Tag Archives: nuclear energy

nuclear power, part 2 – how it works

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PressurizedWaterReactor

There are many tricky questions around nuclear power, and perhaps the most head-scratching one is, why did the most earth-quake prone country in the world embrace this technology so readily? The well-known environmental scientist Amory Lovins was just one to state the bleeding obvious with this remark: “An earthquake-and-tsunami zone crowded with 127 million people is an un-wise place for 54 reactors”. Combine this with a secretive governmental and industry approach to energy production in a cash-strapped economy, and disaster was almost inevitable. There were a number of earthquake-related shut-downs and cover-ups before the Fukushima disaster essentially blew the whistle on the whole industry, turning the majority of Japan’s population against nuclear power almost overnight. After Fukushima, the generation of nuclear power worldwide fell dramatically largely due to the shut-down of Japan’s 48 other nuclear power plants, though facilities in other countries were also affected by the publicity.

Yet it’s reasonable to ask whether other countries, such as Australia, should reject nuclear power outright because of Japan’s bad example. Australia rarely suffers serious earthquakes – South Australia almost never. And there may be safer ways to utilise nuclear fission as energy – now or in the near future – than has been employed in Japan or other countries since the sixties. So, just how do we generate nuclear power, how do we get rid of waste material, and are there any developments in the pipeline that will make generation and storage safer in the future?

How’s the energy produced?

Much of the following comes from How Stuff Works, but for my sake I’m putting it mostly into my own words. We derive energy from nuclear fission in the same way that we derive energy from coal-fired power stations – by turning water into pressurised steam, which drives a turbine generator. The difference, of course, is the source of the heat – uranium rather than carbon-emitting coal. Nuclear reactors create a chain reaction which splits uranium nuclei into radioactive elements, releasing energy in the process. A thorium fuel cycle rather than a uranium one is also possible, though with limited market potential at this point.

Uranium, in the form of isotope U-235, can undergo induced fission relatively easily. However, naturally occurring uranium is over 99% U-238, so the required uranium has to be enriched so that the U-235 content, which is naturally at around 0.7%, is increased to around 3% (weapons-grade uranium enrichment requires over 90% U-235). The enriched uranium is formed into pellets, each about 2.5 cms long and less than 2cms in diameter. These are arranged into bundles of long rods which are immersed in a pressure vessel of water. This is to prevent overheating and melting. Neutron-absorbing control rods are added to or subtracted from the uranium bundle, by raising or lowering, and these control the rate of fission. Completely lowering the control rods into the bundle will shut the reaction down.

The fissioning uranium bundle turns the water into steam, and then it’s just the technology of steam driving the turbine which drives the generator. But then there’s the matter of radio-activity…

Before we get into that, though, I should mention there are different kinds of reactors, which use different systems and different cooling agents. I’ve been rather cursorily describing a Light Water Reactor, the most common type. They use normal or regular water, and there are three varieties: pressurised water reactors, as described; boiling water reactors, and supercritical water reactors. There are also heavy water reactors which use water loaded with more of the heavier hydrogen isotope called deuterium. But whatever is used as a coolant and/or a neutron moderator (a medium that moderates the speed of neutrons, enabling them to sustain a chain reaction), the issue of radio-activity needs to be dealt with.

What are the safeguards against radioactive decay? 

What I previously termed ‘induced fission’ involves firing neutrons at U-235 nuclei. The nucleus absorbs the neutron and then becomes unstable and immediately splits, releasing a great deal of heat and gamma radiation from high energy photons. Among the products of the split are fissile neutrons, which then go on to split more nuclei, a chain reaction which can be controlled with the manipulation of control rods as described above. Uranium 235 and Plutonium 239 are among the very few fissile nuclei – those that lend themselves readily to nuclear chain reactions – that we know of.

The trouble with induced fission is that the products of the reaction are vastly more radioactive than the fissioned material, U-235, and their radioactive properties are long-lasting, leading to the obvious problems of safeguard, storage and elimination.

