Digital Automatic Control System for the TRIGA Reactor
Susumu Harasawa Institute for Atomic Energy, Rikkyo University 2-5-1, Nagasaka, Yokosuka, 240-01, Japan Mohamad Amin Sharifuldin, Syed Nahar Syed Hussin Shahabudin Unit Tenaga Nuklear, Kompleks PUSPATI, 43000 Kajang , Selangor, Malaysia and Kunishiro Mori, Sadayuki Uchiyama Clear Pulse Co. Ltd . 6 - 25 - 17, Chuuoo, Oota-ku, Tokyo, 143 , Japan
1. INTRODUCTION One of the authors has designed a digital automatic control system with two sets of comparators for the TRIGA reactor of the Rikkyo University " . The control system has been designed in resemblence with manual operation of the reactor. The fundamental idea was that the time interval of the digital control action depends on the deviation between the power output and the demand power. In the case of the Rikkyo University Reactor, when the deviation is smaller than ± 0.2 %, no action occurs, when the deviation exceeds ± 0.2 % but below ± 3. 5 %, a regurating rod responds for 0.1 second with stepwise movement at an interval of 1 second, and when the deviation exceeds ± 3.5 % the regulating rod moves continuously. These actions has been materialized by using two sets of comparators and a pulse generator. Another control system for the PUSPATI TRIGA Reactor applying similar idea was designed and tested in 1987. The control system has one comparator which detects the difference of the reactor output and demand power as conventional control systems have, and the time interval of the control action of the newly designed system is determined by a voltage-to-frequency-convertor. The idea and results of the automatic control systems for the Rikkyo University Reactor and PUSPATI TRIGA Reactor are discussed below.
2-27 2. LOGIC CIRCUIT 2.1 The logic circuit for the Rikkyo University Reactor Input-output relation of the logic circuit in Rikkyo University Reactor
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Fig. 1 Illustration of input and output signal of the logic circuit of the Rikkyo University Reactor automatic control system
2-28 While the input to the logic circuit are the signals from the ionization chamber which are continuous, the output from the logic circuit are pulse-like and are divided into three categories according to the deviation of the output power from the demand power :
1) Nan-sensitive region ( dead band ) 2) Region of pulse-like movement of a control rod 3) Region of continuous movement of a control rod
These relations are illustrated in Fig. 1 1) When the deviation of the power-output from a demand power is between ±0.2 1 there is no output from the logic circuit. 2) When the deviation is between 0.2 % and 3. 5 %, or - 0. 2 % and - 3.5 1 the output of the logic circuit are stepwise with 0.1 second width and 1 second interval, and 3) when the deviation exceeds 3.5 %, the output of the logic circuit is constant. The diagram of the circuit is shown in the appendix [ Fig. A-l ] .
Some power output under the automatic control operation in the Rikkyo University Reactor Some results of the power fluctuation of the Rikkyo University Reactor under automatic control are shown in the appendix [ Fig. A - 2 ( 100KW ), Fig. A - 3 ( 100W ), Fig. A - 4 ( 10W ) and Fig. A - 5 ( 1W ) ] . The fluctuations due to the reactor noise are smaller than ± 0.2 % of the operating power higher than about 10 Watt. On the other hand, the reactor noise are larger than ± 0. 2 % of the operating power lower than 10 Watt. As can be seen from the figures, the average power level is satisfactorily controlled even when the noise fluctuation is larger than ± 0. 2 % . At demand power level of higher than 1Q Watt, the noise to singnal ratio is smaller than ± 0. 2 % and the output power is controlled whithin ±0.2 %.
2.2 Modified logic circuit for the PÜSPATI TRIGA Reactor We have designed a new control system with variable interval stepwise action for the PUSPATI TRIGA Reactor in order to reduce the power fluctuation at high power region. In the new logic circuit the concept of resemblence with manual control
2-29 a voltage to frequency converter. The frequency of the pulse is proportional to the power deviation, that is, the pulse interval is inversely proportional to the deviation. The input-output relation of the logic circuit in the system is illustrated in Fig. 2.
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Fig. 2 Illustration of input and output signal of the logic circuit for the PUSPATI TRIGA Reactor automatic control systea Pulse interval r = K / 1 g I , where e is the deviation of the power output from the demand power. K is a constant.
