Storage options

When examining storage options for RAW, it is important to consider the whole storage system rather than concentrating on just the store building itself (CoRWM, 2009). A number of interacting components and operations combine and contribute to create the necessary robust, safe and secure storage arrangements. These factors must be considered in an integrated manner. There are two main concepts in the storage of RAW. If the pack­aged waste forms are basic, then a high quality often shielded store will be needed. On the other hand, if the waste form is high quality and shielded, then the store can be of poorer quality or the waste containers can simply be left in the open. A generic shielded store is shown in Plate I (between pages 448 and 449) and an example of a high quality store has recently been constructed at Hunterston in Scotland (Fig. 1.15(a)) which has 2 m thick reinforced concrete walls and roof and careful control of atmosphere. Figure 1.15(b) also shows the stillages containing 4 ILW drums that will be stacked on top of each other in the store (and eventually in the GDF).

The waste form or product, its container, the building structure, the ven­tilation system, the handling equipment, the monitoring and inspection regime and the maintenance and refurbishment regime all have roles to play in ensuring safety and security of the store. As illustrated in Fig. 1.16, the waste storage system involves a number of levels. The wasteform (1) is the primary protective barrier, the waste container (2) is the secondary barrier. Control of store environment (3) is important in maintaining the

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(a) (b)

1.15 ( a) Inside the store at Hunterston in Scotland, (b) stillage containing 4 ILW drums.

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1.16 The four parts of the storage system (from NDA, 2012b).

integrity of the waste form and waste container, while the store structure (4) is the final layer of weather/atmosphere protection for waste package and an important element of physical security of waste.

Packages inevitably evolve during storage, and those changes affecting the safety function need to be understood and controlled to satisfy the regulators of the safety of the store and waste. Different storage concepts and designs require different performances from these various components and operations and therefore place different degrees of reliance on them. Quite different combinations of them can provide equally safe and secure storage. For example, most existing modern stores in the UK have massive concrete structures holding unshielded containers, but the alternative ‘mini­store’ concepts rely on heavily shielded containers within lightly built stores. This latter concept is used in some other EU countries. In a storage system, not every component need last for the whole design life. It is possible at the design stage to plan to replace or refurbish various components and build in at the outset specific features to enable this. More straightforward items to consider are building fabrics, external ventilation systems and power supplies. The more complex refurbishments or replacements to con­sider are cranes, active area surveillance equipment and major building structures.

In the late 1970s and early 1980s, the need for alternative storage in the US began to grow when the storage ponds at many nuclear reactors began to fill up with stored spent fuel. As there was not a national storage facility in operation, utilities began looking at options for storing spent fuel. Dry cask storage was one of the most practical options for temporary storage. The first dry storage installation in the US was licensed by the Nuclear Regulatory Commission (NRC) in 1986 at the Surry NPP in Virginia. Spent fuel is currently stored in dry cask systems at a growing number of power plant sites. The NRC estimates that the SF ponds at many US NPP will be full by 2015, so requiring the use of temporary storage. The 2008 NRC guidelines call for fuels to have spent at least five years in a storage pool before being moved to dry casks. Due to the demise of the Yucca Mountain project, more US SF and waste is being stored in sealed metal casks filled with inert gas. Examples of high quality containers include CASTOR, which is an acronym for CAsk for Storage and Transport of Radioactive material (Fig. 1.17).

In the UK, options being examined for SF include multi-purpose contain­ers (MPC) suitable for storage, transport and disposal of a range of SF types (Fig. 1.18). As well as high quality packages for SF, they have also been developed for less active wastes. So-called yellow boxes (Fig. 1.19) have been used extensively in Europe and used to store spent resin waste from existing storage tanks at the Dungeness plant in England. The containers are transportable and offer self-shielded protection, weighing around 18 tonnes when empty. The waste is expected to be stored in them for at least a decade.

As more waste is generated and being stored, but in many countries without an end-point of geological disposal in sight, an issue is whether to store all waste at sites or to consolidate wastes at centralised national or regional stores. The BRC, for example, recommended this option be exam­ined in the US and it is also being considered in the UK.

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