ML26033A255
| ML26033A255 | |
| Person / Time | |
|---|---|
| Site: | 05000614, 99902117 |
| Issue date: | 02/02/2026 |
| From: | Long Mott Energy |
| To: | Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML26033A250 | List: |
| References | |
| 2026-PLM-NRC-003 | |
| Download: ML26033A255 (0) | |
Text
Long Mott Generating Station Preliminary Safety Analysis Report Section 2.4 Hydrology 2.4.13-i January 2026 CHAPTER 2 SUBSECTION 2.4.13 ACCIDENTAL RELEASES OF LIQUID EFFLUENTS INTO GROUND AND SURFACE WATERS LIST OF TABLES Number Title 2.4.13-1 Estimated Liquid Radwaste Specific Activities 2.4.13-2 Unity Rule Calculations - Initial Composition 2.4.13-3 Isotope Half-Lives and Retarded Travel Times 2.4.13-4 Unity Rule Calculations - Retarded Travel Time Composition
Long Mott Generating Station Preliminary Safety Analysis Report Section 2.4 Hydrology 2.4.13-ii January 2026 LIST OF FIGURES Number Title 2.4.13-1 Facilities Particle Tracks 2.4.13-2 Facilities Corners Particle Track After 20 Years
Long Mott Generating Station Preliminary Safety Analysis Report Section 2.4 Hydrology 2.4.13-1 January 2026 2.4.13 ACCIDENTAL RELEASES OF LIQUID EFFLUENTS INTO GROUND AND SURFACE WATERS This section describes the hypothetical accidental liquid release scenario for the various areas where liquid radwaste might occur within the nuclear island (NI): Fuel Handling Annex Building (FHAB), Canister Processing Facility (CPF), Helium Services Facility (HSF), Inter-Unit Access Tunnel (IUAT), Reactor Building (RB), and Radwaste Building (RWB). Not all design parameters have been determined at this time, but some bounding assumptions are used in this evaluation. These assumptions are described below.
LME estimates the liquid waste generation rate as 1.23 cubic meters per day or approximately 9500 gallons per month.
(1180 liters per day); th This waste will be containerized and shipped offsite for disposal. The A Sand water-bearing zone is overlain with low permeability clays, and if a release reaches the A Sand water-bearing zone, it would migrate eastward at a relatively slow rate (see Section 2.4.13.1) and would allow the groundwater monitoring program to detect any release prior to migrating off the Long Mott Generating Station (LMGS) site, enabling the required remedial measures, if necessary, to be put into place long before it could reach any potential receptor.
Radioactive wasteswaste will be handled by the Radioactive Waste Management System (RWMS). Final design details of this system are still pending.
The following bounding volumetric estimates of waste material for potential accidental release apply: worst failure case tank volume is 75 cubic meters (75,000 liters or 19,815 gallons) 120 m3 in the Radioactive Waste Building (RWB), 1436 m3 in the RB and Reactor Cavity Cooling System (RCCS),
and 10 m3 in the SFISF. Of the 1436 m3 in the RB and RCCS, 1421 m3 is in the RCCS and contains only tritium at 370 Becquerels/cubic centimeter (Bq/cc).
NRC (NRC 10 CFR Part 20, Appendix B, Table 2 (there are individual tables for each isotope)) sets Effluent Concentration Limits (ECLs) for various isotopes.
Estimated specific activities for expected nuclides are provided in Table 2.4.13-1. This composition excludes the potential 1421 m3 of tritium containing fluids in the RCCS. All the individual isotopes initially exceed their respective ECLs.
In addition, using the NRC unity rule (sum of ratios), the initial assemblage of isotopes exceeds unity (i.e., 1.0).
Long Mott Generating Station Preliminary Safety Analysis Report Section 2.4 Hydrology 2.4.13-2 January 2026 The sum of ratios is calculated:
1.0
Equation 2.4.13-1 Where:
R1 = total activity concentration for radionuclide 1 R2 = total activity concentration for radionuclide 2 Rn = total activity concentration for radionuclide n ECLR1 = Effluent concentration limit (ECL) threshold for radionuclide 1
ECLR2 = ECL threshold for radionuclide 2 ECLRn = ECL threshold for radionuclide n Results of using the unity rule on the initial individual isotope concentrations are included in Table 2.4.13-2. The sum of the ratios is greater than 1, which indicates that attenuating factors (e.g.,
retardation, radioactive decay, dispersion, or dilution) need to be considered, since a release would not meet the ECLs pending their inclusion. Further information regarding a potential accidental release is provided below.
Potential receptor location(s) have not yet been fully identified. There have beenare 18 potential receptors (users of groundwater) identified ranging from 0.87 mi. (1.40 km) to 36.44 mi. (58.64 km) from the center of the site. It is unlikely that any of these potential receptors would use A Sand water bearing zone groundwater because it is not likely present at these distances nor is it an aquifer that could sustain a consistent yield. As a conservative estimate, anything approaching the current groundwater flow model domain limit (such as entering a drain or a constant head boundary cell) is considered a potential release exposure point in this or in any future modeling.
The envisioned accidental release scenario includes the following assumptions:
A worst-case release of liquid waste of 14575 cubic meters (19,815 gallons) with composition as listed in Table 2.4.13-1 at or near land surface (the tritium waste has lower activity and is considered a lesser case).
