Text

Annual Radiological Environmental Operating Report
	ML25129A014
Person / Time
Site:	LaSalle
Issue date:	05/09/2025
From:	Van Fleet J; Constellation Energy Generation
To:	; Office of Nuclear Material Safety and Safeguards, Office of Nuclear Reactor Regulation, Document Control Desk
References
	RA25-012
	Download: ML25129A014 (1)
	v • d • e

Annual Radiological Environmental Operating Report YEAR: 2024 Page 0 of 74 Company: Constellation Plant: LaSalle County Station Units 1 and 2 2024 Docket Number: 50-373/50-374 Annual Radiological Environmental Operating Report

Annual Radiological Environmental Operating Report YEAR: 2024 Page 1 of 74 Company: Constellation Plant: LaSalle County Station Units 1 and 2 TABLE OF CONTENTS 1.0 LIST OF ACRONYMS AND DEFINITIONS................................................................................ 3 2.0 EXECUTIVE

SUMMARY

............................................................................................................ 4 2.1 Summary of

Conclusions:

............................................................................................... 5

3.0 INTRODUCTION

........................................................................................................................ 6 4.0 SITE DESCRIPTION AND SAMPLE LOCATIONS..................................................................... 7 5.0 RADIOLOGICAL ENVIRONMENTAL MONITORING PROGRAM REQUIREMENTS................ 8 6.0 MAPS OF COLLECTION SITES.............................................................................................. 14 7.0 REPORTING LEVELS FOR RADIOACTIVITY CONCENTRATIONS IN ENVIRONMENTAL SAMPLES................................................................................................. 17 8.0 SAMPLING PROGRAM, PROGRAM MODIFICATION AND INTEPRETATION OF RESULTS................................................................................................................................ 18 8.1 Environmental Direct Radiation Dosimetry Results....................................................... 18 8.2 Air Particulate and Radioiodine Sample Results........................................................... 19 8.3 Waterborne Sample Results......................................................................................... 20 8.4 Ingestion Pathway Sample Results............................................................................... 21 9.0 LAND USE CENSUS............................................................................................................... 22 10.0 SAMPLE DEVIATIONS, ANOMALIES AND UNAVAILABILITY................................................ 23 11.0 OTHER SUPPLEMENTAL INFORMATION............................................................................. 25 11.1 NEI 07-07 Onsite Radiological Groundwater Monitoring Program................................. 25 11.2 Corrections to Previous Reports................................................................................... 26 12.0 BIBLIOGRAPHY...................................................................................................................... 27 TABLES Table 1: Radiological Environmental Sampling Program - Exposure Pathway - Direct Radiation......... 8 Table 2, Radiological Environmental Sampling Program - Exposure Pathway - Airborne...................... 9 Table 3, Radiological Environmental Sampling Program - Exposure Pathway - Waterborne............... 10 Table 4, Radiological Environmental Sampling Program - Exposure Pathway - Ingestion................... 11 Table 5, REMP Sampling Locations - Direct Radiation........................................................................ 12 Table 6, Reporting Levels for Radioactivity Concentrations in Environmental Samples....................... 17 Table 7, Maximum Values for the Limit of Detection............................................................................ 17 Table 8: Land Use Census - Nearest Receptors within 5 miles........................................................... 23 Table 9: Sample Deviation Summary................................................................................................... 24 Table 10: LaSalle Data Summary Table.............................................................................................. 29 Table 11, Weekly Air Particulate Gross Beta (E-3 pCi/m3)................................................................... 34 Table 12: Quarterly Air Particulate Gamma Isotopic (E-3 pCi/m3 +/- 2 Sigma)...................................... 37 Table 13, Weekly Air Iodine I-131 (E-3 pCi/m3).................................................................................... 40 Table 14: Annual Food Products Gamma Isotopic (pCi/kg Wet +/- 2 Sigma).......................................... 43 Table 15: Monthly Vegetation Gamma Isotopic (pCi/Kg Wet +/- 2 Sigma).............................................. 45 Table 16, Monthly Surface Water Gross Beta (pCi/L +/- 2 Sigma).......................................................... 48 Table 17: Monthly Surface Water Gamma Isotopic (pCi/L+/- 2 Sigma ).................................................. 49 Table 18: Quarterly Surface Water Tritium (pCi/L +/- 2 Sigma).............................................................. 51

