One thing all the world’s nuclear reactors have in common is that – unless they are constantly cooled with large volumes of water – they will eventually explode. This is because even after nuclear fission has been stopped, the decay heat from the fuel rods is sufficient to melt them and prompt dangerous interactions between water and their zircaloy cladding.
It seems highly likely that many more nuclear reactors will be built around the world, prompted by factors including concern about climate change, worries about fossil fuel availability, and the enthusiasm of states for nuclear technology. Today’s reactor designs suffer from the risks mentioned above. I don’t know how feasible it would be to design reactors which are passively safe (and which will automatically enter a safe state, without human action, after a major accident), but it seems worth investigating seriously. It seems much more prudent to build machines that slow down and cool off when left alone, rather than those that heat up unstoppably until their liquified contents melt through the containment around them and poison the nearby environment.
I don’t know a ton about it, but my impression was that CANDU reactors are of such a design that the shape of the fuel rods are important for a sustained reaction. In the event of meltdown, although they still produce significant decay heat, it is not possible for the core to be critical.
Also, I’ve done some light reading about Thorium reactors and wonder if those will prove to be as promising as they sound in terms of
A) fuel availability
B) passive safety
C) inability to produce weapons.
What do you think about pebble bed reactors and other supposedly safe reactors?
http://en.wikipedia.org/wiki/Pebble_bed_reactor
Reactor designers have been thinking that way for years. Fukushima’s reactors are the oldest example of western-designed reactors. Every design since has had improvements in passive safety.
There are modern reactors that use passive systems that don’t require an outside power sources to remove all decay heat safely. The AP1000 is one such reactor, currently in existence. However, the AP1000, would, in some severe accident scenarios, require replenishment of some water resources (at at rate possible with a garden hose). http://ap1000.westinghousenuclear.com/station_blackout_home/
Also, most current reactors have systems to designed to passively help remove decay heat, delaying a melt-down.
You’re not quite right about the explode part. Maybe melt down (which is very bad), but not explode. The explosion at Fukushima happened because the hydrogen evolved from the melting fuel rod cladding was not properly vented, as the operators thought would be the case: a massive failure of design (but not one necessarily shared by other reactors). Also, it isn’t thought that the Fukushima explosions occurred inside the reactors: the gas exploded outside the reactors’ containment, after it had been vented. Had the hydrogen been released to the environment as the Fukushima reactors had been designed, no explosion would have occurred, and though a meltdown would have progressed, it may have been stopped before releasing as much, or any, radioactivity, as the explosions hampered cooling efforts significantly. Other reactors have different systems designed to neutralise hydrogen evolved in accident scenario similar to Fukushima’s meltdown, including different venting systems, and hydrogen recombiners that can work passively in a station blackout. Hydrogen explosions inside containment are possible, but prevented by other safety systems: high pressure, and a neutral environment (of nitrogen, or helium, or carbon dioxiode, for example).
Some say that Fukushima proved the value of paying extra for safer reactors, such as the EPR. But others argue that the Japanese accident highlighted the need for fully passive safety systems — ie, ones that need no external power—which the EPR does not have.
The biggest customers for nuclear power in the coming years will be developing countries, for which price is crucial. The International Atomic Energy Agency now predicts that nuclear capacity in western Europe could fall by as much as a third by 2030. (Before Fukushima, it said it would expand.) Capacity in Asia, by contrast, will more than double.
You’re not quite right about the explode part. Maybe melt down (which is very bad), but not explode.
I think a meltdown counts as a type of explosion. It certainly involves a violent breach of the reactor’s containment system (if any).
What do you think about pebble bed reactors and other supposedly safe reactors?
I don’t know enough to judge, but I would certainly be more supportive of new nuclear plants based on passively safe designs than on plants based on current designs that tend toward instability when cooling is lost.
Here are a few more great reason whay we should invest in nuclear:
Each plant costs $10 billion to build, it costs over $300 million just to turn a nuclear plant off, nuclear plants are terrorist targets, the fuel is destructive to make, the fuel is dangerous to handle and transport, the fuel is a terrorist target, the spent fuel must be buried in old abandoned mines, the spent fuel is dangerous to the environment and is a terrorist target. In addition, nuclear plants are welfare cases; there has never been a nuclear plant anywhere in the world which has made money without huge permanent subsidies, primarily because the industry is so heavily regulated they are rendered unprofitable. Nuclear plants never have enough time to pay for themselves before they must be completly gutted and rebuilt. Of course we have Three Mile Island and Chernobyl, the two main reasons why they are heavily regulated. And of course, Iran is building nuclear plants for peaceful civilian purposes only. Lol!
Coal/oil power on the other hand is none of these things. It is old technology, plants are cheap to build, cheap to maintain, they are not welfare cases and they are not terrorist targets. The only problem is they emit smoke. Why can’t we solve this simple, old technology issue? I guess coal is not sexy and nuclear is. My suggestion is that instead of spending $10 Billion on a nuclear plant, we spend $1 Billion on R&D to make coal a smoke free energy source, and spend the remaining $9 billion to buy malaria mosquito nets for just about every vulnerable person on earth. And hopefully the whole coal/nuclear issue will go away, perhaps malaria too.
klem,
Coal as a fuel has the unfortunate downside of releasing easily calculable amounts of Carbon dioxide. Coal varies in composition from about 50% to nearly 100% carbon. Therefore, burning it yields the following reaction:
C + 2O = CO2
The atomic weight of coal being 12 and oxygen being 16 means that burning a pound of coal releases ~3 2/3 pounds of carbon dioxide.
The rate at which coal (and other hydrocarbons) are being burned is sufficiently large to alter the chemistry of the atmosphere significantly. Through scientific observation, it is known that CO2 absorbs long wave infrared radiation (present in sunlight). It therefore has a warming or more accurate an insulating effect, much like that of a blanket on one’s bed. It is for this reason that it is undesirable to add more CO2 to the atmosphere, and also why building more coal plants, as well as consuming it is to be avoided.
If most nuclear reactors in the future will be build in developing countries for whom the cost of introducing sufficiently sfe technology is a significant factor, it is in the best interests of the developed world to provide a additional funding to make those nuclear facilities in the developing world safer. As with Chernobyl and Fukushima, we see that the effects of nuclear disasters in not contained within the borders of the country of the facility.
It would also seem prudent if we can change the design of less safe older facililities to make them safer because of new techonologies. \is that possible?
I suspect retrofitting existing plants is quite expensive – not least because the interiors are contaminated with radioactive wastes.
Changing the fundamental design of the reactor (from boiling water or pressurized water to pebble bed, for instance) probably isn’t possible at all, or is possible only at a higher cost than building a whole new reactor.
Some say that Fukushima proved the value of paying extra for safer reactors, such as the EPR. But others argue that the Japanese accident highlighted the need for fully passive safety systems—ie, ones that need no external power—which the EPR does not have.
The biggest customers for nuclear power in the coming years will be developing countries, for which price is crucial. The International Atomic Energy Agency now predicts that nuclear capacity in western Europe could fall by as much as a third by 2030. (Before Fukushima, it said it would expand.) Capacity in Asia, by contrast, will more than double.