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2024 Annual Radioactive Effluent Release Report
	ML25132A066
Person / Time
Site:	Monticello
Issue date:	05/10/2025
From:	; Northern States Power Company, Minnesota, Xcel Energy
To:	; Office of Nuclear Reactor Regulation
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ML25132A064	List: L-MT-25-018, Offsite Dose Calculation Manual; ML25132A065; ML25132A066; ML25132A067;
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ENCLOSURE 1 ANNUAL RADIOACTIVE EFFLUENT RELEASE REPORT JANUARY 1 - DECEMBER 31, 2024 54 Pages Follow

Monticello Nuclear Generating Plant 2024 Annual Radioactive Effluent Release Report fl Xcel Energy 3

AES PONS IBLE BY NAT U A E*

Annual Radioactive Effluent Release Report YEAR: 2024 Page 1 of 53 Company: Xcel Energy Plant: Monticello Nuclear Generating Plant TABLE OF CONTENTS LIST OF ACRONYMS AND DEFINITIONS................................................................................ 3 EXECUTIVE

SUMMARY

............................................................................................................ 5 2.1 Comparison to Regulatory Limits.................................................................................... 6 INTRODUCTION........................................................................................................................ 8 3.1 About Nuclear Power...................................................................................................... 8 3.2 About Radiation Dose................................................................................................... 10 3.3 About Dose Calculation................................................................................................ 12 DOSE ASSESSMENT FOR PLANT OPERATIONS................................................................. 14 4.1 Regulatory Limits.......................................................................................................... 14 4.2 Regulatory Limits for Liquid Effluent Doses................................................................... 15 4.3 40 CFR 190 Regulatory Dose Limits for a Member of the Public.................................. 16 4.4 Onsite Doses (Within Site Boundary)............................................................................ 16 SUPPLEMENTAL INFORMATION........................................................................................... 17 5.1 Gaseous Batch Releases............................................................................................. 17 5.2 Liquid Batch Releases.................................................................................................. 17 5.3 Abnormal Releases...................................................................................................... 17 5.4 Land Use Census......................................................................................................... 19 5.5 Meteorological Data...................................................................................................... 20 5.6 Effluent Radiation Monitors Out of Service Greater Than 30 Days................................ 20 5.7 Offsite Dose Calculation Manual (ODCM) Changes...................................................... 21 5.8 Process Control Program (PCP) Changes.................................................................... 22 5.9 Radioactive Waste Treatment System Changes........................................................... 22 5.10 Water Storage Ponds #2A, #2B, and #2C..................................................................... 22 NEI 07-07 ONSITE RADIOLOGICAL GROUNDWATER MONITORING PROGRAM............... 24 6.1 Voluntary Notification.................................................................................................... 26 BIBLIOGRAPHY...................................................................................................................... 27 TABLES Table 1, Monticello Nuclear Generating Plant Dose Summary............................................................... 6 Table 2, Total Annual Offsite-Dose Comparison to 40 CFR 190 Limits for MNGP................................. 7 Table 3, Onsite Doses (Within Site Boundary)..................................................................................... 16 Table 4, Modeled Abnormal Discharge from MNGP To Mississippi River............................................ 18 Table 5, 2024 Critical Receptor............................................................................................................ 19 Table 6, 2024 ODCM Changes............................................................................................................ 21 Table 7, Groundwater Monitoring Well Sampling Frequencies............................................................. 25 Table 8, Gaseous Effluents Summation of All Releases MNGP.......................................................... 28 Table 9, Gaseous Effluents - Ground Level Release Batch Mode MNGP......................................... 29 Table 10, Gaseous Effluents - Ground Level Release Continuous Mode MNGP............................... 30 Table 11, Gaseous Effluents - Elevated Level Release Batch Mode MNGP..................................... 31 Table 12, Gaseous Effluents - Elevated Level Release Continuous Mode MNGP............................... 33

Annual Radioactive Effluent Release Report YEAR: 2024 Page 2 of 53 Company: Xcel Energy Plant: Monticello Nuclear Generating Plant Table 13, Liquid Effluents - Summation of All Releases MNGP.......................................................... 35 Table 14, Batch Mode Liquid Effluents {Monticello Nuclear Generating Plant}..................................... 36 Table 15, Continuous Mode Liquid Effluents MNGP............................................................................ 37 Table 16, Types of Solid Waste Summary MNGP................................................................................ 38 Table 17, Major Nuclides MNGP.......................................................................................................... 39 Table 18, Solid Waste Disposition MNGP............................................................................................ 40 Table 19, Irradiated Fuel Shipments Disposition MNGP...................................................................... 40 Table 20 MNGP Monitoring Well Locations.......................................................................................... 42 FIGURES Figure 1, Pressurized Water Reactor (PWR) [1]..................................................................................... 8 Figure 2, Boiling Water Reactor (BWR) [2]............................................................................................. 9 Figure 3, Sources of Radiation Exposure (NCRP Report No. 160) [3].................................................. 10 Figure 4, Potential exposure pathways to Members of the Public due to Plant Operations [6]............. 12 Figure 5, Monticello Nuclear Generating Plant Well Locations............................................................. 44 Figure 6, Monticello Nuclear Generating Plant Well Locations - Detailed View................................... 45 ATTACHMENTS, ARERR Release Summary Tables (RG-1.21 Tables)................................................... 28, Solid Waste Information................................................................................................ 38, Radiological Environmental Monitoring Program TLD Results...................................... 41, MNGP Groundwater Supplemental Information............................................................ 42, Groundwater Monitoring Program Results.................................................................... 45

Annual Radioactive Effluent Release Report YEAR: 2024 Page 3 of 53 Company: Xcel Energy Plant: Monticello Nuclear Generating Plant LIST OF ACRONYMS AND DEFINITIONS

1.

