XYLENE POWER LTD.

RADIO ISOTOPE CONTAINERS

By Charles Rhodes, P. Eng., Ph.D.

SCOPE:
This web site addresses design issues relating to containers for economic safe storage and safe transport of nuclear fuel and nuclear waste. The containers must meet identified safety, transportation, interim storage, medium term storage and long term storage requirements.

An issue that the nuclear power industry must accept is that the public has no confidence in the concept of unsupervised geologic disposal of nuclear waste. The only way that nuclear power will be widely accepted is for the nuclear waste containers to be permanently accessible for periodic third party safety inspection. To make such nuclear waste storage and inspection practical the amount of high level waste must be reduced by at least two orders of magnitude and the nuclear waste containers must have features that allow economic ongoing monitoring, inspection, maintenance and repair.
 

DEFINITIONS:
On this web page:
Interim storage means safe storage in anticipation of future use. The storage period could be anything from a few days to a few centuries;

Medium term storage means planned storage for about 300 years to allow the contained short lived radio isotopes to naturally decay;

Long term storage means planned storage for much more than 300 years (eg 50,000 years to 1,000,000 + years) to allow the contained long lived radio isotopes to naturally decay.

A fissionable material container is a shielded container that is intended for safe transport of TRU (TRans Uranium actinide) concentrates or a FNR fuel bundle. The container may contain gadolinium or another neutron absorbing material the purpose of which is to prevent the container contents going critical if water penetrates the container.

A non-fissionable material container is a cylindrical stainless steel container that is designed to contain up to 4 tonnes of non-fissonable radioactive material. Typically this material consists of fission products and salts used in the fission product extraction process.
 

FISSIONABLE MATERIAL SHIPPING CONTAINERS:
A TRU concentrate shipping container is a shielded container partially filled with a neutron absorbing material that is used to safely transport TRU concentrates from CANDU reactor sites to a shared remote fuel reprocessing site, likely at Chalk River, Ontario.

A FNR fuel bundle shipping container is a long contoured shielded container partially filled with a neutron absorbing material that is used to safely transport one FNR fuel bundle between the remote fuel reprocessing site and a FNR site.

These shipping containers have provisions for crane lifting, safe material insertion and extraction and are designed to safely mechanically withstand any credible crane, road or rail accident in combination with prolonged immersion in water.

Note that the fuel bundle shipping container internal dimensions must be sufficient to allow for fuel bundle material swelling due to prolonged exposure to a fast neutron flux.

Note that a movable FNR bundle shipping containers can be thinner and hence not as heavy as a FNR fixed fuel bundle shipping container. Also note that the lower end fittings on these two container types are different. Both of these FNR fuel bundle shipping containers are internally 8.0 m long.

The fissionable material shipping containers must incorporate sufficient neutron absorbing material to prevent the container contents from becoming critical if water penetrates the shipping container. For example, sooner or later a truck or rail car will roll over into a river or other body of water. A FNR fuel bundle that is sub-critical when immersed in liquid sodium might become critical when immersed in water.

For FNR fuel bundles directly outside the fuel bundle core zone it is necessary to have a wall thickness with the mass equivlent of a 12 inch thickness of lead for biosafety shielding.

An issue with FNR fuel bundle shipping containers is the overall weight. There are two important mechanisms that minimize this container weight.
a) The first issue is that in terms of radioactivity the fuel bundles are not uniform. The emitted gamma radiation is minimal at the bottom rising to a maximum 3.5 m from the bottom and declining to a lower minimum at the top. Hence the lead shield thickness, which must be about 30 cm in the middle of the container declines toward the ends.
b) The fuel rods, which are loose in the fuel tubes at temperatures above the melting point of sodium (98 deg C), are locked in place by the internal sodium at temperatures below the melting point of sodium. Hence if the fuel bundle is loaded into the shipping container at 100 deg C to 120 deg C and then is allowd to cool the fuel rods will be locked in place in the fuel tubes until the fuel bundle is reheated.

The strategy is to slide the shipping container into a fuel bundle transfer airlock before either loading or unloading the container. The fuel bundle transfer airlock should slope slightly downwards toward the outside. That slope will keep the fuel rods in place in the fuel tubes until the fuel bundle temperature falls below the melting point of liquid sodium.

The top 2.2 m and the bottom 1.5 m of fuel bundle length have minimal gamma ray emissions. For the 0.6 m directly outside the FNR core fuel the lead shipping container walls should be 30 cm thick. Over the next 1.8 m this lead thickness declines to a minimal 3 inch (7.5 cm) structural thickness.

For FNR fuel bundles it is necessary to have a wall thickness outside the core zone fuel rods with the mass equivlent of a 12 inch thickness of lead for biosafety shielding. Let L be a length of such side wall.

The side walls of a fixed fuel bundle shipping container made of lead have a volume of:
(4 X 13.0 inch X 12 inch X L m) X (.0254 m / inch)^2
+ (1 X Pi X (12 inch)^2 X L m) X (.0254 m / inch)^2
= [(4 X 13.0) + (12 Pi)]inch X [12 inch X L m X (.0254 m / inch)^2]
= [89.7 inch] X [.00774 m^2 / inch] L
= 0.69445 m^2 L

Lead has a density of: 11,340 kg / m^3

Thus the lead directly outside the core zone fuel rods has a volume of:
0.6 m X 0.69445 m^2 = 0.41667 m^2

The lead outside the two blanket rod zones has a volume of:
[2 (1.8 m) / 2] X (3 / 4)0.69445 m^2 + 2 (1.8 m)(1 / 4)(0.69445 m^2
= 0.9375 m^3 + 0.6250 m^3
= 1.5625 m^3

The volume of the remaining sidewall length is:
[8.0 m - 4.2 m](0.69445 m^2 / 4)
= 0.6597 m^3

The volume of the end caps is:
2 X [23(9 / 16) inch + 6 inch]^2 [3 inch]
= 2152 inch^3
= 2152 inch^3 X (0.0254 m / inch)^3
= 0.03526 m^3

Thus the mass of the FNR assembled fuel bundle shipping container is:
(0.41667 m^3+ 1.5625 m^3 + 0.6597 m^3 + 0.03526 m^3) X 11,340 kg / m^3
= 30,325 kg
=30.325 tonnes

Note that the fuel bundle shipping container end sections must be thick enough to safely absorb a maximum accident related impact, which results in a fuel bundle shipping container weight of over 30 tonnes.

For safe loading and unloading the 8.3 m long shipping container must fit inside a fuel transfer airlock. The container width along a diagonal is:
2^0.5 [12 inch + 12 inch + 23(9/16) inch]
= 52.237 inch
= 52.237 inch X(0.0254 m / inch)
= 1.3268 m

In practise the fuel bundle transfer airlocks should be formed from 60 inch diameter pipe.

