Hot Clamp Design for LMFBR Piping Systems

Thin-wall, large-diameter piping for liquid metal fast breeder reactor (LMFBR) plants can be subjected to significant thermal transients during reactor scrams. To reduce local thermal stresses, an insulated “cold” clamp was designed for the fast flux test facility and was also applied to some prototype reactors thereafter. However, the cost minimization of LMFBR requires much simpler designs. This paper presents a “hot” clamp design concept, which uses standard clamp halves directly attached to the pipe surface leaving an initial gap. Combinations of flexible pipe and rigid clamp achieved a self-control effect on clamp-induced pipe stresses due to the initial gap. A 3-D contact and inelastic history analysis were performed to verify the hot clamp concept. Considerations to reduce the initial stress at installation, to mitigate the clamp restraint on the pipe expansion during thermal shocks, and to maintain the pipe-clamp stiffness desired during a seismic event were discussed.