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Exams > 2019 Q29 — Rod Control Speed vs Temperature Error

2019 Q29 — Rod Control Speed vs Temperature Error

⚠️ DRAFT
Q29 — Rod Control Speed vs Temperature Error 001 Control Rod Drive System-K4.05 (3.9)
Given:
• Unit 1 is 100% Reactor Power

At time 1900
• An AUTOMATIC Turbine Runback occurs

At time 1905
• The crew starts a rapid RCS boration in order to raise the control rods above the Rod Insertion Limit
• The Rod Bank Selector Switch is in AUTO

At time 1910
• The Rod Control Summing Unit has calculated that the magnitude of the TOTAL TEMPERATURE ERROR is 4 °F

Which ONE of the following completes the statement below?

At 1910 Control Rods are stepping out at ___ steps per minute.
A. 72
B. 40
C. 24
D. 8
▶ Show Answer & Explanation
✓ B. Correct. With Rods in auto, control speed varies based on the total temperature error. With a temperature error of 1.5 °F to 3 °F, rods will move at 8 spm. With a temperature error of 3 °F to 5 °F, rods will move from 8 spm to 72 spm (linearly). This corresponds to an increase of 32 spm / °F. Consequently, with a TOTAL TEMPERATURE ERROR of 4 °F, rods will move 40 spm (8 spm + (32 spm / °F x 1 °F)).
✗ A. Incorrect but plausible. Since rod control speed can vary from 8 SPM to 72 SPM with Rod Control in automatic, all distractors are plausible.
✗ C. Incorrect but plausible. Since rod control speed can vary from 8 SPM to 72 SPM with Rod Control in automatic, all distractors are plausible.
✗ D. Incorrect but plausible. Since rod control speed can vary from 8 SPM to 72 SPM with Rod Control in automatic, all distractors are plausible.
Ref: NOS05RODS00-12 (ROD CONTROL AND POSITION INDICATION SYSTEMS) | LO: Draw a one-line diagram of the Reactor Control Unit indicating Temperature Error Circuit, Power Mismatch Circuit, Rate Comparator, Non-Linear Gain Unit, Variable Gain Unit, Summer | Source: New | Cognitive: Higher

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