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Clean Energy: What about Nuclear Power Plants?

Posted on April 24th, 2017 by in New Materials & Applications

Nuclear plant

Aerial View of Salem, NJ, Nuclear Power Plant (Source: Nuclear Street, https://nuclearstreet.com)

It has been nearly 75 years since the creation the world’s first artificial fission reactor by Enrico Fermi and his team.  Fermi’s reactor led to the development and construction of civilian nuclear power plants that supply electricity to the public in dozens of countries. The first commercial plant in the United States was opened on May 26, 1958.  From the beginning there has been controversy about nuclear generated power.  Radiation-related risks, terrorist attack and disposal (storage) of the radioactive waste are some of the main societal concerns.  Long lasting effects of radiation are paramount among the objections to nuclear power generation.  Memories of the accidents at Three-mile Island, Chernobyl and especially Fukushima Daiichi have elevated public fears of nuclear technologies and until early 2000’s brought construction of new plants to a halt.

Commercial Nuclear Power Plants

Nuclear power offers advantages over fossil fuels, including minor carbon footprint, low cost electricity and independence from the chaos of fossil fuel markets.  These are significant benefits considering demand for inexpensive electricity and critical necessity of reducing carbon dioxide emission.  Almost 100 reactors operate in 61 US nuclear power plants; the number of reactors for the world is 480 supplying over 10% of global electricity production.

Nuclear construction all but disappeared in the United States, particularly after the partial meltdown at Three Mile Island in Pennsylvania in 1979.  Concerns over climate change led to renewed interest in building new plants under the administration of George W. Bush. The Bush-era energy policy acts authorized $18.5 billion in loan guarantees, plus tax credits like those available for wind and solar. Often-conflicting forces – the desire for greater safety, and the need to contain costs — while bringing to life complex new designs have blocked or delayed nearly all of the projects planned in the United States (Source: D. Cardwell, The Murky Future of Nuclear Power in the United States, New York Times, www.NYT.com, Feb 18, 2017).

Existing plants have outlived their licensed lives.  Research efforts have focused on extending the life of nuclear power plants, which have been paid off during decades of operation and are thus highly profitable. Those efforts have paid off, the oldest commercial plants in the United States reached their 48th anniversary this year, and the average plant has operated for 30 years.  More than half of the nation’s 100 reactors have seen their initial operation licenses extended for an additional two decades.

Nuclear Reactors

A nuclear reactor produces and controls the release of energy from splitting the atoms of certain elements. In a reactor, the energy released is used as heat to make steam to generate electricity.  The principles of using nuclear power to produce electricity are the same for most types of reactor. The energy released from continuous fission of the atoms of the fuel is harnessed as heat in either a gas or water, and is used to produce steam. The steam is used to drive the turbines, which produce electricity as in fossil fuel plants (Source: Nuclear Power Reactors, World Nuclear Organization, www.world-nuclear.org, Feb 2017).

There are six main nuclear reactor types in use around the world. The various designs use different concentrations of uranium for fuel, different moderators to slow down the fission process, and different coolants to transfer heat.  The most common reactor type is the pressurized water reactor (PWR), representing 282 of the world’s 441 reactors operating in 2017 (Source: Nuclear Power Reactors, World Nuclear Organization, www.world-nuclear.org, Feb 2017).

Nuclear Reaction

An atom’s nucleus will spontaneously transform into a different nucleus if the final state nucleus is more stable and if the laws of physics allow the transformation. This process is usually accompanied by the release of ionizing radiation and is called “radio-active decay”.  Nuclei that exhibit this behavior are said to be “unstable” or “radioactive”.  Nuclear Fission energy is released when a very heavy atomic nucleus absorbs a neutron and splits into two lighter fragments. The energy release in this process is enormous. It is 10 million times greater than the energy released when one atom of carbon from a fossil fuel is burned.  As this process happens, heat is produced and converted into electricity via conventional steam and gas turbines like those at fossil fuel power plants.

