As mentioned in NIT 136, on May 6 the Monju Prototype Fast Breeder Reactor (FBR, 280MWe), developed by the Japan Atomic Energy Agency (JAEA), was restarted for the first time in over 14 years. It had been shut down since an elementary design error caused a sodium leak and a fire in December 1995. Each day that the plant was shut down, 55 million yen of taxpayers' money were spent in maintenance costs.
There were several reasons why Monju remained shut down for so long. These included a court decision invalidating the license (NIT 93) and the need to replace degraded fuel (NIT 126). In addition, since 2008 there have been repeated false alarms from sodium leak detectors (NIT 126). These false alarms revealed problems with the quality and installation of the detectors. In response, inspections were carried out on about 3,000 items of equipment.
An alarm indicating a radioactive leak sounded the day the plant restarted. By around midday the following day the alarm had sounded 7 times.
The upper part of the reactor is filled with argon gas. Detectors take samples of this gas in order to detect slight leaks of radioactivity from the nuclear fuel. It takes time to sample gas and detect radioactivity, so three detectors operate consecutively to enable continuous measurement. An alarm went off when one of these detectors malfunctioned. JAEA continued operating the plant with just two detectors, but on May 9 one of the remaining two detectors malfunctioned. Eventually JAEA abandoned this method of leak detection, saying there were no problems because it had another method of detecting radioactive leaks from the fuel assemblies. The Nuclear and Industrial Safety Agency (NISA) accepted this, even though the alternative method is much less accurate. Clearly JAEA and NISA have chosen to prioritize continued operation over safety.
JAEA said "electrical noise" was the cause of the problem, but this is just a guess. The fact is that the cause has not been determined. JAEA said it would replace the relevant computer with another with faster processing capacity, but on June 11 an alarm sounded indicating that transmission was too slow.
Since then all sorts of alarms have sounded. On June 8 Denki Shimbun reported that up to 1pm on June 6 there had been 620 alarms. The greatest number of alarms was from gauges that use pressure difference. They are said to be so sensitive that they respond to low atmospheric pressure. It is doubtful whether accurate judgments can be made using an alarm system that goes off whenever the weather changes.
It must also be remembered that 18 years have passed since the equipment was installed. The reason for some of these alarms is that equipment has deteriorated. The suppliers maintain the equipment and apparently replace it when they find defects. However, many of the detectors are general purpose items, so their performance should be well understood. It should not be necessary to wait for them to break down before replacing them. Quality control is too important to be left entirely to sub-contractors. This situation demonstrates that there are serious problems with JAEA's quality control system and ability.
Motley crew of operators walking a tight rope
JAEA's Monju staff numbers have fallen by about one third in the past 14 years. It is making do by borrowing staff from other sections and from electric power companies. The fact that workers on temporary transfer have not been sufficiently trained was demonstrated by an instance of incorrect operation of a control rod. The problem occurred when the reactor was being shut down on May 10. It did not lead to a major accident, because the reactor is currently being tested at zero power output. However, it turns out that the worker had not been instructed in the fine details of the procedure for inserting control rods. The procedure that went awry on this occasion was not even covered in the manual.
If you go for a tour of Monju, you will be shown a simulator, which precisely simulates the operation of the central control room. Operators are trained using this simulator. The simulator is programmed with accident scenarios, so operators are trained in handling accident situations. JAEA is very proud of this simulator. Hearing JAEA's public relations talk, anyone would imagine that a mistake involving the operation of control rods could not possibly occur. No one would dream that important procedures were not even in the manual, or that there were serious inadequacies in training given in preparation for the restart of Monju.
During the core confirmation tests now being carried out, power output is virtually zero. However, next year power output will be increased and testing of electricity generation will begin. When power output is raised beyond 40%, Monju will be entering totally new territory. The accident in 1995 occurred at 40% power output and that is as high as it went.
It sends a shiver down my spine when I think of how equipment has deteriorated, quality control has been left up to contractors, and operators have been rounded up from all over the place.
Reporting of incidents late as ever
When the accident occurred 14 years ago, notification to the local governments was late, even though this notification is required under the safety agreement with the local governments. Furthermore, video footage of the site was concealed. This became an even bigger issue when the person in charge of the investigation into the cover up died. It is claimed that he committed suicide, but relatives are still fighting the case in the courts.
The problems with notification should have been sorted out, but in 2008 the notification to the local authorities about sodium leak alarms was three hours late. Since then notification has been consistently late. JAEA apologized profusely, but notification was late again this time when an alarm indicated a radioactive leak. On May 8 JAEA received a reprimand from NISA regarding its notification system. Clearly there is no change in JAEA's basic nature. JAEA loves to talk about "assuring transparency", but the fact that notification of incidents is invariably late shows that this is just lip service and JAEA is incapable of living up to its promises in this regard.
Does Monju have a future?
It is planned that Monju will only be used to generate electricity for ten years. It was designed as a prototype for a commercial reactor. However, it is now proposed that a demonstration FBR of a different design will be developed. Hence, the experience gained with Monju will not be applicable to any commercial reactor. The plan is that a demonstration FBR be built by 2025, but technological development has not advanced and no site has been chosen.
The Japanese Government selected sodium as the best coolant for fast breeder reactors, but it is a very problematic substance, burning in air and exploding if it comes into contact with water. Other technologically advanced countries which tried to develop fast breeder reactors were unsuccessful and have already withdrawn. When one considers the problems discussed above, it is hard to believe that Japan will be able to overcome the technological barriers that prevented other countries from commercializing fast breeder reactors.
Hideyuki Ban (CNIC Co-Director)
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