United States Nuclear Regulatory Commission - Protecting People and the Environment

U.S. Nuclear Regulatory Commission

Effluent Radiation Monitor Calibrations

HPPOS-040 PDR-9111210182

Title: Effluent Radiation Monitor Calibrations

See the memorandum from R. L. Baer to C. J. Paperiello

dated November 13, 1985. Regulatory Guides and ANSI

N13.10-1974 do not suggest multipoint calibrations are

necessary beyond the initial preoperational testing for

effluent monitors. Single point calibration using

secondary sources are acceptable where detectors are

inherently linear.

After a review of the existing Regulatory Guides (1.21 and

4.15) and ANSI industry standards (ANSI N13.10-1974) that

establish relevant guidance, it is believed that these

documents do not suggest multipoint calibrations are

necessary beyond the initial preoperational acceptance

testing for these effluent monitoring systems (sometimes

referred to as "primary calibration", as used in ANSI

N13.10-1974, Section 5.4.10). Section 5.4.10 further

states that the primary "...calibration shall be related to

a secondary source or method which will be used for

periodic in-plant recalibrations." This suggests that

routine re-calibrations can be less rigorous than the

one-time, initial primary calibration. These periodic

recalibrations should be viewed as ensuring that the

detection system has remained stable over time. Therefore,

"single-point" calibrations using secondary sources (e.g.,

solid sources), should be considered adequate to meet the

requirements of standard Technical Specifications where

detectors are inherently linear.

Assuming a licensee calibrates at a single point, the

licensee should consider selecting that point at or near an

alarm or action level. Routinely calibrating near an alarm

point, coupled with the ongoing comparison of real-time

monitor readings against laboratory analysis of periodic

grab samples containing "normal" levels of radioactive

effluents, seems to provide an adequate assurance of proper

monitoring operability. However, calibration near an alarm

point or action level is neither a requirement nor a

position in the relevant guides or standards.

Region V provided input pertinent to this discussion which

focused on detector saturation problems. They provided

documented performance testing by a Region V licensee to

determine the potential for saturation problems with the

plants' effluent monitors. In general, the licensee found

Geiger-Muller (GM) tubes were most seriously affected, NaI

scintillator / photomultiplier (PM) tubes less affected, and

plastic scintillator / PM tubes least affected.

Given the overall upgrade in effluent monitoring as a

result of the NUREG-0737 requirements, each licensee should

already be able to demonstrate adequate effluent monitoring

capability at high ranges needed during accidents to

provide meaningful information relative to a monitored

"accident-type" release stream. The evidence demonstrating

monitor operability at high ranges need not be verified by

each licensee as primary calibrations since previous

guidance provided by NRR for calibration of NUREG-0737

monitors suggests other acceptable alternatives.

In summary, "single-point" routine calibrations are

adequate for scintillation monitors, given the monitors

inherent stability and a thorough initial primary

calibration. The use of single-point, routine calibrations

for GM tubes is acceptable, given that the radiation

monitor initiates a fail-safe trip function (isolates, or

re-directs the effluent to another monitored pathway) below

the radiation level where the initial primary calibration

began to show appreciable saturation losses. To ensure

that control room operators understand GM effluent monitor

system limitations, emergency implementing procedures

should clearly define these system limitations. For

example, in the event of a steam generator tube failure,

the procedures should highlight e.g., caution notes)

probable invalid readings from an SJAE GM monitor (down

scale response as the detector saturates, in response to a

worsening primary-secondary leakage).

Regulatory references: ANSI N13.10-1974, Regulatory Guide

1.21, Regulatory Guide 4.15, Technical Specifications.

Subject codes: 6.4, 7.3

Applicability: Reactors

Page Last Reviewed/Updated Thursday, March 29, 2012