Particulate Sampling Line Bend Radii
See the memorandum from L. B. Higginbotham to W. L. Fisher dated March 8, 1977, and the incoming request from W. L. Fisher dated January 24, 1977. Stack and vent sampling lines should have a bend radius equal to or greater than five times the diameter of the sampling line.
During a preoperational inspection of Unit 1 at Davis Besse, several right angle bends were observed in an airborne sample line that lead to a particulate monitor. In response to the deviation for failure to comply with FSAR (Section 18.104.22.168) requirements for representative sampling, the licensee stated that the right angle bends had been replaced with bends of radii equal to five times the line diameters. The licensee further stated that the new line configuration was in conformance with ANSI N13.1-1969.
ANSI N13.1-1969 states: "Elbows in sampling lines should be avoided if at all possible, but when they are required, the bend radius of the elbow should be as long as practicable ..." (Section B5). Although the phrase, "as long as practicable" does not appear to be defined further in the narrative portion of ANSI N13.1-1969, Section A3.4 and Figures A2 and A5 appear to give some credence to the selection of R equal to or greater than 5D for sampling probes, where R is the bend radius of the sampling line and D is the diameter of the sampling line. Section A3.4 does, however, contain the caveat that in "some probe configurations ... deposition may be significant ...."
In examining the installation of stack and vent sampling systems, a bend radius equal to or greater than five times the diameter of the sampling line should be accepted.
However, some sort of an evaluation must be preformed by the licensee to actually demonstrate that representative samples are being collected. Such an evaluation can sometimes be done by collecting special samples at the location of the sample probe and correlating the results with those obtained at the "remote" sample collector.
Regulatory references: ANSI N13.1-1969, Final Safety Analysis Report
Subject codes: 6.9, 7.3, 9.1