Nuclear Energy

Nuclear energy harnesses the power of the atom to generate tremendous amounts of electricity
from a very small amount or fuel. This controversial source is non-renewable because there is a
finite amount of uranium, and while it produces no carbon emissions it is not “green” because of
the radioactive waste it produces.

Nuclear power plants use the heat created by splitting uranium atoms to create steam either by
boiling water or turning pressurized water into steam without boiling it. The steam turns turbines,
which generate electricity. In both boiling water and pressurized water systems the steam is
condensed back into water to be cycled again. 

Nuclear fission in action

Much of the controversy surrounding nuclear energy is a fear of what could happen. In the years
since nuclear energy plants began generating, there have been three major accidents- Three Mile
Island in 1979, Chernobyl in 1986, and Fukushima Daiichi in 2011. An example of what could go
wrong follows.

Three Mile Island was a loss of coolant accident. A mechanical failure prevented water from
reaching the reactor core to cool it. As pressure began to build in the core, a relief valve opened
as it should have, but remained stuck open when pressure returned to normal levels. Cooling
water poured out of the valve, but plant staff was unaware as instruments indicated the valve was
closed. Without correct information from instrument readings, staff incorrectly reduced the amount
of cooling water going to the reactor, which caused it to overheat. The zirconium cladding that
contained the uranium fuel pellets began to melt. A hydrogen bubble formed inside the containment
dome, raising fears of an explosion and containment breach. Pregnant women and small children
were ordered to evacuate, and there was a release of radiation (done intentionally to relieve pressure)
but not enough to cause any health issues. Plant staff resumed the flow of cooling water and were
able to reduce the hydrogen bubble. The reactor stabilized, and it was discovered that about half
of the core had melted. 

Three Mile Island. The cooling towers for the damaged
reactor are in the foreground. (Lancaster Online)

Safety has improved considerably at US plants. In fact, the costs associated with safety, security,
and permitting have become almost prohibitive to opening new plants. A plant in Tennessee will
be coming online in late 2016, over 40 years after construction began because low demand for
electricity and did not justify the cost of completing the plant until recently.

Aside from safety concerns, spent nuclear fuel is an issue no one is quite sure how to deal with.
Currently, spent nuclear fuel is stored on-site at power plants. First, it is stored in a cooling pool
for a minimum of five years. When it has cooled enough, it is encased in a concrete and steel cask.
However, the material will remain radioactive for thousands of years and a permanent location for
disposal has yet to be found. Reprocessing allows uranium and the resulting plutonium to be reused
as fuel, which cuts down on the amount of waste material but only delays the problem.

Spent nuclear fuel in a cooling pool (International Atomic Energy Agency)

One potential solution to the waste problem is transatomic power, which dissolves nuclear waste
into molten salt, would reduce the amount of spent nuclear fuel by using it again. It also has the
potential to reduce the half-life of waste, or amount of time that it takes for half of the mass to decay
and no longer be radioactive.

Another negative environmental impact of nuclear energy is the potential for radioactive release or
water pollution from tailings at uranium mines. Uranium tailings are radioactive, and may contain
sulfides that can produce acids. Tailings should be placed within an engineered dam and then back
inside the mine when operations conclude (World Nuclear Association, 2013).

After examining various methods of energy production, it has become clear that no source is
completely free of environmental impacts. The negative impacts are wide ranging, from localized
to single windmill to a global scale with fossil fuels. Fossil fuels have been widely panned for the
environmental damage they cause at a regional level for oil spills to the global climate change
linked to carbon dioxide emissions. They have been ruled out as the “greenest” energy, but what
about the others? 

Wind, solar, tidal, and geothermal appear to have the least negative environmental impacts but
can be limited by factors such as geology, topography, and weather. As technology advances, it
may be able to overcome these limitations. An ideal solution to the fossil fuel problem is to
increase their generating capacity and incorporate them into an improved and more efficient grid.
Since these sources, as well as hydroelectric, are mainly regional a better grid would blend all
electricity into a single network that can easily transfer energy to rapidly meet demand. Thus,
hydroelectric from the Pacific Northwest could supply power to Iowa when the wind stops blowing. 

