ML25241A083

Attachment 2: Final Technical Report - Architectural History Survey of Dresden Nuclear Power Station

ML25241A083
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Site:	Dresden
Issue date:	08/29/2025
From:	Constellation Energy Generation
To:	Office of Nuclear Reactor Regulation
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ML25241A080	List: ML25241A082 ML25241A083 RS-25-134, Nuclear Power Station, Units 2 and 3 - Subsequent License Renewal Application, Architectural History Survey - Final Report
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August 29, 2025 Constellation Energy Generation, LLC Dresden Nuclear Power Station, Units 2 and 3 Subsequent License Renewal Application Architectural History Survey - Final Report Final Technical Report Architectural History Survey of Dresden Nuclear Power Station August 2025

FINAL TECHNICAL REPORT ARCHITECTURAL HISTORY SURVEY OF DRESDEN NUCLEAR POWER

STATION, GRUNDY COUNTY, ILLINOIS PREPARED FOR CONSTELLATION ENERGY GENERATION, LLC 6500 N DRESDEN ROAD MORRIS, IL 60450 PREPARED BY SEARCH 8600 OAK STREET #2A NEW ORLEANS, LA 70118 SEARCH PROJECT NO. 250020 AUGUST 2025

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FINAL TECHNICAL REPORT ARCHITECTURAL HISTORY SURVEY OF DRESDEN NUCLEAR POWER STATION, GRUNDY COUNTY, ILLINOIS PREPARED FOR CONSTELLATION ENERGY GENERATION, LLC 6500 N DRESDEN ROAD MORRIS, IL 60450 PREPARED BY SEARCH 8600 OAK STREET #2A NEW ORLEANS, LA 70118 REPORT AUTHORED BY ANGELIQUE THERIOT, BRITTANEY LONDON, AND HAILEY KOCH ANGELIQUE THERIOT, MA PRINCIPAL INVESTIGATOR AUGUST 2025 SEARCH PROJECT NO. 250020 WWW.SEARCHINC.COM

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SEARCH August 2025 Architectural History Survey of Dresden Nuclear Power Station, Grundy County, Illinois Final Technical Report iii Executive Summary EXECUTIVE

SUMMARY

SEARCH conducted an architectural history survey of the Dresden Nuclear Power Station (DNPS) in Grundy County, Illinois, on March 11 and 12, 2025 (the Project). SEARCH was contracted by ENERCON on behalf of Constellation Energy Generation, LLC, (CEG) to fulfill historic property identification requirements in association with a Subsequent License Renewal application to the Nuclear Regulatory Commission (NRC), pursuant to Section 106 of the National Historic Preservation Act (NHPA) of 1966 and the National Environmental Policy Act of 1969. The survey included pre-1980 buildings and structures within the DNPS boundary (Survey Area).

Title 10 of the Code of Federal Regulations (CFR) Part 51 (Environmental Protection Regulations for Domestic Licensing and Related Regulatory Functions) states that license renewal applicants must identify historic and cultural resources and historic properties that may be affected by the continued operation of the plant. The purpose of the architectural history survey is to identify and provide National Register of Historic Places (NRHP) recommendations for historic-age cultural resources within the DNPS. The survey was conducted in accordance with Illinois State Historic Preservation Office (SHPO) and NRC requirements, Section 106 of the NHPA, as amended (Public Law 113-287 [Title 54 United States Code]), and the implementing regulations of 36 CFR Part 800 (Protection of Historic Properties). A review of the Historic and Architectural Resource Geographic Information System (HARGIS) and NRHP database determined there are no previously recorded resources located within the Survey Area.

SEARCH identified 57 newly recorded pre-1980 resources within the Survey Area including: 38 buildings, 18 structures, and the proposed DNPS Unit 1 Historic District. Additionally, one of these resources, the Dresden Nuclear Power Station Building, consists of 21 interconnected historic-age facilities. During the survey, SEARCH architectural historians digitally photographed these resources and recorded resource locations on ESRI imagery using ArcGIS Collector and Survey 123. SEARCH recommends the DNPS Unit Historic District is NRHP eligible; furthermore, 9 resources surveyed are NRHP eligible as contributing resources within the proposed DNPS Unit 1 Historic District. The remaining 47 resources are recommended not eligible for NRHP inclusion, neither individually nor as contributing resources. No further architectural history work is recommended for the Survey Area.

Illinois State Historic Preservation Office (SHPO) correspondence provided on June 10, 2025, is included in Appendix A. For security reasons, detailed results figures of the Survey Area, DNPS Building, and DNPS Unit 1 Historic District are included only in Appendix B. Appendix B contains security-related proprietary information under 10 CFR 2.390 and should be withheld.

Angelique Theriot, MA, served as principal investigator for the Project. Ms. Theriot meets the Secretary of the Interiors Standards and Guidelines for Architectural History and Historic Preservation (48 FR 44716-42). The architectural history fieldwork was completed by Ms. Theriot and Hailey Koch, MA. Brittaney London, MA, served as architectural historian, Ben Thompson served as historian, and Sarah St. Pierre provided GIS support for the project.

August 2025 SEARCH Final Technical Report Architectural History Survey of Dresden Nuclear Power Station, Grundy County, Illinois SEARCH Project Team iv SEARCH PROJECT TEAM Management Bill Werner, MA Field Crew Angelique Theriot, MA Hailey Koch, MA Report Preparation Angelique Theriot, MA Brittaney London, MA Hailey Koch, MA Ben Thompson, MA GIS Mapping Sarah St. Pierre

SEARCH August 2025 Architectural History Survey of Dresden Nuclear Power Station, Grundy County, Illinois Final Technical Report v

Table of Contents TABLE OF CONTENTS List of Figures................................................................................................................................. vii List of Tables................................................................................................................................. viii Acronyms and Abbreviations.......................................................................................................... ix Introduction.................................................................................................................................... 1 Background Research..................................................................................................................... 3 Previous Investigations and Recorded Cultural Resources...................................................... 3 Historic Context........................................................................................................................ 3 Nuclear Power Development in the US.............................................................................. 3 Boiling Water Reactors....................................................................................................... 4 Siting, Construction, and Operation of Dresden Nuclear Power Station........................... 5 Map Review.............................................................................................................................. 8 Research Design and Methods..................................................................................................... 15 NRHP Criteria.......................................................................................................................... 15 Background Research............................................................................................................. 16 Architectural History Methods............................................................................................... 16 Architectural History Results........................................................................................................ 17 Architectural Styles Represented in the Survey Area............................................................. 22 Industrial Vernacular......................................................................................................... 22 Vernacular......................................................................................................................... 23 No Style............................................................................................................................. 23 NRHP Evaluations.................................................................................................................... 24 Dresden Nuclear Power Station Building.......................................................................... 24 Unit 1 Crib House.............................................................................................................. 45 Unit 2 & 3 Crib House....................................................................................................... 45 Intake and Discharge Canals............................................................................................. 46 Dresden Cooling Lake........................................................................................................ 49 Spillway............................................................................................................................. 50 Lift Station......................................................................................................................... 51 Wastewater Treatment Facility A..................................................................................... 52 Fuel Oil Storage Tank and Berm........................................................................................ 52 Off Gas Filter Building....................................................................................................... 53 Warehouse 5..................................................................................................................... 53 Safe Shutdown Warehouse.............................................................................................. 54 Administration Building 2................................................................................................. 55 Gatehouse/Main Access Facility....................................................................................... 56 Visitors Center/ NRC Office.............................................................................................. 56 Security/Diesel Generator Building.................................................................................. 57 Storeroom......................................................................................................................... 57 Storeroom Secondary Warehouse.................................................................................... 58 Maintenance Warehouse................................................................................................. 59

August 2025 SEARCH Final Technical Report Architectural History Survey of Dresden Nuclear Power Station, Grundy County, Illinois Table of Contents vi Wastewater Treatment Facility B..................................................................................... 59 Diesel Generator and HPCI Building/Station Blackout Building....................................... 60 Radwaste Building............................................................................................................. 61 Radwaste Building Unit 1.................................................................................................. 62 345 kV Switchyard............................................................................................................. 62 Switchyard Maintenance Building.................................................................................... 63 138 kV Switchyard............................................................................................................. 64 138 kV Relay House........................................................................................................... 65 Substation......................................................................................................................... 65 Elgin, Joliet and Eastern Railroad Spur............................................................................. 66 Railroad Bridge.................................................................................................................. 68 Meteorological Tower....................................................................................................... 69 Storage Barn...................................................................................................................... 69 DNPS Unit 1 Historic District............................................................................................. 70 Conclusions and Recommendations............................................................................................. 75 References Cited........................................................................................................................... 77 Appendix A.

