Future Nuclear Power and the Thermal Storage Option

Jun 25 - Syrian Arab News Agency

India and China have access to the ores that contain thorium hence their growing interest in future thorium based nuclear power generation. Growing concern about storage of spent uranium-based nuclear fuel rods has prompted the Gates Foundation to fund research into making future productive use of the remaining energy. While electrical power consumption may remain constant throughout the year in some nations, other nations and power markets experience seasonal peak power demands. South Africa and Quebec, Canada experience peak demand for electric power during winter, the result of customers operation electrically powered interior heating technologies. The Middle East , regions of Western Europe as well as regions across North America experience peak demand for electric power during the hot summer months, mainly to operate air conditioning systems. To assure reliable and economic operation of their technology, power companies choose to operate nuclear power stations at steady output.

North America ' largest power utility, Ontario Hydro pays outside power companies to take delivery of their winter excess nuclear generating capacity, having found it cheaper that fluctuating nuclear output and covering repair costs that result from thermal stresses causing components to malfunction. Across the river from Ontario , the State of Michigan is home to the 2200MW Ludington pumped hydroelectric storage installation that can take delivery of an outside power utility's excess overnight output. It operates at 75% to 81% recovery efficiency while receiving power from installations that operate at 30% to 35% efficiency.

While it may appear feasible to recharge the batteries of battery-electric transportation vehicles during the overnight off-peak period, electro-chemical batteries generate and dissipate heat during both the recharge cycle and discharge cycle. Depending on the technology, storage efficiency below 75% efficiency may be the norm, with hydrogen fuel cell technology recording a very low efficiency when sourcing electric power from a thermal power station. While the power station operates at 40% efficiency, electrolysis operates at 70% efficiency while the fuel cell can convert hydrogen to electric power at 50% efficiency, yielding an overall efficiency of 14% from point of generation.

Seasonal Stationary Power :

A research team at Massachusetts Institute of Technology explored the possibility of seasonal, high-temperature geothermal storage of energy. Seasonal low-temperature geothermal energy storage is well-proven and involves deep level, water-saturated porous rock being heated during the summer months, usually using concentrated solar thermal energy. At some locations, it is heated to just below the boiling point of water at atmospheric pressure and applied to provide interior heating to building during the frigid winter months. At several locations across the Middle East , seawater is pumped deep underground to displace natural gas and oil.

Extensive concentrations of seawater saturated porous rock provide a basis for several types of seasonal geothermal storage. During winter, air temperature in the region can drop to below 15°C, allowing for cooling of a seawater saturated region of porous rock. During summer, the cooled deposit may serve as the heat sink for district cooling installations or serve as the heat sink for a thermal power station. During a seasonal winter off-peak period for power stations, nuclear thermal power may be pumped into high-temperature seasonal storage for the purpose of summer time generation, with energy return operating at over 90% efficiency.

Solar Thermal Storage:

The solar thermal power industry has developed heat-of-fusion overnight thermal storage technology capable of delivering several gigawatt-hours of electrical power after sunset. While electro-chemical batteries offer a usable life expectancy of between 300 and 2,000-deep cycle recharges and discharges, thermal storage technology offers greatly extended usable life expectancies measured in decades and beyond. The same thermal energy storage technology is compatible with nuclear power conversion, high-temperature seasonal geothermal energy storage and likely compatible with future radiation free nuclear and fusion power conversion. Given earlier precedents, there may be scope to adapt thermal energy storage for transportation propulsion.

At the present time, several nuclear power stations are located next to large bodies of water such as rivers, inland lakes and the oceanic coast. There may be scope at some of these locations and at future coastal nuclear power stations, to introduce seasonal high-temperature geothermal energy storage, perhaps involving a cubic mile of deep level rock heated to a level to allow for future seasonal production of superheated steam. The extent of the underground storage system could allow for sustained year-round high temperature that could in turn allow for thermal recharge of smaller scale technologies.

