A nuclear reactor is effectively a controlled bomb, which could go off at any time.
Absolutely not. It is hard enough to make a nuclear bomb explode like a nuclear bomb. To make a nuclear reactor do such a thing is an impossibility. In a bomb, fissile nuclei are densely packed giving a high value of supercriticality. Fissions in these nuclei rapidly go on to cause a lot more fissions, which in turn go on to cause a lot more fissions still. The reaction cascades and the enormous energy contained in the bomb's fuel is released in a tiny fraction of a second causing a large explosion.
This cannot happen in the fuel in a reactor for one key reason: sufficient supercriticality cannot be achieved. The major difficulty in manufacturing a working nuclear bomb is the obstacle of preignition. If the reaction does not cascade fast enough, the initial release of energy from the first few generations of fission will blow the bomb apart unspectacularly before any large quantity of energy is released. This is always the case in a reactor because the fuel is not dense enough and pure enough to allow this to happen.
Weapons grade uranium is high enriched to more than 90% uranium-235. In a typical reactor, the enrichment is usually less than 5%. Even in naval reactors, which use high enriched uranium for long core life, enrichment never gets above 60%. Uranium-238 is a neutron absorber, which is bad for making a reaction cascade rapidly because it will steal vital neutrons.
Another critical factor is arrangement. The fuel for bombs is dense sphere of fissile material, compressed to even greater densities by a trigger charge. Reactor fuel is mostly arranged as rods, which allows too much surface area to lose neutrons. The neutrons lost from a rod will either be lost to the system or find a fissile nucleus in another rod, but even then it will take too long. Explosions need to happen quickly.
Even in the worst case scenario of a reactor becoming critical on prompt neutrons, leading to a large power surge, the result will be the fuel rapidly heating up and melting, overpressuring and bursting the coolant system in the process. Once the fuel is melted, it will become subcritical and fission will reduce. This is what happened at Chernobyl. It was a steam explosion followed by a chemical explosion. It was not a nuclear explosion.
Nuclear reactors are notoriously unstable. They could easily go out of control and experience a meltdown.
That is just what Greenpeace et al. says. In fact, in over 12,000 reactor-years of commercial reactor operation, only one civil reactor has ever experienced a melting event, and that was not due to a loss of reactor control. There is too much standing between a reactor and loss of control for it to be a likely threat. Reactor safety works on the principle of defense-in-depth and depends on a variety of separate, diverse and redundant systems to minimise the possibility of serious malfunctions like melting events.
All reactors use control rods to regulate the reaction, but they can also rapidly shut it down in the event of an emergency. In most reactors, they are inserted from above, meaning gravity assists their lowering into the reactor to slow the reaction. In the event of total loss of power, they will simply fall into the core, immediately shutting it down. Many hundreds of these controls rods are present. If one fails, there are always many, many more to pick up the slack. This is the principle of redundancy.
Only boiling water reactors insert the control rods from below, but use multiple redundant systems to ensure reliability. They also make use on passive principles such as gas pressure and spring loading. Withdrawing the rods from the reactor must be done against resistance. Failure of the active system means the rods are forced back up into the reactor, just as gravity forces them down in other designs.
But reactors also make use of other independent safety systems as backup. One example is the chemical schimm, which involves the injection of reactor poisons into the coolant, which rapidly absorb neutrons shutting down the reactor. All safety systems are controlled from multiple, isolated, independent control systems.
Even in TMI, the automatic shutdown systems successfully killed the reaction within a second. The reactor was never out of control.
Yeah, yeah, but you mention TMI, which is an example of a meltdown that does not require loss of control of the reactor. It was a simple loss of coolant accident.
The safety systems at TMI-2 worked as planned. Forced cooling compensated for the loss of coolant pressure in the core as designed. The problem was mistaken information communicated to the operators, which caused them to erroneously terminate forced cooling. Had it not been for this interruption by the operators, the forced cooling system, an example of redundancy in reactor engineering, would have prevented the overheating of the fuel. A simple modification in design resolved this problem so it would not re-occur in any other reactors.
But the fact that this incident has only occurred once in over 12,000 reactor-hours of civil experience demonstrates how the various aspects of defense-in-depth, from multiply redundant and independent shutdown systems, to backup forced cooling systems, has maintained the safety of commercial reactors throughout the vast majority of their existence.
One meltdown can mean a massive ecological and humanitarian disaster.
