WO1998044834A1 - Large size, thick-walled ceramic containers - Google Patents

Abstract

A container having a capacity of at least about 0.05 cm3, which comprises a ceramic vessel (6b) having a wall thickness of at least 2.5 cm, wherein the container has been made by a microwave firing process. A containment system is also disclosed for hazardous material or waste which comprises (a) a cylindrical, ellipsoidal or spherical ceramic vessel (6b), having a wall thickness of at least 2.5 cm, optional reinforcing fibers in its walls and; (b) a ceramic lid (6a) having a thickness of at least 2.5 cm, optional reinforcing fibers, said ceramic lid being capable of being seamlessly and nonporously joined to the vessel (7) by microwave energy after the hazardous material or waste is placed in the vessel. An intermediate layer of nuclear shielding material (8) surrounding the first containment system and at least one additional ceramic containment system (12a) surrounding the intermediate layer are also present for nuclear materials or waste.

Description

LARGE SIZE, THICK-WALLED CERAMIC CONTAINERS

BACKGROUND OF THE INVENTION

The present invention relates to a novel container system, which is particularly

useful for containing hazardous materials or waste. The container system is

especially useful for containing hazardous nuclear material or waste, both low level

and high level, particularly for the transport, storage, long-term containerization and

isolation of the nuclear waste for geologic periods of time.

There are currently 109 nuclear reactors in operation in the United States

alone, with a further 424 worldwide. The average nuclear power plant produces about

20 metric tons of spent fuel each year. Current estimates are that the United States

already has 28,000 metric tons of spent fuel stored. This number is expected to rise to

48,000 metric tons by 2003 and to 87,000 metric tons by 2030. These numbers do not

even include waste from military operations. The safe and cost effective disposal of this nuclear waste has created critical problems for the nuclear energy industry, for governments world wide and for the health and safety of humanity.

The U.S. Department of Energy (DOE) Office of Management has described the environmental, safety, and health problems of the nuclear complex and the steps they are taking to address them ("Closing the Circle on the Splitting of the Atom",

January 1995) . They show that the volume of nuclear waste is dramatically

increasing and all existing techniques merely dilute high level radioactive wastes and

byproducts which decrease their concentration with a dramatic increase of the volume of the same environmental and health hazards for both the present and future. The bulk of this spent nuclear fuel is currently in temporary storage pools at the

nuclear reactor sites, awaiting processing and/or transport to permanent storage sites, such as

Yucca Mountain repository (Nevada). Unfortunately, the DOE projects that a significant

number of these temporary sites will be full to capacity by the year 2000. Meanwhile, current

concerns are the Nevada State nuclear waste regulations and new data about the possibility of

a geological cataclysm at a repository site. If such a cataclysm is coupled with a strategy to concentrate a tremendous amount of radioactive materials in one place, it would be difficult

to avoid a spontaneous chain reaction of radioactive materials or to prevent terrorism action.

Nuclear waste may have high or low level of radiation in combination with a

poisoning impact of other chemical hazards. Therefore, a final goal of the nuclear waste

management technology is to keep people and the environment safe in spite of the activities

of the nuclear industry and several thousands of users of radioactive materials in medical and

chemical industries. Up-to-date nuclear waste management methods comprise temporary or

permanent isolation (containment) and/or treatment of the waste. Burying of waste in the

open sea bed or in deep mines are considered to be environmentally irresponsible methods.

Commonly used materials for nuclear waste containment such as concrete, glass and

metals, especially their alloys or contact points with different metals, are more or less

vulnerable to corrosion. This depends on their susceptibility to hydrogen forms and other

dissolved chemicals or their interaction with naturally occurring water vapor (e.g., even the

conventional low air humidity of the Yucca Mountain tunnel). Surplus hydrogen molecules

will also be found within the sealed environment of the waste containment vessel. The

chemical corrosion process can be dramatically accelerated by the combined effects of nuclear radiation and the heat generated within the waste material. Thus, significant leakage

of radioactive waste can be anticipated after only a few dozen years of conventional

containerization. It is a known fact, and all existing government regulations just consider and

limit the radioactive emanation that occurs.

It should also be understood that nuclear or radioactive products cannot lose their

poisoning effects after any chemical and mechanical treatment, such as has been possible

with other chemical hazards. Therefore, chemical treatment and existing clean-up methods

are not applicable to nuclear products, and attempts to do so never produce complete, safe

and permanent isolation of radioactive products at reasonable costs.

However, an existing chemical engineering paradigm recommends the dilution,

extraction and conversion of chemical hazards which appear as byproducts of chemical

manufacturing. However, when glass, metal or concrete are used as diluting agents for the immobilization or incorporation of radioactive waste within an increased volume of the

diluting agents, the critical concentration and poisoning impact of the highest radioactivity is

merely diluted. But the diluting agents are spoiled by the amount of the decreased

concentration of radioactive waste. Glass, metal and concrete packages are second hand

waste products with a dramatically increased volume, and these packages must be stored

again within an additional shell or barrier in order to insulate and confine the diluted nuclear

waste. The present invention does not need to use concrete, glass and metals as the primary

materials for the permanent encapsulation of nuclear waste because any additional treatment or additional material improvement cannot change the chemistry of these materials and their

products being more or less corrosive in any natural environment.

Fortunately, there are naturally occurring minerals and manmade ceramic materials

that have been shown to be thermodynamically, mechanically and chemically stable for geological periods of time (greater than 1 million years). They can withstand the adverse

conditions of temperature extremes, assault by water and other chemicals, intense pressure,

and radioactive bombardment. Extensive study of ceramic behavior in a radioactive

environment has been conducted in the U.S. as well as in the UK and the former USSR with highly encouraging results. They demonstrate structural stability under intense radioactivity.

Certain ceramic compositions can also shield and completely attenuate particular radioactive

emanation.

Thousands of years ago man developed ceramic technology for the conversion of a

plastic clay-water mass into stone-like shaped products of traditional silicate ceramics. More

recent times have seen the development of multi-layer and fiber-containing ceramic

composites and advanced oxide, carbide and nitride ceramics from non-plastic powder

compositions. State-of-the-art methods make it possible to control the structural, mechanical,

refractory, chemical and nuclear resistance and attenuation properties of the ceramic products

by adjusting the ceramic composition and parameters of the technological methods applied.

