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

This web page addresses the issue of sourcing the fuel required to start a Fast Neutron Reactor (FNR).


A CANDU reactor operates with natural uranium oxide fuel in which the uranium fractions are 0.7% U-235 and 99.3% U-238. One function of the heavy water coolant and moderator is to lower the neutron kinetic energies to thermal energies. At thermal neutron energies the U-235 fission capture cross-section for neutrons is very high, which maintains criticality in the reactor in spite of the low U-235 concentration.

A problem common to all nuclear reactors that operate with thermal neutrons is that a fraction of thermal neutrons are captured by U-238 and its neutron capture products and their decay daughters which together form a class of isotopes known as transuranic actinides. A well known example of a transuranic actinide is Pu-239. It is highly toxic and has a half life of about 25,000 years. There is a range of other highly toxic transuranic actinides with atomic weights comparable to uranium and with half lives of the order of 10,000 years.

An important property of the transuranic actinides is that for fast neutrons the fission cross sections are larger than the neutron capture cross sections. Thus in a fast neutron flux the concentration of transuranic actinides will gradually decrease. Hence to prevent net formation of transuranic actinides a FNR operates with fast neutrons.

However, with fast neutrons, such as are emitted by nuclear fission, the fission capture cross section is only about 3% of the fission capture cross section for thermal neutrons. Hence to achieve reactor criticality the fissionable isotope fraction (U-235 or Pu-239) in the reactor core must be increased from about 0.7% to about 20%. Thus a FNR needs a starting fuel load consisting of core fuel rods that have a U-235 or Pu-239 fraction of about 20%. These core fuel rods are surrounded by blanket fuel rods that are nearly 100% UO2 depleted of U-235.

Obtaining the material for the core fuel rods required for FNR startup is one of the challenges of FNR deployment.

Ask the UK to pay us to use some of their excess Pu, since it is costing them money to store it (that’s why they have tenders out to dispose of it). We could either take it for free, or pay something for it. However, the politicians seemed to be petrified by the thought of transporting such material, fearing blockades by anti-nukes and movements greater than what stopped the rather benign transport of steam generators across the Great Lakes and through the St. Lawrence Seaway to Sweden or Denmark. If the gamma emitting fission products are removed from the Pu it may be practical to transport the Pu from the UK to Ontario using a heavy lift military transport aircraft.

Moving the required fuel from the UK to Canada would likely require several flights. The planes could land at Trenton. From Trenton the fuel could be moved by rail. The shipping container(s) could be fitted with buoyancy modules similar to those used for salvaging sunken ships so that even if the transport plane went down in the ocean the container would float.

This author believes that it would be prudent for Canada and Ontario to obtain a written commitment from the UK with respect to possible supply of pilot FNR startup fuel. In view of the highly technical nature of this matter the government of Ontario should subcontract this task to an organization such as Xylene Power Ltd./ Micro Fusion International Ltd. that has the necessary contacts in both Canada and the UK.

Import LEU (Low Enriched Uranium) from the US, since one can start a FNR with U-235 at or below 20%. Again, the politicians would not want to go in that direction if they can help it, even though we import that sort of material regularly for reactors such as the one on the McMaster campus.

This is not a good long term solution because in the future US based FNR suppliers would likely move to restrict LEU exports to Canada if they thought that they were losing business due to Canadian FNR competition. There are precedents for such trade restrictions in other sectors such as softwood lumber and agricultural products. The problem in dealing with the USA is that Congress and the Senate can over ride any treaty signed by the US president. This problem is particularly acute when neither the US Democrats nor the US Republicans have a commanding majority. In those circumstances special interest groups in the US frequently over ride US treaty obligations. The bottom line is that the US is not a good single source of a critical material.

Selectively extract most of the UO2 from spent CANDU fuel and then take the remainder (much smaller volume) and selectively extract the fission products by pyroprocessing (one does not need an excessively large capacity for that). That leaves a mix of U-238, and transuranic actinides with sufficient concentration to start the FNR. This approach also makes major immediate inroads into reducing the amount of currently stored used CANDU fuel. The politicians really like this approach, because relatively little transport of radio isotopes is required and the amount of stored used fuel is visibly reduced up front even before the FNR starts (even if the trans-uranic actinides don’t get reduced until the reactor is actually operating). The politicians see this methodology as a new source of skilled jobs in addition to maintaining the nuclear plant jobs.

A major further advantage of this approach is that it eliminates the tens of billions of dollars of future fuel disposal liability identified by the Nuclear Waste Management Organization (NWMO). These dollars are needed for other purposes such as health care, infrastructure and old age care.