Clearly the contemplated FNR fixed fuel bundles in containers are close to their maximum practical unit weight limit for practical transport by truck or 2 units per railway car.
 

NON-FISSIONABLE MATERIAL SHIPPING CONTAINER:
This container type is used for shipping fission products from the remote fuel reprocesing site to the 300 year storage site.

A shielded shipping container surrounds a stainless steel - porcelain container with a 12 inch thickness of lead biosafety shielding. One such 50 tonne shipping container can be carried by a conventional road truck. Two such shipping containers can be carried by one 100 ton load capacity rated rail car. These shipping containers have provisions for crane lifting and are designed to mechanically withstand any credible crane, road or rail accident and to tolerate immersion in water.

A porcelain container is an porcelain ceramic container that can provide medium term or long term external mechanical protection and air/water exclusion for non-fissionable nuclear fuel waste after placement in a suitable storage location. The storage location must be: shielded, permanently accessible, naturally dry, naturally ventilated and secure. A suitable storage site is a depleted hard rock mine in stable granite with gravity drainage that is situated high above the local water table. The maximum outside diameter of a porcelain container is about 5 feet and its maximum height is about 9 feet for economic transport via conventional railway cars and for easy manipulation in existing 12 foot high mine vaults.
 

CANDU USED FUEL DRY STORAGE CONTAINER:
The CANDU used fuel dry storage containers used by Ontario Power Generation have a design working life of 50 years. They are currently kept in warehouse like storage conditions. They are constructed from two nested concentric layers of 0.500 inch (12.7 mm) steel plate separated by 20 inches (510 mm) of high-density concrete.

The density of iron is: 7300 kg / m^3

The density of high density concrete is:
6400 kg / m^3

The mass per unit area of the CANDU used fuel container wall is:
(7300 kg / m^3 X .0254 m) + (6400 kg / m^3 X 0.510 m)
= 185.42 kg / m^2 + 3264 kg/ m^2
= 3449.42 kg / m^2

Lead has a density of: 11,340 kg / m^3
Hence the equivalent lead wall thickness is:
(3449.42 kg / m^2) / (11,340 kg / m^3)
= 0.30418 m
= 0.30418 m X 1 inch / 0.0254 m
= 11.98 inches
 

ECONOMICS:
The Nuclear Waste Management Organization (NWMO) contemplates transporting unprocessed used CANDU fuel bundles and storing these spent CANDU fuel bundles in a limestone Deep Geologic Repository. It is shown herein that the costs of transporting used CANDU fuel can be reduced about 8 fold by selective extraction of uranium oxide from the used CANDU fuel before the uranium oxide and the TRU Concentrtes leave a CANDU reactor site.
 

The cost of reusable containers that in combination hold fission product concentrates from about 1400 used CANDU fuel bundles is presently estimated to be less than $100,000 per combination container or $71.43 per used CANDU fuel bundle. While that may seem expensive the NWNO budget for disposal of used CANDU fuel bundles is:
$24,000,000,000 / 3,000,000 CANDU fuel bundles = $8,000 per used CANDU fuel bundle and the present NWMO plan provides no nuclear fuel or material recycling benefits.
 

STORAGE CONTAINER APPLICATION:
The radio isotopes in storage should be isolated from the environment in engineered storage containers until the radio isotopes either spontaneously decay to a safe level or until the radio isotopes are recycled as components of Fast Neutron Reactor (FNR) fuel bundles. The storage containers contemplated on this web page are intended for use in permanently accessible, naturally dry, naturally ventilated, subterranean granite storage vaults such as are available in some depleted hard rock mines within granite core mountains. Within the storage vaults the storage containers are manipulated and positioned using remotely controlled equipment. Since there are no personnel in the storage vaults the storage containers do not require individual integral gamma ray shielding for biosafety. However, when outside the storage vault each storage container must be surrounded by a biosafety shield for safe transport.

An important issue in storage of toxic radio isotopes is total exclusion of liquids, especially water, from the waste. All nuclear materials must be converted to chemically stable dry solids prior to being placed in storage containers. Ideally the solids should have an extremely low vapor pressure at room temperature. Wet or liquid radioactive waste is simply not suitable for safe long term storage. The storage containers must be fitted with reliable vents to release inert gas fission products to prevent them causing pressure buildup within the storage containers. These vents should not admit either air or water.

One of the blunt realities of use of nuclear power is that unstable inert gas isotopes with long half lives are impossible to dependably permanently contain and are best vented to the atmosphere in a manner that ensures good gas mixing. When inert gas pressure accumulates in a radioisotope storage container there must be a dependable automatic pressure release.

One way of realizing this reliable pressure release is with a U tube partially filled with mercury. A quartz ball gravity check valve above the open end of the U tube prevents long term evaporation of the liquid mercury.

STORAGE CONTAINER CONCEPTS:
Very long life radioactive material storage can be realized by using an inner stainless steel container that is completely surrounded by a layer of liquid dielectric within an outer capped porcelain container. The inner stainless steel container must be fitted with a device that will reliably vent an internal accumulation of inert gas into the outer container before the rupture pressure of the inner container is approached. The outer porcelain container must repeatedly vent both low molecular weight hydrocarbon gases that result from gamma irradiation of the liquid dielectric as well as inert gases that may be released by the inner container. The porcelain container vent must be designed to reliably exclude air and water.

The main purposes of the outer porcelain container are to: exclude water, exclude air, confine and prevent evaporation of the liquid dielectric, provide structural and corrosion protection for the inner stainless steel container, allow periodic dielectric testing and replacement and allow periodic removal of water. The dielectric should be a heavy oil (bitumen) that has a density greater than water, so that if water penetrates the outer container it will accumulate on top of the heavy oil.

The main purposes of the liquid dielectric are to prevent corrosion of the outer surface of the inner stainless steel container, to provide a venting gas seal for the inner stainless steel container and to initiate an alarm if there is a drop in dielectric level indicating that:
1) there is a failure of either the inner stainless steel container wall or the outer porcelain container wall; or
2) the storage container is no longer upright; or
3) there has been a significant loss of dielectric volume due to dielectric evaporation and/or decomposition.

The gas pressure inside the inner stainless steel container is maintained at a slightly higher pressure than the gas pressure inside the porcelain container to prevent the oil dielectric back flowing into the stainless steel container. Hence the vent on the stainless steel container operates at a higher absolute internal pressure than the vent on the porcelain container.
 

SUPPORT FOR CONTEMPLATED RADIOACTIVE MATERIAL CONTAINER DESIGN:
1. The dead sea scrolls were preserved for over 2000 years in a relatively dry environment by storage in primitive capped ceramic containers;

2.Porcelain containers made over 3000 years ago are on display in museums today.

