Architecture and management of a geological repository - Andra

4 – Waste disposal PackagesIn the United States [52], the "Yucca Mountain" project envisages a container consisting of twoconcentric envelopes, an internal one made of 50 mm thick stainless steel, to guarantee mechanicalstrength, and an outer envelope made of 20 mm thick nickel alloy (Inconel 22), to ensure resistanceagainst corrosion. These materials meet the physicochemical environmental conditions specific to theYucca Mountain project. This container, which is larger than the Andra one, (diameter) could holdseveral primary packages of waste (HLW) equivalent to vitrified C waste.4.2.3 Description, performanceThis section describes the design parameters of the selected solution in greater detail. It justifies thedimensions with respect to the durability performance required, and shows that the object iscompatible with the handling processes.4.2.3.1 Detailed descriptionTwo disposal packages, of standard dimensions, can be used to cover all the primary packages of Cwaste presented in chapter 3:- a so-called "short" geometry (1291 millimetres long, for an overall diameter of 655 millimetres)corresponds to C0.1 (PIVER vitrified waste) and C0.3 (AVM vitrified waste) type packages.- a so-called "long" geometry (1 607 millimetres long for an overall diameter of 590 millimetres)corresponds to C0.2 type packages (CSD-V R7/T7 /UMo), and C1 to C4 from the La Haguefactories.The mass of these disposal packages varies between 1 645 kilogram (package type C0.1) and1 965 kilograms (package type C0.2 and C1 to C4). This mass includes the primary package and allthe over-pack constituents, described in detail below.• The bodyThe body of the over-pack consists of a cylindrical shell with an effective thickness of 55 millimetres,used to ensure a water-tightness for a millennium (see below). This envelope is fitted with ceramicsliding runners. If these sliding runners are embedded, the thickness of the envelope will be increasedby 10 millimetres, to avoid degrading the integrity of the effective thickness. The base has an effectivethickness of 77 or 83 millimetres depending on the type of package. It can be manufactured in a singlepiece, without welding, so that the body has a built-in base.After comparing various possible grades 39 , the material chosen was non-alloy steel type P235. Its lowcarbon content gives it good weldability. Its structure is not very sensitive to cold-cracking duringwelding, because of its low elastic limit. It does not require preheating or heat treatment before or afterwelding. Although it is a commonly used steel, its mechanical characteristics are adequate to ensurethe object's mechanical strength. Finally, its mechanical characteristics are favourable to controllingcertain risks (particularly corrosion under stress and hydrogen embrittlement).• The lidThe lid is made of the same grade of steel as the body. It is thicker than the base because its effectivethickness is increased by about 100 millimetres to create a handling interface. This handling interfaceconsists of a machined groove to enable the over-pack to be gripped by a grab. A hollow shapeprovides a greater weight-bearing area and consequently better load distribution than a "mushroom"type protruding shape. The internal shape of the lid, shown in Figure 4.2.2 match the upper profile ofthe primary package to help limit the void fraction.39Including, in particular, low-alloy steel 16MnD5 used for pressurised water reactor tanks.DOSSIER 2005 ARGILE -ARCHITECTURE AND MANAGEMENT OF A GEOLOGICAL DISPOSAL SYSTEM134/495