Trips, testing

Annually Sprinklers free from corrosion, paint, and obstructions pipe free from corrosion control valves lubricated, closed and opened trip test on dry-pipe, pre-action, and deluge systems... 

The safety demonstration tests in the HTTR are conducted to demonstrate an inherent safety feature, that is an excellent feature in Shutdown of the HTGRs, as well as to obtain the core and plant transient data for validation of safety analsis codes and for establishment of safety design and evaluation technologies of the HTGRs. The safety demonstration tests consist of Reactivity insertion test - control rod withdrawal test and Coolant flow reduction test as shown in Figure 6. In the control rod withdrawal test, a central pair of control rods is withdrawn and a reactivity insertion event is simulated. In the gas-circulators trip test, primary coolant flow rate is reduced to 67% and 33% of rated flow rate by running down one and two out of three gas-circulators at the Primary Pressurized Water Cooler without a reactor scram, respectively. 

After a plant trip test, Monju restarted operation on 6th December 1995. On 8th December, power was being raised for the next plant trip tests, part of 40% electric power tests. The thermal power had reached 43% when an alarm sounded at 19 47 dueto an off-scale sodium temperature at the outlet of IHX in the secondary circuit loop C. Afire alarm (smoke detector) sounded at the same time. A sodium leak alarm in the secondary circuit followed. The plant conditions of Monju at that time are shown in Fig. 1. The presence of smoke was confirmed when the door of the piping room was opened. The plant operators decided to begin normal shutdown operations becausethey judged it was a small sodium leak had occurred. Reactor power-down operations began at 20 00. 

Instruments that have emergency safety functions should be tested by simulating the emergency. If this can be done as part of a normal batch cycle, a test on each cycle is desirable but a weekly trip test is sufficient if the simulation requires a skilled person. 

On Etecember 8, 1995, a leakage of sodium occurred in the piping room (C) of the Secondary Heat Transport System (SHTS) while the output of the reactor was being raised for a plant trip test at 40% output as part of a series of performance tests. The nuclear reactor was shut down manually after the accident, and sodium was drained from the SHTS in which the accident occurred and also from the Loop C of the Primary Heat Transfer System (PHTS). The plant is currently in a low-temperature shutdown state. The plant conditions of Monju at the time of the sodium leak occurrence are shown in Fig. 3.1. 

SPECIAL CAUTIONARY NOTE AU circuit breaker manufacturers recommend that their circuit breakers be exercised annuaUy via the trip test button. Exercising the circuit breaker actuates the trip mechanism. The trip mechanism of the circuit breaker is separate from the on-off handle mechanism, and annual operation of the trip mechanism ensures that the breaker wiU trip when called on to operate. This is also a test indication if the breaker faUs to trip, it has malfunctioned and should be replaced. 

On-line trip testing not really a diagnostic but a proof test. However if the valve can be arranged to trip fully shut (or open) without shutting down the process, perhaps by using parallel paths or bypasses then this test can be performed at regular intervals to improve the PFD of the valve. 

Trip testing with position feedback A position signal from the valve will allow the tester to observe the test response rate and hence verify correct movement characteristics. If a PES logic solver is used it can be arranged to record or even check the response profile and detect deviations from the standard version. 

Partial closure testing The same as trip testing except that the valve trip is performed automatically by the logic solver and then cancelled before the valve can move more than say 25%. The position feedback can be as simple as a limit switch, but a position transmitter is better the disturbance to the process is minimal. 

Trip testing of final elements up to and including the solenoid valve is useful since the reliabilities of solenoids are variable according to quality and environmental conditions. Also the possibilities of wrong connections of cables and pneumatic tubing are quite high... 

The use of a bypass is not permitted since this adds to the risks of failure of joints and valves. In any case the use of a bypass to assist trip testing creates a potentially false result since the supply line pressure is not imposed on the closing valve. It is ability of the ESDV to close against full flow of the pipeline under pressure that is one of its essential features. 

The trip testing work will be of limited value unless it is done to a consistent method and is consistently reported. When this is done the records will support the good safety management practices of the plant. The data available fi om the test records will assist with the evaluation of performance that we have seen must be done periodically as required by the standards. 

The best way to ensure the recording of the testing is done consistently is to set up a trip test procedure sheet for each safety function and to include spaces for the regular data such as test values and times to be filled in. Filing of these reports in a secure manner is essential and if a PC database system is used for the purpose it will further enhance the quality of the record keeping. Indications are that a maintenance software package is the ideal tool for this purpose. 

A 100% functional system test. In practice, this is only possible when the SIS is disconnected from the process. Hence on-line proof testing may leave a small fraction of the SIS untested. Also termed trip testing . 

This approach leads to the identification of hardware or software improvements that address the specific requirements of the installation under consideration. Software improvements cover such issues as safety management systems, incident response procedures, training, quality, maintenance practices, alarm and trip testing, etc. Hardware improvements cover such issues as ventilation, gas detection, interlocks, control system, fuel system, protection systems, etc. 

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