3.Today we have a much better understanding of ceramics, especially porcelain than was possible even 100 years ago. True porcelain in combination with an internal stainless steel container and a suitable dielectric separator in dry storage should last hundreds of thousands of years and containers fabricated from porcelain can be inexpensively remotely monitored.

4. Today high tech ceramics are routinely used in electronics and spacecraft.

5. Alumina (Al2O3) as a container material offers long term stability at room temperature. Alumina melts at 2072 degrees C. It is radiation resistant. It can easily be fabricated and machined. Alumina can be formed into large diameter cylinders. However, if anhydrous alumina is exposed to water it gradually takes on water of hydration according to the chemical equation:
Al2O3 + 3H2O = 2 Al(OH)3

6. For use in a damp environment alumina Al2O3 should be compounded with silica SiO2 at 1400 degrees C to form porcelain in accordance with the chemical reaction:
3Al2O3 + 9SiO2 = (3Al2O3 +2SiO2) +7SiO2
Porcelain does not absorb water. The component (3Al2O3 + 2SiO2) is known as 3:2 mullite. This 3:2 mullite forms randomly oriented needle like crystals in porcelain that give porcelain many of its favorable mechanical characteristics.

7. Silica (SiO2) as a container material offers very long term structural stability at room temperature. Pure fused silica melts at 1600 degrees C. However, mullite forms at 1400 degrees C and melts at 1840 degrees C. If the green ceramic is fired at 1400 degrees C the silica will vitrify all the way through forming porcelain that does not need glazing to prevent absorption of water.

8. Fabricating large containers out of porcelain is much less expensive than fabricating similar size containers out of pure silica. Porcelain material feedstock is available as a byproduct of certain mining activities. These mining activities typically grind the quartz into particles with an average diameter of about 75 um. There are over two million tonnes of ground quartz available at Wells, British Columbia.

9. Some porcelain contains small amounts of impurities such as CaO, MgO, K2O or Fe3O4. These impurities usually come from the source clay or may be added to achieve unique color or other characteristics. These impurities should be chemically extracted to prevent absorption of water of hydration.

10. Sacrificial galvanic magnesium-aluminum electrodes in combination with dielectric isolation have been extensively used for successful external corrosion prevention of buried steel pipelines.
 

STORAGE CONTAINER MATERIALS:
It is crucial that the materials used to fabricate the storage containers be inexpensive both to minimize the cost of nuclear waste storage and to discourage future thieves. While in principle copper is more corrosion resistant than stainless steel, copper is almost useless as a practical container material because it is: relatively rare, relatively expensive, constantly in high demand and attracts thieves. The damage caused by such thieves far exceeds the scrap value of the stolen material. It is likely both impractical and uneconomic to heavily guard the storage facility far into the future. For the inner container it is sufficient to use stainless steel with a sacrificial magnesium-aluminum electrode for galvanic protection against water penetraion of the porcelain container.

Each storage container assembly consists of an outer porcelain container, an inner stainless steel container and an oil dielectric separator between the inner and outer container walls. While in storage fission daughter inert gases will form inside the inner stainless steel container and low molecular weight hydrocarbon gases will collect above the liquid dielectric. For pressure safety gas accumulations inside the inner stainless steel container must automatically vent into the gas space in the porcelain container and gas accumulations above the liquid dielectric inside the porcelain container must automatically vent into the storage vault space. The storage vault space must have sufficient reliable natural ventilation to prevent accumulation of a combustable low molecular weight hydrocarbon gases in the vault space.

The outer container and its vent cap should be made of porcelain. Porcelain is an almost unique ceramic that does not take on water of hydration. Porcelain rarely occurs in nature. Good porcelain consists of randomly oriented needle like mullite crystals in a silica matrix. The randomly oriented needle like mullite crystals give the porcelain immense physical strength and toughness.

The porcelain should vitrify all the way through and should not require an external glaze. Porcelain samples should be tested to ensure that they do not take on water of hydration and that the required toughness is achieved.

If a representative porcelain test tile gains more than 0.5% weight during a 5 hour immersion in boiling water followed by a 24 hour immersion in cool water then the representative test tile is not good porcelain.

One of the functions of the vents is to reseal the openings which allow controlled release of inert gas fission product decay daughters, primarily krypton and xenon. This inert gas will flow out of the inner stainless steel container through the stainless steel container vent, will bubble up through the liquid dielectric and will accumulate between the top surface of the liquid dielectric and the lower surface of the porcelain container top. The porcelain container vent seal material might be mercury or fluorocarbon liquid. The porcelain container perimeter top seal can be a combined wax and ground porcelain seal.

The inner container, being stainless steel, can be sealed with a soft copper gasket. The gasket flange sealing faces must be corrosion resistant and should be machined and polished optically flat. Near the outer perimeter the bolted flange thickness is reduced to transfer pressure onto the flange sealing face. This seal fabrication requirement impacts the choice of stainless steel alloy used to fabricate the inner container. This alloy must be low carbon stainless steel for good welding characteristics. The perimeter top seal should be leak tested with a helium leak detector.

For the purpose of storing fission products embedded in chloride salts the inner stainless steel container needs a glass or ceramic liner to prevent the chloride salts corroding the stainless steel. In this respect it is important to totally exclude water from the inside of the stainlesss steel container.
 

LIQUID DIELECTRIC LEVEL SENSOR:
The liquid dielectric level sensor involves a minimal use of electronics which must be protected from high levels of gamma radiation. One cm of Pb shielding reduces 1 MeV gamma rays by about a factor of 2.0. In order to reduce the gamma ray flux by a factor of:
2000 = 2^11
to protect the dielectric level sensor from gamma ray damage requires about:
11 cm X 1 inch / 2.54 cm = 4.33 inches thickness of lead shielding.
The shielding must be under the sensor and must extend upwards around the sensor to attenuate gamma rays from adjacent containers.
 

DIELECTRIC ISSUES:
The dielectric almost fills the space between the inside wall of the porcelain storage container and the outside wall of the stainless steel container.

The liquid dielectric and its products of gamma radiation must not chemically react with the stainless steel inner container, the porcelain outer container, or any gasket or monitoring system materials or the nuclear waste. The liquid dielectric must not be easily flammable and must not be misible with water.

The chosen liquid dielectric is a hydrocarbon heavy oil known as bitumen that is a stable high molecular weight low vapor pressure liquid with an initial density greater than 1.00 gm / cm^3.

Gamma irradiation of the heavy oil will gradually break it into higher molecular weight and lower molecular weight components. The high molecular weight components will remain in place and if not serviced will gradually change to wax with a density as high as 1.05 gm / cm^3. The low molecular weight gaseous components will form gas bubbles which will rise to the surface of the heavy oil and accumulate below the lower surface of the porcelain container top. During this long term oil density change process low molecular weight hydrocarbon gases must be vented.

