Risks build in nuclear impasse

It is hard to believe that to tour the site of the world’s worst nuclear accident, you are equipped with no more than the apparel for a routine factory visit, apart from a dosimeter to measure radioactivity. Yet that is the reality for visitors to the Chernobyl nuclear power plant. ‘When you go in, they […]

It is hard to believe that to tour the site of the world’s worst nuclear accident, you are equipped with no more than the apparel for a routine factory visit, apart from a dosimeter to measure radioactivity. Yet that is the reality for visitors to the Chernobyl nuclear power plant.

‘When you go in, they issue you with a plastic torch and a plastic hat,’ says Stephen Hall, project director at AEA Technology.

Even for entering the steel and concrete sarcophagus, the Ukritiye, that was hastily and heroically erected over the shattered remains of the Number 4 reactor after the accident in 1986, there is little more in the way of protective clothing, although breathing apparatus is available for the highly radioactive areas.

‘They don’t really have the gear we would consider necessary for these types of areas,’ says Hall.

Two immediately striking features of the Ukritiye are its size it is 60m tall and its apparently good condition. Following numerous reports of how the edifice is crumbling and full of holes, the uniformity of the panels that form its exterior cladding come as a surprise (the gaps on some of its corners were there from the beginning).

This outward appearance somewhat flatters to deceive, however, because the Ukritiye is an intrinsically hazardous structure. It was built with great speed on the wreckage of the reactor’s foundations. The roof is supported by three massive steel beams the largest is about 60m long and 4m deep that rest on what is left of the original building’s walls.

While the Ukritiye itself may consequently be reasonably sound, the integrity of its support structures is difficult to ascertain.

It also houses thousands of tonnes of lethally radioactive debris, including spent fuel and graphite blocks from the reactor core. The 2,000-tonne concrete disc that was the reactor lid is also wedged between wreckage in a just-off vertical position overlooking the mess below.

And lethally radioactive materials are not confined to the inside of the Ukritiye. A bucket on a cooling-stack platform was recently found to contain twisted bits of fuel rod. ‘There’s fuel spread around everywhere,’ says Hall. ‘They keep on finding things like this.’

As the international effort to clean up the wreckage of the 1986 accident finally gets under way 12 years after the event, debate is continuing to assess how great and how imminent a risk the Ukritiye and its contents pose. If the structure collapsed, it would raise a huge cloud of radioactive dust and the extent of the environmental damage would be at the mercy of the winds.

As the Ukritiye and the remains of the buildings that support it have stood for 10 years, there is some evidence to suggest they are stable. However, the safety margins for extended life, and for snow, wind and seismic loads are not known. Furthermore, specific components have been identified as having a high probability of failure under certain possible load conditions.

Another sinister risk is developing inside the Ukritiye. Much of the fuel in the reactor melted into lava-like flows with steel and other components, which ran through pipework into the basement of the building. As these cooled, they solidified they are still highly radioactive but are relatively stable.

With time, however, these solidified lumps have started to degrade. ‘The trouble is that as it’s cooled down it’s begun to break up because of frost damage,’ says Hall.

With water running through the basement of the building, there is a danger that fissile elements will dissolve and migrate into areas of the substructure where they could form a critical mass and begin a localised nuclear reaction that would be difficult to control and dangerous to suppress. Hall says the risks of this happening are increasing. ‘That’s the problem.’

The delays that have arisen with the early remedial projects are a cause of concern. While some people argue that after 10 years of inactivity, a few more months will make little difference, no one knows for sure what margin of error is left.

Of the four contracts for the so-called ‘early biddable projects’ that are part of the programme to maintain the Ukritiye in an environmentally safe state for 20 years, only three have yet been awarded. The first, covering civil engineering studies, has been awarded to the International Chernobyl Consortium of Morrison Knudsen (US), Technipatom (France), Nukem (Germany) and British Nuclear Fuels.

The same consortium, under Technipatom’s leadership rather than MK’s, has also signed a contract for the second project, which will involve drawing up the systems and controls necessary for safe working inside the shelter.

Meanwhile, the contract for the third EBP, to devise emergency systems to deal with dust and contaminated water, has been awarded to a consortium led by France’s SGN and including AEA Technology. But the fourth, to characterise what fuel-containing materials are in each location inside the shelter, will not enter final negotiations with a preferred bidder until mid-September.

The whole process has been delayed for months by disputes between the preferred bidders, the Ukrainians and the European Bank for Reconstruction and Development, which is administering the G7 funding for the project.

Similar delays are looming with parallel projects needed to decommission the other three Chernobyl reactors a spent-fuel store, a liquid waste treatment plant, and short-term improvements to the adjacent reactor Number 3.

A protracted dispute is looming over the first project, for which bids were submitted in July, following the EBRD’s exclusion of BNFL’s bid because of the potential conflict of interest that arose from its acquisition of the nuclear business of Westinghouse, which has the lead role in the project management team. And tenders have yet to be issued for the other two projects.