3. CßmSßL SYSTEM in the PUSPATI REACTOR 3.1 Back-up automatic control system for the PUSPATI TRIGA Reactor As the PUSPATI TRIGA Reactor has an existing automatic control system, we designed the digital automatic control system as a back-up system. Digital automatic systems usually consist of following three parts : Sensor Logic Circuit , and
2-30 Actuator . As the sensor can be shared with the existing control system, we only prepared the logic circuit and the actuator for the back-up system. The back-up control system is connected as shown in Fig. 3..
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automatic controller «—*• neutron sensor e*
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Fig. 3 Automatic Control System of the PUSPATI TRIGA Reactor
3.2 Logic circuit The simplified block diagram of the logic circuit is shown in Fig. 4. The gain of the amplifier for the deviation from the demand power, A, and the pulse interval, v, are designed to be adjustable . The detailed logic circuit diagram is shown in the appendix [ Fig. A - 6 ] .
2-31 4. RESULTS AND DISCUSIONS Power fluctuations of PUSPATI TRIGA Reactor under (a) manual, (b) the original automatic control ( GA AUTO ) and ( c ) the digital automatic control ( DIGITAL AUTO ) are shown in Fig. 5 ( 50 W ), Fig. 6 ( 500ÏÏ ), Fig. 7 ( 5kW ), Fig. 8 ( 50kW ) and Fig. 9 ( 750kW ). It can be seen from these figures that the digital automatic control system has reduced the frequency of the control rod movement compared to the operation under the original automatic control system, and power fluctuation has been improved for demand power of 5 kff or lower. However, there is no improvement of average deviation from demand power at 50 kW or higher. Output power under both automatic control systems of PUSPATI TRIGA Reactor have larger fluctuation than that of manual mode. This is because both automatic control systems tend to enhance the deviation by responding constantly to statistical fluctuations. The digital control system was also designed to solve this enhancement by varying the interval between control action through the use of a voltage- frequency converter. However, the result showed that this is not sufficient to solve the problem. From the experience with the automatic control system of the Rikkyo University Reactor, inclusion of a dead band into PUSPATI TRIGA Reactor digital automatic control system will overcome this problem and reduce the deviation.
ACKNOWLEDGMENT The authors would like to thank Mr. Adnan Bokhari for checking the circuit and connecting the back-up system to the existing control system, and Mr. Gui Ah Auu for fruitful discussions and critical reading . Fund for the back-up system is financed by the Japan International Cooperation Agency.
REFERENCES *) S. Harasawa and K. Kawaguchi : Automatic Control System of Rikkyo Research Reactor, Proceedings of First Asian Symposium on Research Reactors, 247- 252, 1986
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50 .100 150 200 250 . 300 500U GRflUTO
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o 100 150 200 250 300. TIDE! (Sec) Fig. 6 Example of the power output of 2-34 PUSPÄTI TRIGA Reactor at 500 « 5'KbJ HRMUfiL
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100 150 200 250 300 ?-% ^ (Sec) Fig. 8 Example of the power output of 2 3b PUSPATI TRIGA Reactor at 50kff 750K MflNURL
