OUTLINE EXECUTIVE SUMMARY Continuous Type Oil Level Sensors for the Dashpots of Control and Safety Rod Drive Mechanisms in Prototype Fast Breeder Reactor Pulsating type high precision oil level senso
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OUTLINE EXECUTIVE SUMMARY Continuous Type Oil Level Sensors for the Dashpots of Control and Safety Rod Drive Mechanisms in Prototype Fast Breeder Reactor Pulsating type high precision oil level senso

The development includes associated pulse handling data processing and presentation devices for real time monitoring of oil levels in the dashpots of Control and Safety Rod Drive Mechanisms CSRDMs in PFBR The sensors provide continuous indication of

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OUTLINE EXECUTIVE SUMMARY Continuous Type Oil Level Sensors for the Dashpots of Control and Safety Rod Drive Mechanisms in Prototype Fast Breeder Reactor Pulsating type high precision oil level senso




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Presentation on theme: "OUTLINE EXECUTIVE SUMMARY Continuous Type Oil Level Sensors for the Dashpots of Control and Safety Rod Drive Mechanisms in Prototype Fast Breeder Reactor Pulsating type high precision oil level senso"— Presentation transcript:


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OUTLINE EXECUTIVE SUMMARY Continuous Type Oil Level Sensors for the Dashpots of Control and Safety Rod Drive Mechanisms in Prototype Fast Breeder Reactor Pulsating type high precision oil level sensors have been developed from concept to industrial grade products entirely through in-house efforts in IGCAR. The development includes associated pulse handling, data processing and presentation devices for real time monitoring of oil levels in the dashpots of Control and Safety Rod Drive Mechanisms (CSRDMs) in PFBR. The sensors provide continuous indication of oil levels in the

range 0 60 mm within the active sensing region. These will capture rapidly the sudden change in oil level in the event of scram action of the control rods, satisfying the major purpose for which the level sensors have been developed. Real time measurement with high precision may also enable monitoring of onset of oil leak, if any, during normal operation of the reactor. Oil level is sensed by sensitive monitoring of small shift in capacitance of a vertically mounted specially designed capacitive device, caused by change in oil level. An assembly of uniformly spaced multiple number of

rectangular stainless steel plates is the capacitor assembly whose capacitance changes on account of change in fractions of two dielectric media, namely oil and air (or any inert gas), within the electrode gaps. The capacitor is in the timing circuit of a compact logic gate oscillator and, hence, shift in digital pulse frequency at the output of the oscillator is directly related to change in oil level. Photograph of a set of nine sensors is shown in Figure 1. The oil level sensor and the dielectric type thermal sensor are capacitive components in specially designed low power consuming logic

gate oscillator circuits which are embedded in the probe head and require only 5V DC supply from an external source. The trains of rectangular pulses at the outputs of the level and thermal sensors from a given probe are processed by two independent signal processing and data presentation systems (System-A and System-B) (Fig. 2). Each in-house designed and made stand-alone embedded processor in System-A performs the following functions: (i) simultaneous pulse counting in six channels for determination of pulse frequencies at the outputs of level and thermal sensors from three probes, (ii)

evaluates quadratic equations for conversion of pulse frequencies to heights of oil level from the tips of the level sensing electrodes after neutralisation of thermal effect, and (iii) displays and stores oil level data at two seconds interval. The other laboratory made system, System-B, on the other hand, is a computer based data acquisition, processing and presentation unit with built-in user friendly features in addition to those available with System-A. Serial communication with a computer is established through an in-house developed 18- channel embedded pulse handling unit that receives

pulses from nine probes simultaneously and count them for the preset duration. It transmits pulse count data to the computer for further processing, display and storage. The dedicated application software enables real time level visualisation, graphic presentation of level data as a function of time, on-line availability of stored data for last 24 hours in 96 time segments for quick review and analysis, easy navigation between probes and time segments, zooming for ascertaining minor level shifts etc. The pulse frequencies are measured at 5 mm interval over the full range of 0 60 mm along the

entire oil level sensing span. Level height from the tip of the sensing electrodes (h) in millimeter Vs. frequency (f) in kHz are numerically fitted to yield a quadratic equation, [ h = a.f + b.f + c ], which is used later in the system software to convert on-line the output frequencies to oil level heights during operation of the level sensor. Such calibration equations are sensor specific and, hence, are obtained separately for every probe. An example of numerically fitted calibration data is shown in the Figure 3. Fig. 1 : Oil level sensors for the dashpots of CRDMs in PFBR Fig. 2 :

