Resolution of Generic Safety Issues: Item A-42: Pipe Cracks in Boiling Water Reactors (Rev. 2) ( NUREG-0933, Main Report with Supplements 1–34 )
Pipe cracking has occurred in the heat-affected zones of welds in primary system piping in BWRs since mid-1960. These cracks have occurred mainly in Type 304 stainless steel which is the type used in most operating BWRs. The major problem is recognized to be IGSCC of austenitic stainless steel components that have been made susceptible to this failure by being "sensitized," either by post-weld heat treatment or by sensitization of a narrow heat affected zone near welds.
"Safe ends" (short transition pieces between vessel nozzles and the piping) that have been highly sensitized by furnace heat treatment while attached to vessels during fabrication were very early (late 1960's) found to be susceptible to IGSCC. Because of this, the AEC took the position in 1969 that furnace-sensitized safe ends should not be used on new applications. Most of the furnace-sensitized safe ends in older plants have been removed or clad with a protective material and there are only a few BWRs that still have furnace-sensitized safe ends in use. Most of these, however, are in smaller diameter lines.
Earlier reported cracks (prior to 1975) occurred primarily in 4-inch diameter recirculation loop bypass lines and in 10-inch diameter core spray lines. Cracking is most often detected during ISI using UT techniques. Some piping cracks have been discovered as a result of primary coolant leaks.
This USI was RESOLVED60 in February 1981 when NUREG-0313, Revision 1750 was issued to all holders of BWR operating licenses or construction permits and to all applicants for BWR operating licenses. MPA B-05 was established by DL for implementation of the resolution at operating plants.