Proof-of-principle measurements for an NDA-based core discharge monitor Page: 5 of 8
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0Fig. 3. A core face map of the fueling channels.
amounts of lower energy gammna-ray interference. Both of
these methods significantly impact the hardware and the result-
ing spectra seen by the detectors.
The secondary type of detector was an ionization chamber.
There were several reasons for including this type of detector
in the POP measurements. First, the electronics used with the
fission chambers also supports simultaneous use of the ioniza-
tion chambers (as in the GRAND-Fork spent-fuel measure-
ment systems). Shielded and unshielded ionization chambers
provide additional data that make a monitoring system much
harder to fool. Second, tne intensity of the high-energy
gamma rays that exceed the thresholds of the primary detectors
decays rather rapidly. These secondary detectors are sensitive
to the gross radiation inside the reactor vault long after shut-
down of the reactor.
An attractive feature of both the fission and ionization
chambers is that they are very dependable and require a mini-
mum anaunt of auxiliary equipment. They should require
very little maintenance and no adjustment during 20 years of
operation.
Electronics
The electronics package used for the POP measurements
was the commercial version of ion and neutron detector elec.
tronics (ION-1)3 developed at the Los Alamos National Labo-
ratory for use with a spent-fuel measurement fork detector.
The commercial electronics package,* which is called the
*Commenially available from DS Davidson Co , 19 Barnhard
Rd., Norh Haven, Connecticut, :SA.1 2 3 4 S 6
GRAND (Gamma Ray And Neutron Detector electronics
package), is a microprocessor-based electronics system. It
provided biases for the fission chamber and ionization cham-
bers, preamplifier power for the fission chamber, and data
acquisition and transfer. A GRAND has internal battenes that
allow it to operate for more than 24 h if ac power is lost.
The Measurement System
The measurement sys'en continuously made 10-s data ac-
quisitions during its operation. The data from one threshold
detector and one ionization detector, and information on the
setup and performance of the GRAND, were transferred by
the GRAND's sei al port to a computer after each acquisition,
and then a new acquisition was started. All of this was accom-
plished by the GRAND's resident firmware.
To assure the necessary performance, the detectors could
not be separated by more than 10 m from the GRAND elec-
tronics. Hence a 3000-lb (1365-kg) lead shield was built for
the GRAND so that it could be placed on the fueling trolley
next to the detectors. (The placement of the detectors is shown
in Figs. 2(a) and 2(b)]. The GRAND and detectors ran unat-
tended for 5 weeks.
The computer was set up adjacent to the refueling console
in the main reactor control room. The battery-backed com-
puter, a Toshiba 1100, received this data, stored it on a
3.5-in., 0.7-Mbyte floppy dis' , and displayed the last 24
records received. The data were transmitted over lines sup-
plied by the facility using industrial modems.
Data were collected at a rate of approximately 750 kbytes/
day. These data were retrieved and taken to an off-line
Toshiba 2100 computer for treatment and review using the
Symphony spreadsheet program. The detector information
was extracted and put into a large spreadsheet that was only
limited by the memory of the Toshiba. The time periods of
interest were plotted for review, Analysis with a turnaround
time of only 2-4 h after obtaining the disks allowed qucsaons
to be asked of the fueling operator and plans to be made for the
next fueling cycle. Hence, unresolved questions could be an-
swered during the next fueling cycle with the ciose cooperation
of the fueling operators.
RESULTS
Going into the measurements, we had not received firm
estimates of the radiation levels we would see. We were lucky
that the detector sensitivities matched :he radiation levels very
well. (See Fig. 4.)
Figure 4 shows the activities observed by the Bety,n) de-
tector as it entered the reactor vault just after aime 0 on the plot.
The background signal is approximately 1310) counts/s. Ie
fueling machines removed the end and shield plugs frum the
channel to be refueled. This activity is not seen by the detec
tor. Just before 4(XX) s, the first push (push equals two bun
dies discharged from the core) took place. One observes a
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Halbig, J. K. (Los Alamos National Lab., NM (USA)) & Monticone, A. C. (International Atomic Energy Agency, Vienna (Austria)). Proof-of-principle measurements for an NDA-based core discharge monitor, article, January 1, 1990; New Mexico. (https://digital.library.unt.edu/ark:/67531/metadc1415684/m1/5/: accessed July 16, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.