The higher molecular weight components have a higher density and will gradually turn into wax and accumulate at the bottom of the heavy oil. There will also be gradual heavy oil mass and volume losses due to venting of low molecular weight gases.

When the combined pressure of the inert gas and low molecular weight hydrocarbon gases becomes sufficiently high the porcelain container will vent these gases via its gravity sealed top vent. The gravity seal may not be perfect but it will economically minimize heavy oil losses by evaporation and will permit easy periodic liquid level service. Due to the decreasing gamma flux the time intervals between successive oil changes will become longer as the time in storage increases.
 

DIELECTRIC VOLUME:
Dielectric Volume = [volume at asterisk] + [Volume around stainless steel container] + [top volume]
= [Pi (2 inch) (22 inch)^2] + [Pi (43 inch) (1 inch) (79 inch)] + [Pi (28 inch)^2 (7 inch)]
= Pi {968 inch^3 + 3397 inch^3 + 5488 inch^3}
= Pi {9853 inch^3}

The mass of oil is:
Pi {9853 inch^3} X (.0254 m / inch)^3 X 850 kg / m^3 = 431.16 kg
 

PORCELAIN CONTAINER DESCRIPTION:
Evaporation of the heavy oil dielectric is prevented by the porcelain container top which has a combioned wax and ground porcelain seal on its perimeter.

The porcelain container's lid top surface should have a slightly conical shape that will shed water dripping from overhead.

The buoyancy in water of a filled porcelain container must be negative so that if the storage vault floods the container will not float and will remain upright.

An asterisk shaped porcelain cradle at the inside bottom of the porcelain container supports the weight of the inner stainless steel container and provides a bottom reservoir where corrosive substances which are denser than the oil can accumulate and will remain trapped. The porcelain container has a flat external bottom so that it will be stable and upright when placed on a flat floor.

The porcelain container height to diameter ratio is sufficiently small to ensure that the container cannot be overturned by an earthquake triggered ground acceleration.

Indentations in the outside of the porcelain container and its lid are provided for lid lifting, porcelain container lifting and lid clamp attachment.

There should be a two tubes through the porcelain cap and into the porcelain container, such that any low density liquid or gas accumulation at the top of the container can easily be extracted and heavy oil can be added or removed without removing the container top. One of these tubes is fitted with a liquid level sensor. This sensor has its own dedicated lead shield.

The lid on the porcelain container is nominally held in place by gravity, has an internal lip to prevent horizontal sliding and is secured against accidental container roll over by an external stainless steel clamp. A sufficiently high internal gas pressure inside the porcelain container will trigger automatic gas venting.

Once the porcelain container is in place in the storage vault and venting of inert gases has almost stopped the container can be protected by surrounding it with low density pea gravel, which should protect the container from damage caused by a future overhead rock fall.
 

The following diagram gives an approximate representation of the assembled storage container. This diagram shows the inner stainless steel container, the outer porcelain container, the dielectric and a wax perimeter top seal.
 

PORCELAIN CONTAINER DIMENSIONS:
The porcelain container OD is 60 inches above the lifting ledge. This diameter is limited by a railway boxcar internal width. This OD extends 5 inches below the bottom of the stainless steel container top flange

The side wall thickness of the lower part of the porcelain container is 2 inch

The ID of the upper part of the porcelain container is 48.5 inch to accomodate the stainless steel container flanges.

The side wall thickness of the upper part of the porcelain container is:
(60 inch - 48.5 inch) / 2 = 5.75 inch

The OD of the lower part of the container is:
(42 inch OD pipe) + 2(1 inch gap) + 2 (2 inch thick porcelain wall) = 48 inch

The porcelain container bottom thickness = 3 inch

The asterisk thickness = 2 inch

The overall height of the stainless steel container and its lifting ring is 86.625 inch

When the container is vertical there is an additional 2 inches of oil above the lifting ring.

When the container is vertical there is an additional 3 inches of gas space between the oil surface and the bottom surface of the porcelain top.

The porcelain top is 5 inches thick at its center decreasing to 4 inches thick at its perimeter.

The porcelain container top vent and dielectric level sensor projects 5 inches above the porcelain container top.

The overall height of the porcelain container and dielectric level sensor is:
(bottom thickness) + (asterisk thickness) + (stainless steel container overall haight) + (extra oil height) + (gas gap height) + (porcelain top thickness) + (vent projection)
= 3.00" + 2.00" + 86.625" + 2.00" + 3.00" + 5.00" + 5.00"
= 106.625 inch
which will easily fit through a 120 inch high railway boxcar door when on a dolly or fork lift.

The dielectric level sensor lead shield should be recessed into the porcelain container top near its center.
 

PORCELAIN QUANTITY:
(Porcelain Quantity) = [bottom] + [asterisk] + [48 inch OD sidewall] + [60 inch OD sidewall] + [overlap section] + [top]
= [Pi (22^2) 3] + [Pi (22^2) (2 / 2)] + [Pi 2 (23) (5 + 78)] + [Pi 2 (29) (5 + (86.625 - 78.00) + 5)]
+ [Pi (4) (5) (52)] + [Pi (30^2) (4.5)] inch^3
= Pi {1452 + 484 + 3818 + 1080.25 + 1040 + 4050} inch^3
= Pi {11,924.25} inch^3
= 37,461.1 inch^3

The density of porcelain is about:
2.403 gm / cm^3 X 1 kg / 1000 gm X 10^6 cm^3 / m^3 = 2403 kg / m^3
or
2403 kg / m^3 X (.0254 m / inch)^3 = 0.039378 kg / inch^3

Hence the mass of porcelain is about:
0.039378 kg / inch^3 X 37,461.1 inch^3 = 1475.15 kg
= 1.47515 tonnes
 

STAINLESS STEEL CONTAINER DESCRIPTION:
During the FNR nuclear fuel recycling process some of the transported and stored radioactive material is in metallic rather than oxide form. The metallic form is potentially combustible and combustion of a radioactive metal is a situation to be avoided at all costs. To prevent accidents the radio active materials should to be stored in stainless steel containers that are back filled with the inert gas argon. The stainless steel container must be sufficiently rigid to permit complete evacuation for leak detection and argon insertion. The stainless steel containers should have gas tight lids secured by bolted flanges that allow safe material access and allow container reuse. The stainless steel container flanges are sealed with bolted flanges that have soft copper gaskets. The stainless steel containers are size matched to larger enclosing lead shipping containers that permit safe truck and rail transport. The stainless steel containers are also size matched to larger enclosing porcelain containers for long term accessible subterranean storage.

The stainless steel containers have lifting rings welded onto their tops to permit easy insertion and removal of stainless steel containers into either porcelain storage containers or lead shipping containers.

For radio isotope shipment by rail or truck each stainless steel container is enclosed within and protected by a surrounding 40 ton lead shipping container.

