| Novel Nuclear Reactor (Batteries Included)
by David Pescovitz
The latest nuclear
reactor design on the drawing board at UC Berkeley promises less
fuss and muss than today's nuclear power plants. The key to the
safer and more user-friendly reactor is a self-contained nuclear
heat source that only needs to be changed every 20 years.
In this schematic illustration of the ENHS reactor, the ENHS Module is highlighted in color.
(Click for larger image.)
Image courtesy Ehud Greenspan
"I call it a nuclear battery," says Department of Nuclear
Engineering professor-in-residence Ehud Greenspan.
Born from the U.S. Department of Energy's Nuclear Energy Research
Initiative, the Encapsulated Nuclear Heat-Source (ENHS) reactor
design eliminates much of the residual risk associated with traditional
reactors ranging from hardware failure to human operator
error to diversion of nuclear materials for weapons manufacturing.
"We think that current nuclear reactor designs are very safe, but
the DOE was looking for more forgiving designs for developing countries
that may not have the same know-how or infrastructure as industrialized
nations," says Greenspan who collaborated on the project with investigators
from Lawrence Livermore National Laboratory, Argonne National Laboratory,
Westinghouse, and other industrial and academic partners in Korea
The main differentiator between the ENHS and today's operational
nuclear power plants is the ENHS modules, Greenspan's "nuclear
battery." At the factory, the 3.5m in diameter, 20 m long steel
modules are fabricated and fueled with either a uranium-plutonium
alloy or enriched uranium. After being weld sealed, the fueled modules
are shipped to the power plant site where they are installed and
operate for 20 years without refueling, 15 times longer than a traditional
reactors nuclear heat source.
"At no time
do you need to handle the fuel outside of the factory," Greenspan
says. "There's no way to even access the fuel unless you break
the vessel, and that's very, very difficult to do and impossible
Professor Ehud R. Greenspan also researches new designs for Boron-Neutron-Capture-Therapy facilities for irradiation treatment of brain tumors.
(Click for larger image.)
Peg Skorpinski photo
Inside the ENHS module, moving parts are also kept to a minimum.
There are no pumps or valves. The fission-generated heat is removed
from the fuel by a liquid metal coolant that flows through the core
by natural circulation. This heat is transferred to the power plant
through the module walls that act as a heat exchanger.
"The cooling is done by the laws of physics," Greenspan
says. "It's nothing we have to force or actuate. Having no
valves or pumps further reduces the potential for accidents."
Like present-day reactors, the nuclear chain reaction inside the
ENHS core is regulated with control elements made of neutron-absorbing
material. When the control elements are raised from the core, the
fission reaction rate increases resulting in more heat generation.
Pushing them down into the core causes neutrons to be absorbed,
slowing the fission rate. In the ENHS design, once the reactor is
at its nominal power level, the elevation of the control elements
may only need adjustment once each year. This trumps today's reactors
with control elements that must be adjusted practically on a daily
ENHS is running, it doesn't need a team of operators to keep it
going," Greenspan says. "It's self-tuning. If there's
a change in the power demand, it adjusts itself to the new power
view of the ENHS reactor. (Click for larger
Image courtesy Ehud Greenspan
At the end of its life, the ENHS module acts as its own shipping
crate for returning the spent fuel to the factory. There, the spent
fuel can be reprocessed, mixed with a small amount of natural uranium,
and used to fuel a new ENHS module. This recycling is possible,
Greenspan explains, because the ENHS core doesn't degrade the quality
of the fuel as in traditional reactors. The multi-recycling of the
ENHS modules enables an overall increase of fuel utilization nearly
50 times that of today's once-through fuel cycle, Greenspan believes.
The fuel feed for the ENHS can also be prepared from present-day
reactors'waste. According to Greenspan, rather than permanently
storing nuclear waste in the Yucca Mountain repository, it is possible
to extract the fission products and part of the uranium and make
ENHS fuel from what is left over.
result will be a dramatic alleviation of the nuclear waste problem
(from current reactors) combined with a low-waste generating nuclear
energy system," Greenspan writes in his group's project summary
for the Department of Energy,
The ENHS is one of several reactor concepts recently selected by
the Department of Energy to be considered for development under
the government's new Generation IV advanced nuclear energy systems
initiative directed to develop nuclear energy systems to support
world energy supply in the 21st century and beyond. Greenspan says
the small capacity ENHS reactors 50 electrical megawatts
compared to the 1000 megawatt models in use today can be
attractive for small population centers in developing countries
that are far from the national grid as well as for deregulated power
Ehud Greenspan's Home Page
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