Airborne Contamination Monitors - doe-std-1136-20040060

DOE-STD-1136-2004

Guide of Good Practices for Occupational Radiological Protection in Uranium Facilities

Performance Criteria for Fixed Monitoring Instruments

Airborne contamination monitors, surface contamination monitors, and photon area monitors,

and emergency instrumentation are fixed monitoring instruments subject to the following standard

performance criteria.

Airborne Contamination Monitors. Airborne contamination monitors, normally CAMS should

meet the following criteria according to ANSI N317. The primary purpose of any CAM is to detect the

presence of airborne radioactivity and activate an alarm to warn personnel in the area so actions can be

taken to minimize personnel exposures. The goal for any CAM should be to perform this function as

quickly as possible and at the lowest detectable level of radioactive airborne concentration. The quantity of

airborne radioactivity that will result in an alarm within a given time interval is defined

in units of DAC-h for a particular radionuclide and is a function of the nuclide's airborne concentration in

DACs, the sampling rate, the lower limit of detection of the instrument, and the time needed for the alarm to

occur. Mishima et al. provides guidance on each of these functions.

ANSI N42.17B provides additional performance criteria for air monitors used to detect uranium.

This standard provides specifications for general criteria (sampler design, units of readout, alarm

threshold, etc.), electronic criteria (alarms, stability, response time, coefficient of variation, and line noise

susceptibility), radiation response, interfering responses (radiofrequency, microwave, electrostatic, and

magnetic fields), environmental criteria (temperature, humidity, and pressure), and air-circuit criteria.

More detailed specifications are provided in ANSI N42.17B than in ANSI N317; however, the

environmental criteria and the limits of variation are not as restrictive as those in ANSI N317. With

respect to accuracy, ANSI N317 requires less than 20%, and ANSI N42.17B requires 40% at the 95%

confidence level. For the environmental criteria, ANSI N317 requires that the readings change less than

5% under ambient conditions, while ANSI N42.17B gives a 15% limit of variation. As discussed

previously, criteria from ANSI N42.17B are more applicable because they are supported by instrument

testing.

ANSI N13.1 provides detailed guidance on sampling methods from stacks and ducts. One criterion

that relates to CAMs is that air sample lines between air inlet and filter media should be eliminated where

possible; where not possible, they should be designed to meet the sampling criteria contained in the

standard (e.g., short lines, proper sampling rate, smooth bends). The use of Tygon tubing as sample lines

should be minimized or eliminated. Air in- leakage from surrounding areas can be a problem when using

sampling lines. Testing for air in- leakage should be performed at least annually or when seals or "O" rings

are replaced.

Surface Contamination Monitors. Surface contamination monitors include hand and/or shoe

counters and instruments (or probes) with sufficient flexibility to survey pieces of equipment, including

exterior clothing. ANSI N317 states these instruments should have an audible alarm, a frequency that is

proportional to the count rate, or a pre-selectable trip setting, and upon reaching that level, should

activate an audible or visible alarm or both. These instruments should be calibrated according to the

requirements in ANSI N323 and be equipped with a check source. Fixed instruments should be powered by

alternating current (AC) and provided with an emergency power source.

Performance Criteria for Emergency Instrumentation

Meeting the criteria for criticality accident alarm systems, fixed nuclear accident dosimeters, and

other emergency instrumentation is essential.

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