One of the issues with the stainless steel containers is potential for internal pressure accumulation due to radioactive decays that yield inert gas daughters.

The inner stainless steel container is well sealed except via its vent tube. If the inner stainless steel container is unvented over time inert gas radio isotope decay products can build up a substantial pressure inside the inner stainless steel container. An example of a problem radio isotope in this respect is Cl-36. It spontaneously decays into stable Ar-36 which is an inert gas. Thus if the inner container is unvented, for safe long term storage the mass of Cl-36 within the inner steel container must be limited to the mass of argon that the inner stainless steel container can contain at a safe working pressure. The parties must face the reality that the cost of safely containing Cl-36 is high and that in future nuclear reactor design every effort should be made to minimize formation of Cl-36. This issue heavily impacts the future application of Molten Salt Reactors. A related issue is that Cl is normally chemically bound to another element such as Na, K, or Li. Decay of Cl-36 will leave these chemically acitive elements unbound. The possible consequences of a long term gradual accumulation of chemically active unbound elements must be carefully considered. For example, if water penetrates the container and there is an accumulation of Na hydrogen will be formed.

In this respect an open end stainless steel tube should run vertically from the top center of the stainless steel container to above the oil surface level. This tube has a tall loose fitting negative buoyancy porcelain cap that in conjunction with the U tube contents forms a vent valve. Then inert gas formed inside the stainless steel container will vent into the porcelain storage container. If the spent fuel is stored for a sufficiently long time before being inserted in the stainless steel containers and if the chemical makeup of the stored material is appropriate this vent arrangement might be replaced by a simpler rupture disk.

In the event that water somehow finds its way into the porcelain container bottom a sacrificial magnesium-aluminum sheet attached to the stainless steel container provides additional galvanic corrosion protection.
 

STAINLESS STEEL CONTAINER DETAILS:
1. The body of the inner cylinder is made of stainless steel pipe, 1.067 m (42 inch) outside diameter, about 2.02565 m (79.75 inch) high with a wall thickness of 12.7 mm (0.500 inch).

The cylinder top and bottom are stainless steel, 1.25 inch thick. The bottom fits inside the cylinder and is attached to the cylinder by welding both inside and outside. The cylinder extends beyond the bottom by about 0.5 inch. The cylinder top is attached to the cylinder with 3 inch wide bolted flanges. Each lower flange is made in two half circular parts cut from 1.25 inch thick stainless steel sheet. The upper flange is integral to the top plate.

2. The flanges are 48 inch OD and are attached to each other with 48 X (1.00 inch) diameter stainless steel bolts equally spaced on a 45.75 inch diameter bolt circle. After welding but before further machining and polishing the welds are x-rayed. Then flange recesses and optical flats are machined on to the flanges. The fabrication order is important to minimize weld induced distortions.

3. For containers intended to store unprocessed spent CANDU fuel bundles the inner stainless steel container is stabilized against deformation and collapse during evacuation by the 61 4.0 inch ID, 4.5 inch OD tubes that stabilize the positions of the spent CANDU fuel bundles. If these tubes are not present a central external reinforcing ring may be required to give the container stability against deformation and collapse during evacuation.

4. The inner stainless steel container is supported by a porcelain cradle that in plan view looks like an asterisk.

5. The inner stainless steel container has an attached external 0.75 inch thick sacrificial magnesium-aluminum plate near its bottom center that provides galvanic corrosion protection for the inner stainless steel container if any water accumulates at the inside bottom of the porcelain container.

6. The vent tube of the inner stainless steel container has a valve that permits evacuation and argon back filling.

7. The top of the inner stainless steel container has attached to its upper surface a 0.61 m (24 inch) outside diameter 0.0317 m (1.25 inch) wall lifting ring, 0.127 m (5 inches) high. This lifting ring has 4 X 2 inch diameter symmetrically spaced radial holes suitable for attachment of lifting bars or hooks.
 

STAINLESS STEEL CONTAINER DIMENSIONS:
Assume that the inner stainless steel container cylinder wall is fabricated from 42 inch OD, 0.500 inch wall stainless steel pipe. Assume that the pipe is supplied in 20 foot lengths, so an economical way to cut the pipe with minimal waste is to cut it into 3 lengths, each length nominally 79.75 inches long. Assume that the top flange extends the length by o.50 inch, the top perimeter gasket is 0.125 inch thick, that top plate is 1.25 inch thick and the lifting ring is 5 inches high. Then the overall stainless steel container length is:
79.75 + 0.50 + 0.125 + 1.25 + 5.0 inch = 86.625 inches
 

STAINLESS STEEL END THICKNESS:
Let the inner stainless steel container end sheet thickness be Tm. Let the unsupported radius of the end be Rm.

Let P be the differential pressure between the inside and outside of the stainless steel container.

The hoop stress Sc on the cylindrical container walls is:
Sc = P 2 (Rm) dL / 2 Tm dL
= P (Rm) / Tm

The torque on the end wall at its perimeter is:
Integral from R = 0 to R = Rm of:
P (2 Pi R) dR (Rm - R)
= P (2 Pi) Rm (Rm^2 / 2) - P (2 Pi) (Rm^3 / 3)
= P (2 Pi) Rm^3 / 6

The resisting torque is:
Integral from X = 0 to X = (Tm / 2) of:
2 Sd [(X / 2) / (Tm / 2)] (2 Pi Rm) dX (X / 2)
= [2 (Sd / Tm) (Pi Rm) ] [Tm / 2]^3 / 3
= [(Sd) (Pi Rm) ] [Tm / 2]^2 / 3

Equating the two torques gives:
P (2 Pi) Rm^3 / 6 = [(Sd) (Pi Rm)] [Tm / 2]^2 / 3
or
P = {[(Sd) (Pi Rm)] [Tm / 2]^2 / 3} / {(2 Pi) Rm^3 / 6}
= {[(Sd)] [Tm / 2]^2} / { Rm^2}
= Sd (Tm / 2 Rm)^2

Let Sm = the maximum allowable metal working stress for safety (Sm = 10,000 psi).
Then the maximum allowable pressure P = Pm at Sd = Sm is:
Pm = Sd (Tm / 2 Rm)^2
= 10,000 psi (1.25 / 42 inch)^2
= 8.86 psi
This is the maximum safe internal working pressure.

Evacuation of the container will lead to local material stress as high as:
(14.7 psi / 8.86 psi) X 10,000 psi = 16, 591 psi

Hence the end sheets can be 1.25 inch thick low carbon stainless steel. To provide an increased margin of safety choose a flange plate thickness of 1.25 inches.

The stainless steel top should permit lifting the steel container using a 5 inch high lifting ring welded the top sheet. The lifting ring should be formed from a 24 inch outside diameter thick wall stainless steel pipe section with four equally spaced 2 inch diameter radial holes.

