Q. What do you mean by Risers and Downcomers?

Risers and downcomers shall be staggered along the shell of the WHB and steam drum for uniform water/steam circulation in the system, taking into account the varying heat fluxes along the length of tubes. Film boiling (or dry-out) must be avoided in order to prevent tubes from destroying by deformity. The first pair of downcomers and the riser shall not be located further than 150 mm (6") form the inlet tubesheet. This distance of 150 mm is from the edge of the tubesheet to the nearest edge of the downcomer pipes.

The downcomer flow velocity shall be restricted to 1.52 m/s (5 ft/s). impingement plates, if provided shall not be welded to nozzle necks and tubes. Perforated plates are not acceptable.

The circulation of WHB system shall be computed for each circuit of downcomer and risers. A detail FEA shall be performed to predict water/steam circulation ratios. The FEA shall be based on an internationally recognized program, such as ANSIS or ALGOR and shall be submitted to WorleyParsons Canada for approval. Unsuitable programs, unacceptable to WorleyParsons Canada, shall be avoided.