The final WMEAC Energy Forum on Wednesday, April 6, hosted by Muskegon Community College, left us once more with an abundance of unanswered questions. These questions will be addressed here and over the next several days in subsequent posts. Thanks for your interest!
The following questions were highly technical in nature, so we outsourced them to the experts. Follow the links for more info!
Research gathered by Madelyn VanEck
1. What is a Pebble Reactor? Is it safe? Where is it being developed?
The Pebble Bed Modular Reactor (PBMR) is a steel pressure vessel, which holds enriched uranium dioxide fuel encapsulated in graphite spheres. The system is cooled with helium and heat is converted into electricity through a turbine.
This source of energy was established in 1999 in response to the high capital costs a coal-fired power station requires. Environmentally, the PBMR greatly diminishes greenhouse gas emissions since its nuclear power generation produces no carbon dioxide, smoke or any other gases. Compared with the huge atmospheric emissions from fossil-fuel energy, nuclear wastes exist in small, highly manageable amounts that can be stored without harm to people or the environment. One kilogram of uranium in the PBMR fuel has a greater energy output than 430 tons of the best coal with an ash content (waste) of up to 40 percent. A large coal-fired power station uses about 2 200 trainloads of coal per year (six a day), while only 2 truckloads of fuel per week will be required for 24 PBMR nuclear power stations of equivalent capacity. For the PBMR demonstration unit at Koeberg, 10 truckloads will be needed for the initial load, and only 4 truckloads per year for the replacement of spent fuel. The PBMR has a simple design basis, with inherent safety features that require no human intervention, and which cannot be bypassed or rendered ineffective in any way. If a fault occurs during reactor operations, the system, at worst, will shut down and merely dissipate heat on a decreasing curve without any core failure or release of radioactivity to the environment. The PBMR team is currently based in South Africa. The South African project is on schedule to be the first commercial scale High Temperature Reactor (HTR) in the power generation field.
(All information is sourced from PBMR Limited. Additional information can be found at http://www.pbmr.co.za/index.asp?Content=129.)
2. How long will landfills produce gas?
The main gases produced by a landfill site are methane and carbon dioxide. Methane is a gas that can be burned easily. In fact, it is the main component of natural gas. If a landfill is covered after use, this gas will slowly seep through the earth covering and dissipate into the atmosphere, causing a long-term source of pollution and possible irritation for the local population. Until the landfill site has settled and the gas production has died down there is no way of reclaiming the land for building purposes, although the planting of trees and grass is possible in the interim.
The production of gas will probably continue for around 20 to 30 years in many cases from a landfill site, with a gradual reduction after about 10 years. Such figures will vary naturally, depending on the composition of the waste and the temperature in the area. A covered landfill will generally tend to anaerobic decomposition, which is usually slower, since it develops less heat. This means that mostly methane will be produced. A large landfill with a high content of organic waste will probably produce methane for over fifty years after sealing, but the useful economic life of the supply for industrial purposes is more like fifteen years. Constant monitoring with a landfill gas analyzer will ensure that the quality and availability of the gas is known at all times and the processes can be planned or adjusted accordingly. After the fifteen years, when production of biogas has slowed, there is still the option of adding the gas to the existing gas supply system, providing there is a pipeline in the region. If the gas has been used for on-site electricity production (a common choice), there will be no real option, other than to move site and flare the gas in the future. Small-scale bottling may be feasible, but no other industrial use will be possible.
(All information is sourced from this site: http://www.habmigern2003.info/biogas/Landfill-sites.html, where additional information can be found).