The 0.500 inch thick stainless steel cylinder walls permit a deep weld between the cylinder wall and the lower flange. Note that the lower flange overlaps the cylinder side walls by 0.75 inch and is welded on both the inside and outside.. The upper flange is integral to the stainless steel top. The inside length of the container is:
79.75 inch - 0.50 inch - 1.25 inch + 0.50 inch = 78.50 inch (1.9939 m)

Note that a stack of four CANDU fuel bundles is nominally 1.98 m high. An uncertain issue is whether fuel swelling will make a stack of four spent CANDU fuel bundles too tall to fit inside the stainless steel container.
 

STEEL WEIGHT:
Volume of steel exclusive of fastening material is given by:
Outer cylinder + bottom + lower flange + top + lifting ring
= (Pi X 41 inch X 79.73 inch X 0.500 inch) + (Pi X (20.5 inch)^2 X 1.25 inch) + (Pi X 2 (21.75 inch) X (1.25 inch) X (3 inch)
+ (Pi X (24 inch)^2 X 1.25 inch) + (Pi X 24 inch X 1.25 inch X 5.00 inch)
 
= 5134.82 inch^3 + 1650.32 inch^3 + 512.47 inch^3 + 2261.95 inch^3 + 471.24 inch^3
= 10,030.80 inch^3

The weight of stainless steel is given by:
10,030.80 inch^3 X (.0254 m / inch)^3 X (7850 kg / m^3) = 1290.35 kg
 

INTERNAL PRESSURE WITHSTAND CAPABILITY:
As shown above the maximum safe working pressure Pw within the stainless steel container is about:
8.86 psi = 8.86 / 14.7 = 0.603 bar

The internal volume Vol of the stainless steel container is given by:
Vol = Pi (20.5 inch)^2 (78.5 inch)
= 103,639.9 inch^3
= 103,639.9 inch^3 X (.0254 m / inch)^3 X 1000 lit / m^3
= 1698.35 lit

At one bar at 20 degrees C one mole of a gas occupies:
22.4 lit X (293/273) = 24.04 lit.

Hence the number of moles of gas that one stainless steel container can safely store at 20 degrees C before venting is limited to:
[1698.35 lit / (24.04 lit-bar / mole)] X 1.603 bar = 113.25 moles

If the only inert gas emitting substance is Cl-36 changing to Ar-36 then the maximum initial safe quantity of Cl-36 in the container before venting will be tripped is:
36 gm / mole X 113.25 moles = 4.077 kg
 

LEAD SHIPPING CONTAINER DESCRIPTION:
The purpose of a shippiing container is to provide bio-safety shielding and in the event of a transportation accident to provide mechanical protection for the contained stainless steel container.

To realize the required bio-safety shielding the wall thickness of the lead shipping containers has to be 12 inches, which due to the the praactical transport weight limitations constrains the external height of a 42 inch outside diameter stainless steel container to about 82 inches.

The lead shipping container is simply a ~ 40 ton lead cylinder with 12 inch thick lead walls that fits snugly around the stainless steel container to provide both bio-safety shielding and mechanical/structural protection during shipment by truck or rail. This shipping container is sized so that two such shipping containers can be transported by one 100 ton rated railway car and one such container can be transported by a 80 ton rated road truck. The shipping containers are intended to be loaded and unloaded using 50 ton rated cranes. The choice of 12 inch (30 cm thick) lead reduces the intensity of 1 MeV gamma radiation by a factor of about:
2^30 ~ 10^9.

Assume that a stainless steel container contains fission product concentrates from 1400 CANDU spent fuel bundles. Neglecting the shielding effect of the steel the radiation at the outer surface of the shipping container about 1 m from the container axis would be about:
(1400 X 0.3 Sv / hr) / (10^9) = 0.42 uSv / hr
This radiation intensity is further reduced by about a factor of 2 due to the stainless steel and porcelain container walls.
 

LEAD SHIPPING CONTAINER DETAIL:
The shipping container is nominally a lead cylinder with 12 inch thick walls and domed end caps. Allowing a 0.5 inch clearance on radius and a 0.375 inch clearance on overall length with a slot for the lifting ring gives:
Combined end volume = Pi [33.5^2 - 21.5^2] inch^2 [24 inch]
= (24) Pi [1122.25 - 462.25] inch^3
= Pi (15,840 inch^3)

Lead cylinder side wall volume = Pi [(33.5 inch)^2 - (21.5 inch)^2] X 82 inch
Pi (82) [1122.25 - 462.25] = Pi (54120 inch^3)

Hence the total lead volume in the lead shipping container is:
Pi (54,120 inch^3 + 15,840 inch^3)
= 219,785 inch^3
= 219,785 inch^3 x (.0254 m / inch)^3
= 3.602 m^3

The density of lead is:
11,340 kg / m^3

Hence the mass of the shipping container is about:
11,340 kg / m^3 X 3.602 m^3 = 40,843 kg
= 40.85 tonnes
= 44.93 tons.

The actual weight of the lead shipping container is slightly larger due to the fastening, lifting and mounting accessories. The lead container casting contains recesses and slots for the stainless steel container flange and the stainless steel container lifting ring.

The weight of the external biosafety shielding required for shipping spent CANDU fuel reduces the maximum number of stainless steel containers to two per 100 ton rated rail car. These rail cars must be of a type that permits top loading and unloading with a 50 ton rated crane.

A lead shipping container is essentially a large 2 piece lead casting. The methodology used to fasten the pieces together must be extremely robust to safely with stand any transportation accident.

Note that the lead shipping container minimum OD is 67 inches. On a 100 ton rated rail car the lead shipping containers should be positioned directly over the wheel boggies. In a trailer truck the lead shipping container must be positioned to equally distribute the load over the trailer wheels.
 

TRANSPORTATION AND STORAGE OVERVIEW:
A crucial aspect of the nuclear fuel cycle is safe, simple, economical and flexible transportation of radioactive materials.

Storage needs to be robust, natually dry, naturally ventilated, safe, accessible and economical.

CANDU reactors directly produce two major categories of nuclear waste: spent fuel and radio active non-fissionable materials.

After the spent fuel has been in on-site wet/dry storage for ten years, the CANDU spent fuel can be separated on site into two portions: 90% by weight pure uranium oxide and 10% by weight CANDU spent fuel concentrates. The CANDU spent fuel concentrates are a highly radioactive mixture of remaining uranium oxide, fission products and trans-uranium actinides.

The CANDU spent fuel concentrates are intensely radioactive and should be placed in narrow sealed stainless steel tubes within fissionable material stainless steel containers. These tubes are separated by B4C to prevent the stored material becoming critical if through accident or mishandling water enters the fissionable material stainless steel container. The B4C is locked into a binder material to ensure that it will not be washed out in a worst case accident in which the stainless steel container is both fractured and immersed in flowing water.

