NUCLEAR WASTE MANAGEMENT

RESPONSE TO NWMO PLAN FOR LONG TERM STORAGE OF NUCLEAR WASTE

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

EXECUTIVE SUMMARY:
The Nuclear Waste Management Organization (NWMO) has circulated various versions of a document titled "Implementing Adaptive Phased Management". This NWMO document describes the NWMO's plan for long term storage of used CANDU nuclear fuel bundles. Serious problems with this plan are identified herein. The origin of these problems is rooted in a cultural attitude at the NWMO that NIMBY (Not In My Back Yard) political considerations take precedence over basic principles of physics, engineering and safety. In the NWMO plan there are implicit assumptions made that are not rooted in reality. One of these implicit assumptions is that the NWMO can choose a site that will be reliably "geologically stable" for 1,000,000 years. Based on very recent history most of southern Ontario is relatively geologically stable. However, in the longer term this assumption is likely faulty, as is demonstrated by the existence of the 100 m high Niagara Escarpment, which is only 12,000 years old.

The folly of this NWMO attitude of "it can't happen here" has recently been demonstrated at the Fukashima Daiichi nuclear facility in Japan where comparable implicit denial of the possibility of a tsunami caused by a major earthquake led to the critical cooling water pump backup power systems being located in the path of the tsunami rather than up on the hill behind the plant where the backup power systems would have survived both the earthquake and the tsunami. This same attitude of "it can't happen here" is pervasive at the NWMO.

A variation of this attitude of complacency is that if a long term nuclear waste storage methodology is acceptable for use in other countries it should also acceptable for use in for Canada. However, the laws of physics do not obey popular opinion. Unlike other countries, southern Ontario contains or borders much of the world's reserve of drinking water.

A practical alternative to the NWMO plan is proposed herein that:
1) uses proven technologies,
2) permits nuclear fuel recycling,
3) provides much better long term safety and
4) is much less expensive to implement.

However, this alternative plan requires that Canadian federal and provincial politicians face the reality that long term use of nuclear power is essential to provide reliable power while minimizing CO2 emissions to the atmosphere. These politicians must then face and overcome NIMBYism relating to proper safe storage of nuclear waste.

THE PRESENT NWMO PLAN:
The present NWMO Plan contemplates both "containment and isolation of used nuclear fuel in a deep geological repository".

The present NWMO Plan contemplates enclosing multiple 0.1 m diameter X 0.5 metre long used CANDU nuclear fuel bundles inside a 4 metre long cylindrical metal container. Each metal container would each be placed within a borehole in rock at a depth of about 500 metres below grade. The bottom of the borehole, the annular space between the metal container and the borehole wall and the top of the borehole would be filled with bentonite clay.

The present NWMO plan has no requirement that the deep geological repository be above the possible future water table.

Implementation of the present NWMO Plan is projected by the NWMO to cost $16 to $24 billion to store about 2 million used CANDU fuel bundles.

The present NWMO Plan focuses primarily on the politics of choosing a site acceptable to existing nearby residents. The present NWMO plan does not address the much more important issue of initially selecting sites that geologically and economically lend themselves to safe and inexpensive long term storage of used nuclear fuel bundles.

Money spent on potential political action with respect to potential sites that are geologically unsuitable is wasted money.

Finally the present NWMO Plan does not explicitly address the ultimate financial impact of the NWMO plan on the costs of nuclear generated electricity, radio isotopes and nuclear heat for commercial/industrial applications.

PROBLEMS WITH THE PRESENT NWMO PLAN:
The major problems with the present NWMO Plan are that it gives more priority to near term political expediency than to long term safety and that it fails to convey a sense of financial responsibility to the parties that must ultimately fund the plan's implementation.

There is no debate that used nuclear fuel bundles must be safely stored for a very long period of time. However, it is important for the NWMO to acknowledge that its funding must ultimately come from electricity rate payers and commercial/industrial parties that use nuclear heat. The NWMO needs to demonstrate prudent use of funds and reasonable financial projections. That sense of financial responsibility is missing from the present NWMO Plan. The present NWMO plan focuses on politics instead of safe storage engineering. As a minimum a list of the major assumptions and a breakdown of the projected construction and long term operating costs of the contemplated nuclear waste storage facility should be included in the NWMO Plan.

