The head of the Nuclear Regulation Authority is urging the government and utilities to redouble their vigilance to ensure reactor safety, warning them not to drop their guard simply because units have cleared the NRA's tough safety screening.

NRA Chairman Shunichi Tanaka, chairman of the Nuclear Regulation Authority, said passing the screening is "not enough" during an interview Monday ahead of Friday's fifth anniversary of the Fukushima No. 1 disaster.

The government calls the new regulations the best in the world and has promoted the restart of reactors that were taken offline in the wake of the Fukushima crisis.

Tanaka said the strict regulations should not promote any new "safety myth," referring to the pre-Fukushima situation in which nuclear plants in Japan were assumed to be accident-free.

"If they are to establish a new safety myth, it would be better to cancel nuclear power," he said.

Tanaka stressed that it is not just Tokyo Electric Power Co. but the entire nuclear industry that should bear responsibility for Fukushima, and that no reactor should be allowed to resume operations unless it is approved under the new regulations.

The NRA chairman said the situation at Fukushima No. 1 is calm, with cleanup work making steady progress.

But he expressed doubts about the efficacy of an underground ice wall that Tepco has built around reactor buildings to prevent groundwater from flowing into their basements.

The wall "will not essentially help reduce the risk" of an increase in toxic water, he said.

Decontamination work, on the other hand, is effective and should help more people return to their homes in the evacuation zones, as radiation levels in many such areas have fallen to acceptable levels, he said.