Using Weapons-Derived
Plutonium Fuel
in CANDU Reactors

according to
Atomic Energy of Canada Limited

extracts from

Advanced CANDU Systems
for Plutonium Disposition

P. G. Boczar, M. J. N. Gagnon, P. S. W. Chan,
R. J. Ellis, R. A. Verrall, A. R. Dastur,

of Chalk River Laboratories
Atomic Energy of Canada Limited

Canadian Nuclear Society Bulletin,
Vol. 18, No. 1. (Winter 1997)




2.1.   The 1994 CANDU MOX Study

The objective of the MOX strategy is not to destroy the plutonium, but to convert it to a form that has a high degree of diversion resistance through the characteristics of spent fuel, while producing electricity....

Contrary to all the public statements by AECL and government spokespersons that the CANDU MOX plan is to ''destroy'' weapons plutonium, we see that this is simply untrue.

Future generations of Canadians will have to guard the plutonium that remains in the irradiated fuel for millennia to come.

In 1994, the United States Department of Energy (US DOE) commissioned an AECL-led team to examine the use of CANDU reactors for dispositioning excess weapons-derived plutonium. The AECL Washington team worked long and hard to get the DOE commission.

''Dispositioning'' is jargon for ''treating the plutonium to make it less likely to be used for weapons''

The target plutonium disposition rate was 50 tonnes of plutonium metal in 25 yearsThis amount of American weapons-derived plutonium would be matched by an equal amount of Russian weapons-derived plutonium, for a total of up to 100 tonnes.
A detailed assessment was performed, including technical, economic, safety, licensing, safeguards, security, MOX fuel fabrication, transportation, and eventual disposal of the spent fuel. The team concluded that two of the four 850-megawatt reactors at the Bruce "A" Station near Kincardine, Ontario, could achieve this ....For technical reasons, the Bruce "A" reactors are the best-suited CANDU power reactors to burn plutonium (MOX) fuel.

Ironically, the four Bruce "A" reactors are among those that Ontario Hydro shut down in 1997 for safety-related reasons.

The reference fuel ... contains 232 grams of plutonium per bundle.... 26 of these ''reference fuel bundles'' would provide enough weapons-grade plutonium for a Nagasaki-type atomic bomb
An advanced MOX fuel design ... contains 374 grams of plutonium in the fresh fuel.... 16 of these ''advanced fuel bundles'' would be enough for a Nagasaki-type bomb.

Using modern designs, even 8 bundles would be enough for a bomb with the same explosive power as the one that destroyed Nagasaki.

As in the reference bundle, the plutonium is confined to the two outer rings of fuel: 3.5 percent plutonium in ring 3, and 2.1 percent in ring 4, mixed with depleted uranium. If plutonium were used in all four rings, the reactor might undergo a self-destructive ''power excursion'' -- like Chernobyl.

To prevent this kind of accident, ''poisons'' -- jargon for materials, like dysprosium, that absorb neutrons -- are used in the inner rings to keep the nuclear reaction in check.

The central eight elements contain 6 percent dysprosium, mixed with depleted uranium. ''Depleted uranium'' is jargon for uranium-238, a waste product of uranium enrichment.

The use of depleted uranium in the fuel automatically means that new plutonium-239 is created during operation of the reactor.

In both cases, the initial plutonium content is reduced by about one-third in the spent fuel.... The plutonium remaining in the spent fuel -- 2/3 of the original amount -- must be guarded for a period of time that exceeds the span of recorded human history, since the half-life of plutonium-239 is 24,000 years.

2.2   The 1996 CANDU MOX Study

The AECL-led team conducted additional studies for the US DOE in 1996, aimed at further increasing the plutonium disposition rate. A 50 percent increase in the plutonium disposition rate was achieved by increasing the plutonium content of the bundle. To compensate for the excess reactivity, the burnable poison content in the central elements was increased from 7 percent to 15 percent, and the purity of the [heavy water] coolant and moderator was downgraded from 99.75 percent to 97 percent....

