2019 Q9 — PZR Level Variable Leg Leak

✓ C. Correct. For Part 1, the variable leg for 2LT-459 is the low side of the D/P cell. Accordingly, as D/P across 2LT-459 PSID gets larger then indicated PZR level lowers (or as D/P across 2LT-459 goes to 0, then indicated level will be at its maximum). Therefore, with a leak of the variable leg of 2LT-459, D/P will get larger and indicated PZR level will indicate off scale low. Additionally, PZR inventory is also being lost, so actual PZR level and indicated level are both lowering. NOTE, as PZR pressure lowers due to the variable leg leak, this change in pressure is felt on both sides of 2LT-459. Indicated level due to the PZR pressure change will not affect PZR indicated level. For Part 2, the variable leg is connected to the pressurizer. Consequently, when the variable leg develops a leak, actual PZR pressure will lower but since the controlling channel has failed low, the B/U heaters will not energize (indicated level is below 17% which is the low level PZR B/U cutoff setpoint).

✗ A. Incorrect but plausible. For Part 1, many of the licensed operators have demonstrated a misunderstanding on how PZR level instrumentation works (D/P = 0 psid = hi pressurizer level) as demonstrated on the 2018 LOR Bi-Annual Written Exams. Consequently, the ILOT candidate could incorrectly determine that with a variable leg leak on 2LT-459, indicated PZR level will indicate off scale high. Part 2 is correct if level indicated high (heaters would not cut off).

✗ B. Incorrect but plausible. For Part 1, many of the licensed operators have demonstrated a misunderstanding on how PZR level instrumentation works. Consequently, the ILOT candidate could incorrectly determine that with a variable leg leak on 2LT-459, indicated PZR level will indicate off scale high. For Part 2, the candidate could fail to recall that PZR B/U heaters automatically cut off when PZR level indicates less than 17%.

✗ D. Incorrect but plausible. Part 1 is correct. For Part 2, the candidate could fail to recall that PZR B/U heaters automatically cut off when PZR level indicates less than 17%.

Ref: NOS05PZRP&L-10 | LO: NOS05CCW000-11 | Source: Modified Bank (ILOT NRC 1601 RO 32) | Cognitive: Higher