ML25135A436

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Annual Radiological Environmental Operating Report 2024
ML25135A436
Person / Time
Site: Palo Verde  Arizona Public Service icon.png
Issue date: 05/15/2025
From: Dilorenzo M
Arizona Public Service Co
To:
Office of Nuclear Reactor Regulation, Document Control Desk
References
102-08937-MDD/ARS
Download: ML25135A436 (1)
v • d • e


Text

Technical Specification 5.6.2 5.6.2 A member of the STARS Alliance LLC Callaway

  • Diablo Canyon
  • Palo Verde
  • Wolf Creek Palo Verde Nuclear Generating Station P.O. Box 52034 Phoenix, AZ 85072 Mail Station 7636 Tel: (623) 393-3495 102-08937-MDD/ARS May 1, 2025 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, DC 20555-0001

Subject:

Palo Verde Nuclear Generating Station Units 1, 2, and 3 Renewed Operating License Nos. NPF-41, NPF-51, and NPF-74 Docket Nos. STN 50-528, STN 50-529, and STN 50-530 Annual Radiological Environmental Operating Report 2024 Enclosed please find the Palo Verde Nuclear Generating Station (PVNGS) Units 1, 2, and 3 Annual Radiological Environmental Operating Report for 2024. Arizona Public Service Company is submitting this report pursuant to the PVNGS Technical Specification Reporting Requirement, Section 5.6.2.

No new commitments are being made to the Nuclear Regulatory Commission by this letter.

Should you need further information regarding this submittal, please contact me at (623) 393-3495.

Sincerely, Michael D. DiLorenzo Department Leader Nuclear Regulatory Affairs MDD/ARS/cmr

Enclosure:

Palo Verde Nuclear Generating Station Annual Radiological Environmental Operating Report 2024 cc:

J. Monninger NRC Region IV Regional Administrator W. T. Orders NRC NRR Project Manager for PVNGS A. T. Tran Acting NRC Senior Resident Inspector for PVNGS B. D. Goretzki Bureau Chief, Bureau of Radiation Control - Arizona Department of Health Services Dilorenzo, Michael D(Z99838)

Digitally signed by Dilorenzo, Michael D(Z99838)

Date: 2025.05.15 12:04:59 -07'00'

Enclosure Palo Verde Nuclear Generating Station Annual Radiological Environmental Operating Report 2024

1. TABLE OF CONTENTS
1.

Introduction............................................................................................................................. 2 1.1 Overview......................................................................................................................... 2 1.2 Radiation and Radioactivity............................................................................................ 3

2.

Description of the Monitoring Program.................................................................................. 4 2.1 Radiological Environmental Monitoring Program......................................................... 4 2.2 Radiological Environmental Monitoring Program Changes for 2024............................ 4 2.3 REMP Deviations/ Abnormal Events Summary.............................................................. 5 2.4 Groundwater Protection.................................................................................................. 6

3.

Sample Collection Program.................................................................................................. 12 3.1 Water............................................................................................................................. 12 3.2 Vegetation..................................................................................................................... 12 3.3 Milk............................................................................................................................... 12 3.4 Air................................................................................................................................. 12 3.5 Soil, Sludge, and Sediment........................................................................................... 12

4.

Analytical Procedures........................................................................................................... 13 4.1 Air Particulate............................................................................................................... 13 4.1.1 Gross Beta.................................................................................................................... 13 4.1.2 Gamma Spectroscopy.................................................................................................. 13 4.2 Airborne Radioiodine.................................................................................................... 13 4.2.1 Gamma Spectroscopy.................................................................................................. 13 4.3 Milk............................................................................................................................... 13 4.3.1 Gamma Spectroscopy.................................................................................................. 13 4.4 Vegetation..................................................................................................................... 13 4.4.1 Gamma Spectroscopy.................................................................................................. 13 4.5 Sludge/Sediment........................................................................................................... 14 4.5.1 Gamma Spectroscopy.................................................................................................. 14 4.6 Water............................................................................................................................. 14 4.6.1 Gamma Spectroscopy.................................................................................................. 14 4.6.2 Tritium......................................................................................................................... 14 4.6.3 Gross Beta.................................................................................................................... 14 PVNGS ANNUAL RADIOLOGICAL ENVIRONMENTAL OPERATING REPORT-2024 Page ii

4.7 Soil................................................................................................................................ 14 4.7.1 Gamma Spectroscopy.................................................................................................. 14

5.

Nuclear Instrumentation........................................................................................................ 15 5.1 Gamma Spectrometer.................................................................................................... 15 5.2 Liquid Scintillation Spectrometer................................................................................. 15 5.3 Gas Flow Proportional Counter.................................................................................... 15

6.

Isotopic Detection Limits and Reporting Criteria................................................................. 16 6.1 Lower Limits of Detection............................................................................................ 16 6.2 Data Reporting Criteria................................................................................................. 16 6.3 LLD and Reporting Criteria Overview......................................................................... 16

7.

Inter laboratory Comparison Program................................................................................... 20 7.1 Quality Control Program............................................................................................... 20 7.2 Intercomparison Results................................................................................................ 20

8.