Long Mott Generating Station Preliminary Safety Analysis Report Section 2.4 Hydrology 2.4.13-3 January 2026 The release would occur somewhere within the Nuclear/Conventional Island area.
The liquid would make its way through the overlying low-permeability clays to enter the A Sand water-bearing zone.
Conservatively, no dilution of the release with groundwater is assumed.
The released isotopes move relatively slowly eastward with the general groundwater flow in the A Sand water bearing zone..
Attenuation due to adsorptive retardation and radioactive decay are not initially considered. These factors would slow migration rates and reduce total activity of the isotopes identified in Table 2.4.13-1 at potential receptor locations. Mitigating factors will be considered in a later step of this analysis (section 2.4.13.4).
2.4.13.1 Initial Assessment Using Seepage Velocities.
The groundwater flow system downgradient of the point of release was evaluated to identify potential exposure points from an accidental release of radionuclides to groundwater. First, estimates of seepage velocities, based on hydraulic gradient, hydraulic conductivity, and effective porosity were determined. For the A Sand water bearing zone, this resulted in an average groundwater seepage velocity of 0.0693 ft/day (219 mm/day) and a maximum seepage velocity of 0.5318 ft/day (55 162 mm/day). These correspond to seepage velocities of 2511 and 19366 ft/yr (7.673.3 and 5920.0 m/yr),
respectively.
Given the direct distance to the creek is approximately 1000 ft (305 m), the simplistic unattenuated straight-line travel time is estimated to be between 15 and 4091 years. Ignoring both the attenuation of dissolved radionuclides by adsorption to aquifer solids and radioactive decay as well as a more indirect path to the creek, this conservatively (fast) estimate of travel time (15 years) cannot rule out plausible transport and potential for exposure within realistic time periods. These bounding estimates are simplistic and do not necessarily reflect true travel paths and velocities. A more accurate method using particle tracking is presented in Section 2.4.13.2, and is used as the basis for conclusionsneed tousing particle tracking presented 2.4.13.2 Assessment Using Particle Tracking Based on the indeterminantuncertainty in the results of the simplistic assessment using straight-line path assumptions and
Long Mott Generating Station Preliminary Safety Analysis Report Section 2.4 Hydrology 2.4.13-4 January 2026 the potential range of seepage velocities, a more detailed analysis was warranted using particle tracking that considered groundwater flow to determine if they reach potential receptors, and if so, when. The basis for this analysis was the groundwater flow model developed for the site as described in section 2.4.122.3.1.1x.
The release was simulated by placing a particle in every model grid block within the vicinity of the Nuclear and Conventional Plant Facilities area and tracking their movement for various time periods through the modelled groundwater flow regime to see where they go, if they reach potential receptors, and if so, when. The movement of these particles through time was calculated using MODPATH, which is a companion program to MODFLOW, and which uses MODFLOW output to perform the particle tracking. While a steady-state groundwater flow simulation does not require specifying a porosity, an effective porosity is needed in MODPATH to compute particle velocities and estimate travel times between release and receptor locations. The value of effective porosity specified for this model simulation was 0.25 which is somewhat more conservative that the average value of 0.2 and the model was run for varying lengths of time from 1 to 106 years.
In The release was simulated by placing a particle in every model grid block within the vicinity of the Nuclear/Conventional Island and tracking their movement for various periods through the modeled groundwater flow regime, if they reach potential receptors, and if so, when. The movement of these particles through time was calculated using MODPATH, which is a companion program to MODFLOW that uses its output to track the particles. While a steady-state simulation does not require specifying a porosity, an effective porosity is needed in MODPATH to estimate travel times. The value of effective porosity specified for this model simulation was 0.22 25 (22 25 percent), and the model was run for varying lengths of time from 1 year to 100 years.addition to the arrival of the first particle, the arrival of oOther notable particles tracking simulations twere identified. These included racked the earliest particles released at the center of the project site to West Coloma Creek while the median time for particles released at this location was also determined.
According to the MODFLOW/MODPATH simulation, it takes approximately 22 11.6 years for the first of the unattenuated particles to reach the vicinity of the creek drain cells representing West Coloma Creek ("creek"). The particles from the eastern corners reach the creek drain more quickly than the western corners' particles, which are still essentially within or near the boundaries of the Nuclear/Conventional Island by the time the eastern corners' particles have reached the creek
Long Mott Generating Station Preliminary Safety Analysis Report Section 2.4 Hydrology 2.4.13-5 January 2026 drain. Travel times for the other two scenarios were approximately 61approximately 61 and 106 years, respectively.
It is worth reiterating that the particle tracking is done without considering attenuation factors such as radioactive decay and adsorptive retardation onto the aquifer materials. Thus, travel times are conservative, and real travel times would be longer due to these other factors.
Results of the particle tracking are depicted oinn Figure 2.4.13-1.
2.4.13.3 Sensitivity Analysis A more formal sensitivity study on the response of the particle tracking analysis included rerunning the tracking simulation with nine particles seeded all acrossat each of the the four corner locations of the Nuclear/Conventional Island area, and then tracking and noting the location of potential receptors at the creek and their fastest and median travel times. In addition, a hypothetical 1/2 shortest travel time was calculated and a unity rule value calculated as an additional sensitivity analysis. This was for sensitivity analysis only and does not represent a plausible travel time in this analysis.