That is fearmongering and a cliche. A meltdown is a serious reactor malfunction, but not necessarily a public safety risk. It is, as the name implies, the melting of the fuel forming a large puddle of subcritical goop on the floor of the reactor housing. If this happens, the reactor is a write-off and big men from the NRC will come round to break a few kneecaps. But to threaten public safety, significant quantities of radioactive material would need to be released. TMI was a complete non-threat to public safety despite the melting of the fuel due to the final stage in the defense-in-depth principle: containment.
Figure 1- the gleaming white containment structure of Sizewell B is sufficient to keep the hazardous contents inside seperate from the outside through all manner of accidents.
All reactors, with the exception of some old Soviet designs such as the RBMK, are encased in large steel-reinforced concrete containment structures, such as the one shown in figure 1. These are the most hardened structures in all of civil engineering, designed to contain both melted fuel on the inside as it did at TMI, and protect against impacts from fully loaded airliners. They are built around reactors for exactly the purpose of being a failsafe line of defense in the event of a worst case scenario accident such as a prompt criticality. There would have been no damage to the environment from Chernobyl had it been built with a containment structure around it, to contain the radionuclides the fire was trying to disperse.
The containment structure is the critical asset to safety, regardless of what goes on inside, regardless of whatever failures happen in the engineered components of the reactor safety systems, the containment structure will be there to protect the outside. Engineering works on the principle of simplicity being the key to reliability and there is nothing simpler than a six foot thick slab of concrete. It is this beyond all else, which reduces the probability of a repeat of Chernobyl to virtually zero.
Even if most of the radioactive material is contained by the containment structure, a tiny amount of leakage through other pathways could still harm many people.
Even under the remote possibility of some material escaping to the wider environment, the probability that it will be able to cause measurable harm to the public is even smaller. We are now treading dangerously close to FUD. At this point, the risk from a large malfunction occuring and leading to a release of significant radioactive material into the environment and then bringing measurable harm to someone tends to such a smaller value that it is dwarfed simply from the dangers of writing a letter to your MP or congressman to express your concerns. Risks this small must be treated as such.
The nuclear industry is the most dangerous industry in the world.
| Nuclear | 8 |
| Natural gas | 85 |
| Coal | 342 |
| Oil | 418 |
| Hydroelectric | 884 |
| LPG | 3280 |
Table 1- Casualties per TW.yr between 1969 and 1996 according to the Paul-Scherrer Institute
In fact, statistically, you are safer working in a nuclear power station than you are working in a regular office. Safety standards in the nuclear industry are exorbitantly high. This allegation is based purely on hypothetical, caroonish scare stories and not on rational real world experience. Outside of Chernobyl, which was not entirely civilian anyway, no harm has ever come to the public as a result of the civil nuclear industry. A study from the Paul-Scherrer Institute in Switzerland, surveying 4290 accidents in the commercial energy industry between 1969 and 1996, showed that nuclear is by far the safest of all the major energy sources. It has resulted in ten times less deaths per unit of energy produced than the second best option.
How much safer do you want it?
Greepeace has a calendar of events showing that every day of the year is an anniversary of nuclear disasters.
I am fully aware of it and I used to debunk it in detail specifically until I found dedicating so much of the site to it a misplacement. The first version was released for the 10th anniversary of Chernobyl in 1996 and second improved version was released for the 40th anniversary of the IAEA in 1998, complete with a scathing review of them in their introduction. They wanted to use this calendar to demonstrate how nuclear power is responsible for inflicting "damage on humanity".
The problem with debunking this calendar is it is incredibly tedious and repetitive. Most of their examples are vague references to technical failures, which do not really demonstrate much at all. There are also references to failures of certain systems, including a single control rod, overlooking the important principles in nuclear construction of redundancy and diversity in safety, the principles of defense-in-depth. Sometimes they even cite successful shutdowns, which are simply demonstrations of safety systems working as planned. And they have no sense of ageism, citing problems with some of the earliest reactors, including the first reactor to ever produce electricity to power an electrical appliance, the EBR (pdf), in support of their campaign to end today's nuclear technology.
