About a third of the 180 monitoring cameras installed at the experimental Monju fast-breeder reactor were found broken during a safety inspection last month, a source familiar with the matter said, renewing concerns about safety management at the Japan Atomic Energy Agency, which runs it.

In May 2013, the Nuclear Regulation Authority effectively shuttered the reactor on the Sea of Japan coast in Fukui Prefecture after discovering that over 10,000 pieces of equipment had not been properly inspected.

The broken cameras are among 180 that were installed to monitor the area around coolant pipes in a secondary cooling system. They were installed after a major fire in 1995 caused by a sodium coolant leak led to a renovation in 2005. The cameras were put into operation in 2007.

Around a third were broken when the NRA inspected Monju last month — and some had been so for more than 18 months, the source said.

JAEA, which operates Monju, said it was aware of the problem but could not replace the cameras with the same type because they are no longer being made.

"We left (them) as they were because we ran out of backups," a JAEA official reportedly told an NRA official when asked about the cameras. "We will replace them by November."

The lax safety management culture at Monju has baffled many, including officials at other nuclear plant operators. "Leaving broken monitoring cameras unattended is out of the question," one utility official said.

Last month, JAEA said it would extend its intensive management reform effort by six months through March.