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Online embedded integrated scanning system for identifying failed fuel sub assemblies in fast reactor
Nuclear Engineering and Design 241 (2011) 2604–2613
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Online embedded integrated scanning system for identifying failed fuel sub assemblies in fast reactor Metta Sivaramakrishna ∗ , Chandrakant Upadhyay, C.P. Nagaraj, K. Madhusoodanan Power Plant Controls Division, Indira Gandhi Centre for Atomic Research, Kalpakkam 603102, Tamilnadu, India
a r t i c l e
i n f o
Article history: Received 28 September 2010 Received in revised form 11 April 2011 Accepted 14 April 2011
a b s t r a c t The physical integrity of the fuel in fast reactor is of utmost concern for the healthiness of the reactor and operating people. Hence details of the failed fuel location in the core shall be determined at the earliest, to minimize reactor down time and radiation exposure. In the present reactor under construction, i.e., 500 MWe Prototype Fast Breeder Reactor (PFBR), a system for failed fuel identification, was proposed. The system follows a novel scheme to locate the failed fuel using failed fuel location module along with necessary instrumentation and control. This paper details out the scheme followed. © 2011 Elsevier B.V. All rights reserved.
1. Introduction
2. Description
MOX (mixed oxide) fuel sub assemblies are fabricated through the normal powder metallurgy route of powder compaction and sintering. The control of dimensions, quality of clad at each and every stage is essential to avoid any defects in the fabrication. Fuel pins are provided with a leak-tight metal cladding for containment of the fission products of the nuclear reaction. Despite all this, cladding tube failures can happen. In case of fuel clad failure, the fuel might contaminate the coolant, with potential consequences. In view of the above, it is necessary that there should be a system designed for detection and identification of failed fuel subassembly (FSA). This is to be done at the earliest, after detecting the presence of failed fuel, so that it can be removed from the core. A system is developed towards this. The salient feature of this to have single integrated solution for various combinations of inputs and interlocks. In the system developed, the positioning accuracy plays a crucial role. The effect of dilution is proportional to the positioning inaccuracy of the system. But, being heavy structure (the selector valve), backlash and stiction are difficult to control at higher speeds. If the seeking time is too slow, the reactor down time will be more to locate the failed fuel sub assembly. The indexing angle (gap between two holes on the selector valve plate to sample the sodium jets from different sub assemblies) cannot be increased beyond certain level, due to the physical constraints of space within the control plug. Positioning accuracy is also limited by the encoder resolution. This paper presents the details of design, features of the system.
Fuel failures like pinholes and micro fissures, which release only gaseous fission products is detected by Gaseous Fission Product Detection (GFPD) system. In case of direct contact between fuel and coolant i.e., wet rupture, it results in release of both gaseous and solid fission products (140 Ba, 140 La, 134 Cs, 137 Cs, 95 Zr radionuclides, etc.) released in to the coolant that can be detected by means of DN precursors in sodium coolant. Upon detection of failed fuel, in order to locate the failed Fuel Sub Assembly (FSA), around 200 subassemblies are to be scanned. This is done with three numbers of Failed Fuel Location Modules (FFLMs) operating simultaneously, each catering to 66 subassemblies. Failure of fuel pin in central FSA is detected by indirect method and is inferred when there is no indication from any other FSA. Sodium sampling sleeves, concentric over each thermocouple tube sheath, are positioned above the top of each FSA. The sampling tubes from the sleeves are routed to the base plate of the selector valve of FFLM. Selector valve with the help of motor drive, positions the outlet tube to any one of the 66 inlet sampling tubes. An optical encoder attached to the shaft of the selector valve monitors the position of the selector valve. A DC conduction pump is used to pump the sodium from the outlet of the selected assembly to the sodium capacity (refer Fig. 1 given below). An electro magnetic (EM) flow meter is provided at the outlet of the sodium capacity to monitor the flow of sodium. Neutron detectors are provided around the capacity in moderator block, to detect any neutron flux in the sodium sample, due to the fission precursors, which are delayed neutron emitters. The sampled sodium is returned to the pool. In order to reduce temperature difference between hot pool sodium and the sodium returning from sampling tube and to avoid high temperature at detector location,
∗ Corresponding author. Tel.: +91 44 27480500x22491; fax: +91 4427480348. E-mail address: [email protected] (M. Sivaramakrishna). 0029-5493/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.nucengdes.2011.04.030
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Fig. 1. General mechanical arrangement of failed fuel location module.
the sodium capacity is wrapped with thermal insulation. Heaters are provided to maintain a minimum temperature of 423 K (150 ◦ C) for the sodium in the capacity and sampling pipe. Temperature is monitored on sodium capacity, flow meter, sodium-piping, near seals and in moderator. Lead is provided as gamma shield around the capacity to reduce gamma activity. Drive shaft of the selector valve is rotated by a Positional Drive System (PDS) with an encoder. The PDS comprises of permanent magnet DC servo motor, servo controller and encoder. Rotation of the selector valve permits sequential monitoring of each FSA outlet for the presence of delayed neutrons due to failure of fuel pin. Graphical User Interface (GUI) and PDS Control software are designed to operate in sequential mode and in random mode to specify the angle of the fuel sub assembly (FSA) to reach (refer Fig. 2 given below). Under normal conditions, the system is operated once in a week, otherwise the system is maintained in poised state for startup. When the reactor is tripped on the wet rupture type of fuel failure, the reactor is restarted and operated at low powers to identify the location of the failed FSA using FFLM. Total scanning time is approx. 8 h.
Fig. 2. Graphics (GUI).
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3. Theory of operation The basic computation is done using micro controller. The I/O operation was implemented using operational amplifiers, sampleand-hold amplifiers, buffers, displays and output contacts. DC reference voltage source is used to simulate some analog inputs. Single board micro controller based PCB is designed for control and processing the inputs and outputs. The required power supply for the processor is derived from 48 V with isolation. Analog inputs are also taken with 3 port isolation. Digital inputs are taken with opto isolation. Output contacts are given in the form of voltage free contacts. Alarm and error messages are displayed in the local display and also given to data highway. All the data can be stored locally in the memory for 30 min. Test provision is given, which is enabled on command from control room in the form test authorization contact. All the inputs can be varied under this test mode simulating the various combinations of field conditions. All the indications are available locally. Basic code is written in Mishra C and is compiled and stored in the EPROM. The circuit was tested for test inputs using the potentiometer, relays and mode button.
Fig. 3. Velocity profile.
It is a control system to position the selector valve at a required position. Basically it is a closed loop system comprised of motor, driver amplifier and encoder to get feedback. The above system ensures proper positioning of failed fuel location module. From micro controller, the input is given to driver amplifier which is fed to motor to run it. An incremental encoder mounted on the shaft keeps giving pulses which are used to know the angle by which the shaft has rotated.
