The U.S. Navy recently announced a decision to deploy a nuclear-powered aircraft carrier at Yokosuka Naval Base in Kanagawa Prefecture, dismaying residents of the area. Following the decision — made in conjunction with the reorganization of U.S. forces in Japan — the mayor of Yokosuka, the prefectural governor and other local officials urged the U.S. government to continue keeping a conventionally powered carrier at the base.

As Prime Minister Junichiro Koizumi attaches great importance to the Japan-U.S. defense alliance, Japanese people are watching closely which side he will favor — the United States or Japanese local-government authorities.

In 1966 the submarine Snook became the first U.S. nuclear-powered warship to visit Yokosuka. In 1973 the conventionally powered aircraft carrier Midway visited Yokosuka, touching off Japanese opposition against moves to deploy the carrier there. Authorities on both sides tried to allay Japanese concerns by promising that the carrier would remain in Yokosuka for only a few years. The promise was broken as Yokosuka became a carrier home port.

The Kitty Hawk, currently based at Yokosuka, is a third-generation conventionally powered U.S. carrier. Last October the U.S. Navy announced plans to retire it in 2008 and replace it with a nuclear-powered carrier, later identified as the George Washington.

Candidate carriers that the navy had initially planned to assign to Yokosuka included the Harry S. Truman, but it gave up the idea reportedly because the name invoked memories of the U.S. president who ordered the atomic bombings in Japan. Apparently U.S. military authorities are quite aware of Japanese “nuclear allergies.” So it is hard to understand why they decided to deploy a nuclear-powered carrier.

The U.S. Navy says that, compared with their conventional counterparts, nuclear-powered carriers have much higher capabilities and can conduct combat and noncombat operations twice as long, thanks to improved storage of jet fuel and arms. It insists that nuclear-powered carriers are safe.

But according to a citizens’ group in Yokosuka, a 1998 report published by the U.S. General Accounting Office denied the technical superiority of nuclear-powered carriers over conventional ones. It said nuclear-powered carriers needed more time for repairs, limiting the time available for forward deployment. The report noted that nuclear-powered carriers might need less time for rapid development but that a task fleet led by a nuclear-powered carrier would require about the same time as one led by a conventional carrier, simply because the nuclear-powered carriers are accompanied by conventionally powered ships.

The citizens’ group argues that the nuclear reactor on a warship is much more dangerous than a land-based power reactor for the following reasons: (1) Reactor design on a warship is difficult due to limited space, and (2) a reactor powered by highly enriched uranium, and situated close to an explosives depot, could suffer serious damage in a marine accident.

U.S. nuclear-powered warships have been involved in several accidents; two submarines have sunk. In 1999 the nuclear-powered carrier Stennis almost caused a major disaster when it ran aground in San Diego Bay, close to its home port, damaging its coolant-circulation pump and halting its two reactors. (In Japan, the nuclear-powered ship Mutsu was later scrapped after it developed a radiation leak in 1974.)

Yokosuka city authorities have been conducting annual disaster-prevention drills for possible accidents involving nuclear-powered warships, and have compiled a manual on the subject. The U.S. Navy, however, has refused to provide information about warship designs and operations, citing the need for military secrecy and sticking to its mythical position that nuclear-powered ships are not susceptible to serious accidents. Lacking specific data for forecasting potential damage, the city is having trouble making contingency plans.

The nuclear-powered carrier to be deployed at Yokosuka is likely to stay there for up to six months at a time, using repair facilities that may be vulnerable to radiation leakage.

In 1988, W. Jackson Davis, professor of biology at the University of California, conducted an environmental assessment of possible damage from an accident involving a nuclear-powered submarine at Yokosuka. The study found that people within a 100-km radius of the accident site, including Tokyo and all of Kanagawa Prefecture, would be affected. Deaths from exposure to radiation itself and from genetic damage would amount to 100,000 a year. In an accident involving a nuclear-powered carrier, whose thermal output is nine times larger than that of a nuclear submarine, the toll would be much higher.

The reactor on a nuclear-powered carrier is comparable to a land-based reactor. Yet Tokyo Electric Power Co. has built its nuclear power stations in Fukushima and Niigata prefectures, avoiding Tokyo and neighboring areas.

If U.S. authorities remain reluctant to help Japanese authorities in disaster-prevention efforts, such as by providing data on reactor design and operation, and to permit safety checks by Japanese authorities, protests by local citizens against deployment of a nuclear-powered carrier are likely to strengthen. Such concerns are justified.

The U.S. is the only country that deploys a nuclear-powered carrier in Japan’s surrounding areas. For a strictly defensive national security policy, Japan does not need aircraft carriers, nuclear-powered or otherwise. Excessive military power will only invite hostility from neighboring countries and be counterproductive to Japan’s defense. It will also contravene the spirit of Japan’s three nonnuclear principles: the ban on the production, possession or introduction of nuclear arms.

Among U.S. allies, Japan is said to be the only country that provides a home port for U.S. warships. To protect the safety of Tokyo Bay and the lives of citizens in the metropolitan region, the Japanese government should demand that the U.S. Navy rescind its decision to deploy a nuclear-powered carrier at Yokosuka.

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