U.S. patent application number 11/173271 was filed with the patent office on 2005-11-17 for metal alloy and metal alloy storage product for storing fast neutron emitters.
This patent application is currently assigned to Clean Technologies International Corporation. Invention is credited to Wagner, Anthony S..
Application Number | 20050254988 11/173271 |
Document ID | / |
Family ID | 27658266 |
Filed Date | 2005-11-17 |
United States Patent
Application |
20050254988 |
Kind Code |
A1 |
Wagner, Anthony S. |
November 17, 2005 |
Metal alloy and metal alloy storage product for storing fast
neutron emitters
Abstract
A liquid reactant metal alloy includes at least one chemically
active metal for reacting with non-radioactive material in a mixed
waste stream being treated. The reactant alloy also includes at
least one radiation absorbing metal. Radioactive isotopes in the
waste stream, including any fast neutron emitting isotopes alloy
with, or disperse in, the chemically active metal and the radiation
absorbing metals are able to absorb a significant portion of the
radioactive emissions associated with the isotopes. A transmutation
target fraction is included for absorbing fast neutrons and a
transmutation emission absorbing fraction is provided for absorbing
emissions that result from the absorption of a fast neutron by the
transmutation target fraction. Non-radioactive constituents in the
waste material are broken down into harmless and useful
constituents, leaving the alloyed radioactive isotopes in the
liquid reactant alloy. The reactant alloy may then be cooled to
form one or more ingots in which the radioactive isotopes are
effectively isolated and surrounded by the radiation absorbing
metals. These ingots comprise the storage products for the
radioactive isotopes.
Inventors: |
Wagner, Anthony S.;
(Lakeway, TX) |
Correspondence
Address: |
THE CULBERTSON GROUP, P.C.
1114 LOST CREEK BLVD.
SUITE 420
AUSTIN
TX
78746
US
|
Assignee: |
Clean Technologies International
Corporation
|
Family ID: |
27658266 |
Appl. No.: |
11/173271 |
Filed: |
July 1, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11173271 |
Jul 1, 2005 |
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10059808 |
Jan 29, 2002 |
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10059808 |
Jan 29, 2002 |
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09334985 |
Jun 17, 1999 |
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6355857 |
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09334985 |
Jun 17, 1999 |
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09096617 |
Jun 12, 1998 |
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09334985 |
Jun 17, 1999 |
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09274583 |
Mar 23, 1999 |
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6195382 |
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Current U.S.
Class: |
420/1 |
Current CPC
Class: |
B09B 3/00 20130101; G21F
9/30 20130101; G21F 9/007 20130101; Y10S 588/901 20130101; G21F
9/06 20130101; H05B 2206/046 20130101; H05B 6/24 20130101; G21F
9/302 20130101; Y02P 10/25 20151101; C22C 43/00 20130101; G21F
9/308 20130101; G21F 9/12 20130101; G21F 9/16 20130101; Y02P 10/253
20151101 |
Class at
Publication: |
420/001 |
International
Class: |
C22C 043/00 |
Claims
1. A storage product for storing a fast neutron emitting isotope,
the storage product including: (a) a metal alloy including a
chemically active metal fraction in an amount effective for
chemically reducing organic feed materials, the metal alloy also
encompassing a quantity of a fast neutron emitting isotope; (b) a
transmutation target fraction forming part of the metal alloy, the
transmutation target fraction made up of a transmutation target
material for absorbing fast neutrons emitted by the fast neutron
emitting isotope; (c) a transmutation emission absorbing fraction
forming part of the metal alloy, the transmutation emission
absorbing fraction made up of a transmutation emission absorbing
material for absorbing emissions resulting from the absorption of a
respective fast neutron by the transmutation target material; and
(d) wherein the metal alloy is solidified from a molten state to
form a storage ingot with the fast neutron emitting isotope, the
chemically active metal fraction, the transmutation target
fraction, and the transmutation emission absorbing fraction being
substantially evenly distributed within the ingot.
2. The storage product of claim 1 wherein: (a) the transmutation
target fraction includes no less than approximately three hundred
and sixty-five (365) atoms of transmutation target material for
each atom of the fast neutron emitting isotope in the storage
product; and (b) the transmutation emission absorbing fraction
includes no less than approximately three hundred and sixty-five
(365) atoms of transmutation emission absorbing material for each
atom of the fast neutron emitting isotope in the storage
product.
3. The storage product of claim 1 wherein the transmutation target
material is made up of metals selected from the group consisting of
boron, beryllium, lithium, magnesium, aluminum, zinc, and
cadmium.
4. The storage product of claim 1 wherein the transmutation
emission absorbing fraction is made up of metals selected from the
group consisting of boron, cadmium, and gold.
5. The storage product of claim 1 further including a radioactive
isotope that does not emit fast neutrons, and for each type of
expected radioactive emission associated with the radioactive
isotope in the storage product, at least one corresponding
radiation absorbing metal, each corresponding radiation absorbing
metal being capable of absorbing the respective type of expected
radioactive emission.
6. A metal alloy solidified from a molten state to form an ingot
which provides a storage product for a storing a fast neutron
emitting isotope, the metal alloy including: (a) a chemically
active metal fraction in an amount effective for chemically
reducing organic feed materials; (b) a transmutation target
fraction, the transmutation target fraction made up of a
transmutation target material for absorbing fast neutrons emitted
by the fast neutron emitting isotope; and (c) a transmutation
emission absorbing fraction, the transmutation emission absorbing
fraction made up of a transmutation emission absorbing material for
absorbing emissions resulting from the absorption of a respective
fast neutron by the transmutation target material, the
transmutation emission absorbing fraction being substantially
evenly distributed within the ingot with the fast neutron emitting
isotope, the chemically active metal fraction, and the
transmutation target fraction.
7. The metal alloy of claim 6 wherein: (a) the transmutation target
fraction includes no less than approximately three hundred and
sixty-five (365) atoms of transmutation target material for each
atom of the fast neutron emitting isotope in the storage product;
and (b) the transmutation emission absorbing fraction includes no
less than approximately three hundred and sixty-five (365) atoms of
transmutation emission absorbing material for each atom of the fast
neutron emitting isotope in the storage product.
8. The metal alloy of claim 6 wherein the transmutation target
material is made up of metals selected from the group consisting of
boron, beryllium, lithium, magnesium, aluminum, zinc, and
cadmium.
9. The metal alloy of claim 6 wherein the transmutation emission
absorbing fraction is made up of metals selected from the group
consisting of boron, cadmium, and gold.
10. The metal alloy of claim 6 wherein the ingot provides a storage
product for storing a radioactive isotope that does not emit fast
neutrons and further including for each type of expected
radioactive emission associated with the radioactive isotope in the
storage product, at least one corresponding radiation absorbing
metal, each corresponding radiation absorbing metal being capable
of absorbing the respective type of expected radioactive
emission.
