Plutonium stockpiles: searching for solutions

SCK•CEN developed the code REACTOR to study the build-up of stocks of plutonium produced by the civil nuclear power industry and to assess the different options for reducing the amount of this material.

REACTOR makes full use of all relevant information: the basic characteristics of the technology and industrial potential. This includes, for example, the number and types of reactors and their planned lifetimes, fuel parameters (eg enrichment, burn-up, dwell time), reprocessing and MOX production capacities, national nuclear programmes and policies on plutonium, etc. The code can then be used to determine the levels of spent fuel and plutonium generated over time and then consider and assess various scenarios for dealing with the plutonium, such as vitrifying and burial, increased use of MOX fuel and the construction of plutonium burners.

The code includes a database containing most commercial civil nuclear facilities around the world. The database has been elaborated from an IAEA database (MicroPRIS), but provides a more-user friendly interface and additional information about planned reactors, reprocessing facilities, MOX production plants, reprocessing policies plus software routines to calculate several parameters.

NUCLEAR POWER REACTORS

Altogether, thirty countries have nuclear power stations in operation and at least six others are constructing or planning one or more units.

Nearly all nuclear reactors now in operation have been operating less than 25 years and still have a considerable lifetime ahead of them. Assuming a lifetime of 40 years, large-scale decommissioning will not start until about 2010. Although many countries, notably Russia, still list a number of planned reactors, at this time it seems unlikely that many will be built and in our analysis, only those under construction are included. Table 1 gives the number of reactors used.

The evolution of the installed nuclear power over the different regions in the world is shown in Fig 1. Between 1990 and 2010 the total number of reactors remains fairly constant. While only a few new nuclear reactors are under construction in Western Europe and North America, expansion of capacity is still going on in Asia and to a lesser extent in Eastern Europe.

SPENT FUEL PRODUCTION

The evolution of the spent fuel production calculated using REACTOR is given in Fig 2. In 1970 as little as 1240 tHM was produced. At present the annual production is about 10 000 tHM. In future the annual amount of spent fuel produced is expected to decrease, due to an increasing burn-up and a decreasing number of nuclear reactors. The amount of spent fuel accumulated until 1995 was about 170 000 tHM. In the year 2020 this will have reached 368 000 tHM. Should all planned reactors be built, the total amount of spent fuel would only increase 5% in 2020.

Of the 368 000 tHM about 170 000 tHM is produced in countries which favour for the moment the option of direct disposal of spent fuel. If we assume that the direct disposal for PWR spent fuel needs about 40 m3 per GWy, (generating about 26.7 tHM), then 5.5 X 105 m3 of storage capacity will be needed to store all spent fuel produced until 2020.

PU ARISINGS IN SPENT FUEL

The total amount of Pu in spent fuel was about 1075 tonnes in 1995 and is expected to become more than 3000 tonnes by 2020. [In addition, about 6 t of Pu (or 0.5 %) has been produced and is stored in India, Israel and Pakistan, which do not subscribe to the United Nation’s Non Proliferation Treaty.]

REPROCESSING CAPACITY

An overview of the reprocessing facilities around the world is given in Table 2. The earlier reprocessing facilities were designed to reprocess metal fuel (mainly coming from Magnox reactors), while the newer facilities reprocess oxide fuel from LWRs. Some small units in the United Kingdom and France are equipped to handle fast reactor fuel. France has an installed reprocessing capacity of 1600 tHM/y of oxide fuel and 400 tHM/y for metal fuel, whereas the UK has a capacity of respectively 1000 tHM/y and 1500 tHM/y. In the near future large reprocessing facilities will be built in Japan and possibly in Russia. The reprocessing capacity for fast breeder reactor fuel is still very small (14 tHM/y). The annual oxide fuel reprocessing capacity will rise from less then 3000 tHM today to 5000 tHM by 2010.

Combining the results obtained with REACTOR, of the spent fuel production and the reprocessing capacity in the world over the period 1970-2020, with the different national policies for reprocessing, the amount of spent fuel that is reprocessed and, consequently, the amount of separated Pu in the world originating from the nuclear industry, can be estimated.

As mentioned above, more than half of the spent fuel produced is located in countries not reprocessing and this will remain so in the years to come. On the other hand, about 45 000 tHM has been reprocessed by 1995, while more than 90 000 tHM of spent fuel was ready for final disposal. In a maximum reprocessing scenario, the percentage of fuel that will be reprocessed will gradually increase. In the year 2020 the amounts will be 140 000 tHM compared to 160 000 tHM (Fig 3).

