Nuclear Power - Blog Posts
Dome City Blog 3 - Energy production in the city
In today's blog I plan to talk about energy production and use within a Dome City.
In general, residents of cities use less energy per capita, then people in rural areas. Some reasons for this are:
Distances travelled can be less,
Mass transportation systems can work well,
Shared walls in housing lead to lower heating requirements,
If energy sources are located in the city then combined heat and power can be used, and
Less resources are used to provide infrastructure for high density populations compared to low density ones.
A Dome City should have nearby power resources large enough to cover the needs of the population for electricity, heating, cooling and local transport within the city. Transport away from the city would most probably provided in standard cars and trucks powered by gasoline and diesel.
I would propose that the Dome City has a electricity power station sited just beside it. This power station would be located close enough to the Dome City to allow the waste heat, which arises from electricity production, to be used to provide hot water, heating and if required, cooling, to the city. This is known as combined heat and power (CHP) or as cogeneration. When a Dome City is sited in a tropical location then a "trigeneration" systems which includes refrigeration could be provided. The typical efficiency of thermal power plants for electricity is 30% to 40%. This waste heat represents a significant resource. District heating would be feature of the Dome City. This heat supplied to residents and business would form another source of income for the city.
My preferred method of dealing with electricity production would be with Nuclear Power. Nuclear Power is a low-carbon form of electricity production that is not so climate dependent compared to wind or solar. Furthermore, while wind and solar can be excellent sources of low-carbon electricity at the right locations, these forms of energy production are intermittent. This intermittentcy requires back up power sources to cover the times when these renewable sources cannot provide power.
There are proposals for new smaller reactors known as Small Modular Reactors (SMRs). By definition these reactors have electricity outputs of less than 300 MWe (Megawatts electrical). The suggested size of these reactors varies from 2 MWe for the UPower proposal to 130 MWe for the B&W MPower proposal. The system that I would most want to see would be 3 number NuScale 45 MWe reactors to provide electricity and heat to the city. A combined output of 135 MWe would generally provide more power than the city would require. I would estimate that the city will consume around 100MWe. However, the additional supply could be used to entice power hungry industries to move to the city. Some energy intensive industries are data centres or heavy manufacturing. Alternatively, the additional supply above the needs of the city would be a useful source of income for the city.
The NuScale reactors have a refueling cycle of around 2 years. Refueling would be staggered such that no more than one reactor is off line at any one time. In the UK, the city should be connected to the National Grid and any shortfall in power during a refueling shut-down could be supplied from the grid.
The use of 3 number SMR's has the advantage of "right-sizing" the plant to the population of the Dome City. The Dome City will take several years to build. Once the lower levels have been constructed I would expect that people would begin to move in. However, to reach the full population of around 100,000 people will take a number of years. Initially a single reactor would provided for power. The second and third would follow in later years when the population as grown large enough to justify the additional generating capacity.
I would very much hope that the power station for the city be owned and operated by the municipality.
I appreciate that there will be some reading this blog that are opposed to or afraid of nuclear power. In addition, the NuScale SMR is still in the design and licensing phase. We are still waiting for the first one to be constructed. An alternative to an SMR that would accomplish much the same ends is to have a Combined Cycle Gas Turbine (CCGT) power plant producing electrical power for the city.
This brief outline on the supply of electrical power and heat to a proposed Dome City has set out what I consider to be the "best" option. The compact nature of the Dome City would allow Combined Heat and Power to be feasible. The power station would have 2 sources of income. One comes from the Electricity produced and the second is the hot water and heat supplied. This would increase it's financial performance and make it easier to find financing for this aspect of Dome City development.
WELL begun; half done. That proverbor, rather, its obverseencapsulates the problems which have dogged civil nuclear power since its inception. Atomic energy is...
This article from The economist magazine talks about using Thorium as a Nuclear Fuel instead of Uranium. Thorium has several advantages over Uranium and in the view of the author of this article the most important is the relative resistance to proliferation compared to Uranium. I learned a few things from this article. The things I learned was that the US did build a few bombs out of U233 which is the fissile element formed from the fertile Thorium. I was always a bit unsure as to whether or not any bombs had been built. The article also confirms my prior understanding that U233 makes a poor nuclear bomb material because of the presence of small amounts of other radioactive isotopes that emit hard gamma radiation that messes up the other mechanisms required for a bomb.