In-house developed two independent systems for pulse handling, data processing and presentation for real time applications of the sensors: SYSTEM-A (left) and SYSTEM-B (right) 212 TECHNOLOGY-22
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High performance of the sensors stems mainly from direct generation of primary signal in the digital domain. The oil level influences the oscillation frequency of the specially designed very low power consuming oscillator embedded right on top of the probe head. The oscillator oscillates between logic states '0' and '1', resulting in rectangular pulses of 5 V amplitude at its output,

which can easily be driven over long distances. At room temperature the standard deviation of level data, measured after transmission of the primary signals by about 100 meters, is less than 0.1 mm. Stability of signal output has also been satisfactory for continuous operation over eight hours each time on several days by placing the level sensor in contact with hot oil within a top loading furnace controlled at 100 C. Long term structural integrity is ensured by partial embedment of the electrode structure within a resin, use of multiple fasteners and spacers of insulating materials within a

double cylindrical probe covers of teflon and stainless steel. For mounting on the dashpots, the teflon gasket sealed carbon steel locknut arrangement will provide leak tight and stable housing. All components selected for mechanical construction are suitable for continuous operation at elevated temperatures. The rigidity of the electrode structure is adequate for withstanding the turbulence of oil pool within the dashpot during fall of the control rod on scram. Fig. 3 : Pulse frequency to oil level relationship for a typical dashpot oil level sensor. Sensors are designed to operate with hot

oil. The embedded thermal sensor at the probe head permits neutralisation of the overall thermal effect through incorporation of our own pulsating type thermal sensor in each level probe. Minor thermal effect on a typical sensor output for a given oil level can be seen in the time dependent measurement with the imposed thermal profile as recorded by the built-in thermal sensor. Slightly negative slopes (df / df ), derived from the straight line fitted thermal sensor output (f ) vs. the level sensor output (f) are established first and then used later during real time measurements for on-line

conversion of the level sensor output frequency at temperature t (f ) to that at the calibration temperature (f ) before application of the calibration relationship for determination of the height of oil level in millimeter. These slopes are determined for every probe. lt tl A set of equally spaced and vertically mounted rectangular electrodes of the specially constructed parallel plate capacitor assembly acts as the level sensor. At any level of oil within the sensing region, the gaps between the electrodes are filled partially by the oil and the rest by the gaseous medium (air or argon)

above the oil level. Because of significant difference in dielectric permeability between the gaseous medium and the oil, the effective permeability, and hence the capacitance of the level sensing capacitor assembly, is a function of oil level. This assembly being the capacitive component ( C) in the timing circuit of the R-C-oscillator, the time constant (R.C) varies with change in oil level and, hence, the output pulse frequency (which is proportional to 1/RC) is thus a function of oil level. Besides development of the oil level sensors for a reactor as mentioned, the simplified generic

approach is very effective for high precision level sensing of any non-conducting liquid. Such level sensors have also been developed to monitor CCl and silicon oil levels in the process tanks of a sol-gel facility for preparation of fuel micro-spheres. This development has also paved the way for realisation of sensitive and reliable differential pressure sensors for atmosphere control applications. Development notes and technical brochures were prepared for restricted circulation among those concerned with instrumentation in reactors. Further inquiries: Shri B. Saha, Innovative

Instrumentation Section Electronics and Instrumentation Group, IGCAR, e-mail: saha@igcar.gov.in 213 NEUTRALISATION OF MINOR TEMPERATURE EFFECT PERFORMANCE AND RUGGEDNESS BRIEF DESCRIPTION OF THEORETICAL BACKGROUND ACHIEVEMENT PUBLICATIONS ARISING OUT OF THIS STUDY AND RELATED WORK TECHNOLOGY-22