Data Interpretation and Conclusions..................................................................................... 22 8.1 Air Particulates.............................................................................................................. 22 8.2 Airborne Radioiodine.................................................................................................... 22 8.3 Vegetation..................................................................................................................... 22 8.4 Milk............................................................................................................................... 23 8.5 Drinking Water............................................................................................................. 23 8.6 Groundwater................................................................................................................. 23 8.7 Surface Water................................................................................................................ 23 8.8 Sludge and Sediment..................................................................................................... 23 8.8.1 Water Resources Centrifuge Waste Sludge................................................................. 23 8.8.2 Cooling Tower Sludge................................................................................................. 24 8.9 Data Trends................................................................................................................... 24 8.10 Hard-To-Detect Radionuclide Results.......................................................................... 24

9.

Optically Stimulated Luminescent Dosimeter (OSLD)........................................................ 46 Results and Data........................................................................................................................... 46

10.

Land Use Census............................................................................................................... 51 10.1 Introduction................................................................................................................... 51 10.2 Census Results.............................................................................................................. 51

11.

Summary and Conclusions............................................................................................... 56

12.

References......................................................................................................................... 60 PVNGS ANNUAL RADIOLOGICAL ENVIRONMENTAL OPERATING REPORT-2024 Page iii

LIST OF TABLES Table 2-1 TLD - OSLD Comparison.............................................................................................. 5 Table 2-2 Sample Collection Locations.......................................................................................... 7 Table 2-3 Sample Collection Schedule........................................................................................... 8 Table 2-4 Summaries of the REMP Deviations/ Abnormal Events................................................ 9 Table 6-1 ODCM Required Lower Limits of Detection (a priori)............................................... 18 Table 6-2 ODCM Required Reporting Levels.............................................................................. 19 Table 6-3 Typical MDA Values................................................................................................... 19 Table 7-1 Interlaboratory Comparison Results............................................................................. 21 Table 8-1 Particulate Gross Beta in Air - First and Second Quarters.......................................... 25 Table 8-2 Particulate Gross Beta in Air-Third and Forth Quarters............................................ 26 Table 8-3 Gamma in Air Filter Composites................................................................................. 27 Table 8-4 Radio iodine in Air - First and Second Quarters.......................................................... 28 Table 8-5 Radioiodine in Air - Third and Forth Quarters............................................................ 29 Table 8-6 Vegetation..................................................................................................................... 30 Table 8-7 Milk.............................................................................................................................. 31 Table 8-8 Drinking Water............................................................................................................. 32 Table 8-9 Groundwater................................................................................................................. 34 Table 8-10 Surface Water............................................................................................................. 35 Table 8-11 Sludge/Sediment......................................................................................................... 40 Table 8-12 Hard-To-Detect Radionuclide Results...................................................................... 41 Table 9-1 OSLD Site Locations.................................................................................................... 47 Table 9-2 Environmental OSLD Results...................................................................................... 48 Table 10-1 Land Use Census........................................................................................................ 52 Table 11-1 Environmental Radiological Monitoring Program Annual Summary........................ 57 PVNGS ANNUAL RADIOLOGICAL ENVIRONMENTAL OPERATING REPORT-2024 Page iv

TABLE OF FIGURES Figure 1-1 Sources of Radiation Exposure in the United States..................................................... 3 Figure 2-1 REMP Sample Sites-Map (0-10 miles)...................................................................... 10 Figure 2-2 REMP Sample Sites-Map (10-35 Miles)................................................................... 11 Figure 8-1 Gross Beta in Air, 1st-2nd Quarters............................................................................ 41 Figure 8-2 Gross Beta in Air, 3rd-4th Quarters............................................................................ 42 Figure 8-3 Historical Gross Beta in Air (Weekly System Average)............................................ 42 Figure 8-4 Historical Gross Beta in Air (Annual Site to Site Comparisons) Compared to Pre-Op

....................................................................................................................................................... 43 Figure 8-5 Gross Beta in Drinking Water..................................................................................... 43 Figure 8-6 Evaporation Pond Tritium Activity (Pre-Op-2008)................................................... 44 Figure 8-7 Evaporation Pond Tritium Activity (2017-2024)........................................................ 44 Figure 8-8 Sedimentation Basin 2 Cs-137.................................................................................... 45 Figure 9-1 Network Environmental OSLO Exposure Rate.......................................................... 49 Figure 9-2 Environmental OSLO Comparison: Pre-Operational versus 2024............................. 50 Figure 10-1 Historical Comparison of Nearest Resident Dose..................................................... 53 Figure 10-2 Historical Comparison of Nearest Milk Animal Dose.............................................. 54 Figure 10-3 Historical Comparison of Nearest Garden Dose....................................................... 55 PVNGS ANNUAL RADIOLOGICAL ENVIRONMENTAL OPERATING REPORT-2024 Pagev

ABSTRACT The Radiological Environmental Monitoring Program (REMP) is an ongoing program conducted by Arizona Public Service Company (APS) for the Palo Verde Nuclear Generating Station (PVNGS). Various types of environmental samples are collected near PVNGS and analyzed for plant-related radionuclide concentrations.

During 2024, the following categories of samples were collected by APS:

Broadleaf vegetation Groundwater Drinking water Surface water Airborne particulate and radioiodine Goat milk Sludge Optically Stimulated Luminescent Dosimeters (OSLDs) were used to measure environmental gamma radiation.

The Arizona Department of Health Services, Bureau of Radiation Control (BRC) performs radiochemistry analyses on various duplicate samples provided to them by APS. Samples analyzed by BRC include onsite samples from the Reservoirs, Evaporation Ponds, and two (2)

Deep Wells. Offsite samples analyzed by BRC include two (2) local resident wells. BRC also performs air sampling at seven (7) offsite locations identical to APS and maintains approximately fifty (50) environmental dosimetry monitoring locations, eighteen (18) of which are duplicates of APS locations.

