Europe's bill for the France-based ITER project has almost trebled, leaving cash-strapped finance ministers to question the merits of the investment.
Euratom, the European Atomic Energy Community, could be asked to fork out close to €6 billion, with France liable for a further €1.3 billion in its capacity as host country for the plant.
Construction is scheduled to begin in 2012, leading critics to call for the project to be shelved before it gathers further momentum. However, advocates point out that ITER is the subject of an international agreement which would be difficult to break.
The ITER reactor aims to replicate the kind of fusion that occurs in the sun as an abundant source of energy.
Last month, research ministers met in Brussels to discuss the future of the initiative in light of its rising costs. Ministers reiterated their commitment to ITER but could not agree a detailed plan on a way forward. Instead they set up a task force to find a solution by the summer.
Cost-containment measures and improved financial management are likely to be part of the task force's discussions, but the bigger challenge is to pull funding from other sources to save the project.
Conflict on plugging funding gap
National governments are at odds with the European Commission on how the funding shortfall should be addressed. Brussels is pushing for an injection of fresh funds, while ministers insist that the money should be drawn from existing sources. The precise mechanism for doing that has fuelled ongoing political tension.
The Commission has outlined a range of possibilities, including tapping into the EU's framework programme for research. This has met with resistance because it is not clear what programmes would have to be sacrificed to save ITER.
The idea of seeking a loan from the European Investment Bank has also been floated but the Commission is wary of this option – a fact that critics say illustrates the inherent financial risk of the investment.
Delaying the construction timeline would allow the EU to spread its costs over a long period but would likely cause friction with other ITER partners such as China, Japan and the US.
EU position unclear ahead of meeting
The ITER Council, which governs the project, meets in China on 16 and 17 June but it is far from certain that Europe will have a clear position on where it will find additional money.
The task force set up by research ministers has already met twice this month (3 and 5 June) and could meet twice more in the coming weeks. The issue will also be discussed when diplomats meet in Brussels next month ahead of the next Competitiveness Council in July.
Key elements of the ITER Council agenda could be postponed if a deal cannot be reached in the meantime, but diplomats say that unilaterally withdrawing from the international consortium is not an option.
The ITER saga has echoes of the furore that surrounded the runaway budget for the Galileo satellite navigation project, with researchers in other fields wondering whether their funding will suffer if funds are diverted to ITER.