Text

Annual Radiological Environmental Operating Report
	ML24116A174
Person / Time
Site:	Millstone
Issue date:	04/24/2024
From:	Armstrong L; Dominion Energy Nuclear Connecticut
To:	; Office of Nuclear Reactor Regulation, Document Control Desk
References
	24-111
	Download: ML24116A174 (1)
	v • d • e

Dominion Energy Nuclear Connecticut, Inc.

Millstone Power Station F,;. Dominion 314 Rope Ferry Road, Waterford, CT 06385 ii# Energy DominionEnergy.com

U.S. Nuclear Regulatory Commission Serial No.24-111 Attention: Document Control Desk MPS Lie/LO RO Washington, DC 20555-0001 Docket Nos. 50-245 50-336 50-423 APR 2 4 2024 License Nos. DPR-21 DPR-65 NPF-49

DOMINION ENERGY NUCLEAR CONNECTICUT, INC.

MILLSTONE POWER STATION UNITS 1, 2, AND 3 2023 ANNUAL RADIOLOGICAL ENVIRONMENTAL OPERA TING REPORT (REOR)

This letter transmits the Annual Radiological Environmental Operating Report for the Millstone Power Station, for the period January 1, 2023, through December 31, 2023.

This satisfies the provisions of Section 5.7.2 of Millstone Power Station Unit 1 Permanently Defueled Technical Specifications (POTS), and Sections 6.9.1.6A and 6.9.1.3 of the Millstone Power Station Units 2 and 3 Technical Specifications, respectively.

Should you have any questions, please contact Mr. Dean E. Rowe at (860) 444-5292.

Sincerely,

~a~cr L. J. Armstrong Director, Nuclear Station Safety and Licensing

Attachments: 1

Commitments made in this letter:

1. None.

Serial No.24-111 2023 Annual Radiological Environmental Operating Report Page 2 of 4

cc: U. S. Nuclear Regulatory Commission Region I 475 Allendale Rd., Suite 102 King of Prussia, PA 19406-1415

P.Longmire NRC Project Manager Millstone Unit 1 U.S. Nuclear Regulatory Commission One White Flint North, Mail Stop 5-A 10 11555 Rockville Pike Rockville, MD 20852-2738

L. A. Kauffman NRC Inspector U.S. Nuclear Regulatory Commission Region I 475 Allendale Rd., Suite 102 King of Prussia, PA 19406-1415

Nick Eckhoff NRC Inspector U.S. Nuclear Regulatory Commission Region I 475 Allendale Rd., Suite 102 King of Prussia, PA 19406-1415

R. V. Guzman NRC Project Manager Millstone Units 2 and 3 U.S. Nuclear Regulatory Commission One White Flint North, Mail Stop 08 C2 11555 Rockville Pike Rockville, MD 20852-2738

NRC Senior Resident Inspector Millstone Power Station

Serial No.24-111 2023 Annual Radiological Environmental Operating Report Page 3 of 4

Director Bureau of Air Management Monitoring & Radiation Division Department of Energy and Environmental Protection 79 Elm Street Hartford, CT 06106 -5127

A. Honnellio Regional Radiation Representative (EPA Region 1, Boston)

U. S. Environmental Protection Agency (Region 1) 5 Post Office Square Suite 100 Boston, MA 02109

G. Allen Jr.

Department of Health and Human Services U. S. Food and Drug Administration 140 Shrewsbury Street, Suite 1 Boylston, MA 01501

M. Bachman Executive Director Connecticut Siting Council 10 Franklin Square New Britain, CT 06051

J.P. Kelley Waterford-East Lyme Shellfish Commission Waterford Town Hall 15 Rope Ferry Road, Waterford, CT 06385

Justin Folkwein American Nuclear Insurers 95 Glastonbury Blvd.

Glastonbury, CT 06033

David. H. Carey Connecticut Department of Agriculture Aquaculture Division P. 0. Box 97 Millford, CT 06460

Serial No.24-111 2023 Annual Radiological Environmental Operating Report Page 4 of 4

Rob Brule First Selectman Town of Waterford 15 Rope Ferry Road Waterford Town Hall Waterford, CT 06385

Daniel Cunningham First Selectman Town of East Lyme PO Box 519 Niantic, CT 06357

Jane Strudwick Head of Acquisitions & Discovery University Of Connecticut Library 369 Fairfield Way, Unit 1005 Storrs, CT 06269-1005

Serial No.24-111 Docket Nos. 50-245 50-336 50-423 License Nos. DPR -21 DPR-65 NPF-49

ATTACHMENT 1

2023 ANNUAL RADIOLOGICAL ENVIRONMENT AL OPERA TING REPORT

MILLSTONE POWER STATION UNITS 1, 2, AND 3 DOMINION ENERGY NUCLEAR CONNECTICUT, INC. (DENC)

Millstone Power Station 2023 Radiological Environmental Operating Report

}

January 1, 2023 - December 31, 2023

Dominion Energy Nuclear Connecticut, Inc.

Unit License Docket 1 DPR-21 50-245 2 DPR-65 50-336 3 NPF-49 50-423

Dominion Energy Dominion Energy Nuclear Connecticut, Inc. Annual Radiological Environmental Millstone Power Station Operating Report 2023

ANNUAL RADIOLOGICAL ENVIRONMENT AL OPERATING REPORT

MILLSTONE POWER STATION

RADIOLOGICAL ENVIRONMENTAL MONITORING PROGRAM

2023

Millstone Power Station Unit 1, DOCKET NO. 50-245 Millstone Power Station Unit 2, DOCKET NO. 50-336 Millstone Power Station Unit 3, DOCKET NO. 50-423

Dominion Energy Nuclear Connecticut, Inc.

Waterford, Connecticut Dominion Energy Nuclear Connecticut, Inc. Annual Radiological Environmental Millstone Power Station Operating Report 2023

~ TABLE OF CONTENTS,_,

EXECUTIVE

SUMMARY

...................................................................................................................... i

1. INTRODUCTION................................................................................................... 1-1

1. 1. Overview....................................................................................................... 1-1 1.2. Radiation and Radioactivity.......................................................................... 1-1 1.3. Sources of Radiation.................................................................................... 1-2 1.4. Nuclear Reactor Operations......................................................................... 1-3 1.5. Radioactive Effluent Control......................................................................... 1-8 1.6. Radiological Impact on Humans................................................................... 1-1 O

2. PROGRAM DESCRIPTION.................................................................................. 2-1 2.1 Sampling Schedule and Locations................................................................... 2-1 2.2 Samples Collected During Report Period......................................................... 2-8 2.3 Required Samples Not Collected During the Report Period............................. 2-8

3. RADIOCHEMICAL RESULTS............................................................................... 3-1 3.1 Summary Tables............................................................................................. 3-1 3.2 Data Tables.................................................................................................... 3-7

4. DISCUSSION OF RESULTS................................................................................ 4-1 4.1 Gamma Exposure Rate (Table 1)............................................................... 4-1 4.2 Air Particulate Gross Beta Radioactivity (Table 2)..................................... 4-4 4.3 Air Iodine (Table 3).................................................................................... 4-5 4.4 Air Particulate Gamma (Table 4 )................................................................ 4-5 4.5 Soil (Table 5)............................................................................................. 4-5 4.6 Cow Milk (Table 6)..................................................................................... 4-6 4.7 WellWater (Table7).................................................................................. 4-6 4.8 Fruits and Vegetables (Table 8)................................................................. 4-6 4.9 Broad Leaf Vegetation (Table 9)................................................................ 4-6 4.10 Seawater (Table 10).................................................................................. 4-6 4.11 Bottom Sediment (Table 11)...................................................................... 4-8 4.12 Aquatic Flora (Table 12)............................................................................. 4-8 4.13 Fish (Table 13)........................................................................................... 4-8 4.14 Oysters (Table 14)..................................................................................... 4-8 4.15 Clams (Table 15)....................................................................................... 4-8 4.16 Lobsters (Table 16).................................................................................... 4-8

5. REFERENCES...................................................................................................... 5-1

APPENDIX A - LAND USE CENSUS FOR 2023...................................................... A-1

APPENDIX B -

SUMMARY

OF INTERLABORATORY COMPARISONS................. B-1

APPENDIX C - ERRATUM........................................................................................ C-1 Dominion Energy Nuclear Connecticut, Inc. Annual Radiological Environmental Millstone Power Station Operating Report 2023 Dominion Energy Nuclear Connect icut, Inc. Annual Radiological Environmental Millstone Power Station Operating Report 2023

EXECUTIVE

SUMMARY

INTRODUCTION This report summarizes the results of the Radiological Environmental Monitoring Program (REMP) conducted in the vicinity of the Millstone Power Station (MPS) during the period from January 1, 2023, to December 31, 2023. This document has been prepared in accordance with the requirements of the separate MPS Unit 1 (MPS1) Permanently Defueled Technical Specifications and the Technical Spec ifications for Millstone Units 2 and 3 (MPS2 and MPS3).

The REMP has been established to monitor the radiation and radioactivity released to the environment as a result of MPS operation. This program, initiated in April 1967, includes the collection, analysis, and evaluation of radiological data to assess the impact of MPS on the environment and on the general public.

SAMPLING AND ANALYSIS The environmental sampling med ia collected in the vicinity of MPS and at distant locations included aquatic, atmospheric, and terrestrial samples. These samples were air particulate filters, charcoal cartridges, soil, well water, broadleaf vegetation, fruits and vegetables,

seawater, bottom sediment, aquatic flora, fish, oysters, clams, and lobsters.

During 2023, there were 528 samples collected from the atmospheric, aquatic, and terrestrial environments. In addition, 172 exposure measurements were obtained using environmental thermo luminescent dosimeters (TLDs). A discussion of all discrepancies from the sample collection requirements in the MPS Radiological Effluent Monitoring and Offsite Dose Calculation Manual (REMODCM) is given in Section 2.3 of this report. Teledyne Brown Engineering, Inc. of Knoxville, Tennessee performed the sample analyses and Env ironmental Dosimetry Company of Sterling, Massachusetts, performed the TLD analyses.

LAND USE CENSUS The annual land use census in the vicinity of MPS was conducted as required by the MPS REMODCM. To determine the dairy exposure pathway, a list of cow milk and goat milk locations is established. The list of cow milk locations is identified by a review of the annual registration information obtained from the State of Connecticut Department of Agriculture. The list of goat milk locations is identified by the information obta ined from the American Dairy Goat Association list and by inspections performed in the field. Although broadleaf sampling was performed and may be used in lieu of a garden census, gardens were included in the 2023 census. Only vegetable gardens having an area of more than 500 square feet were identified. Due to the difficulty of measuring individual gardens, the nearest garden within each directional sector identified by a drive-by survey is listed. However, for dose calculation, garden distances are based on nearest resident assuming that a resident may plant a new garden. This gives a more conservative dose estimate.

RADIOLOGICAL IMPACT TO THE ENVIRONMENT The radionuclides detected in some samples were from non-station, naturally occurring radionuclides.

All terrestrial samples collected as part of the MPS REMP did not show any station related isotopes.

Dominion Energy Nuclear Connecticut, Inc. Annual Radiological Environmental Millstone Power Station Operating Report 2023

The seawater exiting the stations quarry is monitored for all station generated radionuclides.

Tritium was only found in seawater onsite inside the mixing zone of the quarry discharge at levels that were expected from routine station operation.

Offsite ambient radiation measurements using environmental TLDs beyond the site boundary ranged between 38 - 103 milliroentgens ( mrem) per year. The range of ambient radiation levels observed with the TLDs is consistent with natural background radiation levels for Connecticut.

RADIOLOGICAL IMPACT TO THE GENERAL PUBLIC During 2023, radiation doses to the general public as a result of Millstone's operation continued to be well below the federal limits and much less than the dose due to other sources of man-made (e.g., X-rays, medical) and naturally occurring (e.g., cosm ic, radon) radiation.

The calculated total body (whole body) dose to the maximally exposed member of the public from radioactive effluents and ambient radiation resulting from MPS operations for 2023 was approximately 0.2 mrem for the year. This conservative estimate is well below the Environmental Protection Agency's (EPA) annual dose limit to any member of the general public and is a fraction of a percent of the typical dose received from natural and other sources of man-made radiation.

CONCLUSIONS The 2023 REMP fo r MPS resulted in the collection and analysis of 700 environmental samples and measurements. The data obtained were used to determine the impact of Millstone's operation on the environment and on the general public.

An evaluation of direct radiation measurements, environmental sample analyses, and dose calculations indicates all applicable federal criteria were met with margin. Furthermore, radiation levels and the consequential dose from station operation were small in comparison to those attributed to naturally occurring and man-made background radiation.

Based on this information, there is no significant radiological impact on the environment or on the general public due to Millstone's operation. The 2023 REMP samples results are consistent with previous years with no trends evident.

ii Dominion Energy Nuclear Connecticut, Inc. Annual Radiological Environmental Millstone Power Station Operating Report 2023

1. INTRODUCTION This section provides an overview of the MPS REMP. It also includes background information to allow a reader to have an informed understanding of radiation and nuclear power operation.

1.1 Overview The 2023 REMP performed by Dom inion Energy Nuclear Connecticut (DENG) for MPS is discussed in this report. Since the operation of a nuclear powe r station results in the release of small amounts of radioactivity and low levels of radiation, the Nuclear Regulatory Commission (NRC) requires by regulations and technical specifications that a program be established to monitor radiation and radioactivity in the environment (References 1, 6, 9, 10, & 11 ). This report published annually per Millstone's Technical Specifications (section 5.7.2 for MPS1, section 6.9.1.6a for MPS2 and Section 6.9.1.3 for MPS3), summarizes the results of measurements of radiation and radioactivity in the environment in the vicinity of the MPS and at distant locations during the period January 1, 2023, to December 31, 2023.

The REMP consists of taking radiation measurements and collecting samples from the environment, analyzing them for radioactivity content, and interpreting the results. W ith emphasis on the critical radiation exposure pathways to humans, samples from the aquatic, atmospheric, and terrestrial environments are collected. These samples include, but are not limited to air, soil, well water, broadleaf vegetation, fruits, vegetables, seawater, bottom sediment, aquatic flora, fish, oysters, clams, and lobsters.

Thermoluminescent dosimeters (TLDs) are placed in the environment to measure gamma radiation levels. The TLDs are processed, and the environmental samples are analyzed to measure the very low levels of radiation and radioactivity present in the environment as a result of MPS operation and othe r natural and man - made sources. These results are reviewed by Millstone's radiolog ical staff and have been reported semiannually or annually to the NRC and others for over 30 years.

To more fully understand how a nuclear power station impacts humans and the environment, background information on radiation and radioactivity, natural and man-made sources of radiation, reactor operations, rad ioactive effluent controls, and radiological impact on humans is provided. It is believed that this information will assist the reader in understanding the radiological impact on the environment and humans from the operation of Millstone.

1.2 Radiation and Radioactivity All matter is made of atoms. Nuclear radiation is energy or particles that are given off from atoms in an excited state (e.g., unstable, radioactive atoms).

Radioactive material exists naturally and has always been a part of our environment. The earth's crust, for example, contains radioactive uranium, radium, thorium, and potassium. Some radioactivity is a result of fallout from nuclear weapons testing. Examples of radioactive fallout that could be present in environmental samples are cesium-137 and strontium-90. Some examples of radioactive materials released from a nuclear power station are hydrogen-3 (tritium),

cesium-137, iodine - 131, strontium-90, and cobalt -60.

1-1 Dominion Energy Nuclear Connecticut, Inc. Annual Radiological Environmental Millstone Power Station Operating Report 2023

Radiation is measured in units of mrem, much like temperature is measured in degrees. A mrem is a measure of the biological effect of the energy deposited in tissue. The letter 'm' is for 'milli',

or one-thousandth of a 'rem'. The word 'rem' is an acronym for roentgen equivalent man. One rem is equal to a 'rad' multiplied by factors to account for type of radiation and distribution within the body. The word 'rad' is an acronym for radiation absorbed dose. One rad is equal to the absorption of 100 ergs of energy per gram of tissue. The natural and man-made radiation dose received in one year by the average American is 300 to 600 mrem (References 2, 3, 4 & 5). The per capita dose has increased since the early 1980's because of the increased usage of medical procedures involving exposure to radiation (Reference 3).

Radioactivity is measured in Curies. Levels of radioactivity commonly seen in the environment are typically a small fraction of a Curie, therefore radioactivity in the. environment is typically measured in picocuries. One picocurie (pCi) is one-trillionth of a Curie and is equal to 0.037 disintegrations per second (2.22 disintegrations per minute).

1.3 Sources of Radiation As mentioned previously, naturally occurring radioactivity has always been a part of our environment. Table 1.3-1 shows the sources and doses of radiation from natural and man-made sources.

Table 1.3-1 Rd' f S a Ia I0n ources an orrespon lnQ,pproxIma e d C d' A t D oses (1)

NATURAL MAN-MADE Radiation Dose Radiation Dose Source (mrem/year) Source (mrem/year)

Internal, inhalation( 2 ) 228 MedicaI( 3l 300 External, space 33 Consumer( 4 l 12.3

Internal, ingestion 29 Industrial, security, 0.3 educational, research External, terrestrial 21 Occupational 0.5 Weapons Fallout < 1 Nuclear Power Stations < 1

Approximate Total 311 Approximate Total 314 (1) information from References 3 and 4 (2) from radon and thoron (3) includes computerized tomography (147 mrem), nuclear medicine (77 mrem), interventional fluoroscopy (43 mrem) and conventional radiography and fluoroscopy (33 mrem)

(4) primarily from cigarette smoking (4.6 mrem), commercial air travel (3.4 mrem), building materials (3.5 mrem) and mining and agriculture (0.8 mrem)

1-2 Dominion Energy Nuclear Connecticut, Inc. Annual Radiological Environmental Millstone Power Station Operating Report 2023

Cosmic radiation (external, space) from the sun and outer space penetrates the earth's atmosphere and continuously bombards us with rays and charged particles. Some of this cosmic radiation interacts with gases and particles in the atmosphere, making them radioactive. These radioactive byproducts from cosmic ray bombardment are referred to as cosmogenic radionuclides. Isotopes such as beryllium-? and carbon-14 are formed in this way. Exposure to cosmic and cosmogenic sources of radioactivity results in about 33 mrem of radiation dose per year.

Additionally, natural radioactivity is in our body and in the food, we eat (about 29 mrem/year),

the ground we walk on (about 21 mrem/year) and the air we breathe (about 228 mrem/year).

Most of a person's annual dose results from exposure to radon and thoron in the air we breathe. These gases and their radioactive decay products arise from the decay of naturally occurring uranium, thorium and radium in the soil and building products such as brick, stone, and concrete. Radon and thoron levels vary greatly with location, primarily due to changes in the concentration of uranium and thorium in the soil. Residents at some locations in Colorado, New York, Pennsylvania, New Jersey, and even Connecticut have a higher annual dose because of higher levels of radon/thoron gases in these areas. In total, these various sources of naturally occurring radiation and radioactivity contribute to a total dose of about 311 mrem per year.

In addition to natural radiation, we are normally exposed to radiation from a number of man made sources. The single largest doses from man-made sources result from therapeutic and diagnostic applications of x-rays and radiopharmaceuticals. The annual dose to an individual in the United States from medical and dental exposure is approximately 300 mrem.

Consumer products/uses, such as cigarettes, building materials and commercial air travel contribute about 13 mrem/year. Much smaller doses result from weapons fallout (less than 1 mrem/year) and nuclear power stations (less than 1 mrem/year). Typically, the average person in the United States receives approximately 314 mrem per year from man-made sources.

1.4 Nuclear Reactor Operations MPS generates about 2100 megawatts of electricity at full power, which provides approximately one-third of the power consumed in the State of Connecticut. MPS2 and MPS3 are pressurized water reactors (MPS1, which is permanently shut down, was a boiling water reactor). The nuclear station is located on an approximate 500-acre site about three miles (five kilometers) west of New London, Connecticut. Commercial operation of MPS2 began in December 1975 and MPS3 in May 1986.

In 2023, MPS had two planned refueling outages, MP2 in April and MP3 in October. The annual capacity factor for MPS2 was 71.90% and for MPS3 was 76.90%.

Nuclear-generated electricity is produced by many of the same techniques used for conventional oil and coal-generated electricity. Both systems use heat to boil water to produce steam. The steam turns a turbine, which turns a generator, producing electricity. In both cases, the steam passes through a condenser where it changes back into water and re-circulates back through the system (see Figure 1.4-1 ). The cooling water source for MPS is the Niantic Bay.

1-3 Dominion Energy Nuclear Connecticut, Inc. Annual Radiological Environmental Millstone Power Station Operating Report 2023

The key difference between nuclear power and conventional power is the source of heat used to boil the water. Conventional stations burn fossil fuels in a boiler, while nuclear stations use uranium fission in a nuclear reactor.

Inside the reactor, a nuclear reaction called fission takes place. Particles, called neutrons, strike the nucleus of a uranium-235 atom, causing it to split into fragments called radioactive fission products. The splitting of the atoms releases both heat and more neutrons. The newly released neutrons then collide with and split other uranium atoms, thus making more heat and releasing even more neutrons, and on and on until the uranium fuel is depleted or spent. This process is called a chain reaction. When this chain reaction is self-sustaining, the reactor is called "critical."

The operation of a nuclear reactor results in the release of small amounts of radioactivity and low levels of radiation. The radioactivity originates from two major sources, radioactive fission products and radioactive activation products. Radioactive fission products, as illustrated in Figure 1.4-1, originate from the fissioning of the nuclear fuel. These fission products get into the reactor coolant from their release by minute amounts of uranium on the outside surfaces of the fuel cladding, by diffusion through the fuel pellets and cladding and, on occasion, through defects or failures in the fuel cladding. These fission products circulate along with the reactor coolant water and will deposit on the internal surfaces of pipes and equipment. The radioactive fission products on the pipes and equipment emit radiation. Examples of some fission products are krypton-85 (Kr-85), strontium-90 (Sr-90), iodine-131 (1-131 ), xenon-133 (Xe-133), and cesium-137 (Cs-137).

Pressurized water reactor-a common type of Light Water Reactor

{LWR)

------- *coNDENSER COOLING WATER

- -TAKING WASTE HEAT TO THE ENVIRONMENT

Figure 1.4-1: SIMPLIFIED DIAGRAM OF A PRESSURIZED WATER REACTOR

1-4 Domin ion Energy Nuclear Connecticut, Inc. Annual Radiological Environmental Millstone Power Station Operating Report 2023

Nuclear Fission: fission is the splitting of atoms (e.g., uranium-235) by a neutron to release heat and more neutrons, creating a chain reaction. Radiation and fission products are by - products of the process as illustrated in Figure 1.4-2.

Uran ium 1..,..

Neutrons......

Ne u tron

Uran ium

Fission Produ cts i*~ " -~

Uranium

Fission Produ c ts

Figure 1.4-2: Radioactive Fission Product Formation

1-5 Dominion Energy Nuclear Connecticut, Inc. Annual Radiological Environmental Millstone Power Station Operating Report 2023

Radioactive activation products (Figure 1.4-3), on the other hand, originate from two sources.

The first is by neutron bombardment of the hydrogen, oxygen and other gas (helium, argon, nitrogen) molecules in the reactor cooling water. The second is a result of the fact that the internals of any piping system or component are subject to minute yet constant corrosion from the reactor cooling water. These minute metallic particles (for example: nickel, iron, cobalt, or magnesium) are transported through the reactor core into the fuel region, where neutrons may react with the nuclei of these particles, producing radioactive products. Therefore, activation products are nothing more than ordinary naturally-occurring atoms that are made unstable or radioactive by neutron bombardment. These activation products circulate along with the reactor coolant water and will deposit on the internal surfaces of pipes and equipment. The radioactive activation products on the pipes and equipment emit radiation. Examples of some activation products are manganese-54 (Mn-54 ), iron-59 (Fe-59), cobalt-60 (Co-60), and zinc-65 (Zn-65).

collision with Co-59 Co-60 0

Neutron Stable Radioactive Cobalt Nucleus Cobalt Nucleus

Figure 1.4-3: Radioactive Activation Product Formation

At MPS there are five independent protective barriers that confine these radioactive materials.

These five barriers are:

fuel pellets; fuel cladding; reactor vessel and associated piping and equipment; primary containment; and secondary containment (enclosure building).

1-6 Dominion Energy Nuclear Connecticut, Inc. Annual Radiological Environmental Millstone Power Station Operating Report 2023

The ceramic uranium fuel pellets provide the first barrier. Most of the radioactive fission products are either physically trapped or chemically bound between the uranium atoms, where they will remain. However, a few fission products that are volatile or gaseous may diffuse through the fuel pellets into small gaps between the pellets and the fuel cladding.

The second barrier, the fuel cladding, consists of zirconium alloy tubes that confine the fuel pellets. The small gaps between the fuel and the cladding contain the noble gases and volatile iodines that are types of radioactive fission products. This radioactivity can diffuse to a small extent through the fuel cladding into the reactor coolant water. Radioactivity can also escape into coolant water through cladding defects and failures.

The third barrier consists of the reactor pressure vessel, steel piping and equipment that confine the reactor cooling water. The reactor pressure vessel, which holds the reactor fuel, is typically a steel tank 40 feet high by 14 feet in diameter with walls about five to nine inches thick. These vessels and associated piping provide containment for radioactivity in the primary coolant and the reactor core. However, during the course of operations and maintenance, small amounts of radioactive fission and activation products can escape through valve leaks or upon breaching of the primary coolant system for maintenance.

The fourth barrier is the primary containment. It is a cylindrical enclosure with approximately five foot thick steel reinforced concrete walls lined by steel on the inside. During operation the containment is closed but small amounts of radioactivity may be released from primary containment by venting during operation to maintain proper containment pressure. During maintenance and refueling outages containment is open and small amounts of radioactivity is released during this time when the fuel has been moved out of the reactor cavity in containment.

The fifth barrier is the secondary containment or enclosure building. The enclosure building is a steel building that surrounds the primary containment. This barrier is an additional safety feature at Millstone's reactor units to contain radioactivity that may escape from the primary containment.

This enclosure building is equipped with a filtered ventilation system that is used when needed to reduce the radioactivity that escapes from the primary containment.

The five barriers confine most of the radioactive fission and activation products. However, small amounts of radioactivity do escape via mechanical failures and maintenance on valves, piping, and equipment associated with the reactor cooling water system. The small amounts of radioactive liquids and gases that do escape the various containment systems are further controlled by the liquid purification and ventilation filtration systems. The control of radioactive effluents at MPS will be discussed in more detail in the next section.

1-7 Dominion Energy Nuclear Connecticut, Inc. Annual Radiological Environmental Millstone Power Station Operating Report 2023

1.5 Radioactive Effluent Control The small amounts of radioactive liquids and gases that might escape the first two barriers are processed in the liquid and gaseous waste treatment systems, then monitored for radioactivity, and released only if the radioactivity levels are below the federal release limits.