11. A storage product for storing a fast neutron emitting isotope,
the storage product including: (a) 40% or more of a chemically
active fraction; (b) the fast neutron emitting isotope; (c) a
transmutation target fraction made up of a transmutation target
material for absorbing fast neutrons emitted by the fast neutron
emitting isotope; and (d) a transmutation emission absorbing
fraction made up of a transmutation emission absorbing material for
absorbing emissions resulting from the absorption of a respective
fast neutron by the transmutation target material, the
transmutation emission absorbing material being alloyed with and
substantially evenly distributed with the fast neutron emitting
isotope, the chemically active fraction, and the transmutation
target fraction.
12. The storage product of claim 11 wherein: (a) the transmutation
target fraction includes no less than approximately three hundred
and sixty-five (365) atoms of transmutation target material for
each atom of the fast neutron emitting isotope in the storage
product; and (b) the transmutation emission absorbing fraction
includes no less than approximately three hundred and sixty-five
(365) atoms of transmutation emission absorbing material for each
atom of the fast neutron emitting isotope in the storage
product.
13. The storage product of claim 11 wherein the transmutation
target material is made up of metals selected from the group
consisting of boron, beryllium, lithium, magnesium, aluminum, zinc,
and cadmium.
14. The storage product of claim 1 1 wherein the transmutation
emission absorbing fraction is made up of metals selected from the
group consisting of boron, cadmium, and gold.
15. The storage product of claim 1 1 further including a
radioactive isotope that does not emit fast neutrons, and for each
type of expected radioactive emission associated with the
radioactive isotope in the storage product, at least one
corresponding radiation absorbing metal, each corresponding
radiation absorbing metal being capable of absorbing the respective
type of expected radioactive emission.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 10/059,808, filed Jan. 29, 2002, entitled
"METAL ALLOY AND METAL ALLOY STORAGE PRODUCT FOR STORING
RADIOACTIVE MATERIALS," which is a continuation-in-part of U.S.
patent application Ser. No. 09/334,985, filed Jun. 17, 1999, and
entitled "REACTANT METAL ALLOY TREATMENT PROCESS FOR RADIOACTIVE
WASTE (as amended)," (now U.S. Pat. No. 6,355,857) which was a
continuation-in-part of U.S. patent application Ser. No.
09/096,617, filed Jun. 12, 1998, entitled "REACTANT METAL ALLOY
TREATMENT PROCESS AND STORAGE PRODUCT FOR RADIOACTIVE WASTE," and
also U.S. patent application Ser. No. 09/274,583, filed Mar. 23,
1999, entitled "HIGH TEMPERATURE MOLTEN METAL REACTOR AND WASTE
TREATMENT PROCESS" (now U.S. Pat. No. 6,195,382). The Applicant
claims the benefit of U.S. patent application Ser. Nos. 10/059,808,
09/334,985, 09/096,617 and 09/274,583 under 35 U.S.C. .sctn. 120.
The entire content of U.S. Pat. No. 6,355,857 B1, U.S. Pat. No.
6,195,382 B1, and U.S. patent application publication No.
2002-0173687 A1 (relating to U.S. patent application Ser. No.
10/059,808) are incorporated herein by this reference.
TECHNICAL FIELD OF THE INVENTION
[0002] This invention relates to liquid metal alloys for use in
waste treatment processes and to waste storage products produced
using liquid metal alloys. More particularly, the invention relates
to liquid metal alloys for treating waste streams that include fast
neutron emitting radioactive isotopes. The invention also
encompasses a metal alloy storage product for use in storing
radioactive isotopes that emit fast neutrons.
BACKGROUND OF THE INVENTION
[0003] Many waste treatment processes utilize thermal energy to
break up waste materials into their constituent elements or more
desirable compounds. The use of thermal energy to break down
materials is referred to generally as pyrolization. Molten or
liquid phase metals have also been used to react with certain waste
materials in order to produce more desirable compounds or reduce
the waste to constituent elements. In particular, liquid aluminum
has been used to react with halogenated hydrocarbons and produce
aluminum salts. U.S. Pat. No. 4,469,661 to Shultz described the
destruction of PCBs and other halogenated hydrocarbons by
contacting the hydrocarbon vapor with liquid aluminum. The aluminum
was contained in low-boiling eutectic mixtures of aluminum and zinc
or aluminum, zinc, and magnesium. Shultz also suggested eutectic
reactant mixtures containing iron, calcium, and other metals. U.S.
Pat. No. 5,640,702 to Shultz disclosed a liquid metal treatment for
wastes containing radioactive constituents. This patent to Shultz
disclosed using lead in the liquid reactant metal as a chemically
active material for reacting with non-radioactive constituents in
the waste to be treated.
[0004] U.S. Pat. No. 5,000,101 to Wagner disclosed a process for
treating hazardous waste material with liquid alkaline metal
alloys. The liquid metal alloy comprised approximately 50%
aluminum, 5% to 15% calcium, 5% to 15% copper, 5% to 15% iron, and
5% to 15% zinc. U.S. Pat. No. 5,167,919 to Wagner disclosed a
reactant alkaline metal alloy composition comprising between 40% to
95% aluminum, 1% to 25% iron, 1% to 25% calcium, 1% to 25% copper,
and 1% to 25% zinc. The '919 Wagner patent also disclosed that
magnesium could be substituted for calcium. In both of these Wagner
patents, the waste material was reacted in the liquid alloy held at
about 800 degrees Celsius.
[0005] In the process disclosed in the above-described Wagner
patents, chlorine atoms in the waste material were stripped from
the waste compound primarily by the highly reactive aluminum in the
liquid reactant alloy. The aluminum and chlorine combined to form
aluminum chloride. Carbon from the original waste compound was
liberated either in elemental form or as char (CH, CH.sub.2, or
CH.sub.3). Both the aluminum chloride and liberated elemental
carbon sublimed to a gaseous state at the 800 degree Celsius
reaction temperature and were drawn off and separated.
[0006] Many hazardous waste sites have different types of wastes
mixed together. The mixed waste may include numerous different
types of halogenated hydrocarbons, other non-radioactive wastes,
and radioactive isotopes. These mixed wastes which include
radioactive and non-radioactive materials have proven particularly
difficult to treat. Although, many non-radioactive wastes may be
treated chemically and broken down into benign or less hazardous
chemicals, radioactive constituents of the mixed waste stream
cannot be manipulated to reduce or eliminate their radioactive
emissions. It is desirable to separate the radioactive constituents
from the other materials in the mixed waste and place the
radioactive constituents in an arrangement for safe, long term
storage.
[0007] Storing radioactive waste poses several problems in itself.
For a radioactive isotope which has a long half life, a quantity of
the material remains radioactive for many years. Thus, a storage
arrangement for this long-lived radioactive waste must be capable
of securely holding the waste for a very long period of time.
However, radioactive emissions, particularly alpha radiation, can
interact with the material of a container intended to store
radioactive waste. This interaction can cause the container to
degrade relatively quickly, long before the radioactive waste
itself has degraded.
