Document: NUREG-0800
Document ID: 598d070d-fb96-43ce-ad4f-27f14623be46
Document Type: srp
Title: NUREG-0800
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0523/ML052350119.pdf
Revision Date: 2023-06
Chapter: 15
Section ID: 15
CFR Part: 
CFR Title: 

Content:
to be tripped off the line by abruptly stopping steam flow to the turbine. This is different from the loss of electrical load-condition described above in that fast closure of the turbine stop valves (TSV) is initiated. The TSV have faster (0.1 sec) closure times that the turbine -control valves, result- ing in more severe transients. For typical BWR and PWR plants, position switches on the TSV sense the trip and initiate reactor scram. The remainder of this transient is similar to the previously discussed loss-of electrical load. 3. Loss of Condenser Vacuum A loss of condenser vacuum event is one of the malfunctions that can cause a turbine trip. The remarks in item 2, above, thus apply to this transient. 4. Main Steam Isolation Valve Closure The main steam isolation valve (MSIV) transient for BWRs can be initiated by various steam. line or reactor system malfunctions and by various operator actions. As the MSIVs -close,'position' switches initiate a reactor scram when the valves in three or more of the steam lines are less than 90% open, the reactor pressure is above 600 psi, and the reactor mode switch is in the RUN position. The effect of MSIV closure is to limit steam flow to the turbine. The results are similar to those discussed in item 1, above, but tend to be less severe since the MSIV closure time is much longer than that of the TCV.. 5. Steam Pressure Regulator Failure Steam pressure regulator failure in a closed -position yields a transient similar to the transients discussed above. Generally, because the rate of change of system parameters is slower for a steam pressure regulator failure, a less severe transient results. The review of the transients described above Includes the sequence of events, the analytical models, the values -of parameters used in the analytical models, and the predicted consequences of the transients. The sequence of events described in..the SAR analysis is reviewed by RSB in consultation with the Instrumentation and Control