Annual Radiological Environmental Operating Report YEAR: 2024 Page 2 of 74 Company: Constellation Plant: LaSalle County Station Units 1 and 2 Table 19, Quarterly Ground Water Tritium (pCi/L +/- 2 Sigma)............................................................... 52 Table 20: Quarterly Ground Water Gamma Isotopic (pCi/L +/- 2 Sigma)................................................ 53 Table 21: Semi-Annual Fish Gamma Isotopic (pCi/kg Wet +/- 2 Sigma)................................................. 54 Table 22: Semi-Annual Shoreline Sediment Gamma Isotopic (pCi/kg Dry +/- 2 Sigma)......................... 55 Table 23: Analytics Environmental Radioactivity Cross Check Program.............................................. 59 Table 24: DOEs Mixed Analyte Performance Evaluation Program (MAPEP)...................................... 61 Table 25: ERA Environmental Radioactivity Cross Check Program..................................................... 63 Table 26, Quarterly DLR Results for LaSalle County Station, 2019...................................................... 68 Table 27, Quarterly DLR Results for LaSalle County Station, 2020...................................................... 69 Table 28, Quarterly DLR Results for LaSalle County Station, 2021...................................................... 70 Table 29, Summary and Conclusion, 2022.......................................................................................... 71 Table 30, Listing of Sample Anomalies, 2022...................................................................................... 72 Table 31, Quarterly DLR Results for LaSalle County Station, 2022...................................................... 73 Table 32, Summary and Conclusions, 2023......................................................................................... 74 FIGURES Figure 1, Potential exposure pathways to Members of the Public due to Plant Operations [6]............... 6 Figure 2, Inner Ring OSLD Locations of the LaSalle County Station, 2024.......................................... 14 Figure 3, Outer Ring OSLD Locations and Fixed Air Sampling Locations of the LaSalle County Station, 2024.................................................................................................................................................... 15 Figure 4, Ingestion and Waterborne Exposure Pathway Sample Locations of the LaSalle County Station, 2024....................................................................................................................................... 16 Figure 5, Air Particulate: Analysis for Gross Beta, Average for All Indicator vs. Control Location......... 19 Figure 6: Average Surface Water Tritium Results by Year................................................................... 20 ATTACHMENTS, Data Table Summary.................................................................................................... 29, Complete Data Table for All Analysis Results Obtained In 2024................................... 34, Cross Check Intercomparison Program......................................................................... 56, Environmental Direct Radiation Dosimetry Results....................................................... 65, Errata Data................................................................................................................... 68

Annual Radiological Environmental Operating Report YEAR: 2024 Page 3 of 74 Company: Constellation Plant: LaSalle County Station Units 1 and 2 1.0 LIST OF ACRONYMS AND DEFINITIONS

1.

Airborne Activity Sampling: Continuous sampling of air through the collection of particulates and radionuclides on filter media.

2.

ARERR: Annual Radioactive Effluent Release Report

3.

AREOR: Annual Radiological Environmental Operating Report

4.

BWR: Boiling Water Reactor

5.

Composite Sample: A series of single collected portions (aliquots) analyzed as one sample. The aliquots making up the sample are collected at time intervals that are very short compared to the composite period.

6.

Control: A sampling station in a location not likely to be affected by plant effluents due to its distance and/or direction from the station.

7.

Curie (Ci): A measure of radioactivity; equal to 3.7 x 1010 disintegrations per second, or 2.22 x 1012 disintegrations per minute.

8.

Direct Radiation Monitoring: The measurement of radiation dose at various distances from the plant is assessed using Thermoluminescent Dosimeters (TLD), Optically Stimulated Luminescence Dosimeters (OSLD) and pressurized ionization chambers.

9.

EPA: Environmental Protection Agency

10.

GPI: Groundwater Protection Initiative

11.

Grab Sample: A single discrete sample drawn at one point in time.

12.

Indicator: A sampling location that is likely to be affected by plant effluents due to its proximity and/or direction from the plant.

13.

Ingestion Pathway: The ingestion pathway includes milk, fish, drinking water and garden produce. Also sampled (under special circumstances) are other media such as vegetation or animal products when additional information about particular radionuclides is needed.

14.

ISFSI: Independent Spent Fuel Storage Installation

15.

Lower Limit of Detection (LLD): An a priori measure of the detection capability of a radiochemistry measurement based on instrument setup, calibration, background, decay time, and sample volume. An LLD is expressed as an activity concentration. The MDA is used for reporting results. LLD are specified by a regulator, such as the NRC and are typically listed in the ODCM.

Annual Radiological Environmental Operating Report YEAR: 2024 Page 4 of 74 Company: Constellation Plant: LaSalle County Station Units 1 and 2

16.

MDA: Minimum Detectable Activity. For radiochemistry instruments, the MDA is the a posteriori minimum concentration that a counting system detects. The smallest concentration or activity of radioactive material in a sample that will yield a net count above instrument background and that is detected with 95%

probability, with only five % probability of falsely concluding that a blank observation represents a true signal.

17.

MDC: Minimum Detectable Concentration. Essentially synonymous with MDA for the purposes of radiological monitoring.

18.

Mean: The sum of all of the values in a distribution divided by the number of values in the distribution, synonymous with average.

19.

Microcurie: 3.7 x 104 disintegrations per second, or 2.22 x106 disintegrations per minute.

20.

N/A: Not Applicable

21.

NEI: Nuclear Energy Institute

22.

NIST: National Institute of Standards and Technology.

23.

NRC: Nuclear Regulatory Commission

24.

ODCM: Offsite Dose Calculation Manual

25.

OSLD: Optically Stimulated Luminescence Dosimeter

26.

pCi/L: picocuries / Liter

27.

PWR: Pressurized Water Reactor

28.

