Design of a FPGA-based controller for power and period measurement in the start range of Dalat Nuclear Research Reactor
Nuclear Science and Technology, Vol.10, No. 3 (2020), pp. 41-48
Design of a FPGA-based controller for power and period
measurement in the start range of Dalat Nuclear Research Reactor
Vo Van Tai, Nguyen Van Kien, Nguyen Nhi Dien, Trinh Dinh Hai, Le Van Diep
Dalat Nuclear Research Institute
01 Nguyen Tu Luc, Dalat city, Vietnam
(Received 03 August 2020, accepted 10 November 2020)
Abstract: This paper introduces a new controller module based on a high-speed field-programmable
gate array (FPGA) and digital signal processing (DSP) using moving average (MA) filters for
calculation of the reactor power and period at the start range of the Dalat nuclear research reactor
(DNRR). The reactor power is proportional to the neutron flux in the reactor core, and the reactor
period is the time that the reactor power changes by a factor of 2.718. In the control and protection
system (CPS) of the DNRR, the reactor power and period have been monitored by the 8-bit
microprocessor controller named BPM-107R. There are two main functions of the BPM-107R
controller including 1) measurement and determination of reactor power and period and 2) generation
of warning and emergency protection signals by reactor power or/and by reactor period. Those
discrete signals will access to the logical processing unit of the CPS to prohibit the upward movement
of control rods or to shut down the reactor. The CPS has three BPM-107R controllers corresponding
to three independent neutron flux measurement equipment (NFME) channels working by logic voting
“2 out-of 3”. Each NFME channel was designed for detection of neutron flux density in the full range
from 1×100 to 1.2×1010 n/cm2×s, which is divided into two sub-ranges named start range (SR) and
working range (WR). The designed FPGA-based controller module was tested using simulated signals
as well as signals from the CPS in comparison with the original controller BPM-107R. The
experimental results show that the characteristics and functions of the two controllers are equivalent.
Keywords: Reactor period, reactor power, moving average filter, FPGA, DSP.
(Ppreset can be set from 1% to 100% of 500
kWt by 1% step) or the period is less than 20
s, the emergency protection signal EMR-P or
EMR-T will be generated to shut down the
reactor and hold it at a subcritical state by
inserting neutron-absorbing control rods into
the reactor core. The above-mentioned
functions have been realized by the existing
embedded micro-controller BPM-107R using
DS87C530 processor. Main characteristics of
this controller include the working clock
frequency is of 30 MHz, the data memory
(RAM) is of 32 kbyte, the programme
memory (ROM) is of 64 kbyte and the length
of each neutron parameter generation cycle is
of 200 ms [1, 2].
I. INTRODUCTION
The reactor power (P) and reactor period
(T) are parameters directly related to safety
operation of a nuclear reactor. In reactor
operation condition, the time rate of power
change is very important, particularly at the
start-up stage, then monitoring the reactor
period is an effective way to prevent the
reactor power from increasing rapidly.
Therefore, the on-line and accuracy
calculations of reactor power and period have
been required to avoid uncertain shutdown or
nuclear incidents.
In case of the CPS of DNRR, when the
reactor power is greater than Ppreset by 10%
©2020 Vietnam Atomic Energy Society and Vietnam Atomic Energy Institute
DESIGN OF A FPGA-BASED CONTROLLER FOR POWER AND PERIOD MEASUREMENT...
The digital CPS of the DNRR was
designed and supplied by the SNIIP
SYSTEMATOM JSC of Russia and put into
operation in 2007. It was the second generation
of the instrumentation and control (I&C) system
for nuclear reactors that was designed by this
JSC, meanwhile, the fifth generation of I&C
system has been operated at some nuclear
reactors since 2015. As usual, after 13 years of
operation, many functional electronic modules of
the CPS were out of products in the market for
spare parts and replacement. Besides, taking into
accounts on the advantage of the FPGA
technology for design and construction of nuclear
electronic equipment, nowadays fast integrated
FPGA-based devices are widely developed for
measurement, data storage and acquisition
system in nuclear physics experiments and
nuclear engineering, such as for radiation
measurements with high resolution X-ray
spectroscopy with pulse height analyzer [3], for
readout systems of the cosmic ray angular
distribution based on flash analog-to-digital
converter using FPGA technology [4], and for
nuclear data measurement by (n, γ) and (n, 2γ)
reactions at horizontal experimental neutron
beam ports of nuclear research reactor with high
performance
gamma
spectrometers
[5].
Considering the above-mentioned reasons and
propensity, the main purpose of this work is to
develop the new FPGA-based controller module
which can be a spare-part or replacement for the
BPM-107R controller when necessary. The
developed controller applies DSP principle with
moving average filtering technique using a Xilinx
FPGA Artix-7 with on-board clock of 50 MHz
and two 32-bit counting channels that can sample
and calculate reactor power pulse signals every
20 ms. Some comparisons with the current BPM-
107R controller module were performed by
simulated signals as well as by real signals from
neutron detectors of the start range.