The present NWMO Plan implicitly contains a number of assumptions that are not consistent with practical experience in the mining and tunneling industries. Of particular concern is long term isolation of the used nuclear fuel from ground water. The present NWMO Plan envisages a storage site 500 metres below the water table. At that depth, absent continuous mechanical pumping, the hydrostatic pressure is about 50 atmospheres, which in time will fill the deep underground storage facility with high pressure water and will collapse any voids within the bentonite clay.

The present NWMO plan implicitly assumes that the NWMO can design the storage facility such that corrosive elements dissolved in ground water, such as sulfur, that trigger metal corrosion, will be reliably excluded from the metal containers for at least 100,000 years. However, the NWMO plan does not address practical realization of that exclusion.

Eventually the combination of imperfect bentonite clay seals, hydrostatic pressure, void collapse and corrosion will crush the metal containers contemplated by the NWMO. Hence the NWMO is relying on the bentonite clay to isolate the nuclear material from ground water. However, over a 100,000 year period the bentonite clay could easily fail due to ground shear forces or due to void and/or container collapse, thus allowing high level nuclear waste to mix with ground water. Hence the present NWMO plan fails to safely isolate radioactive nuclear material from ground water.

The NWMO is contemplating possible use of copper or nickel in the metal containers to minimize the metal corrosion rate. However, use of those metals introduces a new risk that at some time in the future the storage system will be compromised by a greedy irresponsible party that seeks to recover the metal containers for their scrap value. Such a party would also break all the bentonite seals.

REMEDIES:
In order to contain costs, instead of trying to investigate many questionable technologies, the NWMO Plan should focus on technologies that have proven performance in long term preservation, hard rock mining and tunnel construction. The NWMO should avail itself of expertise in practical aspects of petrochemicals, rock chemistry, hard rock mining and tunnel boring.

In order to contain costs the NWMO should focus on a plan that does not require ongoing site staff and does not require ongoing water pumping.

THE NWMO should get on with the task of identifying prospective sites that are both geologically and economically suitable (sufficient altitude in a high mountain, unbroken igneous rock mountain core, suitable topography, existing self draining depleted hard rock mine, existing single access road, proximity of electricity supply, etc.).

The NWMO should not concern itself with political matters relating to site choice until after the NWMO has identified several geologically and economically suitable sites. Then each potential host community would have to compete with other potential host communities to become the chosen site for a multi-billion dollar nuclear waste processing and storage facility.

LONG TERM STORAGE CONCEPTS:
1. Wax has been successfully used for thousands of years for preservation of human mummies.

2. Tar has been successfully used for many years for long term water proofing of underground structures;

3. Dinosaur skeletons were preserved for over 65 million years after these dinosaurs became trapped in tar (heavy oil) pits that were later covered by sand;

4. Dinosaur preservation was achieved by the tar/sand barrier preventing transport of trapped dinosaur material to either the atmosphere or ground water;

5. Tar and wax are liquid moderately above room temperature, are solid at room temperature, and are almost incompressible. A tar or wax filling can prevent a fuel bundle container collapsing due to external hydrostatic pressure;

6. When a heavy oil is subject to ionizing radiation it gradually reforms into low molecular weight gaseous components such as methane and high molecular weight liquid/solid components that form tar;

7. The materials that constitute nuclear fuel bundles do not chemically react with pure hydrocarbons (AECL built and operated a research nuclear reactor that used a liquid hydrocarbon coolant);

8. The dead sea scrolls were preserved for over 2000 years in a relatively dry environment by storage in primitive capped ceramic containers;

9. Man made igneous rock structures have survived over 5000 years in a damp climate (eg Stonehenge in England);

10. Man made sedimentary rock structures have survived over 5000 years only in very dry climates (eg The pyramids in Egypt);

11. No man made structure will prevent long term determined attack by thieves if the structure contains substantial amounts of removable high value metals such as gold, silver, copper and nickel;

12. Silica (SiO2) as a fuel bundle container material offers very long term structural stability at room temperature;

13. Silica (SiO2) in the form of dry sand can be used to reliably fill voids and can provide very long term mechanical protection while withstanding an enormous hydrostatic pressure;

14. Alumina (Al2O3) as a container material also offers long term stability at room temperature. It is radiation resistant. It can easily be fabricated and machined. However, if exposed to water anhydrous alumina gradually takes on water of hydration.