So what is the “greenest” energy? It is all a matter of personal preference and an individual’s
tolerance for the different negative impacts. Bird strikes from wind energy may be a more pressing
concern for some people than fish strikes caused by tidal energy. 

This week's information comes from Duke Energy, Nuclear Regulatory Agency, Wired, Nuclear Regulatory Commission, Transatomic Power, and World Nuclear Association.

Species of the Month

Introduction: Summer is road trip season, and many people do a road trip through any of
the western national parks. Most folks have a goal of seeing some wildlife, and one of the
iconic animals of the west is the bighorn sheep. They can be seen picking their way along
sheer cliffs in an amazing feat of agility, but I think more people are impressed by rams
crashing into each other head first as they battle for mating rights.

Scientific name: Ovis canadensis

Kingdom: Animalia (animals)

Bighorn ewe enjoying the view

Class: Mammalia (mammals)

Order: Artiodactyla (even-toed ungulates)

Range: Southern Canada south to Mexico, as far east as Texas

Habitat: Mountain meadows, rocky cliffs, deserts

Bighorn rams

Lifespan: 6-15 years, depending on population status

Diet: Grasses, sedges, forbs

Predators: Mountain lions, wolves, coyotes, bears, lynx

Conservation Status: California bighorn sheep subspecies is listed as endangered.

Bighorn lamb taking a break from frolicking

Other Information: There are three subspecies of bighorn sheep: Rocky Mountain, the most numerous
and widespread; California, which is endangered and can be found in the Sierras; and desert bighorn,
which live in the deserts of the US Southwest and Mexico.

Bighorns use rocky slopes and cliffs to avoid and evade predators. Specially built toes allow them to
navigate along ledges that are only inches wide, and excellent depth perception allows them to
accurately leap from one to another.

Bighorns have a shorter lifespan in dynamic populations with a high birth rate, on average 6 or 7 years.
Those in a more stable population with a lower birth rate tend to live longer, to longer than 10 years.

Ewes lounging at the top of a slope

Bighorns live in segregated herds, males in a smaller herd, while females and lambs (male and female)
form larger herds. The herds mingle during the rut, which takes place in fall and early winter. Lambing
occurs in spring, and newborns are able to keep pace with mom almost immediately.

Sparring for mating rights involves males ramming head first into each other at speeds of up to 20
miles per hour. Horns can weigh up to 30 pounds. The force generated is enough to kill a human. Ram
skulls are made of several plates, like human skulls, but the rams' do not fuse into a single solid piece
of bone. That design lets the plates shift to absorb the shock of the repeated blows. The curl of the
horns might also deflect some of the shock away from the head, while a large tendon connecting the
head and neck helps the head recoil.

Rams battling for a mate (Smithsonian)

This week's information comes from University of Michigan's Animal Diversity Web and
Indiana Public Media. Next week wraps up the energy series with a look at the elephant in the room,
nuclear.

Geothermal Energy

Geothermal energy uses heat from within the earth to provide power. It is considered renewable
because of the constant supply of heat from the earth and is “green” because there are minimal
emissions.

Geothermal plants are developed after exploration for a suitable location. Plants need access to
aquifers that are adjacent to hot rock. A production well is drilled to access the heat and steam used to
generate electricity. Once brought to the surface, there are three methods used to produce electricity.
They are flash, dry steam, and binary. 

Geothermal plant (US Energy Information Administration)

A flash plant uses a steam separator to separate steam from water. Steam goes to turbines that power a
generator, while the water is reinjected into the ground where it becomes steam to start the cycle over.
A dry steam plant functions similarly, but there is no water and no need for a steam separator. Steam
alone turns the turbines. As it cools and condenses into water, it is reinjected back into the ground.

Binary geothermal plants use hot water from beneath the surface to boil another liquid, such as
isobutene, that has a lower boiling point than water. The vaporized fluid powers the turbines. The
water is reinjected into the ground, while the vaporized fluid goes through a condenser and a preheater
before returning to the vaporizing chamber and powering the turbines again.

How a geothermal plant works (Mechanical Technology)

A geothermal heat pump is similar to passive solar heating and cooling. Water circulates into the
ground to bring up the earth’s heat or to carry indoor heat underground to cool a building. Direct use
geothermal uses geothermal heat without use of a plant or heat pump. Hot water or steam is brought to
a plate heat exchanger for heating and cooling of a building.

