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MICROCOPY RESOLUTION TEST CHART
NATIONAL BUREAU OF STANDARDS -1963
CESTI PRICES
1 1967
Conf. 670602-05
*493.00, mails
MAR
REACTOR NOISE ANALYSIS USING A PULSE TYPE DETECTOR*
J. Richard Trinko, Jr. and S. H. Hanaue:
The University of Tennessee
. and
MASTER

***
D. P. Roux and J. T. De Lorenzo
Oak Ridge National Laboratory
.
January 1967
LP
Reactor fluctuation studies using pulse detectors (1, 2) have been
!
extended using a new counter (3) with a collection time of 60 nsec. Pulses
T
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SITY
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were applied to amplifiers and a discriminator with 100-MHz. response,
followed by current integration in a counting-rate meter with RC = 154 sec.
The overall double-pulsu resolving time was ~130 nsec. Fluctuations in
· counting rate were analyzed as previously described(2) for current fluctuations.
Experimentation was perforined with the same Pool Critical Assembly
core loading as that used in earlier noise measurements (4) and in pulsed.
neutron measurements (5). .
In phase I (Table I), counting loss was made negligiwly small by
reducing the neutron flux level. Tape recordings of the reactor noise were .
made at critical, -1$, -2$, and -4$. A point reactor model was least-squares
fitted to the experimentally determined power spectral density (PSD). Inferred.
T
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1
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values for generation time and reactivity for the pulse system, and for a
5
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*
current system used as reference are in satisfactory agreement with each
.
pulse detection efficiency are thought to result from distortions in flux distri-
bution due to changes in rod positions. The current detector was located
where it would be relatively unaffected by these changes.
17
*Research sponsored by the U. S. Atomic Energy Commission under
contract with the Union Carbide Corporation and the University of Tennessee.
an
DISTRIBUTOR OF THIS DOCUMENU IS UNLIMITED
In phase II, the effect of a gamm; background on the observed
spectrum at constant reactivity was investigated using a 42,000-curie buco
source. The detector was insensitive to gamma flux less than 104 rad/hr.
Above this level, however, space charge within the counter caused a reduction
in pulse size. Some neutrcn-induced pulses were lost thereby, thus reducing
the apparent detection efficiency (Table 1). Above 105 rad/hr, the efficiency
deteriorated rapidly with increasing gamma flux, regardless of the magni-
tude of the neutron flux. In a current detector, on the other hand, the effective
efficiency depends on the flux ratio Ph /4x76); no upper limit or tr has yet
been found (7). The results given in Table I show that the reactivity could
be determined from the counter data at background gamma flux levels up
to ~105 rad/hr.
In phase III, the effect of high counting rates was investigated with
the reactor critical; counting loss was controlled by varying the neutron
flux. The counting loss was calibrated experimentally as a function of
counting rate by comparing counting rates of two similar pulse systems, of
which one had a detector less sensitive by a factor of 9. The observed effect
of counting loss upon the PSD is twofold: first, detection efficiency decreases
with increasing counting loss; second, the amplitude of the PSD at high counting
rates does not bear the expected relationship to the counting rate. The
spectrum shapes were not distorted in the range 1-2000 Hz, however, and
a counting loss of 19% changed the estimate of generation time by only ~5%.
In phase IV, a scaler followed by a second discriminator was inserted
between the first discriminator and the counting-rate meter. A scale factor
1
:
of 8 was used with the reactor 1$ subcritical. The spectrum obtained is
identical to that obtained for the - 1$ case of phase I.
In conclusion, it appears that the pulse system is equivalent to the
current system, and that the systems have different advantages and limi-
tations. Development of counters with shorter resolving time (to decrease
counting loss) and with the capability of operation in higher gamma fluxes
would increase the area of applicability of pulse systems.
We gratefully acknowledge the expertise of the PCA Operating Group
and the technical assistance of G. C. Guerrant and C. B. Stokes ,
LEGAL NOTICE
This report was prepared as an account of Government sponsored work. Neither the United
States, nor the Commission, aor any person acting on behalf or the Commission:
A. Makes any warranty or representation, expressed or implied, with respect to the accu-
racy, completene88, or usefulness of the information contained in this report, or that the use
of ny Information, aparatus, method, or process disclosed in this report may not infringe
privately owned rights; or
B. Assumes any liabilities with respect to the use of, or for damages resulting from the
use of any infoi nation, apparatus, method, or process disclosed in this report.
