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Nuclear family

Project 106; BNFL Silo B38; One of the smallest demonstration projects - the supply of rail beams to help decommission a nuclear waste storage silo - thrives on mutual trust. David Hayward has the story.

There can be few more exacting construction operations than the sensitive, tight tolerance, safety-dominated area of providing facilities for handling nuclear waste.

Where such construction involves installation within a live waste storage area of rail tracks laid to +/- 0.5mm accuracy, and along which will run 400t of movable equipment containing extracted radioactive waste, then total trust within the project team is - to say the least - essential.

On a contract to supply complex rail beams for a waste storage silo being decommissioned at Sellafield's nuclear fuel reprocessing plant in Cumbria, this trust from client British Nuclear Fuels, extends to the contractor inspecting its own steelwork within agreed procedures, and to tight machining tolerances being relaxed to ease installation of one very complex section.

Such a joint teamwork approach, through an alliance- style contract, is credited largely to both sides' Egan-like attitude to project implementation.

In an unusual departure from competitive tendering, BNFL offered the rail supply contract by direct negotiation and allowed both main and subcontractors to play a significant role in early design.

With the contract now under way, the team's bible is an innovative memorandum of understanding signed by all parties setting out the co-operation expected in every sector. It even prescribes regular social gatherings which carry a three line whip.

'We have a formal contract, but it sits in a drawer yet to be opened and will only be used as a last resort,' explains Jonathan Thompson, project manager for contractor Fairport Steelwork and the whole alliance team. 'Our memorandum of understanding creates all the right atmosphere for non-adversarial co-operation.'

The 25 page document details joint objectives, including project delivery, pain/gain share deals and even the specific roles of key personnel. Thompson knows this last chapter well, for it states that such personnel, especially the appointed project manager, should not change throughout the project period.

What is occupying a total three years of Thompson's life, encompassing several stages of the project, is the manufacture and supply of 500t of steel rail track. But this is no ordinary railway.

The total 480m of rail beams, and integral turning circle, will be laid on top of the multi-celled concrete silo at Sellafield containing corroded but still radioactive Magnox swarf. This old silo is being decommissioned and the rails will support a vast, highly engineered piece of movable plant, called a mobile cave and used to empty the cells sequentially (see box).

Fairport has previously supplied similar rails through competitive tender for an earlier phase of the same project. But this time the roughly £1.6M contract was negotiated directly with BNFL and a partnering-style alliance set up between contractor and client.

BNFL had been considering its usual competitive tender route for the project's second phase. But both sides were keen to embrace the partnering philosophy and saw the advantage of a negotiated contract. Fairport immediately offered cost saving buildability ideas that were early enough to be incorporated into the track's design.

'Bringing a contractor in during the design stage seemed to offer best value all round,' says BNFL design manager Tony Testa. 'I reckon the move will have saved us some 20% in overall costs.'

Much of this £320,000 saving is credited to such early client-contractor discussions on things like the design for the turning area, which allows the mobile cave to switch between the two rows of tracks. Fairport suggested that an initial suggestion of a modular design for the turning area's rail beams could prove 'unbuildable'. It was subsequently abandoned in favour of a jointly developed design where each section was being shaped individually.

And when the requested +/-0.5mm rail machining tolerance for this crossover also proved impractical, the specification was relaxed in this area only to allow the contractor to achieve a workable scheme.

This joint team approach proved effective when Fairport ran into steel supply problems. The contractor had been sourcing steel from Germany after UK suppliers could not offer the required delivery and price deal. When the German foundry faced a major plant breakdown during the supply of special steel grades and plate sizes, BNFL juggled its design programme to accelerate the specification for other parts of the layout. Supply continuity was maintained and construction kept on schedule.

A second 'supply' problem, this time on the client's side, threatened an even more serious six month holdup. BNFL engineers had been delayed gaining access to the silo roof to survey suitable areas for the complicated 200mm thick solid steel plate sleeper-style rail brackets.

Design drawings were similarly delayed and it was the contractor's turn to juggle the construction programme for what had been a critical path operation.

Sharing is also the buzzword when it comes to costs. Fairport's 15 month contract includes both a target cost and a guaranteed maximum price, with a share gain and pain clause benefiting both sides.

Any overall saving on the target cost will be shared by contractor and client to a formula marginally in favour of Fairport. A similar deal exists if the final bill falls between target cost and GMP, this time to BNFL's benefit . Any expenditure above GMP however falls into the contractor's court.

Fairport receives interim payments through a highly original neutral cashflow arrangement. The contractor gets paid two thirds of the way through a three month period.

It receives payment for the first month's actual work and for the following two months' estimated total. The next quarterly payment sorts out any discrepancies over estimates.

The project

Fairport Steelworks' brief is to supply 40 sections of average 6m long rail beam, plus 11 steel sleeper-style lateral restraint brackets to secure the track in place. But there the simplicity ends.

The two parallel sets of rails, plus an integral turning circle and crossover section, will run along the enclosed top of a 10 celled concrete silo being decommissioned at BNFL's Sellafield nuclear fuel reprocessing plant in Cumbria.

The 16m deep cells are full of Magnox swarf - the stripped off magnesium casings of spent uranium fuel rods from Magnox nuclear power stations. So along the rail beams will run a vast steel open-bottomed, 400t waste retrieval machine, called a mobile cave and equipped with grab and skip to empty the cells.

Supporting such a sensitive cargo means that the specification for the 700mm deep box section rail beams is onerous. A high machining tolerance and a flatness of +/-0.5mm over a 7m length of beam, is matched on site by the demand to position the track to the same accuracy.

The 500t track system, which must resist 0.25g seismic movement, is held in place by lateral restraint brackets. These are 6m long slabs of 200mm thick solid steel plate anchored down to the silo roof with 800mm deep shear keys and bolts.

Trial erection of key rail sections is now under way at machining subcontractor Tees Components in Cleveland to make sure it all fits. Further trails will be held next year so that time spent by the follow on installation contractor at Sellafield, in the radioactive environment of the silo itself, is minimised.

The team

BNFL Engineering,

Fairport Steelwork,

Tees Components

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