seminar report on nuclear battery

8/10/2019 Seminar Report on Nuclear Battery

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INTRODUCTION

The terms nuclear battery is used to describe a device which uses energy from the

decay of a radioactive isotope to generate electricity. Like nuclear reactors they

generate electricity from atomic energy, but differ in that they do not use a chain

reaction. Compared to other batteries they are very costly, but have extremely longlife and high energy density, and so they are mainly used as power sources for

equipment that must operate unattended for long periods of time, such as

spacecraft, pacemakers, underwater systems and automated scientific stations in

remote parts of the world.

Nuclear battery technology began in 1913, when Henry Moseley first demonstrated

the beta cell. The field received considerable in-depth research attention for

applications requiring long-life power sources for space needs during the 1950s and

1960s. In 1954 RCA researched a small atomic battery for small radio receivers and

hearing aids. Since RCA's initial research and development in the early 1950s, many

types and methods have been designed to extract electrical energy from nuclear

sources. The scientific principles are well known, but modern nano-scale technology

and new wide band gap semiconductors have created new devices and interesting

material properties not previously available.

Batteries using the energy of radioisotope decay to provide long-lived power (1020

years) are being developed internationally. Conversion techniques can be grouped

into two types: thermal and non-thermal. The thermal converters (whose output

power is a function of a temperature differential) include thermoelectric andthermionic generators. The non-thermal converters (whose output power is not a

function of a temperature difference) extract a fraction of the incident energy as it is

being degraded into heat rather than using thermal energy to run electrons in a

cycle. Atomic batteries usually have an efficiency of 0.15%. High efficiency

betavoltaics have 68%.


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1. THERMAL CONVERTERS

Their output power is a function of a temperature differential.

1.1. Thermionic Converter

A thermionic converter consists of a hot electrode which thermionically emits

electrons over a space charge barrier to a cooler electrode, producing a useful

power output. Caesium vapor is used to optimize the electrode work functions and

provide an ion supply (by surface ionization) to neutralize the electron space charge.

The converters of this installation are thermionic diodes of the type with cesium

vapor. The electrodes of the diodes are constituted by coaxial cylinders. The interior

cylinders form the emitters (positive electrodes or cathodes), and the external

cylinders form the collectors (negative electrodes or anodes). The nuclear fuel rods

(fissile material) of the atomic reactor are placed on the inside of the cathode

cylinders which receive directly the heat produced in the rods by the nuclear

reactions. In this manner the cathodes are maintained at a sufficiently elevated

temperature (of the order of 2,000 K.) in order that an electron emission takes place

from the cathodes toward the anodes, maintained by a cooling system with a much

lower temperature (of the order of l,000 K.). The diodes, connected in series, are

aligned along a common axis and placed on the inside of a cylindrical jacket, made

of an electric insulating material, which is a good heat conductor' The cooling of the

anodes is realized by the circulation of an alloy (N-aK) in the molten state about the

insulating jacket which is incontact with the anodes.

FIGURE 1 is a cross-sectional

view through a direct thermionic

energy converter in accordance

with the present invention, along

line II.


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FIGURE 2 is a perspective view, partially in cross-section, of the direct thermionic

energy converter.

The converters are diodes formed by C and A blocks disposed in a checkerboard

manner, that is in vertical columns and horizontal rows in which the blocks of the two

types alternately succeed one another both in the same columns and in the rows.

The C blocks constitute the cathodes or emitters and the A blocks the anodes or

collectors, the materials being suitably chosen (for example, copper for the

collectors, and tantalum, molybdenum, or thoriated tungsten for the emitters).

In each vertical column the blocks are separated by very slight intervals 1 which

form the inter-electrode spaces of the diodes. Thus, in the example of FIGURE 1,

each column, counting five blocks, forms four inter-electrode spaces and comprises

consequently four diodes. Each block, disposed between two other blocks of the

same column, constitutes by its two horizontal faces the anodes or cathodes of two

diodes, connected in opposition. On the other hand, the A blocks of the columns 1,

2, and 3 are electrically connected to the C blocks adjacent the following columns by

way of conductors 2. Similar conductors 2 are connected to the C blocks of the first

column and to the A blocks of the last or fourth column.

