TSTF-22-09, Technical Specifications Task Force - Notification of an Error in Approved Traveler TSTF-564, Safety Limit MCPR
| ML22290A167 | |
| Person / Time | |
|---|---|
| Site: | Technical Specifications Task Force, 99902042 |
| Issue date: | 10/14/2022 |
| From: | Joyce R, Lueshen K, Richards A, Sparkman W, Vaughan J BWR Owners Group, PWR Owners Group, Technical Specifications Task Force |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| TSTF-22-09 | |
| Download: ML22290A167 (6) | |
Text
11921 Rockville Pike, Suite 100, Rockville, MD 20852 Phone: 804-339-7034 Administration by EXCEL Services Corporation TECHNICAL SPECIFICATIONS TASK FORCE A JOINT OWNERS GROUP ACTIVITY TSTF October 14, 2022 TSTF-22-09 PROJ0753 Attn: Document Control Desk U. S. Nuclear Regulatory Commission Washington, DC 20555-0001
SUBJECT:
Notification of an Error in Approved Traveler TSTF-564, "Safety Limit MCPR" The TSTF has discovered an error in the justification of TSTF-564, "Safety Limit [Minimum Critical Power Ratio] MCPR." TSTF-564 was approved by the NRC on November 16, 2018, and is applicable to Boiling Water Reactor (BWR) plants. The Experimental Critical Power Ratio (ECPR) formula provided in a response to an NRC Request for Additional Information (RAI) was incorrect. The formula was incorporated into the justification of the traveler and repeated by the NRC in their Safety Evaluation of TSTF-564 and the model Safety Evaluation for plant-specific adoption. However, it does not appear that the formula was material to the NRC's finding that the change is acceptable.
The error is described in the attachment. The incorrect formula does not affect the model application, Technical Specifications, or Technical Specifications Bases. The fuel vendor calculations of the MCPR Safety Limits for their fuel types are correct. Licensees that have adopted TSTF-564 do not need to take any action as a result of the error.
The TSTF is taking corrective actions as described in the attachment.
We apologize for this error.
Should you have any questions, please do not hesitate to contact us.
Andrew M. Richards, Jr. (PWROG/W)
Ryan M. Joyce (BWROG)
Kevin Lueshen (PWROG/CE)
Jordan L. Vaughan (PWROG/B&W)
Wesley A. Sparkman (PWROG/AP1000)
TSTF 22-09 October 14, 2022 Page 2 Attachment cc:
Michelle Honcharik, Technical Specifications Branch Victor Cusumano, Technical Specifications Branch
Description of Error in TSTF-564, "Safety Limit MCPR" Page 1
=
Background===
The TSTF submitted TSTF-564, Revision 0, "Safety Limit MCPR," on August 28, 20171. The traveler revised the Technical Specification (TS) Safety Limit (SL) value and method of calculation for the Minimum Critical Power Ratio (MCPR) limit in SL 2.1.1.2. The traveler included revised SL MCPR limits for Global Nuclear Fuel and Westinghouse fuel designs.
Subsequent to approval of the traveler, Framatome received NRC approval for MCPR SL values for their fuel designs. As a result, all BWR fuel vendors support the revised SL MCPR and method of calculation.
On April 12, 2018, the NRC provided a Request for Additional Information RAI2. Question 1 of the RAI stated:
Section 1 of TSTF-564 states that the proposed change to the MCPR safety limit (SL) is not applicable to plants using AREVA fuel. This is clarified in Section 2.4 of the traveler where it is specifically stated that "the proposed change is not applicable to BWR
[boiling-water reactor] plants using AREVA fuel due to differences in core reload design methodology." It is not acceptable to the NRC staff to categorically exclude fuel from a specific vendor in the manner proposed, because methodologies may be changed and brought into compliance with the intent of the traveler. Instead, please provide the attributes of a core reload design methodology that are necessary for the proposed change to be applicable.
The TSTF responded on May 29, 20183:
Section 1 is revised to state, "SL MCPR limits are provided for Global Nuclear Fuel and Westinghouse fuel designs. These and other fuel vendors may determine SL MCPR limits for other fuel designs using the described methodology." Conforming changes are made in Section 2.4.
There are only three elements required to apply Equation 1 in Section 3.1 of the TSTF-564 justification, and all three elements are related to the fidelity of the relationship of the critical power (CP) correlation relative to the critical power test data for the specific fuel design. Any fuel vendor must have a fuel-specific CP correlation and must have sufficient relevant CP test data to support it. It is therefore within the ability of any fuel vendor to justify the use of the approach defined in TSTF-564.
The TSTF-564 justification, Section 3.1, Equation 1, utilizes the Experimental Critical Power Ratio (ECPR). For each test data point "n", the CP correlation is evaluated at the same conditions as the test to define the Experimental Critical Power Ratio (ECPRn) for that data point as:
(
)
Measured Critical Power ECPR (Critical Power from Correlation) n n
n
(0.1) 1 Agencywide Documents Access and Management System (ADAMS) Accession No. ML17240A265.
