The nuclear watchdog's refusal to compromise on its deadline for utilities to build anti-terror facilities at their nuclear power plants will deal a heavy blow to operators forced to shut down sites next year.

Three operators face the prospect of taking their plants offline over their failure to meet the Nuclear Regulation Authority's time limit to construct the costly buildings.

The requirement to guard against possible terrorist attacks using aircraft was among tougher regulations put in place in the aftermath of the triple meltdown at the Fukushima No. 1 nuclear power plant in March 2011.

The catastrophic event was triggered by the Great East Japan Earthquake and the towering tsunami it generated.

Construction of emergency facilities to enable plant operators to continue to cool reactors through remote-control procedures in the event a terrorist attack destroys the central control room for the reactor buildings is an immensely costly proposition.

Utilities estimate that construction of each anti-terror facility will cost between 50 billion yen ($446 million) and 120 billion yen.

The shutdown of nuclear facilities will force utilities to fire up thermal power plants to compensate for the loss of power supply from nuclear plants. Procuring fossil fuels to do so will also be hugely costly.

Kyushu Electric Power Co. and Shikoku Electric Power Co. estimate that annual outlays to power their thermal reactors will cost an additional 40 billion yen to 60 billion yen, funds that could be saved by keeping a single nuclear reactor in operation.

“The impact will be huge if even one reactor is taken offline,” said a senior official with Kyushu Electric.

Joined by Kansai Electric Power Co., the utilities earlier this month requested an extension of the deadline for the installation of anti-terror facilities at their nuclear plants. But the NRA refused to budge from its position at an April 24 meeting.

Toyoshi Fuketa, the NRA's chairman, said the intention was to make crystal clear to utilities that they will be obliged to suspend operations if they cannot meet regulations put in place in 2013.

The initial deadline for completion was July 2018. But in 2015 the NRA extended it to "within five years after the conclusion of the examinations of reactors" because the screening process took longer than anticipated.

The three utilities affected by the NRA's refusal to back down are those whose nuclear power plants granted watchdog approval to restart after the Fukushima disaster.

The companies say they are behind schedule because of the complex steps involved to build the additional facilities at their nine reactors.

The deadline for the No. 1 and No. 2 reactors at Kyushu Electric’s Sendai nuclear plant in Kagoshima Prefecture is in March and May 2020, respectively. The No. 3 and No. 4 reactors at Kansai Electric’s Takahama nuclear plant in Fukui Prefecture are each obliged to reach the deadline by the following August and October.

Kansai Electric cited the 84 billion yen a year it can save in fossil fuel purchases if it keeps the Takahama nuclear plant going.

As for its two other reactors operating at the Oi nuclear plant in Fukui Prefecture, the company says it could save a combined 120 billion yen or so in fossil fuel costs.

Shutting down Kansai Electric’s reactors is bound to make a huge dent in the company’s bottom line as its estimate for operating profits for fiscal 2018 was about 200 billion yen.

Although the likelihood of a terror attack involving aircraft is believed to be extremely slim, regulators decided to take no chances, noting that nuclear plants in Germany and Switzerland are equipped with similar facilities.

Tadahiro Katsuta, a professor of nuclear policy at Meiji University, was scathing about the inability of the utilities to meet the deadline, calling it a “sign of not taking counter-terrorism measures seriously.”

“They were presumably hoping that the government would step in and do something for them, just like the time prior to the Fukushima nuclear disaster,” he said.

This time around, the government is in a bind as the NRA’s decision was unanimous, leaving it no room to maneuver.

“When it comes to nuclear reactor regulations, we respect the decision by the NRA, which has a high degree of independence,” Chief Cabinet Secretary Yoshihide Suga said at a news conference.