SUMMARY OF THE INVENTION
[0008] A storage product according to the invention includes at
least one chemically active metal for reacting with non-radioactive
material in a mixed waste stream being treated. The storage product
also includes at least one transmutation target metal and at least
one transmutation emission absorbing metal which form a metal alloy
with the chemically active metal or metals. A fast neutron emitting
radioactive isotope from the waste stream is distributed throughout
the chemically active and other metals included in storage product.
With the fast neutron emitting material dispersed and distributed
in the chemically active and other metals, the transmutation target
metals are able to absorb a significant portion of the emitted fast
neutrons, and the transmutation emission absorbing metals are able
to absorb radioactive emissions resulting from the absorption of
the fast neutrons.
[0009] To form the storage product, the chemically active metal,
transmutation target metal, and transmutation emission absorbing
metal are held in a liquid state and the waste stream is added
thereto. Non-radioactive constituents in the waste material are
broken down into harmless and useful constituents, leaving the fast
neutron emitting isotope in the chemically active and other metals.
The chemically active metal, fast neutron emitting isotope, and
other metals may then be cooled to form one or more ingots in which
the fast neutron emitting isotope is effectively isolated and
surrounded by the transmutation target material and radiation
absorbing metals. The ingots may be encapsulated in one or more
layers of radiation absorbing material and then stored.
[0010] The chemically active metal may comprise any metal capable
of reacting chemically with one or more non-radioactive
constituents in the waste stream. Preferred chemically active
metals include magnesium, aluminum, lithium, zinc, calcium, and
copper. In one preferred form of the invention, a combination of
these metals is included in the storage product. The particular
chemically active metal or combination of chemically active metals
used in a particular application will depend upon the makeup of the
wastes in the waste stream and the reaction products which are
desired from the treatment process. The relative amount or fraction
of chemically active metal or combination of active metals in the
alloy (the "chemically active fraction") is preferably sufficient
to both completely react the organic constituents and other
reducible materials in the waste stream and help dissolve and
disperse the radioactive isotopes in the remaining unreacted liquid
metal. Preferably this chemically active metal fraction in the
alloy and resulting storage product is no less than forty percent
(40%) by weight of the storage product.
[0011] The storage product and metal alloy according to the
invention may be adapted to store radioactive isotopes other than
fast neutron emitters. Additional radiation absorbing metals are
included in the storage product to absorb radiation emitted from
these additional radioactive isotopes. These additional radioactive
isotopes are evenly distributed in the metal alloy and resulting
storage product together with the chemically active fraction,
transmutation target material, transmutation emission absorbing
material, and fast neutron emitting isotope. Each radiation
absorbing metal included in the metal alloy is matched with a
particular radioactive isotope to be alloyed with, or dissolved in,
the metals in the liquid metal bath. That is, for each type of
expected radioactive emission associated with a radioactive isotope
to be alloyed, a radiation absorbing metal is included in the alloy
for absorbing that particular type of emission. A particular
radiation absorbing metal for absorbing a particular radioactive
emission will be referred to herein as a corresponding radiation
absorbing metal for that emission. Similarly, a particular
radioactive emission which may be absorbed by a particular
radiation absorbing metal will be referred to herein as a
corresponding radioactive emission for that radiation absorbing
metal. Preferred radiation absorbing metals include particular
isotopes of lead, beryllium, cadmium, vanadium, yttrium, ytterbium,
zirconium, and tungsten. One or more of these radiation absorbing
metals may be used within the scope of the invention depending upon
the radioactive isotopes to be added to the liquid metal bath. For
purposes of this disclosure and the accompanying claims, a
"radiation absorbing metal" comprises a metal which is capable of
capturing a particular expected radioactive emission, that is, a
particular emission at a natural decay energy level.
[0012] As used in this disclosure and the following claims, the
"type of expected radioactive emission" associated with an isotope
in the waste material to be treated refers to the particular type
of both primary and secondary emission (alpha, beta, gamma, or
neutron) characteristic of the isotope and any daughter isotope,
and the characteristic energy level of each emission. The "expected
radioactive emission" refers to each respective emission within
each type of emission. For the purposes of this disclosure and the
following claims, a "primary radioactive emission" comprises the
emission or emissions directly from the radioactive decay of an
isotope. For most radioactive isotopes, the primary radioactive
emissions will include either an alpha or beta emission at a
characteristic energy level and a gamma emission at a
characteristic energy level. A "secondary radioactive emission,"
for the purposes of this disclosure, comprises a radioactive
emission resulting from a primary radioactive emission. A secondary
radioactive emission (commonly gamma radiation or a liberated
neutron) is generated as a primary radioactive emission is absorbed
by an absorbing material or as a primary radioactive emission
otherwise interacts with matter.
[0013] Although the invention has particular application in
treating mixed waste streams that include both radioactive and
non-radioactive wastes, those skilled in the art will appreciate
that a waste stream made up of only radioactive materials may be
treated using the present process. The metal alloy according to the
invention is useful for diluting and alloying or otherwise holding
the radioactive isotopes for storage even in the absence of
non-radioactive wastes.
[0014] Regardless of the particular composition of the chemically
reactive fraction according to the invention, the metal alloy
including the chemically reactive fraction is heated to a liquid
state for receiving the waste stream. It is typically desirable to
use the lowest metal alloy temperature necessary to react any
non-radioactive constituents in the waste stream and to efficiently
melt or dissolve the radioactive material into the alloy. For mixed
wastes that include organic constituents, a metal alloy temperature
of at least 770 degrees Celsius is generally required to quickly
break the organic molecules down into the desired materials. Higher
temperatures may be desirable to better dissolve or melt heavier
radioactive isotopes such as transuranic elements.
[0015] The metal alloy according to the invention may be heated
using fossil fuel burners. Electrical induction heating systems or
any other suitable heating arrangement may also be used to heat the
metal alloy to the desired operating temperature. The waste
material is introduced directly into the liquid metal alloy,
preferably below the surface of the liquid material.
[0016] The aluminum, magnesium, or lithium in the chemically active
fraction chemically strips chlorine or any other halogen atoms from
organic molecules in the waste material to form a metal salt. Some
of these metal salts may remain in a liquid state and separate by
gravity separation in the reactant alloy container. Other metal
salts such as aluminum chloride, for example, go to a gaseous state
at the temperature of the liquid alloy. Gas released in the
treatment process may be drawn off and scrubbed in an aqueous
scrubber/separator to produce a slurry of carbon, char, and salt
solution. The salt solution may then be separated and processed to
recover the salts, carbon, and char. Each material produced in a
reaction with a chemically active metal in the alloy will be
referred to in this disclosure as a reaction product.
[0017] In order to produce a mechanically stable ingot for
long-term storage, the amount of radiation absorbing metal in the
metal alloy is maintained at a particular minimum ratio to the
number of radioactive isotopes in the resulting alloy or as a
function of the corresponding expected radioactive emissions in the
volume of the resulting alloy. The preferred ratio comprises no
less than approximately seven hundred and twenty-seven (727) atoms
of radiation absorbing metal to the corresponding radioactive
emission. This ratio produces an alloy in which radioactive
emissions may be absorbed by the radiation absorbing metals without
significantly degrading the mechanical integrity of the ingot.