Ceramics have low thermal conductivity. Therefore, the speed of conventional ceramic processing or the temperature of the external heat impact should be adjusted in

accordance with the ceramic composition and the body volume and shape of the ceramic

product. The greater the body volume, the longer the firing process, resulting in higher energy consumption and, correspondingly, higher processing cost to decrease the ceramic

body thermal gradients during a long firing process.

There are two known approaches to control and accelerate coupling of microwave

energy and "microwave transparent" ceramics, such as alumina and magnesium aluminum spinel. The first employs an outer ceramic blanket or thick-walled casket. Unfortunately, this

method causes an increase in energy consumption while it keeps the same temperature on the

surface of the treated article as in the center of the ceramic body. Another method comprises an application of the various microwave susceptible additives to the ceramic mass, for

example, metal and carbon powders. Unfortunately, residues of these additives can

negatively influence the final properties of ceramics.

Some of the current accomplishments in microwave ceramic processing are described

in Ceramic Transactions, Volume 59, "Microwaves: Theory and Application in Materials

Processing III", Edited by D.E. Clark, D. Folz, S.J. Oda and R. Silberglitt. The American

Ceramic Society, Westerville, Ohio, 1995 and in Ceramic Transactions, Volume 80,

"Microwaves: Theory and Application in Materials Processing IV", Edited by D. Clark, W.

Sutton, and D. Lewis, The American Ceramic Society, Westerwille, Ohio, 1997.

U.S. Patent No. 4,209,420 was granted on June 24, 1980 to ASEA and describes a

method of containing spent nuclear fuel or high-level nuclear fuel waste in a resistant material

for isolating the fuel or the waste from the environment, including the provision of an open

container and a cover fitting the container opening, with both the container and cover being

made of a ceramic material which is given a high density by isostatic hot pressing. The nuclear fuel or the waste is placed in the container, the cover is placed over the opening of the container, and the container with the cover is contained in a gas-tight casing, whereupon the

container and the cover are joined by isostatic hot pressing into a homogeneous monolithic

body within a completely closed space.

U.S. Patent No. 4,726,916 granted February 23, 1988 describes a method of

containing and immobilizing radioactive waste material comprising the steps of:

(a) forming by molding under pressure a containment vessel having a bottom and side

walls, said containment vessel being formed from a porcelain slip;

) (b) mixing the radioactive waste with a ceramic forming composition in proportions

such that the coefficient of expansion of said mixture is substantially equal to the coefficient

of expansion of said porcelain containment vessel;

(c) depositing the radioactive waste/ceramic-forming composition mixture into said

containment vessel;

(d) compacting said mixture under pressure;

(e) placing a cover over said containment vessel, said cover comprising a layer of the

porcelain slip; and

(f) heating the covered vessel at atmospheric pressure so as to allow any gases formed

during heating to escape from the vessel and to solidify said vessel and the mixture therein.

U.S. Patent No. 4,834,917 granted May 30, 1989 describes a waste material such as

toxic compounds, radioactive waste materials and spent nuclear fuel rods which are

encapsulated in a container system, which is subjected to a hot pressure process to cause a

protective powder material located around the waste material to form a dense matrix and

function as a highly corrosion resistant and protective shroud. Embodiments include hot isostatic pressing and hot uniaxial pressing, the use of metal powder such as copper powder

for the protective powder material or alternatively ceramic powder and, depending upon the

embodiment chosen, the use of a single container or dual container system in which a first container is located within an outer container. Either or both of such containers may be

cylindrical with a bellows-like side wall to facilitate compression thereof in an axial

direction.

U.S. Patent No 5,302,565, granted April 12, 1994, describes a container for the encapsulation of nuclear wastes made from a composition comprising naturally occurring red

roan shale clay inherently having an iron/potassium aluminosilicate component and fired at a

temperature of at least 1800°F. for at least 12 hours, the composition being pressed and fired

said shale and including a mixture of feldspar, hematite and quartz, the aluminosilicate component of the clay containing at least 9.89% by weight K₂O, and at least 9.35% by weight

Fe₂O₃

SUMMARY OF THE INVENTION It is an object of the present invention to provide a unique storage container system for

the storage of hazardous material or waste.

It is an object of the present invention to provide a storage system suitable for the

containment of high or low level solid radioactive nuclear material or waste or mixtures of

nuclear waste with hazardous waste.

It is another object of the present invention to provide a nuclear waste containment

system that is suitable for transporting the hazardous nuclear materials or waste. It is another object of the present invention to provide a nuclear waste containment

system that is suitable for containing initial nuclear waste or nuclear waste after treatment.

It is another object of the present invention to provide a containment system that is

suitable for temporary storage of useful materials.

Yet another object of this invention is to provide a nuclear waste storage system that

is capable of being used in an underground storage facility such as that planned for Yucca Mountain Nuclear Repository.

It is a still further object of this invention to provide such a storage system for

hazardous nuclear waste that will be able to resist nuclear radiation, thermal impacts, shock

impacts and other impacts for geologic periods of time.

It is another object of the present invention to provide such hazardous nuclear waste

containment systems which meet all present and foreseeable government requirements for

such systems, both in the United States and in other countries.

These objects, as well as further objects which will become apparent from the

discussion that follows, are achieved, in accordance with the present invention, by a container

which comprises a ceramic vessel suitable for holding material and having a wall thickness of at least about 2.5 cm.

In another embodiment, the containment system of the invention comprises:

(a) a ceramic vessel, preferably cylindrical, ellipsoidal or spherical in shape, suitable

for holding said waste and having a wall thickness of at least about 2.5 cm, optionally

toughened by the incorporation of reinforcing fibers, e.g., alumina, boron nitride or silicon carbide, in its walls, and; (b) a ceramic lid having a thickness of at least about 2.5 cm, optionally toughened by

the incorporation of reinforcing fibers, e.g., alumina, boron nitride or silicon carbide,

dispersed throughout its thickness, said ceramic lid being capable of being seamlessly and nonporously joined to the vessel after the hazardous waste is placed in the vessel, by

microwave energy applied to the interface between the vessel and the lid.

For nuclear materials or waste, there are also present:

c) an intermediate layer of nuclear shielding material surrounding the first

containment system.

d) at least one additional ceramic containment system surrounding the intermediate layer.

Preferably, the container is sealed so as to be gas-impermeable.

