The Mihama nuclear power plant is been operated in the town of Mihama, Fukui prefecture, about 320 km west of Tokyo were on the 9th of August 2004 a fatal accident happened at the Hihama No.3 nuclear powers station. The Mihama 3 has been in service since 1976, which is an 826 MWe 3-loop Westinghouse type pressurized reactor. The heat from the reactor core to a heat exchanger is carried out by high pressurized water, where its heat turns the water of secondary cooling cycle into steam which in turn is used to drive the power turbines. Due to the reason that the heat exchanger separates the two cooling cycles, water in the secondary cycel and steam turbines are not radioactive. The accident happened when the reactor was about to undergo routine maintenance where Eleven persons who were in the turbine hall at the time of the incident were seriously injured and four of them dies the very day of the accident.
The accident was caused by the sudden rupture of a pipe carrying pressurized the water in the secondary unit of the power station in the non-radioactive part of the reactor. The rupture occurred in a straight part of a black steel tube 56cm in diameter and in the 27 years of operation, the pipe had not been checked once for corrosion. Major inspections on nuclear power plants are usually performed every 10 years. At the time of burst, the walls of the pipe were worn down from an initial 10mm of carbon steel to a 1.4mm thick in the area around the rupture zone. Regulations required the pipes to be replaced when the pipe thickness went below 4.7mm. Before the accident, a subcontractor company had alerted the operators to need of inspection but the corrosion phenomenon was under-estimated or neglected.
The accident raised a serious question regarding the safety culture of Japanese nuclear power plant operation and the legal framework that surrounds them. Below are the list of measures that could have been taken to avert the accident or that could prevent future nuclear power plant accidents from occurring.
- Regulations regarding the safety culture of a nuclear power plant must be considered seriously like shutting down the operating reactors, cooling down the reactors to remove the heat from the nuclear fuel, containing the radioactive materials.
- Monitoring the environment radiation activities around the facility in order to check there is no harmful effect on the surrounding environment
- Developing collaborative robotics to work in a harmful environment such the nuclear power plants, so that in case of an accident the influence on humans can be reduced.
- Reviewing the safety standards and inspecting a nuclear reactor at regular intervals of time.
- Hire experienced and well-trained operators to work on the reactor to decrease the risk due to human error in the nuclear plant.
- Fuel cladding is one of the safest method to ensure that the nuclear reactor runs in a safe manner
- Using containment buildings which are built with concrete and steel which are several feet thick encapsulating the reactor to lessen the effect of a nuclear accident if any nuclear material were to be released