AU479212B2 - Process fcr extracting energy froma nuclear fusion reaction - Google Patents

Description

74 31 0 n4

This invention relates to the Enhancement

of Fusion Reaction and more particularly to increase

of energy of fusion by the presence of a nuclei which, upon absorption of a neutron, will disintegrate,

releasing energy.

Much work is presently being done on the

achievement of ignition and burn of fusion fuel such as, for example, deuterium-tritium in pellet form. While there are a number of different approaches to this problem, one of them includes the utilization of a source of energy from a laser and particular pellet configurations which will make it possible to achieve ignition and burn in a reaction chamber. Patents which illustrate generally the apparatus which can be used in this type of system are:

Whittlesey 3,378,446 April 16, 1968

Daiber 3,489,645 Jan. 13, 1970 Hedstrom 3,762,992 Oct. 2, 1973

It has been proposed to utilize boron in

a process and an apparatus provided for the disso-

ciation of H 2 0 in producing the components of hy-

drogen and oxygen by exposure to heutron radiation.

47 9,2 12

7 4,31 0 n in that the The present invention differs out in a region wherein the oresent process is carried exposed to the radiation process materials are directly

resulting from the fusion reaction. fusion reactor consists A general conception of a in which A central reaction chamber of two principle parts. isotopes or other nuclear nuclear fusion fuel (hydrogen is caused to fuse. An example isotopes that undergo fusion) produce fuel which will fuse to is a deuterium and tritium high neutrons produced have a helium and neutrons. The be reaction chamber, and can energy and escape the fusion in a blanket chamber, the utilized for neutron reactions between is formed by an annulus second principle part, which the outer wall. the fusion chamber and to the use of The present invention relates the fusion burn, may penetrate neutrons which, after a the range of 14 MEV neutrons reaction chamber wall in the deuterium-tritium reactions. originally derived from accord- difficult to confine, and These neutrons are very can be successfully utilized ingly, if the energy thereof to there are distinct advantages in a radiolysis process, be gained.

4 79,2 1 2

74 310 174 The reactions that appear to be most

favorable for the subject invention can be described

in the following formulation:

B1 0 Li7

Q (Energy) 2.5 MEV

Li6 t) He 4

Q 4.8 MEV

In the first reaction, B which is present

in natural boron, reacts with a neutron and releases

the energy shown above in the form of alpha radiation

and Li-7 recoil. The second reaction, Li present

in natural lithium, reacts with a neutron to release

the energy, 4.8 MEV in the form of tritium and

He-4 recoil. 6 The Li used in the latter reaction, can

be utilized, either separated, or enriched, or as

present in natural lithium.

t is thgrgfora an object of the prcont

invention to provide an apparatus and a process for

utilizing the neutrons resulting from a fusion

reaction to increase the energy by exposing them to

selected nuclei.

4 7 9,212

The present invention provides a method for

extracting energy from a fusion reaction including the step

of igniting a fusion fuel within a nuclear reaction chamber

to initiate the emission of high-energy fusion neutrons, the

method further comprising the steps of

establishing a fluid medium which includes

at least one material intimately dispersed therein containing

a constituent which dissociates exothermically upon capture

of high-energy neutrons and which functions as a neutron

moderator to modulate high-energy neutrons for efficient

reaction with said constituent and as a coolant to absorb

energy released by dissociation of said constituent,

circulating said fluid medium externally

of said reaction chamber in a region which receives high-

energy fusion neutrons when said step of igniting fusion

fuel is carried out, and

removing heat energy stored in said fluid

medium.

The features and advantages of the invention

4 7 9,2 i 2

74.310 n4

will be apparent in the following description and

claims in which the principles of operation and use

of the invention are set forth in the best mode

presently contemplated for the practice of the

invention.

A drawing accompanies the disclosure and

may be described as a schematic view of an apparatus

for accomplishing the process.

It should be appreciated that the invention

relates to the reduction of induced radioactivity in

a fusion burn by the absorption of neutrons in a medium

such as boron or lithium which react exothermically

to produce heat, but which produce no radioactive

debris. Thus, the resulting radioactivity is reduced,

the confining apparatus is less subject to deterioration,

and the entire process is easier to deal with.

