ML25265A159
| ML25265A159 | |
| Person / Time | |
|---|---|
| Site: | Vogtle  |
| Issue date: | 09/22/2025 |
| From: | Turner Z Plant Licensing Branch II |
| To: | Jeanne Johnston Southern Nuclear Operating Co |
| References | |
| EPID L-2025-LLA-0080 | |
| Download: ML25265A159 (4) | |
Text
From:
Zach Turner To:
Johnston, Jeanne D.; Rothschadl, Benjamin T.
Cc:
Subject:
Updated Audit Questions - Vogtle 1/2 - LAR for Adoption of RG 1.183 Rev 1 - EPID L-2025-LLA-0080 Date:
Monday, September 22, 2025 9:32:00 AM Attachments:
Vogtle U1-U2 - Audit Questions for LAR to Adopt Rev1 of RG 1.183.docx Ben/Jeanne,
Please see the updated audit questions from those transmitted to you in the audit plan dated July 11, 2025 (ML25190A545). Request if you could add the questions and SNCs responses to the CERTREC audit portal.
For the first two questions in the document, wed like to discuss via teams meeting. Please provide date/times SNC can be available to discuss.
These questions do not represent a final NRC position and are intended to foster the upcoming audit discussion. RAIs, if needed, will be communicated via a separate communication at the conclusion of the audit. Please let me know if you need anything additional Thanks!
Very Respectfully,
Zach Turner, Project Manager Nuclear Regulatory Commission Division of Operating Reactor Licensing NRR/DORL/LPL2-1 (301) 415-2258 Office: OWFN-10C02 Mail Stop: O-08 B01A
1 Vogtle 1&2 License Amendment Request for Adoption of Regulatory Guide 1.183 Rev 1 Updated Audit Questions - September 22, 2025 EPID L-2025-LLA-0080
- 1. The last sentence of section 3.11 of the LAR states that, EQ doses will be assessed under the existing methodology for potential impacts from the core inventory changes.
The staff interprets this sentence to mean that for radiation EQ, if future changes are made to the reactor fuel and operating parameters (such as increasing reactor burnup up to 68 GWd/MTU, increasing enrichment up to 8 weight-percent U-235, increases in power level, or cycle length), that the new core inventory will be used to calculate EQ doses and that the accident EQ doses will be calculated using the release fractions into containment and assumptions consistent with RG 1.89, Revision 1. Is this correct?
- 2. The second to the last paragraph includes the sentence, It also meets 10 CFR 100.11 related to the design basis radiological accidents being assumed to result in substantial meltdown of the core with subsequent release of appreciable quantities of fission products. It appears that the it in this sentence is referring to RG 1.183, Rev. 1. Is this correct?
Audit Questions Related to Met and Offsite and Onsite Dispersion Modeling Analyses Supporting the Review of SNCs LAR to Fully Implement Revision 1 of RG 1.183 The license amendment request (LAR) of May 12, 2025 (ADAMS Accession No. ML25132A313) proposes to adopt the full scope application of an Alternative Source Term (AST) methodology following the guidance in Regulatory Guide [RG] 1.183 Revision 1.
[outer boundary of the Low Population Zone] X/Q values are consistent with the current licensing basis, as given in VEGP Final Safety Analysis Report (FSAR) Table 2.3.4-1 and Table 15A-2. Section 3.1 (Para. 1) continues by referencing a previously submitted AST submittal based on Revision 0 of RG 1.183 (i.e., ADAMS Accession No. ML22181B066, as supplemented by ML23037A856 and ML23083B398) stating that the [s]ources and receptors for the CR
[control room] are unchanged. Neither of the referenced tables nor the corresponding text clearly identify the period(s) of record (POR(s)) of meteorological (Met) data associated with the offsite or onsite dispersion factors (X/Qs).
a) Section 3.1.1 of the current LAR (ML25132A313) is very similar to Section 3.1.1 of the earlier LAR (ML22181B066) in that both state that [t]he same meteorological data
[was] used to calculate the X/Q values applied in the current licensing basis.
However, the text in ML22181B066 goes on to state that the radiological consequence analyses was [sic] determined to remain representative of the site The basis for this additional statement is not explained or referenced.
Based on Revision 25 of the Updated FSAR (UFSAR) submitted October 23, 2024, it appears to the NRC staff that this assertion of representativeness, at least for the offsite receptor dispersion modeling, is inferred from the results listed in Table 2.3.4-1 of the UFSAR. Note that this table is attributed to Revision 14 of the UFSAR from
2 October 2007. It compares X/Q values for the EAB and LPZ using 3 Years of VEGP Site Data that are generally higher than those using what is labeled as the Most Recent Year of VEGP Site Data. Further, Section 2.3.3 (Para. 1) and various figures in Section 2.3.2 of the same earlier vintage in the UFSAR suggests that the three years of onsite Met data used as input to the offsite dispersion modeling was from December 4, 1972, through December 4, 1973, and April 4, 1977, through April 4, 1979) and that the Most Recent Year of VEGP Site Data corresponds to the period from April 1, 1980, through March 31, 1981.
