Technical Assessment of Internal Surface Smoothness and Particle Transmission to the American National Standard ANSI/HPS N13.1-2011

Clause 6.4.4 in the American National Standard ANSI/HPS N13.1 standard Sampling and Monitoring Releases of Airborne Radioactive Substances From the Stacks and Ducts of Nuclear Facilities addresses the internal smoothness of sample transport lines present between the nozzle and the analyzer (or collector). The appropriateness of this clause is evaluated by comparing roughness length of various materials against the required relative roughness and by conducting computational fluid dynamic modeling. The results indicate that the inclusion of numerical criteria for the relative roughness of pipe by the ANSI/HPS N13.1-2011 (clause 6.4.4) is not appropriate. Recommended alternatives would be elimination of the numerical criteria or modification of the standard to include a variable criterion for relative roughness.