[0018] One preferred form of metal alloy according to the invention
includes a compact crystal forming metal to help create a compact
or close packed crystalline lattice structure in the resulting
solidified storage product. A particularly desirable crystalline
lattice structure in the resulting product comprises a hexagonal
crystalline structure which may be produced with tungsten. The
preferred relative amount or fraction of tungsten in the resulting
storage product is one tungsten atom for every twenty-seven atoms
of other elements in the storage product.
[0019] One advantage of the treatment process according to the
invention is that it combines the separation of radioactive waste
from non-radioactive wastes with the chemical treatment of
non-radioactive wastes. Also, the ingots which result from the
process are very stable. There is very little chance for release of
the alloyed or otherwise dispersed radioactive isotopes from the
ingots. Furthermore, radioactive emissions from the ingots are
reduced by the radiation absorbing metals which are distributed
throughout the matrix of the alloy along with the radioactive
isotopes. The radiation absorbing metals also serve to prevent the
radioactive emissions from adversely affecting the other metals in
the ingots and prevent significant mechanical degradation in the
alloy material.
[0020] These and other advantages and features of the invention
will be apparent from the following description of the preferred
embodiments, considered along with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] FIG. 1 is a block diagram showing a treatment process
utilizing a reactant metal alloy embodying the principles of the
invention.
[0022] FIG. 2 is a diagrammatic representation of an apparatus for
performing the treatment process shown in FIG. 1.
DESCRIPTION OF PREFERRED EMBODIMENTS
[0023] A reactant alkaline metal alloy composition embodying the
principles of the invention includes one or more chemically active
alkaline metals and one or more radiation absorbing metals. This
combination of chemically active metals and radiation absorbing
metals is used to treat wastes that include radioactive isotopes
and to produce a storage product for such radioactive isotopes. The
alkaline metals make up a chemically active metal fraction in the
alloy and resulting storage product, and are included for
chemically reacting with hydrocarbon and other non-radioactive
wastes in a waste stream, and for facilitating the alloying or
dissolution of radioactive isotopes. Radiation absorbing metals
generally do not react chemically in any substantial degree with
any material in the waste stream and are included in the metal
alloy only for their radiation absorption characteristics. Also,
the radiation absorbing metals are matched by their radiation
absorption characteristics to radioactive isotopes to be added to
the metal alloy and, more particularly, to the radioactive
emissions expected within the resulting alloy.
[0024] The chemically active alkaline metal or metals in the metal
alloy may comprise, aluminum, magnesium, lithium, calcium, iron,
zinc, and copper. The aluminum, magnesium, and/or lithium in the
chemically active fraction of the metal alloy react with
halogenated hydrocarbons, to produce aluminum, magnesium, and/or
lithium salts. Calcium, iron, zinc, and copper in the metal alloy
may react with certain non-radioactive constituents in the waste
material, but are primarily included as stabilizing agents for the
aluminum, magnesium, and/or lithium in the metal alloy.
[0025] The radiation absorbing metal or metals in the metal alloy
may comprise particular isotopes of beryllium, cadmium, vanadium,
yttrium, ytterbium, zirconium, tungsten, or lead. Various isotopes
of these metals exhibit a low fission neutron cross section which
allows them to absorb radioactive emissions to produce either a
stable isotope or an isotope which emits only relatively low energy
radiation. Table 1 shows a list of preferred radiation absorbing
metals which may be employed in the metal alloy within the scope of
the invention. Table 1 also lists the particular radioactive
emissions which each radiation absorbing metal is capable of
absorbing. The particular radiation absorbing metal or metals
chosen for an application will depend upon the nature of the
radioactive isotopes in the waste stream being treated.
Specifically, a radiation absorbing metal is included in the metal
alloy for each corresponding expected radioactive emission. Thus,
for each type of expected radioactive emission associated with an
isotope added to the alloy, an absorbing metal is included for
absorbing that particular type of radioactive emission.
1TABLE I ABSORPTION ELEMENT ISOTOPE CHARACTERISTIC LEAD 197-207
GAMMA ABSORBER AT .72 MeV AND HIGHER 208-214 BETA ABSORBER TUNGSTEN
173-183 GAMMA ABSORBER 186-189 BETA ABSORBER 184 BETA AT .429 MeV
185 GAMMA AT 0.075 MeV VANADIUM 46 BETA AT 6.03 MeV AND GAMMA AT
.511 MeV 47 BETA AT 1.89 MeV AND GAMMA AT .511 MeV 48 BETA AT .696
MeV AND GAMMA AT .511 MeV 50 GAMMA AT .783 AND 1.55 MeV 52-54 BOTH
BETA AND GAMMA AT CERTAIN ENERGY LEVELS YTTRIUM 82-96 BETA AT
.008-3.06 MeV 89 GAMMA AT .91 MeV 90 GAMMA AT .202 MeV 91 GAMMA AT
.551 AND .534 MeV 95 GAMMA AT 1.3 AND 1.8 MeV YTTERBIUM 154-164
ALPHA 162 BETA 175, 177 BETA 166-169, GAMMA 171, 176 CADMIUM 99-124
BETA ABSORBER, NEUTRONS AT 2,200 M/SEC BERYLLIUM 8 ALPHA ABSORBER
10-11 ALPHA AND BETA ABSORBER ZIRCONIUM ALL BETA ABSORBER AT 0.38
TO 0.65 MeV
[0026] Those skilled in the art will appreciate that many of the
above-identified preferred radiation absorbing metals are
themselves unstable isotopes and are subject to radioactive decay.
However, the emission energies associated with these isotopes are
sufficiently low to avoid substantial radiation leakage from the
resulting storage product and mechanical degradation of the storage
product.
[0027] The metal alloy produced according to the invention includes
sufficient radiation absorbing metal for each corresponding
expected emission to maintain a minimum ratio of radiation
absorbing metal atoms to the respective corresponding expected
radioactive emissions. The preferred ratio is no less than seven
hundred and twenty-seven (727) atoms of radiation absorbing metal
for each corresponding expected radioactive emission. Higher ratios
may also be used within the scope of the invention. Lower ratios
may also be used, albeit with an increased risk of radiation
leakage from the resulting storage product.
[0028] As radioactive isotopes are alloyed into the chemically
active fraction and other metals in the metal alloy, the atoms of
radioactive material are incorporated into the matrix of the metal
alloy and isolated among the atoms of metals in the alloy. Most
importantly, the atoms of radioactive isotopes are substantially
distributed and isolated among the atoms of corresponding radiation
absorbing metal in the alloy. As used herein to describe the
radioactive isotopes added to the liquid metal bath, the term
"alloyed" means dissolved or otherwise dispersed and intimately
mixed with the liquid reactant metal. This dispersion and resulting
isolation of the radioactive isotopes in the metal alloy matrix
among the corresponding radiation absorbing metals at the desired
minimum ratio helps ensure that most radioactive emissions from the
radioactive isotopes will be captured within the metal alloy
storage product, thereby reducing overall radioactive emissions
from the storage product. The specific absorbing metals absorb the
radioactive emissions without substantially reducing the mechanical
integrity of the storage product.
