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NUCLEAR WASTE DISPOSAL

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

NUCLEAR WASTE:
Nuclear waste contains radio active atomic isotopes (radio isotopes) that form as a result of nuclear fission or of absorption of free neutrons by materials in or near a nuclear reactor. These radio isotopes spontaneously decay over time. Each radio isotope has a characteristic half life. However, when a radio isotope decays it often becomes another radio isotope.
 

NUCLEAR WASTE CATEGORY REVIEW:
Nuclear waste containing radio isotopes with half lives of less than 30 years is referred to government as Low Level Waste (LLW). Nuclear waste containing radio isotopes with half lives of greater than 30 years is referred to by government as High Level Waste (HLW). A mixture of HLW and LLW is referred to by government as Intermediate Level Waste (ILW). After ILW has been in storage for 300 years the radio toxicity of the remaining LLW component will be very small relative to the radio toxicity of the remaining HLW component. Hence over a few centuries ILW becomes HLW.
 

PREFERRED NUCLEAR WASTE STORAGE SITE:
The site in Canada that is believed to be most geophysically suitable for long term dry storage of nuclear waste is the Jersey Emerald mine complex in British Columbia. No matter what else is done with spent CANDU fuel and other nuclear waste, the public will remain at risk from extreme natural events until the nuclear waste is moved to a safer location than the existing CANDU reactor sites.

In the view of this author the existing political guidelines from both the government of Ontario and the government of Canada relating to nuclear waste transport, processing and disposal are wrong. These guidelines are founded in irrational public fears and in a political planning horizon that does not extend beyond the next election. In the view of this author it is a huge mistake to let short term political considerations take precedence over scientific fact, good engineering, energy efficiency and public safety.
 

NWMO NUCLEAR WASTE DISPOSAL CONCEPT:
There are two competing nuclear waste disposal concepts. The concept presently advocated by the Nuclear Waste Management Organization (NWMO) and Ontario Power Generation (OPG) is to place all nuclear waste in inaccessible Deep Geologic Repositorys (DGRs) which are located in limestone far below the local water table within a "receptive community". That concept requires ensuring that the HLW remains isolated from ground water and the biosphere for about 3,000,000 years. The practical difficulties of ensuring reliable dry isolation that lasts 600 X the life of the ancient Egyptian Pyramids should not be under estimated.

A fundamental problem with the NWMO/OPG methodology is that it does not allow fuel recycling. The NWMO/OPG concept is to dig a deep hole in limestone, dump the waste down the hole, backfill with limestone and then hope that there is negligible radioisotope transport out of this deep underground dump for the next three million years. The NWMO/OPG concept relies on the collapse of the limestone under gravitational stress to seal the dump. I am not arguing that the NWMO methodology will not work for a few dumps. However, after a few hundred years the province will be littered with such toxic waste dumps. It is like having a few hundred nuclear reactors operating without maintenance. Sooner or later one of them will fail. If such a failure occurs there is almost nothing practical that can be done to remedy the situation.

The NWMO/OPG methodology makes assumptions about the subsurface geology that may or may not be true. For example at Bruce there are less than a dozen documented drill cores. As we saw at the Niagara Tunnel and the Seymour Tunnel, assumptions based on limited core drilling are often wrong with short term construction cost consequences in the $1 billion / incident range.

The NWMO is so divorced from practical mining and tunneling reality that I frankly see no solution other than to completely wind up the NWMO and start again with new professional personnel who have practical Canadian hard rock mining/tunneling experience. As a minimum the NWMO and OPG should have engaged persons who worked on the Niagara Tunnel in order to bring into the NWMO/OPG planning some sense of practical reality with respect to deep underground water seepage and ventilation requirements.

In the Niagara Tunnel shotcrete was applied to the tunnel walls immediately behind the tunnel boring machine. The shotcrete was followed by an olefin plastic water barrier and then a structural liner. There is currently no provision for these measures in the NWMO/OPG plans for the Bruce DGR. For the Niagara Tunnel OPG employed European engineering consultants who had relevant experience with comparable European tunnels.

However, for reasons unknown to me OPG experience gained during construction of the Niagara Tunnel was not considered in OPG planning with respect to the Bruce DGR.

One of the problems that is not adequately appreciated with respect to the proposed Bruce DGR is that the hydraulic pressure head that builds up behind an olefin plastic water barrier is enormous. (680 m head of water at Bruce). A very thick concrete structural liner would be required to prevent that hydraulic pressure head rupturing the liner. Without a liner seepage water has to be constantly pumped out. The cost of that seepage pumping will likely be millions of dollars per year. Ideally in this situation the overhead ground should be dewatered to limit seepage. However, the proximity of the Bruce site to Lake Huron makes such dewatering impossible. Further, adjacent property owners that rely on water wells would scream if the local aquifers were drained.