4. Working principle
4.2. Motor
4.1. Positional drive system
The starting torque is 2.1 Nm at 4000 rpm with Planetary Gear head. The reduction ratio is 100:1 and output torque is 63 Nm at input speed of 4000 rpm. It is provided with Integral Tacho feedback for speed. It needs 310 V dc voltage and its operating current range is 7.4 A. The motor driver amplifier used is L6203.
Positional drive system is a closed loop system. It does the following actions: 1. Accepting an order that defines the desired result, i.e., location of the sub assembly from which the sodium is to be sampled 2. Determining the present conditions by some method of feedback 3. Comparing the desired result with the present conditions and obtaining a difference or an error signal 4. Issuing a correcting order (the error signal) that will properly change the existing conditions to the desired result 5. Obeying the correcting order
4.2.1. Driver IC L6203 For a given target position, the location module is to be positioned at that target. It has to reach its target smoothly i.e., it has to rotate with acceleration for certain angle and then rotate with constant velocity and then rotate with constant deceleration. The velocity profile should be as shown in the following Fig. 3.
Fig. 4. Pulse Sequence.
Fig. 5. Flip flop.
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Fig. 6. PCB-design for encoder interfacing.
4.2.2. Importance of trapezoidal profile There are also other velocity profiles such as sin graph profile, triangular profiles, etc., but the trapezoidal profile (like some typical profiles) is used more for industrial applications and other reason is that when it reaches the maximum velocity it continues with that velocity in trapezoidal profile where as in some other profiles there will be sudden deceleration which may cause jerk in motor. By the time the sampling circuit reaches the required sub assembly its velocity will be zero. This ensures less overshoot. 4.2.3. Generation of profile The velocity profile is divided in to equal samples. For suppose, the maximum velocity is V, it is divided in to some n samples and then each time constant (V/n) is added to reach V. These additions are of n times. Thus acceleration is achieved. • For constant velocity case, the same V is given until required angle is reached. • For deceleration, the V is subtracted by (V/n) so that it is finally reached to zero velocity. • Thus the trapezoidal velocity profile is achieved. 4.2.4. PWM’s duty cycle vs velocity of dc motor PWM duty cycle is proportional to the velocity of the dc motor. This linear equation of duty cycle and velocity is know by taking the samples, for example, for certain duty cycle there will be certain velocity and samples are to be taken. 4.2.5. Usage of intervals At every interval, motor is given increments of the constant value (V/n) to reach V after some samples. 4.3. Incremental encoder It is a position encoder mounted on the shaft to give pulses from three encoder channels. When travelling in forward direction the
channels A and B give pulses. But A leads B. when travelling in backward direction B leads A. It is explained in the following Fig. 4. The flip-flop (Fig. 5 shown below) circuit makes the pulses coming from encoder to following pattern (up count and down count) which are then sent to TMR0 TMR1 to calculate the angle by which the motor has rotated. 4.4. Method to count pulses coming from flip flop circuit The pulses coming from flip flop are fed to TMR modules source pins. TMR0 source pin RA4 and TMR1 source pin Rc1/T1CLK. The registers TMR0L:TMR0H and TMR1L:TMR1H increment their value on each raising of pulse at source pins. Subtracting TMR1 from TMR0 gives number of pulses given out by the encoder. • If rotated clockwise TMR0 increments and TMR1 value remains constant • If rotated anticlockwise TMR1 value increments and TMR0 value remains constant. 4.4.1. Calculation of angle The angle rotated will be (TMR0 − TMR1)/(no. of pulses given by encoder per revolution). The pulses given by encoder per revolution is constant for a incremental encoder. 4.4.2. Calculation of velocity First store the initial difference of TMR0 and TMR1 at time t = 0, then again store the difference of timers at some time t, then the velocity will be the difference of two stored values divided by time t. The picture (Fig. 6) given below shows the complete interfacing of the encoder to TMR modules and to count the number of pulses thereby the angle rotated by the motor. This completes the feedback system. But any error in the feed back should be updated which can be done by industrial application called PID CONTROL (proportional–integrative–derivative) control.
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Interrupt raised For giving the angle by which the valve shall rotate, i.e “angr”
Angle
yes
Then accelerate
no Read pulses from encoder and calculate present angle and v.
If angle >angr /8 && yes Angle
If error(v!=vreq)
no If angle >angr
yes
Calculate pid
no
yes
If angle >angr*7 /8 && angle
no
Add output error to velocity
End of interrupt service subroune
yes Disable mer2 so that no interrupt can be raised
Then constant velocity
Then decelerate
Read pulses from encoder and calculate present angle and v
Read pulses from encoder and calculate present angle If error(v!=vreq)
If error(v!=vreq) no
no
. End of isr
Calculate pid yes Add output error to vel
End of isr
yes
Calculate pid
Add output error to vel
Fig. 7. Flow chart of the scheme.
The following figure (Fig. 7) shows the flowchart which explains the generation of profile, current position and error calculations. 4.5. Explanation of algorithm When the interrupt is raised, the velocity is added to constant value so that the motor accelerates. Then encoder pulses are decoded to know the present angle and also they are subtracted from the previous ones to know the velocity in the next phase. If motor did not attain the velocity required, the error is added to the next velocity. This ensures that it is able to traverse the required angular position. The present angle is compared to the “angle required/8”. If this angle is not reached, then motor has to travel with the constant velocity. The constant velocity is the maximum velocity attained in the previous acceleration part. Then again error is calculated and the velocity to be given is corrected so that it attains the required angle
in a given time period. Then present angle is compared with the “angle required/8” and “angle × 7/8”. If “angle × 7/8” is reached, then the motor is made to decelerate with the constant value that was used into the acceleration part. This deceleration continues until the motor reaches the required angle. 4.6. Interfacing keypad to micro controller A keypad is attached to micro controller. This gets the inputs such as mode in which user wants to move the module and to which sub assembly he wants to move. The keypad is interfaced only to test the board and components i.e., in test mode only, otherwise, the input is taken through RS232 or TCP/IP. Keypad has 16 buttons (as given in the following Fig. 8) comprising 4 rows and 4 columns. Symbols on a row are connected by a single wire as well symbols on single column are connected by a single wire. Wires from rows and columns are connected to I/O
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4.7. Implementation of pump control 4.7.1. Inputs • Flow meter output • Temperature output • Heater on input 4.7.2. Outputs • On/off heater • On/off pump power supply
Fig. 8. Keypad.
ports. The rows are connected as output and are simultaneously given on off condition i.e., when one row is off other rows are on. The wires from columns are connected to +5 V (with a current limiting resistor of 1 k) and also to the ports as inputs. When a row is given off condition that is 0 V, the columns are checked and if any input from column is off then button corresponding to the row and column is switched on.