[0029] One preferred metal alloy according to the invention
additionally includes a fraction of material for producing a
desirable crystalline structure in the storage product. This
material comprises a compact crystal forming metal for producing a
close packed crystalline structure in the resulting storage
product. One preferred close packed crystalline structure comprises
a hexagonal structure such as that produced by tungsten. Generally,
one atom of tungsten will order 27 other atoms within its close
packed hexagonal crystalline structure. The preferred concentration
of tungsten in a storage product according to the invention is one
atom for every 27 atoms of other metals in the storage product. Six
of these groups comprising one tungsten atom and 27 other atoms
combine to form a complete crystalline structure. Including less
that one tungsten atom for every 27 other atoms in the storage
product will result in some of the other atoms in the storage
product being excluded from the desired close packed crystalline
structure. However, the desired crystalline structure will be
present for the 27 atoms ordered for the included tungsten atom.
Providing the close packed crystalline structure throughout the
resulting storage product has the effect of increasing the
likelihood that a particular emission will be absorbed within the
storage product. Thus, tungsten is preferably included in the metal
alloy in sufficient quantity to result in this one to twenty-seven
ratio in the resulting storage product. The desired crystalline
structure may allow fewer radiation absorbing metals to be included
in the storage product and still provide effective absorption of
emissions within the storage product.
[0030] It will be noted that tungsten may also serve as a radiation
absorbing metal in the resulting storage product, depending upon
the nature of emissions expected in the storage product. The
ability to absorb certain radioactive emissions does not diminish
or impact the compact crystal forming effect of tungsten in the
resulting storage product.
[0031] The metal alloy may include one or more of the following
chemically active alkaline metals in the indicated concentration
range: between about 1% to 25% zinc, between about 1% to 25%
calcium, between about 1% to 25% copper, between about 1% to 25%
magnesium, between about 1% to 25% lithium, and between about 10%
to 90% aluminum. The metal alloy may include one or more of the
following radiation absorbing metals: lead, tungsten, beryllium,
cadmium, vanadium, yttrium, ytterbium, and zirconium. Each of these
radiation absorbing metals will commonly be present in the metal
alloy in a concentration range of between about 1% to 25% of the
total alloy. All percentages used in this disclosure are by weight
of the total metal alloy. Table 2 sets out nine different preferred
metal alloys tailored for various waste streams. Each percentage in
Table 2 refers to the percentage of a particular radiation
absorbing isotope chosen from Table 1. Table 3 indicates the
particular applications for which the alloys shown in Table 2 are
tailored.
2 TABLE 2 I II III IV V VI VII VIII IX Zinc 3 2 5 -- -- -- -- 3 --
Calcium 2 2 3 -- -- -- -- 2 -- Copper 2 2 3 -- -- -- -- 2 --
Magnesium 10 3 -- -- -- -- -- 3 -- Lead 42 -- -- 25 20 -- 25 8 25
Aluminum 41 51 50 50 40 60 50 30 50 Lithium -- -- 4 -- -- -- -- 10
-- Beryllium -- 40 -- 25 20 15 -- 10 -- Vanadium -- -- 35 -- 20 10
25 10 13 Yttrium -- -- -- -- -- 5 -- 10 -- Zirconium -- -- -- -- --
10 -- 10 -- Tungsten -- -- -- -- -- -- -- 2 12
[0032] Alloys III, VI, and VII are preferably used at an operating
temperature of about 1000 degrees Celsius. Alloy IV is preferably
used in the process of the invention at an operating temperature of
850 degrees Celsius, while alloy V is used at an operating
temperature of 900 degrees Celsius. The operating temperature for a
particular treatment process according to the invention is chosen
based both upon the constituents of the waste stream and the
reaction products to be produced in the process. Higher operating
temperatures may be required to break double and triple carbon
bonds and other types of chemical bonds in the molecules of waste
material being treated. Higher operating temperatures also
generally allow the radioactive constituents in the waste stream to
better dissolve or melt into the metal alloy. Also, the operating
temperature may be increased to allow certain reaction products to
go to a gaseous state and then be removed in gaseous form from the
metal alloy container.
3 TABLE 3 Alloy Waste Stream I Dioxins, organic compounds, gamma
emitters II Chlorinated hydrocarbons, alpha emitters III
Chlorinated hydrocarbons, beta emitters IV Halogenated
hydrocarbons, gamma emitters, and alpha emitters V Halogenated
hydrocarbons, alpha emitters, beta emitters, and gamma emitters VI
Hydrocarbons, halogenated hydrocarbons, and multiple types
radioactive isotopes VII Many mixed wastes, alpha emitters, and
gamma emitters VIII Many mixed wastes including polychlorinated
biphenyls, dioxins, PCP, battery mud, chrome plating salts, inks,
solid rocket fuels, dyes, alpha emitters, beta emitters, and gamma
emitters IX Mixed halogenated hydrocarbons, beta emitters, and
gamma emitters
[0033] Another preferred metal alloy according to the invention is
tailored for processing waste streams containing relatively high
gamma radiation emitting isotopes at 0.72 MeV and higher. This
preferred alloy includes about 25% lead (197-207), about 25%
tungsten (173-183), and about 50% chemically active metal. The
chemically active metal may comprise aluminum and/or magnesium.
[0034] As indicated by the example reactant metal alloys shown in
Tables 2 and 3 and discussed above, the amount of chemically
reactive metal in the alloy preferably always makes up
approximately 40% or more of the alloy by weight. This level of
chemically active metal in the metal alloy is helpful in dissolving
the metal radioactive constituents in the waste stream. The
dissolved radioactive constituents may then be dispersed freely
throughout the liquid metal to produce the desired storage
alloy.
[0035] The radioactive material storage product according to the
invention comprises one or more chemically active metals and one or
more radioactive isotopes. Also, for each type of expected
radioactive emission in the volume of the storage product, the
product further includes a corresponding radiation absorbing metal
adapted to absorb the respective radioactive emission. The
corresponding radiation absorbing metal may be adapted to absorb
radioactive emissions from different isotopes, and thus the storage
product will not always include a separate radiation absorbing
metal for each isotope. Rather, one radiation absorbing metal may
be capable of absorbing two or more types (that is, type and energy
level) of radioactive emissions in the storage product. In any
event, the storage product preferably includes at least about 727
atoms of radiation absorbing metal for each corresponding expected
radioactive emission.
[0036] In another aspect of the invention, the metal alloy and
resulting storage product includes materials specifically suited
for absorbing fast neutrons that may be emitted from isotopes in
the storage product. Fast neutrons, neutrons emitted at an energy
level of ten MeV or greater, may be absorbed by certain materials.