Reviewing the particle tracks suggests the particles in the corners closest to the creek drain move quickly and would arrive before particles from the two more distant corners.
Results of the particle tracking sensitivity analysis (including the additional particle initiation locations) are depicted on Figure 2.4.13-1.2. As noted above, major changes in the initial positions of potential release points affect travel time and can affect the exact location of discharge into the creek. More specific location(s) for potential release would refine estimates of travel and discharge point(s) into the creek.
2.4.13.4 Attenuation Factors Two particular attenuation factors considered here can significantly affect the transport of released isotopes - radioactive decay and retardation of advective transport due to interaction of the dissolved isotope with the water bearing zoneunits solid matrix.
Radioactive Decay Each identified isotope that may be potentially released has a distinct decay constant that describes how quickly that isotopes nuclei decay by a certain radioactive decay process. One of the common measures of this is an
Long Mott Generating Station Preliminary Safety Analysis Report Section 2.4 Hydrology 2.4.13-6 January 2026 isotopes half-life. This is the time needed for half of a given number of atoms to undergo a radioactive decay process and is a constant value under all practical conditions.
As noted above, a half-lifes value depends on the isotope. An extensive, authoritative list of isotopes half-lives is available from Brookhaven National Laboratories (https://www.nndc.bnl.gov/walletcards). The half-lives used in this calculation were taken from this source where possible. For Ag-110m, I-131, and Ba-137m half-lives from MIRDSOFT MIRDspecs were used.
Advective Retardation (Sorption)
Sorption is a process where the dissolved constituent in groundwater interacts with the solid phase through which it is flowing, retarding its movement relative to the groundwater flow velocity. As described in Kresic (2023):
Sorption results in distribution of a solute between the solution (groundwater, where it is dissolved) and the solid phase (where it is held by the solids of the aquifer). This distribution is called partitioning, and it is quantitatively described with the term distribution coefficient (or sorption coefficient, or partitioning coefficient), and) and denoted with Kd.
Importantly, Kd is a generic term devoid of any inferred mechanism. It is used to describe the general partitioning of aqueous phase constituents to a solid phase due to sorption.
Because of sorption, the contaminant movement in groundwater is slowed down relative to the average groundwater velocity. This effect of sorption is called retardation and the affinity of different solutes (chemicals dissolved in groundwater) to be retarded is quantified with a parameter called the retardation factor, denoted with R. The overall effect of sorption is a decrease in dissolved contaminant concentrations.
Sorption potential varies only minimally among isotopes of an element, especially for the heavier elements where the difference in mass is minimal among isotopes of the same element. Isotope-specific Kd values are not generally cataloged, especially for the heavier elements. For this reason, partitioning coefficients for isotopes of interest in these calculations will be considered the same across all isotopes for a given element. Kd values are available from a number of sources. One frequently used source is the following:
The Atomic Energy of Canada, Limited (AECL) has published A Critical Compilation and Review of Default Soil Solid/Liquid Partition Coefficients, Kd, For Use in Environmental Assessments, AECL-10125 which includes an extensive list of elemental Kd values for sand, silt and clay.
Partition coefficients are dependent on both the constituent being partitioned
Long Mott Generating Station Preliminary Safety Analysis Report Section 2.4 Hydrology 2.4.13-7 January 2026 and the solid material participating in the partitioning. Generally, sand has less interaction with dissolved constituents and causes the least retardation, leading to conservative (shorter) estimates of travel time and (greater) estimates of concentration downgradient of the release. To be conservative, attenuated flow will use the least retarded transport material (sand) while using elemental Kd values from Table 8 of AECL-10125.
A more comprehensive analysis considers the attenuation factors affecting the potential release to receptor locations. As noted above, both sorptive retardation and radioactive decay attenuate the potential exposure.
Retardation slows the travel time allowing greater decay and spreads out the contaminant mass along the flow path, leading to a smaller peak exposure while radioactive decay removes activity from the system, lessening the total amount of contaminant available and slowing arrival times and lowering concentrations.
Sorption Using the retardation factors derived from the element-specific Kd values for sand (as described above in subsection 2.2.5), the various retarded travel times for constituents listed in Table 2.4.13-1 are shown in Table 2.4.13-3.
These retarded travel times are the conservative estimates of when the peak concentration of contaminant will arrive at the potential receptor location.
Because of isotope-specific variable spreading of the mass of contaminants in the flow path due to sorption, some of the contaminants will arrive earlier than this (but no quicker than the unretarded groundwater flow time described above). Also, some of the contaminants will arrive later than the peak. The larger the retardation factor, the more the contaminant mass will be spread along the flow pathpath, and the peak concentration will be relatively lessened.