S1
S2
S3
C1
C2
C3
L1
R1
L2
L3
R3
D D
R2
A
Fig. 1. The "2 out-of 3" data processing and architecture of the DNRR’ CPS
(S – sensor/detector, C – Controller, L – Logic processing, R – Relay block, A – Actuator,
D – Display panel)
The CPS of DNRR is operating based on
neutron detectors are installed in dry channels
outside the reactor core, as shown in Fig. 2.
“2 out-of 3” principle as shown in Fig. 1. Three
42
VO VAN TAI et al.
Fig. 2. Neutron detector unit BDPN-36R2 (left) and detector locations in reactor pool (right)
Where, P(t) is transient reactor power at
time t, P0 is initial reactor power at time t0, T is
the time taken for the power to change by a
factor e (e = 2.718 which is the base of natural
logarithm) that called the reactor period, t is
time during the reactor transient.
II. METHODS
A. Nuclear reactor power and period caculation
Neutron density (power) of a nuclear
reactor follows the exponential function of:
(1)
Fig. 3. Sampling for nuclear reactor power and period calculation
To calculate the reactor period from (1),
it is necessary to convert continuous time
models as Fig. 3 to discrete time form, using
finite difference techniques. The reactor period
in digital nuclear instrumentation system can
be calculated by the equation (2) [6]:
From equation (2) we can see that the
reactor period can reflect the state of a
nuclear reactor. When Pk-Pk-1 = 0, the reactor
is in a stable state (T〜999 s); when Pk-Pk-1
>
0, the reactor power increases; and when Pk-
Pk-1 < 0, the reactor power decreases. The
reactor period can be monitored from 0 to
999 s by 1 s step.
or
or
The reactor power level is proportional
to the reactor neutron flux, therefore, the
output frequency from a pulse amplifier is
proportional to the reactor power level, then
the relationship between the reactor power at
(2)
Where, Pk-1, Pk is the (k-1)-th and k-th
sampled reactor power, △t is the sampling
period in seconds.
43
DESIGN OF A FPGA-BASED CONTROLLER FOR POWER AND PERIOD MEASUREMENT...
the start range (PSR) and the output frequency
of the pulse amplifier can be calculated as:
inputs and makes an output with them, the
formula is expressed as follows: [8, 9]
PSR = KSR×FSR×10-6
(3)
n1
P PM 1 ..... P
1
M
M (n1)
P
P
M i
n
i0
SM
n
Where, PSR is the reactor power at the
start range, KSR is a coefficient, FSR is the
output frequency from the pulse amplifier
which is connected to the fission chamber for
monitoring in the range from 10-6 to 10-1 %
Pnominal (Pnominal = 500 kWt).
(4)
When calculating sequential values, a
new value comes into the sum, and the oldest
value moves out, n is coefficient or window of
filter. Equation (4) can be rewritten as:
B. Design of moving average filters using
FPGA and DSP
1
P PSM , pre (P P
)
(5)
SM
M
M n
n
A moving average (MA) filter is a
type of finite impulse response filter (FIR)
[7]. It is used widely in many applications
P
Where, SM is the average value,
P
SM , pre
is the previous average,
P is the new sample,
M
in
digital
signal
processing,
P
is the n-th old sample, n is the window
communications, control, electrical and
biomedical systems. The main purpose of
MA filter is to increase the signal to noise
ratio and to reduce random noise.
M n
of SMA filter.
Equation (5) can be described in Fig. 4,
in which the reactor power and the reactor
period are calculated by DSP technique
embedded on FPGA.
A simple moving average (SMA) filter
is a filter that averages N points of previous
SMA Filter
Xi
Pulse
circuit
Yi
SUB
DIV
ADD
SAMPLE IN
Clock
SAMPLE OUT
Z(-n)
Z(-1)
n
Fig. 4. Principle schema used for moving average filter
for calculating reactor period
T
1
2
3
F_T
1
2
EMR_T
MULT
MULT
3
SUB
INVERSE
Comp5
Comp6
set_Scram T=20s
Clock
Z(-1)
WRM_T
Dt
set_Alarm T=40 s
Fig. 5. Principle schema used for calculating reactor period
44
VO VAN TAI et al.
SAMPLE IN is the input of the SMA
then calculated period is compared with
set_Alarm T (40 sec) and set_Scram T (20 sec)
to generate discrete signals WRN_T and
EMR_T, respectively. Further, these signals
will access to the logical processing unit of the
CPS, in which signal WRN_T is used for
formulation of a command to prohibit the
upward movement of control rods, meanwhile
EMR_T signal formulates a command to shut
down the reactor.
filter that is processed by a pulse circuit for
normalizing the pulse width, then counting,
accumulating and performing SMA filtering
technique, the output signal (SAMPLE
OUT) is frequency, n is a coefficient of
filter that is dependent on the fluctuation of
input signal.
