The Nuclear Regulation Authority on Wednesday admonished the Japan Atomic Energy Agency for failing to take appropriate measures to protect its Monju prototype fast-breeder reactor from potential terrorist and other attacks.

The rebuke is another black mark against the agency, previously criticized by the NRA over a staggering number of equipment inspection failures at the Monju reactor in Tsuruga, Fukui Prefecture, that uses plutonium-uranium mixed oxide (MOX) fuel. Both materials can be used to make nuclear weapons.

According to a report compiled by the NRA, some fences supposed to restrict access to certain areas at Monju were around 0.3 meters lower than stipulated by JAEA rules, and regular checks to ensure the security of equipment were not conducted appropriately.

The agency also allowed visitors inside areas containing nuclear material without taking copies of their identifications — another rule violation.

“We must say that people (at the JAEA) lacked awareness of nuclear security,” the atomic energy watchdog concluded in its report.

During a meeting Wednesday, NRA commissioners expressed dismay over the lack of security measures, noting the Monju facility requires special attention.

“It is unprecedented. Why did breaches happen at this most important Monju facility?” NRA commissioner Toyoshi Fuketa asked.

NRA Chairman Shunichi Tanaka said, “I hope this incident will not develop into an international issue.”

At a news conference later in the day, Tanaka said: “The international society is very nervous about nuclear terrorism. . . . So it will be (major) trouble if Japan becomes lax about such issues.”

The Monju reactor was effectively banned from operating in May after the JAEA’s lax safety standards were exposed. Yet even before that, the prototype was kept largely offline since achieving criticality in 1994 due to a disturbing safety record, including a sodium coolant leak, fire and coverup attempt.

More than ¥1 trillion has been plowed into the Monju project in hopes it would play a key role in Japan’s nuclear fuel recycling policy by reprocessing spent nuclear fuel so the extracted plutonium and uranium could be reused to power commercial reactors.