They frequently use on-site problems in their attempt to demonstrate the "damage inflicted on humanity" when these incidents, by the nature of being contained to site themselves, could not have inflicated damage on humanity. There are also references to accidents involving benign substances such as heavy water and other materials, which are not specifically used by the nuclear industry, as well as accidents in PWRs involving the secondary coolant loop, which mirrors that of the steam loop in a coal-fired power station. They even had the nerve to cite an anti-nuclear rally on March 1 as an example. If anti-nuclear rallies inflict damage on humanity, maybe we should ban Greenpeace.
It is no surprise to me, coming from an engineering background, that a complex machine such as a nuclear reactor has problems from time to time. It is no surprise that occasionally, out of the many controls rods, one should fail. It is no surprise that a complicated monitoring and control system should sometimes show faults. It is no surprise to me and it is no surprise to the engineers, who designed the reactors. They designed them using the principles of defense-in-depth so that no one failure poses any hazard to the general population.
There are some more legitimate references to radioactive releases into the wider area, however these were not significant in terms of elevating exposure of the surrounding population above natural background and in many cases the release was too small to have caused any measureable effect on the radiation environment. Only through Radiation Boogey Man tactics are these painted into "damage inflicted on humanity", especially when measured against pollution from other sources. There are also legitimate references to some irresponsible Soviet nuclear space practises, which are not done anymore, and in fact it is the Soviet reactors, the VVERs and the RBMKs, which make the most common appearances, which lessens the legitimacy to modern nuclear power and most certainly future nuclear power.
This calendar is a demonstration of the inundation technique. By flooding the reader with 365 examples, ranging to the occasional legitimate one (April 26), to the vast majority of overhyped and unimportant problems, they prevent anyone example from being examined too closely. The reader simply takes away a bucket-load of examples, which Greenpeace says show the "damaged inflicted on humanity" and does not see how so many of them individually fail to amount to anything significant.
In case, you think I am picking on Greenpeace specifically, other do this kind of thing, but it is still worth mentioning how talented the anti-nuclear groups are at spinning relatively insignificant problems into "40 years of disasters".
Building to last even longer
If that is of little comfort, the new generation III and IV reactors coming onto the market boast new passive safety features, which depend not on the engineering and redundancy, but on the basic laws of physics. The Economic and Simplified Boiling Water Reactor from GE does not use pumps to drive the coolant, but rather uses convection, which is an entirely natural and failsafe process. This means that there are no pumps to fail and cooling will continue in the event of total loss of power because it does not require external power to operate in the first place. Another example of new passive safety is in the Westinghouse AP-1000. The emergency cooling water for this design is located in the roof of the containment structure, allowing gravity to deliver it if all else fails.
Then there are the Generation IV high temperature reactors, such as the pebble bed modular reactor. HTRs use billiard balls or prisms of silicon carbide or graphite seeded with specks of fuel, rather than the traditional fuel rods. Because of this different form of fuel, the physical effect known as Doppler broadening produces a large negative temperature coefficient, whereby as the temperature of the fuel increases beyond operating temperature, the neutron absorption cross section decreases, meaning that neutron absorption drops, sending the reactor subcritical in the more extreme cases, exactly when automatic subcriticality is required.
In experiments performed in China, coolant was voided from experimental pebble bed reactors. The temperature of the fuel increased from 1000° to 1600°, about 400° below that of the melting point before the temperature dropped off resulting from reactor self-shutdown. The shutdown was purely due to the fuel responding to the temperature increase through Doppler broadening by going subcritical and not through active measures such as control rods or injectable poisons.
These reactors are physically meltdown proof.
Further, because the silicon carbide or graphite structure of the fuel balls, fission products are safely contained for at least a million years meaning that there is no danger from transportation of leakage. If a fuel ball gets dropped at the side of the road, it just needs to be picked up and put back in the lead lined bin.
Transportation of nuclear materials presents a major hazard to the populated areas.
Figure 2- Type B transport cask used to ship HLW by rail or sea.
Nuclear shipments are regulated and restricted to very high levels, far more than other shipments of dangerous material. There is a restriction on the quantity of nuclear material that may be transported at any one time, to reduce the consequences of any accident. Material must also be shipped in specially designed containers, such as the one shown in figuer 2, which are resistant to all manner of external stresses including thermal stresses, fire and a direct impact from a train travelling at 100mph. The Type B and Type C casks used for shipping high level waste are some of the most durable containers ever made. In 50 years of nuclear transport, there has never been an accident in any form of transport, rail, sea, air, in which a transport container has been breached and released radioactive material in the environment.