In standard light water reactors, the pressure vessel is housed in concrete, which is in turn housed in a steel containment vessel to protect the reactor core. Refuelling and maintenance equipment is housed within this vessel. Surrounding this we have a concrete building, a secondary containment structure to prevent leakage and to protect against earthquakes or other natural (or man-made) disasters. There was no such secondary structure at Chernobyl. The nuclear industry argues that, when these safeguards are properly maintained and monitored, a nuclear power plant releases less radioactivity into the atmosphere than a coal-fired power plant.

Even if this wins some people over, there are the really big issues of mining and transportation of uranium and nuclear fuel and storage of radioactive waste. According to the USA’s Nuclear Energy Institute, 2000 metric tons of high-level radioactive waste are produced annually by the world’s nuclear reactors, which is hazardous to all life forms and can’t be easily contained. This radioactive material takes tens of thousands of years to decay. Low-level waste, which contaminates nuclear plants and equipment, can take centuries to reach safe levels.

Storage, or possible recycling, of waste is probably the major issue for the nuclear power industry’s future, in spite of all the understandable current attention given to melt-downs. The How Stuff Works website summarises the present situation:

Currently, the nuclear industry lets waste cool for years before mixing it with glass and storing it in massive cooled, concrete structures. This waste has to be maintained, monitored and guarded to prevent the materials from falling into the wrong hands. All of these services and added materials cost money — on top of the high costs required to build a plant.

In my next, and hopefully last, post on this subject (for a while at least), I’ll focus more on this storage issue, and on other developments in nuclear fuel, such as they are. I’ll be relying particularly on the MIT interdisciplinary study ‘The Future of the Nuclear Fuel Cycle’, which came out in 2011 – just when the Fukushima-Daiichi disaster hit the headlines…  

energy solutions: nuclear power, part one – the problematic past

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jordan-nuclear-energy-protest2    images

Here in South Australia, our Premier (the leader of the government) has recently announced a major inquiry into the viability of nuclear power for the state, and this is raising a few eyebrows and bringing on a few fevered discussions. The Greens are saying, what need for that old and dangerous technology when we have the prefect solution in renewables? Many scientists are arguing that all options should be on the table, and that our energy future should be flexible with many different technologies in the mix – solar, wind, geothermal but also perhaps clean coal (if that’s not an oxymoron), a new-look nuclear technology, and maybe even a technology of the future, such as fusion – not to mention the harnessing of anti-matter, mentioned to me recently by an enthusiastic 12-year-old.

South Australia already has a great rep for adopting new technologies. According to wind energy advocate Simon Holmes a Court, in a talk podcasted by The Science Show recently, SA gets more than 30% of its energy from wind, and some 5% from solar. If SA was a country, it would be at the top of the table for wind power use, a fact which certainly blew me away when I heard it.

Of course, South Australia also has a lot of uranium, a fact which has presumably influenced our young Premier’s thinking on nuclear energy. I recall being part of the movement against nuclear energy in the eighties, and reading at least one book about the potential hazards, the catastrophic effects of meltdowns, the impossibility of safe storage of nuclear waste and so forth, but I’ve also been aware in recent years of new safer types of fuel rods, cooling systems and the like, without having really focused on these developments. So now’s the time to do so.

But first I’m going to focus on the nuclear power industry’s troubled past, which will help to understand the passion of those opposed to it.

No doubt there have been a number of incidents and close things associated with the industry, but the general public are mostly aware of three disturbing events, Three Mile Island (1979), Chernobyl (1986), and Fukushima (2011). I won’t go into too much detail about these, as you’ll find plenty of information about them here, here and here, and in the links attached to those sites, but here’s a very brief summary.

The Three Mile Island accident was the result of a number of system and human failures, which certainly raised questions about complex systems and the possibility/inevitability of an accident occurring, but the real controversy was about the effects, or after-effects, of the partial melt-down. It’s inevitable that anti-nuclear activists would play up the impact, and nuclear proponents would play them down, but the evidence does suggest that, for all the publicity the accident garnered, the effects on the health of workers and residents of the area were minor and, where strongly claimed, largely unsubstantiated. Anti-nuclear activists have claimed widespread death and disease among animals and livestock in the region, while the local (Pennsylvania) Department of Agriculture denied any link. Research is still ongoing, but with so much heat being generated it’s hard to make sense of any light. One thing is certain, though. When an accident does happen, the costs of a clean-up, one that will satisfy everyone, including many of the nay-sayers, is astronomical.