A linear retardation factor is related to Kd and aquifer properties using the following equation (13.8 from Kresic (2023)):
1
Equation 2.4.13-2 Where:
R = retardation factor (dimensionless) b = bulk density (grams per cubic centimeter) of the aquifer porous media (assumed quartz mineral 2.65 *(1-n) =
1.9875)
Long Mott Generating Station Preliminary Safety Analysis Report Section 2.4 Hydrology 2.4.13-8 January 2026 Kd = distribution coefficient (cubic centimeters per gram) n = porosity of the media at saturation (assumed to be 0.25)
Radioactive Decay Using the isotope-specific half-lives previously described and the retarded travel times just described, total numbers of half-lives elapsed during the retarded travel have been calculated and are included in Table 2.4.13-3. In addition, using the following equations for remaining mass or activity after a set time has elapsed for an isotope with a given half-life (from European Organization for Nuclear Research (CERN, Radioactive Decay: An Introduction, Chris Cassel 2013)):
2
Equations 2.4.13-3 and 2.4.13-4 Where:
= decay constant (1/day) ln(2) = natural logarithm of 2 T = half-life (days)
N = Number of atoms (or activity) at time t N0 = Initial number of atoms (or activity) at time = 0 e = base of natural logarithm (Eulers number) t = time of interest (days)
If a partition coefficient was not available, the retardation factor was set to 1, i.e., no retardation as a conservative assumption.
Table 2.4.13-4 presents the results after calculating each of these quantities for all isotopes of interestAfter calculating each of these quantities for all isotopes of interest the results are shown in Table 2.4.13-4.(Note that the 1/2
Long Mott Generating Station Preliminary Safety Analysis Report Section 2.4 Hydrology 2.4.13-9 January 2026 travel time scenario is included for sensitivity analysis only and does not represent an actual travel time predictionestimate.)
Unity Rule calculations were performed on the resulting maximum concentrations at the point of potential exposure (after radioactive decay and retarded travel). All isotopes would be expected to be below ECLs, and a composite of all maximum concentrations Unity Rule does not exceed 1 (Note
- All of the isotopes emerging at the point of potential exposure is not likely due to variable retardation (different Kd) for each isotope, so a combination of all maximums arriving at the receptor at the same time is a very conservative estimate). See Table 2.4.13-4 for details of expected maximum concentrations after retarded travel and decay.
Sensitivity analysis (taken as 1/2 shortest expected travel time) still has an acceptable unity value, so minor overestimates of shortest travel time will not lead to erroneous conclusions for unity values. Underestimates of travel time would lead to even longer travel times and more attenuation than the shortest travel time - which already has an acceptable unity value.
2.4.13.5 Findings Based on NRC ECLs and unity rule calculations, the composition of the initial potential release material exceeds ECLs both individually and in combination. Due to retardation and radioactive decay during travel, activities of the specific isotopes listed in initial potential release material are expected to decrease to below ECLs individually and in combination before reaching the conservative exposure point location in the creek.
Specific findings of the particle modeling effort include:
Particle tracking suggests that for the closest receptor for an accidental release, the shortest travel time is approximately 2211.611.6 years for an unattenuated particle to arrive at the creek drain (for a release along the eastern edge of the Nuclear/Conventional Island).
Travel times from central or western parts of Nuclear/Conventional Island are much longer.
These estimated travel times are for unattenuated radioisotopes. In an actual release, attenuation due to adsorptive retardation and loss of activity to radioactive decay would, in the first factor, in some cases greatly increase travel times, (from 1 to over 2200 times the unattenuated travel time, depending
Long Mott Generating Station Preliminary Safety Analysis Report Section 2.4 Hydrology 2.4.13-10 January 2026 on the isotope) and in the second factor, reduce radioactivity due to the decay of the isotopes.
Sensitivity analysis (taken as 1/2 shortest expected travel time) still has an acceptable unity value. Minor overestimates of shortest travel time will not lead to erroneous conclusions for unity values.
Use of particle tracking from the Nuclear/Conventional Island provides a conservative estimate of travel time that does not consider adsorptive retardation and radioactive decay. Such particle tracking is independent of actual radioisotope(s) released. Expected retardation increases the travel time, while decay reduces the amounts of remaining radionuclides. Thus, actual releases result in longer travel time and reduced quantities delivered to a point of exposure.
Long Mott Generating Station Preliminary Safety Analysis Report Section 2.4 Hydrology 2.4.13-11 January 2026 References 2.4.13-001 X-Energy: Technical Note:Radioactive Waste Management System Design Reconfiguration Information. Document ID 010335 Rev 1 2.4.13-002 United States Nuclear Regulatory Commission (USNRC),
2015. PART 20STANDARDS FOR PROTECTION AGAINST RADIATION l NRC.gov.
https://www.nrc.gov/reading-rm/doc-collections/cfr/part020/full-text.html (accessed 27 August 2025).
2.4.13-003 GW-003: Accidental Release Evaluation Using a Groundwater Transport Model Calc 6228-23-0083-GW-003 Rev 2 2.4.13-004 Sketch E.1 Sketch E.1 LMGS Offsite Receptor Locations Relative to Site Center, in Normal Effluent Dose Assessment, X-Energy, XE-C-GN-003 Rev 0 2.4.13-005 GW-001: Groundwater Flow Directions, Vertical and Horizontal Gradients, Groundwater Flow Velocity Calc 6228-23-0083-GW-001 Rev 1 2.4.13-006 Nuclear Wallet Cards for Radioactive Nuclides October 2023.
