ML19341C529
| ML19341C529 | |
| Person / Time | |
|---|---|
| Site: | 05000192 |
| Issue date: | 01/31/1981 |
| From: | TEXAS, UNIV. OF, AUSTIN, TX |
| To: | |
| References | |
| NUDOCS 8103030697 | |
| Download: ML19341C529 (15) | |
Text
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- 6. INSTRl2tENTATION AND CONTROL 6.1. CENERAL DESCRIPTION The complete operating and protection system for the TRICA reactor is contained in an operating console similar to that shown in Fig. 6-1. The console cabinet is 59 in. long by 22 in, deep by 50 in high. Because of its profile, the console is positioned so that the operator can easily observe both the reactor experimental area and the console instruments.
The electronic modules, logic system, and relays are accessible from the back of the console or by removing individual panel sections. All meters,
, rod controls, and recorders are placed for optimum readability and accessi-bility. The inportant parameters of log and linear power over the entire range are displayed on the same 11-in. chart paper of a dual-pen recorder.
The log power record allows later determination of the range used for the linear power channel so that both accurate indication and recording of reactor power is obtained. Care has been used in the design of the console to display those variables and annunciate the conditions that are important and necessary for reactor operation and safety without confusing this informa-tion with nonessential auxiliary information.
A block diagram showing the individual safety and control circuit con-figurations Jn the different operating modes are shown in Fig. 6-2. Detec-tors and rod drives are shown to present a complete system diagram.
6.2. NUCLEAR CpANNELS The neutron monitoring channels consist of a log count-rate source range c5 nnel, intermediate range log channel, one Ifnear safety channel, and a multirange linear safety channel used for accurate power measurement.
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The log count-rate source channel consists of a fission chamber, pulse amplifier, and log count-rate circuit. The operation of the count-rate channcI Is displayed on a meter in decades from 1 to 10,000 and is output to an audio speaker. The output meter contair.s a relay to provide a source interlock signal to the rod control circuit that prevents rod move-ment unless the source count rate is above a preset level. An intermediate range log power channel monitors the flux generated current of a compensated ionization chamber. A log circuit converts the chan.ber current to millivolts that are recorded on one channel of a dual pen recorder, power indication is recorded from 3 x 10- 5 to 3 x 10 , ,, A period measuring circuit is connected to the recorder pen motion through a dual slide wire. The period is displayed on a meter with a relay to pro-vide a scram signal for periods of a preset value. The period meter range is from -40 secs to +7 secs. One safety channel consists of an uncompensated ionization chamber, amplifier, and percent power meter indication that operates on a single range from 0 to 110% of full power. A meter relay provides a scram signal for a preset percent power level. A multirange safety channel provides a monitor of reactor power level on 13 power ranges. The channel consists of a compensated ionization chamber, calibrated range conversion switch. and output indication on one channel of a dual pen recorder. Movement of the recorder pen provides a scram signal at approximately 110% of each power range scale. Pen motion on a dual slide . wire also provides a correction signal for application of an automatic steady-state regulating rod control system. In the pulse mode, only one nuclear channel, the compensated ionization chamber is active. The output of the ci. amber is modified to measure peak power and total energy release which is recorded on one channel of the dual pen recorder. A scram signal is provided by the recorder pen movement at full scale. 6-4
i All the outputs of the nuclear measuring channels are at eye level to an operator at the console. The startup channel and single range safety channel are to the Icf t and right, respectively, of the linear and log out-puts which are displayed on the dual channel recorder. I All nuclear channels include a means of calibrating and testing the channel and a means of testing the trip level. These calibrate and test circuits are built into the console as part of each channel. 6.3. TEMPERATURE CHANNEL AND WATER MONITOR CHANNEL One fuel temperature channel with a meter readout and scram is provided in both modes of reactor operation. The fuel temperature channel is mounted in the rear of the console. The channel is provided with a TEST switch located on the front panel to allow checkout of the fuel temperature scram circuits. A second fuel temperature meter readout and scram are provided as part of the water monitor channel. The meter output is switch selectable
; and displayed on the front panel.