Alpha Particle (): A charged particle emitted from the nucleus of an atom having a mass and charge equal in magnitude of a helium nucleus.

2.

BWR: Boiling Water Reactor

3.

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.

4.

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

5.

Counting Error: An estimate of the two-sigma uncertainty associated with the sample results based on total counts accumulated.

6.

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

7.

Direct Radiation Monitoring: The measurement of radiation dose at various distances from the plant is assessed using thermoluminescent dosimeters (TLDs), optically stimulated luminescent dosimeters (OSLDs), and/or pressurized ionization chambers.

8.

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

9.

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

10.

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.

11.

ISFSI: Independent Spent Fuel Storage Installation

12.

LLD: Lower Limit of Detection. 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.

13.

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 5% probability of falsely concluding that a blank observation represents a true signal.

Annual Radioactive Effluent Release Report YEAR: 2024 Page 4 of 53 Company: Xcel Energy Plant: Monticello Nuclear Generating Plant

14.

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

15.

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

16.

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

17.

millirem (mrem): 1/1000 rem; a unit of radiation dose equivalent in tissue.

18.

Milliroentgen (mR): 1/1000 Roentgen; a unit of exposure to X-or gamma radiation.

19.

N/A: Not Applicable

20.

NEI: Nuclear Energy Institute

21.

NRC: Nuclear Regulatory Commission

22.

ODCM: Offsite Dose Calculation Manual

23.

OSLD: Optically Stimulated Luminescence Dosimeter

24.

Protected Area: A 10 CFR 73 security term is an area encompassed by physical barriers and to which access is controlled for security purposes. The fenced area immediately surrounding the plant and around ISFSI are commonly classified by the licensee as Protected areas. Access to the protected area requires a security badge or escort.

25.

PWR: Pressurized Water Reactor

26.

REC: Radiological Effluent Control

27.

REMP: Radiological Environmental Monitoring Program

28.

Restricted Area: A 10 CFRR 20 defined term where access to which is limited by the licensee for the purpose of protecting individuals against undue risks from exposure to radiation and radioactive materials.

29.

TEDE: Total Effective Dose Equivalent, means the sum of the effective dose equivalent (for external exposures) and the committed effective dose equivalent (for internal exposures).

30.

TLD: Thermoluminescent Dosimeter

31.

TRM: Technical Requirements Manual

32.

TS: Technical Specification, also referred to as Tech Spec

Annual Radioactive Effluent Release Report YEAR: 2024 Page 5 of 53 Company: Xcel Energy Plant: Monticello Nuclear Generating Plant

33.

Unrestricted Area: An area, access to which is neither limited nor controlled by the licensee.

34.

WSP: Water Storage Pond EXECUTIVE

SUMMARY

Monticello Nuclear Generating Plant (MNGP) Radiological Effluent Control (REC)

Program was established to limit the quantities of radioactive material that may be released based on calculated radiation doses or dose rates. Dose to Members of the Public due to radioactive materials released from the plant is limited by Technical Specifications,10 CFR 20, and by 40 CFR 190. Operational doses to the public during 2024 were calculated to be within the limits required by regulation and compared to other sources of radiation dose and pose no health hazard. These doses are summarized and compared to the regulatory limits in Section 2.1 Comparison to Regulatory Limits below.

The Annual Radioactive Effluent Release Report (ARERR) is published per REC requirements and provides data related to plant operation, including: quantities of radioactive materials released in liquid and gaseous effluents; radiation doses to members of the public; solid radioactive waste shipped offsite for processing or direct disposal; and other information as required by site licensing documents.

In 2024, the gaseous effluent dose assessments for locations from the Land Use Census showed that the critical receptor for Monticello Nuclear Generating Plant is Child, due to Ground Plane, Inhalation, and Vegetable, at a garden 1.11 miles SE. The maximum Annual Organ Dose calculated for this receptor 3.39E-02 mrem, to the Bone.

The calculated dose to the thyroid was 3.08E-02 mrem.

The maximum dose calculated to any organ due to radioactive liquid effluents was 4.61E-02 mrem for Child Whole Body or Any Organ at the nearest drinking water uptake, the St. Paul Water Intake, 34.2 mi downstream of the plant.

Solid radioactive waste shipped offsite for processing or direct disposal included 39.8 Curies and 371.3 m3, shipped in 14 shipments.

In addition to monitoring radioactive effluents, MNGP has a Radiological Environmental Monitoring Program (REMP) that monitors for levels of radiation and radioactive materials in the local environment. Data from the REMP is published in the Annual Radiological Environmental Operating Report (AREOR).

Annual Radioactive Effluent Release Report YEAR: 2024 Page 6 of 53 Company: Xcel Energy Plant: Monticello Nuclear Generating Plant 2.1 Comparison to Regulatory Limits During 2024 all solid, liquid, and gaseous radioactive effluents from Monticello Nuclear Generating Plant were well below regulatory limits, as summarized in Table 1 and Table 2.