BRIEF DESCRIPTION OF THE DRA WINGS

FIG. 1 is a perspective view of a closed and sealed egg-shaped container system of

small or medium capacity.

FIG. 2 is a perspective view of a closed and sealed cylindrical container system of

large capacity.

FIG. 3 is a partial one-quarter vertical section of an egg-shaped ceramic container

system for nuclear or hazardous waste showing the multiple layers of the container.

FIG. 4 is a one-quarter perspective section of a cylindrical container system showing the joints in the multiple layers of the container. FIG. 5 is a partial cross-sectional view of a microwave thermal system surrounding the joints of an interior and exterior set of ceramic containers vessels and lids which provides

integral joining of the vessels and lids of a ceramic container in a container system similar to

the one shown in FIG. 3.

FIG. 6 shows a ceramic container vessel in vertical cross section.

PREFERRED EMBODIMENTS OF THE INVENTION

The present invention is made possible by new scientific principles and engineering

approaches for rapid, cost effective production of large volume and thick- walled multipurpose ceramic containers (MPCC). The ceramic containers vessels and lids that may be

used in the process of this invention may be produced by the process described in the U.S.

Patent Application of Anatoly E. Rokhvarger and Adam B. Khizh, entitled "Process for the

Preparation of Thick- Walled Ceramic Products," which is being filed concurrently herewith

and is incorporated herein by reference. The process to produce the MPCCs of the invention

uses a high temperature, microwave assisted ceramic heating and sintering process. Since microwave energy is absorbed simultaneously throughout the internal mass of the work-piece,

it provides uniform heating of the entire ceramic unit. This new process thus eliminates the

thermal gradients which cause stresses and cracking during conventional external heating.

Generally, the process for the production of the ceramic container vessels and lids

employs a microwave-assisted tunnel furnace (kiln), which is fully controlled to provide a

versatile and sensitive adaptation of the firing and cooling modes. All industrial processing

may be done on a conveyer, making it possible to automate the forming, drying and firing operations. The invention involves the design and use of an advanced microwave assisted

predryer, dryer and kiln to provide ceramic heating and sintering and then subsequent joining

of the container parts at up to about 1600°C. Theoretically, microwave-assisted ceramic

firing has the potential to be 15 - 30 times faster than conventional firing process since

ceramics can absorb more than 95% of the energy delivered by microwaves.

The container systems of the present invention make use of a discovery of a

phenomenon which controls microwave ceramic interaction at low temperatures (up to

850°C). This discovery makes it possible to use a residual-free natural additive and

inexpensively insert it in a ceramic composition. It allows process and quality control of the

container drying and firing. It also makes it possible to develop ceramic sealing compounds

for the joint between the container vessel and the lid. These ceramic compositions selectively

absorb microwave energy and thus provide heat to a small ring of the composition at the

interface between the vessel and the lid, producing a monolithic joint of the ceramic container

vessel and its lid.

A special advantage of microwave ceramic processing is the potential for joining and

sealing thick- walled ceramic pieces. This is possible because of the relative transparency of

the thick-walled ceramic dielectric materials to microwave energy. The ceramic containers

vessels and lids may be joined by the process described in the U.S. Patent Application of

Anatoly E. Rokhvarger and Adam B. Khizh, entitled "Process for Joining Thick-walled

Ceramic Parts," which is being filed concurrently herewith and is incorporated herein by

reference. The thick- walled ceramic container vessels of the invention may be used wherever

there is a need or desire for a thick-walled vessel that is impervious to impurities and that

does not impart any impurities to the contents of the container vessel. For example, they may

be used in fermentation processes, e.g., in making wine or in producing pharmaceuticals.

They may also be used as reactor vessels. They may also be used as caskets for human

remains in the manner of the ancient Egyptians. In addition, they are suitable and decorative

for use as containers for plants and trees. They may also be used for storage of wine and water as is still done in many Mediterranean countries to this day.

In another embodiment, the invention provides an advanced ceramic container system

for direct loading of radioactive waste at the production site and sealing the container system,

followed by interim storage, transportation, and finally permanent storage of the waste in any

underground repository, for example, in the Yucca Mountain underground tunnel loop.

The container system of the invention is readily manufacturable and cost effective for high and low level dry solid nuclear waste and other hazardous materials.

The invention incorporates scientific discoveries, engineering innovation and know-

how from the fields of nuclear waste management, materials science, and ceramic

engineering, including microwave-induced ceramic heating. The invention solves the critical

problem of nuclear waste management. It utilizes a multi-purpose ceramic container (MPCC)

as the baseline storage package for hazardous materials. The MPCC is hermetically sealed

and has certifiable integrity commensurate with safety and environmental regulations and

requirements. The MPCC modules are produced with different forms, sizes and capacities (from

0.1m³ to 10m³). Various ceramic materials will be selected, depending on the waste production conditions, the shape of the solid waste, the waste radiochemistry and the on-site

production yield, as well as waste handling, loading, transportation and repository disposal

techniques. The container system of the invention retains as much as possible of existing

waste management technology. This includes the following conventional steps:

(a) loading of the nuclear waste product in the container,

(b) covering and sealing the container (packaging process),

(c) temporary storage at the waste production site,

(d) transportation of MPCC from site to site or to a repository via truck and rail,

(e) permanent storage of MPCC within an underground repository, and

(f) backfilling of MPCC in the repository using other mineral materials.

During packaging and disposal, the MPCC must provide a complete radiation shield

and a barrier against chemical hazards. The MPCC must have sufficient compressive

strength, fracture resistance and low material creep to withstand a transit collision, lithographic stress or rock collapse at the underground repository. The MPCC must also

withstand:

• electrochemical and chemical corrosion in the presence of other chemical elements,

radioactive materials and solvents; internal (due to radioactive reactions) and external

continuous heating to 600 °C and even up to 1000°C (from a volcanic geological

cataclysm) • radioactive and thermal enhanced chemical and water corrosion of the waste package

materials, including the container material.

The present invention provides a method for the effective and safe storage of nuclear

and hazardous waste in MPCCs of small, medium and large capacities. The containers are

comprised of one or more ceramic shells and an interim shielding bulk layer between two ceramic shells. Each ceramic shell consists of a vessel and a lid that are joined and sealed to

achieve full integrity as a perpetual mechanical barrier and attenuation shield for the stored

nuclear and hazardous dry materials. By "dry' is meant less than 2% water content.

