China and Russia, which oppose Japan's planned release from Thursday of treated radioactive water from the crippled Fukushima nuclear plant into the sea, jointly urged Tokyo last month to consider a vapor release disposal strategy instead, according to diplomatic sources.
Beijing and Moscow claimed in a document submitted to Tokyo in late July that vaporizing the water and releasing it into the atmosphere would have a smaller impact on neighboring countries compared with the ocean discharge plan. Japan has rejected their proposal, saying it is "impossible" to accept it, the sources said.
By Monday, the Japanese government had told China and Russia that it is difficult to conduct radiation monitoring in the atmosphere or predict how the vapor spreads, according to the sources.
The two countries also sent a joint document of similar content to the International Atomic Energy Agency, the sources said. The IAEA concluded last month that the planned water release would be in compliance with global safety standards and will have "a negligible radiological impact on people and the environment."
Japan once examined the feasibility of vaporizing the treated water and releasing it into the atmosphere but found it would be more difficult to monitor compared to releasing it into the sea.
In the document sent to Tokyo, which contained a list of 20 questions, China and Russia contended that the technology for monitoring radiation in the atmosphere has been established. It argued that Japan's decision is based instead on the high costs of the vapor release option.
They cited Tokyo's own estimate that the ocean discharge plan would require 3.4 billion yen ($23.3 million), only one-tenth of the cost of getting rid of the treated water through vapor release.
IAEA Director General Rafael Grossi has questioned the feasibility of other options besides the ocean discharge plan, saying in an interview with CNN that the vapor release method can be more difficult to control due to environmental factors like wind and rain.
Vaporizing massive amounts of contaminated water was carried out following the 1979 Three Mile Island nuclear accident in the United States.
Chinese Foreign Ministry spokesman Wang Wenbin said at a press conference on Monday that the planned ocean discharge is "not the safest or most prudent option" and that Japan "simply chose it to lower economic costs."
"This will pose unnecessary risks to neighboring countries and the rest of the world," Wang said, urging Japan to "take seriously the legitimate concerns of the international community, have full communication with stakeholders, including neighboring countries," and study other disposal options.
Last year, Beijing and Moscow jointly sent questions to Japan on two occasions regarding the treated water release plan. Tokyo claims it responded to them in a "detailed and transparent manner," but that no dialogue has been held on a scientific basis, despite its repeated proposals to do so.
A massive amount of contaminated water has been generated in the process of cooling melted reactor fuel after the Fukushima plant was devastated by the 2011 earthquake and tsunami.
The water has been kept in tanks after going through the advanced liquid processing system that removes most radionuclides except tritium, but the storage vessels are nearing capacity. Tritium is known to be less harmful than other radioactive materials, such as cesium and strontium.
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