A DC conduction pump is provided for giving the impetus for the sampled sodium jet to reach the detector location, where the activity due to the rupture of the clad in the fuel pin is detected. A high current low voltage DC power supply is provided for creating the required electrical flux in the pump. To assure the required flow in the sampling path, a flow meter is connected in the outlet where the sampled sodium is brought back to the hot pool. Throughout the sampling tubing, heaters are provided to ensure the uniformity of temperature of sodium. During the failed fuel identification process
Fig. 9. Circuit for initialization of thermocouple.
Fig. 10. Schematic of FFLM Positional Drive System.
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Fig. 11. GUI of the system and the drive.
and rotation of the selector valve mechanism, the pump needs to be protected from cavitation, thermal swiping. Hence following protections are provided. If the temp is above the set temperature, the heater is to be switched off. If the temp is below a set value then heater is to be switched on and the pump is to be switched off. If the voltage and current are high then pump is to be switched off. If flow is below the set value, then switch off pump power supply. If flow rate is below a set value under pump on condition, switch off the power supply. There are 12 thermocouples located at different points to get temperature. The thermocouple used is of k type which has sensitivity of 41 V/◦ C. The cold junction temperature for the thermocouple has to be compensated. Other problems of linearization have to be dealt with. Thermocouples are interfaced to AD595 instrumental amplifier and then the conditioned outputs are taken to microcontroller. We have to initialize ADCON registers as per the configuration. The temperature is displayed in the LCD as given in the figure (Fig. 9) given below. A prototype model as given above is designed and tested. The heart of the prototype system (given above in Fig. 10) is the mechanism that is actuated by a DC servomotor with speed feed back from a tachometer. The speed of the motor is reduced used gearing and then the motion is transferred to the output shaft. A brake is used to arrest the output shaft. The position of the output shaft is measured with a rotary incremental encoder. 4.8. Experimental validation The entire system is controlled by a PC based system. The PC actuates the DC servomotor through a servo amplifier. The servo amplifier controls the current in the DC servomotor depending upon the set speed and tachometric feedback. The PC reads the position of the output shaft from the encoder and commands the servo amplifier as required. The prototype system that was developed is shown in the figure (Fig. 11) given below.
Fig. 12. Selector valve assembly.
The brake is operated through an input/output module that is connected to the PC through a serial port. Other inputs and outputs are provided for interlocks with other systems as required.
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Table 1 Positional accuracy of PDS. Location no.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66
Target angle
5◦ 17 10◦ 35 15◦ 52 21◦ 10 26◦ 28 31◦ 45 37◦ 03 42◦ 21 47◦ 38 52◦ 56 58◦ 14 63◦ 31 68◦ 49 74◦ 07 79◦ 24 84◦ 42 90◦ 95◦ 17 100◦ 35 105◦ 52 111◦ 10 116◦ 28 121◦ 45 127◦ 03 132◦ 21 137◦ 38 142◦ 56 148◦ 14 153◦ 31 158◦ 49 164◦ 07 169◦ 24 174◦ 42 180◦ 185◦ 17 190◦ 35 195◦ 01 201◦ 10 206◦ 36 211◦ 45 217◦ 03 222◦ 21 227◦ 38 232◦ 56 238◦ 14 243◦ 31 248◦ 49 254◦ 07 259◦ 24 264◦ 42 270◦ 275◦ 17 280◦ 35 285◦ 52 291◦ 10 296◦ 28 301◦ 45 307◦ 03 312◦ 21 317◦ 38 322◦ 56 328◦ 14 333◦ 31 338◦ 49 344◦ 07 349◦ 24
Achieved angle in
Error in
Manual mode
Auto mode
5◦ 24 10◦ 44 16◦ 01 21◦ 18 26◦ 37 31◦ 54 37◦ 15 42◦ 29 47◦ 43 53◦ 03 58◦ 23 63◦ 39 68◦ 56 74◦ 18 79◦ 34 84◦ 52 90◦ 09 95◦ 26 100◦ 40 105◦ 57 111◦ 14 116◦ 37 121◦ 53 127◦ 12 132◦ 29 137◦ 46 143◦ 02 148◦ 28 153◦ 36 159◦ 00 164◦ 16 169◦ 32 174◦ 53 180◦ 11 185◦ 26 190◦ 43 196◦ 01 201◦ 16 206◦ 36 211◦ 53 217◦ 13 222◦ 29 227◦ 47 232◦ 04 238◦ 26 243◦ 41 248◦ 56 254◦ 17 259◦ 34 264◦ 51 270◦ 11 275◦ 23 280◦ 46 285◦ 00 291◦ 18 296◦ 37 301◦ 55 307◦ 12 312◦ 28 317◦ 47 322◦ 04 328◦ 24 333◦ 44 338◦ 58 344◦ 17 349◦ 33
5◦ 24 10◦ 44 16◦ 00 21◦ 17 26◦ 34 31◦ 55 37◦ 10 42◦ 26 47◦ 49 53◦ 02 58◦ 20 63◦ 38 68◦ 55 74◦ 12 79◦ 30 84◦ 48 90◦ 06 95◦ 24 100◦ 41 106◦ 00 111◦ 17 116◦ 36 121◦ 53 127◦ 11 132◦ 26 137◦ 45 143◦ 02 – – 158◦ 55 164◦ 12 169◦ 30 174◦ 58 180◦ 06 185◦ 26 190◦ 41 196◦ 59 201◦ 16 206◦ 36 – 217◦ 09 – 227◦ 45 232◦ 03 238◦ 20 243◦ 38 248◦ 56 254◦ 12 259◦ 33 264◦ 47 270◦ 07 275◦ 23 280◦ 41 285◦ 00 291◦ 17 296◦ 42 301◦ 55 307◦ 09 312◦ 27 317◦ 46 – – 333◦ 37 338◦ 58 344◦ 16 349◦ 30
With 316 Nm load torque and 16 rpm speed, the positional accuracy was checked both in auto and manual modes of operations. Table 1 gives the values that were obtained from encoder output. At most of the locations the error was within 10 arc-min. But in few locations, it has exceeded 10 arc-min. The maximum value is
Manual mode
Auto mode
+9 +9 +8 +9 +9 +12 +8 +5 +7 +9 +8 +7 +11 +10 +10 +9 +9 +5 +5 +4 +9 +8 +9 +8 +8 +6 +14 +5 +11 +9 +8 +11 +11 +9 +8 +9 +6 +8 +8 +10 +8 +9 +8 +12 +10 +7 +10 +10 +9 +11 +6 +11 +8 +8 +9 +10 +9 +7 +9 +8 +10 +13 +9 +10 +9
+7 +9 +8 +9 +6 +10 +7 +5 +11 +6 +6 +7 +6 +5 +6 +6 +6 +7 +6 +8 +7 +8 +8 +8 +5 +7 +6 – – +6 +5 +6 +6 +6 +9 +6 +7 +6 +7 – +6 – +7 +7 +6 +7 +7 +5 +8 +5 +4 +6 +6 +8 +7 +14 +10 +6 +6 +8 – – +6 +9 +9 +6
15 arc-min. However, when the speed was reduced to 40% of full speed, the error never exceeded 10 arc-min. Specified speed of rotation is ∼0.17 rpm which is ∼10% of full speed. Hence the specified positional accuracy is met by PDS. Typical view of the selector valve is given below in Fig. 12.