These fast neutron absorbing materials transmutate upon absorption
of the fast neutron to produce a different isotope. This
transmutated material will generally decay with additional
radioactive emissions. According to the invention, where the metal
alloy will receive fast neutron emitters, such as materials from
spent nuclear fuel rods, the alloy will include a transmutation
target fraction made up of transmutation target material for
absorbing fast neutrons emitted by the fast neutron emitting
isotope. The metal alloy will also include a transmutation emission
absorbing fraction made up of transmutation emission absorbing
material for absorbing emissions resulting from the absorption of a
fast neutron by the transmutation target material. These resulting
emissions are all emissions occurring after the initial
transmutating absorption and may be emissions occurring in several
steps.
[0037] Transmutation target material and the fraction of such
material in the alloy and resulting storage product may include
appropriate isotopes of boron, beryllium, lithium, magnesium,
aluminum, sodium, zinc, and cadmium. The transmutation emission
absorbing fraction in the alloy and resulting storage product may
be made up of isotopes of boron, cadmium, and gold.
[0038] The transmutation contemplated in the storage product
according to the invention follows the following emission steps:
Transmutation Target (Target)+fast neutron (N.sub.F)=new
nucleus+atomic particles of low atomic weight (hydrogen nuclei
(H.sup.2 or H.sup.1), .alpha., .gamma.)+lowered kinetic energy. The
transmutation emission absorbing materials (Trans/Ab) then absorb
the atomic particles and in turn emit lower energy particles
including slow neutrons (N.sub.S, less than 10 MeV).
[0039] N.sub.F+TargetNew Nucleus+(H.sup.2, .alpha., H.sup.1,
.gamma.)
[0040] H.sup.2+Trans/AbH.sup.1, N.sub.S, .alpha.
[0041] .alpha.+Trans/AbH.sup.1, N.sub.S
[0042] .gamma.+Trans/AbN.sub.S
[0043] It will be noted that some materials may serve both as
transmutation targets and transmutation emission absorbing
materials.
[0044] In the preferred form of the invention, the transmutation
target fraction in the storage product includes no less than
approximately three hundred and sixty-five (365) atoms of
transmutation target material for each atom of fast neutron
emitting isotope in the storage product. Also, the transmutation
emission absorbing fraction in the storage product includes no less
than approximately three hundred and sixty-five (365) atoms of
transmutation emission absorbing material for each atom of fast
neutron emitting isotope in the storage product. These relative
amounts of transmutation target material and transmutation emission
absorbing material provide the preferred coverage around each fast
neutron emitting atom in the storage product to increase the
likelihood that the fast neutron emission will be absorbed within
the primary crystalline matrix within which the fast neutron
emitter is contained.
[0045] With each metal alloy composition according to the
invention, the alloy is heated to a liquid state to prepare the
material for receiving the waste stream. Typically, the temperature
of the liquid alloy must be maintained at no less than 770 degrees
Celsius in order to provide the desired reaction with organic
molecules in the waste material. Higher temperatures for the liquid
alloy may also be used within the scope of the invention as
discussed above with reference to Table 3. Lower temperatures may
also be used where relatively few non-radioactive constituents are
included in the waste stream or only relatively light hydrocarbons
are included in the waste. In any event, the operating temperature
should be a temperature sufficient to place the particular metal
alloy in a liquid state and sufficient to allow the radioactive
metals in the waste material to dissolve or melt into the bath.
[0046] The metal alloy treatment process according to the invention
may be used to treat many types of radioactive waste materials and
mixed waste streams including both radioactive waste and
non-radioactive waste. The treatment process is particularly well
adapted for treating wastes which include radioactive constituents
mixed with halogenated hydrocarbons. The radioactive isotopes may
comprise any isotopes which may be alloyed into the particular
liquid reactant metal including, for example, isotopes of
plutonium, radium, and rhodium.
[0047] Certain radioactive isotopes may not alloy into the liquid
reactant metal. Where these isotopes react with metals in the bath
to form reaction products which remain in solid or liquid form,
these reaction products may be thoroughly mixed with the liquid
reactant metal and then cooled while mixed to produce relatively
low emission ingots. Any gaseous reaction products which include
radioactive isotopes will be entrained with the non-radioactive
gaseous reaction products. Some gaseous radioactive isotopes may be
absorbed from the reaction product gas. For example, tritium may be
absorbed by palladium placed in the stream of gaseous reaction
products. However, it is desirable to maintain the operating
temperature of the liquid metal alloy low enough to reduce the
amount of radioactive isotopes which go into gaseous reaction
products. For example, where a radioactive isotope of iodine is
included in the waste stream, the chemically active metal in the
alloy may include aluminum and the operating temperature is
maintained low enough to ensure that the resulting aluminum iodide
remains primarily in a liquid state.
[0048] The aluminum, magnesium, or lithium in the metal alloy
according to the invention strips halogens from the halogenated
hydrocarbons in the waste stream to produce halogen salts. Other
elements in the non-radioactive waste material, such as
phosphorous, sulphur, and nitrogen, are also stripped from the
carbon atoms in the waste material. Much of this other stripped
material forms metal salts (sulfates, nitrates, phosphates) which
separate from the liquid reactant metal by their respective
density. Where these separated materials include only
non-radioactive constituents, they may be separately drawn or
scraped from the liquid reactant metal by any suitable means. Most
of the halogen salts and char go to a gaseous state and are drawn
off for separation and recovery. Any low boiling point metals, such
as arsenic or mercury, for example, which are liberated from the
waste materials are also drawn off in a gaseous state for recovery.
Non-radioactive, relatively high boiling point metals such as
chromium, and radioactive metals in the waste material remain
safely in the liquid alloy. The original metals which make up the
alloy remain in the liquid alloy unless consumed in the formation
of salts and small quantities of oxides.
[0049] The treatment process according to the invention is
illustrated in FIG. 1. The waste material to be treated is first
analyzed to identify the types and concentrations of
non-radioactive chemicals and radioactive isotopes present in the
waste. This analysis step is shown at box 101 in FIG. 1.
Information regarding the types and concentrations of
non-radioactive constituents in the waste material is used to help
choose the types of chemically active metals to be included in the
liquid metal alloy. Information regarding the radioactive isotopes
in the waste material determines the amount and type of radiation
absorbing metals to be included in the liquid metal alloy.
[0050] The types and concentrations of radioactive isotopes and
non-radioactive chemicals in the waste material are preferably
determined using an analytical technique such as mass spectroscopy
at step 101. Of course, any analytical technique will be limited to
certain minimum detection levels below which an isotope or chemical
cannot be detected. The concentration of radioactive isotopes
detected in the waste stream is then used at step 103 to produce an
estimate of the quantity or amount of each radioactive isotope
present in the waste per unit volume or weight.
[0051] Once the amount and type of non-radioactive constituents and
radioactive isotopes in the waste material are known, the metal
alloy for treating a selected volume or weight of the particular
waste material is constructed at step 104. Specifically, a metal
alloy according to the invention is built with chemically active
metals for reacting with the non-radioactive constituents in the
waste material and with sufficient radiation absorbing metals to
produce the desired storage product.