IL SHPO Correspondence Appendix B.

Architectural History Results Detailed Figures

SEARCH August 2025 Architectural History Survey of Dresden Nuclear Power Station, Grundy County, Illinois Final Technical Report vii List of Figures LIST OF FIGURES Figure 1. Project Location, Grundy County, Illinois........................................................................ 2 Figure 2. USGS topographic maps of Morris and Wilmington, IL (USGS 1892a, 1892b).............. 10 Figure 3. USGS topographic maps of Morris and Wilmington, IL (USGS 1918a, 1918b).............. 11 Figure 4. USGS aerial photographs of Illinois (USGS 1946).......................................................... 12 Figure 5. USGS topographic maps of Channahon, Coal City, Minooka, and Wilmington, IL (USGS 1953, 1954a, 1954b, 1954c)............................................................................. 13 Figure 6. USGS topographic maps of Channahon, Coal City, Minooka, and Wilmington, IL (USGS 1973a, 1973b, 1973c, 1973d).......................................................................... 14 Figure 7. Architectural history survey results............................................................................... 21 Figure 8. Unit 2 and 3 Crib House, facing southeast..................................................................... 22 Figure 9. Storage Barn, facing northwest..................................................................................... 23 Figure 10. Storage Tank and Berm, facing north.......................................................................... 23 Figure 11. Unit 1 Reactor Building, facing northwest................................................................... 25 Figure 12. Diagram of BWR power generation process (NRC 2023)............................................ 26 Figure 13. Unit 1 Reactor Fuel Element Diagram (US Atomic Energy Commission 1958: 45)..... 26 Figure 14. Cross Section of Unit 1 Reactor Core Within its Pressure Vessel (US Atomic Energy Commission 1958:43)................................................................................................. 29 Figure 15. Unit 2 and 3 Reactor Building, facing north................................................................. 30 Figure 16. Unit 1 Turbine Building, center rear, facing south...................................................... 31 Figure 17. Unit 1 Fuel Handling Building, facing west.................................................................. 32 Figure 18. Unit 1 Station Chimney (left); Unit 2 and 3 Station Chimney (right rear), facing west............................................................................................................................. 33 Figure 19. Unit 2 Turbine Building, center rear, facing north....................................................... 34 Figure 20. Unit 3 Turbine Building, facing northeast.................................................................... 35 Figure 21. Unit 2 and 3 Station Chimney, facing west.................................................................. 36 Figure 22. Units 2 and 3 Radwaste Building, center rear, facing southeast................................. 36 Figure 23. Administration Building/Service Building, facing northeast........................................ 37 Figure 24. Technical Support Center, facing northeast................................................................ 39 Figure 25. High Radiation Sampling Building A, far right, facing north........................................ 39 Figure 26. HPCI and Diesel Generator Building, center rear behind cylinders, facing northwest.................................................................................................................... 40 Figure 27. High Radiation Sampling Building, facing west............................................................ 40 Figure 28. Off Gas Recombiner Room A, far right rear indicated with arrow, facing southwest.................................................................................................................... 41 Figure 29. Off Gas Recombiner Room B, center rear, facing southwest...................................... 42 Figure 30. Max Recycle Radwaste Building, facing southeast...................................................... 42 Figure 31. Water Sample Tanks, facing southeast........................................................................ 43 Figure 32. Heating Boiler House, facing east................................................................................ 44 Figure 33. Floor Drain Surge Tank, facing east............................................................................. 44 Figure 34. Unit 1 Crib House slab, facing northeast..................................................................... 45 Figure 35. Unit 2 and 3 Crib House, facing southeast................................................................... 46

August 2025 SEARCH Final Technical Report Architectural History Survey of Dresden Nuclear Power Station, Grundy County, Illinois List of Tables viii Figure 36. Unit 1 Intake Canal, facing northwest......................................................................... 47 Figure 37. Unit 2 and 3 Intake Canal, facing northwest............................................................... 47 Figure 38. Unit 2 and 3 Discharge Canal, cold canal (far left) and hot canal (center), facing northwest from Lift Station........................................................................................ 48 Figure 39. Flow Regulation Station, facing north......................................................................... 49 Figure 40. Dresden Cooling Lake south of cooling lake bridge, facing southeast........................ 50 Figure 41. Spillway, right rear indicated with arrow, facing southwest....................................... 51 Figure 42. Lift Station, center rear, facing southwest.................................................................. 51 Figure 43. Wastewater Treatment Facility A, center rear, facing southwest............................... 52 Figure 44. Fuel Oil Storage Tank, facing northeast....................................................................... 52 Figure 45. Off Gas Filter Building, facing northeast...................................................................... 53 Figure 46. Warehouse 5, facing northwest................................................................................... 54 Figure 47. Safe Shutdown Warehouse, facing southwest............................................................ 54 Figure 48. Administration Building 2, facing west........................................................................ 55 Figure 49. Visitor's Center/NRC Office, facing northwest............................................................ 56 Figure 50. Storeroom, facing southeast....................................................................................... 58 Figure 51. Storeroom Secondary Warehouse, facing southwest................................................. 58 Figure 52. Maintenance Warehouse, facing northeast................................................................ 59 Figure 53. Wastewater Treatment Facility B, facing east............................................................. 60 Figure 54. Station Blackout (SBO) Building, facing southwest..................................................... 60 Figure 55. Radwaste Building, facing west................................................................................... 61 Figure 56. Radwaste Building Unit 1, facing west......................................................................... 62 Figure 57. 345 kV Switchyard, facing west................................................................................... 63 Figure 58. Switchyard Maintenance Building, facing northwest.................................................. 63 Figure 59. 138 kV Switchyard, facing northwest.......................................................................... 64 Figure 60. 138 kV Relay House, facing northeast......................................................................... 65 Figure 61. Substation, facing northeast........................................................................................ 66 Figure 62. EJE Spur south of Unit 1 Reactor Building, facing north.............................................. 66 Figure 63. EJE Spur track adjacent to the Meteorological Tower, abandoned in place and partially infilled with gravel, facing northwest........................................................... 67 Figure 64. Meteorological Tower, facing west............................................................................. 69 Figure 65. Storage Barn, facing northwest................................................................................... 70 Figure 66. DNPS Building, facing north (left); DNPS Building, facing west................................... 71 LIST OF TABLES Table 1. Architectural History Survey Results............................................................................... 18 Table 2. Architectural Styles within the Survey Area................................................................... 22 Table 3. DNPS Unit 1 Historic District Contributing and Noncontributing Resources.................. 71

SEARCH August 2025 Architectural History Survey of Dresden Nuclear Power Station, Grundy County, Illinois Final Technical Report ix Acronyms and Abbreviations ACRONYMS AND ABBREVIATIONS AEC Atomic Energy Commission ac acres ANS American Nuclear Society ca.

circa BORAX Boiling Water Reactor Experiment BWR Boiling Water Reactor CFR Code of Federal Regulations ComEd Commonwealth Edison Company DNPS Dresden Nuclear Power Station EBWR Experimental Boiling Water Reactor EJE Elgin Joliet and Eastern Railroad ER Environmental Report ft feet GE General Electric ha hectares HARGIS Historic and Architectural Resource Geographic Information System IAEA International Atomic Energy Agency ISFSI Independent Spent Fuel Storage Installation kV kilovolt m

meters MWe megawatt electric MWt megawatt thermal NHPA National Historic Preservation Act NPS National Park Service NRC United States Nuclear Regulatory Committee NRHP National Register of Historic Places NRTS National Reaction Testing Station SBO Station Blackout SEARCH SEARCH, Inc.