REMP: Radiological Environmental Monitoring Program

29.

TLD: Thermoluminescent Dosimeter 2.0 EXECUTIVE

SUMMARY

LaSalle County Station Units 1 and 2 Radiological Environmental Monitoring Program (REMP) was established prior to the station becoming operational to provide information on background radiation present in the area. The goal of LaSalle Station REMP is to evaluate the impact of the station on the environment. Environmental samples from different media are monitored as part of the program in accordance with specifications detailed in the Offsite Dose Calculation Manual (ODCM). The program compares data from Indicator locations near the plant, to Control locations farther away from the site to assess operation impacts.

Annual Radiological Environmental Operating Report YEAR: 2024 Page 5 of 74 Company: Constellation Plant: LaSalle County Station Units 1 and 2 The Annual Radiological Environmental Operating Report (AREOR) provides data obtained through analyses of environmental samples collected at LaSalle Station for the reporting period of January 1st through December 31st, 2024. During that time period 1,295 analyses were performed on 1,219 samples. In assessing all the data gathered for this report and comparing these results with preoperational data and/or 10-year average values, it was concluded that the operation of LaSalle Station had no adverse radiological impact on the environment.

2.1 Summary of

Conclusions:

In 2024, the LaSalle Generating Station released to the environment through the radioactive effluent gaseous pathways 641 curies of noble gas, fission, and activation products and 70 curies of tritium. There were no liquid effluent releases beyond the site in 2024. The resultant calculated doses due to gaseous radioactive effluents from LaSalle Station were well below regulatory limits of 40 CFR 190 and summarized below.

Whole Body Thyroid Max Other Organ Gaseous1,2 1.39E-02 3.55E-02 4.71E-02 Liquid 0.00E+00 0.00E+00 0.00E+00 Sky Shine & ISFSI 7.49E-01 7.49E-01 7.49E-01 Total Site Dose 7.63E-01 7.84E-01 7.96E-01 Total w/Other Nearby Facility3 7.63E-01 7.84E-01 7.96E-01 Limit 25 mrem 75 mrem 25 mrem

% of Limit 3.05E+00 1.05E+00 3.18E+00 1 Gaseous dose values include organ dose from Noble Gas, Iodine, Tritium, Carbon-14, and particulates with half-lives > 8 days.

2 Individual groups with the highest dose are used: Total Body: all age groups for Noble Gas and the Infant and Child for particulates, Individual age group sum is lower.

3 Other fuel cycle sources within 5 miles of the site do not exist.

Annual Radiological Environmental Operating Report YEAR: 2024 Page 6 of 74 Company: Constellation Plant: LaSalle County Station Units 1 and 2

3.0 INTRODUCTION

The Radiological Environmental Monitoring Program (REMP) provides data on measurable levels of radiation and radioactive materials in the environment. This program also evaluates the relationship between quantities of radioactive materials released from the plant and resultant doses to individuals from principal pathways of exposure. In this capacity, REMP provides a check on the effluent release program and dispersion modeling to ensure that concentrations in the environment due to radioactive effluents conform to the As Low as Is Reasonably Achievable (ALARA) design objectives of 10 CFR 50, Appendix I [1], and implements the requirements of Section IV.B.2 and IV.B.3 of Appendix I. REMP is designed to conform to the Nuclear Regulatory Commission (NRC) Regulatory Guide 4.1 [2], NUREG 1301/1302

[3] [4], and the 1979 NRC Branch Technical Position [5].

Figure 1, Potential exposure pathways to Members of the Public due to Plant Operations [6]

Quality assurance aspects of the sampling program and TLD/OSLD data collection are conducted in accordance with Regulatory Guides 4.15 [7] and 4.13 [8]. REMP also adheres to the requirements of Illinois, LaSalle Station Technical Specifications, and Offsite Dose Calculation Manual (ODCM). These governing documents dictate the environmental sampling, sample analysis protocols, data reporting and quality assurance requirements for the environmental monitoring program.

Annual Radiological Environmental Operating Report YEAR: 2024 Page 7 of 74 Company: Constellation Plant: LaSalle County Station Units 1 and 2 The Annual Radiological Environmental Operating Report provides summaries of the environmental data from exposure pathways, interpretations of the data, and analyses of trends of the results. Routinely monitored pathways include ingestion, inhalation, and direct radiation. Routes of exposure are based on site specific information such as meteorology, receptor locations, and water usage around the plant.

4.0 SITE DESCRIPTION AND SAMPLE LOCATIONS LaSalle County Station Units 1 and 2 consists of two boiling water reactors, each rated for 3,546 MWt. Both units are owned and operated by Constellation Energy and are located in LaSalle County, Illinois. Unit 1 went critical on 16 March 1982.

Unit 2 went critical on 02 December 1983. The site is located in northern Illinois, approximately 75 miles southwest of Chicago, Illinois.