The water monitor circuits consist of several separate circuits. une circuit monitors water conductivity and another monitors temperature in the purification loop. Both outputs are displayed on the front panel. A GM tube monitors water radioactivity with a count rate circuit and meter located in the rear of the console. Additional circuits provide alarm and indication at the console of pool icvel, bulk water temperature and cooling system differential pressure. 6.4. REACTOR OPERATING MODES
. During reactor operation, the individual control and safety channels are intimately related. There are three operating modes: manual, cutomatic 6-5
and pulse. The manual and automatic modes are steady-state power modes. The manual mode is accomplished by setting the MODE SELECTOR switch to the MANUAL position. The automatic mode is not currently installed. Figure 6-3 shows the approximate channel and detector operating ranges as a function of reactor power level. The manual and automatic reactor control modes are used for reactor operation from source level to 100 percent power (250 kW). These two modes are used for manual reactor startup, change in power level, and steady-state operation. The pulse mode generates high power levels for short periods of time (max 250 MW). 6.4.1. ?bnual Mode The manual mode can be used to control the reactor power level from source level to the full rated power of 250 kW. The source count-rate channel displays the neutron flux level from below the source level to a flux level of approximately one watt. To withdraw control rods, the mini-mum source level rod withdrawal interlock requirement of the source count-rate channel must be satisfied (about 10 nv at the detector which corresponds , to 2 counts per second). At approximately 10~ percent power, depending on the gamma flux level, the multi-range linear channel can detect the neutron flux and the blue pen of the recorder will respond. As the power icvel is increased, the operator advances the linear multirange channel range switch to keep the channel sensitivity compatible with the operating flux level. The output of the log range channel is displayed by the red pen of the strip chart recorder located in the center of the console. The instrument system provided for manual operation consists of an log and linear channels operating from compensated ionization chambers. The output of the log channel provides an input signal for the period channel. The 6-decade log power output is displayed by a pen of a dual-pen 6-6
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recorder. Period information over the full six decades of log power is
, read out on a meter calibrated from -40 seconds to infinity to +7 seconds.
The other pen of the dual-pen recorder displays the output of the multi-
. range linear channel from which a scram signal is initiated at ~110% of the recorder scale.
An additional neutron detector is used to provide the input signal for a second safety channel. The output of the safety channel is displayed on a meter calibrated in percent power (0% - 110%). A relay trip circuit is also provided for a protective action trip. The purification water temperature and radioactivity are monitored by meters on the console. A visual alarm is activated whenever the bulk water temperature exceeds a preset value, normally 40 C; or the pool level varies beyond a preset range, normally 6 in. Thermocouples embedded in the fuel elements are switch selected to relay circuits which provide trip inputs to the protective system. Fuel
. temperature is displayed by meters on the console (0 - 600 C).
6.4.2. Automatic Mode The automatic mode is identical to the manual mode except that the regulating rod position is controlled by a feedback control system to reg-ulate the reactor power icvel as detected by the multirange linear channel. Automatic operation can be initiated at any power level detectabic by the linear multirange channel, but a level above 50 W is preferred. The set-point for the regulator is determined by operator adjustment of the DENMND contro11ocated to the right of the strip chart recorder. The period signal is also connected to the flux regulator to provide a constant logarithmic rate of change of power when a large change in power level is demanded. 9 6-8
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. The regulating rod is now controlled automatically in response to a power level and period signal by means of a servo amplifier. Reactor power
. level is compared with the demand icvel set by the operator and is used to bring the reactor power to the demand level in a fixed preset-period. The demand level is determined by the range switch position and the percent de-mand potentiometer. The period control signal, which is fed into the servo amplifier, allows power level changes to be made automatically on a constant period, usually set for 30 or 60 seconds. 6.4. 3. pulse Mode pulse mode (Fig. 6-2) is used to generate high peak fluxes or power 1cvels for short periods of time. The maximum peak pulse power, ny, is 250 MW, but its limited duration makes the total energy release less than 16 MW-seconds, nyt, per pulse. Before the pulse mode of operation the reactor condition is set at a
. steady-state power level below I kW. It is also necessary to position the transient rod and cylinder to produce the desired reactivity change when air is applied to the cylinder.
- 6. 4. 3.1 Monitoring Channels. Two reactor parameters are measured during pulsing operation: fuel temperature and neutron flux. Flux is measured in two different terms: the peak flux achieved (nv), and the total nyt, or time integral, of the flux during the pulse. Since the pulse duration is extremely short, this infermation is stored and then recorded. The fuel temperature and flux monitoring channels provide the necessary alarms and shutdown mechanisms to help ensure that the reactor is operated safely.
The instrument system contains one safety channel monitoring the core flux and two thermocouple channels monitoring fuel temperature. 6-9
In the pulse mode an uncompensated ionization chamber is switched
. to the input of the peak reading (nv) and flux integrating (nyt) circuits.
The output of the peak and integrated flux is indicated on one pen of the dual-pen recorder. Also, a peak flux scram is provided by the same scram signal used in the steady-state mode. The output of the nvt circuit is automatically recorded following the recording of the nv circuit. The scale is calibrated in both MWs and Mw-seconds. The thermocouple channel located in the rear of the console is diaplayed on the second pen of the re-corder, and the second thermocouple channel is displayed on the front panel meter. Either will provide an automatic shutdown for excessive temperature. 6.5, REACTOR CONTROL SYSTEM The control of reactor flux is accomplished by use of the three control rods. The control rod circuit consists of the three horizontal rows of lighted pushbuttons located on the center of the rod control panel. 6.5.1. Manual Rod Control Circuit Manual rod control is accomplished by the lighted pushbuttons on the rod cantrol panel, similar to Fig. 6-4. The top row of annunciators, when illuminated, indicates magnet contact with the armature and magnet current. Depressing any one of the CONT /CN pushbuttons will interrupt the current to that magnet and extinguish the magnet current ON indicator. If the rod is above the down limit, the rod will fall back into the core and the CONT 6-10
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. light will be extinguished until the magnet is driven to the down limit where it again contacts the armature.
