Q43 — Steam Dump Response to PT-507 Failure
039 A4.07 (2.8)
Given:
• Unit 2 is at 15% Power with a startup in progress.
• Tavg is 552 °F and stable.
• Steam Dumps are in AUTO MS PRESS control mode set to 980 psig.
• 2PT-507, Steam Header Pressure transmitter, fails LOW.
Which ONE of the following describes how the steam dump system will respond?
The steam dump valves will __(1)__ and the steam generator pressure will IMMEDIATELY __(2)__.
• Unit 2 is at 15% Power with a startup in progress.
• Tavg is 552 °F and stable.
• Steam Dumps are in AUTO MS PRESS control mode set to 980 psig.
• 2PT-507, Steam Header Pressure transmitter, fails LOW.
Which ONE of the following describes how the steam dump system will respond?
The steam dump valves will __(1)__ and the steam generator pressure will IMMEDIATELY __(2)__.
A. 1) CLOSE
2) LOWER due to the reactor adding less heat to the RCS.
2) LOWER due to the reactor adding less heat to the RCS.
B. 1) CLOSE
2) RISE due to less heat removal from the RCS.
2) RISE due to less heat removal from the RCS.
C. 1) OPEN
2) LOWER due to more heat removal from the RCS.
2) LOWER due to more heat removal from the RCS.
D. 1) OPEN
2) RISE due to the reactor adding more heat the RCS.
2) RISE due to the reactor adding more heat the RCS.
▶ Show Answer & Explanation
✓ B. Correct. 2PT-507 failing low will cause the steam dumps to close. When the steam dumps close, steam flow from the SGs will lower, Rx power will lower, and SG pressure will immediately rise due to less heat removal from the SGs until SG pressure is maintained by the MS10s opening.
✗ A. Incorrect. First part is correct. Second part is incorrect. SG pressure will rise due to steam flows lowering and less heat removal from the SGs. Plausible because the operator may incorrectly determine that SG pressure will lower when steam flow decreases.
✗ C. Incorrect. First part is incorrect. Steam dumps will close on failure of 2PT-507. Second part is incorrect. SG pressure will rise due to steam flows lowering and less heat removal from the SGs.
✗ D. Incorrect. First part is incorrect. Steam dumps will close on failure of 2PT-507. Plausible because the operator may incorrectly determine how the steam dumps will respond on the instrument failure. Second part is plausible because the applicant may incorrectly determine that with the steam dumps open, reactor power will increase and also increase the RCS temperature (incorrect assumption) which will result in more heat transfer to the SG and a rise in SG pressure.
Ref: NOS05STDUMP-13 | LO: NOS05STDUMP-13, Obj 10.b — Identify and describe the Control Room controls, indications, and alarms associated with the Steam Dump System, including: The function of each Steam Dump System Control Room control and indication | Source: Modified Bank — Byron 2017 NRC RO62 | Cognitive: Comprehension/Analysis
Connections
- Related systems: Steam Dumps, Main Steam
- Related exam: 2022 NRC Written Exam