So this is it, the last required blog for my class.
Though the mandatory three posts a week have sometimes been a major hassle, especially when trying to fit it around working for senior design deadlines, overall I've really enjoyed writing this blog. If even one person has stumbled across this blog (that wasn't one of my classmates) and managed to learn something about nuclear power plants or the nuclear industry, then I'll call it a success. And I like to be successful, so I'm going to assume that it's true. Boom, mission accomplished.
This blog has also lead to me learning a few things about my industry and the power industry as a whole. A big thank you to my classmates for writing interesting blogs that inspired new topics for me, and an especially big thank you for the blogs that were easy to comment on and for leaving comments on my blogs I could reply to; kept those mandatory comment assignments pretty straightforward.
This isn't me signing off. There's still points to be milked from this thing with a bonus blog or eight. But don't let my cynicism fool you: I have enjoyed writing this blog and reading my peers', and it was certainly a unique approach to the class compared to the old, often stale, but effective class methods of the rest of my college experience.
I guess the point that I'm trying to make is: of all the things for school I've done, this is one of them.
Mar 25, 2016
Mar 23, 2016
Other Reactor Designs Part 2: CANDU in Detail
I ended the last part with an introduction to the Canadian Deuterium Uranium (CANDU) reactor design, a heavy-water moderated and naturally-enriched-uranium burning reactor. These two attributes alone make it a very different reactor from a typical light water reactor (LWR), but it has a few more features that make it a very distinct style.
- The natural uranium, since it isn't enriched, can undergo very little burnup before it loses the ability to be used as an effective fuel in the reactor.
- Its fuel assemblies are small hexagonal bundles that are stacked (well, lined up) with each other through assembly vessels, or "callandria", running through the large resevoir that makes up the heavy water moderator region. These callandria are pressurized at PWR operating temperatures, while the moderator region around them is not.
- The callandria are oriented horizontally, with control rods running both parallel and perpendicular. This along with the fuel bundles allows for "on-power" refueling, or the changing of fuel in the reactor while the reactor is operational. This makes up for the low burnup by having a very short fuel cycle, with automated systems removing the oldest fuel bundles at the end of the callandria and placing fresh, new bundles at the start.
- On power refueling causes somewhat of a non-proliferation concern, however. Taking nuclear fuel fresh out of the core will have a higher percentage of material ideal for dirty bombs or other dangerous practices.
- Unlike American LWRs that insist on a negative void coefficient (one of many terms to describe whether or not the reactor will shut itself down if things start to go very wrong), a CANDU generally has a slightly positive void coefficient. This is compensated for by additional safety systems built into the core and surrounding components.
While a lot of what the CANDU does is cool, the net result is a reactor that tends to cost a lot more than a typical LWR, while not producing as much power. This is, of course, less than ideal. However, the CANDU was born out of a perceived necessity by the Canadian government, as they believed they did not possess the means (at the time) to enrich uranium to the level needed to operate a typical LWR. As the ability to enrich has improved for them, they have managed to refit many CANDU facilities to run at higher enrichments, increasing lifetime and power level of the reactor while also making them more cost effective. In addition, the Advanced CANDU Reactor (ACR1000), the next generation of pressurized heavy water reactors, looks very promising.
Mar 21, 2016
Other Reactor Designs Part 1: Heavy-Water Moderated
I spent the entirety of this last weekend on our senior design project so I decided I may as well write a blog on it since it's currently difficult to think about anything else. So far for this blog, any time I've discussed a reactor it's been a light water reactor (LWR), or one that is moderated and cooled by normal, everyday water. But there are so many more reactor designs that the nuclear community have built or at least theorized in the quest for higher thermal efficiency, cost effectiveness, and filling different niches.
Relevant to my group's senior design project are reactors that are moderated by heavy water, or water molecules that have deuterium (an atom with a nucleus of one proton and one neutron) instead of hydrogen bound to their oxygen. A "typical" LWR uses its coolant as its moderator; that is, the flux of neutrons generated by the fuel is slowed by the moderator (which we want), and also reduced through absorption into the water molecules (which we don't necessarily want). Any neutron absorbed by the water is one that cannot be used to cause a fission and produce fuel. So, a higher enrichment of fuel is required in order to produce enough neutrons to compensate for those that are lost to absorption.
