MCO IMPACT ABSORBERS USING CRUSHABLE TUBES 1

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. To protect the MCOs from damage during loading, two impact absorbers are used, one placed below the lower MCO and one between the lower and upper MCOs. Since the MCOs can only move axially in the tube, the impact absorbers need only function in one axis. The impact absorber consists of an array of mild steel tubes arranged symmetrically between relatively rigid end plates. Under impact load, the tubes collapse by a process of regular crippling which safely absorbs the energy of the dropped MCO without exceeding load or deflection limits. In designing tubes which would crush reliably, consistently, and smoothly, three primary design challenges were met: 1. Development of a physical configuration to ensure a stable buckling mode to avoid gross collapse. 2. Mitigation of the force spike which occurrs at the initiation of tube crush. 3. Choice of a design configuration which accommodated material property, dimensional, and temperature variations while keeping the average crush force within a narrow design envelope. The successful approach to these challenges is discussed in this paper, including results of full scale prototype testing.