SHPO Illinois State Historic Preservation Office TW.h terawatt hours US United States USDOE United States Department of Energy USGS United States Geological Survey

August 2025 SEARCH Final Technical Report Architectural History Survey of Dresden Nuclear Power Station, Grundy County, Illinois Acronyms and Abbreviations x

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SEARCH August 2025 Architectural History Survey of Dresden Nuclear Power Station, Grundy County, Illinois Final Technical Report 1

Introduction INTRODUCTION SEARCH conducted an intensive architectural history survey of the Dresden Nuclear Power Station (DNPS) in Grundy County, Illinois, on March 11 and 12, 2025 (Figure 1). The Survey Area includes the entire DNPS boundary: an approximately 385.67-hectare (ha; 953-acre [ac]) area roughly bounded by the Illinois River to the north, by the Kankakee River to the east, by Lorenzo Road to the south, and by E Collins Road and private parcels to the west. SEARCH was contracted by ENERCON on behalf of Constellation Energy Generation, LLC, (CEG) to fulfill historic property identification requirements in association with a Subsequent License Renewal application to the Nuclear Regulatory Commission (NRC), pursuant to Section 106 of the National Historic Preservation Act (NHPA) of 1966 and the National Environmental Policy Act of 1969.

Title 10 of the Code of Federal Regulations (CFR) Part 51 (Environmental Protection Regulations for Domestic Licensing and Related Regulatory Functions) states that license renewal applicants must identify historic and cultural resources and historic properties that may be affected by the continued operation of the plant. The purpose of the architectural history survey is to identify and provide National Register of Historic Places (NRHP) recommendations for historic-age cultural resources within the DNPS. The survey was conducted in accordance with IL SHPO and NRC requirements, Section 106 of the NHPA, as amended (Public Law 113-287 [Title 54 United States Code]), and the implementing regulations of 36 CFR Part 800 (Protection of Historic Properties). A review of the Historic and Architectural Resource Geographic Information System (HARGIS) and the NRHP database determined there are no previously recorded resources located within the Survey Area.

In total, SEARCH identified 57 newly recorded pre-1980 resources within the Survey Area, including: 38 buildings, 18 structures, and the proposed DNPS Unit 1 Historic District.

Additionally, 21 of these 38 buildings are interconnected and comprise the Dresden Nuclear Power Station Building. The proposed DNPS Unit 1 Historic District is further detailed below.

Following this Introduction, the report includes five chapters: Background Research, Research Design and Methods, Architectural History Results, Conclusions and Recommendations, and References Cited.

IL SHPO correspondence provided on June 10, 2025, is included in Appendix A. For security reasons, detailed results figures of the Survey Area, DNPS Building, and DNPS Unit 1 Historic District are included only in Appendix B. Appendix B contains security-related proprietary information under 10 CFR 2.390 and should be withheld.

August 2025 SEARCH Final Technical Report Architectural History Survey of Dresden Nuclear Power Station, Grundy County, Illinois Introduction 2

Figure 1. Project Location, Grundy County, Illinois.

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Background Research BACKGROUND RESEARCH PREVIOUS INVESTIGATIONS AND RECORDED CULTURAL RESOURCES SEARCH reviewed the HARGIS and the NRHP databases prior to fieldwork to identify previous cultural resource investigations and previously recorded resources within the Survey Area. No previously recorded resources are located within the Survey Area.

HISTORIC CONTEXT The DNPS operated the Unit 1 dual-cycle Type 1 boiling water reactor (BWR/1) between 1960 and 1978 and currently operates the ca. 1970 Unit 2 and ca. 1971 Unit 3 General Electric BWR/3 reactors with electrical generating equipment to produce nuclear-derived power. The plant is capable of three cooling modes: direct open-cycle, indirect open-cycle, and closed cycle. The Unit 1 Reactor was permanently decommissioned on October 31, 1978. The plant is located in Grundy County southwest of the Kankakee River and Des Moines River convergence point, where the two join to form the Illinois River. The historic context presented below first situates the DNPS within the technological history of US nuclear power, then discusses its siting, construction, and operation within the Survey Area.

Nuclear Power Development in the US The development of powerful weaponry dominated research on nuclear reactions during World War II and the Cold War. Governments around the world tasked scientists with creating nuclear bombs and missiles during World War II, and nuclear technology related to weaponry progressed rapidly during the mid-to-late twentieth century. Though much of the global focus remained on weaponizing nuclear reactions, scientists and government officials also recognized its domestic energy potential. Soon after World War II, which ended at least partially due to the use of atomic weapons on the Japanese cities of Hiroshima and Nagasaki, the US established governmental infrastructure to develop nuclear power for civilian energy purposes.

Scientists first discovered nuclear fission in the 1930s, learning that splitting atoms produced a release of energy that could be replicated. European scientists -- including Enrico Fermi in Rome, Otto Hahn and Fritz Strassman in Germany, Lise Meitner in Austria, and Niels Bohr in Denmark-tested atom splitting and eventually brought their findings to the US. These scientists involved German-born physicist Albert Einstein in their work. Several researchers led by Fermi, who relocated from Rome to the University of Chicago, successfully created a self-sustaining nuclear reaction in December 1942. With the practical application of nuclear theories complete, the nuclear age began. Though the Manhattan Project created weapons with unprecedented destructive power, the original and future purposes of this research remained in developing a new source of energy (US Department of Energy [USDOE] 1993:4-7).

August 2025 SEARCH Final Technical Report Architectural History Survey of Dresden Nuclear Power Station, Grundy County, Illinois Background Research 4

The US created the Atomic Energy Commission (AEC) in 1946 and tasked it with researching and understanding the uses of nuclear power, including both weaponry and the development of energy technologies for civilian purposes. The Federation of Atomic Scientists pushed for additional civilian control and oversight in nuclear technology experimentation, as the classified nature and secrecy of military weapons development hampered cooperation between scientists and delayed progress. Additionally, many scientists involved with these projects called for a ban on atomic weapons production and a complete focus on creating clean energy solutions through nuclear power (Cantelon et al 1991:69-70). During the late 1940s and 1950s, the AEC directed several projects to assess the ability of nuclear power to provide energy for commercial purposes.

In 1949, AEC authorized the first venture, Experimental Breeder Reactor I in Arco, Idaho. By the end of 1951, the reactor successfully lit four 200-watt lightbulbs, demonstrating the capabilities of commercial energy production with nuclear reactions. By 1955, the facility provided power to the small town of Arco, with a population of around 1,000, making it the first town powered by nuclear technology (USDOE 1993:8-14; NRC 2020).