The MPCCs may be used for on-site loading, transportation, and temporary or

permanent storage of high, medium and low level dry nuclear waste in initial conditions,

including untreated nuclear products, such as dismantled atomic weapons or nuclear fuel rods. These containers may be also used for secondary containerization of previously

produced waste packages or their parts, including immobilized glass and concrete blocks or

other solid waste products, such as chemical and medical solid and dry products, diagnostic ampoules and devices, such as irradiated parts of X-ray apparatus.

The containers of the invention are produced from inexpensive ceramics using

specially developed low cost, effective ceramic technology, including an advanced method

employing a multi-faceted optimization of the versatile engineering system which

interactively considers structural design of the ceramic containers and their manufacturing,

assembly and use. The container development includes:

• determination of the sizes and radiation and chemical hazardous properties of the

containment product; 75

• selection and formulation of raw material composition to provide a reliable and durable service life of ceramics, for example, for millions of years;

• determination of the necessary shielding and attenuation properties of the ceramic containers, leading to the selection of the ceramic shell and bulk materials

compositions which result in shell and interim bulk layer thickness;

• structural design of the container construction and especially the external ceramic

shell, applying a probabilistic approach of the finite analysis to fully satisfy

transportation and repository requirements;

• design of the container as customized products, suitable for loading of waste at the

production site, container sealing and transportation to the final repository and the repository setting;

• the ceramic technology, including forming, drying and firing equipment and

processes, employing several inventive steps and advanced statistical design of Multi-

Factor Experiments and Response Surface Analysis methodology;

• engineering development, design, and erection of the forming and thermal aggregates,

which are developed, such as pre-dryers, dryers and kilns using hybrid microwave-

radiative heating of ceramics; and

• development, design and production of the microwave heating system which provides

on-site joining and sealing of the component parts of the ceramic containers.

The containers may be designed to be adaptable to specific forms of radioactive

waste. The construction of containers meet various environmental and industrial requirements, such as existing customer needs for safe, low cost, on-site waste loading,

container covering and sealing, transportation and storage.

The invention contemplates the design of containers adaptable to specific forms of radioactive waste. It employs versatile (waste adjustable) construction of containers meeting

various environmental and industrial requirements, such as existing customer needs for safe,

low cost, on-site waste loading, container covering and sealing, transportation and storage.

The ceramic production techniques include state-of-the-art microwave-assisted

ceramic processing which decreases production costs, intensifies and speeds thermal

processing and improves the quality of the thermal treatment (drying and firing) of thick-

walled, large-size ceramic vessels and lids and makes possible their integration. In order to

improve process and quality control of the microwave ceramic processing, a few advanced

chemical and physical methods are employed. The invention employs several innovations

from materials science and ceramic engineering. These include the use of:

• alumina-based ceramic compositions with glass-fiber reinforcement for the outer

shell,

• eutectic, rheological and sintering stimulation additives, including hydrogen-form

microwave susceptors,

• high density grain-fraction composition and special material mixing sequences,

• combination of powder-forming processes with microwave- assisted predrying and

drying of ceramic vessels and lids,

• special mechanical preforming of both joining ends of container vessels and lids, and • advanced methods and techniques for material and product quality control to insure

container integrity.

Preferably, a feasibility study of ceramic formulations is conducted to determine the exact ceramic formulation and structure for the MPCC. The studies include:

• optimization of ceramic radioactive and chemical resistance;

• enhancement of mechanical strength and toughness of ceramics;

• development and optimization of container construction, including shielding of the

waste radioactivity;

• development and design of specific container production equipment and container

parts joining equipment, including microwave supported dryers, kilns and furnaces;

• investigation and confirmation of nuclear resistance and shielding properties of the

ceramics developed and the container construction;

• development and optimization of container assembly and on-site joining and sealing

techniques; and

• development of nuclear waste management technology using MPCCs.

There are several principal types of radiation ranging downward from high level

nuclear waste, such as spent reactor fuel or dismantled nuclear weapons. Various low level

radioactive waste usually includes some or all of these types.

The inherently harmful radiation is caused by fast neutrons, thermal (slow) neutrons,

γ rays (primary and secondary), and a and β particles. The impact of the first two should be

considered only for nuclear reactor environments or during a short period of time of the

existence of the unloaded waste. A fraction of an inch of a solid substance, such as, ceramics, can stop the electrically charged α and β particles. Any shield thick enough to provide

protection against γ rays and fast neutrons should automatically eliminate the thermal

neutrons coming from radioactive waste.

The number of photons reaching a detector after going through an absorbing media

obeys an exponential law: N = N₀e ^"^ where N₀ is the number of photons reaching the detector in the absence of the absorber of thickness x; μ₀ is the absorption cross section of the

material characteristic of the absorbing medium, x may be expressed in grams per square

centimeter. μ₀ is then in square centimeters per gram, and this coefficient depends upon the

photon energy and material.

Some primary photons are scattered toward the detector. The intensity, I, (in

Roentgens per hour) is given practically by the complicated formula with a special scattering

coefficient B(x), which is a function of the photon energy. For obliquity incidence, the dose

buildup factor is smaller. Because gamma rays are highly penetrating, they are not easily stopped. It requires several thickness of iron, ordinary concrete, and water to equal the

shielding effectiveness of one centimeter of lead for attenuation factors μ t.

For both major types of radiation - fast neutrons and γ rays - attenuation formulas also

include a parameter x with an exponent basis where x is the shielding thickness of the

particular material composition in centimeters. It makes it possible to provide interactive

calculations in order to optimize the container shell material composition, number and

thickness of shells depending on the radioactive characteristics of the particular waste.

At x centimeters from a source that emits N photons per second, of energy E (in MeV)

and an absorption coefficient μ₀ the energy released, Δ, in MeV per cubic centimeter per second can be calculated by a special formula which includes the coefficient X(E). There are

different values of X(E) in cm^"1 and B(E, ^) for various materials. Concrete has

approximately the same properties as aluminum.

Published tables provide the values of the dose correction factor for a parallel

radioactive beam with a thick shield causing an increase in radiation flux reaching an outside

detector. Another problem for the calculation of the shielding is back-scattering of radiation.

