25-08-2017, 09:32 PM
1461427622-NuclearBatterySeminarReport.pdf (Size: 816.89 KB / Downloads: 5)
INTRODUCTION
A burgeoning need exists today for small, compact, reliable, lightweight and self-contained
rugged power supplies to provide electrical power in such applications as electric automobiles,
homes, industrial, agricultural, recreational, remote monitoring systems, spacecraft and deep-sea
probes. Radar, advanced communication satellites and especially high technology weapon
platforms will require much larger power source than today‟s power systems can deliver. For the
very high power applications, nuclear reactors appear to be the answer. However, for
intermediate power range, 10 to 100 kilowatts (kW), the nuclear reactor presents formidable
technical problems.
Because of the short and unpredictable lifespan of chemical batteries, however, regular
replacements would be required to keep these devices humming. Also, enough chemical fuel to
provide 100 kW for any significant period of time would be too heavy and bulky for practical
use. Fuel cells and solar cells require little maintenance, and the latter need plenty of sun.
Thus the demand to exploit the radioactive energy has become inevitably high. Several
methods have been developed for conversion of radioactive energy released during the decay of
natural radioactive elements into electrical energy. A grapefruit-sized radioisotope thermoelectric
generator that utilized heat produced from alpha particles emitted as plutonium-238
decay was developed during the early 1950‟s.
Since then the nuclear has taken a significant consideration in the energy source of
future. Also, with the advancement of the technology the requirement for the lasting energy
sources has been increased to a great extent. The solution to the long term energy source is, of
course, the nuclear batteries with a life span measured in decades and has the potential to be
nearly 200 times more efficient than the currently used ordinary batteries. These incredibly longlasting
batteries are still in the theoretical and developmental stage of existence, but they promise
to provide clean, safe, almost endless energy.
Unlike conventional nuclear power generating devices, these power cells do not rely on a
nuclear reaction or chemical process do not produce radioactive waste products. The nuclear
battery technology is geared towards applications where power is needed in inaccessible places
or under extreme conditions.
The researchers envision its uses in pacemakers and other medical devices that would
otherwise require surgery to repair or replace. Additionally, deep-space probes and deep-sea
sensors, which are beyond the reach of repair, would benefit from such technology. In the near
future this technology is said to make its way into commonly used day to day products like
mobile and laptops and even the smallest of the devices used at home. Surely these are the batteries of the near future.
HISTORICAL DEVELOPMENTS
The idea of nuclear battery was introduced in the beginning of 1950, and was patented on
March 3rd, 1959 to tracer lab. Even though the idea was given more than 30 years before, no
significant progress was made on the subject because the yield was very less.
A radio isotope electric power system developed by inventor Paul Brown was a scientific
break through in nuclear power. Brown‟s first prototype power cell produced 100,000 times as
much energy per gram of strontium -90(the energy source) than the most powerful thermal
battery yet in existence. The magnetic energy emitted by the alpha and beta particles inherent in
nuclear material. Alpha and beta particles are produced by the radio active decay of certain
naturally occurring and man –made nuclear material (radio nuclides). The electric charges of the
alpha and beta particles have been captured and converted to electricity for existing nuclear
batteries, but the amount of power generated from such batteries has been very small.
Alpha and beta particles also posses kinetic energy, by successive collisions of the particles
with air molecules or other molecules. The bulk of the R &D of nuclear batteries in the past has
been concerned with this heat energy which is readily observable and measurable. The magnetic
energy given off by alpha and beta particles is several orders of magnitude grater than the kinetic
energy or the direct electric energy produced by these same particles. However, the myriads of
tiny magnetic fields existing at any time cannot be individually recognized or measured. This
energy is not captured locally in nature to produce heat or mechanical effects, but instead the
energy escapes undetected.
