Officials at a Japanese power company were finalizing a decision Saturday following a government request that it suspend all three reactors at a coastal nuclear plant while steps are taken to prevent a major earthquake or tsunami from causing another radiation crisis.

Prime Minister Naoto Kan said Friday that he had asked Chubu Electric Power Co. to halt its three reactors at Hamaoka nuclear power plant in central Japan until the operator can improve safety measures. Though not legally binding, the request is a virtual order.

The government is wrapping up a safety review of Japan’s 54 atomic reactors after a March 11 earthquake and tsunami crippled the Fukushima Dai-ichi nuclear plant. The disaster left more than 25,000 people dead or missing on the northeast coast.

The Hamaoka nuclear plant just off the Pacific coast in central Japan is the only one so far where the government has asked that operations be halted over safety reasons.

Chubu Electric president Akihisa Mizuno said in a statement that the company would “swiftly consider” the government’s request.

He was expected to hold a news conference later Saturday to announce a decision.

“It was a decision made after thoroughly considering people’s safety,” Mr. Kan said Friday, citing experts’ forecast of a 90 percent probability of a quake with magnitude of 8.0 or higher striking central Japan within 30 years.

The government asked Chubu Electric to suspend two running reactors and a third currently shut for a regular inspection at the plant in Shizuoka, which is around 124 miles (200 kilometers) west of Tokyo. Two other reactors are currently being decommissioned.

“If an accident occurs at Hamaoka, it could create serious consequences,” Mr. Kan said.

Since the March 11 disasters, Chubu Electric has drawn up safety measures that include building a 40-foot-high (12-meter-high) seawall nearly a mile (1.5 kilometers) long over the next two to three years, company official Takanobu Yamada said. The company also promised to install additional emergency backup generators and other equipment and improve water-tightness of the reactor building.

Chubu also plans to erect concrete walls along 18 water pumps at the plant, to protect them from tsunami or quake damage. It will also install additional backup generators and other emergency equipment to secure cooling capacity, and improve water-tightness of reactor buildings. It will take two to three years to complete the sea wall, Yamada said.

The plant does not have a concrete sea barrier now. Sandhills between the ocean and the plant are about 32 to 50 feet (10 to 15 meters) high, the company said.

Chubu Electric has estimated a tsunami reaching around 26 feet (8 meters).

The company recently said it was considering restarting the third reactor in July, triggering harsh local opposition.

Trade Minister Banri Kaieda said Chubu’s safety measures were insufficient. “Until the company completes safety steps, it is inevitable that it should stop operating nuclear reactors,” he said.

Tokyo Electric Power Co., operator of the stricken Fukushima plant, has said the waves that wrecked critical power and cooling systems there were at least 46 feet (14 meters) high.

Shizuoka Gov. Heita Kawakatsu called the government’s request “a wise decision” and vowed to secure alternative sources of energy.

Residents in Shizuoka have long demanded suspension of the Hamaoka reactors. About 79,800 people live within a 6-mile (10-kilometer) radius of the plant. Some residents have filed a request to a regional court to suspend the Hamaoka plant.

The Hamaoka plant provides power to around 16 million people in central Japan, including Aichi, home to Toyota Motor Corp.’s headquarters and an auto plant. Faced with a possible power crunch due to the shutdown, Kan sought public understanding.

Automakers and other industries have had troubles with interrupted supply lines, parts shortages and damage to manufacturing plants since the March 11 disasters.

The Fukushima Dai-ichi plant lost its power and cooling systems in the magnitude-9.0 earthquake and ensuing tsunami, triggering fires, explosions and radiation leaks in the world’s second-worst nuclear accident.

Radiation leaks have forced 80,000 people living within a 12-mile (20-kilometer) radius of the plant to leave their homes.

Since the Fukushima crisis unfolded, nuclear safety officials have acknowledged that tsunami safety measures at Japanese nuclear power plants were insufficient.

In 2001, TEPCO told Japan’s Nuclear and Industrial Safety Agency that waves would not exceed 18 feet (5.7 meters) at the Dai-ichi plant, based on an anticipation of a magnitude-8.6 quake. It assumed the backup power generators, which were stored in basement areas, would stay dry in a tsunami triggered by a magnitude-9.0 quake.

More In: International | News