The development spurred additional private and commercial interest in using this technology for power purposes and pushed the US government to contribute additional funding and support.

After his 1953 Atoms for Peace speech urging the world to explore the benefits of nuclear power, President Dwight Eisenhower signed the Atomic Energy Act in 1954, bolstering the AECs ability to research and develop commercial nuclear facilities and providing additional support for private investment in the nuclear energy sector (USDOE 1993:8-14; NRC 2020). By 1957, a large-scale nuclear power plant was operational in Shippingport, Pennsylvania, marking the first commercial electricity-generating plant powered by nuclear energy. The Shippingport facility operated as a light-water reactor, which used ordinary water to cool the reactor core during the heating process, creating and cooling the self-sustaining chain reaction nuclear scientists studied since the early 1940s (USDOE 1993:8).

The height of nuclear energy production occurred between the 1950s and 1960s. Though growth continued into the 1970s and 1980s, energy companies invested less in nuclear power because of public concern over the safety of nuclear facilities and the disposal of nuclear waste. Much of this concern stemmed from the 1979 events at Three Mile Island in Pennsylvania. That accident perpetuated the fear of nuclear power reactor failure and the fallout that could occur. In 1971, 21 power plants were operational in the US, which provided 2.4% of the countrys power. This rose to 72 reactors providing 12% of electricity in 1979, and then 109 reactors providing 19% in 1989. By 1992, nuclear power provided 22% of the electricity in the US. Many of the original nuclear power facilities began to close by the 1990s, by which point the industry was in decline and saw minimal investment by energy companies (USDOE 1993:8-21).

Boiling Water Reactors Though researchers hypothesized water could be used as a means of transferring the heat of nuclear reactions to useable energy, it was not a foregone conclusion. The sensitivity of the fission elements and potential for accidental radioactive release meant significant testing was required to assure water boiled at a consistent rate. Slight temperature change or the inability to

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Background Research maintain a smooth, consistent water surface could have devastating effects. Samuel Untermyer II, a vocal proponent of boiling waters potential as a cooling method, began experimenting with this process in the 1950s. After graduating from MIT in 1934, Untermyer and Walter Zinn developed the Boiling Water Reactor Experiment (BORAX) to test the hypothesis (New York Times 31 January 2001:A19; Stacy 2000:128-130). The University of Chicagos Argonne National Laboratory helped conduct experiments at the National Reaction Testing Station (NRTS) in Idaho.

By May 1953, the first testing reactor was complete and ready for experiments. Untermyer and the team conducted over 200 tests within 14 months, solidifying his theory and proving the success of a BWR. At the end of these experiments, the team held a threshold test leading to the assumed destruction of the facilities in order the prepare for potential fallout. After the first threshold test, the team built a new, larger reactor known as BORAX II. The series continued through BORAX V (Stacy 2000:128-131).

The success of the BORAX testing units encouraged the development of private commercial facilities. Several ventures were already in development in the early 1950s and became operational by the mid-to late 1950s. The power provided to Arco, Idaho, beginning in 1955, was made possible by the BORAX III BWR. Other nuclear power facilities came online during the 1950s, including the Sodium Reactor Experiment in Santa Susana, California. It became the first nuclear facility in the state to power a commercial grid serving the City of Moorpark (USDOE 1993:13-15). As opposed to the BWR process, this facility used sodium to cool the reactions.

When it began supplying power to the grid on July 12, 1957, the facility was recognized as the country's first civilian nuclear plant and the first commercial nuclear power plant to provide electricity to the public (California Energy Commission 2020:7).

Siting, Construction, and Operation of Dresden Nuclear Power Station The DNPS is located approximately 80 km (50 mi) southwest of Chicago and was a pioneering facility in the history of nuclear power in the US. Its development was driven by the significant post-World War II expansion of Chicagos suburbs, which created increased demand for a stable and scalable energy supply. Commonwealth Edison Company (ComEd), the primary utility provider for the area, recognized the need to secure a reliable and scalable energy source to meet the increasing power demands of a rapidly expanding metropolitan area (Platt 2005). The selection of the site approximately 13 km (8 mi) northeast of Morris, on the Kankakee, Des Plaines, and Illinois rivers, was based on its proximity to Chicago's growing population, the availability of cooling water from the rivers, and relatively flat, undeveloped land suitable for a large-scale nuclear facility (AEC 1973).

The Atomic Energy Act of 1954 facilitated this shift toward nuclear energy, allowing private companies to build and operate nuclear reactors and marking a significant turning point in the commercialization of nuclear power (Walker and Wellock 2010). DNPS construction began in the late 1950s, and the plant was completed by 1960. The project was spearheaded by ComEd, which entered into a contract with General Electric Company (GE) in July 1955. Under this contract, GE was responsible for designing, constructing, and placing DNPS into operation for $45 million. This cost was partially covered by the Nuclear Power Group, Inc., a consortium of eight utility

August 2025 SEARCH Final Technical Report Architectural History Survey of Dresden Nuclear Power Station, Grundy County, Illinois Background Research 6

companies, which contributed one-third of the cost over a five-year period as a research and development expense. The remaining costs, including site and overhead expenses, were funded by ComEd, which ultimately owned and operated DNPS (AEC 1958; Davis 2015).

The DNPS design was heavily influenced by earlier nuclear reactor research, including GEs BWR at the Vallecitos Laboratory in Alameda County, California, and the AEC Experimental Boiling Water Reactor (EBWR) at Argonne National Laboratory. Engineers from the Nuclear Power Group were trained at these earlier plants and contributed to all phases of the DNPS project, from design to operation. Bechtel Corporation served as the engineer-constructor for the facility (AEC 1958).

The DNPS Unit 1 design featured a spherical containment building, 57.9 m (190 ft) in diameter, housing the reactor, steam separating drum, secondary steam generators, pumps, and other auxiliary equipment. The Unit 1 Turbine building housed the turbine generator and other components necessary for converting thermal energy into electricity. Operations were controlled from a room located at the west end of the Unit 1 Turbine Building. The Unit 1 Fuel Handling Building provided space for inspecting and storing both new and spent fuel. Spent fuel was stored underwater for approximately three to four months before being transferred to shielded containers for disposal. The plant used a 60-ton core of slightly enriched uranium, designed to last up to six years under optimal conditions (AEC 1958). Additionally, the plant utilized two canalsan intake canal drawing water from the Kankakee River and a now-decommissioned discharge canal releasing water into the Des Plaines Riveras part of Unit 1s once-through cooling system. To support the delivery of equipment and materials, the station also included a railroad spur connected to the Elgin Joliet and Eastern (EJE) Railroad (AEC 1973).

The DNPS Unit 1, which began generating power commercially in July 1960, marked a key milestone in the development of nuclear power. It was the first large-scale commercial reactor designed as a BWR/1 and featured an innovative dual-cycle steam system. This system not only generated steam directly from the reactor but also incorporated four additional steam generators, which boiled water using heat from water returning from the reactors overhead steam drum. This design allowed the reactor to adjust more flexibly to shifts in power demand, providing better stability for the grid. Initially rated at 626 megawatt thermal (MWt) and 184 megawatt electric (MWe), it later reached 700 MWt and 207 MWe. The dual-cycle design, though successful in its flexibility and reliability, proved costly due to the larger steam generators and containment structures (Davis 2015). As a result, GE transitioned to the direct-cycle BWR/2 design in 1963, which became the foundation for all subsequent BWR plants (Guerrero and Paredes 2019).