Fast neutrons produced by reactor fuel have energies of several hundred keV. The

shield should first slow down the neutrons, then absorb them with larger cross sections.

Both elastic and inelastic collisions of neutrons can occur. However, inelastic collisions, with high energy incoming neutrons cause emission of energetic gamma rays.

This secondary flux must be stopped by external layers of shielding. The inelastic-scattering

cross section depends upon both the energy of the incident neutrons and upon the energy loss

per collision.

Some elements, such as cadmium and boron, have very large capture cross sections.

A 1 mm thick sheet of cadmium or boron reduces the thermal neutron flux by a factor of 10⁵.

Boron captures neutrons with an emission of gamma rays at an energy of about 0.5 MeV

when iron, water, and cadmium produce more energetic gamma rays upon capturing thermal neutrons.

To specify the strength of the γ radiation in a quantitative manner, the flux /is defined

as the number of particles per second crossing an area of 1cm². This definition is applied for

both fast neutrons and γ rays, but the energy flux J is more convenient as the "intensity" and /

= EJ where E is an energy per single photon. Jis expressed in millions of electron volts per square centimeter per second. The production of fast neutrons and γ rays in waste is

proportional to the rate of fission of the remaining U²³⁵ and hence proportional to the thermal

emission produced from the waste.

There are three principal sources of γ radiation in radioactive material: 1) Approximately 5 MeV of "prompt" γ rays which accompanies fission,

2) Another 5 MeV per fission in equilibrium operation of the γ decay of fission

fragments, and

3) Approximately 7 MeV of γ radiation per neutron capture, where 1.5 neutrons

of the 2.5 neutrons produced per fission are eventually captured in non-fissionable material.

Although each γ ray has a specific energy, there are so many different γ ray energies

that, taken together, they comprise a practically continuous distribution. A useful approximation is to represent the γ ray distribution or spectrum by the discrete lines at 1, 3,

and 7 MeV. Usual fractional energy distribution^, from U²³⁵ fission sources may be

approximated as:

E_y = l MeV 3 MeV 7 MeV

f_y = 0.4 0.4 0.2

An average of this energy distribution is about 3 MeV. It is important that 3 MeV γ

rays are well shielded by light elements while 7-MeV rays should be shielded by heavy

elements. These data and figures from references may lead to a conservative shield design if

particular attenuation properties of the shielding materials are known. Defense and civilian industries produce and store a huge volume of many types of

radioactive waste. Radioactive wastes also contain phosphate, organics, ferrocyanides and

other poisonous chemical products.

All types of radioactive waste require temporary storage, for example, in special tanks

and pools. After further treatments and concrete or glass immobilization procedures,

radioactive waste is then transported to a permanent repository site. For this purpose, a waste

package (WP) is prepared. The WP is incorporated in a metal canister. The metal canister

protects the WP from possible mechanical damage and plays an additional role as a barrier for

radionuclides. Multi-purpose WP canisters must be deposited within an appropriate repository for permanent storage with a time frame of more than 10⁶ years to account for the

possible presence of long-lived nuclides, such as actinides (Pu, Np, and Am) or Tc", or I¹²⁹.

Current professional observations of international activities in nuclear waste disposal

are considered in eight articles in the "Materials Research Society Bulletin", Vol. XIX, No.

12, 6-53 (1994) and in other publications.

It is possible to categorize radioactive waste into the following groups:

• High-level solid radioactive waste (HLSRW) from primary sites of production plants

or storage sites of nuclear products:

-spent nuclear fuel (NF) from commercial and research reactors,

-high-level waste (HLW) from nuclear weapons programs,

-plutonium from the dismantling (PD) of nuclear weapons, and

-highly enriched uranium (EU) from weapons; • Treated and water-dissolved HLSRW, including high-level liquid waste (HLLRW),

resulting from the reprocessing of NF. HLLRW can be converted into radioactive

sludge (RS);

• Industrial and medical medium and low-level solid and liquid radioactive wastes from

the following sources:

-research laboratories and various chemical industries,

-medical facilities,

-mill tailing from uranium mines and from ore treatment and preparation, and

-dissolution of HLLRW;

• Borosilicate glass and concrete blocks with incorporated radionuclides after treatment

and conversion of HLSRW and HLLRW, for example, from the Savannah River

plant.

No existing waste packaging technique is able to withstand the combined chemical

and radioactive induced corrosion processes which occur in nature. Moreover, many studies

have shown that corrosion processes begin to liberate radionuclides from WP after decades

for concrete and after hundreds of years for borosilicate glass within a metal canister. The

rates of glass dissolution and the rates of metal canister corrosion are chemically coupled,

especially in the area of canister welding seams. Furthermore, the speed of chemical

corrosion will be accelerated by radioactive emissions and high temperature radioactive

heating of the waste material.

Mechanical stresses, including those induced from transportation and setting and

movement at the repository site, substantially accelerate all types of water, biological, thermal, radiation, and chemical corrosion processes. They induce micro-cracking and the

eventual loss of integrity of the metal canister, thereby allowing the leaking of radionuclides

into the surrounding environment.

All officially accepted nuclear waste disposal techniques can only isolate the natural

environment from free radionuclides for a maximum period of a few hundred years.

However, certain aggravating conditions may shorten this period to a few dozen years, as has

occurred with concrete immobilization techniques and some metal canisters.

While the "under water table" repository conditions at Yucca Mountain may prevent poisoning of the underground water flow, nothing can prevent an increase in concentration of

free radionuclides within a repository tunnel, which cause ventilation system air pollution and

poisoning of the environment. A critical concentration of radionuclides in a particular

location would induce nuclear chain reactions in the repository.

The present invention provides a technology which overcomes the technical and cost

limitations for the safe encapsulation, shielding, transporting and permanently storing

hazardous nuclear and chemical waste. The invention provides unique ceramic

containerization systems which meet the key engineering (nuclear waste management) and environmental requirements of the worldwide nuclear industry for perpetual storage (more

than 1,000,000 years) of dry nuclear waste of both low and high radioactivity levels. The

containerization systems of the invention utilize large size, thick- walled ceramic container

fabrication and container covering and sealing technologies, employing advanced microwave

processing, as well as radiation isolation and shielding techniques and transportation approaches. These technologies are suitable for existing methods of on-site waste handling, container transportation and storage technologies.