A comparison of pre-operational and operational data indicates no changes to environmental radiation levels.

(NOTE: Reference to APS throughout this report refers to PVNGS personnel)

PVNGS ANNUAL RADIOLOGICAL ENVIRONMENTAL OPERATING REPORT-2024 Page 1

1. Introduction This report presents the results of the operational Radiological Environmental Monitoring Program conducted by Arizona Public Service Company (APS). The Radiological Environmental Monitoring Program (REMP) was established for the Palo Verde Nuclear Generating Station (PVNGS) by APS in 1979.

This report contains the measurements and findings for 2024. All references are specifically identified in Section 12.

1.1 Overview The Radiological Environmental Monitoring Program (REMP) provides representative measurements of radiation and radioactive materials in exposure pathways. The REMP measures radionuclides that lead to the highest potential radiation exposures to members of the public resulting from station operation. This monitoring program implements Title 10 of the Code of Federal Regulations (CFR) Part 50, Appendix I,Section IV.B.2., and thereby supplements the radiological effluent monitoring program by verifying that the measurable concentrations of radioactive materials and levels of radiation are not higher than expected based on the effluent measurements and the modeling of the environmental exposure pathways. Guidance for this monitoring program is provided by the US Nuclear Regulatory Commission (USNRC) in their Radiological Assessment Branch Technical Position on Environmental Monitoring, Revision 1, November 1979 (incorporated into NUREG 1301). Results from the REMP help to evaluate sources of elevated levels of radioactivity in the environment (i.e., atmospheric nuclear detonations or abnormal plant releases).

The Land Use Census ensures that changes in the use of areas at, and beyond the site boundary, are identified and that modifications to the REMP are made if required by the results of this census. This census satisfies the requirements of Section IV.B.3 of Appendix I to 10 CFR Part

50.

The Interlaboratory Comparison Program is provided to ensure that independent checks on the precision and accuracy of the measurements of radioactive material in environmental sample matrices. The interlaboratory comparisons are performed as part of the quality assurance program for environmental monitoring to demonstrate that the results are valid for the purposes of 10 CFR 50, Appendix I, Section IV.B.2.

Results of the PVNGS pre-operational environmental monitoring program are presented in Reference 1.

The initial criticality of Unit 1 occurred May 25, 1985. Initial criticality for Units 2 and 3 were April 18, 1986, and October 25, 1987, respectively. PVNGS operational findings (historical) are presented in Reference 2.

PVNGS ANNUAL RADIOLOGICAL ENVIRONMENTAL OPERATING REPORT-2024 Page 2

1.2 Radiation and Radioactivity Atoms are the basic builcling blocks of matter. Unstable atoms emit radiation; material that spontaneously emits radiation is referred to as radioactive. Radioactive material is frequently categorized as either "Natural" or "Man-made."

Some sources of radiation exist naturally in the environment and include radon, thoron, cosmic, terrestrial, and internal. The sun and stars are sources of cosmic radiation. Atmospheric conditions, the Earth's magnetic field, and differences in elevation can affect the amount of cosmic radiation an individual receives, also referred to as dose. The Earth is a source of terrestrial radiation. Uranium, thorium, and radium exist naturally in rock and soil. All organic matter contains carbon and potassium, and water contains small amounts of dissolved uranium and thorium.

The largest contributor of dose to Americans from natural sources is attributed to radon. Radon is naturally released from rocks, soil and water and found in air. All people are a source of internal radiation. Potassium-40 and carbon-14 are radioactive nuclides and inside all people from birth, making people a source of exposure.

Man-made sources of radiation include consumer products, such as smoke detectors, thorium lantern mantles, color televisions, potassium salt and even tobacco. Some other consumer products that are sources of radiation include building and road construction materials, and combustible fuels, such as gas and coal. Nuclear medicine such as x-rays, diagnostic imaging, and therapeutic procedures are all widely used. Some of the occupational areas that result in individual exposures to radiation include radiography, radiation oncology, commercial power generation and research laboratories. Personnel radiation exposures are tracked in accordance with rules and regulations set forth by the Nuclear Regulatory Commission (NRC). The NRC requires licensees to limit radiation exposures to 5,000 mrem per year, Total Effective Dose Equivalent (TEDE). The largest contributor to personnel radiation exposure from man-made sources come from diagnostic x-rays, and from medical sources, such as Iodine-131, Thallium-201, Tecbnetium-99m and Cesium-134.

The NRC and the U.S. Environmental Protection Agency both state that the average member of the public receives an annual exposure of 620 mrem from ionizing radiation. Approximately half of the exposure is attributed to man-made sources and the other half to natural sources. Figure 1-1 illustrates the contribution of various sources of radiation and the contribution to exposure in the United States (NCRP Report No. 160 (2009)).

V r

Sourct>s ol Radiation Exposu10 In th Unltod St;,tos Internal

  • 59' D Nat\\Jral Sources* 5<m

~310 m1ll11em t0.311eml

  • f 1' l

}I lndustual and

/ Occupallonal *.19' Consume, Products

  • 29' Mam11ade Sources
  • 509'

~310 mllhr m 10.31 *em)

  • N ~'iwei t*

Figure 1-1 Sources of Radiation Exposure in the United States PVNGS ANNUAL RADIOLOGICAL ENVIRONMENTAL OPERATING REPORT-2024 Page 3

2. Description of the Monitoring Program APS and vendor organizations performed the pre-operational Radiological Environmental Monitoring Program between 1979 and 1985. APS and vendors continued the program into the operational phase.