In addition to its technical achievements, DNPS played a pivotal role in the broader development of nuclear power. It was one of the first large nuclear plants to be built entirely without government funding, marking a key turning point in the commercialization of nuclear energy (Davis 2015; Walker and Wellock 2010). By 1960, it was the largest operating nuclear power station in the US, producing electricity for over 6.5 million people in the Chicago area and thousands of industrial and agricultural customers across the region (AEC 1958).

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Background Research The success of DNPS Unit 1 prompted the construction of Units 2 and 3, which began operations in 1970 and 1971 (AEC 1973), respectively. Unit 2 was the first to incorporate GEs advanced BWR/3 design, which featured internal jet pumps instead of the internal steam separator system found in earlier designs. Both Units 2 and 3 were housed in Mark I containment buildings, with Unit 3 also utilizing the BWR/3 system. While these units reinforced DNPSs role in the nuclear power sector, their designs were one part of the broader evolution and refinement of nuclear technology in the US (Davis 2012; Guerrero and Paredes 2019).

By 1971, DNPS encompassed 1,011 ha (2,500 ac), and infrastructure expanded to support the new units. This included the construction of the 516 ha (1,275 ac) Dresden Cooling Lake, two additional intake and discharge canals, and expanded facilities to accommodate the increased power output (AEC 1973).

Despite its early success, Unit 1 was permanently decommissioned on October 31, 1978, after 18 years of service (Davis 2015). The decision to decommission Unit 1 was influenced by several factors, including the cost of required upgrades in response to safety changes following the Three Mile Island incident in 1979. ComEd chose not to invest in these upgrades, and the more modern Units 2 and 3 remained operational. Unit 1 decommission began in the 1980s, with chemical decontamination of the primary system completed in 1984. The formal decommissioning program for Unit 1 was planned in the 1990s, with a revised strategy developed in 1998 (NRC 2024). Unit 1 was placed into SAFSTOR, a long-term storage condition governed by the NRC (NRC 2023), with full decommissioning planned for 2029-2031 (Davis 2015). To begin SAFSTOR, a reactor is defueled, and its radioactivity is monitored long-term. Unit 1s spent fuel was removed from the Reactor Building and transferred into on-site Independent Spent Fuel Storage Installation (ISFSI). An ISFSI is a facility that is designed and constructed for the interim storage of spent nuclear fuel. These facilities are licensed separately from a nuclear power plant (NRC 2024a). The Unit 1 Reactor Buildings spent fuel pool and fuel transfer pool were drained, coated with stainless steel, and chemically decontaminated in 1984 (NRC 2024a). The NRC requires decommissioning and decontamination to be completed within 60 years of a units transition into SAFSTOR.

Units 2 and 3, which remain operational, were granted extended operating licenses by the NRC in 2004, ensuring their operation until 2029 (Unit 2) and 2031 (Unit 3). Based on more advanced GE BWR/3 designs, these units continue to supply significant electrical output, providing power to approximately 2 million homes in the region (Nuclear Powers Illinois 2005). ComEd became part of Exelon Corporation following a 2000 merger that combined ComEds parent company, Unicom, with PECO Energy to form Exelon (Wilson 2004). In 2022, ownership and operation of the DNPS was transferred to Constellation Energy, following the separation of Exelon Corporations regulated and unregulated businesses. Constellation Energy now manages ongoing operations and long-term decommissioning plans for the DNPS (Constellation Energy 2025; Exelon 2022).

The DNPS, with its early role in the commercialization of nuclear energy and its long operational history, remains a critical part of the US nuclear power landscape. It continues to contribute to the energy needs of the Chicago metropolitan area.

August 2025 SEARCH Final Technical Report Architectural History Survey of Dresden Nuclear Power Station, Grundy County, Illinois Background Research 8

MAP REVIEW SEARCH reviewed historic maps and aerial photographs to determine past land use in the DNPS vicinity. Two 1892 topographic maps illustrate three railroad lines crossing through the area. The EJE Railroad has a north-south alignment and follows the western extent of the Survey Area, while the Chicago, Santa Fe & California Railway and the Chicago, Alton & St. Louis Railway run parallel on a northeast-southwest path, passing the southeastern boundary. In addition to the railroad lines, roads cross into the Survey Area in the northern and southern portions of the facility. An unimproved road crosses the EJE Railroad alignment into the Survey Area. Another east-west road intersects the Survey Area and parallels its southern boundary before exiting the boundary and intersecting the other two railroad lines. An unincorporated community named Lorenzo is marked at this intersection but consists only of two buildings adjacent to the railroad tracks. No buildings are illustrated within the Survey Area, and no other features are apparent (Figure 2; US Geological Survey [USGS] 1892a, 1892b).

Topographic maps from 1918 depict several changes within the Survey Area. The railroad lines are depicted in the same alignments and follow the site boundaries as described above. However, labels for the two northeast-southwest railroads indicate name changes for both lines, marked as the Atchinson, Topeka & Santa Fe (AT&SF), formerly the Chicago, Santa Fe & California; and the Chicago & Alton, which dropped St. Louis from its name. A community named Devine is noted at the intersection of the AT&SF and the east-west improved road that crosses into the northern portion of the Survey Area. This road, which terminated within this portion of the Survey Area on the 1892 maps, is now depicted as turning southward and continues through the Survey Area, intersecting with the east-west improved road that follows the southern boundary. Two additional improved roads extend east from the north-south road within the site. An additional improved north-south road is depicted following the county line and crossing through the southern portion of the Survey Area. Four unimproved roads are also evident within the Survey Area, with one in the northwestern section and three in the southeastern portion. A total of 12 buildings are illustrated within the Survey Area, including the Goose Lake School, now within the Dresden Cooling Lakes footprint (Figure 3; USGS 1918a, 1918b).

Few changes to the general development, particularly to transportation routes, are depicted on a 1946 aerial photograph. One additional north-south improved road is depicted in the northwestern portion of the Survey Area, and a canal is evident in the south-central section. The other roads and railroad lines appear as they did on the 1918 maps. Much of the land within the Survey Area is depicted as cleared prairie or marshland, with numerous agricultural properties evident throughout the region (Figure 4; USGS 1946).

Topographic maps created in the mid-1950s confirm these observations and provide additional details. The transportation lines follow the same paths described above, with the addition of two unimproved roads, one in the northern portion and one in the southeastern section. These maps illustrate a canal in the central portion of the Survey Area, connected with the Goose Lake Pumping Station, which is depicted outside of the Survey Area. At least 39 buildings are shown within the Survey Area, with 26 of these illustrated as agricultural support structures, confirming

SEARCH August 2025 Architectural History Survey of Dresden Nuclear Power Station, Grundy County, Illinois Final Technical Report 9

Background Research the areas use as farmland. Numerous small residences are depicted on the south shore of the Kankakee River along Cottage Road. The Goose Lake School is depicted on the north side of Lorenzo Road in the same location noted above. A powerline corridor is illustrated crossing through the southeastern section of the Survey Area. Coal strip mines are depicted south, southwest, and west of the Survey Area and extend into the Survey Areas southwest corner (Figure 5; USGS 1953, 1954a, 1954b, 1954c).

Topographic maps from the early 1970s depict DNPS, including the powerplant, substations, towers, cooling lake, canals, powerlines, and other infrastructure. Most of the DNPS infrastructure is depicted within the northwestern and central portions of the Survey Area, while the Dresden Cooling Lake covers former agricultural land. Buildings north of Lorenzo Road, including the Goose Lake School, have been replaced by the Dresden Cooling Lake footprint. The unincorporated community of Lorenzo is depicted as approximately 12 buildings centered around the intersection of Lorenzo Road and the Atchinson, Topeka and Santa Fe Railroad alignment. A school building is depicted outside the Survey Area on Lorenzo Road west of that intersection. Residential development along Cottage Road increased in density throughout the 1960s and 1970s. Residential development also increased in density on the Dresden Cooling Lakes west bank through the 1980s (Figure 6; USGS 1973a, 1973b, 1973c, 1973d, 1985).

