Q30 — PR NI Failure and Trip Coincidence
015 Nuclear Instrumentation System (NIS)-A4.03 (3.8)
Given:
• Unit 2 is 100% Reactor Power
At time 1900:00
• 2N41 (Power Range NI) fails high
At time 1900:30 (30 seconds later)
• The crew enters S2.OP-AB.NIS-0001 (NUCLEAR INSTRUMENTATION SYSTEM MALFUNCTION)
At time 1945:00
• 2N41 is placed in tripped condition in accordance with S2.OP-SO.RPS-0001 (NUCLEAR INSTRUMENTATION CHANNEL TRIP / RESTORATION)
Which ONE of the following completes the statements below?
In accordance with S2.OP-AB.NIS-0001 and prior to placing 2N41 in tripped condition, the crew _(1)_ REQUIRED to place the Rod Bank Selector Switch in MAN.
After 1945:00, the coincidence for the PR High Neutron Flux Reactor Trip (based on the remaining functional PR NI Channels) is now _(2)_.
• Unit 2 is 100% Reactor Power
At time 1900:00
• 2N41 (Power Range NI) fails high
At time 1900:30 (30 seconds later)
• The crew enters S2.OP-AB.NIS-0001 (NUCLEAR INSTRUMENTATION SYSTEM MALFUNCTION)
At time 1945:00
• 2N41 is placed in tripped condition in accordance with S2.OP-SO.RPS-0001 (NUCLEAR INSTRUMENTATION CHANNEL TRIP / RESTORATION)
Which ONE of the following completes the statements below?
In accordance with S2.OP-AB.NIS-0001 and prior to placing 2N41 in tripped condition, the crew _(1)_ REQUIRED to place the Rod Bank Selector Switch in MAN.
After 1945:00, the coincidence for the PR High Neutron Flux Reactor Trip (based on the remaining functional PR NI Channels) is now _(2)_.
A. _(1)_ is NOT / _(2)_ 1 out of 3
B. _(1)_ is NOT / _(2)_ 2 out of 3
C. _(1)_ is / _(2)_ 1 out of 3
D. _(1)_ is / _(2)_ 2 out of 3
▶ Show Answer & Explanation
✓ C. Correct. For Part 1 and IAW S2.OP-AB.NIS-0001, the crew is REQUIRED to place the Rod Bank Selector Switch in MAN. For Part 2 and IAW DWG 221052, after the bi-stable for 2PR41 is tripped (IAW S2.OP-SO.RPS-0001), the coincidence for the PR High Neutron Flux Reactor Trip (based on the remaining functional PR NI Channels) is now 1 out of 3.
✗ A. Incorrect but plausible. For Part 1, when 2PR41 fails high, this will cause the overpower rod stop block to be enabled (which stops all automatic and manual rod withdrawal). Consequently, the candidate could incorrectly conclude that placing rods in Manual is not required IAW S2.OP-AB.NIS-0001. Part 2 is correct.
✗ B. Incorrect but plausible. For Part 1, when 2PR41 fails high, this will cause the overpower rod stop block to be enabled (which stops all automatic and manual rod withdrawal). Consequently, the candidate could incorrectly conclude that placing rods in Manual is not required IAW S2.OP-AB.NIS-0001. For Part 2, the candidate could incorrectly determine that when 2PR41 is removed from service IAW S2.OP-SO.RPS-0001, this removes the channel from the PR High Neutron Flux Reactor Trip logic. This would then cause the candidate to incorrectly conclude that the logic for the remaining operable channels is 2 out of 3.
✗ D. Incorrect but plausible. Part 1 is correct. For Part 2, the candidate could incorrectly determine that when 2PR41 is removed from service IAW S2.OP-SO.RPS-0001, this removes the channel from the PR High Neutron Flux Reactor Trip logic. This would then cause the candidate to incorrectly conclude that the logic for the remaining operable channels is 2 out of 3.
Ref: S2.OP-AB.NIS-0001, S2.OP-SO.RPS-0001, DWG 221052, NOS05RXPROT-13 (REACTOR PROTECTION SYSTEM) | LO: State the setpoints, coincidence, blocks and permissives for all Reactor Trips and Safety Injections actuations | Source: New | Cognitive: Higher
Connections
- Related systems: Excore NIs, RPS/SSPS, Control Rod Drive
- Related procedures: AB.NIS-0001 — Nuclear Instrumentation System Malfunction, S2.OP-SO.RPS-0001 — Nuclear Instrumentation Channel Trip / Restoration
- Related exam: 2019 NRC Written Exam