15. Glass is an extremely viscous liquid that is widely used for manufacture of food and beverage containers, windows and laboratory equipment. Due to long term liquid flow deformation glass is believed to be structurally unsuitable for making containers that must last over one hundred thousand years. However, glass used as an alumina glaze should protect anhydrous alumina from hydration damage for a very long period of time. Borosilicate glass offers better aggressive chemical and thermal shock resistance than does soda lime glass. However, soda lime glass much more closely matches the Thermal Coefficient of Expansion (TCE) of alumina. TCE for 99.5% alumina = 8.4 X 10^-6 / C. TCE for soda lime glass = 8.9 X 10^-6 / C. TCE for borosilicate glass = 3.25 X 10^-6 / C. Some experimentation may be required to determine the glass composition that is best for long term glazing of Al2O3 containers. Neither soda lime glass nor borosilicate glass will withstand hydrofluoric acid, hot phosphoric acid or hot alkalines;

16. Glass is discolored by high levels of ionizing radiation. Whether or not this discoloration process affects the long term utility of glass as an external glaze for an alumina container is unknown to this author. However, this issue may be irrelevant because oil in that alumina container will likely become tar long before the alumina container fails.

17. Certain types of hard rock mining operations in crack free igneous rock mountain cores result in tunnels and underground spaces that are dry and that naturally drain without mechanical pumping. Such naturally dry tunnels lend themselves to long term storage of radioactive material.

18. Igneous rock is free of thermal stress cracks only if the magma that forms the rock cools extremely slowly. Such crack free rock can be found under about 300 m of overburden at the core of a potential volcano that did not erupt.

SAFE STORAGE OF USED CANDU NUCLEAR FUEL BUNDLES:
There are a number of practical issues related to long term safe storage of used CANDU nuclear fuel bundles:
1. A used nuclear fuel bundle contains a wide variety of radioactive isotopes and decay products that result from fission of uranium and plutonium and from absorption of neutrons. Some of these isotopes and decay products have very long half lives. For bio-safety it is essential to prevent these radioactive isotopes from dissolving in ground water for a period of nearly 1,000,000 years. Hence the storage facility should be 500 m above the surrounding water table to keep the fuel bundles dry and must have natural gravity drainage of seepage water.

2. The radioactive fuel bundles gradually release energy which causes local heating. Natural ventilation should be used to release this heat from the storage facility. This heat and natural ventilation will also assist in keeping the fuel bundle containers and storage facility dry.

3. The storage facility must be sufficiently above the surrounding sea and lake levels that no reasonably foreseeable event will lead to the fuel bundles being below the water table. In this respect melting of the Greenland and Antarctic ice caps could cause about an 80 metre increase in sea level, with corresponding increases in interior lake and water table levels. A slip fault like the Niagara escarpment could add another 100 m. Glaciation, land slides or volcanic eruption could further increase the altitude of the local water table. Hence the altitude of the storage facility gravity drain discharge should be at least 500 metres above the surface of nearby major water bodies such as lakes or the sea.

4. The NWMO concept of using bentonite clay as a waterproof seal for a borehole containing several nuclear fuel bundles in a container is a good idea and should be used to provide a backup level of isolation between the nuclear waste and ground water.

5. The direct alpha, beta, gamma and neutron emission by the fuel bundles is easily absorbed by 10 metres of continuous igneous rock. However, the storage site should be is sufficiently deep to remain undisturbed for at least ten glaciation cycles. In this respect the NWMO concept of the storage facility being 500 m below grade is a good idea.

6. Some of the nuclear decay products are radioactive inert gases which would slowly diffuse out of containment and mix with the atmosphere inside the contemplated storage facility. The number of fuel bundles permitted to be stored at a single site may be limited by the maximum rate of release of such radioactive gases in combination with the storage facility's ventilation rate.

7. CANDU fuel pellets are contained in zirconium tubes. Zirconium easily burns in air. Hence it is important to surround the fuel bundles by materials that will prevent combustion of the zirconium.

8. Advancements in nuclear reactor technology suggest that in the future it will likely be desirable to recycle nuclear fuel. Hence the used fuel bundles should be stored in a dry location within containers that: exclude dirt and water, provide bio-hazard isolation and provide the option of future reprocessing of the radioactive fuel. These containers should resist external pressure and should have a means of relieving internal gas pressure.

9. The contemplated nuclear waste storage facility will likely ultimately contain millions of used fuel bundle containers. The storage process must tolerate occasional container failures and handling accidents without risk of a major fire or radiation hazard.