Radioactivity released from the liquid effluent system to the environment is limited, controlled and monitored by a variety of systems and procedures which include:

reactor water cleanup system;

liquid radioactive waste treatment system;

sampling and analysis of the liquid radioactive waste tanks; and

liquid waste effluent discharge radioactivity monitor.

The purpose of the reactor water cleanup system is to continuously purify the reactor cooling water by removing radioactive atoms and non-radioactive impurities that may become activated by neutron bombardment. A slip stream of the reactor coolant water is diverted from the primary coolant system and is directed through ion exchange resins where radioactive elements, dissolved and suspended in the water, are removed through chemical processes.

The net effect is a substantial reduction of the radioactive material that is present in the primary coolant water and consequently the amount of radioactive material that might escape from the system.

Reactor cooling water that might escape the primary cooling system and other radioactive water sources are collected in floor and equipment drains. These drains direct this radioactive liquid waste to large holdup tanks. The liquid waste collected in the tanks is purified again using the liquid radioactive waste treatment system, which consists of a filter and ion exchange resins.

Processing of liquid radioactive waste results in large reductions of radioactivity in liquids discharged into Niantic Bay. Wastes processed through liquid radioactive waste treatment can be purified and, in some cases, re-used in station systems.

Prior to release, the radioactivity in any liquid radioactive waste tank is sampled and analyzed to determine if the level of radioactivity is below the release limits and to quantify the total amount of radioactive liquid effluent that will be released. If the levels are below the federal release limits, the tank is drained to the liquid effluent discharge header.

This liquid waste effluent discharge line is provided with a shielded radioactivity monitor. This detector is connected to a radiation level meter and a recorder in the Control Room. The radiation alarm is set so that the detector will alarm before radioactivity levels exceed the release limits. In addition to the alarm function, the radiation monitor also signals both discharge valves to close thus terminating the discharge release to the environment. Gamma spectroscopy analysis, tritium analysis and the effluent radiation monitors prevent any liquid radioactivity from being released in excess of release rate and total activity limits. An audible alarm notifies the Control Room operator that this has occurred.

Some liquid waste sources, which have a low potential for containing radioactivity, and/or may contain very low levels of contamination, may be *discharged directly to the environment.

One such source of liquid is the turbine building sump. However, periodic representative samples are collected for analysis of radioactivity content to track the amounts of radioactivity being discharged.

1-8 Dominion Energy Nuclear Connecticut, Inc. Annual Radiological Environmental Millstone Power Station Operating Report 2023

The preceding discussion illustrates that many controls exist to reduce the radioactive liquid effluents released to the environment to as far below the release limits as is reasonably achievable.

Radioactive releases from the radioactive gaseous effluent system to the environment are limited, controlled, and monitored by a variety of systems and procedures which include:

containment building ventilation system; containment building radioactivity monitors; sampling and analysis of containment building vent and purge effluents; process gas treatment system; auxiliary building (and engineered safeguards and fuel building for MPS3) ventilation system;

MPS stack and units' vent effluent radioactivity monitors;

sampling and analysis of MPS stack and units' vent effluents;

process radiation monitors; and

steam jet air ejector (SJAE) monitor.

The primary sources of gaseous radioactive waste are degassing of the primary coolant, gaseous liquid drains, and gaseous vents. Additional sources of gaseous waste activity include ventilation air released from the auxiliary building and purging and venting of the containment building. The radiation level meter and recorders for the effluent radioactivity monitors are located in the Control Room. The station process computer aids in tracking the monitor readings. To supplement the information continuously provided by the detector, air samples are taken periodically from the units' containments, MPS stack and units' vents. These samples are analyzed to quantify the total amount of radioactive gases, radioactive iodine, radioactive particulate, and tritium released in gaseous effluents.

Gases from the primary coolant are held up in waste gas decay tanks for decay at MPS2.

Gaseous waste at MPS3 is purified through a process gas system, consisting of high-efficiency particulate air filters and charcoal absorber beds. Gases from periodic venting of the MPS2 containment are released through a similar process system (Enclosure Building Filtration System) while gases from the MPS3 containment vacuum pumps are released without treatment.

If necessary, MPS3 containment air can be filtered by an internal particulate and charcoal treatment system. Containment purges (purge is the forced ventilation process while containment vents are pressure releases) for MPS2 are filtered by high-efficiency particulate filters while at MPS3 these are not normally filtered. If necessary, particulate and charcoal filters can be used for these purges.

Normally, for MPS2, the air released from the unit vent is from the ventilation of the auxiliary (which includes the fuel pool), service and enclosure buildings. For MPS2, fuel pool and enclosure building ventilation can be redirected to the MPS Site Stack. Normally, for MPS3, the air released from the unit vent is from the ventilation of the auxiliary, fuel, service, waste disposal and enclosure buildings. For MPS3, enclosure building ventilation can be redirected to the MPS Site Stack.

1-9 Dominion Energy Nuclear Connecticut, Inc. Annual Radiological Environmental Millstone Power Station Operating Report 2023

Therefore, for both liquid and gaseous releases, radioactive effluent cor;itrol systems exist to collect and purify the radioactive effluents in order to reduce releases to the environment to as low as is reasonably achievable. The effluents are always monitored, sampled and analyzed to make sure that radioactivity levels are below the release limits. If the release limits are being approached, isolation valves are closed to stop the release and ensure that federal regulatory limits are always met.

1.6 Radiological Impact on Humans

The final step in the effluent control process is the determination of the radiological dose impact to humans and comparison with the federal dose limits to the public. As mentioned previously, the purpose of continuous radiation monitoring and periodic sampling and analysis is to measure the quantities of radioactivity being released to determine compliance with the radioactivity release limits. This is the first stage for assessing releases to the environment.

The second stage is calculation of the dose impact to the general public from MP S's radioactive effluents. The purpose of this calculation is to periodically assess the dose to the general public resulting from radioactive effluents to ensure that the dose is being maintained as far below the federal dose limit as is reasonably achievable. This is the second stage for assessing releases to the environment.

The types and quantities of radioactive liquid and gaseous effluents released from MPS during each year are reported to the NRC annually in the Radiological Effluent Release Report (RERR).

Similar to this report, the RERR is submitted annually to the NRC. The liquid and gaseous effluents were well below the federal release limits and were a small percentage of the MPS REMODCM effluent control limits.

The measurements of the physical and chemical nature of the effluents are used to determine how the radionuclides will interact with the environment and how they can result in radiation exposure to humans. The environmental interaction mechanisms depend upon factors such as the hydrological (water) and meteorological (atmospheric) characteristics in the area.

Information on the water flow, wind speed, wind direction, and atmospheric mixing characteristics are used to estimate how radioactivity will distribute and disperse in the ocean and the atmosphere.

The most important type of information that is used to evaluate the radiological impact on humans is data on the use of the environment. Information on fish and shellfish consumption, boating usage, beach usage, locations of cows and goats, locations of residences, locations of gardens, and other usage information are utilized to estimate the amount of radiation and radioactivity received by the general public.

The radiation exposure pathway to humans is the path radioactivity takes from its release point at MPS to its effect on man. The movement of radioactivity through the environment and its transport to humans is portrayed in Figure 1.6-1.

1-10 Dominion Energy Nuclear Connecticut, Inc. Annual Radiological Environmental Millstone Power Station Operating Report 2023

EXAMPLES OF Millstone's RADIATION EXPOSURE PATHWAYS

~~ ****~ ***~ d ~ *If ll~lt~~, *****~*.

LIQUID **1*:***i*i*i*i*i*i*i*i*i*****i*i***i***************** *-:-:-:-::::::::::::::::::::::::;*:::::::-: -**l EFFLUENTS

3. DIRECT RADIATION (STATION), 2. AIR INHALATION

(/ 1. DIRECT RADIATION

~ (AIR SUBMERSION)

~ V

1. SHORELINE DIRECT RADIATION (FISHING, PICNIC.ING) ~ 5. CONSUMPTION (VEGETATION) ~

DEPOSITION 2. DIRECT RADIATION (IMMERSION IN OCEAN, ~ ~

(OAT;, SWIMMING)

DEPOSITION INGESTION

Figure 1.6-1: Radiation Exposure Pathways

1-11 Dominion Energy Nuclear Connecticut, Inc. Annual Radiological Environmental Millstone Power Station Operating Report 2023

There are four pathways in which liquid effluents affect humans:

external radiation from liquid effluents that deposits and accumulates on the shoreline;

external radiation during boating from radioactivity in ocean water;

external radiation from immersion in ocean water containing radioactivity; and internal radiation from consumption of fish and shellfish containing radioactivity absorbed from the liquid effluents.

There are six major pathways in which gaseous effluents affect humans :

external radiation from immersion in an airborne plume of radioactivity;

external radiation from shine from an overhead, airborne plume of radioactivity;

internal radiation from inhalation of airborne radioactivity;

external radiation from deposition of radioactive effluents on the ground;

internal radiation from consumption of vegetation containing radioactivity deposited on the vegetation from airborne deposition and absorbed from the soil due to ground deposition of radioactive effluents; and internal radiation from consumption of milk and meat containing radioactivity deposited on forage that is eaten by cattle and other livestock.

Drinking water is not a pathway of exposure for radioactivity released in liquid or gaseous effluents from Millstone. All liquid effluents are released to either Long Island Sound or Niantic Bay. Both are saltwater bodies which are not used as sources of drinking water. The closest reservoir is Lake Konomoc, 6.5 miles from Millstone. Radioactivity deposited in the reservoir from MPS gaseous effluents would not yield a significant dose to the public compared to doses from the six major pathways listed.

Ambient (direct) radiation emitted from sources of radioactivity at MPS comes from low-level radioactive waste being processed and stored at the site prior to shipping and disposal. Also, the operation of the Independent Spent Fuel Storage Installation (ISFSI) which began in 2005 results in a small amount of direct radiation at the site boundary.

The radiological dose impact on humans is based both on effluent analyses and modeling and on direct measurements of radiation and radioactivity in the environment. However, the operation of MPS results in releases of only small amounts of radioactivity, and, as a result of dilution in the atmosphere and ocean, even the most sensitive radioactivity measurement and analysis techniques cannot usually detect these tiny amounts of radioactivity above that which is naturally present in the environment. Therefore, radiation doses are calculated using radioactive effluent release data and computerized dose calculations that are based on conservative NRC recommended models that tend to result in over-estimates of the resulting dose. These computerized dose calculations are performed by DENC personnel. These computer codes use the guidelines and methodology set forth by the NRC in Regulatory Guide 1.109 (Reference 7).

The dose calculations are specified in the Millstone's REMODCM (Reference 8), which has been reviewed by the NRC.

It should be emphasized that the conservative assumptions made in the computer code calculations; the maximum hypothetical dose to an individual is considerably higher than the dose that would actually be received by a real individual.

1-12 Dominion Energy Nuclear Connecticut, Inc. Annual Radiological Environmental Millstone Power Station Operating Report 2023

After dose calculations are performed, the results are compared to the dose limits for the public as specified in NRC's techn ical specifications for MPS (References 9-11 ).

The technical specifications limits for the dose to a member of the general public from radioactive mater ial in liquid effluents released to unrestricted areas are:

less than or equal to 3 mrem per year to the total body; and,

less than or equal to 10 mrem per year to any organ.

The technical specifications limits for dose due to release of radioactivity in gaseous effluents is restricted to :

less than or equal to 1 0 mrad per year for gamma radiation from noble gases;

less than or equal to 20 mrad per year for beta radiation from noble gases; and

less than or equal to 15 mrem per year to any organ from iodine-131, iodine-133, tritium, and all particulate radionuclides with half-lives greater than 8 days.

The Technical Specifications limits for total dose from all three MPS units due to release of radioactivity in gaseous and liquid effluents and direct radiation is restricted to :

less than or equal to 25 mrem per year to the total body;

less than or equal to 75 mrem per year to the thyroid; and

less than or equal to 25 mrem per year to any other organ.

1-13 Dominion Energy Nuclear Connecticut, Inc. Annual Radiological Environmental Millstone Power Station Operating Report 2023

2. PROGRAM DESCRIPTION

2.1 Sampling Schedule and Locations The sample locations, types, and frequency of analysis are given in Tables 2. 1-1 and 2.1-2 and are shown in Figures 2. 1-1 and 2.1-2. The program as described in Table 2. 1-1 lists the required samples collected as specified in the REMODCM, as well as any other extra samples collected under the program.

2-1 Dominion Energy Nuclear Connecticut, Inc. Annual Radiological Env ironmental Millstone Power Station Operating Report 2023

Table 2,1-1 Environmental Monjtorjng Program sampling Types and Locations

Distance, No.- Direction From Type* Location Name Release Point *

Sample Media 1-1 Onsite - NAP Parking Lot N 0.6Mi, NNW TLD, A ir Particu late, Iodine, Vegetation 2-1 Onsite - Weather Shack 0.3Mi, S TLD, Air Particulate, Iodine 3-1 Ons ite - Bird Sanctuary 0.3 Mi, NE TLD, Air Particulate, Iodine, Soil 4-1 Onsite - Albacore Drive 1.0 Mi, N TLD, Air Particulate, Iodine, Soil 5-1 Onsite - Quarry East 0. 1 Mi, SSE TLD 6-1 Ons ite - Quarry Discharge 0.3 Mi, SSE TLD 7-1 Onsite - Env. Lab Dock 0.3 Mi, SE TLD 8-1 Onsite - Env. Lab 0.3 Mi, SE TLD 9-1 Onsite - Bay Point Beach 0.4 Mi, W TLD 10-1 Goshen Fire Dept. 1.2 Mi, E TLD, Air Particulate, Iodine, Vegetation 11-1 Great Neck Country Club 1.6 Mi, ENE TLD, Air Particulate, Iodine 13-C Mystic, CT 11.5 Mi, ENE TLD 14-C Ledyard, CT 12.0 Mi, NE TLD, Soil 15-C Norwich, CT 14.0 Mi, N TLD, Air Particulate, Iodine 16-C Old Lyme, CT - Halls Rd. 8.8Mi,W TLD 17-1 Site Boundary 0.5 Mi, NE Vegetation 25-1 Fruits & Vegetables < 10 Miles Vegetation 25-X Fru its & Vegetables < 10Miles Vegetation 26-C Fruits & Vegetables > 10 Miles Vegetation 27-1 East Lyme Police Dept. 1.7Mi, WNW TLD, Air 1 Particulate, Iodine 28-1 Two Tree Island 1 0.8 Mi, SSE Fish 29-1 West Jordan Cove 1 :;; 0.5 Mi, ENE to ESE Clams, Fucus, Fish 1 31-1 Niantic Shoals 1.8 Mi, NW Bottom Sediment, Clams 1, Seawater, Aquatic Flora 32-1 Vicinity of Discharge 1-2 Bottom Sediment, Fish 33-1 Seaside Point 1.8 Mi, ESE Bottom Sediment 34-1 Thames River Yacht Club 4.0 Mi, ENE Bottom Sediment 35-1 Niantic Bay ::;0.5 Mi, SSW to W Lobster, Fish1, Aquatic Flora 36-C Black Point 2.7Mi, WSW Aquatic Flora 37-C Giant's Neck 3.5M i, WSW Bottom Sediment, Seawater 41-1 Waterford - Myrock Avenue 3.2 Mi, ENE TLD 42-1 East Lyme - Billow Road 2.4 Mi, WSW TLD 43-1 East Lyme-Old Black Point 2.6 Mi, SW TLD 44 - 1 Onsite - Schoolhouse 0.1 Mi, NNE TLD 45 - 1 Onsite - Access Road #1 0.5Mi, NNW TLD 46-1 Old Lyme - Hillcrest Ave. 4.6Mi, WSW TLD 47-1 East Lyme - W. Main St. 4.5Mi, W TLD 48 - 1 East Lyme - Corey & Roxbury 3.4Mi, WNW TLD 49-1 East Lyme - Soc iety Rd. 3.6Mi, NW TLD 50-1 East Lyme - Manwaring Rd & 2.1 Mi, W TLD Terrace Ave 51-1 East Lyme - Smith Ave. 1.5Mi, NW TLD 52-1 Waterford - River Rd. 1.1 Mi, NNW TLD 53-1 Waterford - Gardiners Wood Rd 1.4 Mi, NNE TLD 55-1 Waterford - Magonk Point 1.8 Mi, ESE TLD 56 - 1 New London - Ocean & Mott 3.7 Mi, E TLD Ave.

1. Fish required to be sampled from one of three other locations (#28, #29 or # 32).

2. Vicinity of d ischarge includes the Quarry and shoreline area from Fo x Island to western point of Red Barn recreation Area and Offshore out to 500 feet.

Footnotes :

I = Indicator ; C = Control, X - Ex tra - sample not required by the REMODCM

- = The release points are the Millstone Stack for terrestrial location and the end of the quarry for aquatic location.

2-2 Dominion Energy Nuclear Connecticut, Inc. Annual Radiological Environmental Millstone Power Station Operating Report 2023

Table 2,1-1 Environmental Monjtorjng program Sampling Types and Locations (Continues)

No.- Distance, Direction From Type 1 Location Name Release Point2 Sample Media 57-1 New London - Ocean Ave. 3.6 Mi, ENE TLD 59-1 Waterford -Miner Ave. 3.4 Mi, NNE TLD 60-1 Waterford-Parkway South&Cross 4.0Mi, N TLD 61-1 Waterford-Oil Mill&Boston Post 4.3Mi, NNW TLD 62-1 East Lyme - Columbus Ave. 1.9Mi, WNW TLD

63-1 Waterford - Gardiners Wood & 0.8 Mi, Jordon Cove NE TLD

64-1 Waterford - Shore Rd. 1.1 Mi, ENE TLD 65-1 Waterford - Boston Post Rd. 3.2 Mi, NE TLD 66-X NAP Parking Lot - Fit Center 0.4 Mi, NW TLD 71-1 1-MW-XFMR - 03 Onsite Well Water 72-1 MW-GPl-1 Onsite Well Water 73-X Site Switchyard Fence 0.3 Mi, N TLD 74-X Ball Field Foul Pole 0.6Mi, N TLD 75-X Waterford - Windward Way & 0.5 Mi, NE TLD Shotgun 76-X ISFSl-1 Up-gradient of ISFSI Well Water 77-X ISFSl-2 Down-gradient of ISFSI Well Water 78-X ISFSl-3 Down-gradient of ISFSI Well Water 79-1 M3-MW-1 Onsite Well Water 81-1 S2-MW-1 Onsite Well Water 82-1 MW -6B Onsite Well Water 83-1 S3-MW-2 Onsite Well Water 89-C Aquatic background >4 miles of discharge Lobster

1. Fish required to be sampled from one of three other locations (#28, #29 or #32).

2. Vicinity of discharge includes the Quarry and shoreline area from Fox Island to western point of Red Barn recreation Area and Offshore out to 500 feet.

Footnotes:

I = Indicator; C = Control, X - Extra - sample not required by the REMODCM

- = The release points are the Millstone Stack for terrestrial location and the end of the quarry for aquatic location.

2-3 Dominion Energy Nuclear Connecticut, Inc. Annual Radiological Environmental Millstone Power Station Operating Report 2023

Table 2,1-2 Reqyjred Sampling frequency & Type of Analysis

Exposure Pathway No. of Sampling & Collection Type and Frequency and/or Sample Locations Frequency of Analysis

1. Gamma Dose-39 1 Quarterly Gamma Dose - Quarterly Environmental TLD

2. Airborne Particulate 8 Continuous sampler - filter change Gross Beta - Every two every two weeks weeks Gamma Spectrum

- Quarterly on composite (by location), and on individual sample if gross beta is greater than 10 I times the mean of the weekly control station's gross beta results

3. Airborne Iodine 8 Continuous sampler - canister 1-131 - Every two weeks change every two weeks

4. Vegetation 5 One sample near middle and one Gamma Isotop ic on each near end of growing season sample 5. Milk - Refer to Table 2.1-2.1 below

6. Sea Water 2 Continuous sampler with a Gamma Isotopic and monthly collection at indicator Tritium on each sample.

location. Quarterly at control location - Composite of 6 weekly grab samples.

7. Well Water 6 Semiannual Gamma Isotopic and Tritium on each sample 8. Bottom Sediment 5 Semiannual Gamma Isotopic on each sample

9. Soil 3 Annually Gamma Isotopic on each sample

10. Fin Fish 2 Semiannual Gamma Isotopic on each (edible portion) sample

11. Aquatic flora (fucus) 4 Quarterly Gamma isotopic on each sample

13. Clams 2 Semiannual Gamma Isotopic on each (edible portion) sample

14. Lobster 2 Semiannual Gamma Isotopic on each (edible portion) sample Footnotes

1. Two or more TLDs or TLD with two or more elements per location.

Oysters were previously Sample#12, REMODCM revision 27.

2-4 Dominion Energy Nuclear Connecticut, Inc. Annual Radiological Environmental Millstone Power Station Operating Report 2023

Table 2,1-2,1 Milk Sampling Reqyjrements

Number of Locations and Sampling & Collection Type and Frequency Sampling Criteria Frequency of Analysis

If milk location(s) are available, obtain samples from Semimonthly when animals Gamma Isotopic and milking animals from up to three locations within 3 miles are on pasture; Monthly, for 1-131 analysis on each (5 km) distance having the highest dose potential. If non---pasture producers. sample there are none, then one sample from milking animals in each of three areas between 3 to 5 miles (5 to 8 km) distant where doses are calculated to greater than 1 mrem per year. One sample from milking animals at a control location 9 to 18 miles (15 to 30 km) distant and in the least prevalent wind direction.

If milk location(s) are not available, obtain samples of Monthly, if available, or at Gamma Isotopic and three different kinds of broad leaf vegetation grown harvest, (a) 1-131 analysis on each nearest each of two different offsite locations of highest sample predicted annual average ground level D/Q

Footnotes (a) Harvest cons ists of one sample near the middle and one sample near the end of the growing season.

2-5 Dominion Energy Nuclear Connecticut, Inc. Annual Radiological Environmental Millstone Power Station Operating Report 2023

figure 2,1-1, "loner JLP, Air, Grass, Soil, and Aquatic Locations"

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2-6 Dominion Energy Nuclear Connect icut, Inc. Annual Radiological Environmental Millstone Power Station Operating Report 2023

f jgyre 2,1-2, "Outer ILP and Aquatic Locations"

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2-7 Dominion Energy Nuclear Connecticut, Inc. Annual Radiological Environmental Millstone Power Station Operating Report 2023

2.2 Samples Collected During Report Period The following table summarizes the number of samples of each type collected and analyzed during 2023:

Iabl~ 2,2-j Bffllle Samgl~~ ~Qll~"t~~ i 2Q2J

Number of Number of Sample Type Specification Specification Technical Technical Number of Extra Samples Analyzed Required Samples Required Samples Analyzed

Gamma Exposure 156 156 16 (Environmental TLD)

Air Particulates 208 208 0 Air Iodine 208 208 0 Soil 3 3 0 Milk 12 0 0 Well Water 12 12 24 Vegetation 10 10 1 Sea Water 16 16 0 Bottom Sediment 10 10 0 Aquatic Flora 16 16 4 Fish 4 4 0 Oysters 0 0 4 Clams 4 4 0 Lobster 4 4 0 Total All Types 651 639 49

2.3 Required Samples Not Collected During the Report Period During 2023 all required samples were obtained except for Milk.

The 2023 Land Use Census did not locate any milk farms producers within ten miles of Millstone Power Station. As a substitute for milk sampleps, strontium analysis of air samples and gamma analysis of broad leaf vegetation were performed. This fulfills the requirements for Milk sampling as listed in Table 2.1-2.1 of this report, "Milk Sampling Requirements"

2-8 Dominion Energy Nuclear Connecticut, Inc. Annual Radiological Environmental Millstone Power Station Operating Report 2023

3. RADIOCHEMICAL RESULTS

3.1 Summary Table In accordance with the REMODCM,Section I.F.1, a summary table of the radiochemical results has been prepared and is presented on the following pages. The mean and range recorded are based only upon detectable measurements.

A more detailed analysis of the data is given in Section 4.0 where a discussion of the variations in the data explains many aspects that are not evident in the Summary Table because of the basic limitation of data summaries. The data summaries include the extra ("X") samples collected throughout the year. These samples are taken to enhance the monitoring program or replace samples from required locations when they are not available.

Furthermore, in accordance with the REMODCM,Section I.E.3, an inter-laboratory comparison was performed by Teledyne Brown Engineering Environmental Services (TBE-ES) as part of their quality assurance program for environmental monitoring in order to demonstrate that the results are reasonably valid (Appendix B). Quality Control of radioanalyses involves TBE-ES internal process control program and independent third party programs administered by Analytics and Environmental Resource Associates (ERA) and Department of Energy's (DOE)

Mixed Analyte Performance Evaluation Program (MAPEP).

The Teledyne inter-laboratory comparison report concluded that 124 out of 131 quality assurance analyses performed met the specified acceptance criteria. Seven analyses did not meet the specified acceptance criteria addressed in Teledyne Non-Conformance Reports (NCRs), listed in Appendix B. A review of the Teledyne NCRs was performed and none of the seven analyses failures were found to have impacted any of Millstone samples results and data accuracy, addressed and dispositioned in the Millstone Corrective Action Program.

3-1 Dominion Energy Nuclear Connecticut, Inc. Annual Radiological Environmental Millstone Power Station Operating Report 2023

RADIOLOCIAL ENVIRONMENT MONITORING PROGRAM

SUMMARY

MILLSTONE POWER STATION Dockets 50-245, 50-336 & 50-423 2023

Medium or Indicator Control Pathway Locations Location with Highest Mean Locations Sampled Analysis Total LLD* Number Number (Units) Type Number Mean Location I Distance Number Mean (Range) Number Direction Me an (Range) (Range) I Direct Gamma 172 NA 156 8,9 0.3 Mi./0.04 Mi. 4/4 16 Radiation Dose 7.8 SE/W 11.3/11.3 8.0 TLD (uR/hr) (4.3-11.8) (10.7-11.6)/(10.7-11.8) (5.5-10.0)

Air Iodine 1-131 208 0.07 182 NA NA < LLD 26 (pCi/m 3 ) <LLD < LLD

Air Particulate GR-8 208 0.01 182 3.03 Mi. 26 26 (pCi/m 3 ) 0.014 NE 0.015 0.015 (0. 005-0. 030) (0.008-0.029) (0.008-0.027)

SR-89 32 0.1 28 NA NA < LLD 4

< LLD < LLD

SR-90 32 0.01 28 NA NA < LLD 4

< LLD < LLD

GAMMA BE -7 32 NA 28 0.6Mi. 4 4 0.0876 NNW 0.0961 0.0829 (0.0547-0. 1199) (0.0718-0.1072) (0.0548-0.1023)

Other Note 2 < LLD NA NA < LLD <LLD Gammas

Soil GAMMA 3 (pCilg dry) K-40 NA 2 14 12.0 Mi.

