The United States secretly sought Japan's support in 1972 to enable it to dump decommissioned nuclear reactors into the world's oceans under the London Convention, an international treaty being drawn up at the time.
Countries working on the wording of the pact wanted to specifically prohibit the dumping of radioactive waste at sea.
But Washington wanted to incorporate an exceptional clause in the case of decommissioned nuclear reactors.
These facts came to light in diplomatic records held by the Foreign Ministry in Tokyo and released at the request of The Asahi Shimbun.
Japan did not offer a clear answer when it was approached by the United States on the issue. Eventually, however, Washington succeeded in incorporating the clause into the treaty.
In 1972, the United States was already dismantling early-stage nuclear reactors that had been used for testing. However, the disposal method of large-scale nuclear reactors for commercial purposes had not been decided although it was an issue that could not be shelved indefinitely.
Since Japan, a key U.S. ally, had already started its own nuclear power generation program, Washington did not hesitate to seek Tokyo's backing for its request.
It was apparent that the United States constructed nuclear reactors without having decided on disposal methods, forcing it to consider dumping them at sea after they were decommissioned.
The documents obtained by The Asahi Shimbun were signed by Japan's ambassador to Britain and designated as top secret.
According to the records, a U.S. State Department official who was part of the U.S. delegation discussing the terms of the treaty, met his Japanese counterpart in November 1972. In that meeting, the official explained that the United States had a number of early-stage nuclear reactors which had reached their life spans. He said Washington was facing problems disposing of them.
The official noted that any attempt to bury the reactors on land would invite a public backlash.
He also pointed to the financial difficulty of scientifically processing the reactors until the risk of radioactive contamination was totally eliminated.
Then, the official said the only other option was to dump them at sea, and asked Japan for cooperation.
According to Kumao Kaneko, now aged 74 and then a member of the Foreign Ministry team involved in the negotiations, Japan did not take specific steps to assist the United States in this delicate matter.
Eventually, during the general meeting of countries for the London Convention, the United States proposed incorporating a clause that would enable it to dump nuclear reactors at sea in exceptional cases in which all other means of disposal presented a risk to human health.
When presenting the proposal, the United States made no mention of its intention to dump its nuclear reactors at sea far into the future. The proposal was accepted.
In the early 1970s, sea pollution was a huge international issue.
Against that backdrop, countries worked feverishly to put the finishing touches on the London Convention. The treaty designated high-level radioactive substances as well as other materials, including mercury and cadmium, as waste whose dumping at sea is prohibited.
In 1993 revisions to the London Convention, the dumping of radioactive waste at sea was totally prohibited. However, the clause that approved of dumping in exceptional cases remained.
For this reason, under the London Convention, it is possible for member countries of the treaty to dump radioactive waste at sea if they obtain the OK from the other parties as well as the International Atomic Energy Agency.
According to the IAEA, the United States has not dumped radioactive waste at sea since 1970. Instead, it buries decommissioned nuclear reactors underground.
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