LaSalle Station sampling media are selected based on site specific information such as meteorology, receptor locations, and water usage around the plant. Sampling and analysis frequencies are documented in the Offsite Dose Calculation Manual and site procedures. Required sampling, analysis frequencies and location of sample collected are captured in the following tables and figures:

Table 1: Radiological Environmental Sampling Program - Exposure Pathway -

Direct Radiation Table 2, Radiological Environmental Sampling Program - Exposure Pathway -

Airborne Table 3, Radiological Environmental Sampling Program - Exposure Pathway -

Waterborne Table 4, Radiological Environmental Sampling Program - Exposure Pathway -

Ingestion Table 5, REMP Sampling Locations - Direct Radiation Figure 2, Inner Ring OSLD Locations of the LaSalle County Station, 2024 Figure 3, Outer Ring OSLD Locations and Fixed Air Sampling Locations of the LaSalle County Station, 2024 Figure 4, Ingestion and Waterborne Exposure Pathway Sample Locations of the LaSalle County Station, 2024

Annual Radiological Environmental Operating Report YEAR: 2024 Page 8 of 74 Company: Constellation Plant: LaSalle County Station Units 1 and 2 5.0 RADIOLOGICAL ENVIRONMENTAL MONITORING PROGRAM REQUIREMENTS Table 1: Radiological Environmental Sampling Program - Exposure Pathway - Direct Radiation Requirement Sample Location Description, Distance, and Direction Sampling Collection/

Frequency Type and Frequency of Analyses Direct Radiation 42 OSLD monitoring stations with two dosimeters placed as follows:

An inner ring consisting of 16 locations, near and within the site perimeter representing fence post doses.

An outer ring of stations consisting of 17 locations, extending to approximately 5 miles from the site designated to measure possible exposure to nearby populations.

An other set consisting of 8 locations A control/special interest location See Table 5 Quarterly Gamma dose Quarterly

Annual Radiological Environmental Operating Report YEAR: 2024 Page 9 of 74 Company: Constellation Plant: LaSalle County Station Units 1 and 2 Table 2, Radiological Environmental Sampling Program - Exposure Pathway - Airborne Requirement Sample Location Description, Distance, and Direction Sampling Collection/

Frequency Type and Frequency of Analyses Airborne Radioiodine and Particulates Samples from 9 locations:

Four locations close to the site boundary in different sectors of the highest calculated annual average ground level D/Q.

Four samples from the vicinity of a community having the highest calculated annual average D/Q.

One samples from Control Locations between 6.2 -

18.6 miles away in the least predominant wind direction.

L-01 Nearsite 1, 1.5 miles NNW L-03 Onsite 3, 1.0 miles ENE L-04 Rte. 170, 3.2 miles E L-05 Onsite 5, 0.3 miles ESE L-06 Nearsite 6, 0.4 miles W L-07 Seneca, 5.2 miles NNE L-08 Marseilles, 6.0 miles NNW L-10 Streator (C), 13.5 miles SW L-11A Ransom, 6.0 miles S One-week of continuous air sampling through glass fiber filter paper Weekly composite of continuous air sampling through charcoal filter Particulate sampler: Gross Beta analysis following weekly filter change and Gamma isotopic quarterly on composite filters by location on near field and control samples.

Radioiodine canister: I-131 analysis weekly on near field and control samples.

Annual Radiological Environmental Operating Report YEAR: 2024 Page 10 of 74 Company: Constellation Plant: LaSalle County Station Units 1 and 2 Table 3, Radiological Environmental Sampling Program - Exposure Pathway - Waterborne Requirement Sample Location Description, Distance, and Direction Sampling Collection/

Frequency Type and Frequency of Analyses Surface Water One sample upstream (control) and one sample downstream (indicator)

L-21 Illinois River at Seneca, Upstream (C),

4.0 miles NE L-40 Illinois River, Downstream (I), 5.2 miles NNW Monthly and quarterly composite from weekly grab samples Gamma isotopic Monthly Gross beta Monthly H-3 Quarterly Groundwater/Well Water Two control location upgradient from the plant and Two indicator locations down gradient from the plant, only if likely to be affected.

L-27 LSCS Onsite Well (I), 0 miles at station L-28-W4 Marseilles Well (C), 7.0 miles NNW L-28-W5 Marseilles Well (C), 6.7 miles NNW L-28-W6 Marseilles Well (I), 4.1 miles N Quarterly grab samples Gamma isotopic Quarterly H-3 Quarterly Sediment from Shoreline One sample upstream (control) and two of samples downstream (indicator)

L-21 Illinois River at Seneca, Upstream (C),

4.0 miles NE L-40 Illinois River, Downstream (I), 5.2 miles NNW L-41 Illinois River, Downstream (I), 4.6 miles N

Semi-annual grab samples Gamma isotopic Semiannually

Annual Radiological Environmental Operating Report YEAR: 2024 Page 11 of 74 Company: Constellation Plant: LaSalle County Station Units 1 and 2 Table 4, Radiological Environmental Sampling Program - Exposure Pathway - Ingestion Requirement Sample Location Description, Distance, and Direction Sampling Collection/

Frequency Type and Frequency of Analyses Fish One sample upstream (control) and two samples downstream (indicator) of each commercially and recreationally important species in vicinity of site discharge.