Brown invented an approach to “organize” these magnetic fields so that the great amounts
of otherwise unobservable energy could be harnessed. The first cell constructed (that melted the
wire components) employed the most powerful source known, radium-226, as the energy source
The main draw back of Mr. Brown‟s prototype was its low efficiency, and the reason for that
was when the radioactive material decays, many of the electrons lost from the semiconductor
material. With the enhancement of more regular pitting and introduction better fuels the nuclear
batteries are though to be the next generation batteries and there is hardly any doubt that these
batteries will be available in stores within another decade.
ENERGY PRODUCTION MECHANISM
Betavoltaics
Betavoltacis is an alternative energy technology that promises vastly extended battery
life and power density over current technologies. Betavoltaics are generators of electrical current,
ineffect a form of a battery, which use energy from a radioactive source emitting beta particles
(electrons). The functioning of a betavoltaics device is somewhat similar to a solar panel, which
converts photons (light) into electric current.
Betavoltaic technique uses a silicon wafer to capture electrons emitted by a radioactive
gas, such as tritium. It is similar to the mechanics of converting sunlight into electricity in a solar
panel. The flat silicon wafer is coated with a diode material to create a potential barrier. The
radition absorbed in the vicinity of and potiential barrier like a p-n junction or a metalsemiconductor
contact would generate separate electron-hole pairs which inturn flow in an
electric circuit due to the voltaic effect. Of course, this occurs to a varying degree in different
materials and geometries.
A pictorial representation of a basic Betavoltaic conversion as shown in figure 1.
Electrode A (P-region) has a positive potential while electrode B (N-region) is negative with the
potential difference provided by me conventional means.
Direct charging generators
In this type, the primary generator consists of a high –Q LC tank circuit. The energy
imparted to radioactive decay products during the spontaneous disintegrations of radioactive
material is utilized to sustain and amplify the oscillations in the high-Q LC tank circuit the circuit
inductance comprises a coil wound on a core composed of radioactive nuclides connected in
series with the primary winding of a power transformer. The core is fabricated from a mixture of
three radioactive materials which decay primarily by alpha emission and provides a greater flux
of radioactive decay products than the equivalent amount of single radioactive nuclei.
Equitant circuit of the direct charging generator as shown in the figure 3.An LCR circuit 1
is comprised of a capacitor 3, inductor file, transformer T primary winding 9 and resistance 11
connected in series. It is assumed that the electrical conductors connecting the various circuit
elements and forming the inductor file and primary winding 9 are perfect conductors; i.e. ., no
DC resistance. Resistor 11 is a lump resistance equivalent to total DC resistance of the actual
circuit components and conductors. The inductor 5 is wound on a core 7 which is composed of a
mixture of radioactive elements decaying primarily by alpha particle emission.
When the current flows in electrical circuit, energy is dissipated or lost in the form of
heat. Thus, when oscillations are induced in an LCR circuit, the oscillations will gradually damp
out due to the loss of energy in the circuit unless energy is continuously added to the circuit to
sustain the oscillations. In the LCR circuit shown in figure 3, a portion of the energy imparted to
the decay products such as alpha particles. During the radioactive decay of the materials
inductor core 7 is introduced into the circuit 1, when the decay products are absorbed by the
conductor which forms inductor 5. Once oscillations have been induced in the LCR circuit 1, the
energy absorbed by the inductor 5 form the radioactive decay of the core7 material will sustain
the oscillations as long as the amount of energy absorbed is equal to the amount of energy
dissipated in the ohmic resistance of the circuit 1.If the absorbed energy is greater than the
amount of energy lost through ohmic heating, the oscillations will be amplified. This excess
energy can be delivered to a load 17 connected across the transformer T secondary winding 13.
The process involved in the conversion of the energy released by the spontaneous
disintegration of a radioactive material into electrical energy are numerous and complex.