In FIGURE 1, there is illustrated a laser

driven fusion reactor where a laser source 10 directs

pulse to a pellet 12 at the center of a reaction

4 7 9.2 12

7 4 31 Or by a wall 16. A pellet source chamber 14 surrounded of the fusion fuel in 18 is shown for introduction is a Surrounding the wall any suitable manner. 22 of a formed by an outer wall secondary chamber 20 resistant or other highly heat metal such as titanium fuel this chamber that the material. It is in be additional energy will materials for generating

placed. are a arrangement, there Using this general containing which boron and lithium number of ways in There are two ingredients materials may be introduced. is invention. The first required for this process metallic bearing compounds or pure boron or lithium medium for is a heat transport alloys. The second the energy derived through extracting the thermal may be A third material which nuclear reaction. the energy moderator to reduce desirable is a neutron neutron and thus improve the of the neutron flux of the composite. reaction efficiency depends upon The selection of absorber

four considerations: released the amount of energy

per neutron absorbed; after the residual radioactivity

exposure;

47 9.2 12

743 1 0 74 the neutron cross-section which is

indicative of the neutron "stopping power": and

the absorption of radiation in the

surrounding medium.

When a neutron is absorbed in any particular

isotope, the product isotopes emit energy in various

forms (alpha-radiation, beta-radiation, gamma-radiation,

neutrons, etc.). Eventually, the radiation energy is

absorbed in the medium and is converted to thermal

energy. The first consideration evaluates the efficiency

of this energy transformation. The second consideration

evaluates the rate of the energy transfer dictated

by the characteristic decay period of the products.

If the period is long, the radiation may prove a

problem from the standpoint of radiological safety.

The third consideration is the neutron cross-section

for the reaction. This determines the mass or thick-

ness of material required and, therefore, the dilution of

the energy release. The fourth consideration has to

do with the amount of absorbing medium required to

absorb the product isotope radiation. For example,

high energy gamma-radiation would require a large mass

to absorb the radiant energy. Consequently, the

energy density would be low.

4 7 9,21 2

74.310 /4 for this application The isotope preferrea neutron absorbed, energy return per should have a high produced of a long decay period no penetrating radiation

cross-..ection. Boron and lithium and a high nuclear well. meet these objectives in the fusion Other materials employed chamber between the reaction reactor annulus formed moderator material 22 are a neutron and the outer wall reaction down for efficient which slows the neutrons does not and a coolant that with boron or lithium a high neutrons, yet has parasitically capture with construc- and is compatible temperature capabilitY may also be The boron or lithium tion materials.- or ceramic metal, graphite dispersed in a solid The matrix uniform heat extraction. matrix to provide to have a low cross-section materials must also the principle competition with neutrons to avoid for the various Materials suggested neutron reaction. I. tabulated in Table applications are

4 7 9,2 12

74 310 n4 TABLE I

MATERIAL SELECTIONS

Dispersion Absorbers Coolants Medium Moderator

Boron Gases Water

Lithium co2 Gases Graphite Fluoride Beryllium Boron Carbide He CO 2

Lithium Hydride He Beryllium oxide

Water Aqueous solution Metal Hydride

Liquid Metals Dispersion Liquid Lithiu of Solids

Lead Solids Bismuth Aluminum Sodium Graphite NaK Beryllium oxide Fused Salts Alumina

4 7 012 1 2

74,3 1 0 [4 These additive materials which dissociate many ways. Solid exothermically can be introduced in or structures can be built to hold solid boron

lithium containing rods or plates. Provisions for

radiation periodic removal must be made to replace This can be damaged and depleted fuel elements. wall section in accomplished by providing a removable

wall 22. Part of the structure may include a neutron Any of moderator to increase the effective exposure. through a number of known coolants can be circulated to external the structure to transport thermal energy for a turbine applications (such as a steam generator or others). The electric plant, a chemical operation, the fuel in structure can be simplified by introducing salt, liquid a fluid form (aqueous solution, fused of solids, and metal, gas dispersion, fluidized bed

spherical pebbles). These forms permit continuous or

interrupting intermittent replacement of fuel without fuel handling. the reactor operation and simplifies the moderator A further simplification is to combine

and coolant into a fluid. Examples of this

and graphite- are water coolant, liquid lithium,

gas dispersions. A further simplification

47 9.2 1 2

74,310 n4 would be to combine all three functions into one

fluid, namely, a heat exchange fluid which carries,

for example, boron and also a moderator, which is

circulated through the annulus. The thermal energy

extraction and fuel replacement operations are part

of the circuit external of the reactor. The following

published sources are pertinent in connection with

this technology:

C. R. Tipton, Jr., "Reactor Handbook",

Interscience Publishers Inc., (1960).

