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The plant was at 50% power when an ATWS Mitigation System Actuation Circuitry (AMSAC) actuation occurred.Which of the following plant parameters must be checked to verify proper AMSAC operation? A. Verify reactor trip and all auxiliary feedwater pumps running.B. Verify turbine trip and all auxiliary feedwater pumps running.C. Verify reactor trip and turbine trip.D. Verify turbine trip and motor driven auxiliary feedwater pumps running.
B
The ATWS Mitigation System Actuation Circuitry (AMSAC) has a 25 second time delay before a trip is generated.Which of the following is the purpose of this time delay? A. It allows time for a load decrease.B. It allows for level transients and actuation of the SSPS.C. It ensures the turbine trips before steam dumps open preventing excessive cooldown.D. It allows time for a manual AMSAC block in case of spurious signals.
B
The plant is at 75% power with ATWS Mitigation System Actuation Circuitry (AMSAC) operating normally.Which lights at the AMSAC control panel should be illuminated? A. Power on light and AMSAC armed light.B. Power on light and AMSAC master bypass light.C. AMSAC armed and AMSAC master bypass light.D. AMSAC armed and pressure differential light.
A
AMSAC provides a protective function.What is the design requirement of AMSAC? A. Prevent generation of unnecessary and unanticipated reactor trips.B. Ensure mitigation on a high RCS pressure if the PORVs do not operate properly.C. Prevent loss of secondary Heat Removal events that could threaten the RCS fission product barrier.D. Prevent inadvertent loss of feed on an OTDT reactor trip.
C
What is one of the AMSAC design requirements? A. It is a safety-related system and must be maintained in-accordance with NUREG Maintenance Rule 1.B. The associated equipment from sensor to final actuation device is diverse from the Reactor Trip System.C. A direct trip signal is sent to the Reactor Trip Breakers on a low steam generator level of 5%.D. The associated equipment must be operable before entry into Mode 4 from Mode 5, per Technical Specifications.
B
What is the peak RCS pressure for a loss of load ATWS.
2959 psig
What mitigates this pressure increase?
Pressurizer safeties
What is the peak RCS pressure for a loss of normal feedwater ATWS.
3632 psig
Why is the "loss of normal feedwater ATWS" different from the "loss of load" ATWS?
Answer: Steam generator dry out
Does a turbine trip cause RCS pressure to go higher or lower? Why?
Answer: Lower; Mass is conserved in the steam generators.
Which two ATWS events pose significant challenges to fission product barriers?
1) Loss of load, Loss of Feedwater
7: Which of the two ATWS events poses the greatest challenge to fission product barriers?
Loss of normal feedwater
What does AMSAC automatically initiate?
Answer: Auxiliary feed water actuation signal and a turbine trip.
State why the AMSAC system is not a part of the reactor protection system.
Answer: Independent of reactor trip system and not safety related.
Under what conditions is the AMSAC system expected to initiate?
when 3 of 4 SGs are ² 12% level and power is >34.9% or if less than 34.9% 360 seconds have not elapsed since power was less than 34.9%.
What signal is used to indicate when AMSAC must be armed?
Both turbine impulse pressure channels > 240 psig (35% turbine power).
What is the purpose of the 25 second time delay?
Delay AMSAC steam generator low level signal, allowing time for reactor protection system to actuate.
What is indicated on SS001 when the "ATWS SG Level Pre-trip" lamp is lit?
All input conditions for AMSAC actuation exist, actuation will occur after 25 second time delay unless input conditions change.
What is indicated on SS001 when the "AMSAC Armed" lamp is lit?
Both turbine impulse pressures are high enough to arm AMSAC.
What two control room alarms are associated with AMSAC?
1) 00-083A, ATWS SG LEV PRETRIP; and 2) 00-083F, ATWS PANEL TROUBLE
If an ATWS alarm is not valid, what action should be taken?
Place the "Test/Bypass Master" switch on SS001, to ON position.
What is the impact of the AMSAC setpoint change from 5% to 12% SG narrow range level?
Answer: A dP across the mid deck plate of the steam generator varies with % power, but not level. The identified dP results in an indication bias of 6.8% at 100% power. Thus indicated SG level would be greater than actual level. The previous AMSAC setpoint of 5% would never be reached - no protection would be afforded.