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Table 2 Angular positions in almost centred condition and observations after few rotations. Alignment aimed at hole no.
1 9 17
Angular position of drive shaft to have selector plug hole almost centred to aimed hole
Observation of hole in selector plug through aimed hole
Observation of another hole in selector plug through adjacent hole in base plate
64◦ 20 330◦ 13
Almost centred Fully seen and 1 mm more movement required to get centred Fully seen and 0.5 mm more movement required to get centred Fully seen and 1 mm more movement required to get centred Fully not seen and 2 mm more movement required to get centred Almost centred Almost centred Fully seen and 1 mm more movement required to get centred
Not seen Not seen
245◦ 5 ◦
25
159 46
34
70◦ 23
42 50 58
346◦ 7 250◦ 16 164◦ 57
Not seen Not seen Not seen Not seen Not seen Not seen
Fig. 13. Front panel.
The smooth running of PDS was checked before coupling it with FFLM. The drive shaft assembly of FFLM was rotated manually and its smooth rotation was ensured before assembling with PDS. The torque was 30 Nm at dry running condition. 4.9. Positional accuracy of PDS The specified positional accuracy of the PDS at its output shaft is 10 arc-min as mentioned in Table 1. During testing, the difference between the target and the achieved positional accuracy as reported by the encoder was always less than that, or equal to 3 arc-min. 4.10. Positional accuracy of selector valve In FFLM, sodium is sucked from one of the 66 holes in base plate and pumped to the sodium capacity. The design aim is to avoid
sucking of sodium from adjacent hole on PCD 240 while aligning over a hole on PCD 260 and vice versa. To achieve this, the overall angular inaccuracies with the positional drive system should be less than 57 arc-min. During testing, command was given to align the hole in the selector plug with the theoretical location of a particular hole in the base plate. It was visually inspected from the hole in the selector plug, by seeing through the hole in which it is currently positioned and whether the other hole in the selector plug is not seen through the adjacent holes. Starting from the first hole every fourth hole (both in inner and outer PCD) was checked in this way. The results are tabulated in Table 2. The prototype positional drive system was tested for all the positions of the sub assemblies, both manually and in auto mode. The details are given in the following Table 1.
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4.11. Repeatability of observations By visual inspection, the hole in selector plug was almost centred to a particular hole in the base plate. Corresponding angular position of the drive shaft was obtained from the encoder output. In this way data was generated fro few holes as given in Table 2, given below. This data was fed as the input to PDS instead of the theoretical locations.
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totally eliminate the necessity to trip the reactor in case of rupture of clad on the fuel pin. The method described in this paper is only an intermediate step towards it. 6. Conclusion
The integral functioning of the system along with the software was tested both in manual and in Auto modes of operations. All the options given in the software were tested. The software worked satisfactorily. The interface between the software and the hardware was established properly and the system has met the intended function. Typical view of front panel is given in Fig. 13 given below.
The scheme for the determination of the failed fuel is detailed out in this paper. The system consists of failed fuel location module with positional drive system. The system was installed and commissioned. The satisfactory performance of both software and hardware were established. Proper functioning of selector valve was also checked. The test results show the feasibility of making a selector valve and control system for 66 positions of sampling tubes within the limit space available. Accurate and proper sampling will be confirmed during testing of FFLM in water and Sodium. With this, a complete system for the failed fuel identification assembly will be ready for the PFBR.
5. Discussion
Further reading
In the system developed, the positioning accuracy plays a crucial role. The effect of dilution is proportional to the positioning inaccuracy of the system. But being heavy structure (the selector valve), backlash and stiction are difficult to control at higher speeds. If the seeking time is too slow, the reactor down time will be more to locate the failed fuel sub assembly. The indexing angle (gap between two holes on the selector valve plate to sample the sodium jets from different sub assemblies) cannot be increased beyond certain level, due to the physical constraints of space within the control plug. Positioning accuracy is also limited by the encoder resolution. Interpolation (4×) is done to get more no. of pulses for the same resolution. In the old generation reactors, such as FBTR, there are no exclusive systems for identifying failed fuel sub assemblies. The methods are only trial and error methods, consuming lots of time causing reactor down time. For example, in FBTR, the method is estimating the burn up of the failed fuel assembly, by offline cover gas analysis. Then locating the exact one from the group of sub assemblies is by trial and error only. In present reactor under construction, i.e., PFBR, also the method is using industrial PC in auto or manual run mode. This also cannot totally eliminate the need for shutting down the reactor for some time. Hence advanced pro active intelligent methods with embedded systems are being developed for future commercial fast breeder reactors. These methods
Commissioning report of prototype failed fuel location module, ICD, IGCAR, 1998. Project report on development of I&C for failed fuel location module, IGCAR, 2009. Information from www.microchip.com, www.mikroelectronika.com. Proteus Software Package Manual.
4.12. Testing of software
Metta Sivaramakrishna obtained his B.Tech degree in Electronics and Communication from the Institute Jawaharlal Nehru Technological University, Hyderabad, India and joined Power Plant controls Division of IGCAR in 1992. He is working in the field of analog and digital electronics and embedded systems. He has also experience in circuit simulation and numerical simulation techniques. Chandrakant Upadhyay obtained his B.Tech degree in Electronics and Communication from the Institute of Allahabad University, Allahabad, India and joined Power Plant controls Division of IGCAR in 2008. He is working in the field of analog and digital electronics. He has experience in circuit design and analysis techniques. C.P. Nagaraj joined Power Plant Control Division of IGCAR in 1986 after graduating in Electronics and communication engineering from Visweswaraya University, Bangalore under Government of India. Mr. Nagaraj is working in circuit developments and field instrument calibrations for power and research reactors. He did on line equipment design, calibration and repairs. K. Madhusoodanan B.Sc Engineering in Electrical Engineering, from Kerala University, Thiruvananthapuram, India, joined Power Plant controls Division of IGCAR 1982. Presently he is heading the division and is specialist in the field of instrumentation and control systems of nuclear reactors. He has worked on several process related systems, circuits and techniques and produced several papers in national and international seminars and symposiums. He has travelled to several reactor sites and got trained in maintenance, calibration and repairs.