However, deuterium has a much lower cross section for absorption compared to hydrogen, as the deuteron already has an extra neutron from "naturally occurring" hydrogen and really doesn't want another one. So for heavy water, two thirds of your atoms have much smaller cross sections, greatly reducing the neutron absorption in heavy water. This allows reactors to be operated with lower enrichments even all the way down to naturally enriched uranium, saving money and resources that would normally go into the difficult and expensive process of enriching the reactor's fuel.
This design was first put forward by the Canadian energy industry in the form of the Canadian Deuterium Uranium (CANDU) reactor design. It was created out of a perceived necessity by the Canadian government and energy industry, as they believed they did not have solid access to enriched uranium, or the infrastructure to produce their own. The end result is a reactor that is large and pricey, but runs on naturally enriched uranium.
Relevant to my group's senior design project are reactors that are moderated by heavy water, or water molecules that have deuterium (an atom with a nucleus of one proton and one neutron) instead of hydrogen bound to their oxygen. A "typical" LWR uses its coolant as its moderator; that is, the flux of neutrons generated by the fuel is slowed by the moderator (which we want), and also reduced through absorption into the water molecules (which we don't necessarily want). Any neutron absorbed by the water is one that cannot be used to cause a fission and produce fuel. So, a higher enrichment of fuel is required in order to produce enough neutrons to compensate for those that are lost to absorption.
However, deuterium has a much lower cross section for absorption compared to hydrogen, as the deuteron already has an extra neutron from "naturally occurring" hydrogen and really doesn't want another one. So for heavy water, two thirds of your atoms have much smaller cross sections, greatly reducing the neutron absorption in heavy water. This allows reactors to be operated with lower enrichments even all the way down to naturally enriched uranium, saving money and resources that would normally go into the difficult and expensive process of enriching the reactor's fuel.
This design was first put forward by the Canadian energy industry in the form of the Canadian Deuterium Uranium (CANDU) reactor design. It was created out of a perceived necessity by the Canadian government and energy industry, as they believed they did not have solid access to enriched uranium, or the infrastructure to produce their own. The end result is a reactor that is large and pricey, but runs on naturally enriched uranium.
Mar 18, 2016
Advances in Nuclear: Load Following Power Plants
In my comparisons with nuclear to coal and solar, I've described nuclear power plants as being used for the "base load" of the grid, meaning they provide the absolute minimum amount of power expected to be drawn by the grid. Obviously, the grid spends most of the day demanding more than this minimum level of power, and the power requirements can fluctuate across a large range throughout the day. These power fluctuations are covered by "load following" power plants, which means plants that can vary their power outputs easily to match the needs of the grid.
Traditionally, nuclear power plants have been ran as base load and load following plants have been natural gas plants. However, it has been brought to my attention that updates to nuclear power technology allows the possibility for load following operation. [1] Countries that have been a large percentage nuclear powered (like France and Germany) have developed control systems sensitive enough and fast enough to change the power level of the plant as the grid demands.
This is a huge step forward for the possibility for a country to be almost entirely nuclear powered (and proved to be a necessity for France which was 80%+ nuclear before they started shutting plants down for entirely political reasons). Though the technology is still years away from being as sensitive and effective as a gas power plant, the possibility for load following without fossil fuels is an area very deserving in further research.
[1] https://www.oecd-nea.org/nea-news/2011/29-2/nea-news-29-2-load-following-e.pdf
Traditionally, nuclear power plants have been ran as base load and load following plants have been natural gas plants. However, it has been brought to my attention that updates to nuclear power technology allows the possibility for load following operation. [1] Countries that have been a large percentage nuclear powered (like France and Germany) have developed control systems sensitive enough and fast enough to change the power level of the plant as the grid demands.
This is a huge step forward for the possibility for a country to be almost entirely nuclear powered (and proved to be a necessity for France which was 80%+ nuclear before they started shutting plants down for entirely political reasons). Though the technology is still years away from being as sensitive and effective as a gas power plant, the possibility for load following without fossil fuels is an area very deserving in further research.
[1] https://www.oecd-nea.org/nea-news/2011/29-2/nea-news-29-2-load-following-e.pdf
Mar 16, 2016
The Solar Comparison
So we've talked about how nuclear stacks up against the power-house (pun intended) of coal, the two primary competitors for power grid load and surprisingly similar given their very different fuels.
But what about alternative energy? Specifically solar, which claims to be the future of base-load power? How does it stack up?