As used in the above, "person acting on behalf of the Commission" includes any om-
ployee or contractor of the Commission, or employee of such contractor, to the extent that
sich employee or contractor of the Commission, or employoe of such contractor prepares,
Gioveminates, or provides access to, ary information pursuant to his employment or contract
with the Coramission, or his employu nt with such contractor.
1. J. R. Trinko, Jr., S. H. Hanauer, A. R. Buhl, and D. P. Roux,
"Subcritical Reactivity Measurements Using Fluctuations from a
Pulse Type Detector," Trans. Am. Nucl. Soc., 9, 523 (1966),
2. V. Rajagopal, "Noise Analysis in Nuclear Systems," AEC Syniposium
Series, Vol. 4, 427 (1964).
3. Reuter Stokes Electronics Components, Inc., Model 251, RSN-42A.
4. C. W. Ricker, S. H. Hanauer, and E. K. Mann, "Measurement of
Reactor Fluctuation Spectra and Subcritical Reactivity," ORNL-TM-
1066, Oak Ridge National Laboratory (1965).
5. R. Perez-Balles, G. deSaussure, and E. G. Silver, "Neutron Physics
Division Annual Progress Report, September 1, 1.960," ORNL-3016,
Oak Ridge National Laboratory (1961). .
6. D. P. Roux, "Optimization of Reactor Shutdown Margin Measurements
in High Gamma Fluxes," Trans. Arn. Nucl. Soc., 9, 523, (1966).
7. W. E. Ford and S. H. Hanauer, "Measurement of Gamr.a Effects on
Observed Subcritical Power Spectral Density," Trans. Am. Nucl. Soc.,
9, 508, (1966).
ng
Table I. Comparison of Experimental Results
Control
Rod
Phase Positions b
I 000
Gamma
Flux
(rad/ir)
Counting
Loss
(%)
Experimentally De-
termined Reactor
Parameterc, e
Detector Efficiency
(detecjions/fission)
Experiment
negligible
0.939 +0.008
2.77 $ 0.02
3.14 # 0.01
A: 70.3 + 0.6
71.03 0.6
68.031.0
68.35 0.8
F:-1.10 + 0.03
-1.00+ 0.04
000
negligible
0.927 + 0.022
2.57 + 0.07
ⓇOO
negligible
1.05 +0.04
2.67 + 0.1!
OO @
negligible
1.15 + 0.09
2.61 + 0.16
II000
negligible
1.0 x 104
3.3 x 104
6.4 x 104
1.4 x 105
P: -1.95 $ 0.07
-1.78 + 0.08
-1.99 $ 0.02
-1.73 $ 0.04
P: -4.58 + 0.25
-3.81 + 0.16
-4.49 $ 0.06
-5.13 + 0.18
pi-1.28 $ 0.03
-1.21 $ 0.04
-1.05 0.05
-1.08 $ 0.05
-1.05 $ 0.09
: 58.95 0.8
69.7 + 0.6
69.4 + 0.7
69.4 + 0.5
66.35 1.0
III
TII
000
1.13 $ 0.02
0.977 + 0.025
0.69 0.025
0.489 + 0.026
0.178 +0.012
0.957 + 0.012
0.962 + 0.009
0.932 $ 0.010
0.868 $ 0.007
0.712 * 0.013
0.6
1.5
4.3
10
19.3
IV
000
0.951 + 0.041
·p: -1.16 + 0.07
B
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Table I. Comparison of Experimental Results (continued)
Notes:
a.
A - This experiment, pulse system. :
- This experiment, current system.
. C. W. Ricker et al; see reference 4.
. R. Perez-Belles, et al; see reference 5.
Denotes a control rod partially inserted.
Denotes a control rod fully withdrawn.
@ Denotes a control rod fully inserted.
c. The errors given are based on observed statistical fluctuations only.
d. The reactiyities listed are expected to be $0.15 larger than the others
because a 'He current chamber replaced a BF3 current chamber.
e. Reactivity pin $; generation time in u gec.

2.
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6 / 7 /67
DATE FILMED
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