Rod-drop time

MONJU (Japan) less than 1.2 less than 1.2 less than 1.2 

BREST-OD-300 (Russian Federation) less than 2.5 less than 2.5 6.0 (per HSR ) 

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In the case of PFR sodium aerosols caused no operational problems because movement of the absorber rods was carefully monitored and deposits were cleaned off well before ffiey interfered with the mechanisms. The only effect was the operational burden of exercising the rods and cleaning the magnet faces. Aerosols had no observable effects on magnet parting times or rod drop times. 

It has been established that absorber rod drop time should be less than 1 s so that the reactivity transient of a few dollar per second resulting from coolant voiding, fuel melting and slumping can be protected by the shutdown system. Analysis of reactivity transient shows that absorber rod speed can be in the range of 1-4 mm/s. 2 mm/s speed has been decided for CSR and 4 mm/s for DSR. Scram delay time on reactivity events should be less than 250 ms. 

Ageing effects may be detected by a change in measurable parameters. For example, increase in temperature or pressure may be an indication of die accumulation of corrosion products in the tube of a heat-exchanger and instrument drift may be an indication of electronic component degradation. Parameters should be measured periodically in a consistent manner and the readings should be compared and assessed. Physical parameters, such as temperature, pressure, flow rate, control rod drop times, radiation level (e.g. neutron and gamma), water quality, are indicators of the state of a system, structure or component. 

CONTROL RODS AND DRIVE MECHANISMS (cont.) 5.8. Rod-drop time... 

Also regular tests of rod drop time are required. 

Rod drop times and drag forces are required for PWRs and in some plants, they have already been performed. 

A complete rod insertion is required to be verified for each reactor scram and in case any rod does not fully insert, a rod drop time test and rod recoil are required. 

Control rod drop times are measured at least once every 3 months. If any control rod drop time is more than 4 seconds, the next test is carried out within a month. 

If excessive rod drop times are observed at full coolant flow rate, operation with three or two reactor coolant pumps at correspondingly reduced power is permitted, provided that the measured drop time of any rod does not exceed 4 seconds. If the transfer to operation with three or two coolant pumps is not successful, then the unit has to be shut down. 

Tests are completed on the control rod drive system that demonstrate that the control rods have been latched, that the control and position indication systems are functioning properly and that the rod drop time under hot full flow conditions is less than the Tech-Specs limit. 

There are two active shut-down systems. The first has 6 control rods of which 1 is used for temperature compensation, 3 for bum-up compensation, and 2 for r ulation. The second shut down systems has 2 safety rods. These two shut-down systems can scram automatically or by manual operation if necessary. The rod-drop times are designed to be 1.2 1.5s and 0.7s respectively. 

For the routine experiments of two TRIGA reactors and the commissioning experiments of the new 30 MW HANARO research reactor in the Republic of Korea, a stand alone system, with input signals independent from the reactor operation and safety chaimels, is configured. This system has been utilized for the criticality approach, real time reactivity measurement, noise analyses, control rod drop time measurement, and thermal power calibration in a natural convection cooled reactor. It replaces conventional counter modules for the criticality measurement, multichannel analyzer and... 

The program for control rod drop time replaces the memory oscilloscope for this experiment, and offers operators conveniency in documentation and reporting. 

The control rod drop time can be measured if there is any tool to monitor the drop initiation and termination signals with clock. A memory oscilloscope is a typical tool which can be used for this purpose. 

A PC equipped with an ADC can be a better tool for this purpose. The logic is very simple but it needs a program from which drop time can be obtained conveniently. The program made through this work, reads both signals of drop initiation and termination, and graphically displays them on the CRT screen. The user locates cursors at the points of drop initiation and termination and the program displays rod drop time. All data related with this experiment are saved and the experiment can be revived. Fig. 6 shows a sample result of control rod drop time measurement. 

Fig. 6. A Sample Result of Control Rod Drop Time Measurement...

A PC system which can be applied to most of important research reactor experiments is successfully developed. It includes multi-counter, multi-scaler, reactivity computer, control rod drop time measurement and power calibration. So far, it has been focused on identifying and solving any problems or difficulties when counters are used since the analog data acquisition is relatively well known. 

The control rod drop time measuring program which replaces the use of memory oscilloscope, helps operators make a neat report for this experiment with graphic. 

While the measurement time eonstant for P/Q, Lin P and p scram parameters is 0.05 s, it is 0.3 s for 0CSAM- In addition to this, trip logic delay time is 0.2 s. Control rod drop time is 0.8 s. Plant design ineorporates two diverse shutdown systems of worths 8000 pcm (Control... 

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