This page contains discussion of other prominent accidents and incidents at nuclear facilities.
Mihama 2004
Mihama nuclear power station in Japan.
On August 9 2004, a high-pressure steam pipe in the turbine hall of Mihama PWR 3 burst killing five people and seriously injuring another six.
Mihama was the worst nuclear accident in the history of the Japanese nuclear industry.
It was the worst accident at a Japanese nuclear power station, but it was not the worst nuclear accident, because it was not a nuclear accident at all. A PWR has two separate water circuits: the reactor coolant circuit and the steam circuit. The reactor coolant travels through the core, carrying heat to the steam generator where the heat is transferred through a heat exchanger to the steam circuit. The heat boils water in the steam circuit, which drives the turbines. The two circuits are isolated from each other in the PWR and the coolants do not mix. Only heat is transferred. The accident was on the steam side, and so was unrelated to the reactor itself.
It is the kind of accident that can happen, and has happened, in any facility utilising high pressure steam or hot water, be it a coal fired power station or a boiler system. To attempt to use this particular accident to indict nuclear power uniquely would be employing guilt by association.
The fact that a pipe burst in the steam circuit only goes to show that the power plant is improperly maintained and that a nuclear disaster could occur in the reactor circuit.
That does not necessarily follow. Once the secondary circuit reaches the turbine building, it is treated as secondary and as such does not receive as much attention. That has caused problems in the past such as this accident, which is why more attention is now given than before. But ultimately, most of the effort is expended on ensuring the primary side is safe. The level of detail given to the secondary side is not an indicator of the level of detail given to the primary side.
Even if it was, and a similar accident happened, the consequences would likely be less severe than in this accident. The primary side is kept fully within the containment vessel. Because of high temperatures and activity within the containment area, entry is strictly controlled. It is highly likely that no-one would have been present during such a rupture and no-one would have been harmed.
Containment vessels are designed to deal with far worse than pipe bursts and as such, there is no chance of a failure of containment from any such event. The high pressure water would flash into steam and the end result after shutdown would be a containment vessel full of, well, hot air. There is no danger to the public.
Despite the obvious tragedy of the deaths of five people, this accident demonstrates what has already been known for hundred of years. Working with high pressure and high temperature materials is delicate operation and prone to workplace hazards. It does not single out nuclear power as an activity of unprecedented hazard to the population.
Sellafield THORP 2005
The Sellafield facility in Cumbria in the North of England.
In April 2005, the Thermal Oxide Reprocessing Plant at Sellafield was shutdown after a leak was discovered in a pipe carrying nitric acid dissolved spent fuel. In total 83m³ of material was spilt onto the cell floor. The IAEA provisionally rated this incident a level 3, serious incident, on the International Nuclear Event Scale.
Clearly this accident posed a major hazard to the population.
Defense-in-depth still applies, even at reprocessing facilities. A spill tank was incorporated into the design of the cell so capture and contain any leaking material. It is little wonder then that all 83m³ were indeed safely contained within the cell with no harm to any worker or member of the public.
The Nuclear Installations Inspectorate believes the leak had been going on for around eight months. How can a leak of spent fuel go undetected for eight months?
These cells are of course closed off to all personnel because of the hazardous material running through them so only robotic inspection could have detected it. The NII is bringing charges against BNGSL though are remaining quiet on the exact transgressions behind it (no doubt the leak itself is not the reason, but is a symptom of the reasons).
On the face of it, it does seem rather stupid that this went undetected for so long and it is easy to make allegations of incompetence in the inspection procedures at the facility. What is interesting is how despite this seeming incompetence, the material was still safely contained. We see here a glaring demonstration of the success of defense-in-depth. Nuclear facilities are designed to be idiot-proof.
Forsmark 2006
Forsmark nuclear power station in Uppsala, Sweden.
On 25 July 2006, a short circuit in the Swedish National Grid resulted in a power transient, which triggered an automatic SCRAM at Forsmark-1 BWR in the Uppsala region on Sweden. Emergency forced cooling was sustained by two of the four diesel generators the reactor was undamaged. The other two failed to activate due to the effects of the power transient.
This was a close call for a meltdown.
Two out of the four diesel generators is more than sufficient to maintain forced cooling and natural convection in the boiling water reactor can effectively dissipate much of the decay heat even if all had failed (Generation III+ BWRs can depend on natural convection even during operation). Without any diesel backup, it would take several days for the heat build up from the decay of fission products to threaten the integrity of the fuel. It is rather incomprehensible that alternative means of forced cooling could not be established in that time. This was not a loss of coolant accident.
SKI themselves said in a press release:
The incident at Forsmark 1 did not come near a meltdown, no emissions to the environment occurred as a consequence of the event, and the number of safety systems that were activated proved sufficient.
This was the worst accident since Chernobyl and TMI.
This was not an accident at all. This was an equipment failure, which was compensated for long before it posed any threat to the plant. The association with Chernobyl is particularly sensationalist. It was only rated level two on the INES scale. Chernobyl was a prompt criticality accident in an uncontained reactor. Even a comparison to Three Mile Island, rated level five because of the severe core damage, is stretching it since that was caused by operator mishandling leading to a partial loss of coolant. The water line dropped as a result and the exposed portion of the fuel was heated by the decay of fission products and melted. Since there was no loss of coolant, the comparison is slightly off and the threat of melting is significantly reduced.
However, like TMI, even if forced cooling had not been restored and the fuel had been allowed to reach melting point, the prescence of proper containment would have protected the wider world. The concerns of safety, exaggerated as there are, relate to the plant itself, not to the public.
What actions are being taken in light of this?
Three other reactors in Sweden, whose diesel generators are similarly vulnerable to power transients, have been taken offline. The others, which are not, remain operational. SKI identified that there was inadequate independence of the safety systems in accordance with the principles of defense-in-depth. This is being corrected.
Kashiwazaki-Kariwa 2007
Kashiwazaki Kariwa power station in the Niigata prefecture, Japan.
On July 16 2007, an earthquake measuring 6.8 on the Richter scale, struck off the coast of the Niigata prefecture damaging the Kashiwazaki-Kariwa power station. Most notable effects was a fire at a transformer bank and the spillage of 1.5m³ of water from spent fuel cooling pools into the Sea of Japan.
This incident shows how unsafe nuclear power stations are.
First off, it only speaks of their reactions to earthquakes and therefore this example is not applicable to most locations. But when applied to earthquake prone Japan or other places such as the Indian subcontinent, the description "unsafe" needs some definition. Nuclear opponents tend to use the term "unsafe" to mean there is a likelihood of some fault developing. A more correct usage would be for the likelihood of any faults causing harm to people or damage to property. In this case, there was no such harm or damage. The earthquake was more than capable of claiming eleven lives and destroying the homes of hundreds of families without the help of the power station.
The spillage of radioactive water did harm to the Sea of Japan.
The water was spilt from the spent fuel cooling pools as it sloshed over the sides during the tremors. A much larger quantity was spilt but most was contained in the facility as designed. The small quantity that was discharged into the Sea of Japan had an activity of 60kBq.m-3, which is in fact roughly equivalent to the radioactivity of orange juice. Even the most ardent scaremongering cannot legitimately paint this as harmful.
The power station may have to stay closed for a year for repairs.
The earthquake was very severe. Exactly how long the repairs will take it still being determined. However, the engineering success story of this is how the facility endured the geological abuse and did not fail in a dangerous way.