Smaller-Scale Thermal Storage:

When applied to large-scale mobile technologies, heat-of-fusion thermal storage technology offers the potential to be cost-competitive and efficiency competitive against electro-chemical battery and hydrogen fuel cell technologies that source their recharge energy from a thermoelectric energy conversion. Mobile thermal storage technology can recharge from seasonal high-temperature geothermal storage or directly from thermal power stations, should some power utilities be willing to negotiate agreements with potential customers seeking to purchase thermal energy. During the latter 19th century, the United States navy operated a few submarines that stored short-distance propulsive energy in insulate high-pressure tanks of saturated steam.

The railways used the same energy storage technology in shunting yards where industrial steam was available. At the present day, the international maritime transportation sector consumes more energy than the electrical generating output of majority of nations. Gaining access to modern thermal storage technology could indirectly provide coastal ships and tugboats with indirect access to nuclear power, potentially reducing expenditures on hydrocarbon fuels at locations where oil prices may be overly high. Unlike electrochemical batteries that will require frequent replacement, thermal storage technology would offer decades of service at competitive efficiency and at competitive cost.

Heat of Decomposition:

When carefully heated, calcium carbonate decomposes into carbon dioxide and calcium oxide. When combined under pressure, the heat of reaction can exceed 2,000KJ/Kg and raise superheated steam. In mobile application, the calcium carbonate would be decomposed using stored energy from high-temperature geothermal storage while the vehicle would be recharged with compressed carbon dioxide and calcium oxide carried in separate tanks. Some 20-years ago, researchers at several universities in Japan undertook extensive research into heat-of-decomposition and heat-of-formation thermal storage. Modern developments in seasonal grid-scale thermal energy storage could provide an application for calcium carbonate energy storage.

Efficiency Comparison:

Research from MIT suggests that high-temperature seasonal geothermal energy storage could achieve an efficiency of 95%. If a thermal power station produced power at 40% efficiency, a companion thermoelectric technology sourcing stored thermal energy could theoretically achieve an efficiency of 35% to 38%, while thermal energy transferred from underground storage to mobile thermal storage could achieve an efficiency of 25% to 32%. By comparison, a hydrogen fuel cell installation sourcing thermally generated electricity would achieve an efficiency of 12% to 14%, while electrochemical batteries would deliver 0.7 to 0.8 x 40% = 28% to 32% efficiency from the power station.

Mobile Application:

A mixture of 20% lithium fluoride and 80% lithium hydroxide (measured by molecular weight) can store over 1100KJ/Kg at 465°C while a mixture that replaces the lithium hydroxide with a mixture of several alkaline fluoride compounds can store over 600KJ/Kg at comparable temperature. In a supersize of tugboat, most of that energy would convert liquid water into steam, allowing a small amount of higher-temperature thermal storage held in specially insulated containers could further raise superheat temperature to the super-critical range to achieve higher efficiency. Alternatively, calcium carbonate would offer an optional thermal storage technology.

The advantage of extent-of-scale allows maritime to use thermal storage technology. Modern coastal and short-distance maritime transport involve a tug pushing and navigating a barge. A tug of 80,000-tons holding 50,000-tons of thermal storage compound in insulated tanks would sail in the hydraulic shadow of a barge of 200,000-tons deadweight and provide 300 to 500-miles of propulsion at 20,000-Hp output. A rechargeable heat-of-formation thermal system could generate higher propulsive power and/or extend operating range to connect several large Asian ports located in Japan , South Korea and China , possibly also ports located around the Baltic and Mediterranean Seas.

Conclusions:

Developments in high-temperature thermal energy storage aimed at the power grid could offer downstream and spin-off applications in the large-scale transportation sector. While the maritime sector would be the most likely candidate for thermal storage technology, there may be some possible application in short-distance railway propulsion. Thermal energy storage technology is competitive in terms of storage efficiency a

http://www.energycentral.com/functional/news/news_detail.cfm?did=36595144