NUCLEAR WASTE MANAGEMENT

RESPONSE TO NOVEMBER 2009 NWMO PLAN FOR LONG TERM STORAGE OF USED NUCLEAR FUEL BUNDLES

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

EXECUTIVE SUMMARY:
In November 2009 the Nuclear Waste Management Organization (NWMO) circulated a draft document (present NWMO Plan) titled "Implementing Adaptive Phased Management 2010 to 2014 - Draft for Review". Various problems with the present NWMO Plan for long term storage of used nuclear fuel bundles are identified herein. An alternative plan is proposed that uses proven technologies, permits fuel recycling, provides better long term safety and is less expensive to implement.

THE PRESENT NWMO PLAN:
The present NWMO Plan contemplates "containment and isolation of used nuclear fuel in a repository constructed deep underground in an appropriate rock formation". The present NWMO Plan contemplates "refinement of the generic designs and safety cases for a repository in both crystalline and sedimentary rock formations". The present NWMO Plan further contemplates both "containment and isolation of used nuclear fuel in deep geological repository" and "shallow underground storage".

The present NWMO Plan contemplates enclosing seven 0.5 metre long used CANDU fuel bundles inside a 4 metre long copper cylindrical container. This copper cylindrical container would be surrounded by bentonite clay within a bore hole in rock at a depth of about 500 metres.

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

The present NWMO Plan focuses primarily on the politics of site selection. 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.

Finally the present NWMO Plan does not address the issues how the NWMO Plan is to be funded and the ultimate financial impact of this plan on the costs of nuclear generated electricity, radio isotopes and nuclear heat for commercial/industrial applications.

PROBLEMS WITH THE PRESENT NWMO PLAN:
A major problem with the present NWMO Plan is that it fails to convey a sense of financial responsibility to the nuclear industry. 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 tax payers, electricity rate payers and commercial/industrial heat end users. The NWMO has to be responsible for prudent use this money and for reasonable financial projections. That sense of responsibility is missing from the present NWMO Plan. As a minimum a list of the major assumptions and a breakdown of the projected long term costs 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 depth of 500 metres. At that depth, absent continuous mechanical pumping, the hydrostatic pressure is about 50 atmospheres, which would in time crush the copper containers contemplated by the NWMO. The required isolation of nuclear material from ground water is not achieved.

In order to contain costs, instead of trying to investigate many questionable technologies, the NWMO Plan should focus on technologies that have field 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 (unbroken igneous rock, altitude, topography, existing access road, proximity of electricity supply, existing self draining depleted hard rock mine, etc.).

The NWMO should not concern itself with political matters relating to site choice until after the NWMO has identified a multiplicity of geologically and economically suitable sites. Then each potential host community would have to compete with other communities to become a chosen site.

LONG TERM STORAGE CONCEPTS:
1. Tar has been successfully used for many years for long term water proofing of underground structures;

2. 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;

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

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

5. Man made igneous rock structures that predate all historical records have survived in a damp climate (eg Stonehenge in England);

6. Man made sedimentary rock structures have survived for a long time (> 5000 years) only in very dry climates (eg The pyramids in Egypt);

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

8. Zirconium does not chemically react with pure hydrocarbons (AECL built and operated a research nuclear reactor that used a liquid hydrocarbon coolant);

9. When a heavy oil is subject to ionizing radiation it gradually reforms into low molecular weight components such as methane and high molecular weight components such as tar;

10. Silica (SiO2) offers very long term stability at room temperature. However, it is difficult and expensive to form into fabricated containers;

11. Silica (SiO2) in the form of course sand can easily provide very long term water drainage and mechanical protection;

12. Alumina (Al2O3) offers long term stability at room temperature. It is radiation resistant. It can be fabricated, machined and formed into strong vacuum tight containers. However, if exposed to water anhydrous alumina gradually takes on water of hydration.

13. Glass is an extremely viscous liquid that is widely used for manufacture of transparent 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 is required to determine the glass composition that is best for this glaze application. Neither soda lime glass nor borosilicate glass will withstand hydrofluoric acid, hot phosphoric acid or hot alkalines;

14. 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.

15. Certain types of hard rock mining operations result in tunnels and underground spaces that are dry or naturally drain without mechanical pumping. Such naturally dry tunnels and underground spaces lend themselves to long term storage of radioactive material.

SAFE STORAGE OF USED CANDU NUCLEAR FUEL BUNDLES:
There are a number of practical issues related to long term safe storage of used CANDU fuel bundles:
1. A used CANDU fuel bundle contains a wide variety of radioactive isotopes and decay products that result from fission of uranium. Some of these isotopes and/or the decay products have very long half lives. For bio-safety it is essential to prevent these isotopes from mixing with and/or dissolving in ground water and hence entering the food chain for a period in excess of 100,000 years. Hence the storage facility must keep the fuel bundles dry and must have natural gravity drainage of seepage water.

2. The storage location 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. Hence the altitude of the storage facility gravity drain discharge should be at least 100 metres above the surface of nearby water bodies such as lakes or the sea. This altitude should be even higher if the drainage path could be blocked by a land slide or by a volcanic eruption.

3. The direct alpha, beta, gamma and neutron emission by the fuel bundles is easily absorbed by 10 metres of continuous igneous rock. If the storage site is legally protected from both development and subsurface exploration and if the storage site is chosen for glacier resistance, there is little tangible benefit in large amounts of additional rock cover.

4. Some of the nuclear decay products are radioactive gases which would slowly leak out and mix with the atmosphere. The number of fuel bundles permitted to be stored at a single site might be limited by the maximum acceptable rate of release of such radioactive gases.