15.110 NE 21.020 21.020 (11.890-18.330) (21.020) (21.020)

CS-137 0. 18 1/2 4 1.0 Mi.

0. 281 N 0.281 < LLD (0.281)

AC-228 NA 2 14 12.0Mi.

0.885 NE 1.400 1.400 (0.673-1.097) (1.400) (1,400)

Other Note 3 < LLD NA NA < LLD < LLD Gammas

Cow Milk SR-89 10 (pCi/1)

SR -90 2

GAMMA Milk was not available for collection in 2023, as a substitute, K-40 NA Strontium Analysis of Air Particulate filters was performed

Other Note 4 Gammas

3-2 Dominion Energy Nuclear Connecticut, Inc. Annual Radiological Environmental Millstone Power Station Operating Report 2023

RADIOLOCIAL ENVIRONMENT MONITORING PROGRAM

SUMMARY

MILLSTONE POWER STATION Dockets 50-245, 50-336 & 50-423 2023

Medium or Indicator Control Pathway Locations Locat ion with Highest Mean Locations Sampled Analysis Total LLD* Number Number (Units) Type Number Mean Location I Distance Number Mean (Range) Number Direction Mean (Range) I (Range)

Goat Milk SR-89 10 (pCi/1)

SR -90 2

GAMMA Milk was not available for collection in 2023, as a substitute, K-40 NA Strontium Analysis of Air Particulate filters was performed

Other Note4 Gammas

Well Water H-3 36 2000 36 NA NA < LLD NA (pCill) < LLD

GAMMA 36 K-40 NA 36 NA NA < LLD NA

< LLD

Other Note 5 < LLD NA NA <LLD NA Gammas

Fruits & Vegetables GAMMA 11 (pCi/g v1el) K-40 NA 6 25 Within 10 Miles 5 5 1.830 1.826 1.783 (1.038-3. 133) (1.038-3. 133) (0. 832-02. 792)

Other Note6 < LLD NA NA <LLD <LLD Gammas

Broad Leaf Vegetation GAMMA 8 (pCilg oot) BE-7 NA 4/6 10 1.2Mi. 1/2 2 1.772 E 2.820 1.327 (0.520-2.823) (2.820) (0.406-2.247)

K-40 NA 6 26 Beyond 10 miles 2 2 2.649 3.414 3.414 (1.971-3.682) (3.115-3.713) (3. 115-3.713)

Other Note6 < LLD NA NA < LLD < LLD Gammas

3-3 Dominion Energy Nuclear Connecticut, Inc. Annual Radiological Environmental Millstone Power Station Operating Report 2023

RADIOLOCIAL ENVIRONMENT MONITORING PROGRAM

SUMMARY

MILLSTONE POWER STATION Dockets 50-245, 50-336 & 50-423 2023

Medium or Indicator Control Pathway Locations Location with Highest Mean Lo cations Sampled Analysis Total LLD* Number Number (Units) Type Number Mean Location I Distance Number Mean (Range) Number Direction Mean (Range) I (Range)

Sea Water H-3 16 3000 11/12 32 < 0.1 Mi 11/12 (pCi/1) 879 879 < LLD (266-1560) (266-1560)

GAMMA 16 K-40 NA 12 32 < 0.1 Mi 12 4 303 303 266 (164-411) (164-411) (216-308)

Other Note 5 < LLD NA NA < LLD < LLD Gammas

Bottom Sediment GAMMA 10 (pCilg dry) K-40 NA 8 32 < 0.1 Mi 2 2

13. 94 15.26 14.87 (11. 18-17.47) (13.05-17.47) (14.48-15.26)

Ac-228 NA 2/8 31 1.8Mi. 2 2.746 NW 2.746 < LLD (2.396-3.096) (2.396-3. 096)

Other Note 3 < LLD NA NA < LLD < LLD Gammas

Aquatic Flora GAMMA 16 (pCilg \\\\el) BE-7 NA 12 NA NA < LLD 4

< LLD < LLD

K-40 NA 12 32 < 0.1 Mi 4 4 6.0802 6. 3468 5.4830 (5.2070-6. 9170) (5.2070-6.9170) (3.8110-6.8910)

1-131 0.06 12 NA NA < LLD 4

< LLD < LLD

Other Note 6 < LLD NA NA < LLD < LLD Gammas

3-4 Dominion Energy Nuclear Connecticut, Inc. Annual Radiological Environmental Millstone Power Station Operating Report 2023

RADIOLOCIAL ENVIRONMENT MONITORING PROGRAM

SUMMARY

MILLSTONE POWER STATION Dockets 50-245, 50-336 & 50-423 2023

Medium or Indicator Control Pathway Locations Location with Highest Mean Locations Sampled Analysis Total LLD* Number Number (Units) Type Number Mean Location I Distance Number Mean (Range) Number Direction Mean (Range) I (Range)

Fish - Other GAMMA 4 (pCilg oot) K-40 NA 4 29 0.4Mi.

3.768 NNE 4.196 NA (2.818-4.203) (4. 196)

Other Notes <LLD NA NA <LLD NA Gammas

Oysters GAMMA 4 (pCi/g 11et) K-40 NA 1/2 31 1.8Mi. 1/2 2 2.068 NW 2. 068 1.749 (2.068) (2. 068) (1.458-2.039)

Other Note 8 <LLD NA NA < LLD <LLD Gammas

Clams GAMMA 4 (pCilg oot) K-40 NA 4 31 1.8Mi. 2 2.011 NW 2. 080 NA (1.839-2. 122) (2.038-2. 122)

other Note 8 <LLD NA NA <LLD NA Gammas

Lobster GAMMA 4 (pCi/g oot) K-40 NA 2 89 >4.0 miles 2 2 2.265 2.508 2.508 (1.984-2.546) (2.230-2. 785) (2.230-2. 785)

Other Note 8 <LLD NA NA <LLD <LLD Gammas

3-5 Dominion Energy Nuclear Connecticut, Inc. Annual Radiological Environmental Millstone Power Station Operating Report 2023

NOTES FOR

SUMMARY

TABLE

1 - (*) The required LLD is the smallest concentration of radioactivity that will be detected with 95% confidence that the activity is real. See detailed discussion below.

2 - LLDs for air particulate gamma are 0.05 pCi/M3 for Cs-134 and 0.06 pCi/M3 for Cs-137.

3 - LLD for soil and sediment gamma is 0.15 pCi/g for Cs-134.

4 - LLDs for milk gamma are 1 pCi/I for 1-131, 15 pCi/I for Cs-134, 18 pCi/I for Cs-137, 70 pCi/I for Ba-140 and 25 pCi/I for La-140.

5 - LLDs for water gamma are 15 pCi/I for Mn-54, Co - 58, Co-60, Nb-95, 1-131, Cs-134 and La-140; 30 pCi/I for Fe-59, Zn-65 and Zr-95; 18 pCi/I for Cs-137 and 60 pCi/I for Ba-140.

6 - LLDs for fruits & vegetables, broadleaf vegetation and aquatic flora for gamma are 0.06 pCi/M3 for 1-131, 0.06 pCi/M3 for Cs-134 and 0.08 pCi/M3 for Cs-137.

7 - LLDs for other gamma are 0.06 pCi/g for Cs-134 and 1-131.

8 - LLDs for fish and shellfish for gammas are 0.13 pCi/g for Mn - 54, Co - 58, Co - 60 and Cs-134; 0.26 pCi/g for Fe-59 and Zn - 65 ; 0. 15 pCi/g for Cs-137; and 0.93 pCi/g for 1-131.

Discussion of LLD The LLD at a confidence level of 95% is the smallest concentration of radioactive material in a sample that will be detected with a 5% probability of falsely concluding that a blank observation represents a "real" signal.

For a particular measurement system (which may include radiochemical separation):

LLD = ____ 4_._66_S_b --

E

V

2. 22

Y

exp (-J./j_t)

LLD is the lower limit of detection as defined above (as pCi per unit mass or volume)

S h is the standard deviation of the background counting rate or of the counting rate of a blank sample as appropriate (as counts per minute)

E is the counting efficiency (as counts per transformation)

V is the sample size (in units of mass or volume) 2.22 is the number of transformations per minute per picoCurie Y is the fractional radiochemical yield (when applicable)

"A, is the radioactive decay constant for the particular radionuclide flt is the elapsed time between sample collection (or end of the sample collection period) and time of counting

The LLD is defined as "a priori" (before the fact) limit representing the capability of a measurement system and not an "a posteriori" (after the fact) limit for a particular measurement.

Analyses were performed in such a manner that the stated LLDs were achieved under routine conditions. Occasionally background fluctuations, unavoidably small sample sizes, the presence of interfering nuclides, or other uncontrollable circumstances may have rendered these a priori LLDs unachievable. In such cases, the contributing factors are identified and described in this report. As shown in the equation above, for composite samples taken ove r a period of time, the LLD is decayed to the end of the sample period.

3-6 Dominion Energy Nuclear Connecticut, Inc. Annual Radiological Environmental Millstone Power Station Operating Report 2023

3.2 Data Tables The data reported in this section are results of analyses on all samples. All gamma exposure rates (Table 1) and air beta results (Table 2) are positive because of natural radioactivity. For all other results positive results are shown as balded type. Results are considered positive when the measured value exceeds 1.5 times the listed 2cr error (i.e., the measured value exceeds 3cr).

The reported error is two times the standard deviation (2cr) of the net activity. Unless otherwise noted, the overall error (counting, sample size, chemistry, errors, etc.) is estimated to be 2 to 5 times that listed. Because of counting statistics, negative values, zeros and numbers below the Minimum Detectable Level (MDL) are statistically valid pieces of data. For the purposes of this report, in order to indicate any background biases, all the valid data are presented. This practice was recommended by Health and Safety Laboratory (HASL) ("Reporting of Analytical Results from HASL," letter by Leo B. Higginbotham), NUREG 0475 and NUREG/CR-4007 (Sept. 1984).

Data are given according to sample type as indicated below.

1. Gamma Exposure Rate

2. Air Particulates, Gross Beta Radioactivity

3. Air Particulates, Airborne 1-131

4. Air Particulates, Gamma Spectra

5. Soil

6. Milk

7. Well Water

8. Fruits & Vegetables

9. Broad Leaf Vegetation

10. Seawater

11. Bottom Sediment

12. Aquatic Flora (Fucus)

13. Fin Fish

14. Oysters

15. Clams

16. Lobster

3-7 Dominion Energy Nuclear Connecticut, Inc. Annual Radiological Environmental Millstone Power Station Operating Report 2023

TABLE 1 QUARTERLY GAMMA EXPOSURE RATE (uR/hr)*

LOCATIONS PERIOD 1 2 3 4 5 6 7 8 9 10 11

(+/-) (+ /-) (+/-) (+/-) (+/-) (+/-) (+/-) (+/-) (+/-) (+/-) (+/-)

1Q 8.2 0.2 9. 6 0.4 7. 2 0.2 8. 5 0.3 9.6 0. 3 8. 8 0. 3 4. 9 0.2 11. 5 0.3 11.4 0.3 10.9 0. 3 7. 3 0.4 2Q 8.3 0. 3 11. 6 0. 5 7.4 0.3 8. 1 0. 3 9.9 0.4 8. 8 0. 5 4.7 0.4 11.6 0.4 11.8 0.4 10. 3 0.6 7. 2 0. 3 3Q 7.8 0.4 11. 3 0. 5 7.4 0. 3 7.8 0. 3 10.2 0.4 8.4 0.3 4.8 0.3 11.4 0.4 11.3 0.4 9.4 0.4 7.5 0.3 4Q 7. 5 0.4 10. 6 0.5 6.9 0.4 7.8 0.4 9.1 0. 5 8. 1 0. 3 4. 3 0. 3 10.7 0.4 10.7 0.5 9.4 0.4 6. 6 0. 3

PERIOD 13C 14C 15C 16C 27 41 42 43 44 45 46

(+/-) (+/-) (+/-) (+/ - ) (+/-) (+/-) (+/-) (+ / -) (+/-) (+/-) (+/-)

1Q 9.0 0.2 9.4 0. 3 7. 7 0. 2 6.8 0. 3 7.9 0.3 7.5 0.2 7.4 0. 3 7.4 0.2 7.8 0. 3 7. 5 0. 3 8.7 0.4 2Q 8.8 0.4 10. 0 0.4 7.6 0. 3 5.8 0.3 7.8 0.3 7.4 0.3 7. 6 0.4 7. 5 0. 3 7.7 0.5 7.4 0.3 8.2 0.4 3Q 8.8 0.3 9. 3 0.4 7.9 0.4 6.3 0.2 7. 7 0. 3 7. 0 0. 3 7. 7 0.3 7.2 0.4 8. 0 0.4 7.2 0. 3 8. 1 0.3 4Q 8.5 0.4 9. 0 0.4 7. 1 0.3 5.5 0.3 7. 1 0.4 6.2 0. 3 6.9 0. 3 7.0 0. 3 7.5 0.3 6. 8 0. 3 7. 5 0.4

PERIOD 47 48 49 50 51 52 53 55 56 57 59

(+/-) (+/-) (+/-) (+/ - ) (+/ - ) (+/-) (+/ - ) (+/-) (+/-) (+ / -) (+/-)

1Q 8. 1 0.2 9. 3 0.4 8. 1 0. 3 7.4 0.3 7. 0 0. 2 7.4 0.4 7. 5 0. 3 7.7 0. 3 7.9 0.3 7.1 0.2 7. 6 0. 2 2Q 7.7 0. 5 9. 1 0.6 7. 6 0. 3 7.1 0. 3 6.4 0. 3 6. 9 0. 3 7. 6 0.5 7. 3 0. 3 8. 0 0. 3 6.9 0.3 7. 8 0.4 3Q 8.0 0. 3 8. 8 0. 3 7.6 0. 3 7. 5 0.3 7. 0 0.3 7.2 0.4 7.4 0.3 7. 5 0.3 8. 0 0. 3 6.6 0.2 7. 7 0.3 4Q 7.3 0. 3 8.4 0.4 7.4 0. 3 7.1 0.4 5.8 0. 3 6.6 0. 3 6. 9 0.3 7.1 0.4 9. 6 0.4 6. 6 0.4 7. 3 0. 3

PERIOD 60 61 62 63 64 65 66 73 74 75

(+/-) (+/ -) (+/-) (+/-) (+/-) (+/-) (+/-) (+/-) (+/-) (+/-)

1Q 6.4 0.3 6. 5 0.2 9.6 0. 3 9. 0 0.3 7.6 0.2 8. 1 0.3 7.6 0.2 7.7 0.3 7.5 0. 2 6. 8 0.2 2Q 6. 3 0. 3 6.4 0. 3 9.2 0. 5 8.6 0. 5 7.2 0.3 7. 9 0.5 7. 5 0.3 7. 6 0. 3 7.4 0. 5 6.4 0.3 3Q 6.2 0.2 6.7 0.4 9.2 0. 3 9.2 0.5 7. 2 0.4 7. 7 0. 3 7. 0 0.3 7. 5 0.4 7.5 0.3 6.4 0.4 4Q 6.1 0.4 6.0 0. 3 8. 7 0.4 8. 3 0. 3 6. 8 0. 3 7.6 0.4 6. 9 0. 3 7. 3 0. 3 7. 1 0. 3 6.4 0.3

READINGS ARE THE AVERAGE OF MULTI CaSo 4 (Tm) PHOSPHOR ELEMENTS WITHIN ONE PANASONIC TLD BADGE ERRORS ARE TWO SIGMA AND INCLUDE COUNTING, TRANSIT, READER AND FADE UNCERTAINTIES C= Control location, Background location

3-8 Dominion Energy Nuclear Connecticut, Inc. Annual Radiological Environmental Millstone Power Station Operating Report 2023

TABLE 2 AIR PARTICULATES GROSS BET A RADIOACTIVITY (pCi/m 3 )

LOCATIONS PERIOD ENDING 1 2 3 4 10 11 27 15C - (+/-) (+/-) (+/-) (+/-) (+/-) (+/-) (+/-) (+/-)

01/17/23 0.013 0.002 0.013 0.002 0.011 0.002 0.011 0.002 0.014 0. 002 0. 012 0. 002 0.013 0.002 0.014 0.002 01/31/23 0.010 0. 002 0.012 0.002 0.012 0.002 0.011 0.002 0.011 0.002 0.012 0. 002 0. 013 0.002 0.011 0.002

02/14/23 0.018 0.002 0.016 0.002 0.017 0. 002 0.016 0.002 0.018 0.002 0.020 0. 002 0.017 0. 002 0.016 0.002 02/27/23 0.014 0.002 0.014 0. 002 0.015 0. 002 0.013 0.002 0.013 0. 002 0.016 0. 002 0.014 0.002 0.015 0.002

03/13/23 0.014 0.002 0.010 0.002 0.010 0. 002 0.010 0.002 0.011 0.002 0.009 0. 002 0.012 0.002 0.011 0.002 03/28/23 0.013 0.002 0.012 0. 002 0.015 0. 002 0.013 0.002 0. 016 0.002 0.013 0. 002 0.013 0.002 0.015 0.002

04/11/23 0.017 0.002 0. 016 0. 002 0.018 0.002 0.022 0.003 0.020 0.002 0.018 0.002 0. 018 0. 002 0.021 0.002 04/25/23 0.014 0. 002 0.014 0.002 0.013 0. 002 0.012 0.002 0.012 0.002 0.013 0. 002 0.013 0. 002 0.013 0.002

05/09/23 0.008 0.002 0.008 0.002 0.008 0.002 0.007 0.002 0. 005 0.002 0.008 0. 002 0.007 0. 002 0.007 0. 002 05/23/23 0. 011 0.002 0. 012 0.002 0.013 0.002 0.012 0.002 0.012 0.002 0.012 0.002 0.013 0. 002 0.013 0.002

06/06/23 0.008 0.001 0.008 0.002 0.008 0.001 0.006 0.001 0. 007 0. 001 0.007 0. 002 0.008 0.001 0.008 0.001 06/20/23 0.011 0.002 0.010 0.002 0.013 0.002 0.011 0.002 0.012 0.002 0.011 0. 002 0. 011 0. 002 0.011 0.002

07/05/23 0.009 0.002 0.010 0.002 0.009 0.001 0.009 0.002 0. 009 0.001 0.010 0. 002 0. 006 0. 001 0.010 0.002 07/18/23 0.015 0.002 0.015 0.002 0.015 0. 002 0. 018 0.002 0.016 0.002 0.019 0.003 0.016 0.002 0.018 0. 002

08/01/23 0.017 0.002 0.018 0.002 0.014 0. 002 0. 016 0.002 0.015 0.002 0.016 0. 002 0.017 0. 002 0.015 0.002 08/15/23 0.014 0.002 0.015 0.002 0. 015 0.002 0.014 0.002 0. 015 0. 002 0.015 0.002 0.013 0. 002 0.015 0.002 08/29/23 0.013 0.002 0.015 0.002 0.014 0.002 0.014 0.002 0.013 0. 002 0.013 0.002 0.013 0. 002 0.012 0.002

09/12/23 0.030 0. 003 0. 029 0.003 0.029 0.003 0.028 0.003 0.029 0.003 0.029 0.003 0.030 0.003 0.027 0.003 09/26/23 0.012 0.002 0.012 0.002 0.013 0. 002 0. 014 0. 002 0.012 0. 002 0.010 0.002 0.012 0.002 0.012 0.002

10/11/23 0.020 0.002 0.017 0. 002 0.019 0. 002 0. 019 0. 002 0.019 0.002 0.018 0.002 0.019 0.002 0.019 0.002 10/24/23 0.010 0.002 0.010 0. 002 0. 011 0.002 0.008 0.002 0.011 0. 002 0.010 0. 002 0. 010 0.002 0.010 0.002

11/07/23 0.019 0.002 0. 021 0.002 0.022 0.002 0.020 0.002 0.020 0. 002 0.022 0.002 0.020 0. 002 0.021 0.002 11/20/23 0.016 0.002 0.018 0.002 0.018 0.002 0.015 0.002 0.017 0.002 0.017 0.002 0. 018 0.002 0.021 0.002

12/05/23 0.017 0.002 0.016 0. 002 0. 017 0.002 0.017 0.002 0. 016 0.002 0.015 0. 002 0.015 0.002 0. 016 0.002 12/20/23 0.017 0.002 0.018 0. 002 0. 016 0.002 0.016 0.002 0.016 0. 002 0.018 0.002 0.017 0.002 0.016 0. 002 01/02/24 0.010 0. 002 0.012 0.002 0.012 0.002 0. 009 0. 002 0.010 0.002 0.009 0.002 0.012 0. 002 0.011 0.002

C= Control location, Background location 3-9 Dominion Energy Nuclear Connecticut, Inc. Annual Radiological Environmental Millstone Power Station Operating Report 2023

TABLE 3 AIRBORNE IODINE (pCi/m 3 )

LOCATIONS PERIOD ENDING 1 2 3 4 10 11 27 15C

(+/-) (+/-) (+/-) (+/-) (+/-) (+/ -) (+/-) (+/ -)

01/17/23 -0.005 0.030 -0.004 0.025 -0.004 0.025 -0.004 0.025 -0. 013 0.018 -0. 014 0.019 -0.014 0. 019 -0.008 0. 011 01/31/23 -0. 002 0. 025 -0. 002 0. 020 -0.002 0. 022 -0. 002 0. 021 -0. 007 0. 015 -0. 008 0. 016 -0.008 0. 016 -0.003 0. 007

02/14/23 -0. 005 0.013 -0. 004 0. 010 -0. 004 0.011 -0. 004 0. 012 -0.008 0.011 -0.008 0. 011 -0.008 0. 011 -0.007 0. 010 02/27/23 -0.012 0.026 -0.009 0. 019 -0.011 0.022 -0.011 0. 022 -0. 007 0. 027 -0.007 0. 028 -0.007 0. 029 -0. 003 0. 011

03/13/23 0.042 0.031 0.033 0. 025 0. 038. 0.028 0. 038 0. 028 -0. 013 0. 023 -0.014 0. 025 -0.013 0. 023 -0.013 0.022 03/28/23 -0.004 0.018 -0. 003 0. 016 -0.004 0.018 -0. 004 0. 017 -0.006 0. 016 -0. 006 0. 017 -0.002 0. 006 -0. 006 0. 015

04/11/23 -0. 014 0.023 -0. 012 0. 019 -0.014 0.022 -0.007 0. 012 -0.005 0.022 -0. 005 0. 025 -0. 002 0.009 -0. 005 0. 022 04/25/23 0.005 0.022 0. 005 0. 022 0. 005 0.021 0. 004 0. 017 -0. 008 0.023 -0. 009 0.025 -0. 008 0.022 -0. 008 0.023

05 /09/23 -0.015 0.022 -0. 017 0.024 -0.015 0.022 -0. 016 0. 023 -0. 004 0.018 -0. 004 0. 019 -0.004 0. 017 -0.004 0. 018 05/23/23 -0.002 0. 019 -0.002 0.022 -0.002 0. 019 -0. 002 0. 020 0. 003 0.019 0.003 0. 020 0.003 0.017 0. 003 0.018

06/06/23 -0. 009 0.017 -0. 010 0. 021 -0.009 0. 018 -0.009 0. 018 -0.007 0. 021 -0.008 0.023 -0. 006 0.018 -0. 007 0.020 06/20/23 -0. 011 0.023 -0. 013 0. 027 -0.011 0. 023 -0.011 0. 024 -0. 004 0.020 -0.005 0. 023 -0. 004 0.020 -0. 004 0. 019

07/05/23 -0. 009 0. 022 -0. 011 0. 026 -0.009 0. 021 -0.009 0.022 0. 004 0. 012 0. 005 0. 014 0. 004 0.012 0. 002 0.005 07/18/23 0. 000 0. 011 0. 000 0. 012 0. 000 0. 011 0. 000 0. 011 -0.004 0. 007 -0. 005 0. 009 -0. 004 0. 007 -0. 004 0. 007

08 /01 /23 0.004 0.016 0.005 0. 017 0. 005 0.017 0. 005 0.017 -0. 006 0. 016 -0. 008 0.019 -0. 006 0. 016 -0. 006 0. 016 08/15/23 0.010 0.023 0.010 0. 025 0. 011 0. 025 0. 010 0. 025 -0. 012 0. 021 -0.014 0.025 -0. 012 0.022 -0. 012 0. 022 08/29 /23 -0.009 0. 011 -0.010 0. 012 -0. 010 0. 012 -0.010 0.012 0.018 0. 018 0. 022 0. 022 0. 017 0.018 0. 018 0. 019

09/12/23 0. 000 0. 018 0.000 0. 019 0.000 0.019 0. 000 0. 019 -0. 007 0. 008 -0. 016 0. 018 -0.014 0. 015 -0.014 0.015 09/26/23 0. 003 0. 011 0.003 0. 011 0.003 0.012 0. 003 0. 011 -0. 003 0.018 -0. 004 0. 023 -0.003 0.018 -0.003 0.019

10/11/23 0. 006 0. 011 0. 006 0. 011 0. 006 0. 012 0.006 0. 012 0. 004 0.012 0. 005 0. 015 0.004 0. 012 0.004 0. 012 10/24/23 0. 009 0.011 0.010 0.012 0. 010 0.012 0.011 0. 012 0. 003 0.009 0. 003 0. 010 0.003 0. 009 0.003 0. 010

11 /07/23 0.007 0.019 0.008 0. 020 0.008 0. 021 0. 008 0. 021 -0.011 0. 02 3 -0. 011 0. 023 -0. 011 0.023 -0. 012 0.024 11/20/23 -0.002 0.019 -0.002 0. 020 -0. 002 0.021 -0. 002 0. 021 -0. 008 0. 018 -0. 008 0. 018 -0. 008 0.018 -0. 008 0. 019

12/05/23 -0.006 0.012 -0.006 0. 013 -0. 007 0. 014 -0. 006 0. 013 -0.001 0. 012 -0. 001 0.012 -0.001 0.012 -0. 001 0.012 12/20 /23 -0.008 0.012 -0.009 0. 013 -0.009 0. 013 -0. 009 0. 013 -0.010 0. 019 -0. 010 0.019 -0.010 0.019 -0. 010 0.019 01 /02/24 -0.001 0.018 -0.001 0. 020 -0.001 0. 021 -0. 001 0. 020 -0.009 0. 015 -0. 009 0.015 -0.009 0.015 -0. 009 0.015

C= Control location, Background location

3-1 0 Dominion Energy Nuclear Connect icut, Inc. Annual Radiological Environmental Millstone Power Station Operating Report 2023

TABLE 4 AIR PARTICULATES (pCi/m 3 )

GAMMA SPECTRA - QTR 1 (01/03/23 - 03/28/23)

LOCATION Sr-89 Sr-90 Be-7 Mn-54 Co-58 Co-60 Zn-65

(+/- ) (+/- ) (+/-) (+/ -) (+/-) (+/- ) (+ / -)