The NWMO fails to appreciate that a "receptive community" will not exist without a local source of fresh water such as an aquifer, but anywhere with such an aquifer is poorly suited for nuclear waste storage. The NWMO should be looking for "no community" DGR site opportunities where there is not and never will be an overhead aquifer.

The NWMO currently plans to bury untreated HLW in domed end cylindrical copper coated steel containers surrounded by bentonite clay.

In my view the present NWMO plan for dealing with high atomic weight HLW is complete foolishness. Using proven technology high atomic weight HLW can be converted into fuel for liquid sodium cooled fast neutron breeder reactors. Such reactors can fission the HLW atoms so that these atoms become LLW atoms which are relatively simple to deal with from a disposal perspective. Furthermore, fast neutron reactors multiply by 100 fold the useful energy obtainable per kg of natural uranium as compared to a CANDU reactor.

The existing inventory of HLW could be concentrated on existing reactor sites, interim stored at Jersey Emerald and eventually reprocessed at Trail, BC which is about 40 km away. Trail has a long history of bulk processing of highly toxic materials.
 

ALTERNATIVE DGR WASTE DISPOSAL CONCEPT:
The alternative DGR waste disposal concept is completely different from the NWMO concept.

1) A fast neutron reactor is used to fully convert long lived high atomic weight isotopes into short lived low atomic weight isotopes;
2) The fast neutron reactor is designed to avoid production of long lived low atomic weight isotopes;
3) The short lived low atomic weight isotopes are held in isolated storage for 300 years to allow all the short lived low atomic weight isotopes to naturally decay away;
4) Any remaining long lived low atomic weight isotopes, including C-14, Cl-36, Ca-41 and Ni-59, are selectively extracted from the residual material for permanent storage.

The purpose of a DGR is five fold.
1) To provide structural protection for engineered radio isotope containers placed within the DGR for at least 10 half lives of the stored radio isotopes;
2) To provide ongoing physical access to the engineered containers for inspection, material recycling, and container monitoring/repair/replacement.
3) To provide natural gravity water drainage so that the containers remain dry and are never subject to a large external hydraulic pressure head;
4) To provide natural ventilation for heat and water vapor removal.
5) To provide safe default long term radio isotope storage in the event of a future society collapse.

In the alternative methodology the primary barrier to radio isotope transport is the engineered container, not the surrounding rock. About 5000 years ago the ancient Egyptians put mummies in limestone coffins and stored these coffins in pyramids under reasonably dry conditions. These mummies are on exhibition in museums today. It is my belief that we can greatly improve on the ancient Egyptian storage technology using the materials stainless steel, porcelain and a liquid/wax dielectric.

In my view the alternate DGR objectives can be met within the crack free granite core of a selected substantial mountain. The advantages of the alternate concept are:
1) Ongoing radio isotope accessibility for recycling and storage system repair;
2) Capacity to recycle both storage space and storage containers for relatively short lived isotopes such as fission products;
3) Long term certainty that stored radio isotopes will not escape into the environment.
 

METHODOLOGY COMPARISONS:
If one assumes, as does the NWMO, that the storage site must be within a "receptive community" then the NWMO methodology may seem to have a lower first cost.

If on the other hand one assumes that the storage site is an existing depleted hardrock mine far from any significant community, then the alternate methodology is both much less expensive and has many practical advantages. One of these advantages is certainty about the underground geology. As compared to about a dozen documented drill cores at Bruce, Sultan Minerals has about 6000 documented drill cores relating to the depleted Jersey Emerald mine complex and the immediately surrounding area.
 

OTTENSMEYER PLAN CONCEPT:
The alternative concept for storage and disposal of nuclear waste is known as the Ottensmeyer Plan. The Ottensmeyer Plan involves radio isotope recycling and complete energy extraction from nuclear fuel rather than long term storage of highly radio active material.

The key to understanding the Ottensmeyer Plan is understanding that spent CANDU fuel still contains over 99% of its original nuclear potential energy. The fuel is considered "spent" because it contains low atomic weight high neutron cross section fission products. These high neutron cross section atoms shut down a nuclear reactor. If the LLW fission products are selectively removed and are replaced with HLW material the fuel can be recycled. The recycled fuel contains plutonium-239 in place of uranium-235. To maintain the Pu-239 inventory the fuel must be used in a liquid metal or liquid salt cooled fast neutron reactor instead of a water cooled reactor. Of the available coolants sodium has the combined advantages of low density, low melting point, low cost and excellent steel compatibility.

The enhanced Ottensmeyer Plan involves selective chemical extraction of uranium oxide from spent CANDU reactor fuel followed by separation of the remaining nuclear waste into its low atomic weight (LLW) and high atomic weight (HLW) components.