L-34 LaSalle Cooling Lake (I), 2.0 miles E L-35 Marseilles Pool of Illinois River, Downstream (I), 6.5 miles NNW L-36 Illinois River, Upstream of Discharge (C), 4.3 miles NE Semi-annual samples collected via electroshocking or other techniques Gamma isotopic analysis on edible portions Food products/Vegetation Five samples of food products from any area that is irrigated by water in which liquid plant wastes have been discharged.

Three broad leaf vegetation grown nearest each of two different offsite locations of highest predicated annual average ground level D/Q if milk sampling is not performed and one sample collected from the control location.

Quadrant 1 171 Valley View, Seneca IL, 5.2 miles NE Quadrant 2 106 W. Thomas, Ransom, IL, 6.0 miles S

Quadrant 3 2260 N 21st Road, Marseilles IL, 3.2 miles WSW Quadrant 4 2507 N. 2553 Rd., Marseilles IL, 4.3 miles NNW Control Biros Farm, 14.2 miles E L-CONTROL, 9.5 miles ENE L-ESE 1,1.5 miles ESE L-ESE 2,6.0 miles ESE Annual grab samples Monthly grab samples during growing season Gamma isotopic on each sample

Annual Radiological Environmental Operating Report YEAR: 2024 Page 12 of 74 Company: Constellation Plant: LaSalle County Station Units 1 and 2 Table 5, REMP Sampling Locations - Direct Radiation Site #

Location Type Sector Distance Description L-101-1 and -2 Inner Ring N

0.5 miles L-102-1 and -2 Inner Ring NNE 0.6 miles L-103-1 and -2 Inner Ring NE 0.7 miles L-104-1 and -2 Inner Ring ENE 0.8 miles L-105-1 and -2 Inner Ring E

0.7 miles L-106-1 and -2 Inner Ring ESE 1.4 miles L-107-1 and -2 Inner Ring SE 0.8 miles L-108-1 and -2 Inner Ring SSE 0.5 miles L-109-1 and -2 Inner Ring S

0.6 miles L-110-1 and -2 Inner Ring SSW 0.6 miles L-111b-1 and -2 Inner Ring SW 0.8 miles L-112-1 and -2 Inner Ring WSW 0.9 miles L-113a-1 and -2 Inner Ring W

0.8 miles L-114-1 and -2 Inner Ring WNW 0.9 miles L-115-1 and -2 Inner Ring NW 0.7 miles L-116-1 and -2 Inner Ring NNW 0.6 miles L-201-3 and -4 Outer Ring N

4.0 miles L-202-3 and -4 Outer Ring NNE 3.6 miles L-203-1 and -2 Outer Ring NE 4.0 miles L-204-1 and -2 Outer Ring ENE 3.2 miles L-205A-1 and -2 Outer Ring ESE 3.2 miles

Annual Radiological Environmental Operating Report YEAR: 2024 Page 13 of 74 Company: Constellation Plant: LaSalle County Station Units 1 and 2 Table 5, REMP Sampling Locations - Direct Radiation Site #

Location Type Sector Distance Description L-205B-3 and -4 Outer Ring E

5.1 miles L-206-1 and -2 Outer Ring SE 4.3 miles L-207-1 and -2 Outer Ring SSE 4.5 miles L-208-1 and -2 Outer Ring S

4.5 miles L-209-1 and -2 Outer Ring SSW 4.0 miles L-210-1 and -2 Outer Ring SW 3.3 miles L-211-1 and -2 Outer Ring WSW 4.5 miles L-212-1 and -2 Outer Ring W

4.0 miles L-213-3 and -4 Outer Ring W

4.9 miles L-214-3 and -4 Outer Ring WNW 5.1 miles L-215-3 and -4 Outer Ring NW 5.0 miles L-216-3 and -4 Outer Ring NNW 5.0 miles L-01-1 and -2 Other NNW 1.5 miles Nearsite 1 (indicator)

L-03-1 and -2 Other ENE 1.0 miles Onsite 3 (indicator)

L-04-1 and -2 Other E

3.2 miles Rte. 170 (indicator)

L-05-1 and -2 Other ESE 0.3 miles Onsite 5 (indicator)

L-06-1 and -2 Other W

0.4 miles Nearsite 6 (indicator)

L-07-1 and -2 Other NNE 5.2 miles Seneca (indicator)

L-08-1 and -2 Other NNW 6.0 miles Marseilles (indicator)

L-11A-1 and -2 Other S

6.0 miles Ransom (indicator)

L-10-1 and -2 Control/

Special Interest SW 13.5 miles Streator

Annual Radiological Environmental Operating Report YEAR: 2024 Page 14 of 74 Company: Constellation Plant: LaSalle County Station Units 1 and 2 6.0 MAPS OF COLLECTION SITES Figure 2, Inner Ring OSLD Locations of the LaSalle County Station, 2024

Annual Radiological Environmental Operating Report YEAR: 2024 Page 15 of 74 Company: Constellation Plant: LaSalle County Station Units 1 and 2 Figure 3, Outer Ring OSLD Locations and Fixed Air Sampling Locations of the LaSalle County Station, 2024

