Core Cooling Monitor System & RVLIS

Question 1

How do the Reactor Vessel Level Indication (RVLIS) level indicators work, and how are their measurements illustrated on the control board?

Answer 1

The RVLIS level indicators utilize heated junction thermocouples that measure a change in temperature (delta-T) that varies based on the phase of the medium surrounding it. If surrounded by a subcooled liquid, the delta-T is significantly lower than if the thermocouple ends are surrounded by steam.

Thus, when the differential temperature is greater than 200F, the detector is considered to be uncovered, and its associated elevation light on the control room RVLIS instrumentation goes dark.

Question 2

How many RVLIS lights must be illuminated to satisfy operability per TS 3.3.3

Answer 2

TS 3.3.3 requires 4 RVLIS lights per train with a minimum of 1 light in the upper section and 3 in the lower section.

Question 3

The Train A Subcooled Margin Monitor (1-TI-3611-1) receives input from…

Answer 3

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- Loops 1 & 2 WR Thot (TE-0413A & TE-0423A)
- Loops 3 & 4 WR Tcold (TE-0433B & TE-0443B)
- RCS WR Pressure PT-3616 (thimble pressure)
- PRZR Pressure PT-455

The Train A SMM utilizes the HIGHEST measured CET temperature and the LOWEST pressure to calculated the most conservative subcooling margin.

Question 4

The Train B Subcooled Margin Monitor (1-TI-3611-2) receives input from…

Answer 4

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- Loops 3 & 4 WR Thot (TE-0433A & TE-0443A)
- Loops 1 & 2 WR Tcold (TE-0413B & TE-0423B)
- RCS WR Pressure PT-403
- PRZR Pressure PT-458

The Train B SMM utilizes the HIGHEST measured CET temperature and the LOWEST pressure to calculated the most conservative subcooling margin.

Question 5

Per TS 3.3.3, what are the operability requirements concerning CETs

Answer 5

The CETs are considered operable when at least TWO CETs with <75F difference exist in each quadrant for train A, and TWO CETs with <75F difference exist in each quadrant for train B.

Question 6

What is the CPNPP Administrative requirement concerning CETs

Answer 6

One CET per train in each quadrant is available AND one CET per train in the center available. The ‘center’ CET cannot be any of the single CETs chosen to verify acceptance in the ‘each quadrant’ requirement.

CETs in the outer two rows of fuel assemblies are NOT considered acceptable inputs for detection and mitigation of ICC.

Question 7

How many CETs are in the core? How many per train?

Answer 7

50 CETs total split evenly (25/25) between Train A & B.