2.1 Radiological Environmental Monitoring Program The assessment program consists of routine measurements of environmental gamma radiation and radionuclide concentrations in media such as air, groundwater, drinking water, surface water, vegetation, milk, sludge, and sediment.

Samples are collected by APS at the monitoring sites shown in Figures 2-1 and 2-2. The specific sample types, sampling locations, and sampling frequencies, as set forth in the PVNGS Offsite Dose Calculation Manual (ODCM), Reference 4, are presented in Tables 2-1, 2-2, and 9-1.

Additional onsite sampling ( outside the scope of the ODCM) is performed to supplement the REMP. Results are included in this report. Routine sample analyses were performed at the onsite Central Chemistry Laboratory and Operating Unit laboratories. Analyses for hard-to-detect radionuclides were performed by GEL Laboratories LLC.

Environmental gamma radiation measurements were performed by APS using OSLDs at fifty (50) locations near PVNGS. The PVNGS Dosimetry Department is accredited by the National Voluntary Laboratory Accreditation Program (NVLAP) to process personnel dosimeters (NVLAP Code 100536-0).

In addition to monitoring environmental media, a Land Use Census is performed annually to identify the nearest milk animals, residents, and gardens. This information is used to evaluate the potential dose to members of the public for those exposure pathways that are indicated.

2.2 Radiological Environmental Monitoring Program Changes for 2024 Changes to the REMP were identified in 2024 and were added to Revision 32 of the Offsite Dose Calculation Manual (ODCM), effective in June 2024. These changes included the addition of a milk and vegetation donor and assigned as Site #66. The number of ground water wells changed from 4 to 3, as one well was removed from service. And changes were made to the 0- 10 miles map for clarification and ease of use.

ODCM Revision 32 also includes the use of Optically Stimulated Luminescent Dosimeters (OSLDs) as part of the monitoring for direct radiation in the Environmental Monitoring Program.

Also included were modifications to tables 6-1 b and 6-2b with regards to the OSLO implementation.

Air Sampling Site #4 was moved during the 2024 to a new location. The property where this monitoring equipment was located was sold, forcing the relocation. The new location is in downtown Buckeye, north of the intersection of East Arizona Eastern Avenue and North 4th Street. It is positioned on a wooden power pole on the west side of the road.

PVNGS ANNUAL RADIOLOGICAL ENVIRONMENTAL OPERATING REPORT-2024 Page4

Palo Verde began environmental monitoring using the Optically Stimulated Luminescent Dosimeter (OSLD) in January 2024. Prior to 2024, Environmental Direct Radiation Monitoring had always been done using the Thermolurninescent Dosimeter (TLD). The average response between the two dosimeters is less than 4%. This difference is exceptionally low, when considering the comparison is the response of 2 environmental background dosimeters. The overall quarterly comparisons are shown in Table 2-1.

Revision 33 to the ODCM was implemented in March 2025. This revision included the addition of vegetation and milk samples to the REMP for redundancy. The associated tables were both modified to include these additions.

so.o 45.0 40.0 35.0 J:::i C"

30.0

~

t; 250 8

20.0 15.0 10.0 50 I), I 0

Table 2-1 TLD - OSLD Comparison I

le

  • 11
  • 1* *1 *** I** II JO l!t 20 2!.

JO EnviroJllllental Locations 2.3 REMP Deviations/Abnormal Events Summary I* * *

  • Sil There were 2 events involving environmental dosimetry in 2024. During the first quarter, locations 44 (El Mirage, 12315 NW Grande Ave Rental Center) and 47 (Littleton School, 115th Ave & Sagebrush Road) were missing at the time of exchange. Condition Report 24-03327 was generated for trending purposes and provides more details about the event.

There were two (2) events that occurred during 2024 pertaining to Environmental Air Sampling.

The sampling station for Site #4 was found to be missing at the time of collection in March 2024.

The property on which Site #4 was located was sold by APS. Subsequently, all materials used for sampling were missing. One (1) event was attributed to the loss of power at Site Station #6 in July 2024.

PVNGS ANNUAL RADIOLOGICAL ENVIRONMENTAL OPERATING REPORT-2024 Page 5

There were two (2) events that occurred in 2024 relating to the analysis of Milk samples. An unrecoverable error occurred during the counting process of the sample from Site #54. This error caused another sample to be collected. Another counting error occurred for Site #54 during the month of September. Another sample was collected to complete the analysis. There were no samples available for collection during the entire year for Site #49 and only two (2) samples were available for collection during the year at Site #66.

2.4 Groundwater Protection PVNGS has implemented a groundwater protection initiative developed by the Nuclear Energy Institute (NEI). The implementing guidance of this initiative, NEI 07-07 (Industry Ground Water Protection Initiative - Final Guidance Document, August 2007), and later revised in March of 2019, provides added assurance that groundwater will not be adversely affected by PVNGS operations.

In 2018, following a revision, several of the wells included in the PVNGS REMP program were removed from mandated sampling. Now referred to as Legacy Wells, they continue to be sampled for data continuity and in support of the Groundwater Protection Initiative. Sample results for the shallow aquifer wells are reported in the PVNGS Annual Radioactive Effluent Release Report (ARERR). The Area Wide Aquifer Protection Permit (APP) No. 100388-89315 was revised in December 2024. The new permit is APP P-100388-98240 and reflects the efforts to institute advanced evaporation technology. There is no degradation to the Groundwater Protection Program.