A preferred containment system for radioactive material or waste comprises: a) an inner gas-impermeable ceramic vessel suitable for holding said waste and

having a wall thickness of at least about 2.5 cm,

b) an outer ceramic container having a shape similar to that of the inner ceramic

vessel, a wall thickness of at least about 2.5 cm, and inside dimensions larger

than the outside dimensions of the inner ceramic vessel, thereby leaving space

between the inner ceramic vessel and the outer ceramic container,

c) in that space, a middle barrier layer of radiation shielding bulk material, e.g.,

graphite, grain or powdered metal, or metal oxide, carbide or nitrides, and d) ceramic lids for the vessel a) and the container b), each having a thickness of

at least about 2.5 cm, said ceramic lids being capable of being seamlessly and

gas impermeably joined to the vessel and container respectively after the

radioactive material or waste is placed in the vessel, by microwave energy

applied to the interface between the vessel, the container and the respective

lids.

There may be 1, 2 or more ceramic shells in the containment systems of the invention.

Optionally the ceramic vessels and lids may be toughened by the incorporation of reinforcing

fibers, e.g., alumina, boron nitride or silicon carbide, in its walls,

In certain instances, it may be advisable to have matching ridges and grooves on the

mating edges of the ceramic vessels and containers and/or to employ a ceramic composition applied to the mating edges of the vessel after the hazardous or radioactive waste is placed in

the vessel and before the lid is placed on the vessel, said composition being capable of joining

the vessel and lid after microwave energy is applied to the interface between the vessel and

the lid. The containment system comprises a versatile design of multi-layer construction of

ultimate and multi-purpose ceramic containers for high and low level radioactive dry waste

products. The demand for the invention includes radioactive, chemical and other

characteristic waste products and in strict correspondence with a set of health physics,

environmental, transportation and nuclear waste management requirements and rules. This design features: necessary container size and capacity from 0.2m³ up to 10m³ and more with

preferably cylindrical, ellipsoid or even spherical shape of the one or more container shells;

- perpetual radioactive, chemical, and thermal resistance and integrity of the inner ceramic shell from the ultimate ceramic material on the base of material such as alumina

enriched magnesium aluminum spinel with some technological additives for containment of

the high level radioactive waste;

- comprehensive radiation shielding design of the interim bulk layer (between two

ceramic shells) of the particularly determined thickness, employing a mixture of the particular

attenuation materials in particularly determined proportions, such as boron, graphite, barium

sulfate, lead or depleted uranium;

- mechanical stress, corrosion and thermal resistance of the outer shell from ceramic

material from, for example, alumina-kaolin-boron silicate glass composition;

- gas tightness and perpetual structural integrity of the ceramic shells with wall

thickness of at least 2.5 cm and onion-like (Russian doll) wall structure; and - easy to manipulate and use the containers during radioactive waste loading, container covering, sealing, employing microwave-induced ceramic joining process,

transportation and permanent or temporary storage of the container.

The container vessels and lids may be joined in a number of ways, using all sorts of

joints, e.g., overlapping, butt, or tongue and groove, etc. For non-critical purposes, the

vessels and lids may mechanically joined. In a preferred embodiment, the vessels and lids of

the invention are joined by the application of microwave energy to the interface and an

interlayer particulate ceramic composition between the vessel and the lid. The interlayer

composition is capable of joining the vessel and lid after microwave energy is applied to the

interface between the vessel and the lid. In certain instances, it may be advisable to have

matching ridges and grooves on the mating edges of the ceramic vessels and the ceramic lids.

Container assembly is a technical process. Considerable quality control is provided to

assure precise production. This includes nondestructive evaluation of the ceramic body and

finished container parts. Each container vessel is produced together with a matching lid.

Vessel and lid parts of the container are produced and preliminary assembly is done

separately but within the same production cycle, and the container vessel and lid are supplied

to the customer together with a particulate ceramic joining compound. To improve

homogeneity of thermal expansion during container heating, the particulate ceramic joining

compound has a composition similar to that of the vessel and the lid.

Preferably, the container vessel and lid have a circular transverse cross section. To

assure joining of the container vessel and lid, the joining surfaces area of the container vessel

and container lid are preferably formed as a gear tooth clutch and both joining surfaces are preferably precisely machined over their full joining ring surface. A dense set of micro and

macro ridges and grooves is produced to assure the retention of the powdered ceramic joining

compound in the joint. In cross section, the ridges and grooves may be triangular or

trapezoidal. Joining of the vessel and its lid is performed at the waste production site after

the waste loading and vessel covering procedures. A preferred microwave joining system of

the invention has been designed for the vessels and lids.

After loading solid nuclear, other hazardous waste products or a combination of nuclear and hazardous waste products into a ceramic container vessel, the vessel is capped

and hermetically sealed to prevent any leakage forever.

FIG. 1 is a perspective view of the outer protective steel shell 1 of a closed and sealed

egg-shaped container system of small or medium capacity. Protective steel shell 1 has two

parts, a lid la and a vessel lb. Lid la has a flange 2a at its bottom edge and container vessel

lb has a flange 2b at its top edge. Flanges 2a and 2b have a series of holes that are aligned

and are used to accept bolts 3a, one of which is inserted through each set of aligned holes.

Bolts 3 a are then threaded through nuts 3b (not seen in this view) and tightened securely.

FIG. 2 is a perspective view of the outer protective steel shell 20 of a closed and

sealed cylindrical container system of large capacity. Protective steel shell 20 has two parts,

a lid 20a and a vessel 20b. Lid 20a has a flange 21a at its bottom edge and container vessel

20b has a flange 21b at its top edge. Flanges 21a and 21b have a series of holes that are

aligned and are used to accept bolts 22a, one of which is inserted through each set of aligned

holes. Bolts 22a are then threaded through nuts 22b (not seen in this view) and tightened

securely. FIG. 3 is a partial one-quarter vertical section of an egg-shaped container system for

nuclear or hazardous waste showing the multiple layers of the container system shown in

FIG. 1. Outer protective steel shell 1 is comprised of upper section la and lower section lb.