Please confirm for the NRC staff that the POR of onsite Met data used for the offsite dispersion modeling results in Table 2.3.4-1 as referenced in the current LAR (ML25132A313) are from December 4, 1972, through December 4, 1973, and from April 4, 1977, through April 4, 1979. If thats not the case, then please identify the actual POR used as well as the corresponding percent data recoveries of wind speed, wind direction, and atmospheric stability class for these individual parameters and the concurrent percent data recovery of all three parameters during the actual POR if different.
b) Regardless of the POR of Met data used for the offsite dispersion modeling results used in the current LAR, please identify whether the wind measurements were made with mechanical and/or ultrasonic wind instrumentation. If the latter type was used during the three-year modeling POR and/or during the one-year comparative POR, please also identify whether the hourly wind data averages represent scalar, unit vector, or full vector average values. Section 5.3.1 of ANSI/ANS-3.11-2024 (Determining Meteorological Information at Nuclear Facilities) and its predecessor ANSI/ANS-3.11-2005 which is referenced in Regulatory Guide (RG) 1.23 (ADAMS Accession No. ML070350028) indicates that scalar averaged wind data is to be used for straight-line Gaussian dispersion models. This would include the PAVAN model which implements RG 1.145 (ADAMS Accession No. ML003740205) for offsite receptors. The difference between scalar (or unit vector) averaging and full vector averaging has potential implications to the hourly values of wind speed and/or wind direction and, therefore, the resulting X/Qs.
c) It is not clear to the NRC staff whether the resulting offsite X/Qs at the EAB and LPZ were calculated using hourly Met data or joint frequency distributions (JFDs) of wind speed, wind direction, and atmospheric stability. Neither the current LAR (ML25132A313) nor Revision 25 of the UFSAR mention the PAVAN dispersion model (ADAMS Accession No. ML12045A149) which implements RG 1.145 (ADAMS Accession No. ML003740205) but utilizes Met data in the form of JFDs. Figure 2.3.4-1 and the accompanying text in the UFSAR suggest hourly Met data may have been used. Please clarify and confirm the form of the Met data used in that modeling analysis.
d) Nevertheless, Regulatory Position 5.3 (Para. 1) in Revision 1 of RG 1.183 states that Licensees should ensure that any previously approved values remain accurate and do not include any misapplication of a methodology or calculational errors in the identified values. The NRC staff recognizes that year-to-year variations will be present in the Met data. Note also that the last paragraph of Section B (Discussion) in Revision 1 of RG 1.23 suggests that Met data used in dispersion analyses should not be older than 10 years. Assuming that the POR of Met data used in the referenced offsite dispersion
3 analysis could be at least 44 to more than 50 years old, regardless of its form as input to that modeling, the assertion of its representativeness is not clear.
Given that the annual radioactive effluent release reports (ARERRs) for this facility do not include Met data summaries, an option that is allowed for under RG 1.21 (ADAMS Accession No. ML21139A224), the NRC staff is unable to evaluate that assertion. In light of the referenced statement in Revision 1 of RG 1.183, please confirm the validity of that assertion of representativeness relative to current conditions and explain the technical basis for that conclusion.
- 2. Section 3.1.3 (Control Room [CR] Atmospheric Dispersion Factors) of the current LAR (ML25132A313) references the current licensing basis for the CR X/Q analysis to an earlier LAR to implement Revision 0 of RG 1.183 (i.e., ML22181B066, dated June 30, 2022). Further, Section 3.1.1 of the current LAR states [t]he same meteorological data used to calculate the X/Qs applied in the current licensing basis radiological consequence analyses were used.
Neither the current LAR (ML25132A313) nor the earlier referenced LAR (i.e., ML22181B066) appear to indicate the POR of onsite Met data used in the onsite CR dispersion modeling analysis. Section 3.1.1 of the earlier LAR could reasonably be interpreted to mean that the same POR of onsite Met was used for both the offsite (EAB and LPZ) and onsite (CR) dispersion modeling analyses.
However, Section 3.2.1 of the safety evaluation (i.e., ML23158A018) that corresponds to the earlier LAR (ML22181B066) states that [i]n support of the LAR, SNC [Southern Nuclear Operating Company] provided the hourly onsite meteorological data from calendar years 1998 through 2000, that was used in the analysis.
a) Verify that a 1998 to 2000 POR of onsite Met data was used for the onsite (CR) dispersion modeling analysis being referenced in the current LAR. In addition, please specify the start and end dates of this POR.
b) Contrary to what might reasonably be implied from the LAR as written, confirm that two different PORs were used for the offsite and onsite dispersion modeling analyses being referenced in the current LAR.
c) As in Question 1(b) above, please identify whether the wind measurements during the POR were made with mechanical and/or ultrasonic wind instrumentation. If the latter type was used, please also identify whether the hourly wind data averages represent scalar, unit vector, or full vector average values.
d) Also, per Question 1(b) above, scalar averaged wind data is to be used for straight-line Gaussian dispersion models. This would include the ARCON 2.0 dispersion model as indicated in Section 3.1.3 of the current LAR which implements RG 1.194 (ADAMS Accession No. ML031530505) for onsite receptors. If full vector averaging was used to determine the hourly wind speed and wind direction values input to ARCON 2.0, the resulting X/Qs that were previously approved via the corresponding Safety Evaluation Report (ML23158A018) in Section 3.1.3 of the current LAR may be affected.
Therefore, if full vector averaging was used, evaluate any effects on the accident related X/Qs at the various receptors considered in the current LAR as well as the downstream dose calculations to which they are direct inputs.