Let me start by saying that I love solar power. Having spent my whole life so far as a resident in Florida, many of the homes I've lived in have had solar panels on the roof, usually for heating a pool or assisting with the hot water heater to help save energy. A large portion of the world lives in the tropics or near deserts where long sunny days are a fact of life, and utilizing that sun to make our lives easier and cheaper just kinda hits you as an obviously good decision. So I want solar to work on a large scale, I would love for it to be economically viable and provide cheap, emission free energy for the whole world.
Unfortunately, it has yet to prove an ability to do so. So far the technology is limited to the point where economy of scale just doesn't work out. Take Nevada's Solar One, one of the most prominent solar facilities in America: it's exactly what the typical educated person imagines as a solar plant, a bunch of black photovoltaic panels that generate electric current from the sun's photons. The whole plant cost just shy of $300 million, which is a pretty reasonable cost for a power facility. But here's the catch: it generates a whopping 60 megawats [1], a tenth of what a typical small nuclear reactor does. That brings it to a capital cost of 5000 dollars per kilowatt, and as you may recall from a previous blog generally the highest capital cost of a nuclear reactor is 4000 dollars per kilowatt. Add on to that that the facility takes up 400 acres of otherwise untouched desert, and it really starts to fall short of what you might have expected or wanted.
That facility is aging, though. The "cutting edge" right now is the multiple solar facilities that add up to be California's Mojave Solar Project (MSP), the most recent of which went online in this last year. It includes classic solar plants like Nevada's, as well as the almost sci-fi facilities that use focused mirrors to heat molten salt, which is just plain cool. All of MSP's components together generate about 250 MW [2][3], which is the base-load for a small city, and much harder to scoff at. But the total cost so far is estimated around $1.2 billion, bringing the capital cost to 4800 dollars per kilowatt; still not viable, in an economic sense, against a nuclear reactor.
Like I said, I like solar, and I hope it continues to develop especially in the private or residential side of the technology where it makes the most economic sense. Unfortunately it just hasn't proven to be fully viable on the commercial scale. Progress is being made on that front, but it's being made very slowly. When it comes to base load power, in my biased opinion we should still be building more nuclear power plants to bridge the gap into something truly clean, safe, and renewable.
[1] http://energy.sandia.gov/energy/renewable-energy/solar-energy/
[2] http://powerfromthesun.net/Book/chapter10/chapter10.html
[3] http://clui.org/ludb/site/solar-two-experimental-solar-facility-site
But what about alternative energy? Specifically solar, which claims to be the future of base-load power? How does it stack up?
Let me start by saying that I love solar power. Having spent my whole life so far as a resident in Florida, many of the homes I've lived in have had solar panels on the roof, usually for heating a pool or assisting with the hot water heater to help save energy. A large portion of the world lives in the tropics or near deserts where long sunny days are a fact of life, and utilizing that sun to make our lives easier and cheaper just kinda hits you as an obviously good decision. So I want solar to work on a large scale, I would love for it to be economically viable and provide cheap, emission free energy for the whole world.
Unfortunately, it has yet to prove an ability to do so. So far the technology is limited to the point where economy of scale just doesn't work out. Take Nevada's Solar One, one of the most prominent solar facilities in America: it's exactly what the typical educated person imagines as a solar plant, a bunch of black photovoltaic panels that generate electric current from the sun's photons. The whole plant cost just shy of $300 million, which is a pretty reasonable cost for a power facility. But here's the catch: it generates a whopping 60 megawats [1], a tenth of what a typical small nuclear reactor does. That brings it to a capital cost of 5000 dollars per kilowatt, and as you may recall from a previous blog generally the highest capital cost of a nuclear reactor is 4000 dollars per kilowatt. Add on to that that the facility takes up 400 acres of otherwise untouched desert, and it really starts to fall short of what you might have expected or wanted.
That facility is aging, though. The "cutting edge" right now is the multiple solar facilities that add up to be California's Mojave Solar Project (MSP), the most recent of which went online in this last year. It includes classic solar plants like Nevada's, as well as the almost sci-fi facilities that use focused mirrors to heat molten salt, which is just plain cool. All of MSP's components together generate about 250 MW [2][3], which is the base-load for a small city, and much harder to scoff at. But the total cost so far is estimated around $1.2 billion, bringing the capital cost to 4800 dollars per kilowatt; still not viable, in an economic sense, against a nuclear reactor.