The sections la and lb have flanges 2a and 2b respectively. Spaced around the flanges 2a

and 2b is series of holes that are aligned to accept bolts 3a, one of which is inserted in each

pair of aligned holes and screwed into nuts 3b in order to secure the sections la and lb of the

outer protective steel shell 1. Ceramic or metal grain-powder dense pack 4 shrouds a solid

radioactive material or radioactive and hazardous waste material (not seen). Pack 4 is

contained in wire reinforced metal-foil basket 5. Inner (the first) ceramic lid 6a is shown on

top of inner (the first) ceramic vessel 6b. The joint 7 of the container shell, i.e., ceramic lid

6a on ceramic vessel 6b, is indicated as a groove in lid 6a and a ridge on vessel 6b. A first

metal wire reinforced foil bag 8 surrounds the inner container shell, i.e, 6a and 6b.

Surrounding foil bag 8 is intermediate bulk layer comprised of 9a and 9b and made from

graphite-boron ore and barite grain-powder mixture. The joint between the upper portion of

intermediate bulk layer 9a and lower intermediate bulk layer 9b is indicated as 10.

Intermediate bulk layer (9a and 9b) is surrounded by a second metal wire reinforced foil bag

11. An outer (the second) ceramic lid 12a covers an outer (the second) ceramic vessel 12b,

and together form a second container shell, having a joint 13 therebetween in the form of a

ridge and groove. Surrounding the second container shell is an aluminum honeycomb

mitigation layer 14. The aluminum honeycomb mitigation layer 14 is surrounded by

temporary or permanent steel sheath (jacket) 1. FIG. 4 is a partial one-quarter sectional perspective view of a cylindrical container

showing the multiple layers of the container. Outer protective steel shell 20 is comprised of

upper section 20a and lower section 20b. The sections 20a and 20b have flanges 21a and 21b

respectively. Spaced around the flanges 22a and 22b is a series of holes that are aligned to

accept bolts 22a, one of which is inserted in each pair of aligned holes and screwed into nuts

22b (not shown) in order to secure the sections 20a and 20b of the outer protective steel shell

20. An aluminum honeycomb mitigation layer 23 is adjacent to and surrounded by the protective steel shell 20. Adjacent to aluminum honeycomb mitigation layer 23 are outer

ceramic vessel 24 which is covered by outer ceramic lid 25. The inner ceramic vessel 28 is

covered by inner ceramic lid 29. An autoclaved ceramic joining compound having increased

hydrogen forms content is used at the interface 30 between the ceramic vessel 28 and lid 29

and at the interface 31 between the ceramic vessel 24 and lid 25. The interfaces 30 and 31

comprise tongues and grooves. An intermediate layer of graphite powder 26 is in the gap

between the inner and outer sets of vessels and lids: 28-29 and 24-25. The gap is maintained

by means of ceramic stoppers 27.

Both vessel and lid joining surfaces are preferably machined to obtain a dense set of

micro and macro ridges and grooves which makes it possible to absorb and retain a powder of

the ceramic joining compound. The ceramic joining compound preferably comprises micro

particles similar to the composition of the materials of the ceramic vessels and lids. To

reduce processing time and activate microwave induced ceramic sintering (thermal joining

and sealing process), the powdered ceramic compound is initially treated in an autoclave at a

steam pressure of up to 2.5 GPa (21 atmospheres) and/or carbon micro powder doping is added to the ceramic powder composition mixture. After autoclave treatment, this powdered

ceramic compound is dried at 100°C, packed into a plastic bag, and it accompanies the vessel and lid parts of the container to the site of the hazardous waste. At the customer site,

immediately before loading the container with waste, the powdered ceramic compound is

rubbed into the ridges and grooves of both joining surfaces of the containers and lids.

In order to activate microwave thermal processing of the container exterior surface

area and to assure the container cooling process after its microwave thermal treatment, a

ceramic refractory and a thermal insulation blanket layer with a thickness up to a few

centimeters is applied. This thermal insulation blanket layer is symmetrically positioned

around the center of the joint area, and this blanket layer has a height which preferably equals

two to three times the thickness of the wall of the ceramic body. The thermal insulation

blanket is provided to the customer along with the container lid, and it is put on the container vessel and fixed during on-site assembly of the container.

Container waste loading and covering are preferably provided on a railroad car

platform. This platform allows rotation of the container about its axis, which is used to

provide uniform thermal treatment. Assembled containers are treated in the microwave

thermal system (MWTS) whose construction is shown in the FIG. 5.

In order to limit high temperature heating to the joint area only, the MWTS furnace is

preferably constructed as a ring jacket which surrounds the container body at the joint area.

This ring jacket may be constructed as a single slidably mounted circular ring or it may be

constructed of two movable semicircular parts. This makes possible the movement of the container in and out of the MWTS when the container is delivered to the MWTS working space. The ring of the MWTS furnace may be slidably mounted on vertical rails. To provide

uniform and quality thermal treatment, this MWTS furnace has a minimum of two

microwave sources, each of which has a different working frequency.

The microwave treatment process proceeds in accordance with a thermal schedule

tailored to the thickness and ceramic properties of the container walls. After thermal treatment, the car platform holding the container is carefully removed from the MWTS, and it

is held in a closed waiting area at ambient temperature for a minimum of 24 hours to provide

a cooling process of the container body before any further transportation.

FIG. 5 is a partial cross-sectional view of a microwave ring furnace 31 which provides

integral joining of the vessels 6b and 12b and lids 6a and 6b of a ceramic container similar to

the one shown in FIG. 3. Container vessels 6b and 12b are covered by container lids 6a and

12a respectively. The inside diameter of the inner lid 6a is indicated as ø and may be of any

convenient dimension to accommodate the contents intended for the container. The joints 7

and 13 between vessels 6b and 12b and lids 6a and 12a respectively are comprised of double

ridges and grooves of trapezoidal cross section. For simplicity, the joints 7 and 13 are shown

at the same level. They are preferably at different levels as shown in FIG. 3, with the inner

joint 7 at a higher level than the joint 13, thereby allowing access to the joint 7 by the

microwave ring furnace 31 when the time comes to seal the joint between the inner ceramic

container vessel 6b and lid 6a. The ridges and grooves of joints 7 and 13 are coated with an

autoclaved particulate ceramic joining composition (not shown). Between the inner and outer

containers (6a-6b and 12a- 12b), there is a layer of graphite powder 9a-9b. Resilient stopper

metal plate 15 or the end of a metal foil bag maintains the layer of graphite powder 9a in place between the lids 6a and 12a. Thermal insulation ceramic blanket 30 covers the joints 7 and 13 in turn. A cross-sectional view of the ring jacket 31 of the microwave furnace is

depicted surrounding the thermal insulation jacket 30. Microwave waveguides 32 on either

side of ring furnace 31 are attached to ring furnace 31 and deliver microwave energy 33 (from

a source not shown) to the joints 7 and 13, thereby causing the integral sealing of lids 6a and

12a to their respective vessels 6b and 12b. It is preferred to seal the inner ceramic container

(6a-6b) first and then to assemble the rest of the container system before sealing the second

ceramic container (12a- 12b).

