Breaker trip event

This segment foeuses on the breaker trip event and how both the train speed and the differential pressure between the regenerator and reaetor stripper ean be eontrolled during this event. Based on the breaker status, aetion is immediately initiated on the expander. Due to the improved reliability in train operation with these patented eontrol teehniques, the PRT ean be better utilized without saerifieing plant reliability. This leads to more effieient FCCU operation and the pay-baek period for tlie improved eontrol system ean be extremely short. 

In the above situation, even an overspeeding motor on a fault elsewhere would feed back the supply source and require such protection. The protective scheme isolates the faulty source from being fed by the healthy sources. Figure 21,18 illustrates a simple power circuit provided with a directional G/F relay. In the event of a fault in system B, source B alone would isolate. Source A would not feed the fault as relay b would trip the breaker B and eliminate /g. The relays are necessarily set at lower settings and at lower tripping times than the non-directional... 

In the event that eertain faults oeeur in the eleetrieal equipment of the generator, the load eireuit breaker must be opened immediately. The result is that the maehine train is aeeelerated with the full power of the expander. Only if the inlet valves are elosed within 0.6 see ean exeessive overspeed be avoided. Eor this reason, both inlet valves must be able to elose within this time window in the event of an emergeney trip. 

As previously mentioned in Chapter 5, one of the most severe disturbances for the power recovery train (PRT) is a generator breaker opening. This event often causes the PRT to trip on overspeed or other process or machine conditions. A control solution has been developed to keep the PRT and the process under control during breaker opening. 

In the event of accidents with unauthorized addition of reactivity or loss of heat removal, complete failure of protective systems and operator inaction on primary circuit pressure increase, the plant will be tripped by a direct-acting pressure-actuated power breaker cutting supplies to the control rod drives. 

On February 26, 1983, NRC investigators discovered that a similar failure had occurred on at Salem 1 on February 22, 1983. Based on a computer printout of February 22 events, it was evident that on that day (as on February 25) the two reactor trip breakers failed to open upon receipt of an automatic trip signal from the reactor protection system. The operators initiated a manual trip even though they were unaware that the automatic trip had failed. 

Other pressurized water reactors (PWRs) have experienced reactor trip breaker failures, both before and after the February 1983 Salem 1 events. None of them however, involved an ATWS event. The reactor trip breaker failures prior to the February 1983 events at Salem 1 had been the subject of several actions taken since 1971 by the AEC/NRC, Westinghouse, and General Electric. 

Due to the serious nature of Salem 1 ATWS event, the NRC issued Inspection and Enforcement Bulletin No. 83-01 on the same day (on February 25,1983) to all PWR licensees for action and to other nuclear power reactor facilities for information. Subsequent initiatives on the part of NRC and industry identified and corrected potential deficiencies in reactor trip breakers and related maintenance procedures at several other plants as described in Appendix 2B. 

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