The Monju fast-breeder reactor experiment yielded few sufficient results despite an investment of at least ¥1.13 trillion ($10.3 billion) worth of taxpayers money since 1994, state auditors confirmed on Friday.
The trouble-plagued prototype, which only ran for 250 days, was designed to play a key role in Japan's quest to set up a nuclear fuel recycling program, but the project only achieved 16 percent of the intended results, the Board of Audit said.
The government finally decided to scrap Monju in December 2016 at an estimated additional cost of ¥375 billion. But the audit board noted that the 30-year decommissioning plan could cost even more.
The reactor, which started operations in 1994, was designed to produce more plutonium than it consumes while generating electricity, experienced several problems over its more than two-decade run, including a sodium coolant leak and attempted cover-up, and equipment inspection failures.
"Flawed maintenance led to the decommissioning," the auditors concluded in their report.
But the report also spotlights the absence of a systematic evaluation system for the project. During the entire experiment, the auditors expressed their opinions on Monju's research and development costs only once — in 2011.
Monju was only up and running for 250 days in total after repeatedly failing to complete test items, according to the report.
As for the decommissioning costs, the report said they might expand because the current estimate does not include personnel costs and taxes. It also noted that the cost of removing the radioactive sodium coolant could change.
