Q43 — MS10 Atmospheric Relief Valve Flow and AB.STM-0001
039000K1.02 (3.3)
Given:
- Unit 2 is at 100% Power when the 21MS10, 21 SG Atmospheric Relief Valve, fails open.
- The operator is unable to close the valve using the control console valve controller.
- The crew enters S2.OP-AB.STM-0001, Excessive Steam Flow.
Complete the following statements:
1) The rated design flow through the 21MS10 is _(1)_ steam flow.
2) After performing the actions of the Continuous Action Statement of S2.OP-AB.STM-0001 to trip the reactor and initiate a Main Steam Line Isolation, a Safety Injection (SI) _(2)_ required.
- Unit 2 is at 100% Power when the 21MS10, 21 SG Atmospheric Relief Valve, fails open.
- The operator is unable to close the valve using the control console valve controller.
- The crew enters S2.OP-AB.STM-0001, Excessive Steam Flow.
Complete the following statements:
1) The rated design flow through the 21MS10 is _(1)_ steam flow.
2) After performing the actions of the Continuous Action Statement of S2.OP-AB.STM-0001 to trip the reactor and initiate a Main Steam Line Isolation, a Safety Injection (SI) _(2)_ required.
A. (1) 2.5%; (2) is
B. (1) 10%; (2) is NOT
C. (1) 10%; (2) is
D. (1) 2.5%; (2) is NOT
▶ Show Answer & Explanation
✓ A. Correct. The design capacity of the MS-10 (SG Atmospheric Relief Valves) is 10% design rated steam flow total, therefore each valve is 2.5% rated steam flow. After tripping the reactor and initiating a Main Steam Line Isolation, the CAS of AB.STM-0001 asks if the steam leak is isolated. If the leak is not isolated (MS-10 failed open), then initiate a manual Safety Injection.
✗ B. Incorrect. Plausible because the candidate may remember that Design capacity is 10% of rated steam line flow at plant no-load steam pressure (390147 lb/hr at 1005 psig). However, this is incorrect because it is the design rating for all 4 SG atmospheric relief valves together. The second part is plausible if the candidate believes that the leak would be isolated by the Main Steam Isolation signal or thinks the transition is directly to EOP-TRIP-1.
✗ C. Incorrect. Plausible because the candidate may remember that Design capacity is 10% of rated steam line flow at plant no-load steam pressure (390147 lb/hr at 1005 psig). However, this is incorrect because it is the design rating for all 4 SG atmospheric relief valves together. The second part is correct.
✗ D. Incorrect. The first part is correct. The second part is plausible if the candidate believes that the leak would be isolated by the Main Steam Isolation signal or thinks the transition is directly to EOP-TRIP-1.
Ref: S2.OP-AB.STM-0001, Excessive Steam Flow; NOS05MSTEAM-12 Lesson Plan | LO: ELOs 4c, 15.b | Source: New | Cognitive: Fundamental
Connections
- Related systems: Main Steam
- Related procedures: AB.STM-0001 — Excessive Steam Flow
- Related exam: 2020 NRC Written Exam