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Shutdown reactivity measurements using noise techniques
Transactions of the symposium on noise analysis in nuclear systems
11
Paper No. 2-3
SHUTDOWN REACTIVITY MEASUREMENTS USING NOISE TECHNIQUES M. A. SCHULTZ Milletron, Inc., Irwin, Pennsylvania
POWER spectral density measurements were accomplished on the cold, clean CES reactor at Waltz Mill for various amounts of shutdown reactivity and for several source, detector and control rod configurations. The measurements were made with a hydrogen-filled ion chamber, a specially built very low noise preamplifier, and a modified Milletron dynamic filter. The results of these measurements indicated that at very high frequencies (above 200 cps) the noise power varied as the square root of the reactor power level. Specifically, as the subcritical multiplication factor or the normal counts per second from an external detector counting-rate meter increased, the noise power at 600 cps increased directly as the square root of the counting-rate meter reading. The noise from the electronic circuits was completely negligible. As the reactor was essentially cold, y-radiation was also negligible. The conclusion was reached that at very high frequencies the signal was coming from uncorrelated neutrons (bombardment noise) whose average level varied as the reactor power. Measurements were made of the ratio of noise amplitude at the two frequencies of 10 cps and 600 cps. A bandwidth of 4 cps was used for both frequencies. Figure 1 shows that excellent information was obtained upon which to design a shutdown reactivity meter. Shutdown reactivity to -8 per cent in 6k was readable, and when
--AK,
%
Power,
FIG. 1
W -
12
Transactions
of the symposium on noise analysis in nuclear systems
the reactor went critical at any power level, the ratio of the amplitude at 600 cps to the amplitude at 10 cps was constant. Runs were made to determine the effects of rod shadowing. Banks of rods were moved adjacent to the detector, which was mounted close to the edge of the core. Corresponding rods were moved in the opposite direction on the other side of the reactor to maintain either criticality or a similar degree of subcriticality. The results indicated that when the reactor was at critical or close to critical, rod shadowing effects were negligible.
11
Paper No. 2-3
SHUTDOWN REACTIVITY MEASUREMENTS USING NOISE TECHNIQUES M. A. SCHULTZ Milletron, Inc., Irwin, Pennsylvania
POWER spectral density measurements were accomplished on the cold, clean CES reactor at Waltz Mill for various amounts of shutdown reactivity and for several source, detector and control rod configurations. The measurements were made with a hydrogen-filled ion chamber, a specially built very low noise preamplifier, and a modified Milletron dynamic filter. The results of these measurements indicated that at very high frequencies (above 200 cps) the noise power varied as the square root of the reactor power level. Specifically, as the subcritical multiplication factor or the normal counts per second from an external detector counting-rate meter increased, the noise power at 600 cps increased directly as the square root of the counting-rate meter reading. The noise from the electronic circuits was completely negligible. As the reactor was essentially cold, y-radiation was also negligible. The conclusion was reached that at very high frequencies the signal was coming from uncorrelated neutrons (bombardment noise) whose average level varied as the reactor power. Measurements were made of the ratio of noise amplitude at the two frequencies of 10 cps and 600 cps. A bandwidth of 4 cps was used for both frequencies. Figure 1 shows that excellent information was obtained upon which to design a shutdown reactivity meter. Shutdown reactivity to -8 per cent in 6k was readable, and when
--AK,
%
Power,
FIG. 1
W -
12
Transactions
of the symposium on noise analysis in nuclear systems
the reactor went critical at any power level, the ratio of the amplitude at 600 cps to the amplitude at 10 cps was constant. Runs were made to determine the effects of rod shadowing. Banks of rods were moved adjacent to the detector, which was mounted close to the edge of the core. Corresponding rods were moved in the opposite direction on the other side of the reactor to maintain either criticality or a similar degree of subcriticality. The results indicated that when the reactor was at critical or close to critical, rod shadowing effects were negligible.