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| Fig. 1: Diagram of solar cell direct energy conversion. The nuclear battery works the same way except that the electron-hole pairs are created by α or β rays, either directly through impact or indirectly by means of light emitted by a phosphorescent layer. (Source: Wikimedia Commons). |
An oft criticized characteristic of nuclear energy is the waste generated in the fission process that remains radioactive for tens of thousands of years after use. However, the radioactive decay of this waste does not have to be seen as toxic, and can instead be viewed as a source of long lasting potential energy to be captured.
Batteries made from carbon nuclear waste compressed into diamonds offer a way to convert waste products from fission graphite reactors to durable batteries that can provide charge for thousands of years. These small batteries could be embedded in devices that require a low voltage energy source but cannot be easily accessed like pacemakers and space probe components.
Research into small nuclear batteries fabricated from radioactive material began in the 1970s when betavoltaic devices were fabricated to power pacemakers. The first commercially produced device was the Betacel, which used the radioisotope Pm-147 and had a lifetime of 10 years. [1]
Functionally, the concept of the nuclear battery is similar to that which underlies radioisotope electric generators which are used for space probes and rovers. The battery generates charge through direct energy conversion which relies on a semiconductor diode and radioisotope source. [2] This produces a voltage much like how a solar cell does, as seen in Fig. 1. The α or β radiation from the isotope creates electron pair holes in the semiconductor, pulling the electrons in between the semiconductor to generate small amounts of current as seen in Fig. 2. [3]
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| Fig. 2: Radioisotope semiconductor electron hole capture; alpha and beta radiation is converted to charge by semiconductor layers. [6] (Courtesy of the DOD) |
One of the largest nuclear waste products by volume is radioactive carbon-14 which is produced by irradiation of graphite blocks used in graphite-moderated reactors. The graphite acts as a neutron moderator that slows fast moving neutrons produced in the fission process to maintain the stability of the reactor.
The radioactive C-14 could theoretically then be extracted and compressed into radioactive diamonds. These diamonds would then be incased in a regular, non-radioactive diamond, to provide shielding.
The theoretical C-14 diamond battery would have a lower energy density than chemical based batteries like the lithium-ion batteries that power laptops and phones, and the alkaline batteries like AA batteries that are found in calculators and other small electronics.
A typical AA battery stores 13,000 Joules and is exhausted after about 24 hours, while a C-14 diamond battery would produce only 15 Joules per day but have a half life of almost 6,000 years. [4]
Thus far, research groups in Russia and Canada have produced prototype radioactive diamond batteries from Ni-63. [5] Although diamond batteries are by no means a solution to the issue of nuclear waste recycling and storage, they offer a productive channel to put some of the waste to productive use as safe, durable, energy sources to power exploration and medical electronics.
© Travis Lanham. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
[1] L. Olsen, S. Seeman, and B. Griffin, "Nuclear Battery," U.S. Patent 3,706,893, 19 Dec 72.
[2] W. Ko and J. Hynecek, "Implant Evaluation of a Nuclear Power Source - Betacel Battery," IEEE Trans. Bio-Med. Eng. 21, 238 (2007).
[3] C. Delfaure et al., "Single Crystal CVD Diamond Membranes for Betavoltaic Cells," Appl. Phys. Lett. 108, 252105 (2016).
[4] V. Bormashov et al., "Development of Nuclear Microbattery Prototype Based on Schottky Barrier Diamond Diodes," Phys. Status Solidi A 212, 2539 (2015).
[5] J. Conca, "Radioactive Diamond Batteries: Making Good Use Of Nuclear Waste," Forbes, 9 Dec 16.
[6] M. Litz, "Isotope Beta-Battery Approaches For Long-Lived Sensors: Technology Review," Army Research Laboratory, ARL-TR-7048, August 2014.
