3. Reactor Physics and Reactor Engineering

概要

Basic Research for Sophistication of High-power Reactor Noise Analysis (V)

CO3-1

S. Hohara1, T. Sano1, A. Sakon1, M. Goto2, T. Kanda2, K.
Hashimoto1
Atomic Energy Research Institute, Kindai University
Graduate School of Science and Engineering, Kindai
University
1
2

INTRODUCTION: Reactor noise for high-power reactors were actively measured in the 1960’s and 1970’s.
The major focuses of those researches were for the abnormality diagnosis or the output stabilization diagnosis,
and almost researchers were in the field of system control
engineering or instrumentation engineering. High-power
reactor noise measurements for dynamics’ analysis of
reactivity change, reactivity feedback or reactor characteristics itself were few in the time (1960’s and 1970’s),
because of the powerless measurement system. In this
research, we plan to measure KUR’s output with present-day measurement system and plan to analyze with
several analysis methods. The results of this work will
supply some knowledges and technics in the aspect of
sophistication of reactor noise analysis or simulation
methods.
In this year, we tried to measure the reactor nuclide noise
of the critical state KUR core via a 6Li Lithium glass
scintillator (GS20: Scintacor) at B-3 port focused on
epi-thermal neutrons. The experimental work was done
on 24th November 2022. As the result of the experiment,
a result looks like the nuclear reactor noise was observed
in 100W critical state.
EXPERIMENTS:
In this experiment, the output signal of the 6Li Lithium
glass scintillator was put into Spectro Scopy AMPs
(2022: Canberra and 590A: ORTEC), and the output of
the SSAs were measured with a time-series measurement
system (HSMCA4106_LC: ANSeeN Inc.). A schematic
view of the measurement is shown in Fig.1, and the
counter installation overview is shown in Pic.1.

Pic. 1. An overview of the counter installation.
Table 1. Experimental condition.

Reactor
Power
[W]
100

Measurement
Time [sec]

Count Rate
[cps]

1,000

23 ～ 26

RESULTS:
The measurement results were analyzed by Feynman-α /
bunching method and Rossi-α method.
As a result of the Feynman-α analysis, plot shapes like
Feynman's theoretical formula were not obtained, because of the automation operation of the KUR.
As a result of the Rossi-α analysis, plot shapes like
Orndoff’s theoretical formula were obtained on the result.
An analysis results of the Feynman-α and the Rossi-α
analysis are shown in Fig.2. The result of this work has
large error bar even with the high-counting efficiency
counter; GS20, and it means that the nuclide noise of the
water moderate reactor has a trend to be trapped in a water moderator “prison”.
800
Feynman-  's Results
Rossi- 's Results

700

KUR B-3 port
100W / 1,000 sec
Li glass (GS20)

600
500
400
300
200

Fig. 1. Schematic view of the measurement.
The experimental condition is shown in Table.1. The reactor Power was set in 100W. The measurement time was
1,000 sec.

100
0

0

50

100
LLD channel

Fig. 2. A result example of Rossi-α analysis.

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150

Reactor Keinetics Experiment in KUR

T. Sano, J. Hori1, Y. Takahashi1, K. Terada1,
K. Hashimoto

increases the core temperature.

Atomic Energy Research Institute, Kindai University
1
Institute for Integrated Radiation and Nuclear Science,
Kyoto University
INTRODUCTION: Reactor kinetics is the response of
the reactor power obtained when the reactivity is inserted
into a reactor core. This response is usually obtained as a
change in reactor power and includes information on reactor kinetics parameters. Typically, reactor kinetics experiments are conducted using low-power reactors or
critical assemblies. On the other hand, data obtained from
reactor kinetics experiments in power reactor or
high-power research reactor include various feedback
reactivity that does not occur in low-power reactors or
critical assemblies, so obtaining these data is very important for understanding reactor safety. However, in
these high-power reactors, kinetic experiments are mostly
measurements for tests and inspections for facility management, and it is impossible for researchers to utilize
these data with some exceptions.
Therefore, the purpose of this study is to observe the
KUR-specific feedback reactivity, and so on, by measuring the reactor power change during the startup of the
KUR. The obtained data is important because such the
kinetics experiments can be conducted only at KUR in
Japan.
EXPERIMENTS: An experiment was conducted at
the startup of the KUR as following processes.
1. Time series data of the startup system from two fission chambers, linear power meter, core outlet temperature and primary clear up system inlet temperature were
measured at critical state with a thermal power of 20W.
At this time, the A to D control rods has same positions,
and criticality adjustment was operated by R rod.
2. The D rod was withdrawing out from the critical position and the time series data were measured. Here, the
drawing distance was 1.21 cm. In addition, control rod
maneuvers for negative reactivity compensation were not
performed until the end of the measurement.
3. When the reactor power achieved about 15.6 kW, the
measurements were completed. Because the negative
reactivity by core temperature increasing compensated
for the positive reactivity by control rod withdrawal, sot
that the reactor power did not increase.
The time series data were obtained using a digital data
collection system for operator assistance called the Harmonas system already installed on the KUR control console.
The KUR core location was shown in Fig.1. and table 1
shows the control rod positions and core outlet temperature at the low power (20W) criticality. The KUR was
operated by natural circulation cooling mode. Thus, the
generated heat was not cooled by the cooling system and

RESULTS: Fig. 2. shows the time series data of the
reactor power by linear power meter. The initial reactor
period (795 sec to 882 sec in the figure) by D rod withdrawing was 125.5 sec. Without feedback reactivities, a
reactor power would increase exponentially. However,
because of the heat generation in the KUR core, a negative feedback reactivity was observed in the time range
from 1200 sec to 2200 sec.
1

2

3

4

5

6

7

8

9

い

G

R rod

F

F

F

F

SSS

G

G

ろ

G

Pl

F

A rod

F

B rod

F

G

G

は

G

Pl

F

F

HYD

F

F

LI

G

に

G

G

F

C rod

F

D rod

F

G

Pn-2

ほ

G

G

G

F

F

F

G

G

Pn-3

へ

Pl

G

G

G

G

G

G

G

Pn-1

Fig. 1. Core location of the KUR .
F : Fuel element, G : Graphite reflector
Pl : Water plug, LI : Long irradiation element
Table 1. Control rod positions and core outlet temperature
at the criticality with thermal power of 20 W.
A rod
41.65 cm
B rod
41.65 cm
C rod
41.65 cm
D rod
41.65 cm
R rod
24.98 cm
Core outlet temperature
23.83 ℃

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1.0E+5
Reactor Power by Linear meter (W)

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1.0E+4

1.0E+3
1.0E+2
1.0E+1
1.0E+0
0

500
1000
1500
2000
Time from measurement start (sec)

Fig. 2. Reactor power. ...