14.4.1 Overview

As described earlier in Section 14.2.3, there are different ways of looking at spent nuclear fuel, either as a resource to be reprocessed and recycled or as a waste to be disposed of in a geological repository. In the case of reprocessing the valuable materials, plutonium and uranium will be recy­cled as MOX or REPU fuel and the remaining waste will need geological disposal.

The choice between the two options, recycling or disposal, will be based on strategic, political and economic factors. At present about 15-20% of all spent fuel is reprocessed and the plutonium and uranium recycled. The recycling takes place in light water reactors. Although over the years recy­cling has been performed in several countries, it is primarily France that is doing it on an industrial level today. France has both reprocessing and MOX fabrication capacity. Other countries such as Japan, Russia and China are preparing for recycling. Recycling will lead to a better utilization of the natural uranium resource. Recycling in light water reactors will reduce the uranium consumption by about 25%. For more effective use, recycling in fast reactors will be necessary, which will allow multiple recycling of the generated plutonium and which can also utilize the depleted uranium from enrichment, which otherwise would be a waste product, as breeding mate­rial for new plutonium that can be utilized as fuel. Theoretically, recycling in fast reactors could lead to the uranium being utilized at least 50 times more effectively, i. e. one could get 50 times more energy out of the natural uranium. Fast reactors are, however, not yet available on a commercial scale for electricity production. Important development work is going on in several countries, e. g. Russia, France, India, Japan, China and the United States. Except for India, it is, however, not expected that recycling in fast reactors will be of significant importance before 2050. The technical and economic feasibility still needs to be proven before fast reactors can be introduced on a commercial scale. From a waste management point of view there could also be an additional added value in recycling in fast reactors as this could provide the possibility to also burn (transmute into shorter — lived elements that can be disposed of more easily) some of the other transuranic elements, e. g. americium and curium, elements which make an important contribution to the long-term radiotoxicity of the fuel (see Section 14.3.2).

Although the management system for spent nuclear fuel will be different depending on what management strategy is chosen, recycling or disposal, there are also many components in common.

The management system for recycling of the spent nuclear fuel includes the steps shown in Fig. 14.4. Reprocessing is normally performed 3-10 years after the fuel has been removed from the reactor. In principle the fuel can be transported away from the reactor already after about a year, but often the transport is later. At present it is not foreseen to recycle the MOX fuel again in light water reactors, but to store it for later use in fast reactors. It should, however, be realized that the spent MOX fuel has a higher heat generation, radiotoxicity and neutron radiation level than the correspond­ing spent uranium fuel.[86] This will be important should the spent fuel later be considered for direct disposal and not for recycling.

The management system for direct disposal of spent fuel has the compo­nents shown in Fig 14.5. The cooling time before spent fuel can be disposed of in a geological repository will be typically 30-50 years or longer.

Over the years approximately 400,000 tonnes of spent fuel (measured as heavy metal (HM)) have been generated. About 100,000 tonnes of these have been reprocessed and the remaining 300,000 tonnes remain in the reactor pools or are stored in dedicated facilities within the power plant premises or in centrally located storage facilities either for direct disposal or awaiting a later decision to reprocess. More details about different storage facilities at the reactor site or centrally are given in Section 14.4.2.

Except for the reprocessing step, spent fuel management has so far been mainly a national activity. Storage facilities are built at the reactors or cen­tralized in the country. No international storage facilities have been devel­oped. The same is the case for the work on geological disposal. Although there is much international cooperation on research and development for geological disposal, there are no agreements between countries to develop a common geological disposal facility, in spite of the technical/economic advantages it could bear. Discussions have taken place in different fora but no real progress has been seen, mainly due to the political sensitivity of the subject. Reprocessing is the exception. Several countries have jointly financed some reprocessing plants and sent their fuel for reprocessing to these plants. The agreements have, however, included the stipulation that the waste from reprocessing will be returned to the country of origin for further management and disposal.

14.4 Management system for recycling of the spent nuclear fuel.