0. 0079 0. 0136 0.0005 0. 0021 0.1060 0.0330 -0. 0006 0. 0016 -0. 0005 0. 0022 -0. 0012 0. 00 18 -0. 0010 0.0046 2 0. 0121 0. 0122 -0. 0014 0.0015 0.0787 0.0232 0. 0012 0. 0010 -0. 0007 0. 001 7 0. 0005 0. 0009 -0. 0012 0. 0033 3 0. 0055 0. 0108 0. 0004 0.0014 0.0901 0.0268 0. 0002 0. 0011 0.0012 0. 0018 0. 0004 0. 00 10 0.0023 0.0028 4 -0. 0035 0. 0076 0.0018 0. 0016 0.1036 0.0339 -0.0005 0.0017 0.0002 0. 0027 0. 0003 0. 00 18 0. 0010 0. 0024 10 0. 0026 0. 0107 0. 0003 0.0015 0.0737 0.0347 -0. 0008 0. 0017 -0. 0014 0. 0023 -0. 0009 0. 0017 0. 0033 0.0037 11 -0. 0058 0. 0090 0. 0011 0. 00 19 0.0930 0.0322 -0. 0004 0.0010 -0. 0003 0. 0016 -0. 0004 0. 0011 -0.0016 0.0027 27 -0. 0140 0.0129 0. 0008 0. 0021 0.0894 0.0302 -0. 0006 0.0013 -0. 0004 0. 0019 0. 0004 0.0016 -0. 0014 0. 0031 15C 0. 0095 0. 0119 0. 0004 0.0017 0.0758 0.0250 0. 0002 0. 0010 -0. 0003 0. 0014 -0. 0002 0.0012 -0. 0009 0. 0027

LOCATION Nb-95 Zr-95 Ru-103 Ru-106 Cs-134 Cs-137 Ba-140

~ (+/-) (+/-) (+/- ) (+/-) (+/-) (+/ -)

-0. 0003 0. 0028 0. 0039 0.0049 0.0014 0. 0046 0. 00 13 0. 0158 -0. 0005 0. 0018 0.0006 0.0016 -0. 0028 0. 1372 2 0. 0005 0. 001 2 -0. 0004 0.0027 -0.0015 0.0023 -0. 0016 0. 0 1 01 -0. 0017 0. 0012 -0. 0001 0. 0008 -0. 0054 0. 0812 3 0. 0013 0. 0021 -0. 0009 0. 0030 -0.0004 0. 0023 0. 0048 0.0085 0. 0000 0. 0010 0. 0003 0. 0009 0. 0079 0. 0791 4 -0.0020 0. 0027 0. 0003 0. 0042 0.0028 0.0040 -0. 0029 0. 0127 -0.0006 0. 0016 -0. 0001 0. 0013 0. 0092 0. 13 27 10 0.0018 0. 0023 0. 0006 0. 0046 -0. 0125 0. 0044 -0. 0100 0.0145 -0. 0003 0. 0014 0. 0000 0. 0013 -0. 0224 0. 1311 11 0. 0002 0. 0019 0.0003 0. 0035 -0. 0002 0. 0027 -0. 0015 0.0089 -0.0001 0. 0010 -0. 0006 0. 0011 -0. 0437 0. 1 100 27 -0. 0025 0. 0022 0. 0018 0.0036 -0. 0001 0. 0031 -0. 0132 0.0128 -0.0006 0.0012 -0. 0002 0. 0012 0. 0087 0.1431 15C 0.0023 0. 0020 -0. 0006 0. 0035 0.0001 0. 0026 0. 0065 0. 0089 0. 0009 0.0010 -0. 0003 0. 0010 -0. 0675 0.0933

LOCATION Ce-141 Ce-144

(+/-) (+ /- )

-0. 0010 0. 0060 -0. 0016 0. 0085 2 0.0022 0. 0034 -0. 0070 0. 0042 3 -0.0019 0. 0036 -0. 0026 0. 0045 4 0.0004 0. 0058 -0. 0096 0. 0075 10 -0. 0020 0. 0053 -0.0014 0. 0067 11 0. 0003 0. 0041 -0. 0028 0. 0054 27 -0. 0026 0. 0044 0. 0022 0. 0053 15C 0. 0000 0.0039 -0. 0007 0. 0049

C= Control location, Background location Results in bold type are positi1.e.

3-11 Dominion Energy Nuclear Connecticut, Inc. Annual Radiological Environmental Millstone Power Station Operating Report 2023

TABLE4 AIR PARTICULATES (pCi/m 3 )

GAMMA SPECTRA - QTR 2 (03/28/23 - 07/05/23)

LOCATION Sr-89 Sr-90 Be-7 Mn-54 Co-58 Co-60 Zn-65

(+/-) (+/-) (+/-) (+/-) (+/-) (+/-) (+/-)

-0.0025 0. 0073 -0.0010 0. 0014 0. 0994 0.0247 -0.0008 0. 0008 0. 0004 0. 0017 0.0005 0.0008 -0. 0008 0.0027 2 -0. 0012 0.0103 0. 0015 0. 0025 0.0951 0.0211 0.0006 0.0009 -0.0015 0. 0016 0. 0000 0. 0008 -0.0014 0. 0021 3 -0.0096 0.0079 0. 0000 0. 0014 0.0893 0.0195 0. 0000 0. 0013 0. 0003 0.0015 0. 0002 0. 0011 0. 0019 0.0028 4 -0. 0040 0. 0079 -0.0008 0. 0014 0.0666 0.0208 -0.0005 0. 0012 -0.0004 0.0017 -0. 0007 0. 0011 -0. 0006 0. 0029 10 -0. 0001 0. 0077 -0. 0010 0.0012 0.0930 0.0282 -0.0003 0. 0011 0. 0005 0. 0015 0.0000 0. 0011 -0. 0003 0. 0024 11 -0. 0068 0. 0072 -0. 0006 0. 0014 0.1199 0.0317 0. 0004 0. 0014 -0.0005 0.0019 -0. 0001 0. 0015 0. 0026 0. 0030 27 0.0009 0.0085 -0. 0011 0.0010 0.0950 0.0290 -0. 0005 0.0010 0. 0012 0. 0018 0.0004 0. 0011 0. 0010 0.0021 15C 0.0028 0.0098 -0. 0001 0. 0014 0.0985 0.0292 -0. 0005 0. 0012 -0. 0007 0. 0018 0.0003 0.0011 -0.0008 0.0028

LOCATION Nb-95 Zr-95 Ru-103 Ru-106 Cs-134 Cs-137 Ba-140

(+/-) (+/-) (+/-) (+/-) (+/-) (+/-) (+/-)

0.0001 0. 0014 0. 0012 0. 0025 0. 0005 0. 0020 -0. 0034 0. 0069 0.0002 0. 0010 -0. 0001 0. 0006 -0.0326 0. 0872 2 0. 0004 0. 0016 -0. 0004 0. 0023 0.0000 0.0020 -0. 0037 0. 0087 0. 0000 0. 0009 0. 0000 0. 0008 0.0360 0.0891 3 0. 0011 0. 0019 0. 0026 0. 0035 -0.0021 0. 0030 -0. 0028 0. 0108 -0. 0003 0. 0012 -0. 0002 0.0011 -0.0697 0.1 015 4 0. 0001 0.00 17 0. 0012 0. 0034 -0.0017 0. 0029 -0. 0055 0.0106 -0.0002 0. 0012 0. 0003 0. 0011 0.0161 0. 1052 10 0.0010 0.0015 -0. 0003 0. 0031 0.0013 0. 0023 0.0016 0.0084 0.0008 0. 0011 -0. 0003 0. 0008 -0.0104 0. 0850 11 -0.0014 0. 0024 0. 0026 0. 0037 0.0027 0. 0033 0.0073 0. 0125 0. 0006 0. 0017 -0.0009 0. 0014 0. 0348 0. 1203 27 0. 0017 0. 0018 0. 0012 0.0035 0. 0018 0.0029 -0.01 15 0. 0105 -0. 0004 0.0012 -0.0006 0.0011 -0. 0104 0. 1163 15C 0. 0005 0. 0020 0.0022 0. 0037 -0. 0018 0. 0029 0. 0057 0. 0103 -0.0010 0. 0013 0. 0006 0.0010 0. 0062 0.1318

LOCATION Ce-141 Ce-144

(+/-) (+/-)

0. 0001 0.0027 0. 0003 0. 0034 2 -0.0007 0. 0031 0. 0025 0. 0033 3 0.0031 0.0037 0. 0009 0. 0044 4 -0. 0011 0.0042 0. 0001 0. 0054 10 0.0003 0. 0033 0. 0030 0. 0038 11 0. 0015 0. 0047 -0. 0001 0. 0058 27 -0. 0024 0. 0044 -0. 0012 0. 0054 15C -0.0046 0. 0047 -0.0001 0. 0059

C= Control location, Background location Results in bold type are positi...e.

3-12 Dominion Energy Nuclear Connecticut, Inc. Annual Radiological Environmental Millstone Power Station Operating Report 2023

TABLE 4 AIR PARTICULATES (pCi/m 3 )

GAMMA SPECTRA - QTR 3 (07/05/23 - 09/26/23)

LOCATION Sr-89 Sr-90 Be-7 Mn-54 Co-58 Co-60 Zn-65

(+/-) (+/-) (+/-) (+/-) (+/-) (+/-) (+/ -)

1 0. 0134 0. 0138 -0. 0006 0. 0021 0.1072 0.0235 0.0000 0. 0008 0. 0003 0.0009 -0.0003 0. 0008 -0. 0015 0.0022 2 0. 0045 0. 0143 0. 0015 0. 0033 0.0965 0.0222 0.0008 0. 0010 -0. 0002 0.0009 0.0002 0. 0007 -0. 0009 0.0015 3 0.0041 0.0156 -0. 0021 0. 0030 0.1101 0.0269 0. 0001 0. 0009 0. 0002 0.0014 0. 0009 0. 001 1 -0. 0006 0.0020 4 0. 0266 0.0195 0. 0015 0. 0028 0.0895 0.0279 -0. 0007 0. 0010 -0. 0005 0.0011 0. 0002 0. 0010 -0. 0011 0. 0025 10 0. 0053 0.0127 -0. 0006 0.0022 0.1191 0.0272 0. 0000 0. 0010 -0. 0001 0. 0012 0. 0004 0.0012 -0. 0006 0. 0025 11 0. 0065 0. 0126 0. 0018 0.0027 0.0972 0.0399 -0. 0007 0.0011 0. 0016 0.0019 0.0005 0.0011 0.0011 0. 0028 27 0. 0057 0.0138 0. 0040 0.0032 0.0727 0.0245 -0. 0004 0. 0013 -0. 0013 0.0015 0. 0002 0. 0014 -0. 0017 0. 0020 15C 0. 0010 0. 0146 0. 0012 0. 0026 0.1023 0.0235 -0. 0001 0.0008 -0. 0007 0.0010 0. 0002 0.0009 -0. 0015 0.0020

LOCATION Nb-95 --- Zr-95 Ru-103 Ru-106 Cs-134 Cs-137 Ba-140

(+/-) (+ / -) (+/-) (+/-) (+ / -) (+/-) (+/ -)

1 -0. 0009 0. 0012 -0. 0015 0.0017 0.0004 0.0012 -0. 0041 0.0070 0.0000 0. 0007 0. 0005 0. 0007 0. 0677 0. 0414 2 0. 0007 0. 0014 -0. 0005 0. 0015 0.0017 0.0015 -0.003 7 0.0078 0.0006 0. 0009 0. 0000 0.0006 0. 0159 0. 0456 3 -0.0005 0. 0014 0. 0008 0. 0026 -0. 0005 0. 0018 -0. 0012 0.0067 -0. 0003 0.0006 -0.0001 0.0009 0. 0156 0. 0556 4 -0.0001 0.0012 -0. 0011 0. 0022 -0. 0001 0. 0016 -0. 0006 0.0063 -0. 0001 0.0010 0. 0004 0.0007 -0. 0050 0. 0604 10 -0.0013 0.0016 0. 0019 0. 0027 0. 0022 0. 0025 0. 0005 0.0102 -0. 0004 0.0011 -0.0008 0.0010 0. 0237 0. 0734 1 1 0. 0014 0. 0018 0. 0000 0.0033 0.0011 0. 0026 -0.0064 0. 0102 -0. 0003 0. 0009 -0. 0004 0. 0011 0. 0275 0.0826 27 -0. 0003 0. 0014 -0. 0013 0.0026 0.0012 0.0021 -0. 0016 0. 0084 -0. 0009 0. 0009 0. 0007 0. 0009 -0. 0018 0.0795 15C 0.0010 0.0013 0. 0000 0. 0022 0. 0008 0. 0016 0. 0006 0.0055 -0. 0001 0. 0008 -0. 0001 0. 0006 0. 0121 0. 0645

LOCATION Ce-141 Ce-144

(+/-) (+/-)

0. 0004 0. 0019 0.0005 0.0028 2 -0. 0005 0. 0022 0.0008 0.0032 3 0. 0009 0.0021 -0. 0017 0. 0032 4 -0. 0011 0.0023 -0. 0021 0. 0030 10 -0.0003 0.0031 -0. 0025 0. 0038 11 -0. 0001 0. 0032 -0.0005 0. 0055 27 -0. 0011 0. 0029 -0. 0004 0.0047 15C 0. 0007 0. 0019 -0. 0003 0.0029

C= Control locat ion, Background location Results in bold type are positive.

3-13 Dominion Energy Nuclear Connecticut, Inc. Annual Radiological Environmental Millstone Power Station Operating Report 2023

TABLE 4 AIR PARTICULATES (pCi/m 3 )

GAMMA SPECTRA - QTR 4 (09/26/23 - 01/02/24)

LOCATION Sr~9 Sr-90 Be-7 Mn-54 Co-58 Co-60 Zn-65

(+/-) (+/-) (+/-) (+/-) (+/-) (+/-) (+/-)

0.0083 0. 0134 0. 0022 0. 0039 0.0718 0.0165 0. 0001 0.0011 0. 0010 0.0013 0.0005 0.0009 0. 0011 0. 0020 2 0.0057 0. 0126 0.0023 0. 0032 0.0591 0.0187 -0. 0004 0. 0012 -0. 0002 0.0015 -0. 0002 0. 0008 0. 0000 0. 0021 3 0. 0215 0. 0164 0. 0021 0. 0028 0.0726 0. 0252 -0. 0010 0. 0015 0. 0019 0.0022 0. 0002 0.0015 0. 0032 0. 0041 4 0. 0093 0.0139 -0.0001 0. 0025 0.0668 0.0204 0.0004 0.0009 -0.0001 0. 0014 -0.0003 0. 0010 0.0003 0.0027 10 -0.0022 0.0083 0. 0037 0. 0031 0.0740 0. 0181 -0.0012 0.0012 -0.0008 0.0014 -0.0007 0.0011 -0.0001 0. 0026 11 -0. 0055 0. 0095 0. 0015 0.0029 0.0675 0. 0175 -0. 0003 0. 0008 0.0003 0. 0011 -0. 0002 0. 0009 0.0011 0. 0018 27 -0. 0007 0.0077 0.0006 0.0024 0.0547 0. 0217 -0.0002 0.0009 -0. 0003 0. 0012 0.0010 0. 0009 0. 0002 0. 0019 15C -0. 0015 0. 0086 -0. 0005 0. 0018 0.0548 0.0164 -0.0001 0.0010 -0. 0004 0. 0012 -0. 0001 0. 0009 -0. 0006 0.0022

LOCATION Nb-95 Zr-95 Ru-103 Ru -106 Cs-134 Cs-137 Ba-140

(+/-) (+/-) (+/-) (+/-) (+/-) (+/-) (+/-)

0.0007 0. 0013 0.0002 0. 0023 -0.0005 0. 0016 0. 0015 0. 0075 0. 0002 0. 0009 -0.0002 0. 0008 -0.0249 0.0483 2 -0. 0004 0. 0016 0. 0010 0. 0029 -0.0025 0. 0021 0. 0026 0. 0082 -0. 0009 0.0012 -0.0003 0.0009 0. 0438 0. 0623 3 -0.0013 0. 0023 0.0042 0. 0045 -0. 0013 0. 0032 -0. 0079 0. 0111 -0. 0005 0. 0013 0. 0000 0. 0013 0. 0568 0.0969 4 0. 0006 0. 0016 0. 0002 0. 0025 -0. 0004 0. 0021 0. 0024 0. 0091 0. 0001 0. 0010 0. 0002 0. 0009 0.0719 0. 0667 10 0. 0008 0.0017 0.0010 0. 0030 0. 0015 0. 0025 0.0020 0.0097 -0. 0002 0. 0010 -0.0004 0. 0011 0. 0943 0. 0792 11 0. 0005 0. 0012 -0. 0015 0. 0021 -0.0009 0. 0014 -0.0021 0. 0070 0. 0000 0. 0007 -0. 0004 0. 0008 0. 0307 0. 0483 27 -0. 0004 0.0014 0. 0004 0. 0026 0.0005 0.0019 -0. 0004 0.0083 -0. 0001 0. 0008 0. 0003 0.0007 0.0261 0.0595 15C 0. 0006 0. 0012 0. 0000 0. 0021 0.0008 0. 0019 0.0027 0.0070 -0. 0002 0. 0009 -0.0006 0. 0008 -0. 0388 0. 0447

LOCATION Ce-141 Ce-144

(+/-) (+/-)

1 -0. 0007 0. 0025 -0.0022 0. 0035 2 0. 0031 0. 0027 0. 0024 0. 0037 3 -0. 0017 0. 0039 -0. 0013 0. 0053 4 -0. 0007 0. 0029 0. 0008 0. 0045 10 0. 0006 0.0040 0.0027 0. 0058 11 -0. 0018 0. 0023 0. 0009 0.0035 27 -0. 0001 0.0020 0. 0021 0. 0033 15C -0. 0015 0. 0026 -0.0023 0.0038

C= Control location, Background location Results in bo ld type are positi1.e.

3-14 Dominion Energy Nuclear Connecticut, Inc. Annual Radiological Environmental Millstone Powe r Station Operating Report 2023

TABLE 5 SOIL (pCi/g dry wt.)

LOCATIONS COLLECTION LOCATION DATE Be-7 K-40 Cr-51 Mn-54 Co-58 Fe-59

(+/-) (+ / -) (+ / -) (+ / -) (+/-) (+/- )

3 05/09/23 0.189 0. 336 18.330 2.378 -0.312 0.396 0. 022 0.055 -0.028 0. 050 -0.114 0. 100 4 05/09/23 0. 170 0.494 11.890 1.880 -0.259 0.473 -0. 022 0. 063 -0. 019 0.056 -0. 116 0. 118 14C 05/09/23 0.442 0. 324 21.020 2. 160 0. 113 0.326 0. 021 0. 042 -0. 002 0. 043 0. 013 0. 109

COLLECTION LOCATION --- DATE Co-o0 Zn-o5 Nb-95 Zr-95 Ru-103 Ru-106

(+/-) (+/ -) (+/- ) (+/ - ) (+/-) (+/-)

3 05/09/23 -0. 003 0. 047 -0. 120 0. 131 -0. 024 0. 064 -0. 029 0.100 -0. 001 0.048 0. 180 0.451 4 05/09/23 -0.017 0. 074 -0. 152 0. 154 0. 002 0. 063 0. 016 0. 095 0. 070 0. 057 -0. 007 0. 541 14C 05/09/23 0.008 0.048 -0.181 0. 112 -0.005 0. 049 0. 083 0. 079 -0. 010 0. 040 0. 069 0. 352

COLLECT ION LOCATION DATE Sb-125 Cs-134 Cs-137 Ce-141 Ce-144 Ac-228

(+/ - ) (+ / -) (+/- ) (+ / -) (+ / -) (+/-)

3 05/09/23 -0.092 0. 100 0. 012 0. 053 0. 099 0. 064 0. 043 0. 064 -0. 00 3 0. 254 0.673 0.280 4 05/09/23 0. 078 0. 144 0. 072 0.067 0.281 0.140 0. 006 0. 077 -0. 258 0. 339 1.097 0.322 14C 05/09/23 -0. 013 0. 113 0. 049 0. 049 0. 006 0. 044 0. 021 0.057 0. 019 0. 214 1.400 0.268

C= Control location, Background location Results in bold type a re positi1.e.

3-15 Dominion Energy Nuclear Connecticut, Inc. Annual Radiological Environmental Millstone Power Station Operating Report 2023

TABLE 6 MILK (pCi/1)

COLLECTION LOCATION DATE 1-131 Sr-89 Sr-90 K-40 Cs-134 Cs-137 Ba-140 La-140

(+/-) (+/-) (+/ - ) (+/ - ) (+/-) (+/-) (+/-) (+/- )

22 Cow

Milk was not available for collection in 2023.

Strontium analysis of air samples was performed as a substitute (Table 4)

23 Goat

3-16 Dominion Energy Nuclear Connecticut, Inc. Annual Radiological Environmental Millstone Power Station Operating Report 2023

TABLE 7 WELL WATER (pCi/1)

COLLECTION LOCATION DATE H-3 Be-7 K-40 Cr-51 Mn-54 Co-58 Fe-59 Co-60

~ (+/-) (+/-) (+/-) (+/-) (+/-) (+/-) (+/-)

71 02/27/23 209 654 29.3 41.9 -36.6 67.1 -41.1 43.3 -2.98 4. 39 2.43 4.47 7.10 9.62 2.56 4.45 06/06/23 -253 581 30.1 31.2 -15.7 42.9 -5.46 33.5 0. 85 3.24 -2.05 3.23 1.43 6.00 0.57 3. 10 09/07/23 0 724 7.38 26.7 7.11 45.0 -29.6 33.9 0.39 3. 10 0.81 3.00 -1.86 6.39 -0.42 3. 10 11/27/23 -102 799 2.24 29.7 -25.0 40.9 -14.6 30.7 0.81 3. 15 -1.14 3.37 -3. 56 4.89 -0.87 3.26

72 02/27/23 209 655 -8.31 34.8 57.3 65.8 -13.8 31.8 -0.94 3.35 1.10 3.38 -0.95 7.80 0.94 2.84 06/05/23 278 619 -13.2 24.3 -31.7 48.2 5. 03 32.6 0.24 2.87 0.41 2.77 1.02 6.88 1.34 3.21 09/27/23 -148 716 10.9 20.6 34.4 36.6 -16.2 23.9 1.76 2.25 -1.09 2.34 1.96 4.67 1.99 2.32 12/04/23 38 778 -7. 37 32.9 -8.21 67.1 -6. 01 38.8 1.40 4. 95 -1.24 4.00 4.45 8.84 -1.99 5.87

76 02/21/23 178 631 -18. 0 23.7 6.99 41.6 -20.3 22.6 -0.20 2.94 -1.91 2.84 1. 04 4.85 3.30 3.09 05/30/23 240 617 -37. 8 36.0 -22.5 46.0 -14.4 33.3 -3.41 4. 00 -0.12 3.71 -5. 13 6.59 1.13 4.78 08/22/23 425 779 -4. 80 35.9 16.2 72.5 17.9 33.8 -0.33 4.45 -2.54 3.94 -0. 80 7.47 2.40 4.57 11/14/23 108 752 9.63 33.8 -14.9 66.5 -12.7 41.8 -0.33 3.76 -3.08 4. 10 4.44 8.17 0.65 4.32

77 02/21/23 127 627 -9.34 25.8 -36.8 41.6 -7.99 26.7 -0.90 2.79 -2.04 2.68 -3. 86 5. 3 1.55 2.79 05/30/23 -13 600 -4. 76 40.8 14. 1 73.3 -7.15 47.1 3.45 4.40 -5.77 4.91 1. 82 8. 52 0.84 5.36 08/22/23 66 755 31.4 44.3 -4.37 71.8 -34.0 54.3 -0.42 5.38 -4. 19 4.97 -3.63 10. 1 -0. 98 5.37 11/14/23 91 745 -9. 13 29.9 -12. 1 40.8 -30.6 35.8 -2.37 3.25 -4.34 4.04 -0.03 6.74 -1.23 3.34

78 02/21/23 25 620 14.5 35.4 7. 19 53.7 27.8 35.1 -0.07 3.92 -0.81 3.40 -2.70 7.53 0. 11 4. 15 05/30/23 171 613 31.6 33.4 -39.9 62.2 25.4 36.4 0.35 4.38 -4.01 4.09 2.48 7.92 0.46 4.40 08/22/23 -376 740 7. 97 39.6 -53.7 59.7 16.2 46.4 -1.50 3.83 2.10 4.72 4.69 8.86 1.46 3.64 11/14/23 355 762 17.5 34.2 22.5 54.5 -11. 7 37.4 -0.07 4.10 -0.29 3.98 -0.78 7.79 -1.68 4.00

79 02/27/23 -146 630 11.3 32.9 -39.6 56.4 -1.63 41.3 -1.18 3. 38 -0.55 3.65 -0.35 7.52 -3.95 3.30 06/12/23 70 605 16.8 38.1 25. 7 67.1 -23.3 47.3 -2.27 4. 58 -4.80 4.26 12.5 8.35 5.45 4.67 09/26/23 216 729 18.1 43.0 19.2 63.5 -0.27 42.0 -0.49 4.27 -0.68 3.96 -1.26 8.34 1.63 4.86 11/27/23 -443 776 6.57 30.7 -12.9 51.8 9.03 34.7 2.03 4.20 -1.66 3.84 -4.28 7.24 -0.67 4. 30

81 02/27/23 476 672 -7.84 38.1 10.42 57.2 38.2 38.3 -2.23 4.66 0.79 3.72 -5.1 2 8.13 -1.30 4.25 06/06/23 392 626 -3.76 26.6 -9.35 39.2 -23. 1 33. 8 0.64 2.92 -0.59 2.99 4.38 5.20 1.86 2.95 09/06/23 409 749 -1. 15 25.7 21.1 40.7 -14.2 30.2 1. 80 2. 75 -1. 50 2.85 -0.61 5.91 -1.42 3.26 10/17/23 112 754 1.88 38.0 3.24 66.8 11.3 38.1 -2.25 4.36 0. 81 4.47 4.26 8.31 -0.18 4.44

82 01 /26/23 400 600 -19.1 30.3 15.2 41.1 -37. 7 38.5 -0. 97 3.44 -2.70 3.68 1.21 6.87 -0.76 3.78 05/17/23 -19 619 -13.6 32.4 26.3 45.0 -18. 3 39.1 -1.65 3. 83 -4.15 4.08 7.66 6.98 -0.47 3.79 07/18/23 -113 513 -4.59 13.0 0.82 30.0 -8.56 14.6 -2. 19 1.5 1 -1. 95 1.55 -1.11 3.26 0.09 1.8 1 10/16/23 -116 736 -6.15 30.9 -3.1 2 49.5 -34.2 33.6 -2.24 3.70 -0.03 3.71 -1.51 7.36 1.27 3.64