Three subsurface samples are now obtained, one each from Units 2 and 3 tritium monitoring wells. One sample is collected from the shallow aquifer outside of the Unit lRadiologically Controlled Area (RCA). These samples are analyzed for hard-to-detect radionuclides (i.e., C-14, Fe-55, Ni-63, Sr-90) as a verification that there are no underground leaks from plant systems affecting groundwater. All results were <MDA. Refer to Table 8-12 for sample results.

PVNGS ANNUAL RADIOLOGICAL ENVIRONMENTAL OPERATING REPORT-2024 Page 6

3. Sample Collection Program APS Personnel, using PVNGS procedures, collected all samples.

3.1 Water Weekly samples were collected from four ( 4) residence wells for monthly and quarterly composites. Samples were collected in one-gallon containers (plastic cubitainers) and 500 mL glass bottles. The samples were analyzed for gross beta, gamma-emitting radionuclides, and tritium.

Quarterly grab samples were collected from the 45-acre and 85-acre Reservoirs, active Evaporation Ponds lA/B/C, 2A/B, and 3A/B, and onsite wells 27ddc, 34aab, and 27dcb.

Samples were collected in one-gallon containers (plastic cubitainers) and 500 mL glass bottles.

Samples were analyzed for gamma-emitting radionuclides and tritium.

Treated sewage effluent from the City of Phoenix was sampled as a weekly composite at the onsite Water Resources (WR) and analyzed for gamma-emitting radionuclides. A monthly composite was analyzed for tritium.

3.2 Vegetation Vegetation samples were collected monthly, as available, and were analyzed for gamma-emitting radionuclides.

3.3 Milk Goat milk samples were collected monthly, as available, and were analyzed for gamma-emitting radionuclides, including low level 1-131.

3.4 Air Air particulate filters and charcoal cartridges were collected at ten (10) sites on a weekly basis. Particulate filters were analyzed for gross beta. Charcoal cartridges were analyzed for Iodine-131. Particulate filters were composited quarterly, by location, and analyzed for gamma-emitting radionuclides.

3.5 Soil, Sludge, and Sediment Sludge samples were obtained weekly from the WR waste centrifuge ( during operational periods) and analyzed for gamma-emitting radionuclides. Cooling tower sludge was analyzed for gamma-emitting radionuclides prior to disposal in the WR sludge landfill.

PVNGS ANNUAL RADIOLOGICAL ENVIRONMENTAL OPERATING REPORT-2024 Page 12

4. Analytical Procedures The procedures described in this report are those used by APS to routinely analyze samples.

4.1 Air Particulate 4.1.1 Gross Beta A glass fiber filter sample is placed in a stainless steel planchet and counted for gross beta activity utilizing a low background gas flow proportional counter.

4.1.2 Gamma Spectroscopy The glass fiber filters are counted on a multichannel analyzer equipped with a High-purity Germanium (HPGe) detector. The resulting spectrum is analyzed by a computer for specific radionuclides and verified by trained technicians.

4.2 Airborne Radioiodine 4.2.1 Gamma Spectroscopy A charcoal cartridge is counted on a multichannel analyzer equipped with an HPGe detector. The resulting spectrum is analyzed by a computer for Iodine-131.

4.3 Milk 4.3.1 Gamma Spectroscopy The sample is placed in a plastic Marinelli beaker and counted on a multichannel analyzer equipped with an HPGe detector. The resulting spectrum is analyzed by a computer for specific radionuclides and verified by trained technicians. Iodine in milk samples is identified through gamma spectroscopy.

4.4 Vegetation 4.4.1 Gamma Spectroscopy The sample is pureed in a food processor, placed in a one-liter plastic Marinelli beaker, weighed, and counted on a multichannel analyzer equipped with an HPGe detector. The resulting spectrum is analyzed by a computer for specific radionuclides and verified by trained technicians.

PVNGS ANNUAL RADIOLOGICAL ENVIRONMENTAL OPERATING REPORT-2024 Page 13

4.5 Sludge/Sediment 4.5.1 Gamma Spectroscopy The wet/dry sample is placed in a one-liter plastic Marinelli beaker, weighed, and counted on a multichannel analyzer equipped with an HPGe detector. The resulting spectrum is analyzed by a computer for specific radionuclides and verified by trained technicians.

4.6 Water 4.6.1 Gamma Spectroscopy The sample is placed in a one-liter plastic Marinelli beaker and counted on a multichannel analyzer equipped with a HPGe detector. The resulting spectrum is analyzed by a computer for specific radionuclides and verified by trained technicians.

4.6.2 Tritium The sample is evaluated to determine the appropriate method of preparation prior to counting. If the sample contains suspended solids or is turbid, it may be filtered, distilled, and/or de-ionized, as appropriate. Eight (8) milliliters of sample are mixed with fifteen (15) milliliters of liquid scintillation cocktail. The mixture is dark adapted and counted for tritium activity using a liquid scintillation counting system.

4.6.3 Gross Beta A 200-250 milliliter sample is placed in a beaker. Five (5) milliliters of concentrated nitric (HNO3) acid are added and the sample is evaporated down to approximately twenty (20) milliliters. The remaining sample is transferred to a stainless steel planchet.

The sample is heated to dryness and counted for gross beta in a gas flow proportional counter.