August 2025 SEARCH Final Technical Report Architectural History Survey of Dresden Nuclear Power Station, Grundy County, Illinois Background Research 10 Figure 2. USGS topographic maps of Morris and Wilmington, IL (USGS 1892a, 1892b).

SEARCH August 2025 Architectural History Survey of Dresden Nuclear Power Station, Grundy County, Illinois Final Technical Report 11 Background Research Figure 3. USGS topographic maps of Morris and Wilmington, IL (USGS 1918a, 1918b).

August 2025 SEARCH Final Technical Report Architectural History Survey of Dresden Nuclear Power Station, Grundy County, Illinois Background Research 12 Figure 4. USGS aerial photographs of Illinois (USGS 1946).

SEARCH August 2025 Architectural History Survey of Dresden Nuclear Power Station, Grundy County, Illinois Final Technical Report 13 Background Research Figure 5. USGS topographic maps of Channahon, Coal City, Minooka, and Wilmington, IL (USGS 1953, 1954a, 1954b, 1954c).

August 2025 SEARCH Final Technical Report Architectural History Survey of Dresden Nuclear Power Station, Grundy County, Illinois Background Research 14 Figure 6. USGS topographic maps of Channahon, Coal City, Minooka, and Wilmington, IL (USGS 1973a, 1973b, 1973c, 1973d).

SEARCH August 2025 Architectural History Survey of Dresden Nuclear Power Station, Grundy County, Illinois Final Technical Report 15 Research Design and Methods RESEARCH DESIGN AND METHODS NRHP CRITERIA Cultural resources identified within the Survey Area were evaluated according to the NRHP criteria (36 CFR 60.4). As defined by the National Park Service (NPS 1997), the quality of significance in American history, architecture, archaeology, engineering, and culture is present in districts, sites, buildings, structures, and objects that possess integrity of location, design, setting, materials, workmanship, feeling, and association, and:

A. that are associated with events or activities that have made a significant contribution to the broad patterns of our history; or B. that are associated with the lives of persons significant in our past; or C. that embody the distinctive characteristics of a type, period, or method of construction, or that represent the work of a master, or that possess high artistic values, or that represent a significant and distinguishable entity whose components may lack individual distinction; or D. that have yielded, or may be likely to yield, information important in prehistory or history.

In addition to the four criteria used to evaluate above-ground historic resources, the concept of integrity is also considered. Integrity is an important qualification of NRHP eligibility and can be related to any or all of the following (NPS 1997):

• Location: the place where the historic property (or properties) was/were constructed or where the historic event(s) occurred.

• Design: the combination of elements that create the form, plan, space, structure, and style of a property (or properties).

• Setting: the physical environment of the historic property (or properties).

• Materials: the physical elements combined to create the property (or properties) during the associated period of significance.

• Workmanship: the physical evidence of the crafts of a particular culture or people during any given period in history or prehistory.

• Feeling: the propertys (or properties) expression of the aesthetic or historic sense of the period of significance.

• Association: the direct link between the important historic event(s) or person(s) and the historic property (or properties).

The survey evaluated the aboveground resources at DNPS both individually and as potential contributors to historic districts. NRHP-eligible districts must possess a significant concentration, linkage, or continuity of sites, buildings, structures, or objects united historically or aesthetically by plan or physical development. NRHP-eligible districts and buildings must also possess historic significance, historic integrity, and historical context. During a consultation meeting held on May 30, 2025, and in written comments subsequently provided on June 10, 2025, in reference to a previous draft of this report (Appendix A), the SHPO expressed that the decommissioning of the DNPS Unit 1 reactor and its placement in SAFSTOR, along with the abandonment, removal, or

August 2025 SEARCH Final Technical Report Architectural History Survey of Dresden Nuclear Power Station, Grundy County, Illinois Research Design and Methods 16 repurposing of facilities that were designed to support Unit 1 operations, does not significantly diminish the integrity of the reactor building and its extant support facilities.

BACKGROUND RESEARCH Background research involved a review of available information for the Survey Area. This included a review of HARGIS, the NRHP database, historic maps, and aerial photographs. SEARCH conducted this background research and literature review to provide information about the regions environment, general prehistoric and historic development, and to develop a context for resources identified during survey.

ARCHITECTURAL HISTORY METHODS SEARCH conducted architectural history survey in compliance with SHPO survey guidance. The main goals of this survey were to:

• Identify historic-age (45 years or older; pre-1980) architectural history resources within the Survey Area; and

• evaluate historic-age architectural history resources within Survey Area for NRHP eligibility;

• identify and evaluate a potential historic district within the Survey Area.

The architectural history survey used SHPO survey procedures for the location, investigation, and recordation of historic resources 45 years old or older. SEARCH architectural historians reviewed USGS quadrangle maps historic aerial photographs, and DNPS site plans to identify pre-1980 resources within the Survey Area. Fieldwork documented extant historic-age buildings, structures, and objects within the Survey Area. SEARCH architectural historians photographed resources with a digital camera, and recorded pertinent information regarding architectural style, materials, distinguishing characteristics, siting, and condition.

Upon fieldwork completion, SEARCH architectural historians carefully considered architectural characteristics, overall condition, and historic significance to evaluate each resources NRHP eligibility; and recommended resources eligible or not eligible for NRHP inclusion.

SEARCH August 2025 Architectural History Survey of Dresden Nuclear Power Station, Grundy County, Illinois Final Technical Report 17 Architectural History Results ARCHITECTURAL HISTORY RESULTS The architectural history survey resulted in the identification and evaluation of 57 newly recorded historic resources within the Survey Area (Table 1; Figure 7; Appendix B). Of these 57 newly recorded resources, 21 are interconnected and comprise the primary DNPS Building, including:

• Unit 1 Reactor Building

• Unit 1 Fuel Handling Building

• Shop and Warehouse Building

• Administration/Service Building

• Technical Support System

• Unit 1 Turbine Building

• Unit 2 Turbine Building

• Unit 3 Turbine Building

• Unit 2 and 3 Reactor Building

• HPCI and Diesel Generator Building

• High Radiation Sampling Building A

• High Radiation Sampling Building B

• Off Gas Recombiner Room A

• Off Gas Recombiner Room B

• Unit 1 Station Chimney

• Unit 2 and 3 Station Chimney

• Max Recycle Radwaste Building

• Unit 2 and 3 Radwaste Building

• Waste Sample Tanks

• Heating Boiler House

• Floor Drain Surge Tank SEARCH recommends the proposed DNPS Unit 1 Historic District is NRHP eligible; furthermore, 9 newly recorded resources are eligible for NRHP inclusion as contributing resources within the proposed DNPS Unit 1 Historic District. The remaining 47 resources are recommended not eligible for NRHP inclusion, neither individually nor as contributing resources, due to a lack of significance and/or lack of integrity. SEARCH did not survey any buildings, structures, or additions within the Survey Area that were built after 1980 (i.e., those not yet of historic age). Resource descriptions and NRHP evaluations are included in detail below.

For security reasons, detailed results figures of the Survey Area, DNPS Building, and DNPS Unit 1 Historic District are included only in Appendix B.

August 2025 SEARCH Final Technical Report Architectural History Survey of Dresden Nuclear Power Station, Grundy County, Illinois Architectural History Results 18 Table 1. Architectural History Survey Results.

