DESIGN AND TESTING OF CANISTER STORAGE BUILDING IMPACT ABSORBERS

Spent nuclear fuel from the Hanford N-Reactor is currently stored in pools, the K-East and K-West basins. As part of Hanford’s Decontamination and Decommissioning effort, this fuel is to be placed in dry interim storage in the Canister Storage Building (CSB). The storage arrangement consists of an array of sealed vertical storage tubes, each capable of holding two Multi-Canister Overpacks (MCO), one on top of the other, as shown in Figure 1. The MCOs may be removed and replaced in the storage tubes during the life of the facility. To protect the MCOs and the storage tube from damage in the case of a crane failure or other handling accident, two impact absorbers are used, one below the lower MCO (the lower absorber) and one between the lower and upper MCOs (the intermediate absorber). Should one of the MCOs be accidentally dropped, the drop energy would be safely absorbed while keeping the impact force below a specified limit. Since the MCO is contained within a cylinder, there is a single impact orientation to be considered, and consequently, the impact absorbers need only function along a single axis. The development of the impact absorber design was complicated by the application of the following design requirements: • The operating temperature range is between -7°C and 166°C • The energy absorbing material, if organic, must not produce combustible offgas products • The energy absorbing material must not creep under the weight of two MCOs at maximum storage temperature, and must retain its original physical properties for a 75 year design life • The maximum impact acceleration of the MCO during impact must not exceed 34g • The space available for the absorber is limited • Cost must be low since a large quantity of absorbers (approximately 440) is needed. Several of these constraints served to rule out the use of most common, inexpensive energy absorbing materials. For example, the requirement for a 75 year design life at temperatures up to 166°C made use of organic materials of any kind questionable. Therefore, only metallic materials were considered. Furthermore, the restriction of the impact to a value of 34g, when combined with the large weight of an MCO and the small available space, required an absorber design possessing maximum efficiency. It can be shown that the maximum efficiency of an energy absorber is achieved when the crush force is constant at the maximum permissible value. A solution was needed which combines the long lifetime of a metallic material, with a constant force behavior and low cost. This was achieved through the use of crushable tubes.