ML24215A205
| ML24215A205 | |
| Person / Time | |
|---|---|
| Site: | 05200050 |
| Issue date: | 08/02/2024 |
| From: | NuScale |
| To: | Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML24215A000 | List:
|
| References | |
| LO-169995 | |
| Download: ML24215A205 (1) | |
Text
Response to SDAA Audit Question Question Number: A-16.3.1.3-1 Receipt Date: 02/26/2024 Question:
The Bases for SR 3.1.3.2 (Verify MTC is within the lower limit.) does not address the third Frequency. The applicant is requested to revise the Bases for SR 3.1.3.2 by adding a discussion of the third Frequency, which states:
NOTE-------
Only required when projected end of cycle MTC is not within limit.
7 EFPDs Thereafter
Response
NuScale revises the first paragraph of the Bases for GTS SR 3.1.3.1 and SR 3.1.3.2 to include the following sentences:
If the EOC MTC is projected to exceed the limit specified in the COLR, SR 3.1.3.2 requires MTC to be measured every 7 EFPD thereafter. Because the MTC changes slowly with core depletion, the frequency of 7 EFPD thereafter is sufficient to avoid exceeding the EOC MTC limit.
NuScale Nonproprietary NuScale Nonproprietary
Markups of the affected changes, as described in the response, are provided below:
NuScale Nonproprietary NuScale Nonproprietary
MTC B 3.1.3 NuScale US460 B 3.1.3-4 Draft Revision 2 BASES APPLICABILITY (continued)
In MODE 3 with all RCS temperatures < 200 °F and in MODES 4 and 5, this LCO is not applicable because no Design Basis Accidents (DBAs) using the MTC as an analysis assumption are initiated from these conditions.
ACTIONS A.1 MTC is a function of the fuel and fuel cycle designs, and cannot be controlled directly once the designs have been implemented in the core. If MTC exceeds its limits, the reactor must be placed in MODE 2.
This eliminates the potential for violation of the accident analysis bounds. The associated Completion Time of 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> is reasonable, considering the probability of an accident occurring during the time period that would require an MTC value within the LCO limits, and the time for reaching MODE 2 from full power conditions in an orderly manner.
B.1 Operating outside the lower MTC limit means the safety analysis assumptions for the EOC accidents that use a bounding negative MTC value may be invalid. If the lower MTC limit is exceeded, the unit must be placed in a MODE or condition in which the LCO requirements are not applicable. In addition to Required Action A.1, Required Action B.1 also requires the unit to be in MODE 3 with all RCS temperatures < 200 °F within 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br />.
The allowed Completion Time is a reasonable time based on the activities needed to reach the required MODE from full power operation in an orderly manner.
SURVEILLANCE REQUIREMENTS SR 3.1.3.1 and SR 3.1.3.2 The SRs for measurement of the MTC at the beginning and two-thirds of the way through each fuel cycle provide for confirmation of the limiting MTC values. The MTC changes smoothly from least negative to most negative value during fuel cycle operation, as the RCS boron concentration is reduced to compensate for fuel depletion. If the EOC MTC is projected to exceed the limit specified in the COLR, SR 3.1.3.2 requires MTC to be measured every 7 EFPD thereafter. Because the MTC changes slowly with core depletion, the frequency of 7 EFPD thereafter is sufficient to avoid exceeding the EOC MTC limit.