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


Ontario grid supplied electricity presently comes from fossil fuel energy, renewable energy and nuclear energy. Due to Ontario specific geography there are times when the electricity grid is heavily loaded but renewable electricity generation is very low. At these times Ontario relies on nuclear power and on fossil fuels for both electricity generation and transportation. Elimination of fossil fuels at these times, in compliance with the Paris Agreement, requires a 3 fold increase in Ontario's installed nuclear power capacity.

CANDU nuclear power reactors presently provide over 60% of Ontario's electricity. However, CANDU reactors produce a lot of highly toxic spent fuel nuclear waste. Fortunately this waste can potentially be disposed of by liquid sodium cooled Fast Neutron Reactors (FNRs). FNRs can generate electricity while transmuting spent CANDU fuel into fission products that have less than 30 year half lives. After 300 years in isolated storage these fission products can be safely released into the environment. Building the required 300 year storage is not difficult. Today there are many man made structures and depleted mines that are more than 300 years old.

CANDU reactors also neutron activate metals such as zirconium, chromium and iron. Zirconium is used in FNRs as an essential fuel alloy component. Chromium and iron can in principle be recycled in FNRs as fuel tube components, although at this time the economics of such fuel tube component recycling are uncertain.

However, CANDU and other water cooled reactors also pose another waste problem. Free neutrons emitted by these reactors are absorbed by surrounding materials such as stainless steel and concrete where they produce the low atomic weight radio isotopes C-14, Cl-36, Ca-41 and Ni-59 which have half lives ranging from 5,700 to 308,000 years. The only way to avoid dealing with these radio isotopes is to not produce them in the first place. That strategy should be adopted in future FNRs, but for now we have CANDU reactors and we must deal with safe containment of these long lived low atomic weight radio isotopes.

Radio isotopes should be stored in robust containers in circumstances that will keep these isotopes isolated from the environment for at least 10 half lives.

CANDU spent fuel and decommissioning waste may have to be stored for decades before it is recycled in a FNR. These materials will still be strongly radioactive at the time of recycling.

Fission products, which are mainly rare earth radio isotopes, must be stored in isolation for about 300 years before the material can be safely releaed into the environment for recycling into non-nuclear applications.

For the long lived low atomic weight isotopes 10 half lives is 57,000 years for C-14 and 3,080,000 years for Cl-36. C-14 is a containment challenge because if exposed to the atmosphere it eventually forms CO2 gas which is difficult to reliably contain. Cl-36 and Ca-41 are containment challenges because they readily form a wide range of water soluble chemical compounds. Once in contact with ground water these radio isotopes are also extremely difficult to contain.

Hence reliable isolation of these problem radio isotopes requires reliable exclusion of air for 57,000 years and reliable exclusion of water for 3,080,000 years.

The preferred nuclear waste containment strategy is:
1) Process the waste so that only material containing undecayed radio isotopes goes into storage;
2) Using a gamma ray spectrometer sort the material to be stored by radio isotope half life;
3) Ensure that the radio isotopes are chemically bonded into stable solids;
4) Enclose the solids in stainless steel containers that have capacity for gaseous decay product containment or release;
5) Insert each stainless steel container into a robust water tight porcelain container that will automatically vent when there is significant internal gas pressure buildup;
6) Fill the gap between the stainless steel container and the porcelain container with a stable liquid dielectric material such as heavy oil/wax that will reliably exclude oxygen and water;
7) Store the porcelain containers in a secure naturally dry naturally vented location such as a depleted high elevation mine in granite rock where the porcelain containers will be protected from physical damage and from immersion in water for at least 3 million years;
8) Provide for safe long term storage accessibility so that future human generations can inspect the containers in storage and do all necessary to ensure continuing storage integrity.

This methodology, in addition to providing an extremely high level of present and future public safety, enables recycling of irradiated materials. With FNRs this recycling will vastly reduce the amount of new material that needs to be mined, the amount of waste in storage, the required number of waste containers and the required storage volume.

However, the OPG waste disposal methodology, as presented to the Joint Review Panel, does not include any of the above mentioned steps.

