The Monju prototype fast-breeder nuclear reactor will unlikely be able to resume operations by the end of the current fiscal year, the research institute that owns the facility said Thursday.

The remarks were made a day after the Nuclear Regulation Authority decided not to allow the Japan Atomic Energy Agency to engage in preparatory work for resuming operations at Monju because it sees problems in its safety management.

The NRA summoned JAEA President Atsuyuki Suzuki on Thursday to convey the decision and to notify him that the agency will be given an opportunity to explain its views by May 23. Following such a procedure, the NRA is expected to issue, possibly later in the month, an order that will effectively prohibit the reactor's resumption.

Suzuki told NRA Secretary General Katsuhiko Ikeda that he took the situation "seriously."

As for the operation of Monju, Suzuki told reporters, "It takes nearly one year for preparation and it is physically quite difficult (to restart it within the current fiscal year through March)."

The NRA's decision is another blow to the Monju reactor, which has remained largely offline since first achieving criticality in 1994, due to a leakage of sodium coolant and other subsequent problems.

The JAEA has been found to have failed to conduct inspections on appropriate intervals on nearly 10,000 devices, including those that are categorized as important for safety.

The NRA looked into the case in detail and determined that the agency's "safety culture is deteriorating," given that the agency could not address the problems even though people had been aware of the delayed inspections.