Earlier this week, more than 50 tons of radioactive cooling water leaked from the No. 2 nuclear reactor operated by Japan Atomic Power Co. (Genden) in Tsuruga, Fukui Prefecture. Operators had to shut down the system manually, but apparently no radioactivity leaked into the atmosphere. The leaked cooling water was safely restricted to the reactor’s concrete containment building, but the incident once again raises the fundamental issue of the safety of nuclear energy in general, as well as Genden’s ability to handle emergencies.
In Monday’s incident, 141/2 hours passed before operators could pinpoint the leak in the cracked steel pipe and seal it. What makes the latest mishap all the more troubling is that a similar leak occurred in the same primary cooling system at the same power plant in 1996. Genden seems to have failed to learn its lesson. The company must get to the bottom of the whole affair so that the public will not have to suffer a similar scare again. Above all, the company must review its reactor-operating procedures and ensure that they are fail-safe.
The Tsuruga nuclear reactor is of the pressurized light-water type. The primary cooling water absorbs the heat released through nuclear reaction, circulates it to a secondary cooling system — where the steam is used to generate electricity — and flows back to the core of the reactor chamber. The 8-cm crack was found in the bend of an L-shape stainless-steel pipe located in the heat exchange — a device to remove impurities from the high-pressure primary cooling water and regulate its temperature. The pipe in question is 1.1 cm thick and measures 9 cm in diameter.
Allegedly, it took time to detect the crack because the piping system is wrapped in insulating material. Officials also explained that the crack occurred at the back of the steam generator, an awkward place that is out of sight. However, the problem is that this is not the first time a leak has occurred in the primary cooling system of the No. 2 Genden reactor.
This reactor went into operation in 1987. Given the longevity of the average reactor, it should still be in good shape. Three years ago, the piping system of the heat exchange cracked, leaking about 1 ton of radioactive cooling water. The ensuing investigation found impurities in the cracked U-shape portion of the steel pipe, believed to have been left there during the process of manufacturing. That apparently weakened the steel structure at the bend.
At this stage we have no way of knowing what caused the latest crack, but there appears to be a link between the two incidents. Both cracks involved small-diameter steel pipes, supposedly made of similar material. This raises a troubling question: What has Genden done since the 1996 mishap? Has the company done everything it could to improve the inspection of all cooling-water pipes used in the reactors? Whatever the answer, the similarity of both incidents makes it imperative for Genden to promptly carry out a thorough inspection of all small-diameter steel pipes installed in its reactors.
Also, we must ask whether the latest incident represents a problem that is particular to the No. 2 reactor or is of a more generic nature. The large pressurized light-water reactors in operation in Japan share standardized designs. The Ministry of International Trade and Industry and the Agency of Natural Resources and Energy should therefore consider whether a general inspection of all light-water reactors is needed. The government’s Nuclear Safety Commission should also take action, discharging its function as the public watchdog of safety and security in the nation’s nuclear-power system.
Most of the mishaps that have occurred at the nation’s nuclear-power plants involved peripheral devices, not the reactor itself or major ancillary equipment. The fact is nuclear power-plant operators tend to put priority on the safety of main nuclear equipment and the main piping system, imposing stringent requirements on their quality and durability. Regrettably, no comparable safety standards are applied to peripheral devices, which are typically manufactured by subcontractors.
A nuclear-power plant is a mammoth, highly integrated system. The reactor itself and other main equipment may have been built using state-of-the-art technology, but the whole system will go down if a peripheral device is out of order. Unless the government and the power industry can keep a clean slate, nuclear energy will not win full public support.
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