Architecture and management of a geological repository - Andra

2 – General DescriptionHLLL waste packages are usually divided into the following categories, each with its own disposalissues (or questions):- Class B waste has low to medium β-γ activity and therefore releases little or no heat. It regroupsthe longest number of waste. Their total radioisotope inventory is relatively small compared toother packages waste, and is distributed over a large volume.- Class C waste consists of fission products and minor actinides separated out during fuelreprocessing. Their high β-γ activity causes considerable heat release, which declines over timemainly due to the radioactive decay of the medium-lived fission products (cesium-137, strontium-90). This waste is conditioned by incorporating it in a glass matrix. Glass has a particularly highand long-lasting confinement capacity provided the physical-chemical properties of theenvironment are favourable. Because of the high concentration of long-lived radionuclides invitrified C waste packages, the high temperature and the physical-chemical behaviour of theimmobilisation material, disposal conditions need to be specially adapted. Existing and possiblefuture C packages are divided into sub-groups C0, C1, C2, C3 and C4 depending on theircomposition. C0 (old waste such as that stored at the Marcoule site) is markedly less exothermicthan the others.Spent fuel is also highly radioactive and therefore releases considerable heat. This is due to thepresence of fission products having average half-lives, as well as that of plutonium and americium(stemming mainly from plutonium decay), in the bother two responsible for a slower decline if heatrelease. Other features are the large size of fuel rods unloaded from nuclear power reactors if they areto be disposed of as they are, and a larger amount of fissile products, raising the question of criticalityrisk. There are two types of commercial spent fuel, CU1 (UOX fuel) and CU2 (MOX fuel) which arehighly exothermic. Fuel that might come from research and defence reactors (CU3 type fuel) areconsiderably less exothermic.Chapter 3 gives a more detailed description of primary HLLL waste packages, their radiologicalcontent, heat release and physical-chemical properties.In each of the above waste classes, the different families of HLLL wate packages have been groupedinto a smaller number of representative "waste package types". This is in order (i) to make a morethorough study by limiting the number of cases to be specifically addressed, while not ignoring thediversity of the packages, (ii) to propose as far as possible a standardisation of the engineeredstructures and means employed in a disposal facility. Using this approach it is possible to study adisposal solution for each package inventoried, irrespective of whether other types of waste are beingdisposed of.2.2 Functions of a reversible disposal facilityThe functions of a repository have been identified by a functional analysis perfomed by conventionalmethods [4]. This ensures that all expected functions are taken into account.The basic purpose of long-term management of high-level, long-lived waste (HLLL waste) is toprotect human health and the environment against the associated risks. The solution offered by arepository is to confine the waste to the geological formation studied. The waste is passively confinedfor a long period of time; periods studied extend to millions of years.Strong demand has been expressed for reversible disposal if a repository were to be constructed.Andra has taken this into account in its repository concepts, particularly by designing a flexiblemethod of repository management.Operating a repository would involve several industrial activities. These could concern a time scale onthe other of a century, with is not uncommon to other human endeavors. As with any other industrialfacility, they must be performed in such a way as to protect man and the environment.The ability of a repository to protect man from the risks associated with the waste can be assessed inrelation to particular safety objectives. These objectives have been defined both for the industrialoperating phase and for the long term.DOSSIER 2005 ARGILE -ARCHITECTURE AND MANAGEMENT OF A GEOLOGICAL DISPOSAL SYSTEM32/495