KAKUJOHO (Nuclear Information)2005.5.24
Statement at UN meeting
May 24, 2005
Statement at UN meeting
Reprocessing to separate plutonium carries with it two inherent dangers – one associated with the terrorist threat and one with the threat of nuclear proliferation to countries.
First, the plutonium, once separated from the radioactive fission products in the spent fuel, is far more vulnerable to diversion. In the spent fuel, the plutonium is protected from diversion by a very intense radiation field. For example, consider the dose rate from a pressurized water reactor (PWR) fuel assembly for a person varying distances from the assembly. A typical PWR assembly weighs about 0.5 metric tons, has a burn-up of 35,000 megawatt-days per ton, and contains about 5 kilograms of plutonium. For such an assembly even for fuel out of the reactor for 15 years, a person 1 meter from the assembly would receive a lethal dose in a few minutes. Moving 5 meters away from such fuel would increase the time for a lethal dose to a couple of hours. After the first year of discharge, the exposure decays roughly by a factor of two every 30 years. (Japan has about 100 metric tons of plutonium in spent fuel at present).
Separated plutonium has none of this self-protection. This is true even if the plutonium is kept with uranium in the reprocessing product; separation of the plutonium from the uranium is far more readily and safely accomplished than the far more difficult step of separation from the radioactive fission products.
The only near-term use for the separated plutonium is its recycling as mixed-oxide fuel (MOX) in light water reactors. The reprocessing facility and storage area for the separated plutonium, the transportation of the plutonium to a MOX fabrication facility, the fabrication of the plutonium at the facility into MOX, the transportation of the MOX to the reactor sites, and the storage of the MOX at the reactor sites before use will all require extraordinary physical security arrangements.
At present, over 250 tons of separated plutonium from civilian spent fuel has accumulated worldwide – more than has been produced for nuclear weapons. Each year another 18-20 tons is being separated, with perhaps one-third of this fabricated into MOX recycled into LWRs.
The second danger let us call “latent proliferation.”
The two routes to producing nuclear explosive material for nuclear weapons are enrichment of uranium and the reprocessing of reactor spent fuel to separate the contained plutonium from the fuel. The acquisition by countries of either enrichment or reprocessing facilities would put them very close to a nuclear weapons capability if they chose to have them. We see today in the discussions swirling around Iran’s determination to develop a centrifuge enrichment capability a glimpse into the problems raised by countries moving toward such a latent proliferation capability.
In principle, enrichment presents a more complex problem than reprocessing, since enrichment is needed to supply fuel for light water nuclear reactors. This fuel has to be enriched to 3-5% U-235, not the 90% U-235 that would be wanted for weapons, but the centrifuge facility which could do the former could be converted rapidly to do the latter.
Reprocessing to separate plutonium, on the other hand, has no civilian justification – and so the dangers of reprocessing and recycling are for nought! Reprocessing is plainly and indisputably uneconomic – wildly so. The two presumptive uses of the separated plutonium are (as already noted) to recycle it in LWRs as mixed oxide fuel or MOX, or to use it in plutonium breeder reactors (if they are ever developed, a dubious proposition). But for either of these enterprises to make economic sense, the price of uranium would have to rise to unprecedented levels. The simplest way to make this point for plutonium recycling in LWRs is that even were the plutonium free (that is, the cost of reprocessing being ignored altogether), at today’s uranium prices a kilogram of mixed oxide fuel would cost several hundred dollars more than a kilogram of LEU. But of course the cost of reprocessing is not zero. At a reprocessing cost of $2000/kg, it would have to rise to nearly $1000 per kilogram of uranium metal – 25 times greater than the current uranium price of about $40 per kilogram. At the prices now being projected for Rokkasho ($4000/kgHM), the price of uranium would have to reach an incredible $1800/kg or higher.
In some circumstances, reprocessing and recycling could make the final disposal of radioactive waste in a geologic repository somewhat less expensive – but only marginally at best, and perhaps not at all. For one, if, as at present, the plutonium is recycled just once – so that the spent MOX fuel is sent to a repository without further treatment – reprocessing would offer no savings at all. In addition, any savings on the cost of permanent disposal in a repository would in all likelihood be matched or more by the extra costs of treating the medium and low-level wastes from the reprocessing. .Spent fuel, without reprocessing, can be stored for many decades at low cost – on the order of $300/kgHM.
Supporters of reprocessing sometimes point to the risk that the plutonium contained in the spent fuel could eventually become accessible to potential proliferators as the radioactive barrier provided by the fission products decays away – roughly by a factor of ten every 100 years. Thus potentially the geologic repositories to which the spent fuel is destined could become “plutonium mines.” However, mining into a repository would be no easy matter, and certainly far more difficult than acquiring plutonium from an on-going nuclear program. In any case it would be unwise in the extreme to sharply raise the near term risks of diversion and proliferation in return for a reduction in the risks hundreds or thousands of years hence. And finally, the potential attraction of reprocessing would not apply if the MOX spent fuel is sent to a repository, as is currently planned.
A global moratorium on any new reprocessing of civilian spent fuel would be a valuable nonproliferation undertaking. Reprocessing makes no sense economically, and it is not needed for rational disposal of radioactive wastes. Already civilian fuel reprocessing has led to the accumulation worldwide of over 250 metric tons of separated plutonium which will have to be rigorously and stringently secured and safeguarded indefinitely. Any further accumulation is pointless and dangerous. A decision by Japan not to start-up Rokkasho would be an essential and productive first step toward a worldwide moratorium, first on new reprocessing and then on all reprocessing worldwide.