ML24326A127
| ML24326A127 | |
| Person / Time | |
|---|---|
| Site: | 05200050 |
| Issue date: | 11/21/2024 |
| From: | NuScale |
| To: | Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML24326A092 | List: |
| References | |
| LO-175900 | |
| Download: ML24326A127 (1) | |
Text
Response to SDAA Audit Question Question Number: A-16.3.1.2-1 Receipt Date: 03/18/2024 Question:
GTS Surveillance Requirement 3.1.2.1 (Verify overall core reactivity balance is within +/-1% k/k of predicted values.) requires performing this verification before exceeding 60 EFPDs of reactor power operation following the start of each 18-month operating cycle for the purpose of determining if adjustment of predicted core reactivity values is needed, as specified in the surveillance column Note:
Predicted reactivity values may be adjusted to correspond to measured core reactivity prior to exceeding a fuel burnup of 60 effective full power days (EFPDs) after each refueling.
The applicant is requested to add an explicit Frequency for this performance of the Surveillance, even though the equivalent SR in W-AP1000-STS (NUREG-2194, Rev. 1)and Westinghouse STS (NUREG-1431, Rev. 5) do not have such an explicit Frequency. The staff is interested in improving the clarity of the NuScale GTS and associated Bases regarding this event-based Frequency.
Response
NuScale revises Generic Technical Specification (GTS) Surveillance Requirement (SR) 3.1.2.1 to remove the note associated with adjustment of the predicted reactivity values to correspond to measured core reactivity prior to exceeding a fuel burnup of 60 effective full-power day (EFPD) after refueling. NuScale has no basis for the inclusion of this note other than consistency with the Standard Technical Specifications. The note implies that the adjustment of predicted reactivity values is prohibited beyond 60 EFPD. There is no restriction on the timing of NuScale Nonproprietary NuScale Nonproprietary
revision of predicted reactivity values. The Bases for Actions A.1 and A.2 of GTS 3.1.2 discuss the response to anomalies between measured and predicted core reactivity. The described response includes the revision of predictions. The Bases do not discuss any limitations on when in core life the predictions can be revised.
NuScale revises GTS Surveillance Requirement (SR) 3.1.2.1 to remove the note in the Frequency column. A note describing when the surveillance is to be performed is unnecessary.
The Surveillance Frequency Control Program (SFCP) establishes the surveillance frequency.
Any guidance on the timing of the surveillance frequency is established by the SFCP. The removal of this note, and dependance on the SFCP to establish the frequency, eliminates the need to provide an explicit frequency for the performance of this surveillance.
NuScale revises the SFCP basis for SR 3.1.2.1 in Standard Design Approval Application Table 16.1-1 to remove the phrase following the initial 60 EFPD. This change aligns the basis for the Surveillance Frequency Control Program base frequency for SR 3.1.2.1 with the changes to GTS Surveillance Requirement 3.1.2.1. Removal of 60 EFPD from the basis for SR 3.1.2.1 clarifies that the base frequency of 31 EFPD for SR 3.1.2.1 starts after exceeding 5 percent rated thermal power.
Markups of the affected changes, as described in the response, are provided below:
NuScale Nonproprietary NuScale Nonproprietary
Core Reactivity 3.1.2 NuScale US460 3.1.2-2 Draft Revision 2 SURVEILLANCE REQUIREMENTS SURVEILLANCE FREQUENCY SR 3.1.2.1
NOTE--------------------------------
Predicted reactivity values may be adjusted to correspond to measured core reactivity prior to exceeding a fuel burnup of 60 effective full power days (EFPDs) after each refueling.
Verify overall core reactivity balance is within
+/-1% k/k of predicted values.
Once prior to exceeding 5% RTP after each refueling AND
NOTE--------
Only required after 60 EFPDs.
In accordance with the Surveillance Frequency Control Program
Core Reactivity B 3.1.2 NuScale US460 B 3.1.2-5 Draft Revision 2 BASES ACTIONS (continued) acceptable for continued operation, then the boron letdown curve may be renormalized and power operation may continue. If operational restriction or additional SRs are necessary to ensure the reactor core is acceptable for continued operation, then they must be defined.
The required Completion Time of 7 days is adequate for preparing and implementing whatever operating restrictions that may be required to allow continued reactor operation.
