Nuclear powerFukushima and the oceans: What do we know, five years on?

Published 22 July 2016

A major international review of the state of the oceans five years after the Fukushima disaster shows that radiation levels are decreasing rapidly except in the harbor area close to the nuclear plant itself where ongoing releases remain a concern. At the same time, the review’s lead author expresses concern at the lack of ongoing support to continue the radiation assessment, which he says is vital to understand how the risks are changing.

A major international review of the state of the oceans five years after the Fukushima disaster shows that radiation levels are decreasing rapidly except in the harbor area close to the nuclear plant itself where ongoing releases remain a concern. At the same time, the review’s lead author expresses concern at the lack of ongoing support to continue the radiation assessment, which he says is vital to understand how the risks are changing.

Goldschmidt Conference notes that these are the conclusions of a major 5-year review, with multi-international authors who are all working together as part of a Scientific Committee on Oceanic Research (SCOR) Working Group. The report was presented at the Goldschmidt geochemistry conference in Japan. The review paper is also published in Annual Review of Marine Science. The main points made by the report are:

  • The accident. The Tohoku earthquake and tsunami on March 11, 2011 led to the loss of power and overheating at the Fukushima Daiichi Nuclear Power Plants (FDNPP), causing extensive releases of radioactive gases, volatiles and liquids, in particularly to the coastal ocean. The radioactive fall-out on land is well-documented, but the distribution of radioactivity in the seas and onto the wider oceans is much more difficult to quantify, due to variability in the ocean currents and greater difficulty in sampling.
  • Initial release of radioactive material. Although the FDNPP accident was one of the largest nuclear accidents and unprecedented for the ocean, the amount of 137Cs released was around 1/50th of that released by the fall out of nuclear weapons and 1/5th that released at Chernobyl. It is similar in magnitude to the intentional discharges of 137Cs from the nuclear fuel reprocessing plant Sellafield.
  • Initial fallout. The main release of radioactive material was the initial venting to the atmosphere. Models suggest that around 80% of the fallout fell on the ocean, the majority close to the FDNPP. There was some runoff from the land, peaking around 6 April 2011. There is a range of estimates of the total amount of 137Cs release into the ocean, with estimates clustering around 15-25 PBq (PetaBecquerel, which is 1015 Becquerel. One Becquerel is one nuclear decay per second). Other radioisotopes were also released, but the focus has been on radioactive forms of Cs given their longer half-lives for radioactive decay (134Cs = 2 yrs; 137Cs = 30 yrs) and high abundance in the FDNPP source.