Other Emergency Instrumentation. Other emergency instrumentation
levels potentially encountered at the time of an accident. Normally, dose
rate capabilities from a few millirem per hour to a few hundred rem per
hour should be required while capability requirements for the
contamination level may range upward from 200 dpm/100 cm2 for alpha
contaminants and 100 dpm/100 cm2 for beta gamma emitters.
Performance specifications for emergency radiological monitoring
instrumentation can be found in ANSI N320-1979 (ANSI, 1975b) and
BNWL-1742 (Andersen et al., 1974).
Instrument Calibrations and Testing
Radiation doses and energies in the work areas should be well characterized.
Calibration of instruments should be conducted where possible under conditions
and with radiation energies similar to those encountered at the work stations.
Knowledge of the work area radiation spectra and instrument energy response
should permit the application of correction factors when it is not possible to
calibrate with a source that has the same energy spectrum. All calibration sources
should be traceable to recognized national standards. Neutron energy spectral
information is considered particularly important because neutron instruments and
dosimetry are highly energy-dependent.
When the work areas have been well characterized, the calibration facility used by
the plutonium plant should be set up to represent as closely as possible the work
area's radiation fields. Californium-252 or PuBe calibration sources should be used
for work areas that process plutonium metal and plutonium oxide because their
neutron energy distribution is similar to those compounds. Facilities that process
PuF4 should use a PuF4 source. Most work areas at processing plants are high-
scatter areas and thus have significant quantities of low-energy neutrons. Because it
may not be feasible to have sources and scatter geometries representative of all
work locations at the facility, it should be important to determine specific spectra
and correction factors for work locations to correct for the calibration. Scatter
conditions should be taken into account when setting up a calibration facility. The
effect of room scatter in a neutron calibration facility can be significant and may
account for as much as 20% of the measured dose equivalent rate. The Schwartz
and Eisenhauer (1982) methods should be used to correct for room scatter.
ANSI N323 (ANSI, 1997b) provides requirements on the calibration of portable
instruments. The reproducibility of the instrument readings should be known prior
to making calibration adjustments. This is particularly important if the instrument
has failed to pass a periodic performance test (i.e., the instrument response varies
by more than ±20% from a set of reference readings using a check source) or if the
instrument has been repaired. The effect of energy dependence, temperature,
humidity, ambient pressure, and source-to-detector geometry should be known
when performing the primary calibration. Primary calibration should be performed
at least annually.
Standards referenced in Section 3.5.2 discuss specific performance testing of
radiation detection instruments. Testing procedures in these standards should be
used for periodic requalification of instruments or detailed testing of instruments.