Average Power Range Monitor (APRM) - .5

Question 1

APRM STP Upscale Rod Block

Answer 1

1. ≤0.56W + 53.1%
2. ≤0.56(W-10.8%) + 53.1% for SLO
3. ≤108% Max with high flow clamped.

Bypassed:
MSS not in RUN

Question 2

APRM Upscale Rod Block(Setdown)

Answer 2

≤11% of RTP

Bypassed:
MSS in RUN

Question 3

APRM Downscale Rod block

Answer 3

≥ 4% of RTP

Bypassed:
MSS not in RUN

Question 4

APRM INOP Rod Block

Answer 4

• Mode Switch NOT in Operate
• The firmware/Software WDT has timed out
• A critical Self-Test fault is detected.

Question 5

Flow Upscale (Alarm Only)*

Answer 5

111%

*Total Recirc Flow Comparitor – If the diff b/t the min and max flow (from all 4 APRMs) exceeds 10%, and the reference APRM is in RUN, then a flow comparator alarm is issued by the RBM.

Question 6

LPRM Low Count Rod Block

Answer 6

<20 LPRM per APRM
<3 LPRM per String

Question 7

APRM STP Upscale Scram

Answer 7

≤ 0.56W + 58%
≤ 0.56(W-11%) + 58% for SLO
Maximum of 113.5% of RTP

Question 8

APRM Upscale Scram

Answer 8

1. ≤ 116.3% of RTP
2. ≤ 17% of RTP (Bypassed with MSS in RUN)

Question 9

APRM INOP

Answer 9

-Mode Switch NOT in Operate
-The firmware/Software WDT has timed out
-A critical Self-Test fault is detected.
-Less than 20 LRPM

Question 10

APRM Channel explanation.

Answer 10

• The APRM System is divided into four APRM channels and four 2-Out-Of-4 VOTER channels. Each APRM channel provides inputs to each of the four VOTER channels. The four VOTER channels are divided into two groups of two each; with each group of two providing inputs to one RPS trip system. The system is designed to allow one APRM channel, but no VOTER channels, to be bypassed. A trip from any one unbypassed APRM will result in a “half-trip” in all four of the VOTER channels, but no trip inputs to either RPS trip system.

Question 11

A&C Voters power supply

Answer 11

1AD483

Question 12

B&D Voters power supply

Answer 12

1BD483

Question 13

Loss of AD/BD483 inverter effect on Voters

Answer 13

• Loss of an AD/BD483 inverter causes a ½ scram since the voters lose power on that side. A voter -> RPS ch A1, C voter -> RPS ch A2 etc.

Question 14

APRM Gain circuit function

Answer 14

• APRM ‘gain circuit’ adjusts individual APRM circuit average to greater than the reference APRM. The ‘reference APRM’ is an average APRM value derived from the core thermal power calculation.
• Gain remains fixed during changes in core flow – I&C inputs it manually

Question 15

6. An APRM Channel is inoperable if either: (T/S Table 3.3.1-1, note (e))

Answer 15

a) < 3 LPRM inputs per level (4 axial levels total) OR
b) < 20 LPRM inputs to an APRM channel

Question 16

What happens when RPS loses power?

Answer 16

Scram setpoints default to “RUN” non-conservatively

Question 17

What happens when ARPM is bypassed?

Answer 17

1. When an APRM is in BYPASS:
   
   • ALL trip input to the VOTERs is bypassed.
   • The APRM/OPRM status and indication is still active, but it will not cause a trip in the 2 out of 4 logic.
   • An associated APRM should be bypassed before returning an LPRM to operate.

Question 18

OPRM Function

Answer 18

1. Each APRM also includes an Oscillation Power Range Monitor (OPRM) Upscale Function which monitors small groups of LPRM signals to detect thermal-hydraulic instabilities.
2. If an APRM is in BYPASS, it will also bypass its associated OPRM signal.
3. Protects against CDA

Question 19

OPRM Trip

Answer 19

Detection of Thermal Hydraulic Instability

Bypassed:
Rx Power < 24% OR
Total Recirc Flow > 70% (Core Flow > 76%) OR
APRM in Bypass

Question 20

When are OPRMs required?

Answer 20

OPRM’s are required to be OPERABLE when reactor power is ≥ 19% (TS Table 3.3.1-1). The OPRM will enable when reactor power is > 24%, as sensed by APRM power AND recirculation drive flow < 70% (nominal).