The chains PQ and TU comprise each four diodes in series. Between the points Rand S, one has two chains in series, connected in parallel. By connecting together

the points P, R, T, on the one hand, and the points Q, S, U, on the other, one

obtains an assembly of four series chains, connected in parallel. One may thus

regulate, at will, the voltage and the output to be obtained by choosing the number of

diodes in each chain or horizontal row and the number of chains to be connected in

parallel. The C and A blocks are hollow and open at the two extremities thereof. On

the inside of the C blocks are disposed nuclear fuel cores 3 (fissile material, for

example, uranium carbide UC), the length of the cores being greater than that of the

C blocks which surround the same. The hollow spaces of the A blocks are utilizable

for the passage of a coolant liquid.

Walls 4 of a refractory material, which is an electrical insulation and good heat

conductor such as glucina, is provided about the assembly and between the

columns of the blocks, which may serve at the same time as moderator for the

atomic reactor, formed by the cores 3.

The connecting conductors 2 between elements of neighboring columns traverse the

insulating partition walls 4. On the other hand, for sake of convenience of the


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connection, all of the blocks are provided with small support plates 5 which are

embedded in the insulating walls 4 without being in contact with each other. These

support plates 5 may, of course, be suppressed if one obtains another manner of

supporting the blocks.

The operation of the atomic reactor being assured by an adequate dimensioning ofthe cores 3 and of the absorbing walls 4, the emitters C, heated directly by the heat

produced in the cores 3 by the nuclear reactions, find themselves carried at a high

temperature (of the order of 2,000 K.). The diodes then produce an output, an

electron emission taking place from the emitters toward the collectors. The latter are

maintained at a temperature of the order of 1,000 K. by a circulation of refrigerating

fluid on the inside of the A blocks. This fluid may be constituted advantageously by a

molten metal or alloy, for example, NaK.

The electric current, produced in the diodes, may be utilized in external loads, and

the heat due to the nuclear reactions of the reactor is thus converted directly into

electrical energy. The thermionic diodes may be of a vacuum type or filled with gas(for example, cesium vapor), the latter being generally preferred in practice, for they

permit to utilize more important interelectrode spaces than the vacuum-type diodes.

In case of utilization of cesium vapor diodes, the described installation comprises

reservoirs (not illustrated in the drawings) which supply this gas to the interelectrode

spaces of the diodes in a conventional manner.

Significant research on advanced low-temperature thermionic converter technology

for fossil-fueled industrial and commercial electric power production was conducted

in the US, and continued until 1995 for possible space reactor and naval reactor

applications. That research has shown that substantial improvements in converter

performance can be obtained now at lower operating temperatures by addition ofoxygen to the caesium vapor, by suppression of electron reflection at the electrode

surfaces, and by hybrid mode operation. Similarly, improvements via use of oxygen-

containing electrodes have been demonstrated in Russia along with design studies

of systems employing the advanced thermionic converter performance.

1.2. Radioisotope thermoelectric generator

A radioisotope thermoelectric generator (RTG, RITEG) is an electrical generator thatuses an array of thermocouples to convert the heat released by the decay of a

suitable radioactive material into electricity by the Seebeck effect.

The design of an RTG is simple by the standards of nuclear technology: the main

component is a sturdy container of a radioactive material (the fuel). Thermocouples

are placed in the walls of the container, with the outer end of each thermocouple


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connected to a heat sink. Radioactive decay of the fuel produces heat which flows

through the thermocouples to the heat sink, generating electricity in the process.

A thermocouple is a

thermoelectric device thatconverts thermal energy directly

into electrical energy using the

Seebeck effect. It is made of two

kinds of metal (or

semiconductors) that can both

conduct electricity. They are

connected to each other in a

closed loop. If the two junctions

are at different temperatures, an

electric current will flow in theloop.

The radioactive material used in RTGs must have several characteristics:

I. It should produce high energy radiation. Energy release per decay is

proportional to power production per mole. Alpha decays in general release

about 10 times as much energy as the beta decay of strontium-90 or cesium-

137.

II. Radiation must be of a type easily absorbed and transformed into thermalradiation, preferably alpha radiation. Beta radiation can emit

considerable gamma/X-ray radiation through bremsstrahlung secondary

radiation production and therefore requires heavy shielding. Isotopes must

not produce significant amounts of gamma, neutron radiation or penetrating

radiation in general through other decay modes or decay chain products.

III. Its half-life must be long enough so that it will release energy at a relatively

constant rate for a reasonable amount of time. The amount of energy

released per time (power) of a given quantity is inversely proportional to half-

life. An isotope with twice the half-life and the same energy per decay will

release power at half the rate per mole. Typical half-livesfor radioisotopes used in RTGs are therefore several decades, although

isotopes with shorter half-lives could be used for specialized applications.

