Improved BWR recirculation loop piping design for inservice inspection

Existing BWR nuclear power plants Primary Loop Recirculation Pipings (PLR) have large and many welded seams, because the conventional PLR have been mainly constructed by welding of straight pipes and standard fittings such as elbows, crosses, tees, reducers, and nozzles. Inservice Inspection (ISI) of PLR requires considerable radiation exposure of the skilled inspectors owing to the many and large weld seams which have relatively high radiation levels. Improvements in PLR design, proposed in this paper are: (i) to use large diameter pipes having tees and/or elbows made from one piece forgings and/or pipe bending without weld seams (for main pipe); (ii) to use pipe bent by high frequency induction heating (for riser pipe); and (iii) to provide sufficient straight prolongation on the end of fittings such as elbows, crosses, tees, reducers, and branch nozzles. Benefits to be obtained by the improved design are listed. Fabrication procedures and trial fabrication of the pipe are presented. (U.K.)