Under The Hood With Duncan Williams - Searete’s Deflagration Wave Reactor

Searete’s Deflagration Wave Reactor

 - By Duncan Williams -

Searete’s deflagration wave reactor is one of the newest designs of reactor power plants to emerge during the most recent nuclear renaissance.  Only existing on paper, the design is markedly different from previous designs.  For example, at the heart of Searete’s reactor is a cylindrical-shaped nuclear fuel laying on its side.  The fuel is burned continuously over several decades from one end to the other, much like a cigarette.  The design also includes features that allow the reactor to operate automatically with no human oversight or intervention.  By completely automating the operation of the reactor, Searete’s design eliminates the possibility of human errors that caused the reactor accidents at Three Mile Island and Chernobyl.

Since Searete has not submitted any design documents to the Nuclear Regulatory Commission (NRC), however, very few details about the exact operation of the reactor are available to the public.  The fact that no documents have yet been submitted to the NRC also means that this design is many years from being built, much less certified.  However, a recently published patent application owned by Searete does provide some insight into the construction and operation of the inner core of the reactor.  U.S. Patent Publication No. 20100040188, published on February 18, 2010, describes some of the operational principles of Searete’s deflagration wave reactor.

As previously mentioned, the cylinder-shaped nuclear fuel in the Sereate reactor is arranged on its side and burns from one end to the other.  The nuclear fuel must be ignited on one end in order to start the fission deflagration wave.  The ignition-end of the nuclear fuel is made from different material than the rest of the fuel.   The patent application refers to an article, titled “Completely Automated Nuclear Reactors for Long-Term Operation,” by Edward Teller, Muriel Ishikawa, and Lowell Wood, published by the Lawrence Livermore National Laboratory, that describes the make-up of the nuclear fuel.

click for full sizeThe article contains a cross-sectional diagram of the cylindrical nuclear fuel having a 50 cm long igniter section on the left end.  Although the diagram shows the igniter section containing thorium, as well as 10% enriched uranium-233, the article indicates that enriched uranium-235 and/or plutonium-239 can also be used.  The right-hand side of the fuel contains a layer of naturally occurring thorium.  A 40 cm layer of graphite surrounds the entire fuel cylinder.  The core of the cylinder is hollowed out and filled with a foam made from beryllium.  Since neutrons pass through the beryllium with little difficulty, the neutrons will then travel to the unburned fuel region on the right.  The article references experiments that have shown the wave will travel at a speed of .5 meters per year, releasing about 1.5 GWth as it advances.

Since the design mentioned in the article is similar to Searete’s deflagration wave reactor, the United States Patent Office has rejected the patent claims in a related patent application owned by Searete, U.S. Patent Publication No. 20080123796, published on May 29, 2009.  In order to overcome this rejection, Searete argues that although the article discusses the initiation of a nuclear fission deflagration wave on the left-hand side that burns toward the right, it does not discuss the re-initiation of that wave on the right-hand side which causes the fission deflagration wave to travel back towards the left.

In support of this argument, Searete has amended its drawings to include two nuclear fission igniters (110) – one on the left-hand side and one on the right-hand side.  The patent application describes that the igniter (110) on the left-hand side initiates a wavefront (1430) that travels to the unburned fuel area (1420) on the right.

Once the wave reaches the right-hand side, the igniter (110) on the right-hand side may be used to initiate a second deflagration wavefront (1440) that travels back towards the left.  This indicates that Searete is interested in a deflagration wave reactor that burns the nuclear fuel twice.

Another possible construction of the nuclear core is described in U.S. Patent Publication No. 20090285348, published on November 19, 2009.  The patent application describes a cylindrical metal structure that includes nuclear fuel as well as capillary structures that can be used to cool the nuclear fuel.  [heat pipe]  The patent application refers to a structure called a “heat pipe device” (62a), which has at least one layer of nuclear fission material (64a) and at least one layer of structural material (68) (e.g., steel, niobium, vanadium, titanium, tantalum, tungsten, halfnium, rhenium, molybdenum, or some alloy of these).  The heat pipe device (62a) also includes an inner capillary structure (26) surrounding an inner cavity (66).  The nuclear fission material (64a) is placed near the evaporator side (38) of the device.  Although not indicated in this diagram, the other side of the device acts as the condenser.

click for full sizeThe patent application goes on to explain how this structure can cool the nuclear fuel contained on the evaporator side (38).  Fluid in the evaporator section (38) absorbs heat from the nuclear fuel causing the liquid to evaporate, changing its phase from a liquid to a gas.  The evaporated gas (46) travels through the cavity of the heat pipe as shown by the arrows (48) towards the condenser section (40).  Once the gas reaches the condenser section (40), the heat is removed  from the gas as indicated by the arrows (50).