IV. For spaceflight use, the fuel must produce a large amount of power

per mass and volume (density). Density and weight are not as important for

terrestrial use, unless there are size restrictions. The decay energy can be


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calculated if the energy of radioactive radiation or the mass loss before and

after radioactive decay is known.

The first two criteria limit the number of possible fuels to fewer than 30 atomic

isotopes within the entire table of nuclides. Plutonium-238, curium-244 and

strontium-90 are the most often cited candidate isotopes, but other isotopes such aspolonium-210, promethium-147, caesium-137, cerium-144, ruthenium-106, cobalt-

60, curium-242, americium-241 and thulium isotopes have also been studied.

RTGs have been used as power sources in satellites, space probes and unmanned

remote facilities such as a series of lighthouses built by the former Soviet Union

inside the Arctic Circle. RTGs are usually the most desirable power source for

robotic or unmaintained situations that need a few hundred watts (or less) of power

for durations too long for fuel cells, batteries, or generators to provide economically

and in places where solar cells are not practical. Safe use of RTGs requires

containment of the radioisotopes long after the productive life of the unit.

1.3. Thermophotovoltaic Cells

Thermophotovoltaic cells work by the same principles as a photovoltaic cell, except

that they convert infrared light (rather than visible light) emitted by a hot surface, into

electricity.

Components of Thermophotovoltaic System:

The traditional use of photovoltaic conversion has been converting solar flux intoelectrical power in spacecraft. The present section introduces the

thermophotovoltaic system which converts the photon flux radiated from a heat

source into electrical power.

1. The heat source contains thermal energy at temperature, TH, and a radiator

to emit photons for conversion. Chemical, solar thermal, and nuclear

sources have all been used or considered for TPV applications. The

temperature of the heat source is important to system performance because

higher efficiencies are generally possible with higher radiator temperatures.


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2. The spectral control

components increase system

efficiency by ensuring that

photons reaching the TPV device

have sufficient energy for the

photoelectric effect. Selectiveemission tailors the output

spectrum of the heat source

radiator by the use of a selective

or filtered radiator. Reflective

spectral control places a filter/reflector at the surface of the TPV device.

Transmissive spectral control reflects unused photons out of the device and

back to the heat source radiator.

3. The thermophotovoltaic cell is identical in principle and function to the

photovoltaic cell.It convert light down into the infrared range of the spectrum.

4. The cold reservoir of a thermophotovoltaic system maintains the cell atsome low temperature, TC. It provides the necessary thermal sink to ensure

that thermal energy flows through the power converter.

Region 1 in this device

is the substrate upon

which it is grown. This

substrate also acts in

some cases as the

base (current collector).

Region 2 is the base

where distinct from

region 1. Region 3 is an

emitter, which is

diffused into the device. Regions 4 and 5 are front and back contacts.

Thermophotovoltaic cells have an efficiency slightly higher than thermoelectric

couples and can be overlaid on thermoelectric couples, potentially doubling

efficiency. The University of Houston TPV Radioisotope Power Conversion

Technology development effort is aiming at combining thermophotovoltaic cells

concurrently with thermocouples to provide a 3 to 4-fold improvement in system

efficiency over current thermoelectric radioisotope generators.

1.4. Alkali-metal thermal to electric converter (AMTEC)


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The alkali-metal thermal to electric converter (AMTEC) is an electrochemical system

which is based on the electrolyte used in the sodium-sulfur battery, sodium beta-

alumina. The device is a sodium concentration cell which uses a ceramic,

polycrystalline -alumina solid electrolyte (BASE), as a separator between a high

pressure region containing sodium vapor at 900 - 1300 K and a low pressure region

containing a condenser for liquid sodium at 400 - 700 K. The -alumina solidelectrolyte is the critical material in operating AMTEC devices. It is an ionic

conductor for the alkali metal with which it is made; for sodium BASE, the nominal

composition is Na5LiAl32O51. The electrolyte is fabricated as a polycrystalline

sintered ceramic stabilized with Li.

In an AMTEC cell, BASE is used as the

separator between high and low pressure

sides, and the ceramic is coated on both

sides with thin film, porous metal

electrodes. Vapor phase sodium atoms

are oxidized at the high pressure

sodium/electrode/BASE interface and

sodium ions are conducted through the

BASE to the low pressure side. Electrons

are collected in the porous electrode on

the high pressure side and travel through

an external load to recombine with sodium

ions at the BASE electrode interface on the

low pressure side of the BASE. After

recombination of electrons and sodium

ions, sodium vapor travels through theporous electrode, leaves the electrode as

vapor and is collected on a cold

condenser, from which it can be recirculated as a liquid to the hot, high pressure

side of the BASE [1,2].