Annual Radiological Environmental Operating Report YEAR: 2024 Page 16 of 74 Company: Constellation Plant: LaSalle County Station Units 1 and 2 Figure 4, Ingestion and Waterborne Exposure Pathway Sample Locations of the LaSalle County Station, 2024

Annual Radiological Environmental Operating Report YEAR: 2024 Page 17 of 74 Company: Constellation Plant: LaSalle County Station Units 1 and 2 7.0 REPORTING LEVELS FOR RADIOACTIVITY CONCENTRATIONS IN ENVIRONMENTAL SAMPLES Table 6, Reporting Levels for Radioactivity Concentrations in Environmental Samples Radionuclide Water (pCi/L)

Air Particulates or Gases (pCi/m3)

Fish (pCi/kg-wet)

Milk (pCi/L)

Food Products (pCi/kg-wet)

H-3 20,000 (1)

NA NA NA NA Mn-54 1,000 NA 30,000 NA NA Fe-59 400 NA 10,000 NA NA Co-58 1,000 NA 30,000 NA NA Co-60 300 NA 10,000 NA NA Zn-65 300 NA 20,000 NA NA Zr-Nb-95 400 NA NA NA NA I-131 2 (2) 0.9 NA 3

100 Cs-134 30 10 1,000 60 1,000 Cs-137 50 20 2,000 70 2,000 Ba-La-140 200 NA NA 300 NA Table 7, Maximum Values for the Limit of Detection Radionuclide Water (pCi/L)

Air Particulates or Gases (pCi/m3)

Fish (pCi/kg-wet)

Milk (pCi/L)

Food Products (pCi/kg-wet)

Sediment (pCi/kg-dry)

H-3 2,000 NA NA NA NA NA Mn-54 15 NA 130 NA NA NA Fe-59 30 NA 260 NA NA NA Co-58, Co-60 15 NA 130 NA NA NA Zn-65 30 NA 260 NA NA NA Zr-Nb-95 15 NA NA NA NA NA I-131 1

0.07 NA 1

60 NA Cs-134 15 0.05 130 15 60 150 Cs-137 18 0.06 150 18 80 180 Ba-La-140 15 NA NA 15 NA NA 1 For drinking water samples, this is a 40 CFR Part 141 value. If no drinking water pathway exists, a value of 30,000 pCi/l may be used.

2 If no drinking water pathway exists, a value of 20 pCi/l may be used

Annual Radiological Environmental Operating Report YEAR: 2024 Page 18 of 74 Company: Constellation Plant: LaSalle County Station Units 1 and 2 8.0 SAMPLING PROGRAM, PROGRAM MODIFICATION AND INTEPRETATION OF RESULTS At most nuclear stations, data was collected prior to plant operation to determine background radioactivity levels in the environment. Annual data is routinely compared to preoperational and/or 10-year average values to determine if changes in the environs are present. Strict comparison is difficult to make due to fallout from historical nuclear weapon testing. Cesium-137 can be routinely found in environmental samples as a results of above ground nuclear weapons testing. It is important to note, levels of Cs-137 in environment are observed to fluctuate, for example as silt distributions shift due to natural erosion and transport processes, Cs-137 may or may not be observed in sediment samples. Results from samples collected and analyzed during the year, 2024, are described below.

In the following sections, results from direct radiation, air, water, and food products analyzed as part of REMP in 2024 will be discussed. Sampling program descriptions and deviations will also be discussed.

8.1 Environmental Direct Radiation Dosimetry Results Dose is measured as net exposure (field reading less transit reading) normalized to 91-day quarters. Data is treated and analyzed consistent with ANSI/HPS N13.37-2014, which compares the measured dose for each location to the baseline background dose for that location. Environmental dose rates vary by location, depending on geological and land use considerations, and remain relatively constant for any given location (unless land use changes). Some facilities observe seasonal variation in environmental doses. Baseline Background Doses have been determined for both quarterly and annual measurements at each location using historical field measurements.

ANSI/HPS N13.37-2014 uses the concept of minimum differential dose (MDD), which is the minimum facility-related dose that can be detected above background. Due to natural background variations and measurement sensitivities and uncertainties, minimum differential dose is not zero. MDD is calculated based on statistical performance of the dosimetry system in the environment and is site specific.

Normalized doses that exceed the Minimum Differential Dose value above the Baseline Background Dose are considered to indicate Facility-Related Dose; a quality assurance review is performed to verify that any results indicating Facility-Related Dose are accurate.

During the calendar year 2024, a total of 42 locations were monitored and data., Environmental Direct Radiation Dosimetry Results, provides the annual direct radiation dosimetry analysis.

There was no direct radiation dose detected from the facility. All OSLD measurements were analyzed, and none were found to have radiation levels that had increased over normal background radiation levels.

Annual Radiological Environmental Operating Report YEAR: 2024 Page 19 of 74 Company: Constellation Plant: LaSalle County Station Units 1 and 2 8.2 Air Particulate and Radioiodine Sample Results Air particulate filters and charcoal canisters were collected from locations specified in.