4.7 Soil 4.7.1 Gamma Spectroscopy The samples are sieved, placed in a one-liter plastic Marinelli beaker, and weighed. The samples are then counted on a multichannel analyzer equipped with an HPGe detector.

The resulting spectrum is analyzed by a computer for specific radionuclides and verified by trained technicians.

PVNGS ANNUAL RADIOLOGICAL ENVIRONMENTAL OPERATING REPORT-2024 Page 14

5. Nuclear Instrumentation 5.1 Gamma Spectrometer The Canberra Gamma Spectrometer consists of a Canberra System equipped with HPGe detectors, having resolutions of 1.73 keV and 1.88 keV (as determined by full width half max with an energy of 0.5 keV per channel) and respective efficiencies of 21.5% and 38.4% (as determined by the manufacturer with Co-60). The Canberra System is used for all gamma counting. The system uses Canberra developed software to search, identify, and quantify the peaks of interest.

5.2 Liquid Scintillation Spectrometer A Beckman LS-6500 Liquid Scintillation Counter is used for tritium determinations. The system background averages approximately 12-16 cpm with a counting efficiency of approximately 40% using a quenched standard.

5.3 Gas Flow Proportional Counter The Tennelec SSE is a low background gas flow proportional counter for gross beta analysis.

The system contains an automatic sample changer capable of counting 50 samples in succession. Average beta background count rate is about 1-2 cpm with a beta efficiency of approximately 30% for Cs-137.

PVNGS ANNUAL RADIOLOGICAL ENVIRONMENTAL OPERATING REPORT-2024 Page 15

6. lsotop
  • c Detection Limits and Reporting Criteria 6.1 Lower Limits of Detection The lower limits of detection (LLD) and the method for calculation are pecified in the PVNGS ODCM, Reference 4. The ODCM required a priori LLDs are pre ented in Table 6-1.

6.2 Data Reporting Criteria Any results that indicate a greater than the Minimum Detectable Activity (MDA) (a posteriori LLD) are reported as positive activity with its associated 2cr counting enor. All results that are less than the MDA are reported as less than values at the a sociated MDA. For example if the MDA is 12 pCi/liter, the value is reported a < 12.

Typical MDA values are presented in Table 6-3.

Occasionally the PVNGS ODCM a priori LLDs may not be achieved because of:

Background fluctuations Unavoidably small sample sizes The pre ence of interfering radionucl ides Self-absorption corrections Decay corrections for short half-life radionuclides Other uncontrollable circumstances In these instance, the contributing factors will be noted in the table where the data are presented. A summacy of deviations/abnormal events is presented in Table 2-4 and includes a description of any sample results that did not meet a priori LLD requirements.

6.3 LLD and Reporting Criteria Overview Making a reasonable estimate of the limits of detection for a counting procedure or a radiochemical method is usually complicated by the presence of significant background. It must be considered that the background or blank is not a fixed value but that a series of replicates would be nonually distributed. The desired net activity is the difference between the gross and background activity distributions. The interpretation of this difference becomes a problem if the two distributions inter ect as indicated in the diagram.

BACKGROUND GROSS PVNGS ANNUAL RADIOLOGICAL ENVIRONMENTAL OPERATING REPORT-2024 Page 16

If sufficient replicate analyses are run, it is expected that the results would fall in a normal Gaussian distribution. Standard statistics allow an estimate of the probability of any deviation from the mean value. It is common practice to report the mean +/- one or two standard deviations as the result. In routine analysis, such replication is not conducted, and it is not possible to report a Gaussian standard deviation. With counting procedures, however, it is possible to estimate a Poisson standard deviation directly from the count. Data are commonly reported as the measured value +/- one or two Poisson standard deviations. The reported values are then considered to give an indication of the range in which the true value might be expected to occur.

LLD is the smallest amount of sample activity that will yield a net count for which there is confidence at a predetermined level that activity is present. LLDs are calculated values for individual radionuclides based on several different factors, including sample size, counting efficiency and background count rate of the instrument, the background and sample counting time, the decay time, and the chemical recovery of the analytical procedures. A minimum detectable activity value (MDA) is the smallest amount of activity that can be detected in an actual sample and uses the values obtained from the instrument and outcome of the analytical process. Therefore, the MDA values may differ from the calculated LLD values if the sample size and chemical recovery, decay values, or the instrument efficiency, background, or count time differed from those used in the LLD calculation.

The factors governing the calculation of the LLD and MDA values are discussed below:

1. Sample Size: The number of observations included in a statistical analysis.

Sample size dictates the amount of information available about a studied subject to make accurate inferences.

2. Counting Efficiency: The fundamental quantity in the measurement of a radioactive substance is the number of disintegrations per unit time. As with most physical measurements in analytical chemistry, an absolute measurement of the disintegration rate is seldom possible, rather it is necessary to compare the sample with one or more standards. The standards determine the counter efficiency that may then be used to convert sample counts per minute ( cpm) to disintegrations per minute (dpm).
3. Background Count Rate: Any counter will show a certain counting rate without a sample in position. This background counting rate comes from any of several sources: 1) natural environmental radiation from the surrounding materials, 2) cosmic radiation, and 3) the natural radioactivity in the counter material itself. The background counting rate will depend on the amounts of these types of radiation and the sensitivity of the counter to the radiation.