Contents lists available at ScienceDirect
Nuclear Engineering and Design journal homepage: www.elsevier.com/locate/nucengdes
Online embedded integrated scanning system for identifying failed fuel sub assemblies in fast reactor Metta Sivaramakrishna ∗ , Chandrakant Upadhyay, C.P. Nagaraj, K. Madhusoodanan Power Plant Controls Division, Indira Gandhi Centre for Atomic Research, Kalpakkam 603102, Tamilnadu, India
a r t i c l e
i n f o
Article history: Received 28 September 2010 Received in revised form 11 April 2011 Accepted 14 April 2011
a b s t r a c t The physical integrity of the fuel in fast reactor is of utmost concern for the healthiness of the reactor and operating people. Hence details of the failed fuel location in the core shall be determined at the earliest, to minimize reactor down time and radiation exposure. In the present reactor under construction, i.e., 500 MWe Prototype Fast Breeder Reactor (PFBR), a system for failed fuel identification, was proposed. The system follows a novel scheme to locate the failed fuel using failed fuel location module along with necessary instrumentation and control. This paper details out the scheme followed. © 2011 Elsevier B.V. All rights reserved.
1. Introduction
2. Description
MOX (mixed oxide) fuel sub assemblies are fabricated through the normal powder metallurgy route of powder compaction and sintering. The control of dimensions, quality of clad at each and every stage is essential to avoid any defects in the fabrication. Fuel pins are provided with a leak-tight metal cladding for containment of the fission products of the nuclear reaction. Despite all this, cladding tube failures can happen. In case of fuel clad failure, the fuel might contaminate the coolant, with potential consequences. In view of the above, it is necessary that there should be a system designed for detection and identification of failed fuel subassembly (FSA). This is to be done at the earliest, after detecting the presence of failed fuel, so that it can be removed from the core. A system is developed towards this. The salient feature of this to have single integrated solution for various combinations of inputs and interlocks. In the system developed, the positioning accuracy plays a crucial role. The effect of dilution is proportional to the positioning inaccuracy of the system. But, being heavy structure (the selector valve), backlash and stiction are difficult to control at higher speeds. If the seeking time is too slow, the reactor down time will be more to locate the failed fuel sub assembly. The indexing angle (gap between two holes on the selector valve plate to sample the sodium jets from different sub assemblies) cannot be increased beyond certain level, due to the physical constraints of space within the control plug. Positioning accuracy is also limited by the encoder resolution. This paper presents the details of design, features of the system.
Fuel failures like pinholes and micro fissures, which release only gaseous fission products is detected by Gaseous Fission Product Detection (GFPD) system. In case of direct contact between fuel and coolant i.e., wet rupture, it results in release of both gaseous and solid fission products (140 Ba, 140 La, 134 Cs, 137 Cs, 95 Zr radionuclides, etc.) released in to the coolant that can be detected by means of DN precursors in sodium coolant. Upon detection of failed fuel, in order to locate the failed Fuel Sub Assembly (FSA), around 200 subassemblies are to be scanned. This is done with three numbers of Failed Fuel Location Modules (FFLMs) operating simultaneously, each catering to 66 subassemblies. Failure of fuel pin in central FSA is detected by indirect method and is inferred when there is no indication from any other FSA. Sodium sampling sleeves, concentric over each thermocouple tube sheath, are positioned above the top of each FSA. The sampling tubes from the sleeves are routed to the base plate of the selector valve of FFLM. Selector valve with the help of motor drive, positions the outlet tube to any one of the 66 inlet sampling tubes. An optical encoder attached to the shaft of the selector valve monitors the position of the selector valve. A DC conduction pump is used to pump the sodium from the outlet of the selected assembly to the sodium capacity (refer Fig. 1 given below). An electro magnetic (EM) flow meter is provided at the outlet of the sodium capacity to monitor the flow of sodium. Neutron detectors are provided around the capacity in moderator block, to detect any neutron flux in the sodium sample, due to the fission precursors, which are delayed neutron emitters. The sampled sodium is returned to the pool. In order to reduce temperature difference between hot pool sodium and the sodium returning from sampling tube and to avoid high temperature at detector location,
∗ Corresponding author. Tel.: +91 44 27480500x22491; fax: +91 4427480348. E-mail address: [email protected] (M. Sivaramakrishna). 0029-5493/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.nucengdes.2011.04.030
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Fig. 1. General mechanical arrangement of failed fuel location module.
the sodium capacity is wrapped with thermal insulation. Heaters are provided to maintain a minimum temperature of 423 K (150 ◦ C) for the sodium in the capacity and sampling pipe. Temperature is monitored on sodium capacity, flow meter, sodium-piping, near seals and in moderator. Lead is provided as gamma shield around the capacity to reduce gamma activity. Drive shaft of the selector valve is rotated by a Positional Drive System (PDS) with an encoder. The PDS comprises of permanent magnet DC servo motor, servo controller and encoder. Rotation of the selector valve permits sequential monitoring of each FSA outlet for the presence of delayed neutrons due to failure of fuel pin. Graphical User Interface (GUI) and PDS Control software are designed to operate in sequential mode and in random mode to specify the angle of the fuel sub assembly (FSA) to reach (refer Fig. 2 given below). Under normal conditions, the system is operated once in a week, otherwise the system is maintained in poised state for startup. When the reactor is tripped on the wet rupture type of fuel failure, the reactor is restarted and operated at low powers to identify the location of the failed FSA using FFLM. Total scanning time is approx. 8 h.
Fig. 2. Graphics (GUI).
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3. Theory of operation The basic computation is done using micro controller. The I/O operation was implemented using operational amplifiers, sampleand-hold amplifiers, buffers, displays and output contacts. DC reference voltage source is used to simulate some analog inputs. Single board micro controller based PCB is designed for control and processing the inputs and outputs. The required power supply for the processor is derived from 48 V with isolation. Analog inputs are also taken with 3 port isolation. Digital inputs are taken with opto isolation. Output contacts are given in the form of voltage free contacts. Alarm and error messages are displayed in the local display and also given to data highway. All the data can be stored locally in the memory for 30 min. Test provision is given, which is enabled on command from control room in the form test authorization contact. All the inputs can be varied under this test mode simulating the various combinations of field conditions. All the indications are available locally. Basic code is written in Mishra C and is compiled and stored in the EPROM. The circuit was tested for test inputs using the potentiometer, relays and mode button.
Fig. 3. Velocity profile.
It is a control system to position the selector valve at a required position. Basically it is a closed loop system comprised of motor, driver amplifier and encoder to get feedback. The above system ensures proper positioning of failed fuel location module. From micro controller, the input is given to driver amplifier which is fed to motor to run it. An incremental encoder mounted on the shaft keeps giving pulses which are used to know the angle by which the shaft has rotated.