Geothermal plants emit low levels of carbon dioxide and sulfides (hydrogen sulfide mainly) that occur naturally in the subsurface water and steam. Scrubbers can remove most of the hydrogen sulfide. Sulfide emissions are generally lower than fossil fuel plants (US Energy Information Administration, 2015).

This week's information comes from Geothermal Energy Association and US Energy Information Administration. Next week we'll be taking a break for the Species of the Month before returning to check out the pros and cons of nuclear energy.

Solar Energy

Solar power is another “clean” and renewable source that is emission-free and will never exhaust the sun. Not only do photovoltaic panels not drain the sun of energy, they do not diminish the capacity of other panels, so long as one panel is not placed on top of another.

There are two ways to use solar energy, active and passive use. Photovoltaic electricity (PV), solar heating and cooling, and concentrated solar are active systems. Passive solar building use design features capture and utilize solar radiation.

PV cells turn sunlight into electricity. This technology was accidentally discovered in 1954 when a scientist noticed that silicon created an electrical charge when exposed to sunlight. The solar powered calculator was born and eventually evolved into today’s solar panels. The early panels were made of silicon, but second generation panels use thin film and semiconductors. Thin film panels can be used as shingles, tiles, or façades and incorporate electrical generation into the design of a building. PV units can be found powering individual homes or on roadsides, collecting energy for lighting for highway signs.

How solar energy works (Sunpower)

Solar heating and cooling uses the sun’s radiant energy to heat or cool a building with the use of PV panels. A transpired collector is a black metal panel on the south-facing wall of a building that absorbs heat from sunlight. Holes in the panel allow heated air to pass through to the other side, where it is sucked into the ventilation system and throughout the building.

Solar process heating uses a solar collector (usually an evacuated tube or parabolic trough), a pump, a heat exchanger, and water tanks to heat a building. The evacuated tube is a series of glass tubes and reflectors that heat water inside. A parabolic trough is a U-shaped mirror focusing sunlight in a central tube. The focused sunlight heats water in the tube. The heated water is pumped throughout the building to warm it up. Solar cooling uses the same collection system, along with the magic of chemistry to cool the air.

Concentrated solar power is a generating system that reflects and focuses sunlight to create heat and steam that turns a turbine to create electricity. Because the system converts sunlight into thermal energy, it can be stored and generate electricity even on cloudy days or at night. Concentrated solar power can accompany a traditional fossil fuel plant as a carbon offset or as a stand-alone plant.

Solar array collection system (Colorado Springs Business Journal)

Passive solar uses site, climate, and material to use the sun’s radiant energy to heat and cool a building without the use of active mechanical systems like those mentioned above. Energy efficiency measures to reduce the required amount of heating and cooling is the first step. The second step is an unobstructed south face to maximize sun exposure. Sunlight entering the south facing windows is absorbed by thermal mass- material such as concrete, stone, or brick. The thermal mass absorbs heat from the sunlight during the winter and from warm air during the summer. Conduction, convection, and radiance are natural phenomena that circulate the heat throughout the building.

Like all other energy sources examined so far, solar energy is not completely “green”; it too has negative environmental impacts. Habitat loss for large solar arrays and concentrated solar plants can be mitigated by siting these in repurposed areas such as brownfields and reclaimed mine sites. Small scale units that power a single building typically have minimal impact, especially when roof-mounted.

Water use is a concern with concentrated solar plants. The sunniest areas in the US are often the driest, and water is scarce so a massive withdrawal of 600 to 650 gallons per megawatt hour of electricity can have a negative impact on desert denizens.

An additional concern is the hazardous materials used in the manufacture of PV cells. Many are used to polish the semiconductor surface and include hydrochloric acid and acetone. Petroleum is used in the manufacture of PV cells also, so even solar energy is somewhat dependent on fossil fuels. However, new technology that uses cotton and castor beans is being developed.

Next week we'll look at geothermal energy. This week's information comes from Solar Energy Industries Association, National Renewable Energy Laboratory, Renewable Energy World, US Department of Energy, Union of Concerned Scientists, and Scientific American.