United States Nuclear Regulatory Commission - Protecting People and the Environment

U.S. Nuclear Regulatory Commission

Particulate Sampling Line Bend Radii

HPPOS-006 PDR-9111210091

Title: 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 11.4.2.1) 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

Applicability: Reactors

Page Last Reviewed/Updated Thursday, March 29, 2012