The annunicators in the middle row, when illuminated, indicate the upper (UP) and the bottom row indicate the lower (DOWN) limit positions of the rods. By depressing the indicators the control rod will move in the direction indicated. Several interlocks prevent the movement of the rods in the UP direction:
- 1. Two UP switches depressed at the same time
- 2. Scrams not reset
- 3. Source level is below minimum count
- 4. Magnet not coupled to armature S. Mode switch in AUTOMATIC position (regulating rod only)
- 6. Mode switch is in the tulse position (all rods except the transient rod)
- 7. Mode switch in STEADY-STATE (all rods not down, transient rod only)
A DOWN direction interlock may occur on the regulating rod during AUTO. mode operation or on other rods by the source interlock. Rod position may be determined by a digital position indicator for each drive. Position readout is within 0.2%. By pushing the scram bar all rods may be inserted simultaneously in a manual scram. 6.5.2. Autennric Operation Automatic power control can be obtained by switching from manual opera-tion to automatic operation. All of the instrumentation, safety, and inter-
. lock circuitry described above applies and is in operation in this mode.
Ilowever, the regulating rod is now controlled automatically in response to a power level and period signal by means of a servo amplifier. Reactor power 6-12
level is compared with the demand level set by the operator and is used to bring the reactor power to the demand Icvel on a fixed preset period. The demand level is determined by the range switch position and the percent demand potentiometer. The period control signal which is fed into the servo ampli-fier allows power icvel changes within the reactivity limits of the regulating rod to be made automatically on a constant period. The purpose of this feature is to automatically maintain the preset power Icvel during long-term power runs. Limit switches on the regulating rod interlock the servo ampli-fier control when the regulating rod reaches the down limit. 6.5.3. Pulsing Operation Reactor control in the pulsing mode consists of establishing a critical reactor at a flux level below 1 kW in the steady-state mode. This is accom-plished by the use of the two control rods, leaving the transient rod fully
- inserted. The MODE SELECTOR switch is then placed in the pulse range (selec-ted to give an on-scale reading for the flux level of the pulse to be produced).
The MODE SELECTOR switch automatically connects the pulsing chamber to the safety channel input, the dual-pen recorder inputs to the flux and fuel tempera-ture channels, and removes high-voltage from the steady-state neutron detectors. The adjustable transient rod up position is raised to a preselected posi-tion for the desired total reactivity insertion, depending on the peak flux levels desired. When the MODE switch is placed in the pulse position thus arming the transient rod air solenoid circuit and, when all transient opera-tion conditions have been met, air may be applied to the transient rod cylin-der whenever the TRANSIENT ROD UP button is depressed. From the time the TRANSIENT ROD UP button is depressed, the operation of the reactor and control console is automatic. The reactor flut and fuel temperature will increase to a peak value and decrease rapidly. After a preset tiue (less than 15 secs) the transient rod will be released and fall back into the core. The timer which controls the transient rod release is located inside the console. The peak 6-13 l
i flux, integrated flux, and fuel temperature attained during the pulse vill be indicated on the dual-pen recorder. Fuel temperature is monitored by chromel-alumel thermocouples embedded 4 in the fuel elements. The thermocouples are connected to the rear console meter and front panel meter. The rear meter fuel temperature channel is automatically switched to one pen of the dual-pen recorder in the pulse mode. 6.6 REACTOR SAFETY A reactor protective action interrupts the magret current and results in the immediate insertion of all rods under any of the following condi-I tions:
- 1. liigh neutron flux on single range safety channel 1
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- 2. liigh neutron flux on multirange safety channel
- 3. Iligh-voltage failure on safety channels
- 4. liigh fuel temperature
- 5. Manual scram
- 6. Peak flux in pulse mode
- 7. Loss of scram relay power
- 8. Fast period All scram conditions are automatically indicated by the annunciators.
A manual scram will also insert the control rods and may be used for a normal fast shutdown of the reactor. i , Instrument power to console instrumentation consists of three functional systems. With instrument chassis power on,the neutron detector power supply, source range count-rate circuit, and water monitor circuits are continuously active. A console power supply switch provides power to all remaining circuits except the contiol rod magnet power supply. 6-14 l l
. . , _ _ _ _ _ . _. . _ _ _ ___ _____m_. . _ _ _ -_ . _ _ _ _ . _ _ _ _ _ . _ _ . . __ _ _
l The rod drive magnet power can be obtained only with the key switch mounted on the front of the console. The key operation will prevent unauthorized operation of the reactor and yet allow checkout and calibration of instrument
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channels by maintenance technicians, while important monitoring circuits remain continuously active to provide rapid evaluation of reactor conditions. 1 i T i i , 4 1
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