83 03/21/23 -57 611 17.8 32.1 0.32 42.8 -0.21 36. 1 0.27 4. 10 -2.61 3.99 -4.24 5.30 1.10 3.99 05/25/23 -354 611 -1. 17 10.3 6.67 21.3 0.71 12.8 0. 14 1. 01 0.11 1.13 3.71 2.46 0.81 1.05 09/05/23 43 736 13.3 21.6 16.2 31.9 10. 8 30.3 0.31 2.63 -0.52 2.18 -0.54 5.42 -0.35 2.69 10/18/23 11 740 6. 10 38. 9 70.3 74.6 4.67 41. 9 -2. 36 4. 14 -1.00 4. 11 0. 30 7.59 2.13 3.92

3-17 Dominion Energy Nuclear Connecticut, Inc. Annual Radiological Environmental Millstone Power Station Operating Report 2023

TABLE 7 WELL WATER (pCi/1)

COLLECTION LOCATION DATE Zn-65 Nb-95 Zr-95 Ru-103 Ru-106 Sb-125 1-131 Cs-134

(+ / -) (+/ - ) (+ / -) (+ / -) (+ / -) (+ / -) (+ / -) (+ / -)

71 02/27/23 4.63 9.27 0.56 4.29 3.79 6.26 -3. 21 5.13 -2.26 38.6 -5.75 12.4 5.41 8.09 2.02 4.52 06/06/23 -7.48 6.47 -0.99 3. 16 -3.87 5.57 -3.37 3.66 12.2 27.3 -3.34 9.23 -5. 11 9.43 0. 04 3.57 09/07/23 -14. 0 7.77 3.31 3.44 -2.13 5.43 -0.70 3.71 -8.28 26. 9 3.58 9. 15 -1.75 8.90 -0.36 3.21 11 /27/23 -0.68 7. 16 -1.48 3.97 -2.00 5. 21 1.27 3.65 7.67 31.1 6.69 8.88 -1. 71 5.40 2.96 3.45

72 02/27/23 -3.58 8. 03 -2.22 5.22 -4. 73 5.86 -3.73 3.69 5.86 32.8 -0.04 9.67 -0.59 5.08 -1.60 4.19 06/05/23 -7.78 6.85 0.66 2.77 -1.50 5.93 -3.37 3.21 10.8 22.3 -2.45 7.39 -4.57 9.06 0.70 2. 83 09/27/23 -7. 51 5.49 3.47 2.42 -2.82 4.05 1. 06 2.54 -0.05 21.8 2. 18 6.90 2.81 3.8 3 -1. 15 2.48 12/04/23 -22.7 14. 0 -3.49 4.49 -1.72 7.59 -0.38 4.88 37.0 42.2 -7.45 12.4 0.46 5.68 0. 02 4. 51

76 02/21/23 3.05 7.53 0. 10 3.51 1.34 4. 88 -1.06 3.08 2.34 24.6 2.24 8. 0 -0.56 3.46 -3.52 3.27 05/30/23 -8.87 8.54 -2.67 4. 19 0.02 6. 73 -0.29 4.47 -21. 0 36.8 6.75 11. 1 -1.33 7.00 -3. 51 4.09 08/22/23 -20. 6 12. 9 -5.41 5. 15 -4.74 6.78 -4.77 4.28 5. 61 35. 3 5.47 11. 3 0. 17 6.37 3.03 4. 58 11 /14/23 -8.43 11. 3 -4. 01 4.47 -5. 13 6.32 2.24 4.11 -5. 61 36. 5 -6.59 9.47 -2.09 6. 08 0.06 3.86

77 02/21/23 -1.78 6.40 2. 12 3. 12 1.28 4.30 0.83 3.08 -16. 3 24. 7 0.27 8.37 1. 99 3.90 0.29 3.01 05/30/23 -0.25 11. 1 -11.4 5.56 0.94 8. 31 -0. 11 4.87 19. 2 37. 1 -8.84 13.5 1.96 8.23 3.87 5. 21 08/22/23 -40.8 16. 1 6.24 5.62 1.25 8.55 -2.26 5.51 33.9 47.2 -10.2 14. 2 -0.78 8. 97 -1. 18 5. 78 11/14/23 6.64 6.98 -2.77 5. 15 0.41 6. 12 0. 18 3.98 -10.8 31.7 12.7 10. 6 -1.61 6.55 -1.3 3 3. 61

78 02/21/23 -4.41 8. 15 -3.56 4.08 - 1.69 5. 91 -4.45 3.53 -23. 6 28. 8 -6. 76 10. 0 -2.84 5.92 -0.55 3.60 05/30/23 -2.42 7.59 -4.89 4.36 0.49 7.73 1.58 3.73 6.59 33.8 0.24 10. 1 -4.69 5.83 1.04 3.80 08/22/23 -10. 1 11.0 1.53 5.25 -0.86 8.26 -4.26 5.44 2.80 39.0 1. 97 13.8 -0.91 7.70 3.42 4.58 11/14/23 -10. 5 10. 6 3.07 4.31 4.95 7.08 -1. 16 4.27 -25. 0 35.4 7. 96 10.4 0.09 6.32 0.67 3.71

79 02/27/23 -21.5 9.60 0.84 4.15 -3.25 6.93 1.06 4.55 5.77 30. 6 2. 15 11.4 2. 09 7.65 -0.42 3.95 06/12/23 -6.45 10.8 3.66 4.39 -0. 01 7.73 -0.02 5.09 -25.7 34. 9 -6.45 13. 0 -0.61 8.61 -2. 11 5.36 09/26/23 3.73 9. 51 -0.73 4.48 3. 13 7.73 1.50 4.74 18.9 40.1 3.37 13.2 6.40 7.41 -3.12 4.02 11 /27/23 -5.53 11. 1 8.08 4.37 -1.50 5.56 -0.04 4. 11 8. 57 33. 7 4.68 10. 7 -2.24 7. 01 -2.54 4.00

81 02/27/23 -3.89 9.29 3.72 4.32 3.42 7.83 -0.40 4.27 20. 3 42. 1 4.44 12.2 0.92 7.54 1. 91 4.94 06/06/23 -14. 2 7.22 0.07 2.99 0.28 4.90 1.46 3.37 -7. 12 24.5 0.40 7.76 -7.28 9.42 2.68 3. 19 09/06/23 1.48 5.66 1.92 3.07 1.19 5.30 -3.34 3.33 1. 15 24.0 0.37 7.87 5.99 8.20 0. 94 3.01 10/17/23 5.05 9.22 -7. 0 1 5.36 -5.59 6.94 -1. 30 4.66 -18. 0 40. 7 -6.90 12. 1 2.82 7. 09 -0.05 3.88

82 01 /26/23 1. 71 7.40 7.35 4.52 -3.53 6. 17 -0.63 4.17 -14.1 30. 1 2.63 9.65 2.99 8.62 1.09 3.27 05/17/23 -0.56 8.00 6.65 4.83 -1.23 6.70 -0.40 4. 04 -2.17 30.4 -1.62 11.8 -3.23 8. 14 2.55 3.95 07/18/23 -0.92 3.76 4. 10 1.82 0.54 2.52 -2.44 1.69 2.37 13.4 -1. 03 4.26 -0. 08 3.32 0.72 1.59 10/16/23 4.93 7.75 4.27 3.72 -3.29 6.76 -0.62 4.08 10.4 27. 7 8.44 9.81 2.68 6.84 1.39 4. 01

83 03/21 /23 -23.6 10.6 0.82 4.62 0. 11 6.29 -1. 81 4.41 -12. 6 31. 7 4.70 9.92 -2.77 8.69 -0.29 3.66 05/25/23 -4. 10 2.22 1. 14 1.16 -0.76 1.95 -1. 81 1.39 1.27 9.24 -1. 11 2.90 3.60 4.80 0.05 1.13 09/05/23 -1.49 5.06 2.40 2.62 -3.69 3.90 -0.92 2.85 -3. 38 22.2 -1.79 7.16 2.94 7.49 1. 33 2.26 10/18/23 14. 6 10.8 7.30 4.65 -0.66 7.32 -0. 71 4.89 -10.2 37.4 1. 61 12.8 3.61 6.93 1.03 4.92

3-18 Dominion Energy Nuclear Connecticut, Inc. Annual Radiolog ical Environmental Millstone Power Station Operating Report 2023

TABLE 7 WELL WATER (pCi/1)

COLLECTION LOCATION DATE Cs-137 Ba-140 La-140 Ac-228 7 1 02/27/23 -1. 71 4. 84 -18.7 21.4 1.47 6.95 -1.50 14.5 ~ (+ / -) (+ / -) (+ /-)

06/06/23 2.45 3. 33 1.50 20.2 -4. 02 6. 65 -1. 31 11. 5 09/07/23 -2.94 3. 19 -13.5 20.2 -3.75 6.82 0.3 8 10.7 11 /27/23 -1.63 3.38 5.24 14.5 2.72 5.90 6.12 12. 1

72 02/27/23 -1.53 4.07 9.23 16.1 -0.04 6. 58 1.99 15. 2 06/05/23 0.75 2.58 -4. 91 20.6 1. 92 8. 55 1.64 10.3 09/27/23 -0.64 2. 54 -6. 87 10.4 -1.01 3.34 -1.26 9.4 12/04/23 -2. 71 5.22 -8. 97 18.6 0.37 6.02 -3.23 18.9

76 02/21/23 -3.54 3.23 1.33 11.4 3. 96 4. 04 -2.56 12.5 05/30/23 -0.77 3.88 -6.56 18.5 -0. 51 5. 05 -2.05 14.8 08/22/23 -2. 61 4.02 7. 5 3 20.4 -3.23 6.54 -4.06 15.2 11 /14/23 2. 15 3. 97 9. 93 20. 8 3.25 7.90 -1. 8 3 17.6

77 02/21/23 -3. 85 3. 00 -11.4 12.2 2. 69 3.32 0.47 11. 0 05/30/23 -0.49 5.39 -4. 96 21.6 -2. 57 8. 12 0.32 15.7 08/22/23 - 6.60 5. 04 0. 00 21. 9 -0. 36 7. 51 11.5 17.7 11 /14/23 -3.21 4.01 12.8 17.6 0.1 4 5. 90 3.51 14. 9

78 02/21/23 0.02 3.76 2.65 16.0 3. 11 6.16 -9. 09 13. 0 05/30/23 -1.26 3.39 2.67 16.2 7. 88 6.39 -4.09 15. 3 08/22/23 -2.92 5.26 9.29 23. 7 3. 12 6.33 5.58 19.8 11 /14/23 0.53 4.70 7.43 18. 6 1. 30 6.00 -8.8 3 14.3

79 02/27/23 0. 3 3 3.92 13.48 19. 3 - 1. 67 6.32 -4.49 14. 0 06/12/23 -2. 65 4.77 14. 58 22.7 -1. 11 7.51 -2.28 17. 0 09/26/23 1. 68 4.67 11.74 19.2 -2.65 7. 80 9.60 16. 9 11 /27/23 -1. 82 4. 02 -8. 33 17. 0 -0.74 5. 68 -3.16 15.4

81 02/27/23 -4. 83 4. 54 6. 85 20.0 3. 02 5.78 -13.7 15. 1 06/06/23 -0.04 2. 97 -6.7 7 17.8 1.01 5. 92 3.86 10.8 09/06/23 1. 19 2. 88 12.83 18.0 2.01 6.59 8.55 10.9 10/17/23 -6. 56 5.87 -6.43 22.4 2.28 7. 16 1.33 17.4

82 01 /26/23 -2.46 3.81 2. 10 20. 9 6.38 6. 32 -7. 12 13. 1 05/17/23 -5. 14 3.98 16.2 20. 1 -0. 56 5.17 3.67 13.7 07/18/23 1. 21 1.78 2.24 8. 9 5 1.28 3. 18 2.03 6.59 10/16/23 - 0.07 3. 82 -19.0 16.9 -2.68 6.48 -11.7 13.7

83 03/21 /23 1. 55 3. 80 2.55 19.6 -1.29 6. 87 -2. 18 13.5 05/25/23 0. 19 1. 06 4.30 9. 09 2. 31 3. 00 2.94 4. 3 2 09/05/23 0. 17 2.20 -12.6 17.6 1.23 5. 10 8. 19 8.47 10/18/23 - 3. 34 4.91 -15.7 18.7 0. 52 5.29 -7.87 16.9

3-19 Dominion Energy Nuclear Connecticut, Inc. Annual Radiological Environmental Millstone Power Station Operating Report 2023

TABLE 8 FRUITS & VEGETABLES (pCi/g wet wt.)

LOCATION 25 (fruit are extra sam pies not required by the REMODCM)

COLLECTION DATE ______!re_e Be-7 K-40 Cr-51 Mn-54 Co-58 Fe-59 Co-60

(+/ - ) (+/-) (+/-) (+/-) (+/-) (+/-) (+/-)

07/11/23 Lettuce 0.381 0.146 3.133 0.437 -0.013 0.078 -0.006 0.010 -0.003 0.009 -0.005 0.022 -0. 002 0.011 07/11/23 Apples -0.018 0. 084 1.099 0.335 -0.015 0.090 0.003 0.013 0.000 0.013 0.003 0.021 -0. 002 0. 011 09/19/23 Tomatoes 0. 041 0.099 2.023 0.402 0.042 0. 092 0. 007 0.011 0.002 0.012 -0.016 0. 028 0.002 0.011 09/19/23 Apples 0.123 0.097 1.038 0.268 0.052 0.093 0. 002 0.011 -0.009 0.011 0.003 0.021 -0.008 0.011

COLLECTION DATE ______!re_e Zn-65 Nb-95 Zr-95 Ru-103 Ru-106 Sb-125 1-131

(+/ - ) (+/-) (+/-) (+/-) (+/-) (+/-) (+/-)

07/11/23 Lettuce -0.007 0.030 -0.006 0.011 -0.013 0.016 -0.003 0. 009 -0. 048 0.077 0.002 0.026 -0.010 0.010 07/11/23 Apples -0.025 0.029 0.000 0.012 -0.005 0.019 0.004 0.011 -0.049 0.113 0.016 0.033 -0.005 0. 012 09/19/23 Tomatoes -0.032 0. 028 0.003 0.009 -0.004 0.020 0.006 0. 010 -0. 040 0.090 0.015 0.027 0. 001 0.013 09/19/23 Apples 0.002 0.023 0.003 0.011 0.003 0.019 -0.001 0. 010 -0.017 0. 088 0.002 0.025 -0.004 0.016

COLLECTION DATE ____!rpe Cs-134 Cs-137 Ba-140 La-140 Ce-141 Ce -144 Ac-228

(+/-) (+/-) (+/-) (+/-) (+/-) (+/-) (+/-)

07/11/23 Lettuce 0.003 0.012 -0.008 0.010 -0.016 0.037 0.006 0.012 0.008 0.013 0.029 0.057 -0. 014 0.039 07/11/23 Apples -0. 001 0.013 0. 003 0. 013 -0.002 0.039 -0.003 0.012 -0.001 0. 014 -0.020 0.058 0.012 0.037 09/19/23 Tomatoes -0.012 0.013 -0.003 0.013 -0.009 0.049 -0.004 0.016 -0.015 0.015 -0.060 0.064 -0.004 0.041 09/19/23 Apples 0. 002 0. 011 -0. 002 0. 010 -0. 017 0.044 -0. 010 0.015 -0.002 0.014 0.021 0.056 0. 006 0. 038

Results in bold type are positi1.e.

3-20 Dominion Energy Nuclear Connecticut, Inc. Annual Radiological Environmental Millstone Power Station Operating Report 2023

TABLE 8 FRUITS & VEG ET ABLES (pCi/g wet wt.)

LOCATION 25X (fruit are extra samples not required by the REMODCM)

COLLECTION DATE Type Be-7 K-40 Cr-51 Mn-54 Co-58 Fe-59 Co-60

(+/-) (+/-) (+/-) (+/-) (+/-) (+/-) (+/-)

08/29/23 Tomatoes -0. 023 0. 077 1. 837 0. 304 0. 080 0. 074 0. 000 0. 009 0.002 0.008 -0.011 0.016 0. 004 0.010 09/19/23 Tomatoes 0.045 0. 071 1.847 0. 364 0. 040 0.074 -0. 008 0.009 -0.002 0.012 -0.012 0.021 -0. 004 0. 012

COLLECTION DATE T~ Zn-65 Nb-95 Zr-95 Ru-103 Ru-106 Sb-125 1-131

(+/-) (+/-) (+/-) (+/-) (+/-) (+/-) (+/-)

08/29/23 Tomatoes 0. 012 0.021 -0. 005 0. 008 0.006 0.016 -0.011 0.008 -0.011 0.091 0.011 0.022 0.000 0.011 09/19/23 Tomatoes -0.016 0. 022 0. 003 0. 010 -0. 001 0. 017 -0. 008 0. 009 0.007 0. 089 0.021 0. 022 0. 004 0. 014

COLLECTION DATE T~ Cs-134 Cs-137 Ba -140 La-140 Ce-141 Ce-144 Ac-228

(+/-) (+/-) (+/-) (+/-) (+/-) (+/-) (+/-)

08/29/23 Tomatoes 0. 002 0. 011 0. 007 0.009 0.011 0.026 0.003 0.012 0.000 0.014 0.052 0. 059 0.011 0. 030 09/19/23 Tomatoes 0. 003 0. 010 0. 002 0. 010 -0.025 0.036 0.003 0.014 0.001 0. 013 -0.008 0.051 -0.025 0. 038

Results in bold type are positi-..e.

3-21 Dominion Energy Nuclear Connecticut, Inc. Annual Radiological Environmental Millstone Power Station Operating Report 2023

TABLE 8 FRUITS & VEGETABLES (pCi/g wet wt.)

LOCATION 26C (fruit are extra samples not required by the REMODCM)

COLLECTION DATE T~ Be-7 K-40 Cr-51 Mn-54 Co-58 Fe-59 Co-60

(+/-) (+/-) (+/-) (+/-) (+/-) (+/-) (+/-)

07/11/23 Lettuce 0. 328 0.136 2.792 0.460 -0. 002 0.095 0.007 0. 013 0. 001 0.009 0.009 0. 029 -0.006 0.014 07/11/23 Plums -0. 008 0.072 1.508 0.279 -0. 028 0.066 0.003 0.009 0. 002 0.008 -0. 006 0. 018 0. 003 0. 007 08/29/23 Tomatoes 0.053 0.103 1.959 0.439 -0. 105 0. 110 -0. 004 0.009 -0.005 0. 012 -0. 010 0. 027 0. 001 0. 011 09/19/23 Tomatoes 0.026 0. 072 1.826 0.268 0. 010 0. 083 0.006 0.008 -0. 005 0. 009 -0.009 0. 017 0. 001 0. 011 09/19/23 Apples 0. 076 0.065 0.832 0.276 -0. 047 0. 074 0.000 0. 008 0. 003 0.010 0.005 0.020 -0.005 0.009

COLLECTION DATE Type Zn-65 Nb-95 Zr-95 Ru-103 Ru-106 Sb-125 1-131

(+/-) (+/-) (+/-) (+/-) (+/-) (+/-) (+/-)

07/11/23 Lettuce -0. 021 0.034 -0.007 0.013 -0.004 0.022 -0.007 0. 013 0. 147 0.112 -0. 013 0.036 0.010 0. 013 07/11/23 Plums -0.015 0.024 0. 002 0.009 0.002 0.016 -0.003 0. 008 -0.006 0.080 -0. 008 0. 023 -0.002 0.009 08/29/23 Tomatoes 0. 003 0. 030 0. 007 0. 012 0. 001 0. 019 -0.012 0. 013 0.025 0.125 -0. 028 0. 038 -0. 003 0.014 09/19/23 Tomatoes -0. 004 0. 022 -0.002 0.009 -0. 017 0. 013 -0. 001 0. 008 -0.012 0.078 -0.014 0. 024 -0. 014 0.014 09/19/23 Apples -0. 007 0. 018 -0.001 0.009 -0. 016 0. 018 0. 002 0. 009 0. 035 0.080 0.018 0.025 0. 008 0.011

COLLECTION DATE Type Cs-134 Cs-137 Ba-140 La-140 Ce-141 Ce-144 Ac-228

(+/-) (+/-) (+/-) (+/-) (+/-) (+/-) (+/-)

07/11/23 Lettuce 0.013 0.015 0. 003 0.014 -0. 034 0. 042 -0. 002 0.008 0. 001 0. 017 -0. 035 0. 073 0. 001 0.054 07/11/23 Plums 0.005 0. 009 -0.001 0. 009 0.005 0.033 -0.005 0. 010 -0.001 0. 011 0. 030 0. 047 -0.017 0.032 08/29/23 Tomatoes -0. 009 0. 015 -0. 005 0. 014 -0. 013 0. 046 0.007 0. 016 0. 004 0.021 0.031 0.078 0. 004 0.044 09/19/23 Tomatoes -0. 006 0. 010 -0. 008 0.010 -0.060 0. 043 -0.004 0. 014 -0. 004 0.014 -0.015 0. 054 0. 005 0.029 09/19/23 Apples 0. 001 0. 009 -0. 001 0. 009 -0. 008 0. 037 0. 001 0. 017 0.002 0. 012 -0. 007 0. 055 -0. 021 0. 036

C = Control location, Background location Results in bold type are posifr,e.

3-22 Dominion Energy Nuclear Connecticut, Inc. Annual Radiological Environmental Millstone Power Station Operating Report 2023

TABLE 9 BROADLEAF VEGETATION (pCi/g wet wt.)

LOCATION 1 COLLECTION DATE Be-7 K-40 Cr-51 Mn-54 Co-58 Fe-59 Co-60

(+/-) (+/-) (+/-) (+/-) (+/ - ) (+/-) (+/-)

05/23/23 0.520 0.232 3.682 0.601 0. 018 0. 131 -0.002 0. 015 0.005 0.015 0.009 0. 032 -0.007 0.019 09/19/23 2.823 0.392 2.803 0.517 -0.101 0. 139 -0.006 0.017 -0. 001 0.015 0.019 0.038 0. 001 0.018

Zn-65 Nb-95 Zr-95 Ru-103 Ru-106 Sb-125 1-131

(+/-) (+/-) (+/-) (+/-) (+/-) (+/-) (+/-)

05/23/23 -0.063 0.053 -0. 011 0.016 -0.009 0.027 -0.011 0.014 0.081 0.136 -0. 001 0.041 0.009 0. 018 09/19/23 -0.017 0.040 -0. 004 0.016 -0. 005 0.030 -0. 006 0.016 -0.002 0.138 -0. 055 0. 046 -0.016 0. 027

Cs-134 Cs-137 Ba-140 La-140 Ce-141 Ce-144 Ac-228

(+/-) (+/-) (+/-) (+/-) (+/-) (+/-) (+/-)

05/23/23 -0. 005 0. 017 -0. 006 0.015 -0. 004 0.065 0.015 0.019 -0.001 0. 021 0. 024 0.096 0.053 0.061 09/19/23 0. 012 0.019 -0. 002 0.015 0. 019 0.046 -0. 031 0. 028 -0.036 0. 025 0. 086 0. 096 0.051 0.063

LOCATION 10 COLLECTION DATE Be-7 K-40 Cr-51 Mn-54 Co-58 Fe-59 Co-60

(+/-) (+/-) (+/-) (+/-) (+/-) (+/-) (+/-)

05/23/23 0.169 0.121 2.605 0.569 -0. 028 0. 120 0. 005 0.014 -0.008 0. 016 0. 022 0.029 -0.006 0. 017 09/19/23 2.820 0.321 2.318 0.443 -0.080 0.120 0.004 0.012 -0.004 0. 011 -0.001 0.024 0.008 0. 016

Zn-65 Nb-95 Zr-95 Ru-103 Ru-106 Sb-125 1-131

(+/-) (+/-) (+/-) (+/-) (+/-) (+/-) (+/-)

05/23/23 0.006 0.033 -0.001 0.013 0.003 0.021 -0.002 0. 015 0. 012 0.151 -0.022 0.041 -0. 015 0.015 09/19/23 -0. 016 0.031 0.004 0. 013 0.002 0.022 0. 000 0. 011 -0.054 0.104 0. 024 0. 030 0. 002 0.019

Cs-134 Cs-137 Ba-140 La-140 Ce-141 Ce-144 Ac-228

(+/-) (+/-) (+/-) (+/-) (+/-) (+/-) (+/-)

05/23/23 -0.009 0.014 -0.001 0.014 0.036 0. 054 0.010 0.016 -0.005 0.022 0.048 0. 085 0.061 0. 063 09/19/23 0.003 0. 015 0.000 0. 013 -0.020 0.050 0.005 0. 014 -0.020 0.023 -0.026 0. 089 0.154 0.059

Results in bold type are positi-..e.

3-23 Dominion Energy Nuclear Connecticut, Inc. Annual Radiological Environmental Millstone Power Station Operating Report 2023

TABLE 9 BROADLEAF VEGETATION (pCi/g wet wt.)

LOCATION 17 COLLECTION DATE Be-7 K-40 Cr-51 Mn-54 Co-58 Fe-59 Co-60

(+/-) (+/-) (+/-) (+/-) (+/-) (+/-) (+/-)

05/23/23 0. 092 0. 157 2.515 0.532 -0.005 0.122 0. 006 0. 014 -0.010 0.016 -0.006 0.024 -0. 005 0.018 09/19/23 0.925 0.301 1. 971 0.499 -0.014 0. 140 -0. 014 0. 018 -0. 021 0. 019 -0. 058 0.040 0.003 0. 017

Zn-65 Nb-95 Zr-95 Ru-103 Ru-106 Sb-125 1-131

(+/-) (+/-) (+/-) (+/-) (+/-) (+/-) (+/-)

05/23/23 -0. 034 0. 035 -0. 017 0. 018 0.003 0.026 -0. 003 0. 016 -0. 020 0.142 0. 001 0. 046 -0.015 0. 019 09/19/23 -0. 051 0. 042 -0.014 0. 015 -0. 011 0. 031 -0. 004 0. 017 -0.152 0. 185 -0. 025 0.045 -0. 028 0. 025

Cs-134 Cs-137 Ba-140 La-140 Ce-141 Ce-144 Ac-228

(+/-) (+/-) (+/-) (+/-) (+/-) (+/-) (+/-)

05/23/23 0. 015 0.017 0.005 0. 016 -0. 024 0. 057 -0.021 0. 019 -0. 013 0. 025 -0. 010 0.107 0. 037 0. 056 09/19/23 0. 007 0.020 0.007 0.020 0.101 0. 081 -0. 001 0. 026 -0.001 0. 028 -0.007 0. 109 0. 053 0.077

LOCATION 26C COLLECTION DATE Be-7 K-40 Cr-51 Mn-54 Co-58 Fe-59 Co-60

(+/-) (+/-) (+/-) (+/ - ) (+/-) (+/-) (+/-)

05/23/23 0.406 0.241 3.713 0.689 0. 002 0. 124 -0. 006 0. 017 -0. 001 0. 016 -0.010 0. 035 -0.006 0.019 09/19/23 2.247 0.367 3. 115 0.547 -0. 100 0. 146 0. 001 0. 017 0. 015 0.015 -0.002 0.037 0.001 0.011

Zn-65 Nb-95 Zr-95 Ru-103 Ru-106 Sb-125 1-131

(+/ -) (+/-) (+/-) (+/-) (+/-) (+/-) (+/-)

05/23/23 -0. 023 0. 052 0. 014 0. 019 -0. 007 0. 022 -0. 008 0.017 -0.096 0. 151 -0.005 0.042 -0. 010 0. 021 09/19/23 -0.029 0. 040 0. 002 0.016 0.016 0. 027 0.028 0.017 0.115 0.146 0. 003 0. 045 -0. 003 0. 026

Cs-134 Cs-137 Ba-140 La-140 Ce - 141 Ce-144 Ac-228

(+/-) (+/-) (+/-) (+/-) (+/-) (+/-) (+/-)

05/23/23 0. 005 0. 019 0. 006 0. 017 -0. 025 0. 062 -0. 014 0.024 0. 000 0. 021 -0.043 0. 091 0.054 0. 067 09/19/23 0. 012 0.019 0. 011 0. 018 -0. 010 0. 071 -0.001 0.020 0.009 0.025 -0. 028 0. 094 0.128 0. 085

C= Control location, Background location Results in bold type are positil.e.

