Direct conversion of radiation into electricity using carbon nanotubes and a separate new approach to thermoelectrics

Liviu Popa-Simil, former Los Alamos National Laboratory nuclear engineer and founder of private research and development company LAVM and Claudiu Muntele, of Alabama A&M University, US, say transforming the energy of radioactive particles into electricity is twenty times more effective (up to power density of 1 kw/cm^3) than thermoelectric materials. It will be big impact when it is commercialized which they expect will be ten years or more.

After the jump, there is a new thermoelectric approach which could work at the temperatures for power plants and could double the efficiency of nuclear and coal plants. If these two technologies work (or similar technologies are developed) we could revolutionize the efficiency of transportation (cars, planes, space vehicles) and power plants and allow for a more rapid shift away from fossil fuels.

“I believe this work is innovative and could have a significant impact on the future of nuclear power,” says David Poston, of the US Department of Energy’s Los Alamos National Laboratory. However perfecting new nuclear technologies requires years of development, he adds.

Popa-Simil agrees, saying it will be at least a decade before final designs of the radiation-to-electricity concept are built.

Tests of layered tiles of carbon nanotubes packed with gold and surrounded by lithium hydride are under way. Radioactive particles that slam into the gold push out a shower of high-energy electrons. They pass through carbon nanotubes and pass into the lithium hydride from where they move into electrodes, allowing current to flow. “You load the material with nuclear energy and unload an electric current,” says Popa-Simil.

This was presented at session JJ4.14, March 26, 2008 at the Materials Research Society Spring meeting in San Francisco.

Pseudo-Capacitor Structure for Direct Nuclear Energy Conversion. Liviu Popa-Simil1 and Claudiu Muntele; 1LAVM LLC, Los Alamos, New Mexico; CIM_AAMURI, Huntsville, Alabama.

A previous presentation on direct nuclear power conversion was made in 2007 by Dr Liviu Popa-Simil.

The development of the new MEMS devices and micro electronics in the 40 nm technologies provides an excellent background for the production of the electric power harvesting and conversion devices embedded in the fuel. The new nano-structured materials may be produced as radiation energy harvesting tiles that are free of actinides, using them for harvesting the energy of radioactive sources and controlled fusion devices, or may include actinides in the structure achieving critical or sub-critical accelerator driven nuclear reactor assemblies. Another predictable advantage of the nano-structure is the property of self-repairing and self-organizing structure to compensate the radiation damage and improve the lifetime. Due to the direct conversion the power density of the new materials may increase from the actual average of 0.2 kw/cm^3 to about 1 kw/cm^3 driving to miniaturization of nuclear power sources and reductions of the shield weight. At these dimensions and power densities of few thousands horse power per liter the nuclear power source becomes suitable for mobile applications as powering trains, strategic airplanes, etc. These new developments may drive to the production of high power solid-state compact nuclear battery for space applications, leading to a new development stage.

More details on the Johnson Thermoelectromechanical Energy Conversion System, or JTEC which is a new thermoelectric conversion system by the inventor of the Supersoaker.

A prototype of the heat engine, called the Johnson Thermoelectromechanical Energy Conversion System, or JTEC, will be ready in a few months. It will convert heat to electricity at rates reaching just under 40 percent of the maximum theoretical efficiency available in an engine operating between two temperatures—the Carnot efficiency. The former U.S. Air Force and NASA Jet Propulsion Lab engineer says his group’s aim is to produce a commercial version whose efficiency can approach 85 percent of the Carnot ideal. Such a device would be capable of converting 66 percent of the available thermal energy into electrical energy.

In contrast, photovoltaic devices have net conversion efficiencies in the teens and thermionic (or thermoelectric) chips reach only a little higher than 20 percent of Carnot when converting heat to electricity.

As in all other heat engines, JTEC’s conversion efficiency is dependent on the difference in temperature between its hot and cool zones. For example, if the hot side is raised to 1100 °Celsius—which Johnson says an eventual commercial version would be able to withstand—while the cool side remained at room temperature, 25 °Celsius, it could, ideally, be 78 percent Carnot efficient. But what sets JTEC apart is its all-solid-state design. The lack of moving parts such as turbines and pistons eliminates nearly all of the parasitic losses that, in machines like an automobile engine, greatly lower efficiency. The conversion efficiency achieved by the best combustion turnbines is about half of what a commercialized JTEC device would offer, according to Johnson.

The JTEC’s setup is similar to that of a fuel cell [see an animation of how the JTEC works here]. A proton-conducting membrane allows protons from a hydrogen molecule to pass from one zone to another while preventing electrons from crossing the barrier. The electrons are therefore forced to move through an external circuit, in the process delivering current to a load. But instead of consuming hydrogen as fuel and expelling water, the JTEC is a closed system. It uses hydrogen as a working fluid that is conserved within the device.

The device’s net energy output results from the fact that the voltage generated on the hot side is greater than the voltage applied to the cool side: the higher the temperature difference, the greater the net voltage.

An important efficiency-boosting design element is the regenerative heat exchanger located between the hot and cool zones. This allows the hydrogen gas exiting the hot side to transfer its heat to the hydrogen that, having just been reconstituted on the heat engine’s cool side, needs to be reheated in order to prevent a drop in the temperature differential that drives the process. This allows the JTEC to get more out of the heat input. It also ensures that less energy is needed to pump the hydrogen gas up to full pressure at the cold end of the loop.

21 page presentation on the characteristics of fuel (and prices for different kinds of RTGs) for radioisotopic thermal generators (RTGs) that the direct from radiation to electricity would eventually replace. The direct conversion could also change out the steam plants used to convert heat to electricity at nuclear plants.

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