Like I said, I like solar, and I hope it continues to develop especially in the private or residential side of the technology where it makes the most economic sense. Unfortunately it just hasn't proven to be fully viable on the commercial scale. Progress is being made on that front, but it's being made very slowly. When it comes to base load power, in my biased opinion we should still be building more nuclear power plants to bridge the gap into something truly clean, safe, and renewable.
[1] http://energy.sandia.gov/energy/renewable-energy/solar-energy/
[2] http://powerfromthesun.net/Book/chapter10/chapter10.html
[3] http://clui.org/ludb/site/solar-two-experimental-solar-facility-site
Mar 14, 2016
The Coal Comparison Part 2
Last time we compared capital costs of coal and nuclear power plants (in which coal was the obvious victor) and fuel costs (where uranium's insane energy density relative to coal pulls nuclear well ahead). An additional note I forgot to make on fuel last time is thermal efficiency: coal power plants are capable of superheating the steam coming out of their boilers, and as such increase their thermal efficiency (the percentage of heat generated that actually turns into electric power). While nuclear fuel is up to the task itself, the special cladding and other materials needed to make a nuclear core produce power safely cannot withstand the heat needed to superheat steam, so the maximum thermal efficiency of a plant is limited. Even so, the net result is still generally much cheaper power from nuclear power.
Safety and Health
We'll continue our comparison with a discussion of safety between our two competing power sources. Everyone knows to be (or at least thinks they should be) worried about radiation from nuclear power plants. The not-so-fun fact that most people don't know is: coal power plants actually release more radiation to the atmosphere than nuclear. [1] As we discussed with atmospheric dispersion of radionuclides, when operating normally nuclear power plants release virtually in terms of radiation to the environment around them. Coal already releases nasty amounts of greenhouse gasses to the atmosphere, and mixed in with these gases are radioactive versions of carbon--harmless when sitting inside a lump of coal, but much more concerning when you breath it in to your very vunlerable lungs. The net increase in radiation is still negligible compared to your background exposure, but it is higher than what you receive from a nuclear plant.
An additional area of safety you may have never considered is how the fuel is acquired. The mining of nuclear material is certainly not an inherently safe operation, and there has been some concern in regards to radon exposure to uranium miners. [2] The net risk to human life, however, is nothing compared to coal mining. The role of coal miner is historically one of the most dangerous occupations one can have, mainly because unlike uranium, coal and its mining byproducts are inherently explosive. In America alone, the demand for coal has cost the lives of over 100,000 miners in the last century [3]. Combine with this the higher rate of catastrophic (and potentially lethal) failure in a coal boiler over a nuclear core [3], and nuclear doesn't look quite as concerning. Broken down into cold statistics, the expected deaths per unit power produced are about ten times higher for coal power than for nuclear.
Well that was kinda depressing to research and write. Hopefully I find something a little more uplifting to write about next time.
[1] http://www.scientificamerican.com/article/coal-ash-is-more-radioactive-than-nuclear-waste/
[2] http://www.theenergylibrary.com/node/11385
[3] http://www.tandfonline.com/doi/abs/10.1080/10807030802387556
Safety and Health
We'll continue our comparison with a discussion of safety between our two competing power sources. Everyone knows to be (or at least thinks they should be) worried about radiation from nuclear power plants. The not-so-fun fact that most people don't know is: coal power plants actually release more radiation to the atmosphere than nuclear. [1] As we discussed with atmospheric dispersion of radionuclides, when operating normally nuclear power plants release virtually in terms of radiation to the environment around them. Coal already releases nasty amounts of greenhouse gasses to the atmosphere, and mixed in with these gases are radioactive versions of carbon--harmless when sitting inside a lump of coal, but much more concerning when you breath it in to your very vunlerable lungs. The net increase in radiation is still negligible compared to your background exposure, but it is higher than what you receive from a nuclear plant.
An additional area of safety you may have never considered is how the fuel is acquired. The mining of nuclear material is certainly not an inherently safe operation, and there has been some concern in regards to radon exposure to uranium miners. [2] The net risk to human life, however, is nothing compared to coal mining. The role of coal miner is historically one of the most dangerous occupations one can have, mainly because unlike uranium, coal and its mining byproducts are inherently explosive. In America alone, the demand for coal has cost the lives of over 100,000 miners in the last century [3]. Combine with this the higher rate of catastrophic (and potentially lethal) failure in a coal boiler over a nuclear core [3], and nuclear doesn't look quite as concerning. Broken down into cold statistics, the expected deaths per unit power produced are about ten times higher for coal power than for nuclear.