Table 1, Monticello Nuclear Generating Plant Dose Summary1 Quarter 1 Quarter 2 Quarter 3 Quarter 4 Annual Liquid Effluent Dose Limit, Total Body Limit 1.5 mrem 1.5 mrem 1.5 mrem 1.5 mrem 3 mrem Total Body Dose 1.38E-02 8.74E-03 7.64E-03 1.59E-02 4.61E-02

% of Limit 0.92 0.58 0.51 1.06 1.54 Liquid Effluent Dose Limit, Any Organ Limit 5 mrem 5 mrem 5 mrem 5 mrem 10 mrem Max Organ Dose 1.38E-02 8.74E-03 7.64E-03 1.59E-02 4.61E-02

% of Limit 0.28 0.17 0.15 0.32 0.46 Gaseous Effluent Dose Limit, Gamma Air (Noble Gas)

Limit 5 mrad 5 mrad 5 mrad 5 mrad 10 mrad Gamma Air Dose 7.6E-04 1.28E-03 6.43E-04 6.83E-04 3.37E-03

% of Limit 0.02 0.03 0.01 0.01 0.03 Gaseous Effluent Dose Limit, Beta Air (Noble Gas)

Limit 10 mrad 10 mrad 10 mrad 10 mrad 20 mrad Beta Air Dose 2.06E-04 3.86E-04 3.09E-04 2.17E-04 1.12E-03

% of Limit 0.002 0.003 0.003 0.002 0.01 Gaseous Effluent Organ Dose Limit (Iodine, Tritium, Particulates with

> 8-day half-life)

Limit 7.5 mrem 7.5 mrem 7.5 mrem 7.5 mrem 15 mrem Max Organ Dose 4.76E-03 1.29E-02 1.84E-02 4.79E-03 3.23E-02

% of Limit 0.06 0.17 0.25 0.06 0.22 1 Table 1 demonstrates compliance with 10 CFR Part 50, App. I Limits.

Annual Radioactive Effluent Release Report YEAR: 2024 Page 7 of 53 Company: Xcel Energy Plant: Monticello Nuclear Generating Plant Table 2, Total Annual Offsite-Dose Comparison to 40 CFR 190 Limits for MNGP Dose Type Organ Dose 40 CFR 190 Limits

% of Limit Direct Radiation Dose*

All Not detected 0.00%

Noble Gases Whole Body Skin 1.59E-03 mrem 3.11E-03 mrem 0.01%

0.01%

Particulates, Iodines, Tritium and Carbon-14 Whole Body Thyroid Max Other Organ (Bone) 1.09E-02 mrem 2.92E-02 mrem 3.39E-02 mrem 0.04%

0.04%

0.13%

Total Dose **

Whole Body Thyroid Max Other Organ (Bone) 3.08E-02 mrem 3.08E-02 mrem 3.39E-02 mrem 25 mrem 75 mrem 25 mrem 0.05%

0.04%

0.14%

Based on REMP TLD Results, given in Attachment 3.

- For the Critical Receptor identified in Table 5. Because Direct (TLD) dose is 0.0, then this represents the likely most-exposed individual. Doses in bold include contributions due to Iodines, Particulates, Tritium, Carbon-14, and Noble Gases.

Annual Radioactive Effluent Release Report YEAR: 2024 Page 8 of 53 Company: Xcel Energy Plant: Monticello Nuclear Generating Plant INTRODUCTION 3.1 About Nuclear Power US Commercial nuclear power plants are generally classified as either Boiling Water Reactors (BWRs) or Pressurized Water Reactors (PWRs), based on their design. A BWR includes a single coolant system where water used as reactor coolant boils as it passes through the core and the steam generated is used to turn the turbine generator for power production. A PWR, in contrast, includes two separate water systems:

radioactive reactor coolant and a secondary system. Reactor coolant is maintained under high pressure, preventing boiling. The high-pressure coolant is passed through a heat exchanger called a steam generator where the secondary system water is boiled, and the steam is used to turn the turbine generator for power production.

Figure 1, Pressurized Water Reactor (PWR) [1]

Annual Radioactive Effluent Release Report YEAR: 2024 Page 9 of 53 Company: Xcel Energy Plant: Monticello Nuclear Generating Plant 3.1 (Continued)

Figure 2, Boiling Water Reactor (BWR) [2]

Electricity is generated by a nuclear power plant similarly to the way that electricity is generated at other conventional types of power plants, such as those powered by coal or natural gas. Water is boiled to generate steam; the steam turns a turbine that is attached to a generator and the steam is condensed back into water to be returned to the boiler. What makes nuclear power different from these other types of power plants is that the heat is generated by fission and decay reactions occurring within and around the core containing fissionable uranium (U-235).

Nuclear fission occurs when certain nuclides (primarily U-233, U-235, or Pu-239) absorb a neutron and break into several smaller nuclides (called fission products) as well as producing some additional neutrons.

Fission results in production of radioactive materials including gases and solids that must be contained to prevent release or treated prior to release. These effluents are generally treated by filtration and/or hold-up prior to release. Releases are generally monitored by sampling and by continuously indicating radiation monitors. The effluent release data is used to calculate doses in order to ensure that dose to the public due to plant operation remains within required limits.

Annual Radioactive Effluent Release Report YEAR: 2024 Page 10 of 53 Company: Xcel Energy Plant: Monticello Nuclear Generating Plant 3.2 About Radiation Dose Ionizing radiation, including alpha, beta, and gamma radiation from radioactive decay, has enough energy to break chemical bonds in tissues and result in damage to tissue or genetic material. The amount of ionization that will be generated by a given exposure to ionizing radiation is quantified as dose. Radiation dose is generally reported in units of millirem (mrem) in the US.

Figure 3, Sources of Radiation Exposure (NCRP Report No. 160) [3]

Annual Radioactive Effluent Release Report YEAR: 2024 Page 11 of 53 Company: Xcel Energy Plant: Monticello Nuclear Generating Plant 3.2 (Continued)

The National Council on Radiation Protection (NCRP) has evaluated the population dose for the US and determined that the average individual is exposed to approximately 620 mrem per year [3]. There are many sources for radiation dose, ranging from natural background sources to medical procedures, air travel, and industrial processes.

Approximately half (310 mrem) of the average exposure is due to natural sources of radiation including exposure to radon, cosmic radiation, and internal radiation and terrestrial due to naturally occurring radionuclides. The remaining 310 mrem of exposure is due to man-made sources of exposure, with the most significant contributors being medical (48% of total mrem per year) due to radiation used in various types of medical scans and treatments. Of the remaining 2% of dose, most is due to consumer activities such as air travel, smoking cigarettes, and building materials. A small fraction of this 2% is due to industrial activities including generation of nuclear power.

