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Reactor rescue:a race against time

Chernobyl reactor 4, the Ukrainian nuclear plant which catastrophically exploded in 1986, was patched up but never made safe.

It is a long time since anyone stepped inside Chernobyl reactor 4. No one can say precisely how fragile the blasted structure is, or what is the exact composition of the cocktail of radioactive pollutants it has been harbouring for the last 12 years.

'Nobody knows what exactly needs to be done,' says Vince Novak, operations leader for the Chernobyl Sarcophagus Implementation Plan. The SIP is an internationally funded programme to stabilise the hastily built steel clad concrete structure erected around the reactor building to contain radioactivity after the 1986 core melt down.

Developing the plan is a race against the clock. Estimates put a 20- year safe limit on the sarcophagus casing itself. Inside it, the reactor structure could collapse earlier. If this happens it is thought unlikely that the sarcophagus will contain the resulting plume of highly toxic radioactive dust. This could be almost as lethal as the original accident, Novak believes.

A huge international task force of contractors and consultants is being assembled to take on the SIP. It has nominally two years to assess what needs to be done to make the structure safe and work out solutions which must be earthquake-proof. After that there are eight years to make the solutions good.

Novak is handling finance of the SIP for the European Bank for Reconstruction & Development and the G7 group of leading industrial nations which is promoting the plan. So far about £245M has been raised towards project costs estimated at £465M.

Whether the final strategy will involve making good what is already there or building a new sarcophagus has yet to be decided. But as a condition of funding EBRD requires client Energoatom, the Ukrainian nuclear power authority, to meet European Union environmental and industrial safety standards.

Four consortia were assembled last year to assess reactor 4 and work out the rescue strategy. They mix local and international know-how under a project management team led by Bechtel.

US contractor Morrison Knudsen and the UK's BNFL are working on the civils package. This includes structural stabilisation and monitoring, geotechnical investigation, final confinement of the reactor and plans to shield workers from radiation.

The site safety package is led by Ukrainian company Technicatome. SGN of France and AEA Technologies are leading investigations into dust suppression and contaminated water management. And strategies for dealing with the amorphous solidified fuel-containing mass left on the reactor floor is being produced by a Ukrainian consortium led by Technocentre.

The groups are drawing in the mass of data generated since the disaster took place. 'Everybody has wanted to study Chernobyl, and getting material together is a big logistical exercise in itself,' says Bechtel business manager Mark Roupe.

Emergency repairs to the reactor building inside the sarcophagus are already being carried out. According to Novak, the haste with which the sarcophagus was built in 1986 left it full of gaps. The Ukraine's extreme temperature variations have contributed to fast deterioration of the structure. Stabilisation of a ventilation stack damaged by debris hurled out of reactor 4 when it blew up has taken place and at the end of January Ukrainian contractor Ukrenerhobud won a contract to strengthen two massive steel beams supporting the reactor's 2,000t roof.

Ukrenerhobud is now assessing just how serious a problem it has taken on, and will deliver its findings late this month. The two beams span the 50m reactor hall lengthwise. Novak says the junction between the beams and the reactor's west wall was seriously weakened in 1986. Work is expected to involve inserting steel brackets at the junction between the beams and the reactor wall.

Mobilisation for the work is under way and the contractor will be on site by the end of next month. Work is scheduled to start when warmer weather comes in May. 'This is a major technical challenge,' says Novak. 'It involves welding 70m above ground level in an intensely radioactive environment.'

Novak and BNFL business manager Geoff Livesley agree that designing protective equipment for workers is a major challenge. They will encounter constant high level radiation inside the sarcophagus as well as radiation hot-spots outside. Lumps of fuel were spat on to surrounding ground when the reactor exploded and were buried in the rush to make the site safe.

The beam strengthening project will employ 580 workers in rotation to limit exposure to radiation. Rotation and special protective equipment and clothing is expected to limit average annual radiation doses to 1,230 milliSieverts - just under 50% more than the average for people in the UK.

Neil Davies of AEA Technology says the reactor evaluation phase is throwing up fundamental safety questions. 'Ukrainians would like to see fuel removed from the core as soon as possible,' he said. 'They believe the real danger will then be reduced.' But extraction would be difficult and hazardous. Leaving the fuel to decay for another 50 or even 200 years could, he says, be a far safer option.

However, even if the fuel is left in place the reactor has collected large volumes of rain water and water from a dust-suppressing spray system. In the Ukraine's -20degreesC winters and sweltering 30degreesC summers, the fuel mass has cracked, and water in contact with it has become heavily contaminated.

Later this month there will be a review of the SIP based on research to date. Novak says that when the plan was drawn up in 1997, 297 engineering, safety and management tasks were identified. He expects to see a new schedule detailing approximately 1,500 tasks after information from surveys has been collated. One of his chief wishes is for no more emergency stabilisation works to be required. 'I hope the reports will suggest we can proceed with concept design in a sequential way, not in an ad-hoc fashion,' he says.

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