Resource Name Address Resource Type Style Year Built Recommended NRHP Status Dresden Nuclear Power Station Building 6500 N Dresden Road Industrial Industrial Vernacular, No Style ca. 1960-1979 Not Eligible Unit 1 Reactor Building 6500 N Dresden Road Industrial Industrial Vernacular ca. 1960 Eligible (Individual, Contributing)

Unit 2 and 3 Reactor Building 6500 N Dresden Road Industrial Industrial Vernacular ca. 1970-1971 Not Eligible Unit 1 Turbine Building 6500 N Dresden Road Industrial Industrial Vernacular ca. 1960 Eligible (Contributing)

Unit 1 Fuel Handling Building 6500 N Dresden Road Industrial Industrial Vernacular ca. 1960 Eligible (Contributing)

Unit 1 Station Chimney 6500 N Dresden Road Industrial No Style ca. 1960 Eligible (Contributing)

Unit 2 Turbine Building 6500 N Dresden Road Industrial Industrial Vernacular ca. 1970 Not Eligible Unit 3 Turbine Building 6500 N Dresden Road Industrial Industrial Vernacular ca. 1971 Not Eligible Unit 2 & 3 Station Chimney 6500 N Dresden Road Industrial No Style ca. 1970-1971 Not Eligible Units 2 & 3 Radwaste Building 6500 N Dresden Road Industrial Industrial Vernacular ca. 1970-1971 Not Eligible Shop & Warehouse Building 6500 N Dresden Road Industrial Industrial Vernacular ca. 1960 Not Eligible Administration Building/Service Building 6500 N Dresden Road Industrial Industrial Vernacular ca. 1960 Not Eligible Technical Support Center 6500 N Dresden Road Industrial Industrial Vernacular ca. 1975-1979 Not Eligible High Radiation Sampling Building A 6500 N Dresden Road Industrial Industrial Vernacular ca. 1975-1979 Not Eligible HPCI & Diesel Generator Building 6500 N Dresden Road Industrial Industrial Vernacular ca. 1970-1971 Not Eligible High Radiation Sampling Building B 6500 N Dresden Road Industrial Industrial Vernacular ca. 1975-1979 Not Eligible Off Gas Recombiner Room A 6500 N Dresden Road Industrial Industrial Vernacular ca. 1970-1971 Not Eligible Off Gas Recombiner Room B 6500 N Dresden Road Industrial Industrial Vernacular ca. 1970-1971 Not Eligible Max Recycle Radwaste Building 6500 N Dresden Road Industrial Industrial Vernacular ca. 1970-1971 Not Eligible Waste Sample Tanks 6500 N Dresden Road Industrial No Style ca. 1970 Not Eligible Heating Boiler House 6500 N Dresden Road Industrial Industrial Vernacular ca. 1970 Not Eligible Floor Drain Surge Tank 6500 N Dresden Road Industrial No Style ca. 1974 Not Eligible Unit 1 Crib House 6500 N Dresden Road Industrial Industrial Vernacular ca. 1960 Not Eligible

SEARCH August 2025 Architectural History Survey of Dresden Nuclear Power Station, Grundy County, Illinois Final Technical Report 19 Architectural History Results Table 1. Architectural History Survey Results.

Resource Name Address Resource Type Style Year Built Recommended NRHP Status Unit 2 & 3 Crib House 6500 N Dresden Road Industrial Industrial Vernacular ca. 1970 Not Eligible Unit 1 Intake Canal 6500 N Dresden Road Industrial No Style ca. 1960 Eligible (Contributing)

Unit 2 and 3 Intake Canal 6500 N Dresden Road Industrial No Style ca. 1970-1971 Not Eligible Unit 2 and 3 Discharge Canals 6500 N Dresden Road Industrial No Style ca. 1970-1971 Not Eligible Flow Regulation Station 6500 N Dresden Road Industrial No Style ca. 1970 Not Eligible Dresden Cooling Lake North of E Pine Bluff and Lorenzo roads Industrial No Style ca. 1971 Not Eligible Spillway E Bass Island Road Industrial No Style ca. 1974 Not Eligible Lift Station E Bass Island Road Industrial No Style ca. 1970 Not Eligible Wastewater Treatment Facility A 6500 N Dresden Road Industrial Industrial Vernacular ca. 1975-1979 Not Eligible Fuel Oil Storage Tank and Berm 6500 N Dresden Road Industrial No Style ca. 1960-1970 Not Eligible Off Gas Filter Building 6500 N Dresden Road Industrial Industrial Vernacular ca. 1970 Not Eligible Warehouse 5 6500 N Dresden Road Industrial Industrial Vernacular ca. 1970 Not Eligible Safe Shutdown Warehouse 6500 N Dresden Road Industrial Industrial Vernacular ca. 1970 Not Eligible Administration Building 2 6500 N Dresden Road Industrial Industrial Vernacular ca. 1975-1979 Not Eligible Gatehouse/Main Access Facility 6500 N Dresden Road Industrial Industrial Vernacular ca. 1975-1979 Not Eligible Visitors Center/NRC Office 6500 N Dresden Road Industrial Industrial Vernacular ca. 1975-1979 Not Eligible Diesel Generator Building/Security 6500 N Dresden Road Industrial Industrial Vernacular ca. 1975-1979 Not Eligible Storeroom 6500 N Dresden Road Industrial Industrial Vernacular ca. 1975-1979 Not Eligible Storeroom Secondary Warehouse 6500 N Dresden Road Industrial Industrial Vernacular ca. 1975-1979 Not Eligible Maintenance Warehouse 6500 N Dresden Road Industrial Industrial Vernacular ca. 1975-1979 Not Eligible Wastewater Treatment Facility B 6500 N Dresden Road Industrial Industrial Vernacular ca. 1975-1979 Not Eligible Diesel Generator &

HPCI Building/SBO Building 6500 N Dresden Road Industrial Industrial Vernacular ca. 1975-1979 Not Eligible Radwaste Building 6500 N Dresden Road Industrial Industrial Vernacular ca. 1974 Not Eligible

August 2025 SEARCH Final Technical Report Architectural History Survey of Dresden Nuclear Power Station, Grundy County, Illinois Architectural History Results 20 Table 1. Architectural History Survey Results.

Resource Name Address Resource Type Style Year Built Recommended NRHP Status Radwaste Building Unit 1 6500 N Dresden Road Industrial Industrial Vernacular ca. 1960 Eligible (Contributing) 345 kV Switchyard 6500 N Dresden Road Industrial No Style ca. 1960-1970 Not Eligible Switchyard Maintenance Building 6500 N Dresden Road Industrial Industrial Vernacular ca. 1975-1979 Not Eligible 138 kV Switchyard 6500 N Dresden Road Industrial No Style ca. 1960 Eligible (Contributing) 138 kV Relay House 6500 N Dresden Road Industrial Industrial Vernacular ca. 1960 Eligible (Contributing)

Substation Lock Road Industrial No Style ca. 1975-1979 Not Eligible Elgin, Joliet and Eastern Railroad Spur N/A Transportation No Style ca. 1956 Not Eligible Railroad Bridge 6500 N Dresden Road Transportation No Style ca. 1970 Not Eligible Meteorological Tower

.32 mi west of Lock Road Industrial No Style ca. 1960 Eligible (Contributing)

Storage Barn E Collins Road Agricultural Vernacular ca. 1940-1950 Not Eligible DNPS Unit 1 Historic District 6500 N Dresden Road Industrial Industrial Vernacular, No Style ca. 1960-1969 Eligible Italicized resources are interconnected historic-age facilities within the DNPS Building.