Readers that are curious about common sources and effects of radiation dose that they may encounter can find excellent sources of information from the Health Physics Society, including the Radiation Fact Sheets [4], and from the US Nuclear Regulatory Commission website [5].

Annual Radioactive Effluent Release Report YEAR: 2024 Page 12 of 53 Company: Xcel Energy Plant: Monticello Nuclear Generating Plant 3.3 About Dose Calculation Concentrations of radioactive material in the environment resulting from plant operations are very small and it is not possible to determine doses directly using measured activities of environmental samples. To overcome this, dose calculations based on measured activities of effluent streams are used to model the dose impact for Members of the Public due to plant operation and effluents. There are several mechanisms that can result in dose to Members of the Public, including: Ingestion of radionuclides in food or water; Inhalation of radionuclides in air; Immersion in a plume of noble gases; and Direct Radiation from the ground, the plant or from an elevated plume.

Figure 4, Potential exposure pathways to Members of the Public due to Plant Operations [6]

Each plant has an Offsite Dose Calculation Manual (ODCM) that specifies the methodology used to obtain the doses in the Dose Assessment section of this report.

The dose assessment methodology in the ODCM is based on NRC Regulatory Guide 1.109 [7] and NUREG-0133 [8]. Doses are calculated by determining what the nuclide concentration will be in air, water, on the ground, or in food products based on plant effluent releases. Release points are continuously monitored to quantify what concentrations of nuclides are being released. For gaseous releases meteorological data is used to determine how much of the released activity will be present at a given location outside of the plant either deposited onto the ground or in gaseous form. Intake patterns and nuclide bio-concentration factors are used to determine how much activity will be transferred into animal milk or meat. Finally, human ingestion factors and dose factors are used to determine how much activity will be consumed and how much dose the consumer will receive. Inhalation dose is calculated by determining the concentration of nuclides and how much air is breathed by the individual.

Annual Radioactive Effluent Release Report YEAR: 2024 Page 13 of 53 Company: Xcel Energy Plant: Monticello Nuclear Generating Plant 3.3 (Continued)

For liquid releases, dilution and mixing factors are used to model the environmental concentrations in water. Drinking water pathways are modeled by determining the concentration of nuclides in the water at the point where the drinking water is sourced (e.g., taken from wells, rivers, or lakes). Fish and invertebrate pathways are determined by using concentrations at the release point, bioaccumulation factors for the fish or invertebrate and an estimate of the quantity of fish consumed.

Each year a Land Use Census is performed to determine what potential dose pathways currently exist within a five-mile radius around the plant, the area most affected by plant operations. The Annual Land Use Census identifies the locations of vegetable gardens, nearest residences, milk animals and meat animals. The data from the census is used to determine who is the likely to be most exposed to radiation dose as a result of plant operation.

There is significant uncertainty in dose calculation results, due to modeling dispersion of material released and bioaccumulation factors, as well as assumptions associated with consumption and land-use patterns. Even with these sources of uncertainty, the calculations do provide a reasonable estimate of the order of magnitude of the exposure. Conservative assumptions are made in the calculation inputs such as the number of various foods and water consumed, the amount of air inhaled, and the amount of direct radiation exposure from the ground or plume, such that the actual doses received are likely lower than the calculated dose. Even with the built-in conservatism, doses calculated for the maximum exposed individual due to plant operation are a very small fraction of the annual dose that is received due to other sources. The calculated doses due to plant effluents, along with REMP results, serve to provide assurance that radioactive effluents releases are not exceeding safety standards for the environment or people living near the plant.

Annual Radioactive Effluent Release Report YEAR: 2024 Page 14 of 53 Company: Xcel Energy Plant: Monticello Nuclear Generating Plant DOSE ASSESSMENT FOR PLANT OPERATIONS 4.1 Regulatory Limits Regulatory limits are detailed in station licensing documents such as the plant Technical Specifications and the Offsite Dose Calculation Manual (ODCM.) These documents contain the limits to which MNGP must adhere. MNGP drives to maintain the philosophy to keep dose As Low As is Reasonably Achievable (ALARA) and actions are taken to reduce the amount of radiation released to the environment. Liquid and gaseous release data show that the dose from MNGP is well below the ODCM limits. The instantaneous concentration of liquid radioactive material released shall be limited to ten times the concentration specified in 10 CFR 20, Appendix B, Table 2, Column 2, for radionuclides other than dissolved or entrained noble gases. For dissolved or entrained noble gases, the total concentration released shall be limited to 2.0 x 10-4 microcuries/ml.

The annual whole body, skin and organ dose was computed using the 2024 source term using the dose calculation methodology provided in the ODCM. The calculated doses due to gaseous effluents are used to demonstrate compliance with offsite dose limits are presented in Table 1, Monticello Nuclear Generating Plant Dose Summary and Regulatory Limits for Gaseous Effluent Doses:

1.

Fission and activation gases:

a.

Noble gases dose rate due to radioactive materials released in gaseous effluents from the site to areas at and beyond the site boundary shall be limited to the following:

1)

Less than or equal to 500 mrem/year to the total body

2)

Less than or equal to 3000 mrem/year to the skin

b.

Noble gas air dose due to noble gases released in gaseous effluents, from each reactor unit, to areas at and beyond the site boundary shall be limited to the following:

1)

Quarterly a)

Less than or equal to 5 mrads gamma b)

Less than or equal to 10 mrads beta

2)

Yearly a)

Less than or equal to 10 mrads gamma b)

Less than or equal to 20 mrads beta

Annual Radioactive Effluent Release Report YEAR: 2024 Page 15 of 53 Company: Xcel Energy Plant: Monticello Nuclear Generating Plant 4.1 (Continued)

2.