https://www.nndc.bnl.gov/walletcards/doc/radioactive_booklet
.pdf (accessed 29 May 2025) 2.4.13-007 Atomic Energy Canada AECL-10125 A Critical Compilation and Review of Default Soil Solid/Liquid Partition Coefficients, Kd, For Use in Environmental Assessments 2.4.13-008 Kresic: Hydrogeology 101 Introduction to Groundwater Science and Engineering, 2023 Neven Kresic https://hydrogeocenter.com/downloads-and-resources/
(accessed 2 June 2025) 2.4.13-009 CERN: Radioactive Decay: An Introduction, Chris Cassel 2013 https://ardent.web.cern.ch/dl/outreach/Introduction%20to%20 Radioactive%20decay%20-%20Chris%20Cassel.pdf (accessed 29 May 2025) 2.4.13-010 MIRDSOFT MIRDspecs
Long Mott Generating Station Preliminary Safety Analysis Report Section 2.4 Hydrology 2.4.13-12 January 2026 https://mirdsoft.org/resources/mirdspecs (accessed 20 August 2025) 2.4.13-011 X-Energy, 2022. Technical Note: Xe-100 Radwaste Generation Calculation, Service Receipt Inspection Report.
Long Mott Generating Station Preliminary Safety Analysis Report Section 2.4 Hydrology January 2026 Table 2.4.13-1. Estimated Liquid Radwaste Specific Activities X-Energy Isotope X Energy activity concentration Bq/ml X Energy activity Bq X Energy activity Ci Ag-110m 3.60E+03 5.22E+11 1.41E+01 Ba-137m 2.78E+03 4.03E+11 1.09E+01 Ba-140 9.73E+01 1.41E+10 3.81E-01 Cs-134 4.76E+03 6.90E+11 1.87E+01 Cs-137 2.99E+03 4.34E+11 1.17E+01 I-131 4.27E+02 6.19E+10 1.67E+00 La-140 9.73E+01 1.41E+10 3.81E-01 Xe-133 2.89E-01 4.19E+07 1.13E-03 Key: Bq = Becquerel, Ci = Curie; Ag = silver; m = metastable isotope; I - iodine; Cs = cesium; Ba = barium; La = lanthanum, Xe=xenon From: X-Energy, 2022. Technical Note: Xe-100 Radwaste Generation Calculation, Service Receipt Inspection Report.
2.4.13-13
Long Mott Generating Station Preliminary Safety Analysis Report Section 2.4 Hydrology January 2026 Table 2.4.13-1 Estimated Liquid Radwaste Specific Activities X-Energy Isotope Activity concentration Bq/ml Activity Bq Activity Ci Activity concentration uCi/ml Ag-110m 3.60E+03 2.70E+11 7.30E+00 9.73E-02 Ba-137m 2.78E+03 2.09E+11 5.64E+00 7.51E-02 Ba-140 9.73E+01 7.30E+09 1.97E-01 2.63E-03 Cs-134 4.76E+03 3.57E+11 9.65E+00 1.29E-01 Cs-137 2.99E+03 2.24E+11 6.06E+00 8.08E-02 I-131 4.27E+02 3.20E+10 8.66E-01 1.15E-02 La-140 9.73E+01 7.30E+09 1.97E-01 2.63E-03 Xe-133 2.89E-01 2.17E+07 5.86E-04 7.81E-06 H-3 4.93E+01 3.70E+09 9.99E-02 1.33E-03 Key: Bq = Becquerel, Ci = Curie; Ci = microcurie; Ci/ml = microCuries per milliliter; Ag = silver; m =
metastable isotope; I - iodine; Cs = cesium; Ba = barium; La = lanthanum, Xe=xenon, H-3 = tritium 2.4.13-14
Long Mott Generating Station Preliminary Safety Analysis Report Section 2.4 Hydrology January 2026 Table 2.4.13-2: Unity Rule Calculations - Initial Composition Isotope Element X-Energy effluent concentration uCi/ml (Release) 10CFR20 App B Table 2 Effluent limit Ratio Concentration to Effluent Limit (Initial)
Ag-110m Ag 9.73E-02 6.0E-06 16216.22 Ba-137m Ba 7.51E-02 2.0E-08 3756756.76 Ba-140 Ba 2.63E-03 8.0E-06 328.72 Cs-134 Cs 1.29E-01 9.0E-07 142942.94 Cs-137 Cs 8.08E-02 1.0E-06 80810.81 I-131 I
1.15E-02 1.0E-06 11540.54 La-140 La 2.63E-03 9.0E-06 292.19 Xe-133 Xe 7.81E-06 2.0E-08 390.54 Sum Release Ratios (Unity Rule):
4009278.72 Key: NRC = Nuclear Regulatory Commission; Ag = silver; m = metastable isotope; I - iodine; Cs = cesium; Ba = barium; La = lanthanum; Xe = xenon.