3-24 Dominion Energy Nuclear Connecticut, Inc. Annual Radiological Environmental Millstone Power Station Operating Report 2023

TABLE 10 SEAWATER (pCi/1)

LOCATION 32 COLLECTION DATE H-3 Be-7 K-40 Cr-51 Mn-54 Co-58 Fe-59

(+/-) (+/-) (+/-) (+/-) (+/-) (+/ - ) (+/-)

01/31/23 1030 253 -11.2 35.1 304 91 -18.8 44. 8 -1.40 3.52 1. 08 4.16 3.16 8.27 02/27/23 1040 244 17.4 31.7 322 75 -17. 2 32.1 0.99 2.75 -2.76 3. 36 4. 79 6. 83 03/28/23 1060 263 -3.95 33. 9 267 81 11. 2 38.4 1.72 3.93 -3.46 4.01 4.74 8.73 04/25/23 1420 339 19. 1 31. 1 317 78 4. 17 32. 8 2.07 3.85 2.39 3.18 1.86 7.14 05/30/23 788 411 -4. 14 32.2 164 97 -31. 8 31.6 0.97 3.64 -0.43 3.72 0.62 9.00 06/27/23 628 219 -13.5 38.3 230 98 -6. 96 39.0 1. 72 3.66 -4.27 4. 12 5. 60 7.21 07/25/23 266 129 0.20 5.46 330 32 -0.64 5.04 0. 34 0.65 -0. 51 0.54 -0.42 1.25 08/29/23 85 188 -11. 7 24.6 321 76 7.80 24.7 1. 62 3.14 0.50 3.08 2.57 5.79 09/26/23 775 221 -0.46 31.9 348 91 12.4 29. 8 -1.93 3.70 3.14 3.81 5.53 7.54 10/31/23 1560 273 -13.2 41.2 411 100 -37.3 36.6 1.90 4.12 -3.03 4.47 4.99 9.13 11/28/23 562 232 45.7 41.1 302 117 23.7 32.9 2.25 3.69 0.84 4.48 -0.75 7. 39 12/27/23 537 214 2. 93 38.5 322 130 -1.75 38.2 -0.10 3.83 -5. 16 4.72 4.42 9.61

COLLECTION DATE Co-60 Zn-65 Nb-95 Zr-95 Ru-103 Ru-106 Sb-125

(+/-) (+/-) (+/-) (+/ - ) (+/-) (+/-) (+/-)

01/31/23 2. 07 3.91 -7.33 10.3 -1.52 4. 32 -3.62 6. 95 0.65 4.74 14.4 42.4 2.37 11.8 02/27/23 1.33 3.03 -1. 68 7. 01 -0. 81 3.40 0.22 6.00 -1. 36 3.48 11.5 28. 9 -9.17 10.3 03/28/23 3. 62 4.24 -3.76 8.99 3.79 3.64 -7.29 6.35 1. 63 4.20 -4. 60 40. 5 -4. 16 11.9 04/25/23 2. 81 3.46 3.37 7.24 0.14 3.74 -3. 03 6.33 -1. 08 3.32 20.5 29.2 1.27 10.2 05/30/23 -0.19 3. 84 6.90 10.2 -1.28 4.01 0.90 7.73 -3.64 4.20 6.64 33.9 7.29 9.75 06/27/23 -0. 14 4.72 -5. 51 9.68 2. 03 3.70 0. 35 5. 82 -1. 69 4.41 3.75 40.5 -5.22 12.3 07/25/23 1.32 0.96 -1.11 1.42 0.02 0.59 -0. 03 1.01 0.88 0.61 1.98 6.14 0. 99 1.79 08/29/23 0.62 3.14 -1.35 7. 56 -0. 39 2.99 -2.94 5. 82 -0.41 3.20 9. 89 27.8 -4. 97 8. 11 09/26/23 0.14 3. 91 0. 53 8. 51 -0.56 3.79 -0.40 6.43 2.00 3.73 35.7 32.8 1. 12 9. 99 10/31/23 -1.44 5.17 -22. 7 11.9 4. 63 5.20 2. 56 8.46 -0. 18 4.42 -2. 95 38. 6 2.89 12.4 11/28/23 -1. 58 4. 10 -9.61 10.2 1. 89 4.56 2. 1 9 7.64 1.70 4. 21 15.3 34.4 1. 36 12. 6 12/27/23 -2.53 3. 93 -12.2 10.2 3.61 4.87 -0.48 7.44 -0. 84 4.85 1.71 44. 9 -14.2 13.0

Results in bo ld type are positi1.e.

3-25 Dominion Energy Nuclear Connecticut, Inc. Annual Radiological Environmental Millstone Power Station Operating Report 2023

TABLE10 SEAWATER (pCi/1)

LOCATION 32 Cont'd COLLECTION DATE 1-131 Cs-134 Cs-137 Ba-140 La-140 Ac-228

(+ /-) (+ /-) (+/-) (+ /- ) (+/ -) (+/-)

01/31/23 7.74 7. 01 3.69 4. 85 -2.45 4. 38 2. 79 19.6 -2.64 6.23 2. 56 17. 5 02/27/23 - 0.81 5.81 -0.28 3.74 -1. 12 3.49 2. 79 14. 7 2.34 5. 79 7.91 12.6 03/28/23 -1.39 5.73 -2.03 4. 86 -0.49 4.49 -5.72 15.0 -2.70 4.26 2. 10 15. 1 04/25/23 2.43 6.30 -0.64 3.71 0.70 3. 82 3. 51 1 5. 1 1. 00 5.46 -1.65 12.4 05/30/23 1.05 5. 96 -1.91 4. 08 2.12 4. 07 -0.43 16. 7 1.67 5. 17 -7.23 14.0 06/27/23 2.80 5.75 -3.36 4.62 1.75 4.24 11.8 16.2 -2.88 4.65 -10.8 17.4 07/25/23 -1.92 1.22 -0. 15 0.62 0.71 0.69 1. 95 2. 74 " -0.23 0. 85 2.80 2.46 08/29/23 -1.53 3.67 1.86 3. 85 -1.49 3. 11 -1. 14 11.7 -1. 72 3.73 -14.7 12. 7 09/26/23 -0.54 5.46 -0.27 3.63 1.57 3. 56 -3.76 17.4 2. 71 4.94 - 1.93 14. 0 10/31 /23 1.63 7.30 3.78 4. 91 -0.22 4. 08 -6. 34 17.7 -6.62 7.18 -2.43 16. 3 11 /28/23 4.68 6.93 5.11 4. 84 6.93 4.23 11.3 19. 5 -0.75 8.29 -0. 79 16.2 12/27/23 0.25 5.31 -2.57 5. 07 1.31 4.59 -3.42 17. 0 -1. 92 5.46 -8. 11 16. 5

LOCATION 37C COLLECTION DATE H-3 Be-7 K-40 Cr-51 Mn-54 Co-58 Fe-59

~ (+ / -) (+/- ) (+/-) (+ / - ) (+ / -) (+ / - )

03/21 /23 52 174 -5.61 30. 8 286 98 -1.87 36.0 0.44 3. 34 -2. 38 3. 19 3.20 7. 73 06/20/23 -36 176 17.8 28. 8 257 84 3. 56 29. 9 0. 78 3. 39 -0.09 3. 33 5.06 6.78 09/12/23 106 103 19.7 31. 0 308 82 -27. 3 31. 8 -0. 58 3.42 -0.56 3. 18 -1.23 7. 80 12/20/23 -217 180 -23. 1 36.1 216 87 28.7 32.6 1.70 3.67 - 0.57 3. 61 -0.85 8.28

COLLECTION DATE Co-60 Zn-65 Nb-95 Zr-95 Ru-103 Ru-106 Sb-125

~ (+ / -) (+ / - ) (+ / -) (+/- ) (+ /-) (+/- )

03/21 /23 1. 06 3. 74 3.44 7.44 -0.37 3.25 2.88 5.67 0. 17 3. 93 - 11. 1 34. 0 - 1. 66 9.41 06/20/23 2.20 3. 60 0. 79 6.75 0. 55 3.71 -5.67 6. 12 -0.73 3.49 -22. 6 33.3 -0. 32 9.21 09/12/23 1. 83 2. 91 -7. 07 7. 92 -1.78 2.96 -1.04 6. 16 -1.43 3. 93 -19.8 39.0 9. 37 8. 71 12/20/23 -0.75 4. 06 -8.41 8.29 2.48 3.86 3.53 5. 97 -3.94 4. 31 25. 1 36. 7 -3.46 11. 5

COLLECTION DATE 1-131 Cs-134 Cs-137 Ba-140 La-140 Ac-228 F+l" (+/-) (+ / -) (+/ -) (+ / -) (+/ -)

03/21 /23 0. 96 6.35 -0.67 3. 96 1.84 3. 63 -15. 8 16. 3 6.85 5.10 -5.49 13.4 06/20/23 -2.26 6. 30 -0.50 4. 03 0.36 3.42 8. 57 14. 5 -0.22 6.36 12.1 12. 3 09/12/23 -0.57 5. 00 0.72 3.40 -1.40 3. 61 14. 0 16. 6 1.48 4.82 -5.91 13. 6 12/20/23 0.16 7.43 2.46 4. 05 -1.26 4.19 -6. 07 18. 3 0. 83 6.48 2.30 13. 3

C= Control locat ion, Background locat ion Results in bold type are positi1.e.

3-26 Dominion Energy Nuclear Connecticut, Inc. Annual Rad iological Environmental Millstone Power Station Operating Report 2023

TABLE 11 BOTTOM SEDIMENT (pCi/g dry wt.)

COLLECTION LOCATION DATE Be-7 K-40 Cr-51 Mn-54 Co-58 Fe-59

(+/-) (+/-) (+/-) (+/-) (+/-) (+/-)

31 06/26/23 0.479 0.437 15.05 1.679 -0. 120 0.456 0. 018 0.048 -0. 020 0. 044 -0. 090 0. 112 31 11/07/23 -0. 120 0.394 15.44 1.793 -0.143 0. 374 0. 050 0.052 0. 003 0. 045 -0.007 0. 100

32 06/12/23 0.446 0.423 17.47 1.543 -0.036 0.478 -0. 004 0. 052 -0.023 0. 048 0. 040 0. 098 32 12/14/23 0.718 0. 502 13.05 1.545 0.405 0.575 0. 023 0. 050 -0. 072 0. 052 0. 000 0. 122

33 06/26/23 -0.130 0.255 11.56 1.342 0. 067 0.274 -0. 012 0. 028 -0.002 0.033 -0.001 0. 076 33 12/07/23 0.038 0. 338 15.02 1.608 -0.180 0. 334 -0. 039 0. 050 0.011 0. 045 -0.010 0. 103

34 06/26/23 -0.017 0.297 11.18 1.424 0. 174 0.336 0.001 0. 037 -0. 029 0.042 0. 033 0.091 34 12/07/23 -0. 197 0.263 12.75 1.390 0.286 0.268 -0.013 0. 028 -0. 009 0. 031 -0. 037 0.078

37C 03/28/23 0.206 0. 244 15.26 1.321 0. 026 0.242 0. 014 0.029 -0.017 0.030 0. 019 0. 062 37C 11/09/23 0. 180 0. 232 14.48 1.650 -0.103 0.266 -0. 004 0. 035 0. 008 0. 035 0. 049 0. 078

COLLECTION LOCATION DATE Co-60 Zn-65 Nb-95 Zr-95 Ru-103 Ru-106

(+/-) (+/-) (+/-) (+/-) (+/-) (+/-)

31 06/26/23 -0.008 0.049 -0. 152 0. 115 0. 005 0. 053 0. 039 0. 093 -0. 046 0.056 -0.041 0.469 31 11/07/23 0. 001 0.046 0.033 0.1 11 -0.012 0.052 0.064 0. 096 0. 020 0.047 -0. 060 0.473

32 06/12/23 0.020 0.044 -0. 062 0. 119 0. 013 0. 053 0. 030 0. 091 0.033 0. 055 -0.041 0.469 32 12/14/23 0. 034 0.059 -0. 074 0. 139 0. 018 0. 066 -0. 032 0.1 05 -0. 003 0. 061 0.236 0. 511

33 06/26/23 -0. 014 0.039 -0. 087 0. 090 0.010 0. 032 0. 040 0. 043 -0. 004 0.032 0.100 0.237 33 12/07/23 0. 005 0.041 -0. 025 0. 150 0. 045 0. 050 -0. 021 0. 077 0. 025 0.046 -0.053 0. 369

34 06/26/23 0. 006 0.037 0.029 0. 108 0.043 0. 040 -0.010 0.065 0.000 0.033 0. 122 0. 327 34 12/07/23 -0. 002 0. 032 0. 030 0. 086 0. 031 0. 039 0. 012 0. 049 0. 013 0. 031 0. 039 0. 300

37C 03/28/23 0.004 0.035 0. 037 0.080 -0. 003 0.032 0. 023 0. 053 0. 012 0. 029 -0. 050 0.244 37C 11/09/23 0.038 0. 037 -0.069 0.109 -0.009 0. 035 -0. 024 0. 069 0. 027 0. 037 -0. 334 0.276

C= Control location, Background location Results in bold type are positi..e.

3-27 Dominion Energy Nuclear Connecticut, Inc. Annual Radiological Env ironmental Millstone Power Station Operating Report 2023

TABLE 11 BOTTOM SEDIMENT (pCi/g dry wt.)

COLLECTION LOCATION DATE Ag -110M Sb -125 1-131 Cs-134 Cs-137 Ac-228

(+ / -) (+ / -) (+/- ) (+ / -) (+ / -) (+/-)

31 06/26/23 0. 027 0.044 0. 071 0. 135 -0. 067 0. 123 0. 067 0. 054 -0. 016 0. 051 2.396 0.331 31 11/07/23 -0. 010 0.050 0. 078 0. 113 -0. 041 0. 070 0. 108 0. 061 -0. 001 0. 054 3.096 0.513

32 06/12/23 0.009 0.049 0. 019 0.131 0. 018 0. 097 0.093 0. 060 0. 014 0. 056 2.305 0.378 32 12/14/23 0. 019 0. 050 -0. 041 0. 136 -0. 077 0.177 0.080 0.058 0.011 0.054 0.903 0.342

33 06/26/23 0. 001 0. 031 0. 110 0. 089 0.008 0.067 0.024 0.030 -0. 016 0.033 0.289 0. 142 33 12/07/23 -0. 003 0.043 -0. 015 0.116 0.039 0.060 0. 010 0. 04 8 -0. 008 0. 048 0. 134 0. 171

34 06/26/23 -0. 013 0.032 -0. 020 0. 096 -0. 010 0. 0 8 9 0.019 0.042 -0. 003 0.040 0. 185 0. 162 34 12/07/23 -0.009 0.028 0. 019 0. 08 8 -0. 014 0. 056 0. 015 0. 035 -0.022 0.033 0. 085 0. 134

37C 03/28/23 0. 001 0. 026 0.018 0. 081 0. 038 0. 047 -0.015 0. 031 -0.007 0.027 0.056 0.132 37C 11 /09/23 -0. 020 0. 028 -0. 041 0. 083 -0. 025 0. 076 -0. 002 0. 038 -0.023 0.031 0.213 0. 162

C= Control location, Bac kground locat ion Results in bold type a re positi-..e.

3-28 Dominion Energy Nuclear Connecticut, Inc. Annual Radiological Environmental Millstone Power Station Operating Report 2023

TABLE12 AQUATIC FLORA - FUCUS (pCi/g wet wt.)

COLLECTION LOCATION DATE Be-7 K-40 Cr-51 Mn-54 Co-58 Fe-59

(+/ - ) (+/-) (+/-) (+/-) (+/-) (+/-)

29 03/01/23 0. 12 80 0. 1341 5.8050 0.6226 0. 0271 0. 0913 0.0036 0. 0119 -0.0011 0. 0142 0. 0156 0. 0339 29 06/01/23 0. 0517 0. 1267 6.7850 0.6265 0. 0062 0. 1135 0. 0007 0. 0146 -0.0121 0. 0156 -0. 0086 0.0243 29 09/19/2 3 0. 1956 0. 0964 5.3710 0.5095 0. 0278 0. 0783 -0.0072 0. 0110 0.0055 0. 0093 -0. 0020 0.0239 29 11/07/23 0. 0994 0. 1005 6.5770 0.5313 0. 0706 0.0949 0.0041 0. 0134 -0. 0030 0. 0113 -0.0334 0.0291

32 03/01/23 0. 0268 0. 1008 5.2070 0.6028 0. 0298 0. 0873 0. 0063 0. 0111 -0. 0064 0. 0111 -0.0183 0.0283 32 06/08/23 0. 0812 0. 1319 6.9170 0.6926 -0.0057 0.1297 -0.00 74 0. 0152 -0.0002 0. 0160 0. 0192 0.0291 32 09/19/23 0. 0922 0. 1247 6.7760 0.7087 -0. 0571 0. 0972 0. 0063 0. 0124 0.0076 0. 0140 -0.0006 0. 0326 32 12/04/23 -0. 0044 0.1224 6.4870 0.6139 0. 0408 0.1022 -0. 0132 0. 0144 -0.0053 0. 0138 -0. 0018 0. 0305

35 03/06/23 0.2228 0. 1015 5.8460 0.5428 0. 0207 0. 0763 -0. 0017 0. 0105 0. 00 1 3 0. 0112 -0. 016 8 0.0289 35 06/06/23 0. 0355 0. 0983 5.4850 0.5507 -0. 0642 0. 1025 -0. 0049 0. 0126 -0.0045 0. 0122 0. 0075 0. 0256 35 09/19/23 0. 0931 0.0970 5.7890 0.5374 -0.0289 0. 0821 0. 0033 0. 0112 -0. 0016 0.0105 0. 0087 0. 0277 35 12/05/23 0.2175 0. 1158 5.9170 0.5365 0. 0388 0.1109 -0.0021 0. 0121 0.0019 0. 0123 -0. 0113 0.0275

36C 03/28/23 0. 1723 0. 1166 3.8110 0.5079 0. 0935 0.0819 0. 0084 0.0119 -0.0103 0. 0094 -0.0149 0.0263 36C 06/12/23 0. 0560 0.1079 5.8820 0.6156 0.0175 0. 0850 -0. 0020 0. 0125 0. 0001 0. 0116 0. 0159 0. 0259 36C 09/19/23 0. 1481 0. 0959 5.3480 0.4604 0.0132 0. 0890 0. 00 18 0. 0104 -0. 0029 0. 0092 0. 021 2 0.0231 36C 12/07/23 0. 1984 0. 1044 6.8910 0.5344 0. 0048 0.0875 0. 0015 0. 0104 - 0.0045 0. 0112 -0.0051 0.0273

C= Control location, Background location Results in bold type are positi-..e.

3-29 Dominion Energy Nuclear Connecticut, Inc. Annual Radiological Environmental Millstone Power Station Operating Report 2023

TABLE12 AQUATIC FLORA - FUCUS (pCi/g wet wt.)

COLLECTION LOCATION DATE Co-60 Zn-65 Nb-95 Zr-95 Ru -103 Ru-106

(+/-) (+/-) (+/ -) (+/- ) (+/-) (+/-)

29 03/01/23 0. 0066 0. 0143 -0. 0441 0. 0372 0. 0039 0.0111 -0. 0001 0. 0226 0. 0008 0. 0119 -0. 0497 0. 1159 29 06/01/23 0. 011 3 0.0130 -0.0170 0.0366 0.0107 0. 0127 0.0119 0. 0259 0. 0086 0. 0134 -0. 1192 0. 121 5 29 09/19/23 0. 0027 0. 0096 -0. 0073 0. 0242 -0. 0050 0. 0086 0. 0060 0. 0159 0. 0017 0. 0087 0.0174 0.0803 29 1 1/07/23 0.0045 0.0130 -0.0056 0. 0362 0. 0052 0. 0120 0. 0206 0.0213 0. 0119 0.0110 -0. 0294 0. 1062

32 03/01/23 0. 0093 0. 0129 0. 02 1 3 0. 0363 -0. 0052 0. 0129 -0. 0056 0. 02 3 0 -0.0066 0.0115 0. 0581 0. 1 134 32 06/08/23 0. 0142 0. 0169 0. 0220 0. 0428 -0. 0079 0. 0161 0. 0038 0. 0317 0. 0026 0. 0 143 0. 0375 0. 1423 32 09/19/23 -0.0023 0. 0141 -0.0075 0. 0392 0. 0009 0. 0141 -0. 0127 0. 0229 0.0145 0. 0112 0. 0716 0.1212 32 12/04/23 0. 0128 0. 0146 -0. 0418 0. 0394 0. 0031 0. 0135 0. 0152 0. 0245 -0. 0080 0. 0134 0. 0260 0. 1231

35 03/06/23 -0. 0111 0. 0114 -0.0146 0. 0293 -0. 0037 0.0113 -0. 0119 0.0207 0.0040 0. 0092 -0.0384 0. 0999 35 06/06/23 -0. 0014 0. 0118 -0. 0055 0. 0278 -0. 0013 0. 0116 -0.0074 0. 0211 -0. 0057 0. 0121 0. 0445 0. 0988 35 09/19/23 -0. 0075 0. 0 134 0. 0059 0. 0302 0. 0059 0. 0106 -0.0157 0.0207 -0. 0002 0. 0102 -0. 0134 0. 0859 35 12/05/23 0. 0137 0.0144 0.0153 0. 0337 0. 0216 0. 0124 -0.0116 0. 0204 -0. 0072 0. 0124 -0. 0242 0. 1062

36C 03/28/23 -0. 0003 0. 0117 0. 0050 0. 0254 0.0115 0. 0103 0. 0000 0. 0223 -0. 0003 0. 0114 0.0417 0. 1021 36C 06/12/23 0. 0031 0. 0139 -0. 0192 0. 0272 -0. 0018 0.0139 0. 0084 0. 0224 -0.0010 0.0109 -0.0763 0. 1080 36C 09/19/23 -0. 0012 0. 0111 -0. 0067 0. 0235 -0. 0012 0.0098 -0.0051 0. 0167 -0. 0048 0. 0099 -0. 0398 0. 0779 36C 12/07/23 0.0090 0. 0127 -0. 0253 0. 0290 -0. 0036 0. 0115 -0.0071 0. 0210 0.0014 0.0104 -0. 0106 0. 1107

C= Control location, Background location Results in bold type are positi.e.

3-30 Dominion Energy Nuclear Connecticut, Inc. Annual Radiological Environmental Millstone Power Station Operating Report 2023

TABLE12 AQUATIC FLORA - FUCUS (pCi/g wet wt.)

COLLECTION LOCATION DATE Ag-110M Sb-125 1-131 Cs-134 Cs-137 Ac-228

(+/-) (+/-) (+/-) (+/-) (+/-) (+/-)

29 03/01/23 -0. 0010 0. 0128 -0.0085 0.0303 -0.0052 0.0179 -0. 0035 0. 0151 0. 0114 0. 0135 0. 0503 0. 0559 29 06/01/23 -0. 0091 0. 0115 -0. 0072 0. 0347 0. 0160 0. 0286 0.0172 0. 0156 0.0070 0. 0123 0.0903 0.0540 29 09/19/23 0. 0011 0. 0089 0. 0174 0. 0231 0. 0069 0. 0142 -0.0013 0. 0111 0. 0014 0.0098 0. 0617 0. 0433 29 11/07/23 -0. 0053 0. 0112 -0. 0083 0. 0282 0. 0166 0. 0173 0. 0025 0. 0129 0.0100 0. 0113 0.0719 0.0497

32 03/01/23 -0. 0029 0. 0124 0. 004 2 0. 0295 -0. 0152 0. 0172 0. 0021 0. 0130 0. 0034 0. 0140 -0. 0020 0. 0542 32 06/08/23 0.0260 0. 0159 0. 0297 0. 0444 0. 0121 0. 0259 0. 0075 0.0183 -0. 0108 0. 0171 0. 1161 0. 0557 32 09/19/23 -0. 0086 0. 0126 -0. 0234 0. 0318 -0. 0098 0.0176 -0. 0025 0. 0149 -0. 0027 0.0159 0. 0598 0. 0529 32 12/04/23 -0.0008 0. 0140 0. 0038 0.0350 0. 0023 0. 0177 -0.0016 0. 0171 -0. 0097 0.0155 0.1172 0. 0693

35 03/06/23 0.0071 0.0092 0. 0098 0.0277 -0. 0091 0. 0144 0.0160 0.0128 -0. 0074 0.0114 0. 0490 0. 0489 35 06/06/23 -0.0105 0.0123 0. 0032 0. 0273 0. 0090 0. 0196 0. 0018 0. 0137 0. 0054 0.0131 0.0661 0. 0521 35 09/19/2 3 -0. 0005 0. 0110 0. 0122 0. 0268 0. 0052 0.0133 -0. 0009 0.0114 -0. 0001 0. 0120 0.0083 0. 0449 35 12/05/23 0. 0008 0. 0118 -0. 0013 0. 0341 -0. 0043 0. 0159 0. 0062 0. 0134 -0. 0013 0. 0128 0. 0721 0. 0557

36C. 03/28/23 -0. 0021 0. 0115 0. 0112 0. 0246 0. 0103 0. 0128 0.0082 0.0137 0. 001 7 0.0115 0.0663 0. 0531 36C 06/12/23 0. 0018 0. 0106 0. 0182 0.0287 -0. 0084 0.0146 -0. 0037 0. 0159 -0. 0075 0.0129 0. 0663 0. 0535 36C 09/19/23 -0. 0001 0.0094 -0. 0132 0. 0243 0. 0084 0. 0150 0.0031 0. 0109 0. 0039 0.0097 0. 0547 0. 0418 36C 1 2/07/23 0. 0014 0. 0100 0. 0152 0. 0283 -0. 0001 0. 0157 0. 0101 0. 0132 -0. 0003 0. 0111 0. 0455 0. 0543

C= Control location, Background location Results in bold type are pos itil.e.