The OPG waste disposal methodology can be summarized as:
1) Dig a deep shaft in soft sedimentary rock to about 600 m below Lake Huron;
2) Horizontally excavate about 1 km of unlined tunnel like storage chambers at 600 m depth;
3) Fill the storage chambers with nuclear waste over a period of several decades;
4) Plug the access shafts;
5) Hope that at the chosen storage depth the soft rock collapses sufficiently to make a water tight and air tight seal around the waste that will remain intact for 3,080,000 years. There is disagreement amongst experts relating to the formation and long term integrity of this seal.
6) If this seal should fail rely on the large volume of the great lakes to sufficiently dilute the leaking radio toxins so that they do not pose a risk to human health.

The OPG plan has multiple potential problems related to exclusion of water:
1) The plan lacks a rigid concrete tunnel liner with a plastic water tight barrier to exclude ground water from the DGR while it is open. That methodology is normally used for ground water exclusion in subway tunnels, undersea tunnels, the Niagara Tunnel, etc;
2) The inability to de-water the overhead soil due to the close proximity of Lake Huron;
3) The problem of seepage water penetrating the DGR while the DGR is open;
4) The problem of  near surface aquifer water penetrating the DGR behind the access shaft liner walls while the DGR is open;
5) The potential for DGR flooding due to a surface flood analogous to the Alberta flood;
6) The ongoing cost of pump energy and pump maintenance required to continuously extract water from the DGR while it is under construction and open;
7) The potential for DGR flooding due to a pump mechanical/power/labor failure;
8) The problem of what to do with the radioactive water if the DGR floods while it is open. This issue of radioactive ground water processing is presently a huge problem at Fukushima. OPG should not expose Ontario tax payers/rate payers to this enormous financial risk;
9)The failure of OPG to make a test well to measure the actual water seepage rate at the contemplated DGR location and depth.

All of the aforementioned water exclusion problems can be solved in a single stroke by relocating the DGR to 600 m above the local water table instead of 600 m below the local water table. Put simply, the DGR should be located within the granite core of a high mountain. Seepage water would then run downhill out of the DGR, eliminating any need for pumping and any risk of flooding. Natural ventilation would keep the DGR interior dry. In 2013 OPG had the opportunity to purchase at the bargain price of $67.5 million a suitable large depleted Canadian hard rock mine complete with 10 km of truck size access tunnels and a 4000 hectare security zone, but OPG failed to act. Instead control of the mine passed to Chinese investors. Today purchase of of that mine property could easily cost Ontario taxpayers/ratepayers in excess of $1 billion.

The widespread lack of public education with respect to nuclear matters has led to all kinds of irrational demands relating to transport of nuclear waste from a reactor site to a safe long term storage site. As non-fossil energy systems evolve, the public will gradually come to understand that nuclear power is essential and that for public safety concentrated nuclear waste must be moved by either road or rail to permanent safe storage in a distant DGR.

CANDU reactors are located close to lake level for access to cooling water. Climate change has already triggered major flash floods in both Calgary and Toronto. Ongoing nuclear waste storage on a low elevation CANDU reactor sites is not a good idea. For public safety nuclear waste should be moved to high ground where the waste will never be exposed to tidal waves or flash floods.

The present OPG policy of letting nuclear waste related decisions be driven by short term political expediency rather than by good engineering must be abandoned. The issue is one of public education. The government needs to devote whatever resources and time are necessary to fix this education problem. OPG and the NWMO must also address the lack of knowledge about FNRs and climate change within their own employee ranks.

Ontario will remain heavily dependent on nuclear power far into the future. Canada should adopt an economical and sustainable nuclear waste disposal methodology that does not rely on use of drinking water for potential dilution of long lived toxic nuclear waste. Nuclear waste should be stored in engineered containers in high, dry and accessible DGRs, not open in low, wet and inaccessible DGRs.

If governments continue to stall on the matter of investing in Fast Neutron Reactor development, the Ontario CANDU reactor fleet will likely grow 7 fold during the lifetimes of children now living and the DGR requirement will likely grow 14 fold. Our energy policies should be based on making much less, not much more nuclear waste. Design and construction of a pilot power FNR with supporting CANDU spent fuel reprocessing should be one of our highest priorities. Failure to do so triggers huge future costs and major long term public health concerns.

This web page last updated February 7, 2016

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