Airborne Contamination Monitors - doe-std-1128-98

DOE-STD-1128-98

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 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.

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