For transport each stainless steel container of radioactive concentrates is inserted into a lead shipping container with 12 inch thick lead walls. The primary purpose of the lead shipping container is to provide biosafety shielding during shipment. A secondary purpose of the lead shipping container is to provide physical protection for the inner stainless steel container in the event of a severe transportation accident.

These composite containers can then be transported to Chalk River for further material reprocessing. At an interim storage location the stainless steel container of concentrates can be removed from the lead shipping container and inserted into a porcelain storage container for interim storage.

At Chalk River the concentrates are separated into uranium oxide, fission products and core rod material. Chalk River is far from any metropolitan area.

At Chalk River the trans-uranium actinides are combined with uranium metal and zirconium metal and are formed into FNR core rods. The FNR core rods are transported to FNR sites in fissionable material containers within lead shipping containers. At the FNR site the fuel rods are inserted into fuel tubes, the fuel tubes are assembled into fuel bundles and the fuel bundles are loaded into the FNR.

The pure uranium oxide is only very weakly radioactive. If it is pure it can be stored and transported in simple unshielded stainless steel containers. If it contains a significant concentration of radioactive impurities the uranium oxide can be stored and transported in the same manner as radioactive non-fissionable materials. This uranium oxide is depleted in the isotope U-235 but is still useful as a fast neutron reactor (FNR) blanket fuel feedstock. The uranium oxide must be reduced to uranium metal and alloyed with zirconium prior to use as FNR blanket rod material. Much of the uranium oxide is placed in interim storage for future use as FNR fuel.

The fission products are intensely radioactive but pose no threat of going critical, even if immersed in water. The fission products are transported to a naturally dry site for medium term storage. At a medium term storage site each stainless steel container is removed from its lead shipping container and is transferred into a porcelain storage container. The gap between the two containers is back filled with heavy oil and then the storage container is capped. The storage container is then placed in a permanently accessible safe naturally dry naturally vented Deep Geologic Repository (DGR).

Every year a portion of the fuel bundles in a FNR is removed from the spent fuel storage zone for reprocessing. The extracted blanket rods and core rods are transported in fissionable material containers to Chalk River for reprocessing. At Chalk River fission products are extracted and new core and blanket rods are formed. The fission products are transported to medium term storage in non-fissionable material containers. The new core and blanket rods are transported to FNRs in fissionable material containers.
 

MATERIAL FLOW:
This web site shows that CANDU spent fuel bundles, after ten years in wet/dry storage at the reactor site, should be preprocessed on the reactor site to selectively remove 90% of the spent fuel bundle weight in the form of very weakly radioactive uranium oxide. The remaining spent fuel concentrates can be placed inside stainless steel fissionable material containers and transported to storage or material reprocessing sites within surrounding lead shipping containers at the equivalent rate of about 2800 CANDU fuel bundles per 100 ton rated rail car trip or about 1400 CANDU fuel bundles per 80 ton road truck trip.

At the storage site each stainless steel container is transferred from its enclosing lead shipping container to an enclosing porcelain storage container. A heavy oil low vapor pressure liquid dielectric is used to fill the gap between the porcelain container and the stainless steel container. The porcelain container is then capped and moved into a naturally dry naturally ventilated subterranean granite storage vault. The cap is retained by a stainless steel clamp.

The cost of reusable stainless steel and porcelain storage containers that in combination each hold fission products from about 1400 spent CANDU fuel bundles is presently estimated to be less than $100,000 per combination container or $71.43 per CANDU fuel bundle. While that may seem expensive the NWNO budget for disposal of spent CANDU fuel bundles is:
$24,000,000,000 / 3,000,000 CANDU fuel bundles = $8,000 per spent CANDU fuel bundle and the present NWMO plan provides no fuel or material recycling benefits.
 

SPENT CANDU FUEL HANDLING:
Spent CANDU fuel bundles are kept in wet storage at the reactor site for about 10 years after ejection from a CANDU reactor until the fission product decay thermal emission falls to less than 5 watts / CANDU fuel bundle and the gamma ray emission falls to less than 0.3 Sv / hour / bundle at a distance of 1 m.

The uranium oxide component of a CANDU fuel bundle emits very little decay energy. The essence of the Ottensmeyer Plan is to start by selectively removing 90% of the CANDU spent fuel bundle weight in the form of weakly-radioactive uranium oxide from the spent CANDU fuel bundles. The outputs from this process are 90% by weight uranium oxide, that has little radio activity, and 10% by weight of highly radioactive concentrates consisting of zirconium, fission products, transuranium actinides and remaining uranium oxide. The radio activity of the concentrates is about 10X higher per unit weight than the radio activity of the original CANDU spent fuel bundle.

The concentrates are then loaded into stainless steel containers, as described herein, each of which holds concentrates from about 1400 spent CANDU fuel bundles. The contents of each such stainless steel container immediately after loading will emit gamma radiation at about:
1400 bundles X 0.3 Sv / hour-bundle = 420.0 Sv/ hour 1 m from the container axis.
Each such filled stainless steel container weighs about 4.0 tonnes (4.4 tons).

For safe shipping and handling each such filled stainless steel container should then be loaded into an enclosing 45 ton lead shipping container that provides a 12 inch thickness of surrounding lead shielding and that is strong enough to withstand any road, rail or crane handling accident.

The lead shipping containers should then be loaded onto suitable trucks or railway cars using a 50 ton rated crane. Typically a suitable railway car is rated for 100 tons of top loaded cargo (2 lead shipping containers) whereas a suitable conventional road truck is rated for 50 tons of top loaded cargo (1 lead shipping container).

Near the storage site another 50 ton rated crane transfers the shipping containers from railway cars to trucks.

Each truck is driven into a shielded truck bay within the storage facility where the shipping container is unloaded using a 50 ton rated crane. The truck is then driven away. When there is no one in the shielded truck bay remotely controlled equipment is used to remove the stainless steel container from the shipping container and to transfer the stainless steel container into a porcelain storage container. The porcelain storage container is then back filled with liquid dielectric, capped and moved by remotely controlled equipment into a subterranean granite storage vault that is natually dry, naturally vented, gravity drained and high above the local water table.

After all gamma emitters are removed from the shielded truck bay the lead shipping containers are loaded back onto trucks and are driven away for reuse. Thus a small number of 45 ton lead shipping containers can support a large inventory of seldom accessed porcelain storage containers. Each porcelain storage container in the storage vault has within it a stainless steel container that can safely contain fission product concentrates from about 1400 spent CANDU fuel bundles or can contain about 140 unprocessed spent CANDU fuel bundles.