In the AMTEC cycle, liquid sodium at T1is pumped into the hot zone by the capillary

wick where it absorbs thermal energy and reaches T2. Sodium evaporates from the

pump and comes into contact with the anode on the high pressure side of the BASE

and the sodium ionizes. The pressure difference between the anode and cathode

sides of the BASE drives Na' across the separator and the electrons travel through

the load. At open circuit, Na' is driven toward the low pressure side by thermal

kinetic energy, and a potential difference is created by charge build-up on the

cathode side.

The AMTEC units, placed behind the radiation shadow shield, arc heated by a

multitude of sodium heat pipes, which are thermally coupled to the reactor's Na heat


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pipes (Figure7).

The AMTEC units

in the SAIRS

power system are

grouped into six

blocks of three orfour units each.

Each AMTEC

block is cooled by

a multitude of

potassium (K) heat

pipes, assembled

into a separate

radiator panel. The heat rejection radiator panel for each AMTEC block is made of

two sections, a stationary forward section attached to the AMTEC units and a rear

conical deployable section, which is folded on to the stationary section in the stowedlaunch configuration. The K-heat pipes in the forward fixed and rear deployable

sections of the radiator panels are hydraulically coupled using flexible joints. The

surface of the radiator is covered with CC composite armor to protect against

impact by meteoroids. The SAIRSs hexagonal core, fast spectrum nuclear reactor is

cooled using a total of 60 1.5-cm- OD. Mo-14% Re sodium heat pipes. To minimize

the physical penetrations through the radiation shadow shield behind the reactor, the

Na-heat pipes exiting the reactor vessel and the axial BeO reflector are bent around

the shadow shield before entering the radiator cavity.

1.5. Advanced Stirling Radioisotope Generator (ASRG)

Stirling Radioisotope Generator is a Stirling engine driven by the temperature

difference produced by a radioisotope.

An ASRG produces electricity by a triple energy transformation. It first turns the

thermal energy from the hot radioisotope fuel into the high-speed kinetic motion of a

small piston and its companion displacer. In turn, this magnetized piston oscillates

back and forth through a coil of wire, thereby generating a flow of electrical energy

(using a property of physics known as Faradays Law).

Inside the ASRG, the oscillating piston and its companion displacer are sealed

inside a closed cylinder, suspended in helium gas. The displacer moves in sync with

the piston, rapidly forcing the helium gas back and forth between the hot side

heated by the radioisotope fuel at one end, and a passive cooler at the other end.


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The steady alternating expansion and contraction of gas within this Stirling heat

cycle drives the magnetized piston through the coil of wire more than 100 times per

second, thus creating an alternating current of electricity.

Each ASRG contains two sets of

pistons and displacerseachset known together as an

Advanced Stirling Convertor.

The two convertors are aligned

endto-end in the middle of the

generator; this configuration

helps to cancel out the small

linear vibrations produced by

the pistons when their motion is

synchronized. The helium gas

sealed inside each converter

also functions as a hydrostaticbearing, keeping the displacer and the piston from

rubbing the walls of the cylinder and eliminating almost all physical wear. This

enables the ASRG to be designed for a long operating lifetime of 17 years.

A controller connected by electrical cables to the ASRG synchronizes the two

pistons, provides data about the status of the ASRG to the spacecraft carrying it,

and transforms the alternating current (AC power) produced by the generator into

about 130 watts of direct current (DC power) at a voltage that a spacecraft can use.

The far end of each convertor is connected to a General Purpose Heat Source

(GPHS) that contains the radioisotope fuel heat source. The ASRG uses two of the

identical GPHS modules, the same type used in the MultiMission RadioisotopeThermoelectric Generator (MMRTG) that powers the Curiosity Mars rover. The

GPHS contains the power sources nuclear fuel within several layers of rugged and

heat resistant carbon-carbon material, graphite and iridium metal.

These tough layers help ensure the safety of the power source in the unlikely event

of an accident during launch of an RPS-powered mission or in an accidental

atmospheric reentry during an Earth-swingby maneuver. In addition, the nuclear

radioisotope fuel in an RPS (plutonium dioxide) is used in a ceramic form that would

break primarily into large, non-inhalable and non-soluble pieces, rather than fine

particles that could be harmful to human health or the environment.