Ba-137m, Xe-133 have no Table 2 entry - using most conservative unknown isotope limit 2.4.13-15
Long Mott Generating Station Preliminary Safety Analysis Report Section 2.4 Hydrology January 2026 Table 2.4.13-2 Unity Rule Calculations - Initial Composition Isotope X-Energy effluent concentration Ci/ml (Release)
NCR 10CFR20 App B Table 2 Effluent limit Ci/ml Ratio Concentration to Effluent Limit (Initial)
Ag-110m 9.73E-02 6.0E-06 1.62E+04 Ba-137m 7.51E-02 2.0E-08 3.76E+06 Ba-140 2.63E-03 8.0E-06 3.29E+02 Cs-134 1.29E-01 9.0E-07 1.43E+05 Cs-137 8.08E-02 1.0E-06 8.08E+04 I-131 1.15E-02 1.0E-06 1.15E+04 La-140 2.63E-03 9.0E-06 2.92E+02 Xe-133 7.81E-06 2.0E-08 3.91E+02 H-3 1.33E-03 1.0E-03 1.33E+00 Key: NRC = Nuclear Regulatory Commission; Ag = silver; m = metastable isotope; I - iodine; Cs =
cesium; Ba = barium; La = lanthanum; Xe = xenon. H-3 = tritium Ba-137m, Xe-133 have no Table 2 entry
- using most conservative unknown isotope limit Ci/ml = microCuries per milliliter 2.4.13-16
Long Mott Generating Station Preliminary Safety Analysis Report Section 2.4 Hydrology January 2026 Table 2.4.13-3: Isotope Half-Lives and Retarded Travel Times Isotop e
Elemen t
Effluent concentratio n uCi/ml Activity Ci half-life (days)
Kd (sand)
Retardatio n Factor Retarded Travel Time Days Number of Half-lives Percent of Original Activity Remainin g
Ag-110m Ag 9.73E-02 1.41E+0 1
249.86 90 716.5 5753495 23026.9 0.0%
Ba-137m Ba 7.51E-02 1.09E+0 1
0.00177222 2
Missin g
1 8030 4531034.
5 0.0%
Ba-140 Ba 2.63E-03 3.81E-01 12.751 Missin g
1 8030 629.8 0.0%
Cs-134 Cs 1.29E-01 1.87E+0 1
754.298188 9
280 2227 17882810 23707.9 0.0%
Cs-137 Cs 8.08E-02 1.17E+0 1
10986.4853 4
280 2227 17882810 1627.7 0.0%
I-131 I
1.15E-02 1.67E+0 0
8.0252 1
8.95 71869 8955.4 0.0%
La-140 La 2.63E-03 3.81E-01 1.67858 Missin g
1 8030 4783.8 0.0%
Xe-133 Xe 7.81E-06 1.13E-03 5.2475 Missin g
1 8030 1530.3 0.0%
Key: Ag = silver; m = metastable isotope; I - iodine; Cs = cesium; Ba = barium; La = lanthanum; Xe = xenon.
2.4.13-17
Long Mott Generating Station Preliminary Safety Analysis Report Section 2.4 Hydrology January 2026 Table 2.4.13-3 Isotope Half-Lives and Retarded Travel Times (1 of 2)
NearestPerimeter Isotope X Energy activity Ci half-life (days)
Kd (sand)
Retardation Factor Retarded Travel Time Days Number of Half-lives Activity Remaining Ci Percent of Original Activity Remaining Ag-110m 7.30E+00 249.86 90 716.5 3033661 12141.4 0.00E+00 0.0%
Ba-137m 5.64E+00 0.001772222 Missing 1
4234 2389090.9 0.00E+00 0.0%
Ba-140 1.97E-01 12.751 Missing 1
4234 332.1 2.17E-101 0.0%
Cs-134 9.65E+00 754.2981889 280 2227 9429118 12500.5 0.00E+00 0.0%
Cs-137 6.06E+00 10986.48534 280 2227 9429118 858.2 2.66E-258 0.0%
I-131 8.66E-01 8.0252 1
8.95 37894 4721.9 0.00E+00 0.0%
La-140 1.97E-01 1.67858 Missing 1
4234 2522.4 0.00E+00 0.0%
Xe-133 5.86E-04 5.2475 Missing 1
4234 806.9 7.56E-247 0.0%
H-3 9.99E-02 4499.783889 0.1 1.795 7600 1.7 3.10E-02 31.0%
NearestCenter Isotope XEnergy activityCi halflife (days)
Kd(sand)
Retardation Factor Retarded TravelTime Days NumberofHalf lives Activity Remaining Ci Percentof Original Activity Remaining Ag-110m 7.30E+00 249.86 90 716.5 15952873 63847.2 0.00E+00 0.0%
Ba-137m 5.64E+00 0.001772222 Missing 1
22265 12563322.9 0.00E+00 0.0%
Ba-140 1.97E-01 12.751 Missing 1
22265 1746.1 0.00E+00 0.0%
Cs-134 9.65E+00 754.2981889 280 2227 49584155 65735.5 0.00E+00 0.0%
Cs-137 6.06E+00 10986.48534 280 2227 49584155 4513.2 0.00E+00 0.0%
I-131 8.66E-01 8.0252 1
8.95 199272 24830.8 0.00E+00 0.0%
La-140 1.97E-01 1.67858 Missing 1
22265 13264.2 0.00E+00 0.0%
Xe-133 5.86E-04 5.2475 Missing 1
22265 4243.0 0.00E+00 0.0%