The diagram for reactor period
calculation by Eq. (2) can be described in Fig. 5.
To calculate the reactor power at the start
range, Eq. (3) is described in Fig. 6.
F_T is the output signal from SMA filter
that is used for calculating reactor period, and
Psr
for calculating reactor power Psr
F_Psr
1
3
MULT
1
2
EMR_Psr
DIV
3
2
Comp1
Comp2
Clock
set_Scram P
Ksr
1000000 set_Alarm P
WRN_Psr
Fig. 6. Principle schema used for calculating reactor power at start range
As shown in Fig. 6, the F_Psr signals are
controller module in the start range (named
FPGA-SR). The experiment which was setup
to measure the power and the period for
testing FPGA-SR and BPM-107R controllers
is shown in Fig. 7(a). The values of power
and period of both the controllers were
recorded (data logging) using a computer via
Terminal v1.9b software.
performed to calculate the reactor power for the
start range (Psr). Then these values are
compared with set_Alarm P (5% Ppreset) and
set_Scram P (10% Ppreset) for generating discrete
signals WRN_Psr and EMR_Psr, respectively.
Further, these discrete signals will access to the
logical processing unit of the CPS, in which
signal WRN_Psr is used for formulation of a
command to prohibit the upward movement of
control rods, meanwhile EMR_Psr signal
formulates a command to shut down the reactor.
In the CPS, the KSR coefficient for
calculating reactor power was calibrated to be
4.04. The initial value of simulated frequency
was 10 Hz and the final value was 50,000 Hz.
The simulated period was chosen to be 20 s.
The relative error of the monitored reactor
power in the range from 4×10-5 to 2×10-1 %
Pnominal is within 5% and that of the monitored
reactor period is within 10%, which are
reported in [10]. Figure 7(b) shows the testing
results for period measurement at 20 s by the
BPM-107R and FPGA-SR controllers. The
III. EXPERIMENTAL RESULTS
AND DISCUSSION
A. Testing of the designed controller in the
start range by simulator
The simulator module PGT-17R,
designed by SNIIP SYSTEMATOM JSC,
was used for testing of the new designed
45
DESIGN OF A FPGA-BASED CONTROLLER FOR POWER AND PERIOD MEASUREMENT...
period curve of the BPM-107R controller
reaches to 20 s slower than that of the FPGA-
SR controller, in which the period curve
reaches to 20 s only after about 100 s.
BPM-107R
F
COMPUTER
COMPUTER
Data logging
LCD&KEYPAD
PGT-17R MODULE
FPGA-SR
KEYPAD
F: 10 to 50 000 Hz
LCD&KEYPAD
(a)
(b)
Fig. 7. Principle schema for measurement of power and period using PGT-17R simulator module (a)
and Testing results of BPM-107R and FPGA-SR controllers using PGT-17R module with FSR from 10 Hz to
50,000 Hz at 20 s period (b)
The main reason of different results
between two controllers is due to their different
architectures. The BPM-107R controller is
based on the 8-bit DS87C530 microprocessor
operating with 30 MHz clock frequency that
can sample and calculate reactor power pulse
signals between 20 ms to 200 ms. Meanwhile,
the new developed controller is based on the
high speed FPGA with 50 MHz on-board clock
and two 32-bit counting channels that can
sample and determine the above procedures
every 20 ms. The other reason is that in the
range of reactor power lower than 5×10-4 %
Pnominal, the statistic counting of simulated
pulses is still very low, therefore, in order to
achieve the ideal curve from 5×10-4 % Pnominal
(from this value the emergency protection is
started monitoring), the filter coefficient in the
BPM-107R was changed as jumping steps.
Instead of that, the coefficient n (or window) of
SMA filters in the FPGA-SR controller with
embedded DSP circuits can be flexibly
changed to achieve the such ideal curve.
Fig. 7(b) also shows that both the BPM-
107R and FPGA-SR controllers give almost
the same results in the case of simulation for
power measurement.
B. Testing of the designed controller by
neutron signals in start range of the reactor
The experimental schema to measure the
reactor power and period at the CPS using
neutron signals from neutron detectors in the
reactor is shown in Fig. 8.
FSr
FSr
BPM-107R
SIGNAL
F_OUT
+400VDC
PULSE
LCD&KEYPAD
COMPUTER
AMPLIFIER
-400VDC
Data logging
FPGA-SR
+12VDC
-12VDC
LCD&KEYPAD
Fig. 8. Principle schema for measurement of reactor power and period
46
VO VAN TAI et al.