[0052] With the metal alloy built for the particular waste and held
in a liquid state at the desired operating temperature, the process
includes metering the waste material into the liquid reactant metal
at step 105. Any suitable metering device may be used to perform
the metering step according to the invention. Preferably, the
metering device provides a continuous output of volumetric
information (or weight information if it is desired to meter the
waste stream by weight). Since the amount of waste material which
may be added to the liquid metal alloy to produce the desired
storage product (desired minimum ratio) is known, waste material
may be metered into the metal alloy until that known amount is
reached. Alternatively, the continuous output showing the
cumulative amount of waste added to the metal alloy may be used at
step 106 to calculate the total radioactive isotopes in the alloy
and the ratio of radiation absorbing atoms to corresponding
expected radioactive emissions at step 106. This calculation step
also requires the radioactive isotope concentration or amount
information from step 103 and the alloy information from step 104.
The calculation may be performed using a suitable processor (not
shown) connected to receive the required inputs, or may be
performed manually. The calculated ratio or the cumulative amount
may be compared to a corresponding set value at step 107 to provide
a control signal which may be used to automatically stop the
introduction of waste material into the metal alloy.
[0053] The metered amount of waste material is added to the liquid
metal at step 108 in FIG. 1. Also, the preferred form of the
invention includes a separate emission monitoring step to monitor
radioactive emissions from the waste material stream as it is being
directed to the liquid metal alloy. This separate monitoring step,
108 in FIG. 1, may be performed using any suitable radioactive
emission detector to detect anomalous high concentrations of
radioactive isotopes. Suitable devices include gas-filled,
scintillation, or semiconductor type detectors. Regardless of the
detector type, an unexpected spike in radioactive emissions may be
used at decision box 109 to produce a control signal to stop the
waste stream from being introduced into the metal alloy. This
control signal may be automated or may be made manually by an
operator overseeing the treatment process.
[0054] In the preferred treatment process according to the
invention, the metal alloy composition is contained in a reactant
alloy container such that the alloy is substantially isolated from
oxygen. The metal alloy is then heated by a suitable heating
arrangement to the desired operating temperature, which is
generally greater than 770 degrees Celsius as discussed above. Any
remaining oxygen in the reactor vessel quickly reacts with the
metal in the alloy to produce metal oxides which appear as dross at
the surface of the liquid material or sink to the bottom of the
reactant alloy container. In the preferred process, a layer of pure
carbon in the form of graphite is placed at the surface of the
liquid reactant metal alloy. The graphite layer may be from
approximately one-quarter inch to several inches thick and helps
further isolate the liquid alloy from any oxygen which may be in
the reactant alloy container.
[0055] Once the liquid alloy reaches the desired operating
temperature, the waste material is introduced into the liquid alloy
to perform the contacting step shown in FIG. 1. The waste material
is preferably introduced below the surface of the liquid alloy but
may be introduced at the surface of the alloy within the scope of
the invention. The temperature of the metal alloy is maintained at
least at the desired operating temperature as waste material is
added to the liquid alloy. Heat will commonly need to be added
continuously by the heating arrangement in order to maintain the
desired operating temperature. Also, it will be appreciated that
pockets of relatively cooler areas may form momentarily in the
alloy as waste material is added. The bulk of the metal alloy,
however, is maintained at least at the desired operating
temperature. A suitable mixing arrangement may be used with the
reactant alloy container to ensure that the relatively cool waste
material is distributed quickly within the metal alloy and to
ensure that the radioactive isotopes and radiation absorbing metals
are evenly distributed within the alloy. A mechanical stirring
device (not shown) to continuously stir the liquid material
provides a suitable mixing arrangement.
[0056] Once the desired minimum level of radiation absorbing metal
to corresponding expected radioactive emissions is reached for a
given volume of metal alloy according to the invention, the waste
stream is halted and the metal alloy cooled to form one or more
solid ingots of the storage material. Where isotopes of cadmium are
to be included in the storage product, it is necessary to cool the
liquid metal to a temperature low enough to allow the cadmium to go
to a liquid form (725 to 765 degrees Celsius). Thereafter, the
liquid material may be thoroughly mixed prior to further cooling.
The resulting solid ingots each include unreacted alkaline metals,
the radiation absorbing metals, and the radioactive isotopes from
the waste stream, all substantially evenly distributed. Each ingot
is preferably encapsulated with a radiation absorbing encapsulant
material for storage. The encapsulant material preferably includes
a material or combination of materials which together are capable
of absorbing each type of radioactive emission expected from the
resulting ingot. Also, the encapsulant material preferably includes
a close packed crystal forming metal such as tungsten to produce a
desirable crystalline structure in the encapsulant material which
holds the emission absorbing metals closely and thereby increase
the likelihood that a given emission from the storage product will
be absorbed in the encapsulant material and will not penetrate the
encapsulant material. The preferred tungsten concentration in the
encapsulant material is one tungsten atom for each 27 other atoms
in the encapsulant material.
[0057] FIG. 2 shows an apparatus for performing a treatment process
embodying the principles of the invention. The apparatus includes a
reactant alloy container 202, a recovery/recirculation arrangement
240, a feed arrangement 241, and a heating arrangement 242. The
reactant alloy container 202 is preferably built from a suitable
metal which will maintain structural integrity at the desired
elevated temperatures. However, due to the highly reactive nature
of the alloy 210, the reactant alloy container 202 is lined with a
ceramic or other suitable refractory material to prevent the metal
of the container from reacting with the metal alloy. Also, due to
the radioactive material to be alloyed in the process, container
202 also preferably includes a layer S of suitable radiation
absorbing shielding. This shielding is adapted to block or absorb
each type of radioactive emission which may emanate from the
interior of container 202. A cover 203 is connected over container
202 for collecting gaseous reaction products and helping to isolate
the metal bath from oxygen. Although not shown in the drawing,
radiation shielding material is also preferably included in cover
203 and with the feed arrangement 241.
[0058] An expendable hook 205 may be placed in the alloy 210 at the
termination of the process and, after cooling, may be used to lift
the solidified alloy ingot from the reactant alloy container 202.
Alternatively, a suitable drain may be included in container 202
for draining off metal alloy once the desired minimum ratio of
radiation absorbing atoms to corresponding radioactive emissions is
reached.
[0059] Solids may be mixed with liquids to form a slurry and the
slurry introduced similarly to liquid wastes as discussed below.
Also, solids either alone or in the form of a slurry may be
introduced into the container 202 through an auger arrangement or
other suitable arrangement such as that shown in U.S. Pat. No.
5,431,113, the disclosure of which is hereby incorporated herein by
this reference.
[0060] The heating arrangement 242 includes an induction heater,
including an induction heater power supply 206 and induction coils
204 built into the reactant alloy container 202. The coils 204 may
be water-cooled and the water may be used to cool the metal alloy
210 as desired, either during the treatment process or at the
completion of the treatment process. The induction heater
arrangement 242 includes a heater control 209 with a suitable
sensor 209a inside the reactant alloy container 202 for controlling
the induction heater and maintaining the temperature of the metal
alloy 210 at the desired operating temperature. Although the
induction heating arrangement is illustrated in FIG. 1, any
suitable heating arrangement, including a fossil fuel burning
heater may be used to heat the alloy 210 to the desired
temperature. U.S. Pat. No. 5,452,671 to the present inventor
illustrates a fossil fuel fired heating arrangement which may be
used according to the present invention. The disclosure of U.S.