Materials that are naturally radioactive, decay by the emission of either an alpha particle or a
beta particle and gamma rays may accompany either process. Radioactive materials that decay
primarily by alpha particle emission are preferred as inductor core 7 material. Alpha particles are
emitted a very high speeds, in the order of 1.6*107 meters per second (m/s) and consequently
have very high kinetic energy. Alpha particles emitted in radium, for example, decays are found
to consist of two groups, those with a kinetic energy of 48.79*105 electron volts (eV) and those
having energy of 46.95*105 electron volts. This kinetic energy must be dissipated when the alpha
particles are absorbed by the conductor forming inductor 5. During the absorption process, each
alpha particle will collide with one or more atoms in the conductor knocking electron from their
orbits and imparting some kinetic energy to the electrons. This results in increase number of
conduction electrons in the conductor there by increasing its conductivity.
Since the alpha particle is a positively charged ion, while the alpha particle is moving it
will have an associated magnetic field. When the alpha particle is stopped by the conductor, the
magnetic field will collapse thereby inducing a pulse of current in the conductor producing a net
increase in the current flowing in the circuit 1. Also, there will be additional electrons stripped
from orbit due to ionization reduced by the positively charged alpha particles.
Optoelectrics
An optoelectric nuclear battery has been proposed by researchers of the kurchatov
institute in Moscow. A beta emitter such as technetium-99 are strontium-90 is suspended in a gas
or liquid containing luminescent gas molecules of the exciter type, constituting “dust plasma”.
This permits a nearly lossless emission of beta electrons from the emitting dust particles for
excitation of the gases whose exciter line is selected for the conversion of the radioactivity into a
surrounding photovoltaic layer such that a comparably light weight low pressure, high efficiency
battery can be realized. These nuclides are low cost radioactive of nuclear power reactors. The
diameter of the dust particles is so small (few micrometers) that the electrons from the beta decay
leave the dust particles nearly without loss. The surrounding weakly ionized plasma consists of
gases or gas mixtures (e.g. krypton, argon, xenon) with exciter lines, such that a considerable
amount of the energy of the beta electrons is converted into this light the surrounding walls
contain photovoltaic layers with wide forbidden zones as egg. Diamond which converts the
optical energy generated from the radiation into electric energy.
The battery would consist of an exciter of argon, xenon, or krypton (or a mixture of two
or three of them) in a pressure vessel with an internal mirrored surface, finely-ground
radioisotope and an intermittent ultrasonic stirrer, illuminating photocell with a band gap tuned
for the exciter. When the electrons of the beta active nuclides (e.g. krypton-85 or argon-39) are
excited, in the narrow exciter band at a minimum thermal losses, the radiations so obtained is
converted into electricity in a high band gap photovoltaic layer (e.g. in a p-n diode) very
efficiently the electric power per weight compared with existing radionuclide batteries can then
be increased by a factor 10 to 50 and more. If the pressure-vessel is carbon fiber / epoxy the
weight to power ratio is said to be comparable to an air breathing engine with fuel tanks. The
advantage of this design is that precision electrode assemblies are not needed and most beta
particles escape the finely-divided bulk material to contribute to the batteries net power. The
disadvantage consists in the high price of the radionuclide and in the high pressure of upto
10MPa (100bar) and more for the gas that requires an expensive and heavy container.
FUEL CONSIDERATIONS
The major criterions considered in the selection of fuels are:
Avoidance of gamma in the decay chain
Half life
Particle range
Watch out for (alpha, n)reactions
Any radioisotope in the form of a solid that gives off alpha or beta particles can be
utilized in the nuclear battery. The first cell constructed (that melted the wire
components) employed the most powerful source known, radium-226, as the energy
source. However, radium-226 gives rise through decay to the daughter product bismuth-
214, which gives off strong gamma radiation that requires shielding for safety. This adds
a weight penalty in mobile applications.
Radium-226 is a naturally occurring isotope which is formed very slowly by the
decay of uranium-238. Radium-226 in equilibrium is present at about 1 gram per 3
million grams of uranium in the earths crust. Uranium mill wastes are readily available
source of radium-226 in very abundant quantities. Uranium mill wastes contain far more
energy in the radium-226 than is represented by the fission energy derived form the
produced uranium.
