A government panel investigating the Aug. 9 nuclear reactor accident, which killed five workers and injured six others, has published an interim report that reveals a pattern of loose safety management. The central message is that the tragedy — the worst in the history of Japan’s nuclear power industry — would have been prevented if strict safety measures had been taken.
The report, published by the Nuclear and Industrial Safety Agency, blames the operator, Kansai Electric Power Co. (KEPCO), for failing to conduct sufficient quality and maintenance checks. In a meeting with the company president, Mr. Yosaku Fuji, Economy, Trade and Industry Minister Shoichi Nakagawa ordered a suspension of the reactor involved. It is the first time that a power company has received such a penalty under the Electric Utility Law.
The accident occurred in one of the light-water reactors (pressurized-water type) at KEPCO’s nuclear power plant in Mihama, Fukui Prefecture. Investigations have revealed that a section of piping in the secondary loop ruptured due to stress and corrosion, spewing tons of superheated steam. There was no radiation exposure, however, because only the primary loop contains radioactive material.
The piping, particularly the steel thickness, should have been checked regularly. The report says, however, that no such checks had been conducted during 28 years of reactor operation. The steel was 10 millimeters thick when the piping was installed. At the time of the accident, a part of the damaged section had a thickness of only 0.4 millimeter. It is well known that pipe wall thinning could cause a major rupture. The warning had been around for years, both at home and abroad.
At a KEPCO nuclear plant in 1983, steam leaks from branch piping occurred. At a U.S. plant in Surry, Virginia, in 1986, piping in the same type of reactor system broke, killing four people. In 1990, KEPCO and other power companies running light-water reactors set guidelines for checking pipe thickness.
One area that required inspection was a section of piping where the flow of hot water becomes turbulent because a flow meter, installed immediately upstream, creates higher pressure inside the pipe. That is precisely where the rupture occurred Aug. 9. That section was not inspected, however, because, investigators say, the company that was in charge of inspections — Mitsubishi Heavy Industries — did not mention it on the checklist. Since no corrective action was taken, they say, the carbon steel in that high-tension area continued to erode, leading eventually to its rupture.
The lesson is clear: If the guidelines had been strictly followed, the trouble would have been spotted early on. As the report points out, KEPCO had neglected to take the necessary measures over an extended period of time.
Inspections following the accident reveal that 15 other places had also been left off the checklist. Moreover, part of the secondary piping in a different reactor system had thinned to 1.8 millimeters; substandard thinning had also occurred, though to a lesser extent, in parts of the piping for two other reactors. But the company had left nearly all quality and maintenance checks to affiliated companies.
In other words, KEPCO lacked an effective system of checking and correcting errors. Lax safety management is a recipe for disaster. It is only natural that the report should emphasize the need to investigate the accident from the administrative (as opposed to technical) standpoint.
The company, meanwhile, is moving in the right direction: It has decided to conduct its own inspections of pipe thickness in the secondary loop. But checking the piping is not enough. To regain public confidence in nuclear safety, the management system for nuclear plants must be reviewed from the ground up. Strict safety controls are required not only for nuclear-plant piping but also for steam piping in the thermal power plants, most of which are said to be neglecting thickness checks. It is also necessary to tighten the inspection system for nuclear plants that have been in operation for about 30 years.
It has been five years since an accidental critical-mass chain reaction at a fuel processing company in Tokaimura, Ibaraki Prefecture, caused the deaths of two workers. Meanwhile, Tokyo Electric Power Co. (TEPCO) has been accused of covering up technical problems. No country has seen as many serious accidents in recent years as Japan.
It is time for the nuclear plant operators, as well as regulatory authorities, to discover all defects, actual and potential, and re-examine the quality control system. Disclosure of errors, such as omissions from checklists, would help. What is needed is a renewed commitment to nuclear safety.
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