During the calendar year 2024, a total of 457 samples were collected and analyzed for gross beta, gamma emitters and iodine. Particulate samplers are used to continuously collect airborne particulates on a filter. The samples are analyzed for gross beta activity following filter changeout which occurs weekly. Gamma isotopic analysis is also performed on the samples collected at each location and is analyzed quarterly. Radioiodine (I-131) analysis is performed weekly on radioiodine sample cartridges.

All gross beta analyses of air particulate filters detected gross beta activity at levels consistent with previous years. All air particulate quarterly gamma composite samples were below the detection limit except for naturally occurring radionuclides.

Figure 5, Air Particulate: Analysis for Gross Beta, Average for All Indicator vs. Control Location 0

5 10 15 20 25 2015 2016 2017 2018 2019 2020 2021 2022 2023 2024 E-3 pCi/cu.m Year Air Particulate: Analysis for Gross Beta, Indicator vs.

Control Indicator Control

Annual Radiological Environmental Operating Report YEAR: 2024 Page 20 of 74 Company: Constellation Plant: LaSalle County Station Units 1 and 2 Air particulate and radioiodine results from this monitoring period, 2024, were compared to 10-year average as shown in Figure 5, and there were no significant changes.

8.3 Waterborne Sample Results 8.3.1 Surface Water Composite water samples are collected monthly at the upstream control location and at the downstream indicator locations. Monthly composite samples are analyzed for gamma emitters. Aliquots from the monthly composites are combined to form a quarterly composite which is then analyzed for tritium. During the calendar year 2024, a total of 32 surface water samples were collected and analyzed in accordance with the requirements in the ODCM and shown in Table 3, Radiological Environmental Sampling Program - Exposure Pathway - Waterborne. Gross Beta was detected in 24 of the 24 samples with a range of 4 to 13 pCi/L. The required LLD for Gross Beta was met for all samples. Samples from both locations were analyzed for gamma-emitting nuclides. No nuclides were detected and all required LLDs were met. Tritium was detected in 5 of the 8 samples with a range of 198 to 430 pCi/L.

Concentrations detected were consistent with those detected in previous years.

Tritium concentrations in surface water were well below the EPA tritium drinking water limit of 20,000 pCi/L.

Figure 6: Average Surface Water Tritium Results by Year 0

50 100 150 200 250 300 350 400 450 500 2015 2016 2017 2018 2019 2020 2021 2022 2023 2024 pCi/L Year Surface Water: Analysis for Tritium, Indicator vs.

Control Indicator Control

Annual Radiological Environmental Operating Report YEAR: 2024 Page 21 of 74 Company: Constellation Plant: LaSalle County Station Units 1 and 2 8.3.2 REMP Groundwater Groundwater samples were collected from control location upgradient from the plant and indicator location down gradient from the plant. During the calendar year 2024, a total of 12 groundwater water samples were collected from offsite monitoring wells and analyzed in accordance with the requirements in the ODCM and shown in Table 3: Radiological Environmental Sampling Program - Exposure Pathway - Waterborne.

A total of 2 control sample locations and a total of 2 indicator sample locations were collected. These samples were analyzed for tritium and gamma quarterly. All groundwater samples were collected in new containers, which were rinsed with source water prior to collection.

Samples from all locations were analyzed for gamma-emitting nuclides. No nuclides were detected and all required LLDs were met. Tritium concentrations in groundwater were well below the EPA tritium drinking water limit of 20,000 pCi/L. There has been no detectable tritium in any REMP groundwater samples in 2024 or the previous 10 years. Therefore, no trend has been established above the detection limit to plot on a trending graph.

8.3.3 Sediment from Shoreline Shoreline sediment collections were made in May through October of 2024 and analyzed for gamma-emitting isotopes. Samples are collected at both indicator and control locations. A total of 6 shoreline samples were analyzed in accordance with requirements in the ODCM and shown in Table 3, Radiological Environmental Sampling Program - Exposure Pathway - Waterborne.

No nuclides potentially associated with LaSalle Station were detected and all required LLDs were met.

8.4 Ingestion Pathway Sample Results 8.4.1 Fish A total of 12 fish samples were collected in 2024. These samples were analyzed for gamma-emitting radionuclides in edible portions, in accordance with requirements of the ODCM and summarized in Table 4, Radiological Environmental Sampling Program - Exposure Pathway - Ingestion. These samples are collected from the indicator and control areas as required by the ODCM.

Naturally occurring potassium-40 was identified in all fish samples with concentrations consistent with previous years.

8.4.2 Food Products A total of 18 food product type samples were analyzed in 2024, for gamma emitting radionuclides in accordance with requirements of the ODCM, as summarized in Table 4, Radiological Environmental Sampling Program - Exposure Pathway - Ingestion.

No nuclides were detected and all required LLDs were met.