Today there is no reprocessing capacity for about 10 000 tHM. This shortfall will continue to grow to more than 40 000 tHM in the year 2020, without the construction of new reprocessing facilities. In the main, additional reprocessing capacity for oxide fuel is needed in the West. Practically all GCR fuel can be treated with the existing capacity and, if the reprocessing facility at Krasnoyarsk in Russia becomes operational as planned (Table 2), there will be no problem for the reprocessing of VVER fuel. Another factor that should be considered is that the expected lifetime for reprocessing facilities is shorter than for reactors (25 years versus 40 years). This means that additional reprocessing facilities will have to be built during the lifetime of existing and planned reactors, if the reprocessing capacity is to keep track with spent fuel production.

Given the level of reprocessing capability, the amount of separated civil Pu will be more than 1000 tonnes by the year 2020. Since a certain amount of that plutonium will be used for the production of MOX, the actual amount of separated Pu will be lower.

The impact on the spent fuel stock of adding new reprocessing facilities, with the capacity of UP3 in France (800 tHM/year) was calculated. With four additional facilities it would be possible to reprocess the entire stock of spent fuel considered for reprocessing by 2020.

THE PRODUCTION AND USE OF MOX

One of the possible ways to use the separated Pu stored in the different countries is the recycle of the Pu in the form of MOX in light water reactors. Today, several LWRs around the world are charged with 25 to 33% MOX. The principal benefits of this option are conservation of uranium, minimisation of spent fuel waste volumes and reduction of the world’s separated Pu inventory. Substitution of uranium by MOX in nuclear fuel can result in a net reduction in Pu, since spent MOX fuel contains about one quarter less Pu than the original loading. The irradiated MOX could theoretically be recycled several times, until the quality of the Pu has been degraded too much; the Pu-238, Pu-240 and other actinide fractions become too high, gradually making the separated Pu useless for further cycling in LWRs. An overview of the MOX fabrication facilities is given in Table 3. Practically all facilities are equipped to produce LWR MOX. Only small amounts of MOX for fast reactors were produced, mainly in Belgium (Dessel P0) and France (Cadarache). The annual MOX production is about 85 tHM/y but will rise to 400 tHM/y by 2010. LWR MOX contains 5%-7% fissile Pu. We assume that the Pu in the spent fuel immediately after unloading contains about 70% fissile Pu (60% Pu-239 and 10% Pu-241).

Fig 4 gives an estimate of Pu used in MOX. Assuming a maximum reprocessing scenario, there is an excess of separated Pu, even if the existing MOX production capacity is 100% used. It is clear that additional capacity is needed to eliminate the stock of separated Pu. Now only about 75 tonnes of Pu is used in MOX, where we estimate a stock of 200 tonnes Pu. With the existing and planned MOX production capacity this difference will continue to grow for several years. If we assume that the new plant in Dessel, Belgium (P1) is commissioned and starts operation in the year 2000 then the Pu stock by the year 2020 would be about 70 tonnes less (330 instead of 400 tPu).

For the time being, since there is not enough MOX capacity to treat all separated Pu, an option is to defer reprocessing of spent fuel partially and adapt the production of both processes to each other. There are several practical advantages to defer reprocessing: smaller safeguards efforts are required and it is easier to process freshly separated Pu, because it is free of americium. In the deferred scenario even larger stocks of spent fuel considered for reprocessing will remain (see Fig 3). If from now on only the amount of spent fuel is reprocessed which is needed for MOX production, then the separated civilian Pu stock would become zero by the year 2010 (Fig 5).

Today, MOX technology is in industrial use in France, Germany, Switzerland and Belgium. About 1000 tonnes of MOX for LWRs has been fabricated, from which about 400 tonnes is successfully irradiated. Currently, there are 34 reactors licensed to use MOX fuel and 25 others are in the licensing process. In addition, in OECD countries, there are another 165 reactors where licensing for MOX fuel is considered to be technically feasible. Today, no recycle of spent MOX fuel is done due to the degrading quality of the Pu. This means that the total Pu inventory does not decrease drastically. The Pu inventory could be further reduced by burning Pu in fast neutron reactors.