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Exams > 2020 Q10 — Loss of MFW / Dry SG Feed Restriction

2020 Q10 — Loss of MFW / Dry SG Feed Restriction

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Q10 — Loss of MFW / Dry SG Feed Restriction 000054AK1.02 (3.6)
Given:
• Unit 2 was at 100% Power when a Loss of all Main Feedwater occurred.
• Operators have not been able to initiate Auxiliary Feedwater (AFW) and have transitioned to 2-EOP-FRHS-1, Response to Loss of Secondary Heat Sink.
• Bleed and Feed has been initiated.
• Core Exit Temperatures (CETs) are now LOWERING.
• All SG Wide Range (WR) Levels are 7 % and stable.

Subsequently, feed flow capability has just been restored and the crew has returned to the major action step for "SECONDARY HEAT SINK RESTORATION".

Based on the above conditions and In accordance with 2-EOP-FRHS-1, complete the statement below concerning the limitation when restoring feed flow and why?

Feed one SG…
A. at maximum flowrate to prevent lifting a PZR Safety Relief Valve.
B. at maximum flowrate to prevent a severe challenge to the Core Cooling CFST.
C. between 1E04 and 5E04 lbm/hr to prevent thermal shocking SG tubes.
D. between 1E04 and 5E04 lbm/hr to prevent thermal shock of the reactor pressure vessel.
▶ Show Answer & Explanation
✓ C. Correct. The bases states the following; "If RCS temperatures are stable or decreasing when feedwater flow is restored the flow should be directed to one steam generator and the rate should be limited to the plant-specific equivalent of 25 - 100 gpm until wide range level is established. With stable or decreasing RCS temperatures, the feedwater flow rate is limited to minimize the potential impact of excessive thermal stresses since a direct measure of the steam generator temperature is not available. The remaining dry SGs may have their levels recovered at the direction of the plant engineering staff (TSC)."
✗ A. Plausible because if core exit temperatures were still rising, the procedure requires feeding at desired rate. This is incorrect because the stem states that CETs are lowering. The second statement is plausible because the candidate may believe that if CETs are still rising and feed is not initiated at a maximum rate, RCS pressurization could result in a PZR Safety lifting.
✗ B. Plausible because if core exit temperatures were still rising, the procedure requires feeding at desired rate. This is incorrect because the stem states that CETs are lowering. The second statement is plausible because the candidate may believe that if CETs are still rising and feed is not initiated at a maximum rate, a severe challenge to the Core Cooling CFST could occur.
✗ D. Plausible because the first part is correct. Plausible as the candidate may believe that this action will result in preventing thermal shock to the reactor vessel by preventing excessive cooldown of the RCS. Incorrect as the specific step is protecting the steam generator.
Ref: 2-EOP-FRHS-1 and BASES | LO: N/A | Source: New | Cognitive: Comprehension

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