Going the route of obtaining the fissile starting material from spent CANDU fuel puts the emphasis on eliminating the radioactive fuel “waste” (which no one could argue against, and for which monies have already accumulated in trust). To do that right one of course will need a FNR once the start fuel has been extracted from the stored spent CANDU fuel.

To minimize implementation delays relating to nuclear licencing, a small amount of the spent CANDU fuel inventory at Pickering should be moved to Chalk River to enable testing and debugging of the selective uranium oxide extraction process, the selective fission product extraction process and the zirconium recovery process in a suitably licenced facility. This small amount of spent CANDU fuel could be moved by rail using existing CNSC approved spent fuel transport containers.

The advantage of starting fuel sources #1 and #2 is that Ontario could proceed directly to implementation of a pilot FNR now and could then develop the chemical process necessary for fuel reprocessing after the pilot FNR was in operation. In this respect sources #1 and #2 have a major commercial advantage. The additional revenue from earlier FNR electricity sales would largely offset the pilot FNR and fuel reprocessing development costs.

The electricity output of the pilot FNR would be less than 10% of the generation connected to the Ontario grid, Hence the impact of the pilot FNR on the Ontario Long Term Energy Plan (LTEP) would be insignificant. Moreover, since the pilot FNR can load-follow, one could think of not renewing some of the contracts for gas-fired generation that are up for renewal in a few years. That would reduce Ontario’s CO2 emissions even further.

However, the strong emphasis on eliminating the fuel “waste” meant that using extraneous Pu was negating getting rid of transuranics in used CANDU fuel by importing more transuranics (Pu) instead. Similarly, one “burns” fewer used fuel transuranics if one buys enriched uranium to start the reactor. Therefore from a political perspective the best solution is to concentrate on Source #3 and get the fuel recycling/fabrication going. Then the FNR is merely required for fuel cycle completeness and not primarily for power, which just happens to be a very useful bonus, similar to the fact that avoiding CO2 emissions is just a normal by-product of the whole process.

The contemplated Pickering Advanced Recycling Compex (PARC) is a very useful happening, since conversion of the Pickering facility to recycling the stored used fuel saves jobs politically and also in reality. The Pickering site is licensed at least for nuclear activity, though perhaps not yet for fuel refabrication. It’s inventory of 15,000 tons of used CANDU fuel serve as a useful and easy mathematical example of the fuel recycling process.

The following process is appropriate for fuelling of a 700 MWe pilot FNR.

a) Move 75% of the existing spent CANDU fuel inventory (0.75 X 50000 tonnes = 37,500 tonnes) to safe, secure long term accessible naturally dry off-site storage. This material will be needed to start future FNRs.

b) If after evaluation of the long term risks related to the Pickering location it is decided that these additional FNRs are to be built at Pickering to take advantage of existing electricity transmission facilities, then there is limited merit in use of off-site storage for the spent CANDU fuel inventory.

c) Process the remaining 12,500 tonnes of spent CANDU fuel to selectively remove uranium oxide so as to obtain 1250 tones of fuel precursor and 11,250 tonnes of depleted pure uranium oxide which go to interim storage.

d) Use part of the remaining residue to form blanket rods.

e) Use the remainder of the residue as an FNR blanket rod material.

f) Further extract fission products from the fuel precursor.

g) Place the extracted fission products into naturally dry, safe, secure accessible off-site storage for 300 years to allow most of the fission products to decay into stable elements.

h) Form the remaining fuel material into core fuel rods.

i) Run the FNR. Extract fuel bundles when they reach their design cycle time.

j) While the reactor is running in step (i) draw another 50 tonnes per annum of UO2 from on-site storage to form new blanket rods;

k) When each bundle reaches its design cycle time move the bundle from the reactor and store it in liquid sodium around the liquid sodium pool periphery, out of the neutron flux. This bundle will remain in such storage for several years to allow decay of short lived fission products.

l) Every year remove the fuel bundles that have been in peripheral liquid sodium storage and send them for reprocessing. This reprocessing effectively selectively extracts fission products, transfers Pu-239 from blanket rods to core fuel rods, adds pure UO2 to replace the lost weight of fission products and adjusts the zirconium concentration in the core rods.

m) Move the fuel bundles that have been in the reactor for one fuel cycle time to the now vacated storage positions around the periphery of the liquid sodium pool.

n) Load the reactor with new fuel bundles formed during step (j).

o) Repeat steps (l) to (n) every year.

p) Eventually the reserve of pure UO2 stored will be exhausted and either more spent CANDU fuel must be drawn from off-site storage or new UO2 obtained from other sources will be required to maintain reactor operation.