3-31 Dominion Energy Nuclear Connecticut, Inc. Annual Radiological Environmental Millstone Power Station Operating Report 2023

TABLE13 FISH (pCi/g wet wt.)

COLLECTION LOCATION DATE Be-7 K-40 Cr-51 Mn-54 Co-58 Fe-59

(+/-) (+/-) (+/-) (+/-) (+/-) (+/ - )

28 06/13/23 0. 064 0. 186 2. 818 0. 649 -0.102 0.204 -0. 011 0. 020 -0. 006 0. 021 0. 020 0. 046

29 11 /09/23 0. 026 0. 189 4. 196 0. 625 -0. 022 0. 206 0.003 0.021 0.004 0. 023 0. 025 0. 046

35 06/08/23 0.233 0.299 4.203 0. 951 0. 033 0.283 -0. 002 0. 034 0. 010 0. 032 0.086 0.075 35 11/13/23 0. 083 0. 205 3.856 0.702 0.109 0. 233 0. 000 0. 023 0.012 0.024 -0. 023 0. 052

COLLECTION LOCATION DATE Co-60 Zn-65 Nb-95 Zr-95 Ru-103 Ru-106

(+/ - ) (+/-) (+/-) (+/-) (+/-) (+/-)

28 06/13/23 -0. 006 0. 018 -0. 035 0. 050 0. 013 0.023 -0. 018 0.038 -0. 005 0. 021 0.042 0. 177

29 11/09/23 0. 013 0. 024 -0.070 0. 057 0.011 0. 023 0. 010 0. 041 -0. 014 0. 022 0. 034 0. 192

35 06/08/23 -0. 006 0.042 -0. 081 0.076 -0.018 0.037 0.016 0.064 -0. 001 0. 030 -0. 108 0.303 35 11/13/23 -0. 010 0. 028 -0. 027 0. 058 0. 004 0. 027 0. 018 0.041 -0. 003 0.025 -0. 028 0.250

COLLECTION LOCATION DATE Ag-110M Sb-125 1-131 Cs-134 Cs-137 Ac-228

(+/-) (+/-) (+/-) (+/-) (+/-) (+/-)

28 06/13/23 0. 001 0.020 0. 009 0. 048 -0.028 0.057 -0. 006 0. 020 0. 024 0. 020 0. 021 0. 077

29 11/09/23 -0. 012 0. 021 -0. 004 0. 056 -0. 022 0. 053 0.016 0.023 0. 006 0. 023 -0.037 0. 094

35 06/08/23 0. 063 0.034 0. 013 0.086 -0.014 0.057 0.009 0. 040 0.024 0.027 -0.056 0.139 35 11/13/23 0. 001 0. 020 0. 009 0. 066 0.039 0. 045 0. 000 0. 025 -0. 013 0.023 0.100 0. 121

Results in bold type are positi1.e.

3-32 Dominion Energy Nuclear Connecticut, Inc. Annual Radiological Environmental Millstone Power Station Operating Report 2023

TABLE14 OYSTERS (pCi/g wet wt.)

COLLECTION LOCATION DATE --- Be-7 K-40 Cr-51 Mn-54 Co-58 Fe-59

(+/-) (+/-) (+/-) (+/-) (+/-) (+/-)

31 06/26/23 0.092 0.262 2.068 0.929 -0. 077 0. 270 0. 004 0. 032 0. 010 0. 026 -0. 024 0. 066 31 11/14/23 0.073 0.288 1.475 0. 779 -0. 111 0.246 0. 037 0. 039 -0.005 0. 030 0.014 0.069

89C 05/11/23 0. 056 0.207 2.039 0.581 -0. 016 0. 200 0. 010 0. 023 -0. 002 0. 024 0.007 0.053 89C 07/13/23 0.102 0.203 1.458 0.690 0. 183 0. 250 -0. 017 0. 018 -0.018 0. 021 -0.016 0. 053

COLLECTION LOCATION DATE Co-60 Zn-65 Nb-95 Zr-95 Ru-103 Ru-106

(+/-) (+/ -) (+/-) (+/-) (+/-) (+/-)

31 06/26/23 -0.019 0. 034 -0. 046 0. 080 0. 020 0.033 0. 006 0. 055 0. 001 0. 029 -0.101 0. 302 31 11/14/23 0.002 0. 038 -0. 118 0.105 0. 019 0.039 0. 038 0. 060 0. 012 0. 037 -0.007 0.351

89C 05/11/23 -0.005 0.028 0. 016 0. 055 -0. 018 0.025 -0.020 0. 041 -0. 017 0. 025 -0.041 0.205 89C 07/13/23 0. 020 0. 025 -0.003 0.067 -0. 037 0. 026 0. 031 0. 043 -0. 002 0.026 -0.221 0.261

COLLECTION LOCATION DATE Ag-110M Sb-125 1-131 Cs-134 Cs-137 Ac-228

(+/-) (+/-) (+/-) (+/-) (+/-) (+/-)

31 06/26/23 -0. 002 0. 026 -0. 067 0. 078 -0. 021 0. 042 -0. 016 0.032 0. 006 0.032 0.143 0. 128 31 11/14/23 -0.001 0. 037 0.040 0.087 -0.061 0. 050 0. 014 0. 038 0.022 0.041 0. 005 0. 130

89C 05/11/23 -0. 022 0. 023 -0. 012 0.048 -0.011 0. 047 0. 020 0. 020 0. 011 0. 022 -0. 023 0. 090 89C 07/13/23 0. 012 0. 022 -0.009 0.061 0.0 14 0. 042 -0.029 0.026 -0. 018 0.024 0. 043 0. 098

C= Control location, Background location Results in bold type are positi1.e.

3-33 Dominion Energy Nuclear Connecticut, Inc. Annual Radiological Environmental Millstone Power Station Operating Report 2023

TABLE15 CLAMS (pCi/g wet wt.)

COLLECTION LOCATION DATE Be-7 K-40 Cr-51 Mn-54 Co-58 Fe-59

(+/-) (+/-) (+/-) (+/ -) (+/-) (+/-)

29 06/06/23 0.066 0. 235 1.839 0.632 -0.185 0.260 -0. 004 0. 028 0. 018 0. 025 -0. 001 0. 059 29 11/27/23 0. 047 0. 232 2.046 0.637 -0.010 0.264 -0. 007 0. 028 0. 000 0. 030 -0. 044 0. 057

31 06/29/23 0. 033 0. 225 2.038 0. 668 0.056 0.243 0. 002 0. 026 0. 007 0. 026 0.021 0. 052 31 12/05/23 0. 021 0. 172 2.122 0.696 0.047 0.209 -0. 014 0. 026 -0. 019 0. 025 0. 014 0. 038

COLLECTION LOCATION DATE Co-60 Zn-65 Nb-95 Zr-95 Ru-103 Ru-106

(-iT-) (+/-) (+/-) (+/-) (+/-) (+/-)

29 06/06/23 0. 007 0. 033 -0. 023 0. 059 0. 003 0. 029 -0. 001 0. 055 0. 022 0. 028 0. 178 0.298 29 11/27/23 -0. 002 0. 033 0.054 0. 064 -0.006 0.034 0.038 0. 048 -0. 022 0. 027 -0.061 0.219

31 06/29/23 0. 038 0. 036 0. 017 0. 073 -0.010 0. 029 0. 000 0. 049 0. 012 0. 028 0. 037 0.246 31 12/05/23 0. 024 0. 031 -0.029 0.058 0.003 0. 025 0. 04 1 0. 042 -0.015 0.022 0. 033 0.243

COLLECTION LOCATION DATE Ag-110M Sb-125 1-131 Cs-134 Cs-137 Ac-228

(+/-) (+/-) (+/-) (+/-) (+/-) (+/-)

29 06/06/23 0. 000 0. 030 0. 052 0.067 0. 022 0.045 0. 000 0. 032 -0. 009 0. 033 -0.015 0. 124 29 11/27/23 0. 008 0.022 0. 035 0. 070 -0.010 0.045 -0.019 0. 029 -0.021 0.030 -0.014 0. 098

31 06/29/23 0. 017 0. 027 -0. 016 0. 067 -0. 012 0. 056 0. 014 0. 029 -0.002 0.031 -0.052 0. 115 31 12/05/23 0. 007 0. 022 -0. 028 0. 073 0. 005 0. 029 -0. 009 0. 025 -0. 024 0. 025 -0. 020 0.107

Results in bold type are positi1.e.

3-34 Dominion Energy Nuclear Connecticut, Inc. Annual Radiological Environmental Millstone Power Station Operating Report 2023

TABLE16 LOBSTERS (pCi/g wet wt.)

COLLECTION LOCATION DATE Be-7 K-40 Cr-51 Mn-54 Co-58 Fe-59

(+/-) (+/-) (+/-) (+/-) (+/-) (+/-)

35 06/08/23 0. 128 0. 097 1. 984 0.321 -0. 042 0. 103 0. 000 0. 010 0.001 0. 010 -0.008 0.022 35 07/17/23 -0. 184 0. 235 2. 546 0.886 -0. 133 0.260 -0. 013 0.026 -0.012 0. 031 -0.005 0.078

89C 05/30/23 0.187 0. 244 2.785 0.823 -0. 058 0.225 -0.010 0. 023 0. 022 0. 032 0. 006 0.057 89C 08/16/23 0.205 0. 247 2. 230 0.700 0. 039 0.208 0. 008 0.029 -0.004 0. 028 0.023 0.049

COLLECTION LOCATION DATE Co-60 Zn-65 Nb-95 Zr-95 Ru-103 Ru-106

(+/-) (+/-) (+/-) (+/-) (+/-) (+/-)

35 06/08/23 0.005 0. 010 0. 005 0.026 0. 012 0. 013 -0.017 0. 021 -0. 010 0. 011 -0.038 0. 097 35 07/17/23 -0.013 0. 036 -0. 016 0. 083 -0. 038 0. 029 -0. 029 0. 062 -0. 008 0.029 -0.184 0. 318

89C 05/30/23 0. 023 0. 032 -0. 060 0. 065 -0. 005 0. 037 0. 065 0. 051 0. 011 0. 029 -0. 049 0.247 89C 08/16/23 0. 017 0.038 -0. 096 0. 073 -0. 010 0.028 0.006 0. 049 0. 010 0. 024 0. 104 0.240

COLLECTION LOCATION DATE Ag-110M Sb-125 1-131 Cs-134 Cs-137 Ac-228

(+/-) (+/-) (+/-) (+/-) (+/- ) (+/-)

35 06/08/23 -0. 006 0. 010 0.011 0.029 0. 011 0. 020 0. 012 0. 013 0.001 0. 011 0.162 0.064 35 07/17/23 -0. 002 0. 032 0. 025 0.079 -0. 007 0.038 0.013 0.043 -0. 005 0.038, 0. 087 0. 140

89C 05/30/23 0. 016 0. 025 -0. 006 0. 066 -0. 020 0.046 -0.003 0.042 0. 011 0. 026 0.040 0.118 89C 08/16/23 -0. 002 0. 022 -0. 031 0. 079 -0. 005 0.039 -0. 012 0.028 -0. 002 0. 021 0. 091 0.099

C= Control Location, Background location Results in bold type are positi~.

3-35 Dominion Energy Nuclear Connecticut, Inc. Annual Radiological Environmental Millstone Power Station Operating Report 2023

4. DISCUSSION OF RESULTS This section summarizes the results of the analyses on the REMP samples. Station related tritium (H-3) radioactivity was detected in seawater collected at the quarry discharge point. This was within the station boundary. The naturally occurring nuclides of Be-7, K-40, and Ac-228, were detected in some samples. Be-7 is from cosmic radiation. It was observed in fruits, vegetables, air, and broad leaf vegetation samples. K-40 and Ac-228 are two common terrestrial isotopes. K-40 was not seen in well water samples but was observed in other samples. Ac-228 was observed in bottom sediment, soil, and lobsters samples. Cs-137 and Sr-90 from atmospheric nuclear weapons testing in the 1960's has been observed in the past. A study by the Connecticut Department of Energy and Environmental Protection in 2006 affirmed that radioactivity from nuclear weapons testing has decreased to almost non-detectable levels (Reference 19). Since 2006 detection of Cs-137 and Sr-90 in environmental samples has been rare. Cs-137 from nuclear weapons testing was detected above MDC at two locations and at MDC (Minimum Detectable Concentration) at one location in 2023. Based on sample location, it is expected to identify the presence of Cs-137 in undisturbed soil22

The remaining REMP samples obtained during 2023 did not indicate the presence of Cs-137 and the overall trend is decreasing (Figure 4.5-1 ).

4.1 Gamma Exposure Rate (Table 1)

Gamma exposure rate is determined from the integrated exposure measured over a calendar quarter using TLDs. Prior to 1990, Victoreen CaF2(Mn) glass bulb dosimeters were used for these measurements. In 1990, these were replaced by Harshaw CaF2(Mn) chips. In 2000, the CaF2(Mn) TLDs, were replaced with the CaSO4(Tm) Panasonic model UD-814 AS1 TLDs.

Readings are recorded as µR/hr. The unit µR stands for 'micro-roentgen' with a 'micro' being one-millionth of a roentgen. A roentgen is the quantity of radiation equal to 87.6 ergs of energy per gram of air. For gamma exposure a micro-roentgen is equivalent to a micro-rem, a measure of dose to man.

The dosimeters are strategically placed at several onsite locations, as well as at inner and outer offsite locations. Starting in 2001, the collection of TLDs was changed from monthly to quarterly and additional measurement locations were incorporated into the REMP requirements listed in the REMODCM (Reference 8). Three more locations (73-75) were added in mid-2003 to prepare for monitoring the potential effect from the ISFSI. Two dry cask containers were loaded in the first quarter of 2005, three in 2006, three in 2007, three in 2009, three in 2010, four in 2012, six in 2015, five in 2016, three in 2018, seven in 2019, six in 2021, two in 2022, and three in 2023.

Prior to any cask loading, the background readings average recorded from mid 2003 - 2004 were: 9.5 µR/hour at Location 73, 7.5 µR/hour at Location 74, and 6.9 µR/hour at Location 75.

In 2023, the annual average exposure rate measurement for the ISFSI area was 7.5 µR/hour at Location 73, 7.4 µR/hour at Location 74, and 6.5 µR/hour at Location 75. The station offsite dose from ISFSI for 2023 was 0.041 mrem/year, which is below the 25 mrem/year limit per 40.190 CFR.

4-1 Dominion Energy Nuclear Connecticut, Inc. Annual Radiological Environmental Millstone Power Station Operating Report 2023

Table 1 in Section 3.2 lists the exposure rate measurements for all 43 monitored locations.

These measurements demonstrate the general variations in background radiation between the various onsite and offsite locations and include gamma exposure from all sources of radioactivity.

For example, the Weather Shack (Location 2), Quarry East (Location 5), Environmental Laboratory (Location 8), Bay Point Beach (Location 9), Goshen Fire Dept (Location 10), and Corey Road (Location 48) experience higher exposure rates due to their proximity to granite beds and stonewalls. In addition, the control locations in Mystic, Ledyard, Norwich, and Old Lyme (Location 13C, 14C, 15C, and 16C) had background exposure rates consistent with rates seen in the past years.

Figure 4.1-1 shows a historical trend of TLD exposure rate measurements, comparing an annual average of all indicator TLDs, an annual average of all control TLDs, and the annual average of the two most critical indicator locations, location 1 and 3, which are used to represent the two closest site boundary residences in the North-northwest and Northeast directions. The average indicator and control readings were both about 8.0 µR/hour.

Figure 4.1 - 1 also relates the difference in indicator locations 1 and 3 and the annual average of all indicator TLDs to the annual average of the control TLDs collected and measured during coincident periods throughout the year. Locations 1 and 3 are important because they are onsite and located between the plant and nearby populated areas. As discussed earlier, the exposure measurements of many indicator locations onsite (and two of the control locations) are influenced by natural background exposure differences caused by the many granite outcroppings typical of the local area. Figure 4.1-1 shows that the annual average at indicator Location 3 was lower in gamma exposure rate than the average control gamma exposure rate. These differences are the result of the differences in granite at these locations. Location 3 was moved in the second quarter 2009 to minimize the effect of tree covering for the air sampler also located at this location. The 2000 to 2009 data for Location 3 shows an increase likely attributable to 1-3 µR/hr gradients observed from the granite bedrock of the MPS Site (Reference 21 ). Over the last 10 years there has been no significant change in the annual gamma exposure rate (Figure 4.1 - 1 ); the small variation in the results for all indicators, location 1, and locations 3 are expected due to counting statistical variation.

4-2 Dominion Energy Nuclear Connecticut, Inc. Annual Radiological Environmental Millstone Power Station Operating Report 2023

Figure 4.1-1 Annual Gamma Exposure Rate - 20 Year History 10

? All Indicators All Controls

-.c i...

-'s. 9 ? Indicator Location #1 Indicator Location #3

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4-3 Dominion Energy Nuclear Connecticut, Inc. Annual Radiological Environmental Millstone Power Station Operating Report 2023

4.2 Air Particulate Gross Beta Radioactivity {Table 2)

Air is continuously sampled at seven inner ring (0 to 2 miles) locations and one control location (14 miles N) by passing it through glass fiber particulate filters. These samples are collected every two weeks and analyzed for gross beta radioactivity. Results are shown on Figure 4.2-1 and Table 2. Gross beta activity remained at levels similar to that seen over the last decade.

Indicators and control monitoring locations continue to show no significant variation in measured activities and are within the expected calculated uncertainty of +/-0.002 pCi/m3 (see Figure 4.2 -2).

This indicates that any station contribution is not measurable.

Figure 4.2-1 Air Particulate Gross Beta Activity Monthly Average - 2023

0.024

-+- lndkators ~ Cont rol 0.022

0.020 1...... 0.018 iJ

.:!: 0.016 C

0

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Figure 4.2-2 Air Particulate Gross Beta Activity Monthly Averages - 5 Year Trend

-+- Indicators -o-Control 0.025 t-- - ---t::=========================::t- ---

0.02 1 0 0 C

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4-4 Dominion Energy Nuclear Connecticut, Inc. Annual Radiological Environmental Millstone Power Station Operating Report 2023

4.3 Airborne Iodine (Table 3)

Charcoal cartridges are included at all the air particulate monitoring stations for the collection of atmospheric iodine. These cartridges were analyzed for 1-131 every two weeks. No detectable levels of 1-131 were seen in the 2023 charcoal samples.

4.4 Air Particulate Gamma (Table 4)

The air particulate samples that are utilized for the gross beta analyses are composited quarterly and analyzed for gamma emitting isotopes including strontium analysis as a substitute for milk analysis. The results, as shown in Table 4, indicate the presence of naturally occurring Be-7, which is produced by cosmic radiation. No other positive results are seen. These analyses indicate that there was not any detectable station related radioactivity in the air samples.

4.5 Soil (Table 5)

This media is collected annually from one control and two indicator locations. MPS has collected and analyzed soil since 2001. Prior to 2001, soil had not been sampled for over fifteen years because station related detectable activity had not been detected. Since 2001 no station detectable activity has been seen in these samples. Naturally occurring nuclides K-40 and Ac-228 were detected in soil. Cs-137 from nuclear weapons testing was detected slightly above MDC (Minimum Detectable Concentration) in one soil indicator samples in 2023. The control location was below MDC. The results of these samples, allows for the determination of baseline activity levels in soil. This is particularly important for Cs-137 since significant levels from past weapons testing fallout remain in the soil. Figure 4.5-1 shows the trend of Cs-137 in soil samples, the trend appears to be declining with time with an expected counting statistical variation observed over the last 15 years. Baseline levels should be useful in the future, when site characterization and decommissioning of the station become the focus during preparations for license termination.

Figure 4.5-1 Cs-137 In Soil 2

- - Bird Sanctuary, 0.3 Mile NE - Albacore Dr 1.0 Mile N, **, Ledyard 12 Miles NE I 1.8

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~ 1.4 u

Q. 1.2..

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0 '<J.*... **,,

2001 2003 2005 2007 2009 2011 2013 2015 2017 2019 2021 2023

4 -5 Dominion Energy Nuclear Connecticut, Inc. Annual Radiological Environmental Millstone Power Station Operating Report 2023

4.6 Milk (Table 6)

Each year the Land Use Census is used to identify locations of milk animals that should be included in the monitoring program. It is performed annually and is maintained by observations, door-to-door surveys, and consulting with local agriculture authorities. The 2023 census is listed in Appendix A. If a new dairy farm is identified close enough to MPS to be considered an indicator location, the collection of milk at that location would be added.

In 2023, the Land Use Census did not locate any location of commercial milk farms within 1 O miles of Millstone Power Station. Prior to 2018, milk samples were obtained and analyzed for strontium from a farm that is no longer producing milk. A valid substitute for milk analysis is air filters strontium analysis and gamma analysis of broad leaf vegetation. This strontium analysis of air filter was determined to be more effective than milk analysis, (Reference 23). The air sampling stations are located closer to the plant and in the predominant downwind direction.

4. 7 Well Water (Table 7)

All REMP wells samples including ISFSI wells samples were less than the Lower Level of Detection Limit (LLD). Additional samples from other wells were obtained as part of the Groundwater Protection Program (GWPP). Results from the GWPP are reported in the MPS annual " Radioactive Effluent Release Report" for 2023. ISFSI wells results have been documented in Table 7 as required by the Connecticut Siting Council.

4.8 Fruits and Vegetables (Table 8)

Consistent with past years, this media did not show any station effects. Naturally occurring nuclides Be-7 and K-40 were the only isotopes detected in the samples.

4.9 Broad Leaf Vegetation (Table 9)

Consistent with past years, this media did not show any station effects. Most samples had detectable levels of cosmic produced Be-7 and naturally occurring K-40. Occasionally these samples have indicated positive levels of Cs-137 in the past. This can be attributed to fallout from weapons testing which has been widespread in terrestrial samples for many years. Cs-137 was not detected in any of the 2023 collected Broad Leaf Vegetation samples.

4.10 Seawater (Table 10)

The guidance in Reference 15 specifies one sample upstream (control - beyond significant influence of the discharge) and one sample downstream (indicator-beyond but near the mixing zone) for surface water samples. Historically the downstream sample for MPS has been located in the vicinity of discharge (Location 32) which is prior to the mixing zone. This location was chosen since it was readily accessible and not affected by cold weather conditions. Operation of an automatic sampler at the indicator location is necessary for providing a representative sample.

Any dose consequences can be assessed by use of the appropriate dilution factors. It is not necessary to have a continuous sampler at the control location due to the historical relative consistency noted in seawater background activity near the Millstone.

A technician collects an aliquot from the automatic sampler at Location 32 on a weekly frequency.

These samples are composited for monthly analyses. For the Control Location, Giant's Neck (Location 37C), six weekly grab samples are obtained for quarterly compositing.

Naturally occurring K-40 was the only detectable gamma activities seen in these samples.

Measured station related levels of H-3, beta activity, in seawater from the vicinity of discharge (Location 32) were observed in most samples. Tritium releases are typically higher near outages due to the need for increased liquid processing during these times. As mentioned above, these

4-6 Dominion Energy Nuclear Connecticut, Inc. Annual Radiological Environmental Millstone Power Station Operating Report 2023

samples are taken directly from liquid effluent flow prior to dilution into the Long Island Sound.

Tritium builds up in the reactor coolant during each fuel cycle. It is generated during station operation from fission and neutron reactions. Figure 4. 10-1 shows an eighteen-year trend of Tritium (H-3) releases in the MPS liquid effluents versus the measured environmental concentrat ions from the vicinity of discharge location. In 2023 MPS had one outage requiring the processing and subsequent discharge of processed refueling water. The highest quarterly average H-3 value in 2023 for seawater was 1,043 pCi/I, which is well below the drinking water limit established by the Environmental Protection Agency (EPA) of 20,000 pCi/1. The total annual exposure from the liquid discharge pathway for 2023 was 0.001 mrem/yr.

Figure 4.10-1 H-3 Curies Released versus Seawater Concentration 18 Year Trend

-*- Curies discharged -- REMP pCi/liter

2,000 2,000

'i:' QI

2. ~

] 1,500 1,500 s u e.4 ~

n,

.c u C VI 0 i5..

3 1,000 1,000 ~ ~

C

QI

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500 500

Date

4-7 Dominion Energy Nuclear Connecticut, Inc. Annual Radiological Environmental Millstone Power Station Operating Report 2023

4.11 Bottom Sediment (Table 11)

There was no station related radioactivity detected in bottom sediment samples in 2023.

Naturally occurring K-40 is seen in all samples and naturally occurring Ac-228 in some samples.

Bottom sediment is not a significant dose pathway to man, especially at areas not typically used by the public.

4.12 Aquatic Flora (Table 12)

Aquatic flora is a sensitive indicator of low levels of man-made radioactivity (e.g., Mn-54, Co-58, Co -60, Zn-65, 1-131 and Ag-11 Om) in the environment so it was added as a required sample at four locations in revision 28 of the REMODCM. Naturally occurring K-40 was the only isotope detected in the samples.

4.13 Fish (Table 13)

The activity in fish is the same as that seen in the past. No activity was observed except for the naturally occurring K-40.

4.14 Oysters (Table 14)

All locations utilize oysters stocked in trays. Oyster sampling has occasionally presented challenges in obtaining the sample size required for analysis. In 2023 four adequately sized for analysis samples were obtained. Only naturally occurring K-40 was detected in the collected samples. No plant related radioactivity was detected in oysters in 2023.

4.15 Clams (Table 15)

In 2023, only the naturally occurring K-40 was detected in the collected samples.

4.16 Lobsters (Table 16)

In 2023, only the naturally occurring isotopes, K-40 and Ac-228, were detected in the collected samples

4-8 Dominion Energy Nuclear Connecticut, Inc. Annual Radiological Environmental Millstone Power Station Operating Report 2023

5. REFERENCES

1) United States of America, Code of Federal Regulations, Title 10, Part 50, Appendix A Criteria 64.

2) Donald T. Oakley, "Natural Radiation Exposure in the United States," U.S. Environmental Protection Agency, ORP/SID 72-1, June 1972.

3) National Council on Radiation Protection and Measurements, Report No. 160, "Ionizing Radiation Exposures of the Population of the United States," March 2009.