The energy conversion process used by an ASRG allows it to use about one quarter

of the plutonium-238 used in previous radioisotope systems to produce a similar

amount of power. This greater efficiency helps extend the limited supply of this

special material.

NASA and the scientific community are studying a wide variety of missions that

might require an ASRG, from orbiters, landers and rovers to balloons and planetary


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boats. Possible destinations for future missions that would carry an ASRG include

Mars, Saturns moon Titan, Jupiters moon Europa, or the outer planets Uranus and

Neptune. It may be possible to build a small Stirling-powered RPS that would use

only one GPHS module, to power smaller spacecraft, highly mobile missions, or

those that might require a network of small stations.

2. NON-THERMAL CONVERTERS

Non-thermal converters extract a fraction of the nuclear energy as it is being

degraded into heat. Their outputs are not functions of temperature

differences.

2.1 Direct Charging Nuclear Battery

The operating principle of the Direct Charge Nuclear Battery (DCNB) is the direct

collection of charged particles emitted from a source electrode on an opposite

electrode. DCNB can be built using beta or

alpha emitters.

In the simplest case, the DCNB is a

radioactive source on or in a conductive foil

facing a metal foil on which the

electrostatic charge is accumulated. The

source and metal foil are separated by a

dielectric. The scheme of the direct charge

cell with load for describing the charging

process is shown in Figure 9.

English physicist H.G.J. Moseley constructed the first of these. Moseleys apparatus

consisted of a glass globe silvered on the inside with a radium emitter mounted on

the tip of a wire at the center. The charged particles from the radium created a flow

of electricity as they moved quickly from the radium to the inside surface of the

sphere. As late as 1945 the Moseley model guided other efforts to build

experimental batteries generating electricity from the emissions of radioactive

elements.


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The primary generator

consists of a capacitor

which is charged by the

current of chargedparticles from a

radioactive layer

deposited on one of the

electrodes. Spacing can

be either vacuum or

dielectric. Negatively

charged beta particles or

positively charged alpha particles, positrons or fission fragments may be utilized.

Although this form of nuclear-electric generator dates back to 1913, few applications

have been found in the past for the extremely low currents and inconveniently high

voltages provided by direct charging generators. Oscillator/transformer systems are

employed to reduce the voltages, then rectifiers are used to transform the AC power

back to direct current.

On the other hand, the Direct Charge Nuclear Battery has these features:

i. Open circuit voltage (multiplied on elementary charge) of DCNB is

comparable with the average energy of charging particles, i.e. several,

several dozen, or several hundred kilovolts;ii. Conversion efficiency of DCNB was demonstrated at a few percent. But,

theoretical analysis performed by G. Miley, et al., shows that the theoretical

efficiency of the Direct Charge Nuclear Battery reaches 15-17%;

iii. In the design of nuclear batteries with direct charge radiation sensitive

materials, like semiconductor voltaics and phosphors, are absent. Therefore,

power loss with time is from isotope decay only and the lifetime such type of

battery is reliably longer;

iv. During operation of nuclear batteries with direct charge, temperature,

pressure, and humidity sensitive materials are absent. Therefore, these

devices can work in a wide range of environmental conditions;v. Some applications of nuclear batteries, such as electrostatic motors which

require high voltage, can be provided without up-conversion.


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2.2. Betavoltaics

Betavoltaics are generators of electrical current, in effect a form of battery, which

use energy from a radioactive source emitting beta particles (electrons). A common

source used is the hydrogen isotope, tritium. Unlike most nuclear power sources,which use nuclear radiation to generate heat, which then is used to generate

electricity (thermoelectric and thermionic sources), betavoltaics use a non-thermal

conversion process; converting the electron-hole pairs produced by the ionization

trail of beta particles traversing a semiconductor.

Betavoltaic devices are self contained power sources

that convert high energy beta () particles emitted from

the decay of radioactive isotopes into electrical current.

As shown in Fig. 11, a typical betavoltaic device, in its

simplest form, consists of a layer of beta-emitting

material placed adjacent to a semiconductor p-n

junction or Schottky diode. A convenient way to

understand the fundamental operation of a betavoltaic

device is to consider it as the "nuclear" analog to the

familiar solar cell, where, in place of the sun, a beta-

emitting isotope provides the source of ionizing

radiation. When the semiconductor material is

bombarded by high energy beta particles, electron-hole pairs are generated by

impact ionization (see Fig. 11). Since the average kinetic energy of typical beta

particles used for betavoltaic devices is in the kiloelectron volt (keV) range, a single

beta particle can be responsible for generating multiple electron-hole pairs.According to the Klein formula, the average kinetic energy required to beta-generate

an electron-hole pair of energy equal to the semiconductor band gap (Eg) is 2.8 Eg +

0.5 eV. In addition, during the conversion process,

1.8 Eg eV and 0.5 eV are lost by emission of

acoustic and optical phonons, respectively.