Iodine, tritium, and all radionuclides in particulate form with half-lives greater than 8 days.

a.

The dose rate for iodine-131, iodine-133, tritium, and all radionuclides in particulate form with half-lives greater than 8 days in gaseous effluents released from the site to areas at and beyond the site boundary shall be limited to the following:

1)

Less than or equal to 1500 mrem/yr to any organ

b.

The dose to a MEMBER OF THE PUBLIC from iodine-131, iodine-133, tritium, and all radionuclides in particulate form with half-lives greater than 8 DAYS in gaseous effluents released, from each reactor unit, to areas at and beyond the site boundary shall be limited to the following:

1)

Quarterly a)

Less than or equal to 7.5 mrem to any organ

2)

Yearly a)

Less than or equal to 15 mrem to any organ 4.2 Regulatory Limits for Liquid Effluent Doses

1.

The dose or dose commitment to a MEMBER OF THE PUBLIC from radioactive materials in liquid effluents released, from each reactor unit, to unrestricted areas shall be limited to the following:

a.

Quarterly

1)

Less than or equal to 1.5 mrem total body

2)

Less than or equal to 5 mrem critical organ

b.

Yearly

1)

Less than or equal to 3 mrem total body

2)

Less than or equal to 10 mrem critical organ

Annual Radioactive Effluent Release Report YEAR: 2024 Page 16 of 53 Company: Xcel Energy Plant: Monticello Nuclear Generating Plant 4.3 40 CFR 190 Regulatory Dose Limits for a Member of the Public

1.

Total Dose (40 CFR 190)

a.

The annual (calendar year) dose or dose commitment to any MEMBER OF THE PUBLIC in the unrestricted area due to releases of radioactivity and to radiation from uranium fuel cycle sources shall be limited to the following:

1)

Less than or equal to 25 mrem, Total Body or any Organ except Thyroid.

2)

Less than or equal to 75 mrem, Thyroid.

4.4 Onsite Doses (Within Site Boundary)

MNGP classifies individuals within the site boundary as either occupationally exposed individuals or members of the public. This section evaluates dose to non-occupationally exposed workers and members of the public that may be onsite for various reasons.

The report must include any other information as may be required by the Commission to estimate maximum potential annual radiation doses to the public resulting from effluent releases as required by 10 CFR 50.36a(a)(2). While within controlled or restricted areas, the limits from Sections 4.1 through 4.4 do not apply; however, 10 CFR 20.1301 dose limit of 100 mrem per year TEDE and dose rate limit of 2 mrem per hour from external sources continue to apply. Occupancy times within the controlled areas are generally sufficiently low to compensate for increase in the atmospheric dispersion factor above the site boundary. Groups of concern include individuals working in the Site Admin Building and/or Sub Yard. Use of a conservative assumption of 40 hour4.62963e-4 days <br />0.0111 hours <br />6.613757e-5 weeks <br />1.522e-5 months <br />s/week spent inside the site boundary by these groups conservatively represents the most-exposed individual.

Table 3, Onsite Doses (Within Site Boundary)

Location Sector Approx.

Distance (Meters)

X/Q s/m^3 D/Q 1/m^2 Total Body Dose (mrem)

External Dose Total Noble Gas

Iodine, Particulate, C-14 & H-3 TLD or OSLD Site Admin Building /

Sub Yard SSE (H) 100 m 2.10E-05 2.00E-07 4.13E-04 1.12E-02 0.00E+00 1.16E-02

Annual Radioactive Effluent Release Report YEAR: 2024 Page 17 of 53 Company: Xcel Energy Plant: Monticello Nuclear Generating Plant SUPPLEMENTAL INFORMATION 5.1 Gaseous Batch Releases 5.1.1 MNGP Number of batch releases 2

Total time period for a batch release 1393.0 minutes Maximum time period for a batch release 1020.0 minutes Average time period for a batch release 696.5 minutes Minimum time period for a batch release 373.0 minutes 5.2 Liquid Batch Releases 5.2.1 MNGP Number of batch releases 0

Total time period for a batch release 0 minutes Maximum time period for a batch release 0 minutes Average time period for a batch release 0 minutes Minimum time period for a batch release 0 minutes Average total flow during period of release 0 gpm 5.3 Abnormal Releases 5.3.1 Gaseous Abnormal Releases Number of releases 0

Total activity released 0 Ci MNGP did not have any abnormal gaseous releases in the 2024 reporting period.

Annual Radioactive Effluent Release Report YEAR: 2024 Page 18 of 53 Company: Xcel Energy Plant: Monticello Nuclear Generating Plant 5.3.2 Liquid Abnormal Releases & Discharges Number of releases 12 Total activity released 2.31E-02 Ci As part of Monticello Nuclear Generating Plants ongoing response to the Abnormal Release to groundwater reported in 2022, MNGP has been monitoring the migration of the plume from that release. The plume reached MW-33A and MW-37A on July 27, 2023 and since that date MNGP has been reporting a modeled Abnormal Discharge to the Mississippi River. MNGPs groundwater vendor used the software MODFLOW to determine flux to the river from each respective monitoring well interface. The model assumed each interface extended half the distance to the adjacent monitoring wells in either direction. The flux was calculated daily using the developed model. Tritium concentrations at each well interface were determined daily by linearly interpolating between samples. The wells containing Tritium were considered part of the interface until a sample was taken that was below the minimum detectable concentration. These results were composited monthly and reported as an Abnormal Discharge. The results of the analysis for the modeled Abnormal Discharge to the Mississippi River are given below in Table 4. In 2024 this analysis resulted in a total of 2.31E-02 Ci being discharged.

