Q77 — EOP-LOPA-1 MS10 Cooldown Rate
EPE 55 EA2.04 (4.1)
Given:
• BOTH Units were at 100% Power when a Loss of Offsite and ALL AC Power occurs.
• Both crews enter EOP-LOPA-1, Loss of All AC Power.
• The RO on Unit 2 reports that the 2A and 2B control air headers are indicating 20 psig and lowering.
• The crew is at step 17.2, ARE SG MS10s (RELIEF VALVES) OPERABLE FROM THE CONTROL ROOM.
Which ONE of the following describes how the CRS will proceed and what is the MAXIMUM cooldown rate?
• BOTH Units were at 100% Power when a Loss of Offsite and ALL AC Power occurs.
• Both crews enter EOP-LOPA-1, Loss of All AC Power.
• The RO on Unit 2 reports that the 2A and 2B control air headers are indicating 20 psig and lowering.
• The crew is at step 17.2, ARE SG MS10s (RELIEF VALVES) OPERABLE FROM THE CONTROL ROOM.
Which ONE of the following describes how the CRS will proceed and what is the MAXIMUM cooldown rate?
A. 1) Manually open MS10s from the control room.
2) 50°F/hr.
2) 50°F/hr.
B. 1) Locally open MS10s from the field.
2) 50°F/hr.
2) 50°F/hr.
C. 1) Manually open MS10s from the control room.
2) 100°F/hr.
2) 100°F/hr.
D. 1) Locally open MS10s from the field.
2) 100°F/hr.
2) 100°F/hr.
▶ Show Answer & Explanation
✓ C. Correct. Loss of all control air will cause both CA330s to fail close isolating air to containment. The MS10s controls are available with DC battery power (also requires vital instrument power which is available from inverters via batteries). Each MS10 has bottle rack with four bottles of nitrogen at greater than or equal to 2000 psig. A regulator reduces pressure to 20% less than normal operating pressure to maintain tank inventory until needed. On loss of control air, nitrogen will be supplied for control and to air operator. Bottle rack capacity designed for minimum of 72 hours of MS10 operation. Individual nitrogen bottles can be changed out to extend time until manual operation required. IAW 2-EOP-LOPA-1, step 17.2, the cooldown rate will not exceed 100°F/hr.
✗ A. Incorrect. Part 1 is correct. Part 2 is incorrect. Plausible because the 50°F/hr cooldown rate is used in other EOPs (For example, step 3 of EOP-TRIP-6, Natural Circulation Without RVLIS). The applicant may believe that the 50°F/hr cooldown rate is required based on limiting the cooldown with the plant in a Loss of all AC power condition, as well as considering the effects of a rapid cooldown on damaging the RCP seals.
✗ B. Incorrect. Part 1 is incorrect. Plausible because there are actions in procedures to operate the MS10s locally when a loss of instrument air is lost. Part 2 is incorrect. Plausible because the 50°F/hr cooldown rate is used in other EOPs (For example, step 3 of EOP-TRIP-6, Natural Circulation Without RVLIS). The applicant may believe that the 50°F/hr cooldown rate is required based on limiting the cooldown with the plant in a Loss of all AC power condition, as well as considering the effects of a rapid cooldown on damaging the RCP seals.
✗ D. Incorrect. Part 1 is incorrect. Plausible because there are actions in procedures to operate the MS10s locally when a loss of instrument air is lost. Part 2 is correct. See Ans. C for further explanation.
Ref: EOP-LOPA-1 (R40), NOS05CONAIR, S2.OP-AB.CA-0001 | LO: NOS05LOPA00, Objective 10 | Source: New | Cognitive: Comprehension/Analysis
Connections
- Related systems: Main Steam, Control Air
- Related EOPs: EOP-LOPA-1 — Loss of All AC Power
- Related exam: 2022 NRC Written Exam