4. Working principle
4.2. Motor
4.1. Positional drive system
The starting torque is 2.1 Nm at 4000 rpm with Planetary Gear head. The reduction ratio is 100:1 and output torque is 63 Nm at input speed of 4000 rpm. It is provided with Integral Tacho feedback for speed. It needs 310 V dc voltage and its operating current range is 7.4 A. The motor driver amplifier used is L6203.
Positional drive system is a closed loop system. It does the following actions: 1. Accepting an order that defines the desired result, i.e., location of the sub assembly from which the sodium is to be sampled 2. Determining the present conditions by some method of feedback 3. Comparing the desired result with the present conditions and obtaining a difference or an error signal 4. Issuing a correcting order (the error signal) that will properly change the existing conditions to the desired result 5. Obeying the correcting order
4.2.1. Driver IC L6203 For a given target position, the location module is to be positioned at that target. It has to reach its target smoothly i.e., it has to rotate with acceleration for certain angle and then rotate with constant velocity and then rotate with constant deceleration. The velocity profile should be as shown in the following Fig. 3.
Fig. 4. Pulse Sequence.
Fig. 5. Flip flop.
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Fig. 6. PCB-design for encoder interfacing.
4.2.2. Importance of trapezoidal profile There are also other velocity profiles such as sin graph profile, triangular profiles, etc., but the trapezoidal profile (like some typical profiles) is used more for industrial applications and other reason is that when it reaches the maximum velocity it continues with that velocity in trapezoidal profile where as in some other profiles there will be sudden deceleration which may cause jerk in motor. By the time the sampling circuit reaches the required sub assembly its velocity will be zero. This ensures less overshoot. 4.2.3. Generation of profile The velocity profile is divided in to equal samples. For suppose, the maximum velocity is V, it is divided in to some n samples and then each time constant (V/n) is added to reach V. These additions are of n times. Thus acceleration is achieved. • For constant velocity case, the same V is given until required angle is reached. • For deceleration, the V is subtracted by (V/n) so that it is finally reached to zero velocity. • Thus the trapezoidal velocity profile is achieved. 4.2.4. PWM’s duty cycle vs velocity of dc motor PWM duty cycle is proportional to the velocity of the dc motor. This linear equation of duty cycle and velocity is know by taking the samples, for example, for certain duty cycle there will be certain velocity and samples are to be taken. 4.2.5. Usage of intervals At every interval, motor is given increments of the constant value (V/n) to reach V after some samples. 4.3. Incremental encoder It is a position encoder mounted on the shaft to give pulses from three encoder channels. When travelling in forward direction the
channels A and B give pulses. But A leads B. when travelling in backward direction B leads A. It is explained in the following Fig. 4. The flip-flop (Fig. 5 shown below) circuit makes the pulses coming from encoder to following pattern (up count and down count) which are then sent to TMR0 TMR1 to calculate the angle by which the motor has rotated. 4.4. Method to count pulses coming from flip flop circuit The pulses coming from flip flop are fed to TMR modules source pins. TMR0 source pin RA4 and TMR1 source pin Rc1/T1CLK. The registers TMR0L:TMR0H and TMR1L:TMR1H increment their value on each raising of pulse at source pins. Subtracting TMR1 from TMR0 gives number of pulses given out by the encoder. • If rotated clockwise TMR0 increments and TMR1 value remains constant • If rotated anticlockwise TMR1 value increments and TMR0 value remains constant. 4.4.1. Calculation of angle The angle rotated will be (TMR0 − TMR1)/(no. of pulses given by encoder per revolution). The pulses given by encoder per revolution is constant for a incremental encoder. 4.4.2. Calculation of velocity First store the initial difference of TMR0 and TMR1 at time t = 0, then again store the difference of timers at some time t, then the velocity will be the difference of two stored values divided by time t. The picture (Fig. 6) given below shows the complete interfacing of the encoder to TMR modules and to count the number of pulses thereby the angle rotated by the motor. This completes the feedback system. But any error in the feed back should be updated which can be done by industrial application called PID CONTROL (proportional–integrative–derivative) control.
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Interrupt raised For giving the angle by which the valve shall rotate, i.e “angr”
Angle
yes
Then accelerate
no Read pulses from encoder and calculate present angle and v.
If angle >angr /8 && yes Angle
If error(v!=vreq)
no If angle >angr
yes
Calculate pid
no
yes
If angle >angr*7 /8 && angle
no
Add output error to velocity
End of interrupt service subroune
yes Disable mer2 so that no interrupt can be raised
Then constant velocity
Then decelerate
Read pulses from encoder and calculate present angle and v
Read pulses from encoder and calculate present angle If error(v!=vreq)
If error(v!=vreq) no
no
. End of isr
Calculate pid yes Add output error to vel
End of isr
yes
Calculate pid
Add output error to vel
Fig. 7. Flow chart of the scheme.
The following figure (Fig. 7) shows the flowchart which explains the generation of profile, current position and error calculations. 4.5. Explanation of algorithm When the interrupt is raised, the velocity is added to constant value so that the motor accelerates. Then encoder pulses are decoded to know the present angle and also they are subtracted from the previous ones to know the velocity in the next phase. If motor did not attain the velocity required, the error is added to the next velocity. This ensures that it is able to traverse the required angular position. The present angle is compared to the “angle required/8”. If this angle is not reached, then motor has to travel with the constant velocity. The constant velocity is the maximum velocity attained in the previous acceleration part. Then again error is calculated and the velocity to be given is corrected so that it attains the required angle
in a given time period. Then present angle is compared with the “angle required/8” and “angle × 7/8”. If “angle × 7/8” is reached, then the motor is made to decelerate with the constant value that was used into the acceleration part. This deceleration continues until the motor reaches the required angle. 4.6. Interfacing keypad to micro controller A keypad is attached to micro controller. This gets the inputs such as mode in which user wants to move the module and to which sub assembly he wants to move. The keypad is interfaced only to test the board and components i.e., in test mode only, otherwise, the input is taken through RS232 or TCP/IP. Keypad has 16 buttons (as given in the following Fig. 8) comprising 4 rows and 4 columns. Symbols on a row are connected by a single wire as well symbols on single column are connected by a single wire. Wires from rows and columns are connected to I/O
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4.7. Implementation of pump control 4.7.1. Inputs • Flow meter output • Temperature output • Heater on input 4.7.2. Outputs • On/off heater • On/off pump power supply
Fig. 8. Keypad.
ports. The rows are connected as output and are simultaneously given on off condition i.e., when one row is off other rows are on. The wires from columns are connected to +5 V (with a current limiting resistor of 1 k) and also to the ports as inputs. When a row is given off condition that is 0 V, the columns are checked and if any input from column is off then button corresponding to the row and column is switched on.