Fig. 9. Results of reactor power and period measurement by FPGA-SR and BPM-107R controllers in
the range from 4×10-5 to 2×10-2 % Pnominal
Fig. 10. Results of reactor power and period measurement by FPGA-SR and BPM-107R controllers in
the range from 10-2 to 2×10-1 % Pnominal
The start range was designed for
monitoring the reactor power in the range from
4×10-6 to 2×10-1% Pnominal. In practice, the
lowest power level is about 4×10-5 % Pnominal
due to epithermal and fast photoneutrons,
filters can be flexibly changed, so its response
time is faster than that of the BPM-107R
controller as shown in Fig. 7(b).
IV. CONCLUSIONS
9
4
which are produced by the Be(γ, n)2 He and
Based on the application of DSP
technique with moving average filters
embedded on FPGA, the functional circuits for
the controller module have been designed for
measuring and determining the reactor power,
the reactor period, and generating the
protection signals whenever the value of the
reactor power or period is beyond the preset
threshold value.
4
9Be(n, 2n)2 He reactions, respectively, are
significant in the reactor core, especially when
the reactor operates frequently.
Fig. 9 and Fig. 10 show the results of the
reactor power and period measurement in the
range from 4×10-5 to 2×10-1% Pnominal by the
FPGA-SR and BPM-107R controllers. The
results show that both the controllers have
almost the same value.
The developed FPGA-based controller
was tested in comparison with the BPM-107R
module of the CPS, which was designed by
As mentioned above, in case of the
FPGA-SR controller, the coefficient n of SMA
47
DESIGN OF A FPGA-BASED CONTROLLER FOR POWER AND PERIOD MEASUREMENT...
SNIIP SYSTEMATOM, Chief Designer А.
А. Zaikin, 2006.
SNIIP SYSTEMATON JSC of Russia. The
testing was performed both by pulse-generated
simulator PGT-17R and by real neutron signals
from the reactor. The experimental results of
measuring reactor power and period by the
FPGA-SR and BPM-107R controllers indicate
a good agreement of their functions and
characteristics, including the reactor power
measured in the range from 4×10-5 to 2×10-1 %
Pnominal with the accuracy less than 5% and the
reactor period is monitored in the range from 1
to 999 s with the accuracy less than 10%.
Additionally, the emergency protection signal
EMR-P or EMR-T is generated, when the
reactor power is greater than Ppreset by 10% or
the period is less than 20 s.
[2]. Safety Analysis Report for the Dalat Nuclear
Research Reactor, Dalat Nuclear Research
Institute, Chief Editor Nguyen Nhi Dien, 2012.
[3]. Buzzetti S., Capou M., Guazzoni C. et al.,
“High-speed FPGA based pulse-height
analyzer
for
high
resolution
x-ray
spectroscopy”, IEEE Trans. Nucl. Sci. 52, pp.
854–860, 2005.
[4]. V. H. Hai, N. Q. Dao and M. Nomachi,
“Cosmic ray angular distribution employing
plastic scintillation detectors and flash-
ADC/FPGA-based
readout
systems”,
Kerntechnik, 77, pp. 462–464, 2012.
[5]. Pham Dinh Khang, Nguyen Nhi Dien, Dang
Lanh, Nguyen Xuan Hai, Pham Ngoc Tuan,
Nguyen Duc Hoa, Nguyen An Son, “A design
configuration of an FPGA-based coincident
spectrometry system”, J. of Analytical
Sciences, Methods and Instrumentation, 2164–
2745, Vol. 3, pp. 158–162, 2013.
The obtained results also permit to
conclude that the new developed FPGA-based
controller meets the design purposes and can
perform all functions of the existing BPM-
107R controller, therefore, it can replace the
BPM-107R controller when needed.
[6]. E. P. Gytfopoulos and P.M. Coble, A digital
nuclear reactor control system, 1960.
ACKNOWLEDGEMENTS
[7]. Huasheng Xiong, Duo Li, “Nuclear reactor
doubling time calculation using FIR filter”,
Energy Procedia, 39, pp. 3–11, 2013.
The authors are thankful to Dalat
Nuclear Research Institute and Vietnam
[8]. “Moving
average”
Atomic
Energy
Institute
for
their
administrative assistance. This research is
supported by Ministry of Science and
Technology of Vietnam under grant number
ĐTCB. 08/19/VNCHN.
[9]. The Scientist and Engineer's Guide to Digital
Signal Processing, by Steven W. Smith,
Chapter 15 “Moving average filters” pp. 277–
REFERENCES
[10]. Complex of Equipment for Control and
Protection System ASUZ-14R, Passport
[1]. Complex of Equipment for Control and
Protection System ASUZ-14R, Operating
Manual RUNK.506319.004 RE-E, JSC
RUNK.506319.004
SYSTEMATOM, Chief
Zaikin, 2006.
PS-E,
JSC
SNIIP
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