ML25098A284
| ML25098A284 | |
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|---|---|
| Site: | |
| Issue date: | 04/10/2025 |
| From: | Dukes O NRC/NRR/DANU/UAL2 |
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| Download: ML25098A284 (1) | |
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1 NOTES FOR THE FEBRUARY 12, 2025, OBSERVATION MEETING WITH X ENERGY, LLC, TO DISCUSS LONG MOTT GENERATING STATION (LMGS) PSAR CHAPTER 2 - SITE CHARACTERISTICS The table below contains the questions and corresponding responses for the topics discussed during the meeting.
NRC Question X-energy Response (Slide 9) Why does X-energy consider the data from South Texas Project (STP) and Victoria National Weather Service Station (KVCT), that it plans to use for atmospheric evaluation, to be representative of the Long Mott Generating Station (LMGS) site? The NRC staff will be looking for that discussion in the construction permit (CP) application, along with information on the KVCT data which is aviation focused including the period of record used, data recovery, wind monitoring instrumentation, and whether unit vector was used in averaging wind data.
NRC staff will also need to know if the airport data was recorded to the nearest degree or nearest 10 degrees. The NRC staff noted that the Turner method does not include the G stability class, so X-energys discussion needs to provide an explanation of the Turner methods conservatism.
X-energy does detail the towers that the data comes from in the CP application, along with the years associated with the data and how it is used. There is also a discussion using the Turner method included.
(Slide 10) Will X-energy be using the methods described in the Xe-100 Atmospheric Dispersion and Dose Calculation Methodology topical report (e.g.,
ARCON, long term X/Q calculations)?
Long term X/Q is discussed in sections 2.4 and 2.5 of the preliminary safety analysis report (PSAR), and X-energy explains how it was calculated.
(Slide 10) Can X-energy provide further clarification on the stability factors for atmospheric dispersion being conservative, what is the comparison?
Will X-energy include those descriptions in the PSAR?
Stability class F was used, and wind speed was 2-3 miles/hour, which X-energy considers very conservative.
Yes.
(Slide 10) What is the basis for X-energys statement indicating that initial calculations suggest improvement by up to 10x when comparing the PSAR atmospheric dispersion factors based on regional meteorological data to the expected factors for the final safety evaluation report that will reflect site-specific meteorological data?
X-energy will take that as a lookup and discuss with the safety team.
2 (Slide 11) If the initial X/Qs do not bound the site-specific data, the NRC staff would be looking for a discussion in the CP application detailing the next steps.
X-energy will look into that to determine if there are any issues, but the current data is very well correlated.
To clarify for context, the NRC staff notes that vector averaging of wind data tends to, depending on the site, change the wind direction which may alter the point of maximum impact. NRC staff will need to see how that data was averaged.
X-energy does discuss this in the CP application.
The NRC staff also notes that the Turner method only goes up to F stability and the X/Qs that would be controlling are 95th percentile values, which may dwarf the expected factor of 10 reduction using site-specific Met data or the stated conservatism of the data. X-energy should note how the G stability affects the X/Q distributions, as G stability class in this area appears to occur as often as F stability class.
None.
X-energy should ensure that the loading calculations for the onsite meteorological tower account for the periodic climbing of the tower unless an elevator system is used for the instrumented levels. Potential interference effects of obstructions to airflow should be considered as well although the prevailing wind direction at the site may also provide some flexibility.
X-energy will pass this information along to make sure the team is considering the climb.
Airflow interference is considered, the nearest structure is a one story (12-15ft tall) building. The current meteorological tower is sufficient distance from that.
To clarify, the NRC staffs understanding is that accident-related onsite and offsite dispersion modeling will be done with the ARCON model using the Victoria meteorological data and the Turner method for stability. Annual average X/Qs will be based on XOQDOQ modeling which will use JFDs based on South Texas meteorological data.
X-energy confirmed this is correct.
(Slide 13) Considering the multiple submittals, how can X-energy conclude that the analysis submitted in the CP application is bounding?
It is noted that there is a 2D local intense precipitation (LIP) analysis to be provided later as a supplement. How is it different from the bounding LIP analysis?
X-energys intent is to convey the message that the LIP data for the CP application is bounding due to the consideration for site grading. X-energy expects that site grading activities will add margin to the LIP calculation.
How does the statement Conservatively, the site is considered flat in the CPA analysis, demonstrate that the LIP flooding analysis is In the analyses all drainage systems are considered completely blocked and, therefore, do not contribute to the LIP
3 bounding and how will the final site grading support this statement?
Also, would the LIP flooding model consider guidance provided in NUREG-0800 regarding the assumption of drainage closure in the site-specific model?
analysis - neither does infiltration. The hydraulic gradient is not high and there will be some onsite ponding, but it will drain away from the site, the current reporting values include ponding.
There is mention of a 2D LIP model to be provided later in the supplement. How is this 2D analysis different from the bounding LIP analysis mentioned. Is the 2D LIP analysis considered bounding?
