Home > Introduction > Hitachi's Response to Nuclear Reactor Turbine Problems
In June 2006, a malfunction occurred in the low-pressure steam turbine in the Hamaoka Nuclear Power Station Unit No. 5 of Chubu Electric Power Co., designed and manufactured by Hitachi. A similar problem occurred the following July in the identically designed Shika Nuclear Power Station Unit No. 2 of Hokuriku Electric Power Co. Hitachi has since worked with Chubu Electric and Hokuriku Electric to identify the cause of these problems and is making every possible effort to enhance reliability and prevent similar problems from reoccurring. Moreover, through these efforts to address these problems, we are determined to reaffirm our commitment to Hitachi's corporate credo of "contributing to society through the development of superior, original technology and products," to raise our technical strength and reliability to higher levels than ever, and to bolster confidence in Hitachi's monozukuri (manufacturing).
Investigation of Turbine Problem and Remedial Steps
In the Hamaoka Nuclear Power Station Unit No. 5 of Chubu Electric, damage was found in 663 out of 840 of the moving blades on the twelfth stage of the low-pressure turbine.*1 One of the blades was found to be fractured. In the Shika Nuclear Power Station Unit No. 2 of Hokuriku Electric, damage was found in 258 out of 840 of the moving blades on the twelfth stage of the low-pressure turbine.
Regarding the cause, it was determined that unanticipated vibration (random vibration*2 and vibration from flashbacks*3) during test operations caused metal fatigue that led to cracks at the base of the blades, which progressively worsened. The turbines in question, embodying the latest in high-performance turbine design, had been subject to repeated testing using a scale model. However, the phenomenon was something that engineers were unable to anticipate during the design stage. Hitachi deeply regrets the trouble and anxiety that resulted. To remedy these turbine problems, Hitachi redesigned and manufactured the turbines so that they can reliably tolerate any foreseeable vibration stress, this time taking full account of random vibration and flashbacks. During the design stage, we used cutting-edge testing equipment to improve verification accuracy by analyzing the results of tests using a scale model and by simulating actual operating conditions. We manufactured the new turbine blades based on this testing and analysis.
At the same time, because the design and manufacture of the new turbine blades required much time, we put in place an interim solution: taking out the moving and stationary blades on the twelfth stage of the turbines and replacing the stationary blades with pressure plates. After doing this, the Hamaoka Unit 5 was able to resume operation in March 2007.
- *1
- Low-pressure turbine
A low-pressure turbine is a second-stage turbine designed to turn efficiently on steam that has lost pressure after passing through the first-stage high-pressure turbine, which is turned by high-temperature, high-pressure steam. - *2
- Random vibration
An irregular vibration of the turbine blades caused by steam turbulence within the turbine - *3
- Flashback
A rapid reverse flow of steam caused by a drop in pressure within the turbine when, for instance, the turbine stops automatically
Public Disclosure of the Problem
Aware of the importance of nuclear power stations and the circumstances of the incident, Hitachi held a briefing on the causes on the same day that Chubu Electric and Hokuriku Electric submitted their reports to Japan's Nuclear and Industrial Safety Agency. Stakeholders were notified during a briefing that was conducted in the presence of an executive officer, who is also the head of the task force charged with resolving the turbine problem, and the general manager of the Nuclear Systems Division.
Boosting Technical Strength and Reliability
Hitachi regards the turbine problem as a serious incident that calls into question Hitachi quality and monozukuri. Hitachi responded on September 15, 2006, by establishing a Supervisory Office for Power Systems and a Supervisory Office for Monozukuri, both directly under the president, to reexamine and strengthen our core monozukuri technologies.
In the Supervisory Office for Power Systems, we are working tirelessly to restore both power stations as soon as possible, while at the same time supervising the design, manufacture, and installation of the new turbines. In the Supervisory Office for Monozukuri, in addition to identifying and analyzing all the potential risks of monozukuri, we have established six committees to review development and manufacturing processes in each of Hitachi's business areas. Through these committees, we are working hard to prevent similar accidents in the future by improving the development
and design process, redoubling our commitment to quality assurance training, and strengthening process management and human resource development. (For more on strengthening monozukuri, see page 26.)