5. 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.

6. Advancements in nuclear reactor technology suggest that in the future it may 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 have a means of relieving internal gas pressure.

7. A used nuclear fuel bundle storage facility may ultimately contain millions of used fuel bundle containers. The storage process must tolerate a few container failures without causing a fire or radiation hazard.

8. 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 copper for fuel bundle containment. Recently when the price of copper was high there were problems with thieves stealing bronze plaques from monuments and copper pipe from buildings. The damage caused by such thieves far exceeds the scrap value of the stolen material. There is no budget to guard this facility for 100,000 years! Hence it is essential to develop a fuel bundle container that will not attract thieves.

9. This author contemplates the use of an individual cylindrical ceramic container for each fuel bundle. The contemplated container would be formed from dense alumina and glazed with borosilicate glass to minimize hydration. 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 gas space above the heavy oil to relieve stress from out gassing and differential thermal expansion.

10. The ceramic container should have a ceramic cap with a concave downward protrusion that is machined to slide fit into the top of the alumina cylindrical container. This protrusion would hold the cap in place laterally and would extend down below the surface of the heavy oil. When the heavy oil cools its highly viscosity will resist removal of the container cap. At all times the ceramic containers should be kept in the upright position with the ceramic cap on top.

11. Each ceramic container in storage is surrounded by silica sand. In the event of a ceramic container failure the consequent oil/sand mixture will form an asphalt like barrier that will prevent radioactive material transport to either the atmosphere or ground water.

12. If a fuel bundle needs to be recovered the surrounding silica sand should be removed by vacuum suction and the ceramic container should be lifted out of storage. Then the ceramic container should be gently heated 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 should then be cleaned by a steam jet and then by immersion first in a flow of superheated water and then in a flow of organic solvent.

13. 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 natural ventilation will also assist in keeping the storage facility dry.

14. The storage facility should be in solid 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.

15. To keep the cost of this 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 Big Becky tunnel under 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 material ahead of the TBM when the tunnel is deep. In each case a temporary 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. From this author's perspective the only way to keep the cost of the contemplated storage facility under control is to find a site with suitable natural drainage where the topography reasonably permits core drilling ahead of the TBM path. Ten to thirty metres of solid igneous rock surrounding the storage facility is sufficient for structural strength and radiation absorption.

16. 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 conveyor mechanism.

17. 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 should be grouted to minimize water entry and to prevent water exit via other paths.

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

19. The storage facility should be located in a remote area with only one 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 enough heavy equipment to prevent terrorists gaining access to the radio active material using only air transport.

20. Within the storage facility at the upper end of each radial storage tunnel the ceramic containers should be positioned vertically on a level gravel base to ensure good stacking and good local drainage. Lateral movement of the containers will be prevented on three sides by the tunnel's rock walls. The fourth wall facing the open tunnel should be built of saw cut igneous rock components, similar to an arched hydro-electric dam. This wall is concave towards the open tunnel and convex towards the stacked ceramic containers. This design is extremely earthquake resistant. This wall must have a drain hole at its lowest point.

21. The spaces between the ceramic containers are back filled with course silica sand for drainage, for long term ceramic container position stability and for even distribution both vertical and horizontal forces.

22. The successive layers of ceramic containers are also separated by silica sand. It is anticipated that the maximum height of a ceramic container stack will be about 1 metre less than the height of the tunnel.

23. 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.

24. If a ceramic container fails the contained heavy oil will be mostly trapped by the surrounding silica sand. The oil drainage path will indicate the location where the leak occurred. The oil and seepage water are easily separated through the use of an in-line sump (the oil will float on the surface of the sump). Even if all the oil is lost from a ceramic container the alumina and the silica sand should prevent either a zirconium fire or a heavy oil fire.

25. Over a long period of time the heavy oil will get thicker trapping the stored nuclear material in place even if the ceramic container fails.

SUMMARY:
The used nuclear fuel storage facility should be built into one side of a mountain composed of solid igneous rock and located in a remote seismically stable area. The site should be legally protected from both development and subsurface exploration. 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 topography of the selected mountain should provide a plateau or similar area that can easily be vertically core drilled ahead of the contemplated TBM path. The core holes should be located to also serve as long term air vent holes. These core holes should be fitted with water sealed goose neck tops to prevent ongoing rainwater entry.

The TBM entry point altitude must be at least 100 metres above the highest surrounding lake or sea level. There should be a mountain plateau 20 to 40 meters above the TBM entry point.

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

Each fuel bundle should be enclosed in a cylindrical glazed ceramic container which is almost filled with heavy oil for additional strength and to exclude air and water. Many such containers can be stacked upright at the end of a blind tunnel in igneous rock. The container stack should be back filled with course silica sand which may have an additive with a high neutron absorption cross section. The container stack is laterally held in place by an engineered igneous rock wall.

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 the 500 metre deep underground used nuclear fuel bundle storage facility 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 and the fuel bundles will not remain accessible. The alternative used nuclear fuel bundle storage facility design concept contemplated herein is safer, more practical and considerably less expensive than the storage facility presently contemplated by the NWMO.

COMMENTS:
A HTML version of this document is available at http://www.xylenepower.com/NWMO%20Response.htm. Parties with constructive comments relating to the alternative used nuclear fuel bundle storage plan set out herein are invited to email their comments to charles.rhodes@xylenepower.com or charles.rhodes@microfusion.ca

This web page last updated December 16, 2009