H-3 9.99E-02 4499.783889 0.1 1.795 39966 8.9 2.12E-04 0.2%
2.4.13-18
Long Mott Generating Station Preliminary Safety Analysis Report Section 2.4 Hydrology January 2026 Table 2.4.13-3 Isotope Half-Lives and Retarded Travel Times (2 of 2)
MedianCenter Isotope X Energy activity Ci half-life (days)
Kd (sand)
Retardation Factor Retarded Travel Time Days Number of Half-lives Activity Remaining Ci Percent of Original Activity Remaining Ag-110m 7.30E+00 249.86 90 716.5 27721385 110947.7 0.00E+00 0.0%
Ba-137m 5.64E+00 0.001772222 Missing 1
38690 21831348.0 0.00E+00 0.0%
Ba-140 1.97E-01 12.751 Missing 1
38690 3034.3 0.00E+00 0.0%
Cs-134 9.65E+00 754.2981889 280 2227 86162630 114228.9 0.00E+00 0.0%
Cs-137 6.06E+00 10986.48534 280 2227 86162630 7842.6 0.00E+00 0.0%
I-131 8.66E-01 8.0252 1
8.95 346276 43148.5 0.00E+00 0.0%
La-140 1.97E-01 1.67858 Missing 1
38690 23049.2 0.00E+00 0.0%
Xe-133 5.86E-04 5.2475 Missing 1
38690 7373.0 0.00E+00 0.0%
H-3 9.99E-02 4499.783889 0.1 1.795 69449 15.4 2.26E-06 0.0%
1/2NearestPerimeter(SensitivityAnalysisOnly)
Isotope XEnergy activityCi halflife (days)
Kd(sand)
Retardation Factor Retarded TravelTime Days Numberof Halflives Activity Remaining Ci Percentof Original Activity Remaining Ag-110m 7.30E+00 249.86 90 716.5 1516831 6070.7 0.00E+00 0.0%
Ba-137m 5.64E+00 0.001772222 Missing 1
2117 1194545.5 0.00E+00 0.0%
Ba-140 1.97E-01 12.751 Missing 1
2117 166.0 2.07E-51 0.0%
Cs-134 9.65E+00 754.2981889 280 2227 4714559 6250.3 0.00E+00 0.0%
Cs-137 6.06E+00 10986.48534 280 2227 4714559 429.1 4.01E-129 0.0%
I-131 8.66E-01 8.0252 1
8.95 18947 2361.0 0.00E+00 0.0%
La-140 1.97E-01 1.67858 Missing 1
2117 1261.2 0.00E+00 0.0%
Xe-133 5.86E-04 5.2475 Missing 1
2117 403.4 2.10E-125 0.0%
H-3 9.99E-02 4499.783889 0.1 1.795 3800 0.8 5.57E-02 55.7%
2.4.13-19
Long Mott Generating Station Preliminary Safety Analysis Report Section 2.4 Hydrology January 2026 Table 2.4.13-4: Unity Rule Calculations - Retarded Travel Time Composition Isotope Element Effluent concentration uCi/ml (After Travel to Exposure Point) 10CFR20 App B Table 2 Effluent limit Ratio Concentration to Effluent Limit (Exposure Point after Travel)
Ag-110m Ag 0.00E+00 6.0E-06 0.00 Ba-137m Ba 0.00E+00 2.0E-08 0.00 Ba-140 Ba 1.01E-190 8.0E-06 0.00 Cs-134 Cs 0.00E+00 9.0E-07 0.00 Cs-137 Cs 0.00E+00 1.0E-06 0.00 I-131 I
0.00E+00 1.0E-06 0.00 La-140 La 0.00E+00 9.0E-06 0.00 Xe-133 Xe 0.00E+00 2.0E-08 0.00 Sum Exposure Point Ratios (Unity Rule): 0.00 Key: NRC = Nuclear Regulatory Commission; Ag = silver; m = metastable isotope; I - iodine; Cs = cesium; Ba = barium; La = lanthanum; Xe =
xenon. Ba-137m, Xe-133 have no Table 2 entry - using most conservative unknown isotope limit 2.4.13-20
Long Mott Generating Station Preliminary Safety Analysis Report Section 2.4 Hydrology January 2026 Table 2.4.13-4 Unity Rule Calculations - Retarded Travel Time Composition (1 of 2)
NearestPerimeter Isotope XEnergyeffluent concentration Ci/ml(Release)
XEnergyeffluent concentration Ci/ml(AfterTravel toExposurePoint) 10CFR20 AppBTable2Effluent limitCi/ml RatioConcentrationto EffluentLimit(Initial)
RatioConcentrationto EffluentLimit(Exposure PointafterTravel)
Ag110m 9.73E02 0.00E+00 6.0E06 1.62E+04 0.00E+00 Ba137m 7.51E02 0.00E+00 2.0E08 3.76E+06 0.00E+00 Ba140 2.63E03 2.90E103 8.0E06 3.29E+02 3.62E98 Cs134 1.29E01 0.00E+00 9.0E07 1.43E+05 0.00E+00 Cs137 8.08E02 3.54E260 1.0E06 8.08E+04 3.54E254 I131 1.15E02 0.00E+00 1.0E06 1.15E+04 0.00E+00 La140 2.63E03 0.00E+00 9.0E06 2.92E+02 0.00E+00 Xe133 7.81E06 1.01E248 2.0E08 3.91E+02 5.04E241 H3 1.33E03 4.13E04 1.0E03 1.33E+00 4.13E01 SumExposurePointRatios(UnityRule):
4.13E01 NearestCenter Isotope XEnergyeffluent concentration Ci/ml(Release)