The selectively removed uranium oxide, which constitutes over 90% of the spent CANDU fuel mass, and which may contain a very small fraction of actinide impurity, is stored for future use as fast neutron reactor blanket rod material.

Containers of LLW should be kept in isolated dry storage for 300 years to allow the LLW to naturally decay into stable isotopes. Containers of HLW are used to form core fuel rods for use in fast neutron reactors.

In one fuel cycle a fast neutron reactor fissions 10% to 20% of its original HLW fuel weight into LLW. This newly formed LLW is selectively extracted from the used core rod material and is placed in containers for 300 year dry storage. The extracted weight of LLW is replaced by an equal weight of new HLW and/or stored uranium oxide drawn from inventory and the resulting mixture is again used as core fuel rod material in a fast neutron reactor.

The cycle of LLW extraction, replacement of extracted LLW weight by an equal weight of new HLW/uranium oxide and reuse as fuel in a fast neutron reactor is repeated over and over again to gradually consume the entire HLW/uranium oxide inventory.

The atomic weight based separation process used to extract LLW from HLW is imperfect. A small fraction of low atomic weight long lived isotopes such as C-14, Cl-36, Ca-41 and Ni-59 will remain in the stored LLW. After a container of LLW has been stored for 300 years the radio activity of the container is dominated by a few long lived isotopes. The container is scanned with a gamma ray spectrometer. Based on the recorded gamma ray spectrum chemical treatments are used to selectively extract the long lived isotopes from the decayed LLW. These long lived isotopes are then consigned to very long term storage.

A second neutron irradiation stage of processing is effective at suppressing the longer lived fission products Tc-99, Sn-126, Se-79, Zr-93, Cs-135, Pd-107 and I-129. After a second 300 year storage cycle the container contents are again scanned with a gamma ray spectrometer and again any remaining long lived isotopes can be selectively extracted.

When the radio activity of a container of processed waste is less than the radio activity of an identical container of natural uranium, the container contents can be safely removed and recycled. The decayed LLW primarily consists of rare earths that have high commercial value. The released DGR storage space and the released storage containers are then available for reuse.
 

OTTENSMEYER PLAN IMPLEMENTATION:
The Ottensmeyer Plan uses technologies that have proven performance in long term preservation and water exclusion. The Ottensmeyer Plan takes into consideration practical aspects of petrochemicals, hard rock mining and sulfur induced corrosion.

In the Ottensmeyer Plan water exclusion problems are avoided by storing the radioactive material for several centuries in engineered containers. These containers are located within an accessible naturally dry (gravity drained) Deep Geologic Repository (DGR) that is at least 300 m above the local water table and by keeping the DGR at atmospheric pressure. Resistance to DGR damage by glaciation and other events is ensured by forming the DGR inside the high density granite core of a mountain that provides over 400 m of overhead rock above the DGR. There is no attempt to find a "receptive community" because at geologically suitable DGR sites there is insufficient fresh water to support a community. In the Ottensmeyer Plan the DGR location is determined primarily by favorable geophysical criteria, not by political criteria.

In the Ottensmeyer Plan double wall storage containers (outer wall porcelain, inner wall stainless steel, liquid/wax dielectric between the inner and outer walls) are used to store the radioactive material while it is in the DGR. While in the DGR the physical integrity of each nuclear waste storage container is constantly remotely monitored by sensing the container dielectric level and dielectric loss tangent.
 

LONG TERM SAFETY CERTAINTY:
The primary advantage of the Jersey-Emerald mine facility in British Columbia over other large depleted mines in Canada for spent fuel storage and radioactive waste disposal is very long term certainty of naturally nearly dry conditions spanning numerous ice ages. These nearly dry conditions are key to prevention of contact of the stored radioactive waste with ground water. This author is not aware of any other large existing Canadian mine with comparable natural protection that provides comparable long term certainty regarding separation of toxic radioactive materials from ground water. The simple reality is that the hard rock mountains in Ontario are simply not high enough to provide comparable protection from long term changes in the level of the local water table.

The ongoing failure of mankind to adequately address the problem of fossil carbon CO2 emissions has already initiated a process that will over the coming centuries almost certainly lead to an 80 m increase in sea level due to melting of polar icecaps and thermal expansion of the oceans. Glacial pressure could easily reduce the storage site elevation by more than another 100 m, the height of the Niagara escarpment. If we accept the NWMO recommendation of requiring 400 m to 500 m of top cover, we are looking for a large naturally dry existing hardrock mine half way up a solid granite mountain with a present height of over 1000 m above the surrounding water table. The simple reality is that there are few sufficiently high mountains in Ontario and there is no existing major hardrock mine in Ontario that meets these specifications.
 

This web page last updated February 29, 2016

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