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Cause of the Stationary Low-Power Plant No. 1, also known as the SL-1 nuclear accident is believed to have resulted from manual removal of central control rods. According to Adams, (1996), “Investigators found the central control rod lying across the top of the reactor vessel. All the other rods were clamped in their fully inserted positions.” After the accident, the reconstruction process postulated the thought that withdrawal of a 40.6cm core control rod from the reactor would be fatal. The reconstruction process further suggested that withdrawing a 50.8cm core rod would be more severe than the 40.6cm core rod. These findings lead to a conclusion that the possible cause of the accident was manual removal of the reactor’s central core rod during maintenance, (Reed and Stillman, 2009).
Withdrawing the core increased reactivity rate that led to a deadly power surge. The power surge in the reactor was so fast that it reached 20,000MW in millisecond. This melted the plate-type fuel, which interacted with water vessel leading to steam explosion. The steam hit the vessel’s lid with much force that raised it almost 3m above ground.
Reasons for Lifting the Rod
A number of reasons have been given for lifting the rod of the reactor, but the one that draws much public attention is that, operators wanted to use the rod as either suicide or murder weapon. The suicide/murder motive is propelled by the notion that the investigators’ report was intended to protect those who designed and permitted the setting up of the SL-1 nuclear reactor. This meant that the designers and project leaders were not to be held responsible for the accident.
The second perspective of analyzing the accident is the possibility that those on duty were not able to move the control rod as ordered during the maintenance operation. It is likely that, “when it finally moved it moved much farther than expected,” (Adams, 1996). It is also likely that the operators took preventive maintenance at a time when the control rod was not linked to the main drive system of the reactor.
The cause of the accident remains a mystery because the reason given above may not be convincing. According to Hewitt and Collier, (2000), “The exact reason for the accident has never been discovered; the removal of the control rod could have been accidental or deliberate, but no one will ever know,” (p. 143).
Lessons from the SL-1 Accident
The SL-1 nuclear reactor was operated with rods that were not interlocked. Operations of the SL-1 ran even after discovering that the system had problems with sticking the control rods. “A review of the operating logs showed that the rods had exhibited stickiness more than 80 times and that they had failed to fall freely during a scram 46 times,” (Adams, 1996). It is dangerous to have even an experimental reactor that has no interlocks to maintain control rods in position. In addition, there should not be any attempt to remove control rods from a nuclear power reactor.
Another lesson that emanates from the SL-1 accident is that water ejection from a reactor’s core helps in decreasing rate of nuclear reaction. This action involuntarily shuts down further reactivity as it creates a void within the system, if the process is controlled. However, a very rapid power increase like the case of SL-1 can melt down fuel prior to formation of voids and this can shut down reactivity of a nuclear plant.
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