10. It is crucial that the materials used to fabricate the storage facility and the fuel bundle containers be inexpensive both to minimize the initial cost of the facility and to discourage future thieves. In this respect it is important to not use gold, silver, copper or nickel (stainless steel) for fuel bundle containment. Recently when the price of copper was high there were problems with thieves stealing bronze plaques from monuments, ground wire from electrical substations and copper pipe from buildings. The damage caused by such thieves far exceeds the scrap value of the stolen material. It is impractical and uneconomic to guard this nuclear waste storage facility for 100,000 years. Hence it is essential to develop a fuel bundle container that will not attract thieves.

11. This author contemplates the use of an individual cylindrical ceramic container for each fuel bundle. The contemplated container would be formed from silica or glazed dense alumina. The ceramic container would be partly filled with a warm high molecular weight hydrocarbon (heavy oil) before insertion of the fuel bundle. After insertion of the fuel bundle the top surface of the heavy oil should be several cm above the top of the fuel bundle and there should be a small gas space above the heavy oil to relieve stress from out gassing and differential thermal expansion.

12. The fuel bundle container should have a ceramic cap with an internal downward protrusion that fits into the top of the container. This protrusion would hold the cap in place laterally and would have a perforated section that extends down below the surface of the heavy oil. On cap insertion the warm oil will fill the perforations. When the heavy oil cools its high viscosity will resist removal of the cap. At all times the ceramic containers should be kept in the upright position with the ceramic cap on top.

13. Each fuel bundle container is installed in a water tight bore hole that is vertically drilled downwards into solid rock and is lined with bentonite clay. Lateral movement of the containers is prevented by the bentonite clay lined borehole walls. The voids around and between the fuel bundle containers are filled with dry silica sand.

14. The successive layers of fuel bundle containers in boreholes are separated by dry silica sand.

15. If the fuel bundles contain excess fissionable material the silica sand back fill can have an additive that is solid, insoluble in water and has a high neutron absorption cross section.

16. The top of the bore hole is plugged with bentonite clay.

17. If a ceramic container fails the contained heavy oil will be trapped in the surrounding silica sand. The resulting oil/sand mixture will form an asphalt like barrier that will prevent radioactive material transport.

18. Over a long period of time the heavy oil in which the nuclear fuel bundle is immersed will get thicker trapping the stored nuclear material in place even if the ceramic container fails.

19. Each storage chamber must have a drain hole at its lowest point. If a bore hole cracks the oil drainage path will indicate the location where the leak occurred. Oil and seepage water are easily separated through the use of an in-line sump (the oil will float on the surface of the pump's inlet sump). Even if all the oil is lost from a ceramic container the silica sand should prevent either a zirconium fire or a heavy oil fire.

20. This storage system design is extremely resistant to earthquake caused vibration.

21. If a fuel bundle needs to be recovered the bentonite clay plug is cut away, the silica sand surrounding the ceramic fuel bundle containers is removed by air blast/vacuum suction and the ceramic containers are lifted out of the boreholes. Then each ceramic container is gently heated in an inert atmosphere to reduce the viscosity of the heavy oil. When the heavy oil is warm the ceramic container cap can be lifted off and the fuel bundle can be lifted out of the ceramic container. The fuel bundle can then be cleaned first by a steam jet, then by immersion in a flow of superheated water and then by immersion in a flow of organic solvent.

22. The nuclear waste storage facility should be in crack free igneous (crystalline) rock. When damp and in the presence of carbon dioxide igneous rock (CaSiO3) at normal temperatures decays to sedimentary rock (CaCO3 + SiO2) in about 100,000 years according to the weathering equation:
CaSiO3 + CO2 + H2O = CaCO3 + SiO2 + H2O
However, in the presence of similar amounts of water and carbon dioxide sedimentary rock fails in less than 1000 years according to the equation:
CaCO3 + H2O + CO2 = Ca(HCO3)2
because Ca(HCO3)2 is water soluble.
The only place where man made sedimentary rock structures have lasted over 5000 years is North Africa where the climate is very dry. There is nowhere in Canada where we can reasonably forecast such dryness.

