China and Russia have accused Japan of basing its decision to dispose of radioactive waste water from the Fukushima nuclear plant in the sea on economic rather than scientific grounds.

They made the charge in a series of letters to the International Atomic Energy Agency, including a joint list of technical questions to Japan on July 26 questioning the choice of water discharge when another potential option, vapour release, “has less impact on the ocean and neighbouring countries”, and is less likely to cause leakage or pollution.

Last month’s letter went on to say: “Japan also mentioned that ‘facility configuration for discharge into the sea is simple compared to that for vapour release’, which shows that Japan chooses ocean discharge based on economic considerations.”