Saturday, February 4, 2012

BRC on America's Nuclear Future - Part I

I'm still reading the 180 page report issued recently by the Blue Ribbon Commission. I urge everyone to read this report as well. You can get your copy by going to Final Report January 2012 . .


Front End of Cycle: Mining, Milling, Conversion, Enrichment, Fuel Fabrication > Nuclear Reactor

The nuclear fuel cycle begins with extraction of uranium from ores or other natural sources. Uranium provides the basic "fuel" for nearly all nuclear reactors. In its natural state mined uranium is only weakly radioactive, which means it can be handled without need for radioactive shielding.

Before natural uranium can be used in a commercial reactor it must be purified and enriched to produce the amount of fissionable U-235 present in the fuel. Enriched uranium oxide is cast into hard pellets and stacked inside long metal tubes to form fuel rods. Fuel rods are then bundled into fuel assemblies that are 12 to 14 feet long.

Inside the reactor the enriched uranium sustains a series of controlled nuclear reactions that collectively liberate substantial quantities of energy. This energy is converted to steam and used to drive turbines that generate electricity.

Meanwhile the fission process inside the reactor creates new elements or "fission products", these heavier products are know collectively as "transuranics" - which may take part in further reactions, the most important is plutonium-239.

After the natural, low radioactive level of uranium goes through the fission process, the radioactivity level of nuclear fuel increases to a high and dangerous radioactive state.

Back End of Cycle: Nuclear Reactor > Interim Storage, Spent Fuel, Reprocessing, Final Disposition 

Nuclear fuel will remain in a commercial power reactor for about four to six years, it then can no longer efficiently produce energy and is considered used or spent. Spent fuel that has been removed from a reactor is thermally hot and emits a great deal of radiation. Upon removal from the reactor each spent fuel assembly emits enough radiation to deliver a fatal dose in minutes to someone in the vicinity that is not adequately shielded.

Spent fuel is transferred to a deep, water-filled pool where it is placed on a rack to cool and to protect workers from radiation. Typically the spent fuel is kept in the pool for about five years. There is approximately 50,000 metric tons of commercial spent fuel currently stored in pools in the United States.

After the spent fuel has cooled sufficiently in these pools it can be moved to a Dry Cask storage system. This storage takes many forms but generally consists of a fuel storage grid placed within a steel inner container and a concrete and steel outer container. The amount of commercial spent fuel stored in dry casks in the United States is about 15,000 metric tons.

Because of the residual hazard of spent fuel, transportation of spent fuel must be shipped in containers or casks that shield and contain the radioactivity and dissipate the heat. In the United States spent fuel has typically been transported via truck or rail.

Reprocessing or recycling - fuel considered 'spent' still contains unused uranium and other re-usable elements, mostly plutonium. Current reprocessing technologies separate the spent fuel into three components: uranium, plutonium and waste. The plutonium is mixed with uranium and fabricated into new fuel; because this new fuel is more difficult to use than freshly mined uranium, it has only been done to a limited extent. The fission products and other waste elements are packaged into a new form for disposal.

Disposal - Regardless of whether spent fuel is reprocessed or directly disposed of, every foreseeable approach to the nuclear fuel cycle still requires a means of disposal that assures the very long-term isolation of radioactive wastes from the environment. Many nations, including those engaged in reprocessing, are working to develop disposal facilities for spent fuel and/or HLW (high level waste), but no such facility has yet been put into operation.

Definition of terms: The term "disposal" is understood to mean permanent disposal; the term "storage" is understood to mean storage for an interim period prior to disposal or other disposition.

Obvious facts: High-level wastes and spent fuel exist and will continue to accumulate so long as nuclear reactors continue to operate. An essential component of a nuclear waste management system is that a very long-term isolation from the environment is the only responsible way nuclear waste can be managed.

Source for the above information comes solely from the Blue Ribbon Commission on America's Nuclear Future: Report to the Secretary of Energy - January 2012

Upcoming Part Two will cover the historical background of Nuclear Waste Management in the United States

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