Table 4, Modeled Abnormal Discharge from MNGP To Mississippi River On April 11, 2025, samples taken from MW-26B and MW-28B were positive for tritium at concentrations of 13,400 pCi/L and 9,000 pCi/L respectively. These Sentinel Wells were less than detectable for their last sample period on May 22, 2024. Tritium was detected at the nearest upgradient well, MW-15B, on May 23, 2024, at a concentration of 350 +/- 167 pCi/L. This is due to the ongoing migration of the plume resulting from the release first reported in 2022; this is not due to a new release. The above analysis and MODFLOW model are currently developed for the shallower A wells. These newly positive wells require further analysis by our groundwater vendor to model, since the B Wells are deeper wells and sample from a different aquifer than the shallower A wells.

The modeling and analysis are ongoing; however, if the plume is determined to have interacted with the Mississippi River in 2024, then an errata will be submitted within 90 days following approval of the analysis.

Month 3H Activity Discharged (Ci)

January 2024 5.78E-04 February 2024 2.44E-03 March 2024 2.94E-03 April 2024 2.77E-03 May 2024 3.05E-04 June 2024 1.67E-04 July 2024 1.03E-03 August 2024 2.07E-03 September 2024 7.37E-04 October 2024 3.25E-03 November 2024 3.40E-03 December 2024 3.45E-03 Total 2024 2.31E-02

Annual Radioactive Effluent Release Report YEAR: 2024 Page 19 of 53 Company: Xcel Energy Plant: Monticello Nuclear Generating Plant 5.4 Land Use Census In the 2024 Land Use Census there was 1 sector where the highest meat animal receptor D/Q changed by more than 20%. This was due to the Sector J (South) Cows no longer being present at 4.4 miles, resulting in a 100% change. Of note, there is a Meat & Garden location within the sector. The sector with the highest D/Q remained the same for Meat animals.

For 2024, the Critical Receptor identified by the MNGP Land Use Census has remained the same since the last Land Use Census. The Critical Receptor was identified as a Child at a Garden in the SE Sector 1.1 miles away from the plant and the max organ being Thyroid. The 2024 Land Use Census is performed using the 2023 effluent data as the input; the 2024 data identified the same location but with the max organ being Bone.

Table 5, 2024 Critical Receptor SECTOR SE DISTANCE 1.1 miles PATHWAYS Ground Plane, Inhalation, and Vegetable Age Group Child Organ Thyroid

Annual Radioactive Effluent Release Report YEAR: 2024 Page 20 of 53 Company: Xcel Energy Plant: Monticello Nuclear Generating Plant Since 2019, one milk cow has been located in the NNE sector at 3.2 miles. The cow gave birth approximately four years ago and discussion with the owner confirmed they now milk the newer cow. Discussion with the owner indicates that when the cow is producing milk there is enough for the family to use, but not enough extra to provide samples in the quantity/frequency required for the site. There is also a beef cow and a garden at this location (Milk, Meat, and Vegetable exposure pathways present.) Due to the relatively low deposition parameter, the calculated dose at this location remains lower than other vegetable locations that are closer to the plant in high D/Q sectors.

Milk samples are required for three locations within 1 mile or three locations where doses are calculated to be > 1mRem/year per ODCM-07.01. The currently identified milk location is outside 3 miles and maximum calculated dose by all pathways was 0.0172 mRem to infant thyroid.

Milk samples were not available during 2024 due to the limited milk supply of the animal, as discussed above. The required compensatory vegetation samples were collected and analyzed (per ODCM-07.01, Table 1.)

Corn and Potato sampling was not required because no routine liquid discharges were made during the growing season. Additionally, the Land Use Census found that there are no water use permits for irrigation using water from the Mississippi River within 5 miles downstream of the plant.

5.5 Meteorological Data MNGP accumulated 99.92% of meteorological data in 2024, satisfying the 90%

requirement. Joint Frequency Distribution Tables are held onsite and available for review upon request.

5.6 Effluent Radiation Monitors Out of Service Greater Than 30 Days No effluent radiation monitors were out of service beyond 30 days in the 2024 reporting period. 110/03/2025

Annual Radioactive Effluent Release Report YEAR: 2024 Page 21 of 53 Company: Xcel Energy Plant: Monticello Nuclear Generating Plant 5.7 Offsite Dose Calculation Manual (ODCM) Changes MNGP made 10 revisions to the ODCM during the 2024 reporting period. These changes are detailed in Table 6 below.

Table 6, 2024 ODCM Changes Date of Change ODCM Section Revision Description of Change 02/25/2025 ODCM-01.01 10 Revised Definition of Instrument Functional Test to allows for the insertion of simulated or an actual signal for performance of test.

10/30/2024 ODCM-02.01 15 Added Water Storage Pond #2A and its associated instrumentation.

11/19/2024 ODCM-02.01 16 Revised 2.5.2 Water Storage Pond Leak Detection Systems to place a control on the level within the interstitial liner space.

12/19/2024 ODCM-02.01 17 Added Water Storage Ponds #2B and 2C and their associated instrumentation 3/6/2025 ODCM-02.01 18 Added the Water Storage Pond Transfer System Radioactivity Monitor and Water Storage Pond Transfer System Flow Meter.

Defined AUTOMATIC mode operation of the Water Storage Pond Transfer System.

Revised Water Storage Pond Transfer System

- BATCH mode operation to allow for the Rad Monitor or Flow Meter to take credit for the new equipment for the respective requirements.

10/30/2024 ODCM-03.01 17 Added Water Storage Pond #2A and its associated instrumentation.

12/19/2024 ODCM-03.01 18 Added Water Storage Ponds #2B and 2C and their associated instrumentation.

2/25/2025 ODCM-04.01 5

Added the Water Storage Pond Transfer System Radiation Monitor and the calculated ODCM setpoint for the detector.

