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procedures > S2.OP-SO.RPS-0001 — Nuclear Instrumentation Channel Trip / Restoration

S2.OP-SO.RPS-0001 — Nuclear Instrumentation Channel Trip / Restoration

⚠️ DRAFT

S2.OP-SO.RPS-0001 — Nuclear Instrumentation Channel Trip / Restoration

Purpose

Provides procedural guidance for removing NIS channels from service (tripping) and restoring them to service. Used when NIS channel malfunctions are identified per AB.NIS-0001.

Key Actions / Information

Exam — 2020 Q22
IR channel removal from service: SO.RPS-0001 places the LEVEL TRIP switch in bypass, which causes OHA E-29 (SR & IR TRIP BYP) to annunciate. IR channels are NOT removed from service by removing control power fuses or instrument power fuses — fuse removal is used for PR channels, not IR channels. There is no POWER MISMATCH BYPASS switch for IR channels (that is a PR channel feature).
JPM — 2020 Sim-f
PR channel 2N41 removal from service (Section 5.1): Steps 5.1.1-5.1.4 pre-checks (no ESF/RPS actuation risk, not selected on 2NR45, rod control in Manual, enter TS 3.3.1.1). Then at NI Rack No. 81, five switch manipulations in Steps 5.1.5.A-E: Detector Current Comparator Upper Section in PRN41 → Detector Current Comparator Lower Section in PRN41 → Power Mismatch Bypass in BYPASS PR N41 → Rod Stop Bypass in BYPASS PR N41 (OHA E-31 clears, 2RP4 bypass light illuminates) → Comparator Channel Defeat in N41 (OHA E-39 clears). RO-only JPM.
Exam — 2019 Q30
After PR NI channel 2N41 bistable is tripped per S2.OP-SO.RPS-0001, the coincidence for the PR High Neutron Flux Reactor Trip changes from 2/4 to 1 out of 3. The tripped bistable counts as a permanent "tripped" input in the coincidence logic — it is NOT removed from the logic. Trap: candidates may think the tripped channel is removed from the logic, resulting in 2/3 coincidence. In fact, the tripped bistable satisfies one leg permanently, so only 1 of the remaining 3 functional channels needs to exceed the setpoint to complete the trip logic.

Connections