Similar to photovoltaics, electron-hole pairs that

are beta-generated inside of or within a minority

carrier diffusion length of the depletion region are

separated by the built-in electric field and drifted

apart (see Fig. 12). The accumulation of separated

electron-hole pairs in the quasi-neutral regions of

the semiconductor, electrons on the n-side and

holes on the p-side, results in the junction

becoming forward biased and current flowing through an externally connected load.

Despite their operational similarities with photovoltaic devices, betavoltaic devices

are usually strictly limited to low power applications. This is directly related to the fact


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that the typical flux of beta particles emitted from a beta source is a minute fraction

of the photon flux emitted by the sun. As a result, betavoltaic devices typically

generate currents on the order of nano- to micro-amperes, which are several orders

of magnitude smaller than currents generated by similarly sized photovoltaic

devices.

When selecting a beta source for a betavoltaic device, fluence rates and isotope

half-lifetimes are important aspects that must be considered. Obviously, utilizing long

half-lifetime isotopes that can generate sufficient beta particle fluxes is critical to the

design of long-lasting betavoltaic power sources. However, the effects of radiation

damage in the semiconductor material must also be taken into account. Ideally, the

maximum kinetic energy (Emax) of the beta particles emitted from the beta source

should be smaller than the radiation damage threshold of the material (Eth).

Otherwise, the emitted beta particles would have sufficient energy to displace atoms

in the semiconductor lattice. Radiation induced defects in the semiconductor

material can result in shortened minority carrier diffusion lengths, increased leakage

currents, and overall device performance degradation.

Betavoltaics fill a unique nicke among

energy storage devices. Their

distinguishing feature is their longevity, but

in addition, the energy density of a tritium

or147

Pm powered betavoltaic battery can

be many times greater than that of a lithium

battery. In the defence market, tritium

based betavoltaics are already being

introduced to power the encryption keys infield-programmable gate arrays. Although

their power requirements are quite low (150

nW), the arrays tend to experience extreme

temperatures that can cause chemical batteries to fail. A betavoltaic decice trickle

charging a second secondary battery or capacitor can provide burst power in the

range of milliWatts to watts, for critical device operations such as wireless

communications which can be used in extreme conditions. Implanted medical

devices are a natural application for betavoltaic power sources, whose long life

spans can help minimize trauma to patients, like pacemakers, with other possibilities

including defibrillators, cerebral neurostimulators, cohlear implants, brain computer

interface devices, etc.


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2.3. Alphavoltaics

Alphavoltaic power sources are devices that use a semiconductor junction toproduce electrical particle from energetic alpha particles. The concept of an alpha

voltaic battery was proposed in 1954 as disclosed in W. G. Pfann and W. van

Roosbroeck.

In an alpha voltaic battery a radioactive substance that emits energetic alpha

particles is coupled to a semiconductor p/n junction diode. As the alpha particles

penetrate into the p/n junction, they decelerate and give up their energy as electron-

hole pairs. These electron-hole pairs are collected by the p/n junction and converted

into useful electricity much like a solar cell.The main reason alpha voltaic batteries

are not commercially successful is that the alpha particles damage the

semiconductor material so as to degrade its electrical performance in just a matter ofhours.

Referring to FIG. 14,

an alpha voltaic

battery 10(1) in

accordance with

embodiments of the

present invention is

illustrated. The alpha

particle emitter14(1)

emits energetic alphaparticles which are

converted by the alpha

voltaic battery 10(1)

into energy. The alpha particle emitter 14(1) comprises Am-241 which is thermally

diffused in the metal foil 16 and is then over-coated with another metal, such as

silver.

The absorption and conversion layer 12(1) prevents alpha particles from the alpha

particle emitter 14(1) from damaging one or more p/n junctions in the layer of

semiconductor material 18(1). The absorption and conversion layer 12(1) also

successfully converts the photons or energy from the alpha particles into electron-

hole pairs for collection by the p/n junction in the layer of semiconductor

material18(1). The thickness of the absorption and conversion layer 12(1) depends

upon the energy or the alpha particles and the resulting penetration depth in the

absorption and conversion layer 12(1). The thickness of the absorption and

conversion layer 12(1) can be chosen to prevent any radiation damage to the layer

of semiconductor material 18(1) or to permit partial amounts of the energy to be


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deposited into the layer of semiconductor material 18(1) and to decrease the self-

absorption of photons by absorption and conversion layer 12(1).