10/30/2024 ODCM-05.01 15 Added terms for new gaseous release points, Water Storage Ponds #2A, 2B, and 2C to equations used for dose calculation contained within the ODCM.

10/30/2024 ODCM-APP-A 7

Adds dispersion and deposition parameters for the new gaseous release points Water Storage Ponds #2A,2B, and 2C.

Annual Radioactive Effluent Release Report YEAR: 2024 Page 22 of 53 Company: Xcel Energy Plant: Monticello Nuclear Generating Plant 5.8 Process Control Program (PCP) Changes Monticello Nuclear Generating Plant did not revise the Process Control Program in 2024.

5.9 Radioactive Waste Treatment System Changes Monticello Nuclear Generating Plant did not make any changes to any radioactive waste treatment systems in 2024.

5.10 Water Storage Ponds #2A, #2B, and #2C MNGP has established a new gaseous release point within this reporting period. The site in-serviced the Water Storage Pond #2A on October 30, 2024. The site identified Water Storage Ponds #2B and #2C as additional gaseous release points; Water Storage Ponds #2B and #2C were not in-serviced during the 2024 release period. The original Water Storage Pond mentioned in the 2023 ARERR was renamed to Water Storage Pond #1. The Water Storage Ponds are designed to hold the pumped groundwater as part of the ongoing tritium remediation efforts. Over time an amount of tritiated water within the respective Water Storage Ponds has naturally evaporated.

The site used temporary above ground storage tanks to contain remediated Tritiated water while the additional ponds were constructed. The evaporation from these tanks was accounted for as well. In the 2024 release period the amount Tritium released from Water Storage Ponds was 0.57 Ci.

5.10.1 Independent Spent Fuel Storage Installation (ISFSI) Monitoring Program The ISFSI at Monticello Nuclear Generating Plant was constructed west of the plant in 2007. The initial loading campaign was completed in 2008 with 10 Horizontal Storage Modules (HSMs) loaded with spent fuel. In 2013 an additional five HSMs were loaded with spent fuel. In 2016 one additional HSM was loaded. In 2018 an ISFSI campaign loaded an additional 14 HSMs, bringing the total number of stored modules to 30.

There were no additions to the ISFSI in 2024.

Annual Radioactive Effluent Release Report YEAR: 2024 Page 23 of 53 Company: Xcel Energy Plant: Monticello Nuclear Generating Plant 5.10.2 Carbon-14 Carbon-14 (C-14) is a naturally occurring radionuclide with a 5,730-year half-life.

Nuclear weapons testing in the 1950s and 1960s significantly increased the amount of C-14 in the atmosphere. Nuclear power plants also produce C-14, but the amount is infinitesimal compared to what has been distributed in the environment due to weapons testing and what is produced by natural cosmic ray interactions.

In accordance with Regulatory Guide 1.21, Measuring, Evaluating, and Reporting Radioactive Material in Liquid and Gaseous Effluents and Solid Waste, the NRC recommended re-evaluating principal radionuclides and reporting C-14 as appropriate. Carbon-14 production and release estimates were calculated using active core coolant mass, average neutron flux by energy and reactor coolant nitrogen concentrations to determine Carbon-14 generation based upon an effective full power year. The estimated generation for Monticello Nuclear Generating Plant during 2024 was 7.45 Curies.

Public dose estimates were performed using methodology from the ODCM which is based on Regulatory Guide 1.109 methodology. C-14 dose is included in dose calculation results in Tables 1 and 2.

5.10.3 Errata/Corrections to Previous ARERRs Included with this report is a correction to the 2023 ARERR. The Water Storage Pond

1 Level Monitor was improperly reading 0.2 feet lower than the actual water level due to an improper calibration; this was captured in MNGP QIM 501000082876. Water Storage Pond #1 has slanted walls, so as the pond level rises the number of gallons required to raise the level increases. The total level rise in the WSP was used when quantifying the release of tritium via natural evaporation. By the instrument displaying a level 0.2 ft lower than actual, it appeared that a lower number of gallons remained in the pond than the actual remaining volume. This resulted in MNGP overreporting the amount of Tritium released to the atmosphere via natural evaporation of Water Storage Pond #1. The following corrects the reported dose in Q4 to the Critical Receptor given in Table 2 (page 8) and the amount of Tritium reported in Tables 11 (pg. 25) & 13 (pg.

27) for Summation of all Releases and Ground Level Releases, respectively. The three results are lower than what were previously reported. No limits or guidelines are challenged due to this errata.

Annual Radioactive Effluent Release Report YEAR: 2024 Page 24 of 53 Company: Xcel Energy Plant: Monticello Nuclear Generating Plant NEI 07-07 ONSITE RADIOLOGICAL GROUNDWATER MONITORING PROGRAM Monticello Nuclear Generating Plant has developed a Groundwater Protection Initiative (GPI) program in accordance with NEI 07-07, Industry Ground Water Protection Initiative - Final Guidance Document [9]. The purpose of the GPI is to ensure timely detection and an effective response to situations involving inadvertent radiological releases to groundwater in order to prevent migration of licensed radioactive material off-site and to quantify impacts on decommissioning. During 2024, MNGP collected and analyzed groundwater samples in accordance with the requirements of FP-CY-GWPP-01.

This section is included in this report to communicate results of NEI 07-07 Radiological Groundwater Monitoring Program. Monitoring wells installed as part of GPI program are sampled and analyzed as summarized in Table 6. In addition to reporting results from NEI 07-07 monitoring wells, voluntary communications to offsite governmental agencies for onsite leaks or spills per NEI 07-07 Objective 2.2, are also reported as part of this report. It is important to note, samples and results taken in support of NEI 07-07 groundwater monitoring program are not part of the Radiological Environmental Monitoring Program (REMP) but should be reported as part of ARERR.