By increasing the concentration of plutonium in the MOX fuel,
  • the fast ''safe shutdown'' of reactors under abnormal conditions becomes more demanding;

  • the inventory of radioactive poisons that can be released from each fuel bundle under accident conditions is greatly increased;

  • the heat and radiation levels of the resulting irradiated fuel is significantly elevated.

2.3   Status of CANDU MOX Option for Plutonium Dispositioning

... Preparations are now in place for the first physical tests towards qualifying the use of CANDU MOX fuel, fabricated from weapons-surplus plutonium. The program consists of the fabrication of a small amount of CANDU MOX fuel in the United States and in Russia, for testing under simulated CANDU reactor conditions in AECL's NRU research reactor at the Chalk River Laboratories.

Even if weapons plutonium is donated free of charge, the handling of plutonium is so dangerous that MOX fuel fabrication has to take place in a glovebox -- an operation which is extraordinarily expensive.

As a result, MOX fuel is much costlier (from three to seven times greater) than the natural uranium fuel now used in CANDU reactors.

It is also much trickier to make MOX -- serious quality control problems have already begun to emerge, resulting in defective fuel pellets. Due to the elevated cost, there is a financial incentive to ''cut corners''.

Although AECL has tested MOX fuel for decades, these new tests will confirm the behaviour of fuel using weapons-grade plutonium. This type of small-scale experimental test was endorsed by the G7 leaders at the Nuclear Summit in Moscow in 1996 April.AECL is careful not to discuss WHY they have been testing MOX fuel for decades.

At the April 1996 Moscow meeting, Prime Minister Jean Chrétien signed a paper saying that Canada is in favour of burning weapons plutonium in CANDU reactors. He had no political mandate to do so.

There is a real interest in Russia in the CANDU option. A joint Canada-Russia feasibility study sponsored by the Canadian government builds upon previous US DOE studies. Its aim is to establish the viability of a CANDU MOX fuel fabrication plant in Russia, addressing related safeguards and security issues. Using a controversial two million-dollar grant from CIDA, the Canadian International Development Agency (set up to assist needy countries with economic development), AECL sent 13 teams of experts on junkets to Russia, and brought Russian scientists to Canada.

Russia needs American capital to get its own domestic MOX industry established; if the Canadian project can be helpful in achieving that goal, Russia is interested.

The first interim report, issued in the fall of 1996, establishes the feasibility of CANDU MOX fuel fabrication in Russia.Evidently, AECL's activities are designed to increase expectations year by year until the momentum behind the project will be difficult to overcome.

4. CANDU Plutonium-Thorium

The final CANDU plutonium-annihilation option to be considered in this paper employs the use of thorium dioxide as a carrier for the plutonium.

Thorium is a naturally-occurring radioactive material, about 3 times more abundant than uranium. Thorium is not a nuclear fuel, but it can be transmuted into uranium-233 inside a nuclear reactor. U-233 is a human-made element that, like plutonium, can be used either as a nuclear explosive or as a nuclear fuel.
This is a responsible, forward-looking strategy that uses plutonium to convert thorium-232 into uranium-233, to be used as a future energy resource.... Uranium-233 is the best fissile material in a thermal reactor [such as CANDU].... This CANDU "near-breeder" fuel cycle provides long-term assurance of fissile fuel supplies....According to this scheme -- not likely to be utilized in the foreseeable future -- plutonium would be mixed with thorium as fuel to breed fissile uranium-233 (U-233), an artificial isotope of uranium that is similar to plutonium in many respects:

  • U-233 is virtually non-existent in nature, but, like plutonium, it can be created in a nuclear reactor;

  • U-233 is immediately weapons-usable; in fact it can be used in much simpler bomb designs than plutonium can (''gun-type'' as opposed to ''implosion'' bombs);

  • U-233 is a powerful nuclear explosive; more powerful, in fact, than either uranium-235 or plutonium-239;

  • it is also usable, like plutonium, as a reactor fuel;

  • U-233 is, like plutonium, a highly toxic alpha-emitting radioactive material;

  • U-233 can only be obtained for use by reprocessing spent fuel.

This passage re-confirms the fact that AECL ultimately wants to move towards reprocessing in Canada, as outlined in their 1977 Ottawa Seminar on advanced fuel cycles, available on the ccnr web site.

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