Two reactors were built at the Three Mile Island site in 1974, and they were state-of-the art at the time. The second reactor, TMI-2, was destroyed by the accident, but TMI-1 is still functioning, and ‘remains one of the best-performing units in USA’, according to the World Nuclear Association, which, unsurprisingly, claims that ‘there were no injuries or adverse health effects from the accident’.

A much more serious accident occurred at Chernobyl in the Ukraine, then part of the Soviet Union. It has received a level 7 classification on the International Nuclear Event Scale, the highest possible classification (Fukushima is the only other accident with this classification; Three Mile Island was classified level 5). Thirty-one people died as a direct result, and long-term radiation effects are still under investigation. The figures on cancer-related deaths are enormously varied, not necessarily due to ideological thinking, but due to different methodologies employed by different agencies in different studies. The difficulties in distinguishing the thousands of cancers resulting from the radiation and the millions of cancers suffered by people in the region over the 20 years since the accident can hardly be underestimated. Most analysts agree, however that the human death toll is well into the thousands.

The Chernobyl disaster is notorious, of course, for the response of the Soviet government. No announcement was made to the general public until two days afterwards. When it came, it was as brief as possible. Workers and emergency services personnel who attempted to extinguish the fire were exposed to very high (that’s to say fatal) levels of radiation. Others involved in the massive clean-up were also heavily exposed. The cost of the clean-up, and of building a new containment structure (the largest civil engineering task in history) amounted to some 18 billion roubles. A half a million workers were involved.

The Fukushima disaster was caused by a tsunami triggered by a 9 magnitude earthquake, and the destruction caused (a meltdown of 3 of 6 of the plant’s reactors and the consequent release of radioactive material) was complicated by the damage from the tsunami itself. It was a disaster waiting to happen, for a number of reasons, the most obvious of which was the location of the reactors in the Pacific Rim, the most active seismic area on the planet. Some of the older reactors were not designed to withstand more than magnitude 7 or 8 quakes, but the most significant design failure, as it turned out, was a gross under-estimate of the height required for the sea-wall, the fundamental protection against tsunamis. To read about the levels of complacency, the unheeded warnings, the degree of ‘regulatory capture’ (where the regulators are mostly superannuated nuclear industry heavyweights with vested interests in downplaying problems and overlooking failures) and the outright corruption within and between TEPCO (the Tokyo Electric Power Company) and government, is to be alerted to a whole new perspective on human folly. It is also to be convinced that, if the industry is to have any future whatsoever, tight regulation, sensible, scientific and long-term decision-making, and complete openness to scrutiny by the residents of the area, consumers and the general public must be paramount.

Though there’s ongoing debate about the number of fatalities and injuries caused by the nuclear power industry, that number is lower than the numbers (also hotly debated of course) caused by other major energy-generating industries. Commercial nuclear power plants were first built in the early seventies and 31 countries have taken up the technology. There are now more than 400 operational reactors worldwide. The Fukushima disaster has naturally dampened enthusiasm for the technology; Germany has decided to close all its reactors by 2020, and Italy has banned nuclear power outright. However, countries such as China, whose government is rather more shielded against public opinion, are continuing apace – building almost half of the 68 reactors under construction worldwide as of 2012-13.

It’s probably fair to say that Fukushima and Chernobyl represent two outliers in terms of operating nuclear power plants, both in terms of accident prevention and crisis management, and the upside of these disasters is the many lessons learned. I presume modern reactors are built very differently from those of the seventies, So I’m interested to find out what those differences are and what ongoing innovations, if any, will make nuclear fission a safer and more viable clean energy option for the future. That’ll mean going into some technical detail, for my education’s sake, into how this energy-generating process works. So that’ll be next up, in part 2 of this series.