PVNGS ANNUAL RADIOLOGICAL ENVIRONMENTAL OPERATING REPORT-2024 Page 17

4. Background and Sample Counting Time: The amount of time devoted to the counting of the background depends on the level of activity being measured. In general, with low level samples, this time should be about equal to that devoted to counting a sample.
5. Time Interval between Sample CoUection and Counting: Decay measurements are useful in identifym.g certain short-lived nuclides. The disintegration constant is one of the basic characteristics of a specific radionuclide and is readily determined if the half-life is sufficiently short.

To ensure the required LLDs are achieved, appropriate decay correction values are used to account for radioactive decay during transit time and sample processing.

Table 6-1 ODCM Required Lower Limits of Detection (a priori) irb rn Parli ulate Fre h Jilk F d Pr du l

. nal, i Wnler IP 'i/J r a pCi/m31 Ip "j/1)

IP 'i/k:,t., 't>l Gr B ta 4

0.0 H-

_()()()*

, In-Fe-9 30 0- 8. -60 I

Zn 0 Zr-95 30 b-9_

I 1-131 0.0 1

c-134 I

0.0 15 Cs-I 7

0.

I B -14 60 La-140 15 15 If no drinking water pathway exists, a value of 3000 pCi/liter may be used

    • If no drinking water pathway exists, a value of 15 pCi/liter may be used NOTES:

This list does not mean that only these nuclides are to be detected and reported. Other peaks that are measurable and identifiable, together with the above nuclides, shall also be identified and reported.

PVNGS ANNUAL RADIOLOGICAL ENVIRONMENTAL OPERATING REPORT-2024 Page 18 60 60 0

7. Interlaboratory Comparison Program 7.1 Quality Control Program APS maintains an extensive QA/QC Program to provide assurance that samples are collected, handled, tracked, and analyzed to specified requirements. This program includes appropriate elements of USNRC Regulatory Guide 4.15, Quality Assurance for Radiological Monitoring Programs (Normal Operations) - Effluent Streams and the Environment, Revision 1. The program includes procedures for sample collection preparation and tracking, sample analysis, equipment calibration and checks, and ongoing participation in an interlaboratory comparison program. Duplicate/replicate samples are analyzed to verify analytical precision and sample methodology. Comprehensive data reviews are performed including trending of data where appropriate.

During 2024, APS analyzed the following sample types under the interlaboratory comparison program:

  • Beta/Gamma/ in Air Filter
  • 1-131 in Air
  • Beta in Water
  • Gamma in Water
  • Gamma in Milk 7.2 Intercomparison Results APS participates in a crosscheck program using vendor supplied blind radionuclide samples. Results for the interlaboratory comparison program are presented in Table 7-1 PVNGS ANNUAL RADIOLOGICAL ENVIRONMENTAL OPERATING REPORT-2024 Page 20
8. Data Interpretation and Conclusions Associated with the analytical process are potential random and systematic errors. Systematic errors can be caused by instrument malfunctions, incomplete precipitation, back scattering, and self-absorption.

Efforts are made to minimize both systematic and random errors in the data reported. Systematic errors are minimized by performing reviews throughout the year. For example, instruments are checked routinely with radioactive sources, and recovery and self-absorption factors based on individual sample analyses are incorporated into the calculation equations where necessary. Random errors are reduced by comparing all data to historical data for the same site and performing comparisons between analytical results when available. In addition, when data appears to not match historical results, analyses may be rerun on a separate aliquot of the sample to verify the presence of the activity. The acceptance of data is dependent upon the results of quality control samples and is part of the data review process for all analytical results.

The "plus or minus value" reported with each analytical result represents the counting error associated with the result and gives the 95% confidence (2cr) interval around the data.

Most samples contain radioactivity associated with natural background/cosmic radioactivity (i.e., K-40, Th-234, Be-7). Gross beta results for drinking water and air are due to natural background. Gamma-emitting radionuclides, which can be attributed to natural background sources, are not indicated in this report.

Results and interpretation of the data for samples analyzed during 2024 are presented in the following sections.

8.1 Air Particulates Weekly gross beta results, in quarterly format, are presented in Table 8-land Table 8-2. Gross beta activity at indicator locations ranged from 0.006 to 0.083 pCi/m3. Mean quarterly activity is normally calculated using weekly activity over a thirteen (13) week period. Also presented in the tables are the weekly mean values of all the sites as well as the percent relative standard deviation (RSD % ) for the data.

Table 8-3 displays the results of gamma spectroscopy on the quarterly composites of the weekly samples. No plant-related activity was identified.

8.2 Airborne Radioiodine Table 8-4 and Table 8-5 present the quarterly radioiodine results. Radioiodine was not observed in any samples.

8.3 Vegetation Table 8-6 presents gamma isotopic data for the vegetation samples. There were no vegetation samples available from Site 4 7 or Site 49. All samples from Site 62 met the required LLD values for 1-131, Cs-134 and Cs-13 7.

PVNGS ANNUAL RADIOLOGICAL ENVIRONMENTAL OPERATING REPORT-2024 Page 22

8.4 Milk Table 8-7 presents gamma isotopic data for the goat milk samples. No gamma-emitting radionuclides were observed in any of the samples.

8.5 Drinking Water Samples were analyzed for gross beta, tritium, and gamma-emitting radionuclides. Results of these analyses are presented in Table 8-8. No tritium or gamma-emitting radionuclides were detected in any samples. Gross beta activity ranged from less than detectable to a high of 7.58 pCi/liter. The gross beta activity is attributable to natural (background) radioactive materials.

8.6 Groundwater Groundwater samples were analyzed from three onsite wells (regional aquifer) for tritium and gamma-emitting radionuclides. Results obtained from the analysis of the samples are presented in Table 8-9.