Neutrons are effectively the trigger for nuclear power. Each time uranium splits in a nuclear reactor neutrons are shot out at high energies. These neutrons in turn cause more uranium splits, resulting in a self-sustaining reaction. But while causing these divides, the neutrons also relentlessly pummel the steel and other metals that enfold the nuclear reactor, known as the pressure vessel.  “There are millions of millions of millions of neutron impacts per year. At some point, it begins to impact the reactor vessel,” said Gary Was, the director of the University of Michigan’s Phoenix Energy Institute and an expert in aging materials. (Source: How Long Can a Nuclear Reactor Last? Scientific American: www.ScientificAmerican.com, Nov 2009).

Aging

Physical ageing issues include those affecting the reactor pressure vessel (including embrittlement, vessel head penetration cracking, and deterioration of internals) and the containment and the reactor building, cable deterioration, and ageing of transformers.  Conceptual and technological ageing issues include the inability to withstand a large aircraft impact, along with inadequate earthquake and flooding resistance.

Exposed to decades of radiation, some metal parts harden and grow brittle thus more likely to crack under stress.  One potential source of stress is the emergency core cooling system; if the system sensed a leak in the piping, it could start up and dump huge volumes of cold water into a reactor, keeping it at operating pressure but at a far lower temperature. Engineers say that could lead to a condition called pressurized thermal shock in which a reactor vessel would crack open.

Fortunately, nearly every part of a nuclear reactor can be replaced and retrofitted.  If the cost of modifications is relatively low, life-extended nuclear power plants can be highly profitable because the capital cost of the plant (making up most of the cost of a unit of nuclear-generated electricity) will already have been paid off, leaving only the operations and maintenance cost to-be-paid. Other advantages to the owner include the fact that the plant is a known quantity.

Very few nuclear reactors have been retired because they have reached the end of their licensed or designed lifetime. Much more probable life-determining factors are: the economics of the plant; the existence of national phase-out policies; serious and unexpected equipment failures; and, for older designs in particular, existence of design issues that make continued operation unacceptable. However, during the time since lifetime extension began to occur, the perception of the risk of granting a reactor a significantly longer life has increased. Permission for a reactor to operate for 60 years appears to be far from a guarantee that it will actually complete a 60-year life. A longer permitted lifetime has given utilities a reason to justify upgrades aimed at improving the economics of a plant (Source:  Lifetime extension of ageing nuclear power plants: Entering a new era of risk, Report commissioned by Greenpeace, www.out-of-age.eu, March 2014).

Future

What does the future look like considering the strong push to build nuclear power plants to reduce CO2 emissions, the pressure to build safer plants and the need to control cost?  An article in February 18, 2017, issue of New York Times describes the complex circumstances surrounding the building of nuclear power plants.  “A remarkable confluence of events is bringing that [renewed interest in early 2000’s] to an end, capped by Toshiba’s decision to take a $6 billion loss and pull Westinghouse, its American nuclear power subsidiary, out of the construction business.”   Among other reasons, in addition to safety considerations and cost, is the unexpected slow-down in demand for electricity. Natural gas prices have also tumbled, eroding nuclear power’s economic rationale.  Alternative-energy sources like wind and solar power have come into their own.” (Source: D. Cardwell, The Murky Future of Nuclear Power in the United States, New York Times, www.NYT.com, Feb 18, 2017)

The main stage for nuclear development will move overseas to places like China, Russia, India, Korea and a handful of countries in the Middle East, where Westinghouse will have to find partners to build its designs. In China, plants using earlier model reactors are moving toward completion. If they are successful, that may stir up more interest in the technology, and future installations may go more smoothly. “But Toshiba’s ambitions of installing 45 new reactors worldwide by 2030 no longer look feasible.”

“In the process, the United States could lose considerable influence over standards governing safety and waste management, nuclear experts say. And the world may show less willingness to move toward potentially safer designs.” (Source: D. Cardwell, The Murky Future of Nuclear Power in the United States, New York Times, www.NYT.com, Feb 18, 2017)


 

All opinions shared in this post are the author’s own.

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