A former US nuclear regulatory chief said yesterday that leaks of contaminated water at the crippled Fukushima plant had been recognised since early in the crisis and have worsened because Japan acted too slowly.
Gregory Jaczko said US and Japanese officials knew leaks would occur when massive amounts of water were used to cool molten reactors at the Fukushima Dai-ichi plant after the tsunami in March 2011.
Jaczko said he was surprised how long it took Japan to start tackling the problem.
"It's been known for a long time that this would be an issue," he said in Tokyo.
"My biggest surprise is to some extent how it's been allowed to deteriorate, a little bit, and how it's almost become a surprise again that there are contamination problems, that there is leakage out into the sea."
When the plant was in a critical condition with three reactor cores melted, Jaczko said Japanese and US officials disputed how much water should be put in because of the imminent leaks of radiation-contaminated water and measures needed to contain that problem.
He said the Japanese government was concerned that the flooding of the reactor vessels and reactor buildings with cooling water "would lead to greater leakage of ground water".
But US Nuclear Regulatory Commission officials emphasised the need to keep reactors cool and under control to minimise airborne contamination.
But the "focus was lost" on the need to keep addressing the radioactive water problem, apparently delaying urgent action, he said.
Japanese officials confirmed for first time in July that contaminated ground water has been leaking into the Pacific since soon after the accident.
Leaders of the opposition Democratic Party of Japan, which was in power during the crisis, acknowledged last week that a plan to build a seawall to block contaminated water leaks into the sea had been put off for nearly two years after plant operator Tokyo Electric Power Co allegedly resisted the plan for financial reasons.
The government is funding the development of more advanced water treatment equipment and paying for a costly ice wall to surround the reactor and turbine buildings.
Jaczko resigned as chairman of the Nuclear Regulatory Commission last year.