If 3,000,000 unprocessed spent CANDU fuel bundles are all stored at one location the required number of stainless steel and porcelain container pairs is:
3,000,000 CANDU fuel bundles / (140 bundles / container pair) = 21,429 container pairs

However, if only the radio active concentrates are stored in porcelain containers the required number of stainless steel and porcelain container pairs decreases to:
3,000,000 CANDU fuel bundles / (1400 bundles / container pair) = 2,143 container pairs

One of the merits of this container handling plan is that the storage facility can be operated by relatively few personnel who need only limited training. Hence the storage facility is economical to operate and can be located at a geophysically advantageous site that is far from any population center. Furthermore, due to multiple redundant radio isotope isolation barriers plus a naturally dry DGR there is no possibility of ground water contamination once the material is in storage.

The number of 100 rail car trains necessary to move the concentrates to the storage site is:
(3,000,000 CANDU fuel bundles) X (1 rail car / 2800 CANDU fuel bundles) X (1 train / 100 rail cars) = 10.7 trains.

Every porcelain storage container in the storage vault is individually remotely monitored to detect out of design range dielectric level. A dielectric level change may indicate a cap failure, an inner wall failure, an outer wall failure, a non-vertical container position or dielectric evaporation or decomposition.. Each storage vault is naturally ventilated to maintain a low temperature and is individually monitored. Over time the containers will release heat and low molecular weight hydrocarbon gases which must be removed by the natural ventilation.

The minimum natural ventilation rate must be sufficient to ensure that even if there is a major heavy oil spill inside the DGR the temperature and vapor pressure of the heavy oil will not support combustion in air.
 

RECORD KEEPING:
Precise permanent records must be maintained regarding the exact contents of each container and their chemical and nuclear history.
 

MAXIMUM CANDU FUEL BUNDLE LOAD:
Assume that a CANDU nuclear fuel bundle has an OD of 4.0 inches and a length of 19.5 inches. The theoretical number of such fuel bundles that will fit in a single layer inside a 36 inch ID metal container is given by:
1 + 6 + 12 + 18 + 24 = 61
We actually have a 41 inch ID so the available container inside diameter per CANDU fuel bundle is:
41 inch / 9 = 4.555 inch.
Hence there is tolerance to allow for the 0.25 inch wall thickness of the fuel bundle guide pipes. Hence the basic number of fuel bundles / container is given by:
(4 layers / container) X (61 fuel bundles / layer) = 244 fuel bundles / container

The steel tube metal volume is:
61 tubes X 2 m X Pi (4.25 inch) X 0.25 inch X (.0254 m / inch)^2
= 0.2627 m^3

The mass of this tube metal is about:
0.2627 m^3 X 7850 kg / m^3 = 2062.41 kg = 2.06241 tonnes

Assume that each fuel bundle weighs 22.5 kg. Then the maximum spent nuclear fuel bundle weight is given by:
244 bundles / container X 22.5 kg / bundle = 5490 kg / container
 

MAXIMUM LOADED STORAGE CONTAINER WEIGHT:
The maximum loaded storage container weight =
[CANDU fuel bundles] + [steel tubes] + [stainless steel container] + [porcelain container] + [oil]
= [5490 kg] + [2062.41 kg] + {1290.35 kg] + [1475 kg] + [431.16 kg]
= 10748.92 kg
= 10.749 tonnes

Thus a storage container fully loaded with 244 spent CANDU fuel bundles weighs about 10.75 tonnes.
 

STORAGE AREA REQUIREMENT:
Assume that the porcelain containers are placed three deep on each side of a 30 foot wide aisle. Due to the centre to centre distance in effect each container takes up a square 5 feet to a side. This a 5 foot length of aisle services 6 containers. The containers take up:
6 X 25 ft^2 = 150 ft^2.
The corresponding asile area is:
5 ft X 30 ft = 150 ft^2.

Thus on average each container requires a storage area of:
300 ft^2 / 6 containers = 50 ft^2 / container.

Each container holds 5.490 tonnes of CANDU spent fuel. Thus storing unprocessed CANDU spent fuel in this matter requires a DGR with a floor space of:
(50 ft^2 / 5.490 tonnes) X 50,000 tonnes = 455,373 ft^2
which is less than (1 / 10) of the storage space presently available at Jersey Emerald.
 

MAXIMUM STORAGE VAULT FLOOR LOADING:
The storage area floor loading where the containers are concentrated is:
11 tons / 25 ft^2 = 22,000 lb / 25 ft^2
= 880 lb / ft^2
 

CANDU SPENT FUEL BUNDLE INVENTORY:
Assume that there are 3,000,000 CANDU spent fuel bundles. The storage space required is given by:
(3,000,000 bundles) X (1 container / 244 bundles) X (50 ft^2 / container) = 614,754 ft^2
 

INTERMEDIATE WASTE FROM RETUBING REACTORS:
When a CANDU reactor is retubed the 4 inch diameter high pressure zircalloy fuel channels and the 132 mm OD moderator tubes are replaced. Each tube can be cut into six 52 inch lengths. The fuel channel tube sections will fit inside moderator tube sections. One container can store 37 moderator tube cutoffs of lengths varying from 40 inches to 80 inches. Assuming an average cutoff length of 52 inches each container stores (37 / 6) = 6.17 moderator tubes. Thus if a reactor has 380 tubes the number of containers required to store the used tubing is:
(380 / 6.17) = 63 containers

Each tube assembly has two end fittings. Assume that 14 end fittings will fit in one container. Then the number of containers requred for the end fittings is:
(380 X 2) / 14 = 55 containers.

Thus retubing a 380 tube CANDU reactor requires:
63 + 55 = 118 containers.

The average annual storage space requirement triggered by reactor retubing is:
20 reactors X 1 retubing / 20 reactor-years X 173 containers / retubing X 50 ft^2 / container
= 8,650 ft^2 / year

This irradiated zirconium has value as an important component of future FNR fuel.
 

TRITIUM FILTER CARTRIDGES
Tritium has a half life of 12.6 years. In a CANDU reactor it natually forms as a result of neutron absorption by deuterium, which is a component of the moderating heavy water. After 126 years 99.9% of the tritium has become stable helium-3 and its radioactivity has decreased 1024 fold. These low level waste cartridges should be stored in hydrogen tight fusion bonded epoxy coated 48 inch diameter steel pipe with an applied DC bias. There is no need to use an elaborate long term storage container. Sand can be poured around these pipes to protect them from a partial overhead cave in. The tritium filter ion exchange cartridges are only of long term concern if there has been major metal corrosion or erosion that has been captured by the cartridge. Generally the weight of metal captured by these ion exchange cartridges is microscopic. After 252 years in dry storage the radioactivity of these cartriges should be checked before the remaining helium-3 is made available for use and the cartridge material is released to the environment.
 

This web page last partially updated April 25, 2023.