B.1 If the core reactivity cannot be restored to within the 1% k/k limit, the unit must be brought to a MODE in which the LCO does not apply. To achieve this status, the unit must be brought to at least MODE 2 within 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />. If the SDM for MODE 2 is not met, then boration may be required to meet SR 3.1.1.1 prior to entry into MODE 2. The allowed Completion Time is reasonable, for reaching MODE 2 from full power conditions in an orderly manner.
SURVEILLANCE REQUIREMENTS SR 3.1.2.1 Core reactivity is verified by periodic comparisons of measured and predicted RCS boron concentrations. The comparison is made considering that other core conditions are fixed or stable, including CRA position, moderator temperature, fuel temperature, fuel depletion, xenon concentration, and samarium concentration. The Surveillance is performed prior to exceeding 5% RTP as an initial check on core conditions and design calculations at BOC. The Surveillance is performed again prior to exceeding 60 effective full power days (EFPDs) to confirm the core reactivity is responding to reactivity predictions and then periodically thereafter during the fuel cycle in accordance with the Surveillance Frequency Control Program. The SR is modified by a Note indicating that the predicted core reactivity may be adjusted to the measured value provided this normalization is performed prior to exceeding a fuel burnup of 60 EFPDs. This allows sufficient time for core conditions to reach steady state, but prevents operation for a large fraction of the fuel cycle without establishing a benchmark for the design calculations.
The subsequent Surveillance Frequency is controlled under the Surveillance Frequency Control Program.
NuScale Final Safety Analysis Report Technical Specifications NuScale US460 SDAA 16.1-5 Draft Revision 2 Audit Question A-16-7, Audit Question A-16.3.1.2-1 Table 16.1-1: Surveillance Frequency Control Program Base Frequencies Surveillance Requirement Base Frequency Basis 3.1.1.1 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> The Frequency of 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> is based on the generally slow change in required boron concentration and the low probability of an accident occurring without the required shutdown margin (SDM). This allows time for the operator to collect the required data, which includes performing a boron concentration analysis, and to complete the calculation.
3.1.2.1 31 effective full-power days (EFPDs)
The required subsequent Frequency of 31 EFPDs, following the initial 60 EFPDs after exceeding 5% rated thermal power (RTP), is acceptable based on the slow rate of core changes due to fuel depletion and the presence of other indicators (e.g. axial offset (AO)) monitored by the core monitoring system for prompt indication of an anomaly.
3.1.4.1 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> Verification that individual control rod assembly (CRA) positions are within alignment limits at a 12 hour1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> Frequency provides a history that allows the operator to detect a CRA that is beginning to deviate from its expected position. The specified Frequency takes into account other CRA position information that is continuously available to the operator in the control room so that during actual rod motion deviations can immediately be detected.
3.1.4.2 92 days The 92 day Frequency takes into consideration other information available to the operator in the control room and SR 3.1.4.1, which is performed more frequently and adds to the determination of OPERABILITY of the CRAs.
3.1.5.1 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> Because the shutdown CRAs are not moved during routine operation, except as part of planned surveillances, verification of shutdown CRA position at a Frequency of 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> is adequate to ensure that the shutdown CRAs are within their insertion limits. Also, the Frequency takes into account other information available in the control room for the purpose of monitoring the status of shutdown rods.
3.1.6.1 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> Verification of the regulating group insertion limits at a Frequency of 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> is sufficient to detect a CRA that may be approaching the insertion limits because, normally, very little rod motion is expected to occur in 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />.
3.1.8.1 30 minutes Verification that the THERMAL POWER is 5% RTP ensures that the unit is not operating in a condition that could invalidate the safety analyses.
Verification of the THERMAL POWER at a Frequency of 30 minutes during the performance of the PHYSICS TESTS ensures that the initial conditions of the safety analyses are not violated.
3.1.8.2 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> The Frequency of 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> is based on the generally slow change in required boron concentration and on the low probability of an accident occurring without the required SDM.
3.1.9.1 31 days A 31 day Frequency is considered reasonable in view of other administrative controls that ensure a misconfiguration of the chemical and volume control system (CVCS) makeup pump demineralized water flow path is unlikely.
Also, the Frequency takes into account other information available in the control room for the purpose of monitoring the status of CVCS makeup pump demineralized water flow path configuration.
3.1.9.2 24 months The 24 month Frequency is based on the potential for unplanned plant transients if the surveillances were performed with the unit at power. The 24 month Frequency is also acceptable based on consideration of the design reliability of the equipment. The actuation logic is tested as part of engineered safety features actuation system (ESFAS) actuation and logic testing, and valve performance is monitored as part of the Inservice Testing Program.