Strontium-90 gives off no gamma radiation so it does not necessitate the use of thick
lead shielding for safety.strrrontium-90 does not exist in nature, but it is one of the
several radioactive waste products resulting from nuclear fission. The utilizable energy
from strontium-90 substantially exceeds the energy derived from the nuclear fission
which gave rise to this isotope.
Once the present stores of nuclear wastes have been mined, the future supplies of
strontium-90 will depend on the amount of nuclear electricity generated hence strontium-
90 decay may ultimately become a premium fuel for such special uses as for perpetually
powered wheel chairs and portable computers. Plutonium-238 dioxide is used for space
application. Half life of tantalum-180m is about 1015 years. In its ground state, tantalum-
180 (180Ta) is very unstable and decays to other nuclei in about 8 hours but its isomeric
state, 180m Ta, is found in natural samples. Tantalum 180m hence can be used for
switchable nuclear batteries.
ADVANTAGES
The most important feat of nuclear cells is the life span they offer, a minimum of 10years!
This is whopping when considered that it provides non stop electric energy for the seconds
spanning these 10long years, which may simply mean that we keep our laptop or any hand held
devices switched-on for 10 years nonstop. Contrary to fears associated with conventional
batteries nuclear cells offers reliable electricity, without any drop in the yield or potential during
its entire operational period. Thus the longevity and reliability coupled together would suffice the
small factored energy needs for at least a couple of decades.
The largest concern of nuclear batteries comes from the fact that it involves the use of
radioactive materials. This means throughout the process of making a nuclear battery to final
disposal, all radiation protection standards must be met. Balancing the safety measures such as
shielding and regulation while still keeping the size and power advantages will determine the
economic feasibility of nuclear batteries. Safeties with respect to the containers are also
adequately taken care as the battery cases are hermetically sealed. Thus the risk of safety hazards
involving radioactive material stands reduced.
As the energy associated with fissile material is several times higher than conventional
sources, the cells are comparatively much lighter and thus facilitates high energy densities to be
achieved. Similarly, the efficiency of such cells is much higher simply because radioactive
materials in little waste generation. Thus substituting the future energy needs with nuclear cells
and replacing the already existing ones with these, the world can be seen transformed by
reducing the green house effects and associated risks. This should come as a handy savior for
almost all developed and developing nations. Moreover the nuclear produced therein are
substances that don‟t occur naturally. For example strontium does not exist in nature but it is one
of the several radioactive waste products resulting from nuclear fission.
DRAWBACKS
First and foremost, as is the case with most breathtaking technologies, the high initial
cost of production involved is a drawback but as the product goes operational and gets into bulk
production, the price is sure to drop. The size of nuclear batteries for certain specific applications
may cause problems, but can be done away with as time goes by. For example, size of Xcell used
for laptop battery is much more than the conventional battery used in the laptops.
Though radioactive materials sport high efficiency, the conversion methodologies used
presently are not much of any wonder and at the best matches conventional energy sources.
However, laboratory results have yielded much higher efficiencies, but are yet to be released into
the alpha stage.
A minor blow may come in the way of existing regional and country specific laws
regarding the use and disposal of radioactive materials. As these are not unique worldwide and
are subject to political horrors and ideology prevalent in the country. The introduction legally
requires these to be scrapped or amended. It can be however be hoped that, given the
revolutionary importance of this substance, things would come in favor gradually.
Above all, to gain social acceptance, a new technology must be beneficial and
demonstrate enough trouble free operation that people begin to see it as a “normal” phenomenon.
Nuclear energy began to loose this status following a series of major accidents in its formative
years. Acceptance accorded to nuclear power should be trust-based rather than technology based.
In other words acceptance might be related to public trust of the organizations and individuals
utilizing the technology as opposed to based on understanding of the available evidence
regarding the technology