Term
| Explain the purpose and function of the ATWS system. |
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Definition
| To mitigate the consequences of the extremely unlikely failure of the Reactor Protection System to effect reactor shutdown when required. |
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Term
| State the parameters and limits which the ATWS system will maintain below. |
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Definition
| Reactor vessel pressure less than 1500 psig; Fuel energy deposition less than 280 calories/gram and clad oxidation less than 17% by volume; Containment pressure less than 56 psig and suppression pool local temperature less than 170 degrees F. |
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Term
| Explain the functions of the major component of the ATWS System. |
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Definition
| "Each ATWS System logic channel is made up of two sub-channels designated A and C for Channel A, and sub-channels B and D for Channel B. For each input parameter, there is one independent sensor for each of the sub-channels. The inputs are: reactor vessel low-low water level, reactor vessel high pressure, and manual initiation." |
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Term
| "Given a one-line diagram of the ATWS logic channels, explain how the two-out-of-two once logic is incorporated into the system function." |
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Definition
| Both sub-channels are required for an ATWS initiation. |
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Term
| Given a one-line diagram of the ATWS logic channels explain how the one-out-of-two twice logic is incorporated into the reactor feed pump and turbine trips. |
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Definition
| There are four ATWS level transmitters that drive four master trip units. Each master trip unit drives a slave trip unit. Relay logic from these four slave trip units is arranged in a one-out-of-two taken twice logic to trip main turbine and reactor feed pumps when reactor water level reaches +48 inches. These trips prevent damage to the main turbine due to excessive moisture carryover. |
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Term
| Power supply(s) for ATWS Channel A logic: |
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Definition
| Y70 and D11 are auctioneered. |
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Term
| Power supply(s) for ATWS Channel B logic: |
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Definition
| Y80 and D21 are auctioneered. |
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Term
| Power supply for Alt Rod Insertion (ARI) solenoid valves: |
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Definition
| SV-3-142A: D-11; SV-3-142B: D-21; NOT AUCTIONEERED. |
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Term
| Describe the low-low reactor water level input to ATWS |
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Definition
| "The setpoint is -47 inches. To prevent this trip from affecting ECCS system performance, a 7.3 second time delay is provided. If the low-low level clears prior to 7.3 seconds elapsing, the relay will reset and a trip will not occur." |
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Term
| Describe the Reactor Vessel high Pressure input to ATWS. |
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Definition
| Setpoint is 1135 psig. There is no time delay associated with this input. |
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Term
| What happens if ATWS subchannels 'A' and 'C' are actuated? |
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Definition
| BOTH recirc pump field CKT Bkrs trip and the associated ARI valve (SV-3-142A) energizes to bleed off the scram air header. |
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Term
| What happens if ATWS subchannels 'B' and 'D' are actuated? |
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Definition
| BOTH recirc pump field CKT Bkrs trip and the associated ARI valve (SV-3-142B) energizes to bleed off the scram air header. |
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Term
| Describe the General Precaution regarding both sources of power to a given ATWS channel de-energized. |
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Definition
| "In this situation, additional steps must be taken prior to re-energizing a source to preclude an inadvertent alternate rod insertion and recirc MG set field breaker trips. This is required because when re-energized, the logic is re-energized immediately, while the instrument loop potentially has an inherent time delay, thus causing a false initiation signal." |
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Term
| "With a manual ATWS initiation, how long does it take for all rods to be inserted?" |
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Definition
| Twenty-five to thirty seconds from first rod movement. |
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Term
| List the steps for manual initiation of ATWS. |
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Definition
| 1. Set arming collars of one pair (A/C or B/D) and actuate; 2. Verify recirc pump field breakers are tripped; 3. Trip MG Set drive motors; 4. Verify control rod insertion occurs by observing the full-core display (Panel C-05). NOTE: 25-30 seconds for all rods to be inserted. |
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Term
| Describe the difference in terminology between the B-manual and Tech Specs with respect to ATWS. |
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Definition
| "B-Manual: Each ATWS logic CHANNEL is made up of two SUB-CHANNELS designated 'A' and 'C' for CHANNEL A, and 'B' and 'D' for CHANNEL B. There is one INDEPENDENT FUNCTION for each channel. In Tech Specs, a CHANNEL is referred to as a TRIP SYSTEM; a SUB-CHANNEL is referred to as a CHANNEL; and each INDEPENDENT SENSOR is referred to as an INSTRUMENTATION FUNCTION. (See Tech Spec LCO 3.3.4.1)" |
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Term
| Tech Spec 3.3.4.1 LCO/Applicability and Conditions with less than or equal to one hour completion time |
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Definition
Section 3.3: Instrumentation Tech Spec 3.3.4.1: Anticipated Transient Without Scram Recirculation Pump Trip (ATWS-RPT) Instrumentation LCO 3.3.4.1: Two Channels per trip system for each ATWS-RPT instrumentation Function listed below shall be OPERABLE: CONDITION C. Both Functions with ATWS-RPT trip capability not maintained; Required Action C.1 Restore ATWS-RPT trip capability for one Function COMPLETION TIME: 1 hour. |
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Term
| What are the consequences of a complete loss of a 125 VDC system on ATWS? |
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Definition
| Trip coil power comes from 125 VDC. A loss of one 125 VDC system means a loss of a complete CHANNEL/TRIP SYSTEM. |
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