This causes the gas to condense, changing its phase from a gas to a liquid.  The liquid then enters the capillary structure (26) and begins traveling back towards the evaporator section (38) as indicated by the arrows (54).  Once the liquid (54) reaches the evaporator section (38), heat is transferred from the nuclear fuel to the liquid which starts the cycle again.

U.S. Patent Publication No. 20080123795, published on May 29, 2008, and owned by Searete, describes a thermostatic system that automatically regulates the temperature and power in the Searete reactor.

As can be seen in Figure 11c from the patent, the system includes a small bulb (1160’) located in the nuclear fuel which contains a liquid that is sensitive to temperature (e.g., lithium-7).  When the temperature increases, the lithium-7 in the small bulb (1160’) expands causing the liquid to travel out of the bulb through a capillary tube to a piston assembly (1150’).  The lithium-7 exerts pressure on the bottom of the piston (1150’), causing the piston (1150’) to move upwards, forcing the liquid contained on the top of the piston (1150’) to be expelled.  The liquid on the top of the piston (1150’) is preferably a substance that is highly neutron absorbent, such as lithium-6.  The moving piston causes the lithium-6 to travel through an attached capillary tube to a large bulb (1140’) located in the wall of a coolant tube near the nuclear fuel.  As the bulb (1140’) is filled with lithium-6, more neutrons are absorbed by the lithium-6 instead of the nuclear fuel.  Since neutrons must be absorbed in the nuclear fuel in order to sustain a fission chain reaction, the reactor power level drops due to a lack of available neutrons.  The temperature of the reactor lowers in conjunction with the power, resulting in a lower temperature in the reactor.

As the temperature drops, the lithium-7 contained in the small bulb (1160’) contracts, causing the pressure to lower at the bottom of the piston (1150’).  This causes the piston (1150’) to fall downwards, which causes the lithium-6 contained in the large bulb (1140’) to flow from the large bulb (1140’) to the top of the piston (1150’).  Since there is less lithium-6 in the large bulb (1140’), less neutrons are absorbed by it and are instead absorbed by the nuclear fuel.  This causes an increase in the fission process resulting in higher power, and eventually higher temperature.  By strategically placing a plurality of these thermostatic systems throughout of the reactor, the power and the temperature can be automatically regulated without any human intervention.

The patent also discusses substituting the small bulb (1160’) with a detector which then sends an electrical signal to the piston (1150’), causing the piston to move up or down.  For example, the detector can be a neutron detector that, upon detecting a large amount of neutrons, sends an electronic signal to the piston (1150’) causing lithium-6 to fill the large bulb (1140’) and thereby decreasing the power level of the reactor.

It should be noted that many different variations of Sereate’s deflagration wave reactor are described in its patent application documents.  Therefore, it is difficult to discern the exact reactor structure that Searete would use if it were to actually apply for a design certification with the NRC.  If and when Searete submits documents to the NRC regarding its design, then even more details about the operation of the reactor will become available.

Last Week's Column:  

Under The Hood With Duncan Williams - The Evolution of Neutron Detectors

The Evolution of Neutron Detectors  - By Duncan Williams - The most important particle in nuclear reactor physics is the neutron.  Without it, there can be no sustained nuclear fission and no electricity generated from nuclear power.  Given its importance in today’s reactor physics, it is hard to imagine that no one had ...
 
About Duncan Williams
Duncan Williams graduated from the University of Florida in 1994 with a B.S. in Physics, and a minor in mathematics.  Upon graduation, he was commissioned  in the U.S. Navy where he completed training in the Navy’s Nuclear Propulsion program.  He then served onboard an aircraft carrier, the USS Theodore Roosevelt, as a reactor control division officer.  Onboard, he was responsible for the operation and maintenance of the electrical and mechanical components that make up the reactor control systems.  This includes the control rod drive mechanisms, the reactor safety and emergency systems, the reactor coolant pump systems, and the ion exchangers.  He also developed and implemented ship-wide reactor safety drills in order to educate sailors in reactor safety.

Duncan then transferred to the U.S. Naval Academy, where he served as a senior instructor teaching Thermodynamics to senior cadets.  While serving as an instructor at the Naval Academy, Duncan attended night law school at the George Washington University Law School.  After receiving his J.D. in 2004, he resigned his commission and began working as an intellectual property associate with Kenyon & Kenyon LLP.  While at Kenyon & Kenyon, he drafted numerous patents relating to medical devices, electronic devices, telecommunications, as well as other technologies.  He also has experience in all stages of patent litigation, and has represented numerous Fortune 500 companies in protecting their intellectual property rights.  Duncan is currently an intellectual property associate at Blank Rome LLP.

If you have questions, comments, or know of a patent that you think Duncan should review E-mail Duncan Williams>> duncan@nuclearstreet.com 

Anonymous comments will be moderated. Join for free and post now!