4) National Council on Radiation Protection and Measurements, Report No. 94, "Exposure of the Population of the United States and Canada from Natural Background Radiation,"

December 1987.

5) United States Nuclear Regulatory Commission, Regulatory Guide 8.29, "Instructions Concerning Risks from Occupational Radiation Exposure," Revision 0, July 1981.

6) United States of America, Code of Federal Regulations, Title 10, Part 20.1302.

7) United States Nuclear Regulatory Commission, Regulatory Guide 1.109, "Calculation of Annual Doses to Man from Routine Releases of Reactor Effluents for the Purpose of Evaluating Compliance with 10 CFR Part 50, Appendix I," Revision 1, October 1977.

8) Millstone Power Station Radiological Effluent Monitoring and Offsite Dose Calculation Manual, Revision 30, September 19, 2018

9) Millstone Power Station Unit 1 Defueled Technical Specifications, License No. DPR-21.

10) Millstone Power Station Unit 2 Technical Specifications, License No. DPR-65.

11) Millstone Power Station Unit 3 Technical Specifications, License No. NPF-49.

12) United States Nuclear Regulatory Commission, Regulatory Guide 4.1, "Program for Monitoring Radioactivity in the Environs of Nuclear Power Plants," Rev. 1, April 1975.

13) ICN/Tracerlab, "Millstone Power Station Pre-Operational Environmental Radiation Survey Program, Quarterly Reports," April 1967 to June 1970.

14) International Commission of Radiological Protection, Publication No.43, "Principles of Monitoring for the Radiation Protection of the Population," May 1984.

15) United States Nuclear Regulatory Commission, NUREG-1301, "Offsite Dose Calculation Manual Guidance: Standard Radiological Effluent Controls for Pressurized Water Reactors," April 1991.

16) United States Nuclear Regulatory Commission, Branch Technical Position, "An Acceptable Radiological Environmental Monitoring Program", Rev. 1, November 1979.

17) Reassessment of Millstone Power Station's Environmental Monitoring Data, Connecticut Department of Environmental Protection, Division of Radiation, March 2006.

18) Nuclear Regulatory Commission Regulatory Guide 4.1, Radiological Environmental Monitoring for Nuclear Power Plants, Revision 2, June 2009.

19) Division of Radiation, CT Dept. of Energy and Environmental Protection, "Reassessment of Millstone Power Station's Environmental Monitoring Data," January 2006.

20) Connecticut Sitting Council Decision and Order for ISFSI, Docket No. 265, May 27, 2004.

21) RP-16-08, "Take-Home Thermoluminescent Dosimeter Variance", June 17, 2016.

22) MP-HPO -98137, "Determination of Cs-137 In Undisturbed Soil At Locations Greater Than 10 Miles From Millstone Site", July 28, 1998.

23) MP-HPO-17067, "Milk Availability for the Radiological Environmental Monitoring Program",

October 11, 2017.

5-1 Dominion Energy Nuclear Connecticut, Inc. Annual Radiological Environmental Millstone Power Station Operating Report 2023

APPENDIX A

LAND USE CENSUS FOR 2023

A-1 Dominion Energy Nuclear Connecticut, Inc. Annual Radiological Environmental Millstone Power Station Operating Report 2023

The annual land use census in the vicinity of MPS was conducted as required by the MPS REMODCM. Table A-1 is a list of closest residents in each of twelve over-land compass sectors around Millstone. The list of residents was determined by a survey of properties around Millstone using Google Earth and verified by a field survey. It was assumed that the closest resident was also the closest garden. No changes from the 2022 closest resident list were identified.

Table A-2 is a list of milk and other foods within ten miles of Millstone. Cow and goat milk producers were identified using the State of Connecticut Agriculture Department list of licensees and using American Dairy Goat Association (ADGA). There were no animals producing milk located within ten miles of Millstone Power Station. As a substitute for milk samples, strontium analysis of air filter and gamma analysis of broad leaf vegetation are being performed on quarterly basis.

Other sources of food were obtained from the Internet at http://www.farmfresh.org by searching for businesses closest to Waterford, CT. A search using Google Earth and field surveys were used to identify additional sources, Figure A-1. No changes from the 2022 sources of food locations were identified.

The 2023 Land Use Census also evaluated aquatic sampling exposure pathways from the fish and shellfish located around MPS. Figure A-2 shows shellfish beds around MPS from the Bureau of Aquaculture of the Department of Agriculture. The saltwater fishing areas are identified in Figure A-3. No changes from the 2022 aquatic sampling exposure pathways were identified.

The dose modeling incorporates the distances listed in Tables A - 1, A-2.

A-2 Dominion Energy Nuclear Connecticut, Inc. Annual Radiological Environmental Millstone Power Station Operating Report 2023

Table A-1 2023 S urvey

Downwind Resident/Garden 1 Direction miles meters N 0.95 1,529

NNE 0.53 853 NE 0.47 756 ENE 0.50 805

E 0.92 1,481 ESE 1.06 1,706 SE 2 N/A N/A

SSE 2 N/A N/A s2 N/A N/A ssw 2 N/A N/A

SW 2.28 3,669 WSW 1.95 3,138 w 1.78 2,865

WNW 1.51 2,430 NW 1.35 2,173 NNW 0.51 821

Notes:

1. No gardens located closer than resident.

2. Sectors SE thru SSW are N/A because they are over water.

A-3 Dominion Energy Nuclear Connecticut, Inc. Annual Radiological Environmental Millstone Power Station Operating Report 2023

Table A-2 Dairy and food producers within Ten miles of Millstone - 2023

Sector Miles Business Location Comments

NW 1.95 Smith's Acres Niantic Fruits and vegetables NE 1.96 Mingo Goat Waterford Registered ADGA member only, no goats on site.

ENE 2.8 Secchiaroli Farms Waterford Has pigs, fed nonlocal sources and have concrete pens N 3.2 Scotts' Farm & Waterford Fruits Garden and vegetables

WNW 5.0 Four Mile River Farm Old Lyme Eggs, Meat

NW 5.2 Scott's Yankee East Lyme Fruits, Farmer vegetables, and cider

NNW 5.3 White Gate Farm East Lyme Vegetables, Herbs, Eggs, Meat, Nursery, and Flowers

ENE 6.8 Leverett Goat Groton Registered ADGA member only, no goats on site.

N 7.4 Hunts Brook Farm Quaker Hill Honey, Maple, and Vegetables

ENE 7.5 Groton Family Farm Groton Vegetables, Honey, Maple, and Eggs NE 8.3 Red Fence Farm Groton Fruits, vegetables, cows, and pig.

Cows not producing milk N 9.2 Valchris Farm Oakdale Organic Fruits & Vegetables

Table A-3 C urren ts amI DlnQ ocaIons or eqe a I0n -I' L t' f V tt' 2023 No. DescriQtion Farm Name City Sam12le TyQe

25 -1 Indicator Within 10 Miles Red Fence Farm Groton Vegetation

25-X Extra Within 10 Miles Scotts' Farm & Garden Waterford Vegetation

26-C Control Beyond 10 Miles Scott's Orchard Farm Market Old Vegetation Saybrook

26-X Extra Beyond 10 Miles Scott's Orchard Farm Market Old Vegetation Saybrook

A-4 Dominion Energy Nuclear Connecticut, Inc. Annual Radiological Environmental Millstone Power Station Operating Report 2023

Figure A-1 Farms and Goats Products within ten miles of Millstone

...* ~ricultural Farms

o> Goat Farms

A-5 Dominion Energy Nuclear Connecticut, Inc. Annual Radiological Environmental Millstone Power Station Operating Report 2023

Figure A-2 Shellfish Beds in Vicinity of Millstone

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cr_SheUrls h_Cl nalfl c.a U on CT Department of Agriculture Bureau of Aquaculture -~

East Lyme / Waterford N - boon_t-- o ~A;ie,t.....e Recreat iona l Shellfishing A f2ZJ Caea _!.,._R<<r*- -~ c:J ~ y ~A.-cnal CT_Rocn atlo na l_Bed s - ~,R-.JtN y

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A-6 Dominion Energy Nuclear Connecticut, Inc. Annual Radiological Environmental Millstone Power Station Operating Report 2023

Figure A-3 Saltwater Fishing Resource Map Saltwater Fishing,. Resource Map

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A-7 Dominion Energy Nuclear Connecticut, Inc. Annual Radiological Environmental Millstone Power Station Operating Report 2023

APPENDIX B

SUMMARY

OF INTERLABORATORY COMPARISONS

B-1 Dominion Energy Nuclear Connecticut, Inc. Annual Radiological Environmental Millstone Power Station Operating Report 2023

Summary of Results - Inter-laboratory Comparison Program (ICP)

The TBE Laboratory analyzed Performance Evaluation (PE) samples of air particulate (AP), air iodine, milk, soil, vegetation, and water matrices that represent test & matrix combinations available for REMP programs. The PE samples supplied by Analytics Inc., Environmental Resource Associates (ERA) and Department of Energy (DOE) Mixed Analyte Performance Evaluation Program (MAPEP), were evaluated against the following pre-set acceptance criteria:

A. Analytics Evaluation Criteria

Analytics' evaluation report provides a ratio of TBE's result and Analytics' known value. Since flag values are not assigned by Analytics, TBE evaluates the reported ratios based on internal QC requirements based on the DOE MAPEP criteria.

B. ERA Evaluation Criteria

ERA's evaluation report provides an acceptance range for control and warning limits with associated flag values. ERA's acceptance limits are established per the US EPA, National Environmental Laboratory Accreditation Conference (NELAC), state-specific Performance Testing (PT) program requirements or ERA's SOP for the Generation of Performance Acceptance Limits, as applicable. The acceptance limits are either determined by a regression equation specific to each analyte or a fixed percentage limit promulgated under the appropriate regulatory document.

C. DOE Evaluation Criteria

MAPEP's evaluation report provides an acceptance range with associated flag values. MAPEP defines three levels of performance:

Acceptable (flag = "A") - result within +/- 20% of the reference value

Acceptable with Warning (flag = "W") - result falls in the +/- 20% to +/- 30% of the reference value

Not Acceptable (flag = "N") - bias is greater than 30% of the reference value

Note: The Department of Energy (DOE) Mixed Analyte Performance Evaluation Program (MAPEP) samples are created to mimic conditions found at DOE sites which do not always resemble typical environmental samples obtained at commercial nuclear power facilities.

For the TBE laboratory, 124 out of 131 analyses performed met the specified acceptance criteria.

Seven analyses did not meet the specified acceptance criteria and were addressed through the TBE Corrective Action Program. A summary is found below:

1. The MAPEP February 2023 Soil Ni-63 result was evaluated as Not Acceptable. TBE's reported value was 294 Bq/kg and the known result was 1130 Bq/kg (range 791 - 1469).

The sample was reprepped by a different (senior) lab technician with results of 1120 &

1250 Bq. It was determined that there was a difference between the two techs during the sample prep (technique) and the procedure was revised to reflect these differences including using a specific aliquot amount. (NCR 23-08)

2. The MAPEP February 2023 vegetation Sr-90 result was evaluated as Not Acceptable.

The reported value was 0.05 Bq (not detected) and the known result was a "false positive". This was considered to be a statistical failure because TBE's reported result with 3 times the uncertainty resulted in a slightly positive net result (0.03194 Bq/kg). The B-2 Dominion Energy Nuclear Connecticut, Inc. Annual Radiological Environmental Millstone Power Station Operating Report 2023

reported result was significantly below TBE 's average detection limit for vegetation samples. (NCR 23-09)

3. The ERA RAD February 2023 water Ba-133 result was eva luated as Not Acceptable. The reported value was 26.0 pCi/L and the known was 22.3 (acceptance range 17.1 - 25.8 pCi) or 117% of the known (acceptable for TBE QC). The sample was used as the workgroup duplicate with a result of 25.4 (114%). The sample had also been counted on a different detector with a result of 21.9 (98%). The was TBE ' s first failure for Ba - 133.

(NCR 23-10)

4. The MAPEP August 2023 soil Fe-55 result was evaluated as Not Acceptable. The reported value was 346 Bq/kg and the known result was 1280 (acceptance range of 896-1664 Bq/kg). This was TB E's initial evaluation for Fe-55 in soils. The result was received at the end of December and the root cause in under investigation. No client samples were associated with this cross-check. (CAR 23-31)

5. The Analytics September 2023 milk Sr-90 result was evaluated as Not Acceptable. The reported result was 7.28 pCi/L and the known result was 12.8 (57% of known). This sample was used as the workgroup duplicate and the carrier yields for both samples were 107% and 75%. The LCS recovery for the workgroup was at 106%. The ERA drinking water Sr-90 cross check that was analyzed around the same time was acceptable at 108%. There was no explanation for the failure. This is the first low biased fa ilure for Sr-90 milk. The last failure (high) was in 2016. (NCR 23 -24)

6. The ERA RAD October 2023 water Gross Alpha result was evaluated as Not Acceptable.

The reported result was 53.2 pCi/L and the known result was 70.6 (acceptable range of 54.0- 87.2 pCi/L). The reported result was the workgroup duplicate and was within 75%

of the known value (within TBE QC range). The original result was 63.3 pCi/L (90% of the known). Because the LCS result was biased slightly high, the decision was made to report the lower value. (NCR 23-20)

7. The ERA RAD October 2023 water 1-131 result was evaluated as Not Acceptable. The reported value was 23.5 pCi/L and the known result was 29.7 (acceptable range of 25.8

- 33.6) The reported result was 79% of the known, which is within the acceptable TBE QC range. The workgroup was reviewed with no anomalies found. The LCS/LCSD results were 109% and 86.1 %. The sample was not processed in a timely manner as per the ERA instructions which stated to analyze shortly after receipt due to the short half life. Going forward, the QA &/or Lab Mgr. will ensure that this analysis is started sooner.

(NCR 23-21)

The Inter-Laboratory Comparison Program provides evidence of " in control" counting systems and methods, and that the laboratories are producing accurate and reliable data.

B-3 Dominion Energy Nuclear Connecticut, Inc. Annual Radiological Environmental Millstone Power Station Operating Report 2023

Analytics Environmental Radioactivity Cross Check Program I~l!Ub£ll~ ac12l0!1J i;;1Jgiml~Ci1Jg i;;1Jll:i[!21llll~llli1I S~Cll:i!.~l:i

Month/Year Number Matrix Nuclide Units Reported Value (a) Analytics Result Evaluation ibl Identification TBE Known Ratio ofTBE to

Value

March 2023 E13826 Milk Sr-89 pCi/L 70.5 93.1 0.76 w Sr-90 pCi/L 12.3 14.7 0.84 A

E13827 Milk Ce-141 pCi/L 127 139 0.91 A Co-58 pCi/L 119 131 0.91 A Co-60 pCi/L 250 279 0.90 A Cr-51 pCi/L 246 302 0.82 A Cs-134 pCi/L 172 200 0.86 A Cs-137 pCi/L 125 140 0.89 A Fe-59 pCi/L 122 122 1.00 A 1-131 pCi/L 70.2 82.0 0.86 A Mn-54 pCi/L 165 180 0.92 A Zn-65 pCi/L 306 306 1.00 A

E13828 Charcoal 1-131 pCi 79.0 89.9 0.88 A

E13829 AP Ce-141 pCi 91.9 87.8 1.05 A Co-58 pCi 87.5 82.5 1.06 A Co-60 pCi 199 176 1.13 A Cr-51 pCi 218 191 1.14 A Cs-134 pCi 119 126 0.94 A Cs-137 pCi 92.4 88.7 1.04 A Fe-59 pCi 95.5 76.9 1.24 w Mn-54 pCi 120 113 1.06 A Zn-65 pCi 179 193 0.93 A

E13830 Soil Ce-141 pCi/g 0.224 0.220 1.02 A Co-58 pCi/g 0.193 0.207 0.93 A Co-60 pCi/g 0.406 0.441 0.92 A Cr-51 pCi/g 0.464 0.477 0.97 A Cs-134 pCi/g 0.334 0.316 1.06 A Cs-137 pCi/g 0.270 0.288 0.94 A Fe-59 pCi/g 0.183 0.193 0.95 A Mn-54 pCi/g 0.263 0.284 0.93 A Zn-65 pCi/g 0.475 0.484 0.98 A

E13831 AP Sr-89 pCi 99.4 90.8 1.09 A Sr-90 pCi 14.6 14.3 1.02 A

(a) The Analytics known value is equal to 100% of the parameter present in the standard as determined by gravimetric and/or volumetric measurements made during standard preparation (b) Analytics evaluation based on TBE internal QC limits:

A= Acceptable - reported result falls within ratio limits of 0.80-1.20 W = Acceptable with warning - reported result falls within 0.70-0. 80 or 1.20-1.30

B-4 Dominion Energy Nuclear Connecticut, Inc. Annual Radiological Environmental Millstone Power Station Operating Report 2023

Analytics Environmental Radioactivity Cross Check Program I~l!U;i)!D~ ac'2l0£D l;agia~~ciag l;Dl£iC'2DW~Dtii!I S~Cl£i!.~li

Month/Year Number MatriIdentification TBE Known Ratio ofTBE to x Nuclide Units Reported Value (al Analytics Result Evaluation (bl Value N = No t Acc ep tabl e - reported result fa lls o utside the ra tio limits of < 0. 70 a nd > 1.30

September 2023 E13832 Milk Sr-89 pCi/L 49.8 71.4 0.70 w Sr-90 pCi/L 7.28 12.8 0.57 N(1l

E13833 Milk Ce - 141 pCi/L 93.4 104 0.90 A Co -58 pCi/L 58.2 65.8 0.88 A Co -60 pCi/L 190 223 0.85 A Cr-51 pCi/L 207 205 1.01 A Cs-134 pCi/L 96.0 114 0.84 A Cs-137 pCi/L 121 141 0.86 A Fe - 59 pCi/L 78.8 78.8 1.00 A 1-131 pCi/L 27.9 37.4 0.75 w Mn -54 pCi/L 128 146 0.88 A Zn-65 pCi/L 185 203 0.91 A

E13834 Charcoal 1-131 pCi 76.9 78.7 0.98 A

E13835 AP Ce-141 pCi 91.9 87.1 1.05 A Co-58 pCi 58.7 55.2 1.06 A Co-60 pCi 200 187 1.07 A Cr-51 pCi 192 172 1.12 A Cs-134 pCi 89.6 96 0.94 A Cs-137 pCi 109 119 0.92 A Fe-59 pCi 68.3 66.1 1.03 A Mn -54 pCi 129 123 1.05 A Zn-65 pCi 163 171 0.96 A

E13836 Soil Ce-141 pCi/g 0.228 0.184 1.24 w Co-58 pCi/g 0.103 0.116 0.89 A Co -60 pCi/g 0.364 0.394 0.92 A Cr-51 pCi/g 0.371 0.362 1.02 A Cs-134 pCi/g 0.176 0.202 0.87 A Cs-137 pCi/g 0.285 0.315 0.90 A Fe-59 pCi/g 0.140 0.139 1.00 A Mn-54 pCi/g 0.237 0.259 0.92 A Zn-65 pCi/g 0.349 0.359 0.97 A

E13837 AP Sr-89 pCi 74.6 80.2 0.93 A Sr-90 pCi 13.9 14.4 0.96 A

(a ) The Analytics kn ow n va lue is equ a l to 100 % of the param eter present in the sta ndard a s de termin ed by gravim e tric a nd/ o r volum etric m eas ure m ents m a de during standard prepa ratio n (b} An a lytics e va lua tio n b ase d o n TBE inte rnal QC limits:

A= Ac c epta ble-reported result fa lls within ratio limits o f0.80- 1.20 W= Acceptabl e w ith warning - reported re sult falls within 0. 70-0.80 or 1.20-1.30 N = Not Acce pta ble - repo rted result fa lls out side the ratio limits of < 0. 70 a nd > 1.30

(1) See NCR 23-24

B-5 Dominion Energy Nuclear Connecticut, Inc. Annual Radiological Environmental Millstone Power Station Operating Report 2023

DOE's Mixed Analyte Performance Evaluation Program (MAPEP)

Teledyne Brown Engineering Environmental Services

Month/Year Number Matrix Nuclide Units Reported (a) Range Evaluation (b) Identification TSE Known Acceptance Value

February 2023 23-MaS48 Soil Ni-63 Sq/kg 294 1130 791 - 1469 N(3)

23-MaSU48 Urine Cs-134 Sq/L 9.92 10 6.7 - 12.4 A Cs-137 Sq/L 0.0994 (1) A Co-57 Sq/L 9.35 8.67 6.07-11.27 A Co-60 Sq/L 9.03 8.13 5.69 - 10.57 A Mn-54 Sq/L 11.80 10.0 7.0-13.0 A U-234 Sq/L 0.01 Not spiked U-238 Sq/L 0.01 Not spiked Zn-65 Sq/L 10.60 9.29 6.50 - 12.08 A

23-MaW48 Water Ni-63 Sq/L 23.1 27.3 19. 1 - 35.5 A

23-RdV48 Vegetation Cs-134 Sq/sample 5.6 7.6 5.32 - 9.88 w Cs-137 Sq/sample 0.03 (1) A Co-57 Sq/sample 5.9 6.9 4.85 - 9.01 A Co-60 Sq/sample 5.00 6.51 4.56 - 8.46 w Mn-54 Sq/sample 6.08 8.03 5.62 - 10.44 w Sr-90 Sq/sample 0.05 (1) N(4)

Zn-65 Sq/sample 5.49 7.43 5.20- 9.66 w

August 2023 23-MaS49 Soil Fe-55 Sq/kg 346 1280 896 - 1664 N(s)

Ni-63 Sq/kg 1260 1370 959 -1781 A

23-MaW49 Water Ni-63 Sq/L 1.0 (2) A

23-RdV49 Vegetation Cs-134 Sq/sample 3.860 4.98 3.49 - 6.47 w Cs-137 Sq/sample 0.027 (1) A Co-57 Sq/sample 3.88 4.24 2.97 - 5.51 A Co-60 Sq/sample 2.37 2.79 1.95 - 3.63 A Mn-54 Sq/sample 2.04 2.56 1.79-3.33 w Sr-90 Sq/sample 0.96 1.17 0.82 - 1.52 A Zn-65 Sq/sample -0.514 (1) A

(a ) The MAPEP known value is equal to 100% of the parameter present in the standard as determined by gravimetric and/or volumetric measurements made during standard preparation (b) DOEIMAPEP evaluation:

A= Acceptable - reported result falls within ratio limits of 0.80-1.20 W = Acceptable with warning-reported result falls within 0.70-0.80 or 1.20-1.30 N = Nol Acceptable - reported result falls outside the ratio limits of< 0. 70 and> 1.30

(1) False positive test (2) Sensitivity evaluation (3) See NCR 23-08 (4) See NCR 23-09 (5) Initial evaluation - See CAR 23-31

B-6 Dominion Energy Nuclear Connecticut, Inc. Annual Radiological Environmental Millstone Power Station Operating Report 2023

ERA Environmental Radioactivity Cross Check Program Teledyne Brown Engineering Environmental Services

Number Value Value I*MonthNear Identification Matrix Nuclide Units TBE Reported Known Acceptance Evaluat ion lhl > Limits

March 2023 MRAD-38 Water Am-241 pCi/L 28.1 32.1 22.0 - 41.0 A Fe-55 pCi/L 1180 1380 811-2010 A Pu-238 pCi/L 65.6 70.7 42.5 - 91.6 A Pu-239 pCi/L 82.9 92.4 57.2 - 114 A

Soil Sr-90 pCi/kg 2630 2580 803 -4020 A

AP GR-A pCi/filter 69.6 76.8 40.1 -127 A GR-B pCi/filter 36.8 32.8 19.9 - 49.6 A

April 2023 RAD-133 Water Ba-133 pCi/L 26.0 22.3 17.1 - 25.8 Nl'l Cs -134 pC i/L 72.1 77.6 63.4 - 85.4 A Cs-137 pCi/L 62.1 63.1 56.8 - 72.2 A Co-60 pCi/L 32.6 30.3 26.7 - 36.1 A Zn-65 pCi/L 253 242 218 - 283 A GR-A pC i/L 34.2 29.2 14.9 - 38.2 A GR-8 pCi/L 64.3 60.7 41.8-67.4 A U-Nat pCi/L 61.75 62.7 51.2 - 69.0 A H-3 pCi/L 13,300 12700 11,100-14,000 A Sr-89 pCi/L 67.0 61.1 49.2 - 69.0 A Sr-90 pCi/L 36.5 36.0 26.4-41.5 A 1-131 pCi/L 24.3 28.7 23.9 - 33.6 A

September 2023 MRAD-39 Water Am-241 pCi/L 54.0 71.0 48.7 - 90.8 A Fe-55 pCi/L 2430 2630 1550 - 3830 A Pu -238 pCi/L 172 177 106 - 229 A Pu-239 pCi/L 171 182 113 - 224 A

Soil Sr-90 pCi/kg 9580 6800 2120 - 10,600 A

AP GR-A pCi/filter 82.2 79.8 41.7 -131 A GR-8 pCi/filter 54.3 42.6 25.8 -64.4 A

October 2023 RAD-135 Water Ba-133 pCi/L 86.3 92.2 73.8 - 111 A Cs-134 pCi/L 38.4 41.2 27.9 - 54.5 A Cs -137 pCi/L 194 199 161 - 237 A Co-60 pCi/L 49.5 47.8 33.8 - 61.8 A Zn-65 pCi/L 59.7 57.0 23.7 - 90.3 A GR-A pCi/L 53.2 70.6 54.0 - 87.2 Nl'l GR-8 pCi/L 46.9 42.2 30.5 - 53.9 A U-Nat pCi/L 51.26 51.7 45.9 - 57.5 A H-3 pCi/L 20,100 22,900 19,700 - 26,100 A Sr-89 pCi/L 51.1 38.2 25.2 - 51.2 A Sr-90 pCi/L 31.7 35.7 30.3 - 41.1 A 1-131 pCi/L 23.5 29.7 25.8 - 33.6 Nl'l (a) The ERA known value is equal to 100% of the param eter present in the standard as determined by grav imetric and/or volumetr ic measurements made during standard preparation.

(b) ERA evaluation:

A = Acceptable - Reported value falls within the Acceptance Limits N = Not Acceptable - Reported value falls outside of the Acceptance Limits (1) See NCR 23-10 (2) See NCR 23-20 (3) See NCR 23-21

B-7 Dominion Energy Nuclear Connecticut, Inc. Annual Radiological Environmental Millstone Power Station Operating Report 2023

APPENDIX C

ERRATUM

C-1 Dominion Energy Nuclear Connecticut, Inc. Annual Radiological Environmental Millstone Power Station Operating Report 2023

Erratum-Correction to Previously Published Annual Radiological Environmental Operating Report

In the 2023 Annual Radiological Environmental Operating Report there were no correction identified to previously published Annual Radiological Environmental Operating Reports.

C-2

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