No tritium or gamma-emitting radionuclides were observed in any of the samples.

8.7 Surface Water Surface water samples from the Reservoirs and Evaporation Ponds were analyzed for tritium and gamma-emitting radionuclides. The two Reservoirs contain processed sewage water from the City of Phoenix and are approximately 45 and 85 acres in size. The three Evaporation Ponds receive mostly circulating water from main turbine condenser cooling and are about 200-250 acres each.

Sample results are presented in Table 8-10. 1-131 is sometimes observed in Reservoirs and Evaporation Ponds, which is the result of radiopharmaceutical 1-131 in the Phoenix sewage effluent and is not attributable to plant effluents. Except for WRF Influent, I-131 was not observed in these surface water samples during 2024.

Tritium was routinely observed in the Evaporation Ponds. The highest concentration was 1086 pCi/liter. Tritium was not detected in the Reservoirs. The tritium identified in the Evaporation Ponds has been attributed to permitted plant gaseous effluent releases and secondary plant liquid discharges (i.e., condensate overboard discharge, secondary side steam generator drains, secondary plant sumps, demineralizer regeneration waste).

The tritium concentrations were compared to historical values and are considered typical for the Evaporation Ponds. Evaporation Pond 3A has been drained for liner repairs and has not received any influent from the plant since 2016; therefore, no sample was obtained.

8.8 Sludge and Sediment 8.8.1 Water Resources Centrifuge Waste Sludge Sludge samples were obtained from the Water Resources (WR) centrifuge and analyzed by gamma spectroscopy. I-131 activity in the sludge is consistent with historical values and, as previously discussed, is due to radiopharmaceuticals in the WR Influent. The concentration of I-131 ranged from "no detectable" to 918 pCi/kg.

Results for WR centrifuge waste sludge can be found in Table 8-11.

PVNGS ANNUAL RADIOLOGICAL ENVIRONMENTAL OPERATING REPORT-2024 Page 23

8.8.2 Cooling Tower Sludge Sludge/sediment originating from the Unit 2 and Unit 3 Cooling Towers and Circulating Water canals was disposed of in the WR sludge landfill during 2024. Sample results can be found in Table 8-11.

8.9 Data Trends Figure 8-1 through Figure 8-8 present data in graphical format. Historical data are displayed for comparison where practical. All data are consistent with historical values.

8.10 Hard-To-Detect Radionuclide Results Table 8-12 shows the results of the three subsurface samples obtained from 3 tritium monitoring points. These samples were analyzed for hard-to-detect radionuclides (i.e., C-14, Fe-55, Ni-63, Sr-90) and all results were

<MDA. These results indicate that no leaks from plant systems have affected groundwater.

PVNGS ANNUAL RADIOLOGICAL ENVIRONMENTAL OPERATING REPORT-2024 Page 24

11. Summary and Conclusions Summary The conclusions are based on a review of the radioassay results and environmental gamma radiation measurements for the 2024 calendar year. Where possible, the data were compared to pre-operational sample data.

All sample results for 2024 are presented in Table 8-1 through Table 8-12 and do not include observations of naturally occurring radionuclides, except for gross beta in air and gross beta in drinking water. Table 11-1 summarizes the ODCM required samples and is in the format required by the NRC BTP on Environmental Monitoring.

1-131 is occasionally identified in the evaporation ponds, Water Resources influent, Water Resources centrifuge sludge, and reservoirs is the result of offsite sources and appears in the effluent sewage from Phoenix. The levels of 1-131 detected in these locations are consistent with levels identified in previous years.

Tritium concentrations identified in surface water onsite have been attributed to PVNGS permitted gaseous effluent releases and secondary plant releases. These concentrations are consistent with historical values.

Environmental radiation levels are consistent with measurements reported in previous Pre-operational and Operational Radiological Environmental annual reports, References 1 and 2.

Conclusion There was no measurable radiological impact on the environment in 2024 resulting from the operation of PVNGS.

PVNGS ANNUAL RADIOLOGICAL ENVIRONMENTAL OPERATING REPORT-2024 Page 56

12. References
1. Pre-Operational Radiological Monitoring Program, Summary Report 1979-1985
2. 1985-2024 Annual Radiological Environmental Operating Reports, Palo Verde Nuclear Generating Station
3. Palo Verde Nuclear Generating Station Technical Specifications and Technical Reference Manual
4. Offsite Dose Calculation Manual, Revision 32, PVNGS Units 1, 2, and 3
5. Regulatory Guide 4.1, Programs for Monitoring Radioactivity in the Environs of Nuclear Power Plants
6. Regulatory Guide 4.8, Environmental Technical Specifications for Nuclear Power Plants
7. NRC Radiological Assessment Branch Technical Position on Environmental Monitoring, Revision 1, November 1979 (Incorporated into NUREG-1301)
8. "Sources of Radiation." NRC: Sources of Radiation. Nuclear Regulatory Commission, 20 March.

2020. Web. l 7-Apr-24.

9. "NCRP Report No. 160: Ionizing Radiation Exposure of the Population of the United States."

Journal of Radiological Protection J. Radial. Prat. 29.3 (2009): 465. Web.

10. NEI 07-07, Nuclear Energy Institute, Industry Groundwater Protection Initiative - Final Guidance Document, Rev. 1, March 20 PVNGS ANNUAL RADIOLOGICAL ENVIRONMENTAL OPERATING REPORT-2024 Page 60
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