Thus four 700 MWe FNRs will efficiently consume all the transuranium actinides presently in storage. In so doing these FNRs will form the Pu-239 that is necessary to maintain future FNR criticality. This Pu-239 is integral to the recycleable FNR fuel that will be required to sustain FNR operation for many centuries into the future. These four FNRs will be sufficient to replace 3000 MWe of output from the Pickering Nuclear Generating Station.

After the extracted fission products have been in off-site storage for 300 years a few longer lived fission products remain. These fission products are removed by selective chemical extraction and are placed in storage for another 300 years.

After all of the spent CANDU fuel has been processed, each reactor requires only about 0.5 tonne per annum of additional depleted UO2 per fuel load to keep going. It uses the U-238 to create and replenish its own fissile material (Pu-239) as fast as that fissile material is used up by being split into 1.0 tonne of fission products. The fission products are the only residue that leaves the system. These fission products naturally decay to stable elements while in engineered containers stored in a secure naturally dry location such as a depleted hardrock mine located within a suitable mountain.

An important facet of a FNR operated using first-in first-out refuelling is that it is imposible to use such a reactor for weapon production because the at the contemplated fuel cycle time the (Pu-240 / Pu-239) ratio is too large for fission bomb purposes.

This same fuel recycle process sequence could potentially be repeated at any nuclear generating station world wide that possess a FNR and a substantial inventory of spent CANDU fuel. This option of adding a FNR to an existing CANDU reactor facility for on-site nuclear waste dispoal may enable additional CANDU reactor sales. This opportunity should be pursued with CANDU Energy Inc.

We must stop treating spent CANDU fuel as a liability and start treating it as a potential asset. The existing 50,000 tonne inventory of spent CANDU fuel when reprocessed should be used to start 3 to 4 CANDU 6 size FNRs.

From a practical perspective I suggest that we think in terms of MFI charging OPG a disposal fee of:
$16 billion / 50,000 tonnes = $320 / kg
for spent CANDU fuel disposal over a 10 year period.

MFI reprocesses the spent CANDU fuel inventory into sufficient FNR fuel to start about 4 FNRs that can each displace a CANDU 6E.

The high tech storage containers may cost: $20,000 / tonne X 50,000 tonnes = $ 1 billion.

The storage and transportation costs for a facility like Jersey Emerald might cost $1 billion.

Thus for this plan to hang together the radio chemistry must cost less than $ 5 billion / 50,000 tonnes = $100 / kg.

There will be lots of unexpected expenses, so we really need to think in terms of $50 / kg.

Can we selectively extract 90% of the uranium for less than $25 / kg? That would leave about $250 / kg X 5,000,000 kg = $1.25 billion for the rest of the process.

Think in terms of $300 million for salaries and benefits related to the sophisticated part of the process. The balance would be for equipment, materials and expenses.

Over ten years that is $30 million per year for salaries, Which allows an operation with a staff about half the size of the NWMO. Clearly these people have to be workers, not parasites doing primarily public relations. The plant gross input has to be:
50,000 tonnes spent CANDU fuel / 2000 working days = 25 tonnes / day.

The processed FNR core fuel rod output has to be 1 to 2 tonnes / working day.

I think that these are likely workable numbers in the private sector but they do not allow for a lot of costs related to overhead for dealing with government rubber necks.

Thus the plan must envisage the work being done in circumstances where government, CNSC, NWMO erc. cannot easily interfere. Similarly, to raise the required investment capital the investors must have assurance that once their money is invested government and its agencies cannot interfere. We cannot have circumstances like Darlington where part way through construction government agencies changed the safety requirements. Hence the core rod fabrication portion of this work needs to be done in a remote location, not at Pickering. At an urban location it may be impossible to raise the public liability insurance required to avoid government interference, whereas at a remote location public liability insurance would not be a major issue.

One important detail. If the purity of the selectively extracted uranium oxide is sufficiently high the uranium oxide could be stored in conventional barrels, not high tech containers. That issue alone might save $500 million. Thus the issue of the purity and radioactivity of the selectively extracted uranium oxide needs very careful attention.

Another important detail. If the processes for conversion of oxide fuel into metallic fuel, selective uranium oxide extraction and blanket rod fabrication are all sufficiently simple then these processes could be performed on existing nuclear generation station sites. Then the core fuel rod related processes could be performed elsewhere because most of the transportation costs would be eliminated. For example, blanket rod fabrication could be done at Pickering and the core rod fabrication done at Chalk River.

These matters need careful consideration in the spent CANDU fuel processing plan.

This web page last updated August 29, 2015

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