Well that was kinda depressing to research and write. Hopefully I find something a little more uplifting to write about next time.
[1] http://www.scientificamerican.com/article/coal-ash-is-more-radioactive-than-nuclear-waste/
[2] http://www.theenergylibrary.com/node/11385
[3] http://www.tandfonline.com/doi/abs/10.1080/10807030802387556
Mar 11, 2016
The Coal Comparison
As promised, here's a more detailed comparison between the two competitors for the electric grid's base load. We'll break it down into a few key categories.
Capital Costs and Construction Time
The "capital costs" of a power plant are the net total costs of licensing, construction, and any other one-time purchases associated with the creation of the plant, but not its operation. To aid in objective comparison between power plants of different power levels, capital cost is usually given in units of dollars per kilowatt ($/kW).
We've been building and using coal plants for a long time now, at least compared to nuclear. The process is pretty streamlined, the components cheap, and the licensing relatively easy. The end result is a usual capital cost around 1800-2000 $/kW. [1]
Nuclear, on the other hand, doesn't look as good. A long and expensive licensing process, components that are both made from expensive materials and expensive to machine, and a long construction time all lead to capital costs around double those expected from coal (3500-4000 $/kW) [2]. So as much as it pains me, nuclear definitely comes in second for this topic.
Fuel and Operating Costs
Nuclear very quickly makes up for its expensive start when you consider its costs once it starts operating. An easy comparison to make is in the fuel each plant uses, and its energy density. "Energy density" is the amount of energy released by a full combustion/fission reaction in a kilogram of fuel.
The average average density of coal is a reasonable 8 kilowatt-hours (kWh) per kilogram. The average energy density of uranium-235 is over three million times greater, at 24 gigawatt-hours (GWh) per kilogram. To produce the same amount of power in a coal plant as a nuclear plant, trainloads of coal are required to match the energy production of a lump of uranium. [3]
Combine this with the fact that uranium is surprisingly cheap, and nuclear plants produce much cheaper power than coal.
Part two will come later this weekend, and cover health and environmental effects of the two.
[1] http://schlissel-technical.com/docs/reports_35.pdf
[2] http://www.world-nuclear.org/information-library/economic-aspects/economics-of-nuclear-power.aspx
[3] https://www.euronuclear.org/info/encyclopedia/f/fuelcomparison.htm
Capital Costs and Construction Time
The "capital costs" of a power plant are the net total costs of licensing, construction, and any other one-time purchases associated with the creation of the plant, but not its operation. To aid in objective comparison between power plants of different power levels, capital cost is usually given in units of dollars per kilowatt ($/kW).
We've been building and using coal plants for a long time now, at least compared to nuclear. The process is pretty streamlined, the components cheap, and the licensing relatively easy. The end result is a usual capital cost around 1800-2000 $/kW. [1]
Nuclear, on the other hand, doesn't look as good. A long and expensive licensing process, components that are both made from expensive materials and expensive to machine, and a long construction time all lead to capital costs around double those expected from coal (3500-4000 $/kW) [2]. So as much as it pains me, nuclear definitely comes in second for this topic.
Fuel and Operating Costs
Nuclear very quickly makes up for its expensive start when you consider its costs once it starts operating. An easy comparison to make is in the fuel each plant uses, and its energy density. "Energy density" is the amount of energy released by a full combustion/fission reaction in a kilogram of fuel.
The average average density of coal is a reasonable 8 kilowatt-hours (kWh) per kilogram. The average energy density of uranium-235 is over three million times greater, at 24 gigawatt-hours (GWh) per kilogram. To produce the same amount of power in a coal plant as a nuclear plant, trainloads of coal are required to match the energy production of a lump of uranium. [3]
Combine this with the fact that uranium is surprisingly cheap, and nuclear plants produce much cheaper power than coal.
Part two will come later this weekend, and cover health and environmental effects of the two.
[1] http://schlissel-technical.com/docs/reports_35.pdf
[2] http://www.world-nuclear.org/information-library/economic-aspects/economics-of-nuclear-power.aspx
[3] https://www.euronuclear.org/info/encyclopedia/f/fuelcomparison.htm
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