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Volume 2, Issue 8
October 2002

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Novel Nuclear Reactor (Batteries Included)

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Novel Nuclear Reactor (Batteries Included)
by David Pescovitz

In this schematic illustration of the ENHS reactor, the ENHS Module is highlighted in color. (Click for larger image.)
Image courtesy Ehud Greenspan

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.

"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 and Japan.

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 reactor’s nuclear heat source.

Prof. Ehud Greenspan

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

"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 to hide."

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 basis.

expanded view of ENHS reactor

An expanded view of the ENHS reactor. (Click for larger image.)
Image courtesy Ehud Greenspan

"Once the 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 level."

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.

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"The net 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 markets.

Related Sites

Ehud Greenspan's Home Page

Greenspan Research

Lab Notes is published online by the Public Affairs Office of the UC Berkeley College of Engineering. The Lab Notes mission is to illuminate groundbreaking research underway today at the College of Engineering that will dramatically change our lives tomorrow.

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Writer, Researcher: David Pescovitz
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