FIG. 6 shows a ceramic container vessel in cross section. The container lid is similar

and therefore is not shown. D is the outside diameter of the cylindrical portion of the vessel.

H is the height of the vessel. T is the thickness of the wall of the vessel. T can vary from at

least about 2.5 cm to about 12.5 cm or greater. R is the radius of the spherical portion of the

vessel. It is preferred that the height of the cylindrical portion of the vessel be at least about 2

to 3 times the thickness of the vessel.

The following Table presents sample data for two ceramic layers for small (0.5m³)

and medium (1.5m³) containers having a wall thickness T = 125mm: reramir. Part No Description

1.1 & 1.2 lid and vessel parts of the inner shell (first ceramic shell) of the small container

2.1 & 2.2 vessel and lid parts of the outward shell (second ceramic shell) of the small container or

2.1 & 2.2 lid and vessel parts of the inner shell (first ceramic shell) of the medium container

3.1 & 3.2 vessel and lid parts of the outward shell (second ceramic shell) of the medium container

Table of Size and Weight Characteristics of the Ceramic Shells Ceramic Part Nos. D mm* Hmm** W kg*** 1.1 1050 650 820 1.2 1050 850 1100

2.1 1550 900 1790

5 2.2 1550 1100 2200

3.1 2050 1150 3230

3.2 2050 1350 3910

* D = outside diameter of the spherical part of the shell in Millimeters

** H = height of the contianer part in millimeters Q * * * w = weight of the container part in kilograms (for alumina or highly alumina enriched magnesium aluminum spinel ceramics)

The foregoing specification and drawings have thus described and illustrated a novel

ceramic container, and especially a container system for the storage of hazardous material or

waste, particularly hazardous nuclear material or waste, which fulfills all the objects and

5 advantages sought therefor. Many changes, modifications, variations and other uses and

applications of the subject invention will, however, become apparent to those skilled in the

art after considering this specification which discloses the preferred embodiments thereof.

All such changes, modifications, variations and other uses and applications which do not

depart from the spirit and scope of the invention are deemed to be covered by the invention,

0 which is to be limited only by the claims which follow.

Claims

What is claimed is:

1. A container which comprises a ceramic vessel suitable for holding material and

having a wall thickness of at least about 2.5 cm.

2. A container as claimed in claim 1 , wherein the ceramic vessel has a capacity of at least about 0.05 m³.

3. A container as claimed in claim 1, wherein the ceramic vessel has been made by a

process employing microwave firing of the container vessel.

4. A containment system for hazardous material or waste which comprises:

a) a ceramic vessel suitable for holding said material waste and having a wall thickness of at least about 2.5 cm, and

b) a ceramic lid having a thickness of at least about 2.5 cm, said ceramic lid being capable of being seamlessly and nonporously joined to the vessel after

the hazardous waste is placed in the vessel, by microwave energy applied to

the interface between the vessel and the lid.

5. A containment system as claimed in claim 4, wherein the containment system has a capacity of at least about 0.05m.

6. A containment system as claimed in claim 4, wherein the containment system is

cylindrical, ellipsoidal or spherical in shape.

7. A containment system as claimed in claim 4, wherein the vessel is toughened by the incorporation of reinforcing fibers in its walls.

8. A containment system as claimed in claim 7, wherein the fibers are boron nitride,

silicon carbide, or alumina.

9. A containment system as claimed in claim 4, wherein the lid is toughened by the

incorporation of reinforcing fibers dispersed throughout its thickness.

10. A containment system as claimed in claim 9, wherein the fibers are boron nitride,

silicon carbide, or alumina.

11. A containment system for radioactive material or waste which comprises: a) an inner ceramic vessel suitable for holding said waste and having a wall

thickness of at least about 2.5 cm,

b) an outer ceramic vessel having a shape similar to that of the inner ceramic

vessel, a wall thickness of at least about 2.5 cm, and inside dimensions larger

than the outside dimensions of the inner ceramic vessel, thereby leaving space

between the inner ceramic vessel and the outer ceramic vessel, c) in that space, a middle barrier layer of radiation shielding bulk material, and

d) ceramic lids for the vessel a) and the vessel b), each having a thickness of at

least about 2.5 cm, said ceramic lids being capable of being seamlessly and

nonporously joined to the vessel and container respectively after the

radioactive material or waste is placed in the vessel, by microwave energy

applied to the interface between the vessel, the container and the respective

lids.

12. A containment system as claimed in claim 11 , wherein the containment system has a capacity of at least about 0.5m³.

13. A containment system for radioactive waste as claimed in claim 11, wherein the

vessel is cylindrical, ellipsoidal or spherical in shape.

14. A containment system for radioactive waste as claimed in claim 11 , wherein the

vessel and lid are toughened by the incorporation of reinforcing fibers in their walls.

15. A containment system as claimed in claimed in claim 14, wherein the reinforcing

fibers are boron nitride, silicon carbide, or alumina.

16. A containment system for radioactive waste as claimed in claim 11, wherein the radiation shielding bulk material comprises graphite powder or other bulk mixtures of

metal or metal oxide, carbide or nitride inorganic materials or mixtures thereof.

17. A containment system for radioactive waste as claimed in claim 16, wherein the

radiation shielding bulk material is a mixture of graphite-boron ore and barite grain-

powder.

18. A containment system for radioactive waste as claimed in claim 11, wherein the

radiation shielding bulk material is contained in a metal foil bag.

19. A containment system for radioactive waste as claimed in claim 11 , which

additionally has an outer aluminum honeycomb mitigation layer, which in turn is

surrounded by a steel sheath.

20. A containment system for radioactive waste as claimed in claim 11, wherein there are

more than two sets of container vessels and lids and there is more than one barrier

layer of radiation shielding bulk material.