The emitted photons in the absorption and conversion layer 12(1) are either emitted

towards the layer of semiconductor material 12(1) or are substantially reflected at

the interface between the metal foil 16 and the absorption and conversion layer12(1)towards the layer of semiconductor material 12(1). Since the photons have energy

greater than the bandgap of the p/n junction in the layer of semiconductor material

18(1), the photons are absorbed in the p/n junction layer of semiconductor material

12(1) creating electron-hole pairs that are converted into useful electricity. This

generated electricity or power is transferred to a load 20(1) which is coupled

between the absorption and conversion layer 12(1) and the layer of semiconductor

material 18(1) across the p/n junction.

Alphavoltaic batteries have at least two unique properties when compared to

conventional chemical batteries that make them outstanding candidates for deep

space missions:

I. The alpha emitting materials have half-lives from months to 100's of years, so

there is the potential for everlasting batteries; and

II. Alpha voltaic batteries in accordance with the present invention can operate

over a tremendous temperature range. Ordinary chemical batteries all fail at

temperatures below 40 C., while alpha voltaic batteries have been

demonstrated to work at 135 C.

2.4. Optoelectric Nuclear Battery

An opto-electric nuclear battery is a device that converts nuclear energy into light,

which it then uses to generate electrical energy.

A nuclear-cored battery that emits alpha, beta, or gamma radiation and is

surrounded by a ceramic phosphor material. The ceramic material within the ceramic

phosphor material is a high temperature ceramic and is used to shield and absorb

the radiation emitted by the nuclear core while the phosphors are excited by the

radiation causing them to produce energy in the form of photons. Structural defects

are used to increase the bandwidth of the ceramic material and phosphor material

such that photons are produced and radioactive radiation is prevented from beingemitted past the ceramic material. Surrounding the ceramic phosphor material is a

photovoltaic layer that transforms the photons into a flow of electrons to create a

sphere. Surrounding a plurality of these spheres is a conductive material that is an

intermediate layer that carries the spheres. A P and N layer sandwiches the spheres

therebetween to harness the electron flow created by the photovoltaic layer to create

the nuclear-cored battery.


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FIG. 15 shows an atomic battery or

nuclear-cored battery 10. Nuclear-cored

battery 10 is created by producing a plurality of energy sources in the form of

spheres 12 (FIG. 16) that each have a nuclear core 14 that emits alpha, beta, or

gamma radiation. Nuclear core 14 is comprised of any radioactive material including,

uranium, uranium carbonate, uranium oxide, strontium, and strontium oxide.

The nuclear core 14 is surrounded by a ceramic phosphor material 16 that is in one

embodiment a crystalline having a carbon defect such that the ceramic phosphor

material 16 in combination with the nuclear core forms a light dissipating material 17.

In one embodiment, the ceramic phosphor material comprises a high temperature

ceramic. In another embodiment this high temperature ceramic comprises a matrix

having Al2O3:C. In yet another embodiment zinc sulfide, or another high

temperature ceramic having a carbon defect is used. The ceramic material within the

ceramic phosphor material 16 is used to shield and absorb the radiation emitted by

the nuclear core 14 while the phosphors are excited by the radioactive radiation of

the nuclear core 14 causing the phosphors to produce energy in the form of photons.

In another embodiment lanthanides are used as a defect for the phosphors. The

carbon defect increases the bandwidth of the ceramic material, and the lanthanides

are used to increase the bandwidth of the phosphors. Thus, the ceramic material

prevents radiation from being emitted past the ceramic phosphor material 16, yet

this material 16 is still able to produce photons.

Another example of a material that is added to the ceramic phosphor material 16 to

manipulate the output frequency of the photons being emitted is yttrium oxysulfide

doped with titanium and magnesium material that forms a crystal that emits red to

orange wavelengths of light. Thus for red and orange wavelengths the ceramic

phosphor material comprises the matrix MOS:Mg,Ti,Eu wherein MO is chosen froma group consisting of MgO, ZnO, ZrO, CuO, Yttrium Oxide, or Gallium Oxide.

The excitation of the base light emitter, such as Al2O3:C, causes the stimulation of

the crystals and the combined frequency gives the final output color. Thus the output

frequency of the ceramic phosphor material 16 is manipulated to any color in the

visible spectrum.


