated with the Buffer sump level. Between 01/07/04 and 22/03/05 the alarm has flagged a Lo or Lo-Lo status over 100 times. There is no evidence of investigation or corrective action during this period". (BNG BoI)
Source and Contact: Cumbrians Opposed to a Radioactive Environment.
98 Church St, Barrow, Cumbria LA14 2HJ. Tel +44-1229 833851. Fax +44-1229 812239.
E-mail: info@core.furness.co.uk
Web: www.corecumbria.co.uk