Inside the curtain is Japan, along with the UK and France, who want to sell the reprocessed plutonium, and the United States. Outside are nations who do not want the toxic cargo to pass through their territorial waters.
In Tokyo a furious debate is being waged in private over the country's avowed plutonium-based energy self-sufficiency policy. The prospect of being stuck behind an international lead curtain is boosting the arguments of those calling for a rethink of nuclear energy policy.
This week Argentina became the latest nation to complain about the passage of the plutonium close to its shores. The plutonium carrier, the Akatsuki Maru, which left Japan in August, is due in France this month and to return with its first plutonium shipment to Japan by the end of the year.
South Africa has said it will not allow the ship to pass within its 200-mile territorial waters around the Cape of Good Hope, and Chile, Brazil and Uruguay have expressed concern should the ship take the South American route.
Hawaii and an association of South Pacific islands have made official statements opposing the plutonium shipment and, tomorrow, delegates from countries on the likely routes meet in Tokyo to try to stop the return shipment.
The most likely route is through the Straits of Malacca. Several recent shipping collisions in the Straits, between Malaysia, Indonesia and Singapore, have heightened fears of the dangers of an accident involving the plutonium carrier.
Japan is sensitive to international opinion and opposition to the plutonium shipments is thought to be causing concern in the Science and Technology Agency which oversees the country's nuclear programme. The agency has received at least 20 inquiries from foreign countries about the safety measures to be taken for the Akatsuki Maru and the single small military escort vessel that is to accompany it.
This comes on top of domestic opposition to the accumulation of plutonium. In April the head of Japan's plutonium programme caused a stir by suggesting that the plan might be reconsidered and, in July, the Science and Technology Agency said it would set up a panel to re-examine Japan's long-term nuclear energy policy. 'I think there is a lot of disagreement now,' said Yuriko Hase, a Socialist MP critical of the plutonium programme. The programme foresees Japan becoming self-sufficient in energy.