Airborne Contamination Monitors - STD-1128-98master0080

DOE-STD-1128-98

Guide of Good Practices for Occupational Radiological Protection in Plutonium Facilities

Airborne Contamination Monitors. Airborne contamination monitors, normally

CAMS (see Section 3.5.1), should meet the following criteria according to ANSI

N317 (ANSI, 1980a). 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 that

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. (1988)

provides guidance on each of these functions.

The minimum detection level of 239Pu, in terms of derived air concentration (DAC),

should be 8 DAC-h at the point of sampling in the presence of nominal amounts of

naturally occurring alpha-emitters such as radon and thoron and their decay

products. (No guidance is provided on what a "nominal" amount is, however.) The

operating range should be at least 100 minimum detection levels (i.e., up to 800

DAC-h for 239Pu). Instrument error should not exceed 20% of the reading over

the upper 80% of the operating range. The reproducibility of the system for any

given measurement should be within 10% at the 95% confidence level for a

mid-scale or mid-decade reading. The instrument should be capable of operating

with less than a 5% change in calibration over the ambient temperature range

expected. The instrument should be equipped with an adjustable alarm set point

(audible and visible alarms) that can be set at any point over the stated range. The

air flow rate should be indicated and adjustable. Voltage and frequency variations

of 15% within design values should result in reading variations of no greater than

5% at the minimum detection level.

ANSI N42.17B (ANSI, 1987b) provides additional performance criteria for air

monitors used to detect plutonium. 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 (ANSI, 1980a); 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

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