2 ADAMS Accession No. ML18095A229.
3 ADAMS Accession No. ML18149A320.
Description of Error in TSTF-564, "Safety Limit MCPR" Page 2 From all appropriate N of these individual test data points the mean µ and standard deviation of the ECPR distribution is determined. The sample size N determines the value of as explained in Section 3.1 of the TSTF-564 justification. Note that the "i" subscript in Section 3.1 refers to the statistics for a particular BWR fuel product.
This additional explanation of ECPR is added to Section 3.1, providing all the information needed for a fuel vendor to utilize the proposed approach.
Should a licensee wish to use this approach for another fuel vendor, appropriate Bases changes must be developed. Note that the NUREG-1433 and NUREG-1434 BWR Standard Technical Specifications (STS) Chapter 2 Bases currently contain sections applicable to specific fuel vendors, and not all fuel vendors are included. Including all fuel vendors in the Bases or revising the Bases to provide a more generic description of methodologies would require a significant revision to the Chapter 2 STS Bases that is outside the scope of the traveler.
Question 5 of the RAI asked a similar question and the TSTF's response referenced the answer to Question 1.
The RAI response also provided Revision 1 of the traveler, which incorporated the ECPR formula given in the RAI response into Section 3.1, "Statistical Treatment of MCPR95/95," of the traveler justification. The model application used by licensees to request adoption of TSTF-564 does not include the incorrect information.
On October 24, 2018, the TSTF provided Revision 2 of the traveler4. The revision rounded up the Safety Limit values and updated the references.
The NRC issued the final Safety Evaluation for TSTF-564, Revision 2, on November 16, 20185.
The NRC staff discovered a typographical error in the final SE (not related to the ECPR formula) and issued a corrected SE on May 13, 20206. Section 1.2, "Background on Critical Power Correlations," repeated the ECPR formula provided by the TSTF, and added the following sentence, "For ECPR values less than or equal to 1, the calculated critical power is greater than the measured critical power and the prediction is considered to be non-conservative." The final model Safety Evaluation for plant-specific adoption of TSTF-564 also included the incorrect formula for ECPR and the descriptive sentence.
As of the date of this letter, TSTF-564 has been adopted by seventeen BWR plants. An amendment to adopt TSTF-564, submitted on July 23, 2021, is under review for Browns Ferry Units 1, 2, and 3. All BWR plants except Dresden 2 & 3, Nine Mile Point 1, and Quad Cities 1
& 2 have adopted or submitted TSTF-564.
4 ADAMS Accession No. ML18297A361.
5 ADAMS Accession No. ML18299A054.
6 ADAMS Accession No. ML20133J816.
Description of Error in TSTF-564, "Safety Limit MCPR" Page 3 Description of the Error The TSTF has been informed by Global Nuclear Fuel (GNF) that the ECPR formula they provided for the response to the RAI was incorrect.
The RAI response incorrectly stated:
ECPR (Measured Critical Power)
(Critical Power from Correlation)
The correct formula is:
ECPR (Predicted Critical Power)
( Critical Power)
The terms "critical power from correlation" and "predicted critical power" are synonymous.
This error also affects the descriptive sentence in the NRC's Safety Evaluation.
The correct formula appears in the Global Nuclear Fuels (GNF) GEXL17 correlation (NEDC-33292, "GEXL17 Correlation For GNF2 Fuel"7).
Global Nuclear Fuels, Westinghouse, and Framatome have confirmed that the correct formula was used in the SL MCPR calculations described in References 1, 2, and 3.
Corrective Actions The TSTF and Boiling Water Reactors Owner's Group (BWROG) are reviewing how incorrect information was incorporated into the traveler, and the issue has been entered into the GE Nuclear Corrective Action Program.
The BWR fuel vendors (GNF, Westinghouse, and Framatome) have been informed of the error and they have confirmed that their SL MCPR calculations are correct.
The BWR licensees have been informed of the error.
The TS, TS Bases, and model application were not affected. It does not appear that the ECPR formula was material to the staff's approval of TSTF-564. Therefore, no licensee reporting under 10 CFR 50.9 is required.
The incorrect formula in the RAI response and traveler did not result in calculation of an incorrect Safety Limit, and therefore, does not satisfy the definition of a "defect" in 10 CFR 21.
The TSTF traveler has been annotated with a reference to this letter to ensure that future submittals to adopt the traveler will consider and acknowledge the error.
7 ADAMS Accession No. ML080310378.
Description of Error in TSTF-564, "Safety Limit MCPR" Page 4 References
- 1. Letter from Brian R. Moore, Global Nuclear Fuel, to U.S. NRC, "Revised Information Supporting TSTF-564 Safety Limit Minimum Critical Power Ratio," July 30, 2018, ADAMS Accession Nos. ML18212A018, ML18212A019, ML18212A020, ML18212A021.
- 2. Letter from James A. Gresham, Westinghouse Electric Company, to U.S. NRC, "Submittal of 'Calculation for Technical Specification SLM CPR Values Applying to Westinghouse Fuel in Support of TSTF-564'," May 16, 2017, ADAMS Accession No. ML17142A319.
- 3. Letter from John A. Krakuszeski (Duke Energy) to U.S. NRC, "Application to Revise Technical Specifications to Adopt TSTF 564, 'Safety Limit MCPR'," March 9, 2020.
ADAMS Accession No. ML20070H937.