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100 .150 200 250 300 ... TirF (Sec) -37 fig- 9 Example of the power output of PUSPATÏ TRTGA Reactor at 750! Fig. A - 1 , Diagram of logic circuit of Rikkyo University Reactor automatic control system. Example of the controlled power output ,„ of Rikkyo University reactor at 100 KW . Fig. A - 3 , Example of the controlled power output of Rikkyo University reactor at 100 W . Fig. A - 4 , Example of the controlled power output of Rikkyo University reactor at 10 W . Fig. A - 5 , Example of the controlled power output of Rikkyo University reactor at 1 W . Fig. A - 6 , Diagram of logic circuit of PUSPATI TRIGA Reactor automatic control system. Fig. A - 7 , Diagram of actuator of PUSPATI TRIGA Reactor automatic control system. 2-38 § § s § © Fig- A " ! ' DÄ?cf ÄColCisry?t?iL0f Rikky° UniVersity Reactor 2-39 T " ~" L^ — — LJJI^_: S=^ j__ y—i . •—.—*= i £1* —• • ï— - -•i •!••-! 1 H 1 r- •: i —. , . J . . —• ; : 1 . —; j : j 1 • '—r^p^rri. i r ._. _ , ' ' | p :zrz. -4 f- •• i i i = •: 1 i-l.-:::- • .- ; ..•;•: |—. : :. : : : 1 • • i. - __ _, _.._.,,.,,.,,. ._, ..... i- X \ -1 • é== — - _; 1 1 :—:—:—J 1 j 7* •:••)::: ! ••• • i:!1: ; • ::r:-i':! 1 1 ••—1 .—i ••:..'! :—i . «^•-•••l : . •••:; i ; i' —: r—! ;—: , , . , , , . i :—K^— - ___ i 1 1 ..." ' • ' • •: ••!• - ; " i: ,; ' i: : - : : : - • 1 • :^|7H ' - • Ï : 1 •. i • - . • • | • • . 1 t: 1 J i 1 . ' • • . • • 1 -_ .: . I • i i ; . .• • • 1 • 1 : - r- < i J . . 1 • . . . i • • i ••. 1i . .,i i -. -0..jq '. .- • ; ,•'•'• i... ^ 1 j 1 • •-:••.•;•; UL_ —i-^i-i , , , _; —• i •- 1—*—-H i. ' : ' \ l ' •. '~ j—: , ; 1 ; "—1 i . • t .-,...• | • r1) • • i ••!••.. r • i J •i . " -.]• • <£U » ' • : • • -4U .- : , . i • • -. -jj : • 1 . . 1U IÙ . . j . . • l j . : : 1 • • - . ..,-*: • j i i . i • • ' t | t i : . i • i i • j • • ( | i • • 1 i • • . 1 . , i . 1 • . . . | i , . . • • i • .... 1 • \ Vi*<_| ("• '; . i , , , i ....,.,.. | . ... , , . " •• • . . • i i • . , 1 1 .. 1 1 1 i I . : 1 , . -/; !.*_* I 1 . 1 . 1 1 1 . 1 1 -1 I 1rf— • . j ,,.,,.,, 1 . • ,(,..., . i . , M 1 I > 1 < . < - 1 1 i 1 1 i 1. 1 , 1 .. 1 ..... | • ! | | : ..• i .... | •• ' • •• V ' ' .' ?•] .","" 1 , | , j • , . j j , -, . , , 1 , !. L- ' 1 : . •• 1 .... | ..i- | i -.. —;, I ' Lr*"1-' l i . i ; . . 1 1 i ' i . . . . ; 1 • ' i ' • • i i 1 . 1 , ." 1 1 | • , . • 1 . . 7\ . il •i l .'. ' ' j . •• ...... 1 • • : | • . . . 1 . . 1 • i 1 1 1 . : • • 1 . . l: 1 II] 1 1 t i i • i i | i • : : : i i • _ • 1 i "'I • • ! • ' ) • . - j • 1 : 1 , ... i i j ! i i , J : * t i i . , • J .t , . : 1 1 t ( f • 1 1 ] 1 1 1 1 J . r 1 I . • i . 1 1 . ' 1 j -« " '• 1' ' ' 1 1 T > 1 :' ' i i ; t t i | J i i . | i \ i i t ' ? 1 J -H • ' i • • : i L • i • > i • • • • i • i • < 1 ' • i . • i i . • ; . i i ' i i i i i t j • ' i i | ; i » i . J- t i • . . . 1 .'il- | • . . i . • 1 • 1 • i • • j • . . i . . • • | i • i . . . i ... •' , ' "f i" I ' ' 1 1 r • 1 r \ t , i -. i i i i i ! ! ! : : . 1 1 : : : : [,i-> 1 1 1 i . . ! . i . ii(l 1 1 1 l"l 1 1 1 i 1 [ 1 1 . . • 1 1 • ! 1 • ' • 1 . . . t ... j . . | i I 1 i ' i ' ' ' . S; • I • i i i i i i ; j i i > i i t 1 i . 1. 1 1 1 1 I . . I • :. » = ' 1 • ' . : • : i i • • • i --;••• i • : - ( • J - • • 1 • 1 . J I jç..,.. i - - • • • • 1 • i . .- . . 1 . 1 . . 1 . . . . *""'• "1 .' Fig. A - -2 , Example of the controlled power output of Rikkyo university reactor at 100 KW . 2-40 Fig. A - 3 , Example of the controlled power output of Rikkyo University reactor at 100 W 2-41 Fig. A - -4 , Example of the controlled power output s of Rikkyo University reactor at 10 W 2-42 Fig. A -'5 , Example of the controlled power output of fiikkyo University reactor at 1 W . 2-43 I î * % 3 ^ «î 1 1 5 S VF3 ' îl-l « I . | « I j TMm RSffF^w. Fig. A - 6 , Diagram of logic circuit of PUSPATI TRIGA Reactor automatic control system.2-44 1 »0 SS ad -*—t ! r o i ____ *5t 1 Ç* ? Ci a at Fig. Diagram.of actuator of PUSPATI TRIGA Reactor automatic control system. 2-45