A DC conduction pump is provided for giving the impetus for the sampled sodium jet to reach the detector location, where the activity due to the rupture of the clad in the fuel pin is detected. A high current low voltage DC power supply is provided for creating the required electrical flux in the pump. To assure the required flow in the sampling path, a flow meter is connected in the outlet where the sampled sodium is brought back to the hot pool. Throughout the sampling tubing, heaters are provided to ensure the uniformity of temperature of sodium. During the failed fuel identification process
Fig. 9. Circuit for initialization of thermocouple.
Fig. 10. Schematic of FFLM Positional Drive System.
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Fig. 11. GUI of the system and the drive.
and rotation of the selector valve mechanism, the pump needs to be protected from cavitation, thermal swiping. Hence following protections are provided. If the temp is above the set temperature, the heater is to be switched off. If the temp is below a set value then heater is to be switched on and the pump is to be switched off. If the voltage and current are high then pump is to be switched off. If flow is below the set value, then switch off pump power supply. If flow rate is below a set value under pump on condition, switch off the power supply. There are 12 thermocouples located at different points to get temperature. The thermocouple used is of k type which has sensitivity of 41 V/◦ C. The cold junction temperature for the thermocouple has to be compensated. Other problems of linearization have to be dealt with. Thermocouples are interfaced to AD595 instrumental amplifier and then the conditioned outputs are taken to microcontroller. We have to initialize ADCON registers as per the configuration. The temperature is displayed in the LCD as given in the figure (Fig. 9) given below. A prototype model as given above is designed and tested. The heart of the prototype system (given above in Fig. 10) is the mechanism that is actuated by a DC servomotor with speed feed back from a tachometer. The speed of the motor is reduced used gearing and then the motion is transferred to the output shaft. A brake is used to arrest the output shaft. The position of the output shaft is measured with a rotary incremental encoder. 4.8. Experimental validation The entire system is controlled by a PC based system. The PC actuates the DC servomotor through a servo amplifier. The servo amplifier controls the current in the DC servomotor depending upon the set speed and tachometric feedback. The PC reads the position of the output shaft from the encoder and commands the servo amplifier as required. The prototype system that was developed is shown in the figure (Fig. 11) given below.
Fig. 12. Selector valve assembly.
The brake is operated through an input/output module that is connected to the PC through a serial port. Other inputs and outputs are provided for interlocks with other systems as required.
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Table 1 Positional accuracy of PDS. Location no.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66
Target angle
5◦ 17 10◦ 35 15◦ 52 21◦ 10 26◦ 28 31◦ 45 37◦ 03 42◦ 21 47◦ 38 52◦ 56 58◦ 14 63◦ 31 68◦ 49 74◦ 07 79◦ 24 84◦ 42 90◦ 95◦ 17 100◦ 35 105◦ 52 111◦ 10 116◦ 28 121◦ 45 127◦ 03 132◦ 21 137◦ 38 142◦ 56 148◦ 14 153◦ 31 158◦ 49 164◦ 07 169◦ 24 174◦ 42 180◦ 185◦ 17 190◦ 35 195◦ 01 201◦ 10 206◦ 36 211◦ 45 217◦ 03 222◦ 21 227◦ 38 232◦ 56 238◦ 14 243◦ 31 248◦ 49 254◦ 07 259◦ 24 264◦ 42 270◦ 275◦ 17 280◦ 35 285◦ 52 291◦ 10 296◦ 28 301◦ 45 307◦ 03 312◦ 21 317◦ 38 322◦ 56 328◦ 14 333◦ 31 338◦ 49 344◦ 07 349◦ 24
Achieved angle in
Error in
Manual mode
Auto mode
5◦ 24 10◦ 44 16◦ 01 21◦ 18 26◦ 37 31◦ 54 37◦ 15 42◦ 29 47◦ 43 53◦ 03 58◦ 23 63◦ 39 68◦ 56 74◦ 18 79◦ 34 84◦ 52 90◦ 09 95◦ 26 100◦ 40 105◦ 57 111◦ 14 116◦ 37 121◦ 53 127◦ 12 132◦ 29 137◦ 46 143◦ 02 148◦ 28 153◦ 36 159◦ 00 164◦ 16 169◦ 32 174◦ 53 180◦ 11 185◦ 26 190◦ 43 196◦ 01 201◦ 16 206◦ 36 211◦ 53 217◦ 13 222◦ 29 227◦ 47 232◦ 04 238◦ 26 243◦ 41 248◦ 56 254◦ 17 259◦ 34 264◦ 51 270◦ 11 275◦ 23 280◦ 46 285◦ 00 291◦ 18 296◦ 37 301◦ 55 307◦ 12 312◦ 28 317◦ 47 322◦ 04 328◦ 24 333◦ 44 338◦ 58 344◦ 17 349◦ 33
5◦ 24 10◦ 44 16◦ 00 21◦ 17 26◦ 34 31◦ 55 37◦ 10 42◦ 26 47◦ 49 53◦ 02 58◦ 20 63◦ 38 68◦ 55 74◦ 12 79◦ 30 84◦ 48 90◦ 06 95◦ 24 100◦ 41 106◦ 00 111◦ 17 116◦ 36 121◦ 53 127◦ 11 132◦ 26 137◦ 45 143◦ 02 – – 158◦ 55 164◦ 12 169◦ 30 174◦ 58 180◦ 06 185◦ 26 190◦ 41 196◦ 59 201◦ 16 206◦ 36 – 217◦ 09 – 227◦ 45 232◦ 03 238◦ 20 243◦ 38 248◦ 56 254◦ 12 259◦ 33 264◦ 47 270◦ 07 275◦ 23 280◦ 41 285◦ 00 291◦ 17 296◦ 42 301◦ 55 307◦ 09 312◦ 27 317◦ 46 – – 333◦ 37 338◦ 58 344◦ 16 349◦ 30
With 316 Nm load torque and 16 rpm speed, the positional accuracy was checked both in auto and manual modes of operations. Table 1 gives the values that were obtained from encoder output. At most of the locations the error was within 10 arc-min. But in few locations, it has exceeded 10 arc-min. The maximum value is
Manual mode
Auto mode
+9 +9 +8 +9 +9 +12 +8 +5 +7 +9 +8 +7 +11 +10 +10 +9 +9 +5 +5 +4 +9 +8 +9 +8 +8 +6 +14 +5 +11 +9 +8 +11 +11 +9 +8 +9 +6 +8 +8 +10 +8 +9 +8 +12 +10 +7 +10 +10 +9 +11 +6 +11 +8 +8 +9 +10 +9 +7 +9 +8 +10 +13 +9 +10 +9
+7 +9 +8 +9 +6 +10 +7 +5 +11 +6 +6 +7 +6 +5 +6 +6 +6 +7 +6 +8 +7 +8 +8 +8 +5 +7 +6 – – +6 +5 +6 +6 +6 +9 +6 +7 +6 +7 – +6 – +7 +7 +6 +7 +7 +5 +8 +5 +4 +6 +6 +8 +7 +14 +10 +6 +6 +8 – – +6 +9 +9 +6
15 arc-min. However, when the speed was reduced to 40% of full speed, the error never exceeded 10 arc-min. Specified speed of rotation is ∼0.17 rpm which is ∼10% of full speed. Hence the specified positional accuracy is met by PDS. Typical view of the selector valve is given below in Fig. 12.