Yes, the 2D LIP analysis is the bounding analysis and will be based on the assumption that the site drainage remains blocked during the flooding analysis.
(Slide 14) It is stated that the data for the probable maximum precipitation (PMP) analysis will be obtained from the National Weather Service (NWS)/ National Oceanic and Atmospheric Administration (NOAA) and other sources. Please confirm whether the NWS data is from the hydrometeorological reports (HMR), and what the other data sources are used?
The data is based on HMR 51/52. In addition, Texas has a state specific PMP. Both will be considered and the bounding of the two will be used to perform the probable maximum flood (PMF) analysis.
(Slide 15) Is the dam failure analysis used in the CP application a copy of the Victoria County Station (VCS) analysis, except where final flood will be located?
Yes, what is presented in the CP application is a copy of what was performed in VCS.
Are the two watersheds (San Antonio and Guadalupe) contiguous or nested? How is the drainage and flow contribution from one watershed to the other?
The direct contributor of flooding from dam failure analysis is the Guadalupe River watershed. The San Antonio River joins at a distance upstream from the site. This will be considered in the supplement.
(Slide 16) Will the Sea, Lake, and Overland Surges from Hurricanes (SLOSH) model be used for screening purposes, and then will ADvanced CIRCulation (ADCIRC) and/or Simulating WAves Nearshore (SWAN) be used for the final analysis?
X-energy mentioned that the ADCIRC results are going to be lower than that of SLOSH.
Are the model resolutions and configurations comparable to make this comparative analysis?
The NRC staff understanding is correct. X-energy established hurricane parameters from NWS, did simulations on the SLOSH model, and then developed the SLOSH model to establish water levels. ADCIRC is also used to establish surge flooding levels, and the model results will be provided in the CP application.
(Slide 17) If the supplement is going to be based on 12-month, site-specific data what is the record length of data used for the calibration of the initial groundwater flow model?
Considering that a site-specific ground water model has been developed and will be updated using 12 months of site-specific X-energy has one water level measurement currently being used for calibration, it will continue for an additional12 months and then the model will be recalibrated.
4 data, what is the record length of the model currently being worked for calibration?
What is X-energy relying on for initial model development including establishing initial and boundary conditions?
Is X-energy calibrating just to one year?
Does X-energy expect the record to be representative of ambient groundwater flow and level conditions that will help determine gradient, understand impacts of seasonality and trend?
The revised model will include physical boundary conditions such as elevations of creek.
Correct, the model is currently at one year record and will retake at 12 months. The current record was from September 2024.
Not necessarily, thats why X-energy is taking 12 months of data.
Will the existing wells outside of the boundary be considered to understand trends and seasonality?
There are wells included in the network right now, in the near-distant area mostly at the Dow site. X-energy is avoiding the use of data that is not nuclear certified.
(Slide 18) With regard to the analysis of accidental release of liquid radioactive effluents, what would be the source term and the tank/component from which the accidental release is postulated to originate from?
For accidental release, there is guidance in NUREG-0800 - SRP-2.4, and it is based on postulated failure of a tank that has the highest level of activity. Has the applicant identified that appropriate tank/component and the source terms?
That is the failure location, what about the source term?
X-energy used a conservative approach and looked at the outside perimeter of equipment area. It should be within that area, but the exact point has not yet been identified.
X-energy has identified the maximum amount of released material and looked at the boundaries.
Since the analysis and the data used for the analysis are going to be updated and revised, they are subject to change. Therefore, the analysis is provisional, and this makes the assertion of a bounding analysis challenging.
X-energy expects the information in the CP application to be representative. The information provided in the CP application will be updated with the supplements.
The NRC staff understands that the geophysical data uses regional data in the CP application, and site-specific data in the supplement. Is that data within the nuclear island (NI) area and the original plant development areas shown on slide 24 and slide 28?
The geophysical data /surface data was obtained across the site (blue, green and unboxed areas shown on slides 24 and 28).
The supplement will include the unboxed area, a portion in the green, and a portion in the blue.
5 (Slide 25) What does X-energy mean by the supplement will revise or replace portions of the CP application submittal? Is the plan to replace the complete text?
This depends on the section (and the topic),
some sections will be a full replacement (e.g.,
liquefaction), but others (e.g., foundation interface and support structures) would be minor revisions without significant rewording, if modified.
What differences does X-energy expect between the CP application and supplement in terms of using regional information? Will the regional data be confirmed in the supplement or will X-energy use site-specific data to the extent possible?
How will this be tracked if there are changes that need to be made to the information in the initial CP application submittal?
X-energy will discuss with the NRC staff to determine the best approach for presenting the information clearly. The initial plan was for the supplement to be a revision to the PSAR accompanied by a redline document to show the changes.
Can X-energy explain what other areas may fall within the same type of approach as liquefaction (i.e., completely deferred to one of the supplements). What should staff expect to see in those areas in the initial CP application submission?
The CP application will identify any additional items that are also deferred.