Pat. No. 5,452,671 is hereby incorporated herein by this
reference.
[0061] The feed arrangement 241 includes feed tank 212 and feed
coil 208. Feed tank 212 contains waste material to be processed. A
feed pump 214 pumps the waste material from feed tank 212 to the
reactant alloy container 202 through a metering device 215.
Metering device 215 serves two functions. First, metering device
215 is operated to meter waste material into the alloy 210 at a
rate which does not exceed the capacity of the heater arrangement
242 to maintain the desired operating temperature in the liquid
metal alloy 210. Second, metering device 215 provides information
regarding the amount of waste material added to the liquid reactant
metal. This quantity information may be used to calculate the ratio
of radiation absorbing atoms in the alloy 210 to the atoms of
corresponding expected radioactive emissions. As described above
with reference to FIG. 1, the ratio calculations are preferably
computed automatically and continuously in a suitable control
processor shown at reference number 243 in FIG. 2. Control
processor 243 also receives information concerning the radiation
absorbing metals in container 202 and information concerning the
concentration (or amount) of various radioactive isotopes in the
waste material to be treated. Alternatively to calculating the
ratio as waste material is being added to the liquid metal bath,
the quantity information used to build the liquid reactant alloy
can be used to limit the amount of waste material metered through
metering device 215.
[0062] Feed system 241 also preferably includes a radioactive
emission monitoring device 244 connected in position to monitor the
stream of waste material being directed to the liquid metal 210 for
treatment. Monitoring device 244 may be located in a recirculation
manifold shown generally at 245. Should monitoring device 244
detect a spike in radioactive emissions from the waste stream,
controller 243 (or an operator) may close valve 245a and open valve
245b to circulate the waste stream back to feed tank 212.
Alternatively to the manifold arrangement, the feed pump 214 can
simply be turned off to halt the flow of waste material into the
metal alloy 210.
[0063] Feed coil 208 is coated on its interior and exterior
surfaces or formed from a ceramic or other suitable refractory
material to prevent the coil from reacting with the liquid alloy
210 in container 202. The outlet end of the coil is preferably
positioned well below the surface of the alloy 210 to ensure good
contact between the waste material and liquid metal alloy 202. The
feed system 241 also preferably includes a gas purging arrangement
including a gas storage cylinder 216 for containing a suitable
purge gas such as nitrogen. The gas purging arrangement is operated
to purge the feed lines and coil 208 of air prior to operation of
the system. Gases other than nitrogen may be used to purge the
system of oxygen, including flue gases from a fossil fuel burning
heater arrangement.
[0064] The recovery/recirculation system 240 includes an aqueous
scrubber/separator 224, a char/water separator 230, a salt recovery
arrangement 231, and a recirculation arrangement 232. Off-gas from
the area above the liquid alloy 210 in container 202 comprising
gaseous halogen salts, char, and other gases are drawn off through
line 218. Line 218 is preferably made of stainless steel and
includes a relief valve 220 to maintain atmospheric pressure on
line 218. A water spray nozzle 222 is associated with the
scrubber/separator 224 and serves to spray water into the off-gas
at the inlet to the scrubber/cyclone separator. The water sprayed
into the off-gas causes the char to coalesce while the salt in the
off-gas goes into solution in the water. The amount of water
supplied through nozzle 222 is preferably controlled with
temperature controller 223 to maintain the temperature below about
100 degrees Celsius in the scrubber/separator 224. A char slurry
forms in the bottom of the scrubber/separator 224 and is drawn off
through valve 226. The slurry comprises char and water with salt in
solution. The char slurry is directed to char/water separator 230
which separates out the fine char particles from the water solution
and passes the water solution through pump 233 on to salt recovery
system 231. Salt recovery system 231 may comprise an evaporative
system. Water from salt recovery system 231 may be recycled to
nozzle 222. Any gas from separator/scrubber 224 may be vented to
the atmosphere through a suitable radiation monitoring arrangement
(not shown). Alternatively, gas from separator/scrubber 224 may be
drawn off through recirculation fan 228 and reintroduced to the
area above the liquid alloy 210 for recycling through the
system.
[0065] It will be appreciated that a metal alloy according to the
invention may be used in other types of apparatus to produce the
desired storage product. The invention is not limited to the
illustrated apparatus. For example, an apparatus such as that shown
in U.S. patent Ser. No. 10/014,976, entitled "MOLTEN METAL REACTOR
UTILIZING MOLTEN METAL FLOW FOR FEED MATERIAL AND REACTION PRODUCT
ENTRAPMENT" may be used with an alloy according to the invention to
produce the desired storage product. The entire content of this
application to the present invention is incorporated herein by this
reference.
EXAMPLE I
[0066] A waste material is analyzed with a mass spectrometer and
found to comprise thorium 229 at 9 parts per million (ppm), PCBs at
500 ppm, and creosote at 1000 ppm in water. To treat one ton of the
waste material, a liquid metal alloy according to the invention may
include predominantly aluminum and perhaps small percentages of
zinc, iron, copper, and calcium. The primary emissions of thorium
229 include alpha particles at 5.168 MeV. Beryllium 11 is added to
the chemically active fraction as a corresponding absorber for the
alpha emissions and lead 206 is added to absorb the primary gamma
emissions from the thorium 229 and secondary gamma emissions as the
alpha particles interact with materials in the bath. The 9 ppm of
thorium 229 equates to 6.412 grams of the isotope per ton of the
waste material. 6.42 kilograms of beryllium 11 is included in the
metal bath to provide a one thousand to one correspondence between
the beryllium and the expected alpha emissions. 12.84 kilograms of
lead 206 is included in the metal bath to provide a one thousand to
one correspondence between the lead and the expected primary and
secondary gamma emissions.
[0067] The above described preferred embodiments are intended to
illustrate the principles of the invention, but not to limit the
scope of the invention. Various other embodiments and modifications
to these preferred embodiments may be made by those skilled in the
art without departing from the scope of the following claims. For
example, although the invention is described above with the metal
alloy being heated to a liquid state in the reactant alloy
container, the alloy constituents may be heated to a liquid state
together or individually outside the reactant alloy container and
added to the container as a liquid material. Heating the
constituent alloy metals outside of the reactant alloy container is
to be considered an equivalent to the embodiment in which the
metals are initially heated to the liquid state within the reactant
alloy container. Furthermore, constituents of the desired metal
alloy may be added while the waste material is being added.
Adjusting the alloy composition of the bath after some waste
material has been added is to be considered equivalent to adding
the waste material to a completely pre-built metal bath. Also,
numerous solid and liquid recovery arrangements may be used within
the scope of the invention instead of the example arrangement 240
shown in FIG. 2.
* * * * *