Geo-engineering with Nuclear Power - Biorock
Geo-engineering to me means man as a species doing something to change the whole world. It is of interest because it has been suggested that perhaps we could use geo-engineering to either mitigate or delay the impacts of climate change caused by our proliferate use of fossil fuels. Proposals range from the simple such as painting all roofs white to reduce the earth's albedo. To the grandiose of deploying large mirrors in space to reduce the the amount of solar radiation reaching the earth.
In this blog I wish to suggest nuclear power be used to undertake geo-engineering. I would like to think the proposal contained in this blog is at the simpler end of the geo-engineering scale. The proposal is to use a nuclear reactor to produce electricity that in turn would power Biorock coral reef growth and restoration. From Wikipedia - "Biorock, also known as Seacrete or Seament, is a trademark name used by Biorock, Inc. to refer to the substance formed by electro-accumulation of minerals dissolved in seawater." The nuclear power plant (NPP) would be the source of the electricity in this process.
In this proposal, a NPP would be located near the coast and provide electricity for the electro-accumulation. The wikipedia article suggests "that one kilowatt hour of electricity will result in the accretion of about 0.4 to 1.5 kg (0.9 to 3.3 lb) of biorock, depending on various parameters such as depth, electrical current, salinity and water temperature." The main components of biorock are mainly calcium carbonate and magnesium hydroxide, again as provided by the Wikipedia article.
The chemical formula for limestone, a major component of biorock is Calcium Carbonate (CaC03). Therefore one mole of CaCO3 weights (40g + 12g + 3*16g) = 100g. I don't know the typical ratio of calcium carbonate and magnesium hydroxide in biorock but let me guess it is 50% calcium carbonate and 50% magnesium hydroxide. Assume that 1 kw-hr of electricity will produce 0.4 kg of biorock which converts to 0.2 kg Calcium Carbonate. Therefore each 0.2 kg of Calcium Carbonate contains 24g of Carbon (Chemical symbol "C").
Now assume we build a NuScale SMR which has a nominal output of 45Mw electric with 90% availabilty and typical carbon lifecycle output of 16g CO2 per kw-hr which converts to 4.4g Carbon per kw-hr (4.4g = 16g *12/44). Therefore each kw-hr of electricity can remove 19.6g (24g - 4.4g = 19.6g) of Carbon from seawater. The NuScale reactor produces 45,000 * 0.9 = 40,500 kw electric over the life of the reactor. Therefore each year a NuScale reactor would remove (40,500 * 24 * 365)kw-hr * 19.6 g per kw-hr = around 7,000,000,000 grams or 7 million kg or 7000 tonnes of carbon per year. It is also expected that the new or repaired reefs will sequester further Calcium Carbonate by biologic means as corals reestablish
Is this worth doing? It turns out that according to Tesco the average British person has a carbon footprint of 15 tonnes of CO2 (around 4 tonnes carbon per year). Therefore, 1 NuScale plant will offset the carbon emissions of 1750 people. On this basis this doesn't seem a very sensible idea. That seems to me to be a large effort to offset the emission of 1750 Brits or 0.003% of the population. This shows just how hard it is to remove carbon from the world once we have dumped it by burning fossil fuels.
On the other hand some low lying topical islands might consider this a reasonable idea if it were to make their communities less vulnerable to storm surges or rising sea levels. The NuScale reactor would allow the production of around, 40,500 * 24 * 365 * 0.4 / 1000 = 141,912 tonnes of biorock per year. The typical density of limestone is around 2.5 tonnes per cubic metre. I will assume that biorock has the same density. Therefore, the NuScale reactor would allow around 56,000 cubic metres of biorock to be produced in a year. If the biorock were grown in a strip 100m wide and 1m thick each year around 560m of coastline could be protected.
The above is a very simple calculation with simple assumptions. I recognise that the above has not considered the carbon input required for the metal used to make the initial structure. It is my understanding that the biorock process can continue for many years as the biorock accumulates. There are probably other carbon inputs that I have missed. On the other hand some of the assumptions above are conservative. Two conservative assumptions are the production of biorock per kw-hr and the availability factor of 0.9 for the NuScale reactor. Both numbers could well be larger.
The next time I write about geo-engineering with nuclear power I will look at biochar.
Have a nice day.