Table 7 contains the current sampling frequencies for MNGP. The sampling frequencies below reference the frequency at which samples were sent to our certified vendor for analysis. There are some exceptions to this list. Monitoring Wells that were below detectable for multiple consecutive samples in Monticellos in-house laboratory were not sent for analysis. Monitoring Well 33A was not sent for analysis during August and September due to being less than detectable in our in-house laboratory.

Monitoring/Pumping Well 13A was unable to be sampled between June and August due to pump failure. Monitoring Well 37A was not sent in January since it was less than detectable in MNGPs in-house laboratory.

Annual Radioactive Effluent Release Report YEAR: 2024 Page 25 of 53 Company: Xcel Energy Plant: Monticello Nuclear Generating Plant Table 7, Groundwater Monitoring Well Sampling Frequencies Frequency

of Wells Wells*

Quarterly 10 MW-1, MW-1B, MW-2, MW-3, MW-10B, MW-11, MW-14, MW-15B, MW-23A, MW-24 Monthly 18 MW-4, MW-4B, MW-9, MW-9B, MW-10 (PW-10A), MW-12A, MW-12B, MW-13A (PW-13A), MW-13B, MW-15A, MW-16A, MW-16B, MW-30A, MW-26B, MW-27B, MW-28B, MW-33A, MW-37A Annual 13 MW-5, MW-6, MW-7, MW-8, MW-17A, MW-23B, MW-29A, MW-31B, MW-101R1, MW-1021, MW-1031, MW-1041, MW-1051 Sampled on Site, Not Currently Sent to Vendor 12 MW-20A, MW-21A, MW-26A, MW-27A, MW-28A, MW-29B, MW-30B, MW-31B, MW-33B, MW-37B, MW-48B, MW-50A Sampled When Gradient Control Wells are Operating 4

MW-17A, MW-66A, MW-67A, MW-67B, MW-68A Developed, Not Currently Sampled 5

MW-17B, MW-19A, MW-19B, MW-48A, MW-58A,

Monitoring Wells in BOLD typeface are considered sentinel wells 1 MW-101R, MW-102, MW-103, MW-104, MW-105 are tested for Tritium only The current groundwater monitoring program includes 62 monitoring wells and 8 pumping wells at 42 different locations. 20 of the locations include a nested configuration, where one sample is taken at the level of the water table (GWPP locations ending with an A) while a second sample can be taken from deeper water (GWPP locations ending with a B). The site has also developed 3 Gradient Control Wells, wells that pump clean water from the ground and return it to the river. The purpose of these wells is to maintain a flat gradient on the water table to mitigate further migration of the plume offsite. The sites groundwater vendor recommends when to operate these wells based on the water table and water level measurements.

As a part of the Water Storage Pond expansion, Monitoring Wells 101R, 104, and 105 have been developed around the ponds. The construction of the Water Storage Ponds required MW-101 to be sealed and capped. At the conclusion of construction, MW-101R was developed in a near-by location. This, along with the Water Storage Pond Leak Detection Systems, ensures the ponds are not leaking into the surrounding groundwater. They are only tested for Tritium currently, for there is no pathway for

Annual Radioactive Effluent Release Report YEAR: 2024 Page 26 of 53 Company: Xcel Energy Plant: Monticello Nuclear Generating Plant gamma isotopes to these wells. The contents of water transferred to the pond are verified free of gamma nuclides before addition.

The 2024 Radiological Groundwater Monitoring Program results are provided in, Groundwater Data. No groundwater monitoring locations had detectable gamma or HTD (hard-to-detect) in 2024.

As a result of the ongoing migration of the plume from the Abnormal Release first reported in 2022, 24 monitoring wells had detectable Tritium in 2024. The results do not indicate any additional release has occurred. The highest result seen in 2024 was MW-9s duplicate January sample with a concentration of 291,000 +/- 2,300 pCi/L. As of the end of 2024, 2 wells, MW-13B and MW-23A, remain above the Tritium concentration EPA drinking water standard of 20,000 pCi/L. MNGP continues remediation activities.

A result of note is MW-17As October 22, 2024 sample which was positive for Tritium at a concentration of 731 +/- 166 pCi/L. MW-17A is labeled as a Sentinel Well in Table

7. This result was not considered a release due to no positive samples at the downgradient Gradient Control Wells; the gradient control wells were turned off following this result to prevent pulling the plume further in this direction. Subsequent samples at MW-17A analyzed in MNGPs onsite laboratory returned to less than detectable. This was captured in MNGP QIM #501000091320.

6.1 Voluntary Notification During 2024, Monticello Nuclear Generating Plant did not make a voluntary NEI 07-07 notification to State/Local officials, NRC, and to other stakeholders required by site procedures.

Annual Radioactive Effluent Release Report YEAR: 2024 Page 27 of 53 Company: Xcel Energy Plant: Monticello Nuclear Generating Plant BIBLIOGRAPHY

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[14] "NUREG-0324 - XOQDOQ, Program for the Meteorological Evaluation of Routine Effluent Releases at Nuclear Power Stations," Nuclear Regulatory Commission, September, 1977.

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Nuclear Regulatory Commission, July, 2007.

Annual Radioactive Effluent Release Report YEAR: 2024 Page 28 of 53 Company: Xcel Energy Plant: Monticello Nuclear Generating Plant Attachment 1, ARERR Release Summary Tables (RG-1.21 Tables)

GASEOUS EFFLUENTS Table 8, Gaseous Effluents Summation of All Releases MNGP 2 A.

Fission & Activation Gases Units Quarter 1 Quarter 2 Quarter 3 Quarter 4 Est. Total Error %

1.

Total Release Ci 3.25E+01 2.22E+01 2.02E+01 2.12E+01 5.00E+01

2.