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Table 2 Angular positions in almost centred condition and observations after few rotations. Alignment aimed at hole no.
1 9 17
Angular position of drive shaft to have selector plug hole almost centred to aimed hole
Observation of hole in selector plug through aimed hole
Observation of another hole in selector plug through adjacent hole in base plate
64◦ 20 330◦ 13
Almost centred Fully seen and 1 mm more movement required to get centred Fully seen and 0.5 mm more movement required to get centred Fully seen and 1 mm more movement required to get centred Fully not seen and 2 mm more movement required to get centred Almost centred Almost centred Fully seen and 1 mm more movement required to get centred
Not seen Not seen
245◦ 5 ◦
25
159 46
34
70◦ 23
42 50 58
346◦ 7 250◦ 16 164◦ 57
Not seen Not seen Not seen Not seen Not seen Not seen
Fig. 13. Front panel.
The smooth running of PDS was checked before coupling it with FFLM. The drive shaft assembly of FFLM was rotated manually and its smooth rotation was ensured before assembling with PDS. The torque was 30 Nm at dry running condition. 4.9. Positional accuracy of PDS The specified positional accuracy of the PDS at its output shaft is 10 arc-min as mentioned in Table 1. During testing, the difference between the target and the achieved positional accuracy as reported by the encoder was always less than that, or equal to 3 arc-min. 4.10. Positional accuracy of selector valve In FFLM, sodium is sucked from one of the 66 holes in base plate and pumped to the sodium capacity. The design aim is to avoid
sucking of sodium from adjacent hole on PCD 240 while aligning over a hole on PCD 260 and vice versa. To achieve this, the overall angular inaccuracies with the positional drive system should be less than 57 arc-min. During testing, command was given to align the hole in the selector plug with the theoretical location of a particular hole in the base plate. It was visually inspected from the hole in the selector plug, by seeing through the hole in which it is currently positioned and whether the other hole in the selector plug is not seen through the adjacent holes. Starting from the first hole every fourth hole (both in inner and outer PCD) was checked in this way. The results are tabulated in Table 2. The prototype positional drive system was tested for all the positions of the sub assemblies, both manually and in auto mode. The details are given in the following Table 1.
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4.11. Repeatability of observations By visual inspection, the hole in selector plug was almost centred to a particular hole in the base plate. Corresponding angular position of the drive shaft was obtained from the encoder output. In this way data was generated fro few holes as given in Table 2, given below. This data was fed as the input to PDS instead of the theoretical locations.
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totally eliminate the necessity to trip the reactor in case of rupture of clad on the fuel pin. The method described in this paper is only an intermediate step towards it. 6. Conclusion
The integral functioning of the system along with the software was tested both in manual and in Auto modes of operations. All the options given in the software were tested. The software worked satisfactorily. The interface between the software and the hardware was established properly and the system has met the intended function. Typical view of front panel is given in Fig. 13 given below.
The scheme for the determination of the failed fuel is detailed out in this paper. The system consists of failed fuel location module with positional drive system. The system was installed and commissioned. The satisfactory performance of both software and hardware were established. Proper functioning of selector valve was also checked. The test results show the feasibility of making a selector valve and control system for 66 positions of sampling tubes within the limit space available. Accurate and proper sampling will be confirmed during testing of FFLM in water and Sodium. With this, a complete system for the failed fuel identification assembly will be ready for the PFBR.
5. Discussion
Further reading
In the system developed, the positioning accuracy plays a crucial role. The effect of dilution is proportional to the positioning inaccuracy of the system. But being heavy structure (the selector valve), backlash and stiction are difficult to control at higher speeds. If the seeking time is too slow, the reactor down time will be more to locate the failed fuel sub assembly. The indexing angle (gap between two holes on the selector valve plate to sample the sodium jets from different sub assemblies) cannot be increased beyond certain level, due to the physical constraints of space within the control plug. Positioning accuracy is also limited by the encoder resolution. Interpolation (4×) is done to get more no. of pulses for the same resolution. In the old generation reactors, such as FBTR, there are no exclusive systems for identifying failed fuel sub assemblies. The methods are only trial and error methods, consuming lots of time causing reactor down time. For example, in FBTR, the method is estimating the burn up of the failed fuel assembly, by offline cover gas analysis. Then locating the exact one from the group of sub assemblies is by trial and error only. In present reactor under construction, i.e., PFBR, also the method is using industrial PC in auto or manual run mode. This also cannot totally eliminate the need for shutting down the reactor for some time. Hence advanced pro active intelligent methods with embedded systems are being developed for future commercial fast breeder reactors. These methods
Commissioning report of prototype failed fuel location module, ICD, IGCAR, 1998. Project report on development of I&C for failed fuel location module, IGCAR, 2009. Information from www.microchip.com, www.mikroelectronika.com. Proteus Software Package Manual.
4.12. Testing of software
Metta Sivaramakrishna obtained his B.Tech degree in Electronics and Communication from the Institute Jawaharlal Nehru Technological University, Hyderabad, India and joined Power Plant controls Division of IGCAR in 1992. He is working in the field of analog and digital electronics and embedded systems. He has also experience in circuit simulation and numerical simulation techniques. Chandrakant Upadhyay obtained his B.Tech degree in Electronics and Communication from the Institute of Allahabad University, Allahabad, India and joined Power Plant controls Division of IGCAR in 2008. He is working in the field of analog and digital electronics. He has experience in circuit design and analysis techniques. C.P. Nagaraj joined Power Plant Control Division of IGCAR in 1986 after graduating in Electronics and communication engineering from Visweswaraya University, Bangalore under Government of India. Mr. Nagaraj is working in circuit developments and field instrument calibrations for power and research reactors. He did on line equipment design, calibration and repairs. K. Madhusoodanan B.Sc Engineering in Electrical Engineering, from Kerala University, Thiruvananthapuram, India, joined Power Plant controls Division of IGCAR 1982. Presently he is heading the division and is specialist in the field of instrumentation and control systems of nuclear reactors. He has worked on several process related systems, circuits and techniques and produced several papers in national and international seminars and symposiums. He has travelled to several reactor sites and got trained in maintenance, calibration and repairs.