S. Glasstone, "Principles of Nuclear

Reactor Engineering", D. Van Nostrand

Co., Inc., (1955)..

With reference to the drawing, the annulus

chamber 20 has openings 24, 26 and 30 which serve as

inlets or outlets with suitable closures.

For example, a steam or mist of H20 in

which boron is dissolved may be introduced through

openings 24 and 26 prior to a burn with an outlet

to permit proper flow. If desired, a fluid carrying

a particulate of boron or lithium may be introduced

under pressure through any of the openings. A fluidized

quantity of a particulate could be introduced at

to maintain a desired amount of boron, for example, in

the chamber 20 surrounding the reaction chamber.

4 7 9,2 1 2

74 310 With the use of a fusion reactor as a there source of neutrons to expose boron or lithium,

are a number of advantages. The unit can be operated

additive steadily with a non-destructive burn and the obtain can be supplied continuously, if desired, to There the highest efficiency of energy output. of energy will result a high neutron yield per unit boron will and the introduction of a material such as As not interfere with the operation of the reactor. product has been pointed out, there is no fission handling of radioactivity involved in the system and the

the material additions is relatively simple.

4 7 9,2 12

Claims (4)

74. 3 107 THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:

1. A method for extracting energy from a fusion

reaction including the step of igniting a fusion fuel within

a nuclear reaction chamber to initiate the emission of high-

energy fusion neutrons, the method further comprising the

steps of

establishing a fluid medium which includes

at least one material intimately dispersed therein containing

a constituent which dissociates exothermically upon capture

of high-energy neutrons and which functions as a neutron moderator to modulate high-energy neutrons for efficient

reaction with said constituent and as a coolant to absorb

energy released by dissociation of said constituent, circulating said fluid medium externally

of said reaction chamber in a region which receives high-

energy fusion neutrons when said step of igniting fusion fuel is carried out, and

removing heat energy stored in said fluid

medium.

2. The method set forth in claim I wherein said

step includes the step of dispersing into said fluid

medium a finely-divided particulate material containing said

constituent.

3. The method set forth in claim 1 or 2 wherein

said constituent is selected from the group consisting of lithium-6 and

4. The method set forth in any one of the foregoing

claims wherein said step includes the step of dispersing

into said fluid medium a material selected from the group

consisting of water, liquid lithium, a graphite-gas

47 9.212

74. 3 1 0 4 dispersion, oari. oxide and metal hydrides to function as

said neutron moderator.

The method set forth in any one of the foregoing

claims wherein said step includes the step of dispersing

into said fluid medium a material selected from the group

consisting of carbon dioxide, helium, water and fused salt

to function as said coolant.

6. The method set forth in any one of the claims 1-4

wherein said step includes the step of dispersing into

said medium a liquid metal selected from the group consisting

of lead, bismuth and sodium to function as said coolant.

7. The method set forth in any one of the foregoing

claims wherein said fluid medium comprises a liquid, said one

material comprising a particulate material dispersed in said

liquid.

8. The method set forth in any one of the foregoing

claims wherein said fluid medium comprises a finely-divided

mist, said one material comprising a particulate material dispersed in said mist.

9. The method set forth in any one of the foregoing

claims wherein said fluid medium comprises a gas, said one mat-

erial comprising a particulate .material dispersed in said gas. A method of enhancing fusion energy substantially

as hereinbefore described with reference to the accompanying

drawings.

DATED THIS 28TH DAY OF OCTOBER, 1976.

TEXAS GAS TRANSMISSION CORPORATION By Its Patent Attorneys:

CLEMENT HACK CO. -ellows Institute of Patent Attorneys of Australia.

S4 7 9.212

74.3l 01

PFLUT 'I z~I 6

4 7-9.2Z 1 2