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Below is a list of examples of different ceramic phosphors and the color wavelengths

of the photons that are emitted by each depending on the amount of each element

provided:

I. GreenA mixture of polycrystalline carbon doped Alumina, Europium Oxide,

Strontium Carbonate, and Dysprosium Oxide.II. BlueA mixture of polycrystalline carbon coped Alumina, Europium Oxide,

strontium Carbonate, and Dysprosium Oxide.

III. YellowA mixture of polycrystalline carbon doped Alumina, Europium Oxide,

Strontium Carbonate, Barium Carbonate, and Dysprosium Oxide.

IV. OrangeA mixture of polycrystalline carbon doped Alumina, Yittrium

Oxysulfide, Europium Oxide, Strontium Carbonate, and Dysprosium Oxide.

V. RedA mixture of polycrystalline carbon doped Alumina, Yttrium Oxysulfide,

Europium Oxide, and Magnesium Titanium.

VI. WhiteA mixture of polycrystalline carbon doped Alumina, Europium Oxide,

Strontium Carbonate, Neodymium Oxide, and Dysprosium Oxide.

VII. VioletA mixture of polycrystalline carbon doped Alumina, Europium Oxide,

Calcium carbonate, and Neodymium Oxide.

Surrounding the ceramic phosphor material 16 is a photovoltaic layer 18 that

transforms the photons into a flow of electrons to create an energy source, or sphere

12. One will appreciate that in one embodiment the photovoltaic layer 18 is made of

an amorphous silicon that also is altered with defects by, for example, doping the

material with magnesium in order to manipulate a stimulating frequency of the

photovoltaic layer 18. Other examples of defects include titanium and chromium.

Thus the output frequency of the photons generated by the ceramic phosphormaterial 16 is manipulated or tuned while manipulating or tuning the stimulating

frequency of the photovoltaic layer 18 so that the most efficient amount of light

created by the ceramic phosphor material 16 is converted into an electron flow by

the photovoltaic layer 18.

After a plurality of spheres 12 are created a battery is formed by surrounding a

plurality of spheres 12 with a conductive material 20 that is an intermediate layer that

carries the spheres 12. This conductive material 20 comes into direct contact with

the spheres 12 and in one embodiment is a conductive polymer, one example of

which is a sulfidized polymer. One such conductive polymer is poly(3,4-

ethylenedioxythiophene) polystyrenesulfonate. A P and N layer 22 comprising a P

layer 22 aand an N layer 22 b sandwiches the spheres therebetween to harness the

electron flow created by the photovoltaic layer 18to create the nuclear-cored battery

10. Additionally, a layer of insulating material 23 can be used to surround the P and

N layer 22.


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Finally, spheres 12 in one embodiment are in powder form and will range in size

from 50 microns to sub micron in size depending on the application and output.

Nonetheless, in another embodiment a metal is added to the nuclear core 14 of the

battery 10 in order to increase the size of the spheres 12 for macro-sized

applications.

Major disadvantages of Opto-electric Nuclear Battery:

I. High price of the radionuclides.

II. High-pressure (up to 10 MPa (100 bar)) heavy containment vessel.

III. A failure of containment in this form of device would release high-pressure

jets of finely divided radioisotopes, forming an effective Dirty Bomb.

The inherent risk of failure is likely to limit this device to space-based applications,

where the finely divided radioisotope source is only removed from a safe transport

medium, and placed in the high-pressure gas, after the device has left Earth orbit.

SUMMARY

There is no argument that batteries are the necessities of modern life, powering

everything from cell phones to vehicles. The traditional batteries, powered up by

chemical reaction that convert stored chemical energy into electrical energy, are

omnipresent and very economical but they have their own limitations.

These chemical batteries can be used only for a certain period of time and even the

rechargeable ones can be recharged only a specific no of times. Nuclear batteriesboast of their longevity as their working is directly dependent on the half-life of the

radioactive core.

Although at the moment chemical batteries are a lot safer than the nuclear batteries

for general purposes, but their use it limited to normal working conditions as they

tend to fail in extreme conditions. Right now nuclear batteries can be used and are

generally used in extreme conditions only where there is less manual labor and

minimal chances of a widespread hazard.

Nuclear batteries are already being used in space exploration, underwater systems,

automated satellite stations in remote parts of the world, for medical applications andvarious other purposes. With further scientific advancement in the field of nuclear

batteries aiming to decrease the risk factor for the user and/or the environment,

nuclear batteries can be used to power the future.


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seminar report on nuclear battery

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