Annual Radiological Environmental Operating Report YEAR: 2024 Page 22 of 74 Company: Constellation Plant: LaSalle County Station Units 1 and 2 8.4.3 Vegetation In accordance with the ODCM and as described in Table 4, Radiological Environmental Sampling Program - Exposure Pathway - Ingestion, 57 vegetation samples were collected from growing locations nearest site boundary in areas of highest predicted annual average ground level D/Q. Samples are collected and analyzed for gamma isotopic from the indicator and control locations monthly during growing season.

No nuclides were detected and all required LLDs were met.

9.0 LAND USE CENSUS An annual land use census is required by the Offsite Dose Calculation Manual and is performed to ensure that changes in the use of areas at or beyond the site boundary are identified and modifications to REMP are made if required by changes in land use. The land use census satisfies the requirements of Section IV.B.3 of Appendix I to 10 CFR 50 [1]. NUREG-1301/1302 Control 3.12.2 specifies that "a Land Use Census shall be conducted and shall identify within a distance of 8 km (5 mi.) the location in each of the 16 meteorological sectors of the nearest milk animal, the nearest residence and the nearest garden of greater than 50 m2 (500 ft2) producing broad leaf vegetation. Note, per NUREG-1301/1302, Broad leaf vegetation sampling of at least three different kinds of vegetation may be performed at the SITE BOUNDARY in each of two different direction sectors with the highest predicted D/Qs in lieu of the garden census.

A Land Use Census was conducted during the calendar year, 2024, within the growing season to identify changes in land use, receptor locations, and new exposure pathways. The results for the 2024 Land Use Census are listed in Table 8: Land Use Census - Nearest Receptors within 5 miles. In summary, the highest D/Q locations for nearest livestock, nearest residence and nearest milk animal did not change following the 2024 census.

Annual Radiological Environmental Operating Report YEAR: 2024 Page 23 of 74 Company: Constellation Plant: LaSalle County Station Units 1 and 2 Table 8: Land Use Census - Nearest Receptors within 5 miles Sector Direction Residence Distance (Miles)

Milk Farm Distance (Miles)

Livestock Distance (Miles)

A N

3.9 4.0 B

NNE 1.6 1.7 C

NE 2.1 3.5 D

ENE 3.3 3.8 E

E 3.2 14.2 F

ESE 1.4 G

SE 1.7 5.1 H

SSE 1.8 4.7 J

S 1.5 1.5 K

SSW 0.7 L

SW 1.0 5.8 M

WSW 1.5 N

W 1.7 3.0 P

WNW 0.9 3.0 Q

NW 1.7 3.3 R

NNW 1.7 4.5 10.0 SAMPLE DEVIATIONS, ANOMALIES AND UNAVAILABILITY Sampling and analysis are performed for media types addressed in the Offsite Dose Calculation Manual. Sampling and analysis challenges may be experienced due to a multitude of reasons including environmental factors, loss of TLDs/OSLDs, contamination of samples, etc. To aid classification of sampling and analysis challenges experienced in 2024, the following three terms are used to describe the issues: Sample Anomalies, Sample Deviation, and Unavailable Samples.

Media that experienced downtime (i.e., air samplers or water samplers) during a surveillance period are classified a Sample Deviation. Sample Anomalies are defined as errors that were introduced to a sample once it arrived in the laboratory, errors that prevents the sample from being analyzed as it normally would, or may have altered the outcome of the analysis (i.e., cross contamination, human error).

Sample Unavailability is defined as sample collection with no available sample (i.e.,

food crop, TLD).

All required samples were collected and analyzed as scheduled except for the following:

Annual Radiological Environmental Operating Report YEAR: 2024 Page 24 of 74 Company: Constellation Plant: LaSalle County Station Units 1 and 2 Table 9: Sample Deviation Summary Sample Type Location Collection Date or Period Reason for not conducting REMP sampling as required by ODCM Plans for preventing reoccurrence AP/AI L-04 1/18/24 The timer indicates approximately 63 hours7.291667e-4 days 0.0175 hours 1.041667e-4 weeks 2.39715e-5 months less than expected due to a power outage. During the next collection period (1/25), the timer indicated an expected reading of 167.8 hours9.259259e-5 days 0.00222 hours 1.322751e-5 weeks 3.044e-6 months AP/AI L-06 2/15/24 Pump was found not running with the timer indicating 4 hours4.62963e-5 days 0.00111 hours 6.613757e-6 weeks 1.522e-6 months less than expected due to a power outage. The flow rate was estimated.

The power restored within 2 hours2.314815e-5 days 5.555556e-4 hours 3.306878e-6 weeks 7.61e-7 months and the time indicated an expected reading of 166.4 hours4.62963e-5 days 0.00111 hours 6.613757e-6 weeks 1.522e-6 months .

The power company was notified.

AP/AI L-01 4/25/24 The sample was marked as a missed sample.

Pump found flipped on its side and broken due to very strong winds The pump was replaced.

AP/AI L-06 5/9/24 The pump stopped running after 137.8 hours9.259259e-5 days 0.00222 hours 1.322751e-5 weeks 3.044e-6 months due to a blown fuse The fuse was replaced.

AP/AI L-03 8/7/24 The sample was marked as a missed sample.