23. To keep the cost of the nuclear waste storage facility reasonable, much of the facility should be built using Tunnel Boring Machine (TBM) technology. However, one of the weaknesses of TBM technology is that it fails when it encounters deep underground broken rock or deep underground mud pockets. There have been several recent cases in Canada relating to this problem. eg. Tunnel between the Seymour Dam filtration plant and the Cleveland Dam in North Vancouver, the hydroelectric power tunnel under the City of Niagara Falls, a drainage tunnel under Toronto and a flooded uranium mine in the Yukon. In each case the problem was the inability of current technology to accurately forecast the quality of the rock ahead of the TBM when the tunnel is deep. In each case a fix cost multi-hundred million dollars. At this time the only reliable way of ensuring rock quality ahead of a TBM is to core drill ahead of the TBM. That core drilling is only economically feasible if the tunnel is not very deep or if much of the core drilling is funded by mining rather than by nuclear waste storage. From this author's perspective the practical way to minimize the cost of the contemplated nuclear waste storage facility is to choose a site where there has already been extensive mining. Then the site's subsurface geology will be well understood and there will be basic services such as an access road, electricity, potable water, etc.

24. The TBM path should slope upward at about 3 degrees above horizontal to provide positive gravity water drainage out of the storage facility and to allow cut rock to be removed by a gravity driven mechanism.

25. The storage facility should be designed so that all drainage water from the facility flows past a common point where instrumentation can be mounted to detect any dissolved radioactive leakage from the facility. The storage facility access tunnels and ventilation shafts should be grouted to minimize water entry and to prevent water exit via unmonitored paths.

26. The nuclear waste storage facility should be built in a seismically stable area to ensure that the fuel bundles remain accessible for the life of the facility.

27. The nuclear waste storage facility should be located in a remote area with only one access road leading to the storage facility, so that in the event of a terrorist break-in the terrorists are easily detected, contained and trapped. Entry into the storage facility should require heavy equipment so that terrorists cannot gain access to the radio active material using only air transport.

SUMMARY:
The nuclear waste storage facility should be built in a mountain with a crack free solid igneous rock core. This mountain should be located in a remote seismically stable area where there has been extensive mining so that the subsurface geology is well known. The site should be legally protected from both future development and future mining. A Tunnel Boring Machine (TBM) should bore into the side of the mountain at an angle about three degrees above horizontal to provide positive gravity drainage to the outside. The nuclear waste storage facility should be fitted with at least two redundant vertical air vent shafts. These shafts should be fitted with goose neck caps to prevent entry of rain water. These shafts can also serve as emergency exit routes from the storage facility.

The TBM entry point altitude should be at least 500 metres above the highest surrounding lake or sea level. The storage facility should be about 500 metres below grade. Hence the mountain will have to be well over 1000 m high. To obtain sufficient mountain height in combination with a crack free igneous rock mountain core the storage facility will likely have to be located in British Columbia, Alberta or the Yukon.

The preliminary site selection process should include altitude determination, core drilling and rock analysis to determine site's physical suitability prior to any political discussions with area residents.

Each nuclear fuel bundle should be enclosed in a cylindrical ceramic container which is almost filled with heavy oil for additional strength and to exclude air and water. A multiplicity of such containers can be stacked upright in a vertical bore hole in igneous rock that is lined with bentonite clay. The void space around the containers should be back filled with dry silica sand which may have an additive with a high neutron absorption cross section. The top of each bore hole should be sealed with bentonite clay.

Based on well known chemistry sedimentary rock is unsuitable for construction of the proposed used nuclear fuel bundle storage facility. In the presence of water and carbon dioxide its CaCO3 component dissolves away too quickly.

Practical field experience indicates that a deep underground used nuclear fuel bundle storage facility located 500 m below the water table, as is presently contemplated by the NWMO, is neither economic to build nor feasible to keep dry. If the storage facility is not kept dry there will be an ongoing bio-safety hazard related to future earth shear and the fuel bundles will not remain accessible.

The alternative nuclear waste storage facility design concept contemplated herein is much safer, much more practical and much less expensive than the storage facility presently contemplated by the NWMO.

CONTEMPLATED LOCATION:
Geologically the most suitable location known to this author for a long term nuclear waste storage facility is the existing Jersey-Emerald mine in southern British Columbia. The elevations are right, the igneous rock mountain core appears to be crack free, the subsurface has been extensively explored, the location is remote, and there is only one access road. The disadvantages of this location are almost entirely of a federal-provincial NIMBY political nature.

This web page last updated April 3, 2011