XEnergyeffluent concentration uCi/ml(AfterTravel toExposurePoint) 10CFR20 AppBTable2Effluent limitCi/ml RatioConcentrationto EffluentLimit(Initial)
RatioConcentrationto EffluentLimit(Exposure PointafterTravel)
Ag110m 9.73E02 0.00E+00 6.0E06 1.62E+04 0.00E+00 Ba137m 7.51E02 0.00E+00 2.0E08 3.76E+06 0.00E+00 Ba140 2.63E03 0.00E+00 8.0E06 3.29E+02 0.00E+00 Cs134 1.29E01 0.00E+00 9.0E07 1.43E+05 0.00E+00 Cs137 8.08E02 0.00E+00 1.0E06 8.08E+04 0.00E+00 I131 1.15E02 0.00E+00 1.0E06 1.15E+04 0.00E+00 La140 2.63E03 0.00E+00 9.0E06 2.92E+02 0.00E+00 Xe133 7.81E06 0.00E+00 2.0E08 3.91E+02 0.00E+00 H3 1.33E03 2.82E06 1.0E03 1.33E+00 2.82E03 SumExposurePointRatios(UnityRule):
2.82E03 2.4.13-21
Long Mott Generating Station Preliminary Safety Analysis Report Section 2.4 Hydrology January 2026 Table 2.4.13-4 Unity Rule Calculations - Retarded Travel Time Composition (2 of 2)
MedianCenter Isotope XEnergyeffluent concentration Ci/ml(Release)
XEnergyeffluent concentration uCi/ml(AfterTravel toExposurePoint) 10CFR20 AppBTable2Effluent limitCi/ml RatioConcentrationto EffluentLimit(Initial)
RatioConcentrationto EffluentLimit(Exposure PointafterTravel)
Ag110m 9.73E02 0.00E+00 6.0E06 1.62E+04 0.00E+00 Ba137m 7.51E02 0.00E+00 2.0E08 3.76E+06 0.00E+00 Ba140 2.63E03 0.00E+00 8.0E06 3.29E+02 0.00E+00 Cs134 1.29E01 0.00E+00 9.0E07 1.43E+05 0.00E+00 Cs137 8.08E02 0.00E+00 1.0E06 8.08E+04 0.00E+00 I131 1.15E02 0.00E+00 1.0E06 1.15E+04 0.00E+00 La140 2.63E03 0.00E+00 9.0E06 2.92E+02 0.00E+00 Xe133 7.81E06 0.00E+00 2.0E08 3.91E+02 0.00E+00 H3 1.33E03 3.01E08 1.0E03 1.33E+00 3.01E05 SumExposurePointRatios(UnityRule):
3.01E05 1/2NearestPerimeter(SensitivityAnalysisOnly)
Isotope XEnergyeffluent concentration Ci/ml(Release)
XEnergyeffluent concentration uCi/ml(AfterTravel toExposurePoint) 10CFR20 AppBTable2Effluent limitCi/ml RatioConcentrationto EffluentLimit(Initial)
RatioConcentrationto EffluentLimit(Exposure PointafterTravel)
Ag110m 9.73E02 0.00E+00 6.0E06 1.62E+04 0.00E+00 Ba137m 7.51E02 0.00E+00 2.0E08 3.76E+06 0.00E+00 Ba140 2.63E03 2.76E53 8.0E06 3.29E+02 3.45E48 Cs134 1.29E01 0.00E+00 9.0E07 1.43E+05 0.00E+00 Cs137 8.08E02 5.35E131 1.0E06 8.08E+04 5.35E125 I131 1.15E02 0.00E+00 1.0E06 1.15E+04 0.00E+00 La140 2.63E03 0.00E+00 9.0E06 2.92E+02 0.00E+00 Xe133 7.81E06 2.81E127 2.0E08 3.91E+02 1.40E119 H3 1.33E03 7.42E04 1.0E03 1.33E+00 7.42E01 SumExposurePointRatios(UnityRule):
7.42E01
Key:NRC=NuclearRegulatoryCommission;Ag=silver;m=metastableisotope;I-iodine;Cs=cesium;Ba=barium;La=lanthanum;Xe=
xenon;H3=tritium.Ba137m,Xe133havenoTable2entry-usingmostconservativeunknownisotopelimit;Ci/ml=microCuriesper milliliter 2.4.13-22
Long Mott Generating Station Preliminary Safety Analysis Report Section 2.4 Hydrology January 2026 Figure 2.4.13-1 Facilities Particle Track After 22 Years 2.4.13-23
Long Mott Generating Station Preliminary Safety Analysis Report Section 2.4 Hydrology January 2026 Figure 2.4.13-1 Facilities Particle Tracks (Sheet 1 of 3) 4234 days - First particle from perimeter 2.4.13-24
Long Mott Generating Station Preliminary Safety Analysis Report Section 2.4 Hydrology January 2026 Figure 2.4.13-1 Facilities Particle Tracks (Sheet 2 of 3) 22265 days - First particle from center 2.4.13-25
Long Mott Generating Station Preliminary Safety Analysis Report Section 2.4 Hydrology January 2026 Figure 2.4.13-1 Facilities Particle Tracks (Sheet 3 of 3) 38690 days - Median particle from center 2.4.13-26
Long Mott Generating Station Preliminary Safety Analysis Report Section 2.4 Hydrology January 2026 Figure 2.4.13-2 Facilities Corners Particle Track After 20 Years 2.4.13-27