SEARCH August 2025 Architectural History Survey of Dresden Nuclear Power Station, Grundy County, Illinois Final Technical Report 21 Architectural History Results Figure 7. Architectural history survey results.

August 2025 SEARCH Final Technical Report Architectural History Survey of Dresden Nuclear Power Station, Grundy County, Illinois Architectural History Results 22 ARCHITECTURAL STYLES REPRESENTED IN THE SURVEY AREA The Survey Area contains styles that represent the development of industrial and utilitarian architecture in the US during the mid-twentieth century. Table 2 provides the architectural styles in the Survey Area, along with the number and percentages of resources of each style. The DNPS building as a whole and the DNPS Unit 1 Historic District are omitted from Table 2 because they include multiple styles.

Industrial Vernacular There are 36 Industrial Vernacular-style buildings within the Survey Area (Figure 8).

Buildings erected for commercial and industrial use characterize the Industrial Vernacular style.

Metal or wood frame materials are commonly used in construction. Wood, concrete, masonry or metal panel clad the building exteriors, with factory-produced metal paneling more prevalent throughout the mid-to late-twentieth century. There are typically no predominant decorative architectural details, as the buildings responded to the functional needs of the operations they housed and seldom were influenced by design innovations or stylistic movements (Ochsner 2014:353).

Industrial Vernacular buildings are frequently found within energy sector-related facilities and nuclear power plant properties nationally.

Characteristics of the Industrial Vernacular style often include, but are not limited to:

Utilitarian or unornamented design; Use of popular, mass produced twentieth century materials such as concrete, aluminum, glass, steel, asbestos, and plastics; Metal framed windows of various configurations; and, Flat roofs. (Jevremovic et al. 2012)

Table 2. Architectural Styles within the Survey Area.

Architectural Style Number of Examples Percentage Industrial Vernacular 36 65.45%

Vernacular 1

1.82%

No Style 18 32.73%

Total 55 100%

Figure 8. Unit 2 and 3 Crib House, facing southeast.

SEARCH August 2025 Architectural History Survey of Dresden Nuclear Power Station, Grundy County, Illinois Final Technical Report 23 Architectural History Results Vernacular There is one Vernacular style building within the Survey Area (Figure 9). The Vernacular style represents those ordinary wood frame or masonry buildings designed on a basis of local need, material availability, and tradition. The local environment and experience of the builder, often not architecturally

trained, provide more influence over the end product than that of most other styles (Glassie 1990). Decoration is often sparse; however, examples of Vernacular buildings may incorporate elements of common styles.

Characteristics of the Frame Vernacular style often include, but are not limited to:

Balloon frame or masonry construction; Simple geometric plans; One to two stories; Unornamented exterior or minimal ornamentation; Design dictated by need; Original exterior materials often replaced with vinyl, aluminum, asbestos shingle, etc.

(McAlester 2013).

No Style This term is generally applied to buildings, structures,

objects, or transportation resources that do not display one singular style, or to which style does not pertain.

Eighteen resources within the Survey Area possess no style (Figure 10).

Figure 9. Storage Barn, facing northwest.

Figure 10. Storage Tank and Berm, facing north.

August 2025 SEARCH Final Technical Report Architectural History Survey of Dresden Nuclear Power Station, Grundy County, Illinois Architectural History Results 24 NRHP EVALUATIONS The DNPS consists of 57 newly recorded historic-age resources on an approximately 386 ha (953 ac) parcel, and includes the DNPS building, its supporting facilities, transportation infrastructure, the proposed DNPS Unit 1 Historic District, and a ca. 1940-1950 agricultural storage barn that predates the DNPS (Table 1; see Figure 7; Appendix B). The earliest topographic quadrangle maps of the Survey Area, 1892 Morris, IL and 1892 Wilmington, IL, depict the DNPS within an undeveloped area south of the Illinois and Kankakee rivers, defined by low topography, approximately 13 km (8 mi) northeast of Morris, Illinois (USGS 1892a, 1892b). The DNPS is first depicted on 1985 Ottawa, IL, though resources documented during survey date to ca 1956-1979 (USGS 1985). For a full description of the resources historic context and development, see Historic Context above.

Resource descriptions and NRHP eligibility evaluations are included below. The DNPS Building and the historic-age interconnected facilities that comprise it are described and evaluated first.

Free-standing historic-age buildings and structures, and the plants canal system are discussed following the DNPS Buildings resources. The Storage Barn within the Survey Area that predates DNPS construction is discussed following the plants free-standing facilities and canals. The section concludes with a discussion of the proposed DNPS Unit 1 Historic District and its contributing and noncontributing resources.

Dresden Nuclear Power Station Building The DNPS Building is comprised of numerous interconnected facilities with primary and auxiliary functions and serves as the primary loci for electrical power generation at the facility (Table 1; Appendix B). Fieldwork determined the building consists of 21 ca. 1960-1979 facilities, which were included in the survey; and approximately 13 post-1980 facilities omitted from survey and evaluation (NETR 1973, 1974, 1983, 1998). The 21 historic-age resources are described below.

The historic age facilities comprising the DNPS Building are Industrial Vernacular in style or possess no style, are utilitarian in design, and lack exterior ornamentation.

The DNPS Building as a whole comprises the Unit 1, 2, and 3 reactor buildings, turbine buildings, and other support facilities (see Table 1). The Unit 1 reactor building was the first privately funded reactor building in the US; and is an example of a ca. 1960 spherical reactor building.

SEARCH recommends the DNPS Building is significant under Criterion A and C for these associations. Background research indicates the resource lacks association with any person(s) significant in history, and is recommended not significant under Criterion B. The resource is not significant under Criterion D because it lacks the potential to yield further information of historical importance.

The DNPS Building remains in its original location and retains significance of location. Since the ca. 1960 construction of Unit 1, the DNPS Building has been altered subsequently over time. The ca. 1970 construction of Unit 2 included an additional reactor building, turbine building, and support buildings attached to Unit 1s facilities, and expanded the buildings footprint to the

SEARCH August 2025 Architectural History Survey of Dresden Nuclear Power Station, Grundy County, Illinois Final Technical Report 25 Architectural History Results west. These additions also included interior alterations to the Unit 1 Turbine building, which was combined with Unit 2 and 3 control operations, spanning both the Unit 1 and Unit 2 Turbine Buildings. The ca. 1971 construction of Unit 3 included an additional turbine building attached to the Unit 2 Turbine Buildings west elevation, and additional support buildings. The DNPS Building also includes approximately 9 nonhistoric facilities. Nonhistoric additions are located on the west elevation of the Unit 3 Turbine building, and on the north elevations of the Off Gas Combiner Rooms. Backup generators are located north of Turbine Building 3. The ca. 1960 Shop and Warehouse Building has been altered by an addition on its south elevation, and by nonhistoric additions on its west elevation. Due to the expansion and alteration of the building ca. 1970 through post-1980, the resource no longer retains its integrity of design, materials, workmanship, of feeling. Prior to Unit 2s construction, only the Unit 1 Intake Canal was sited north of the DNPS Building. Following Unit 2 and 3s ca. 1970-1971 construction, the cooling system expanded to include the Unit 2 and 3 Intake Canal, Unit 2 and 3 Discharge Canal, and the Dresden Cooling Lake. The site surrounding the DNPS Building is no longer representative of its ca. 1960 scale associated with the construction of Unit 1. The DNPS Building no longer retains its integrity of setting. Though the Unit 1 reactor was permanently shut down in 1978, the facility continues in operation and retains its integrity of association. Due to this loss of physical and setting integrity, SEARCH recommends the resource no longer retains sufficient integrity to convey its significance.

SEARCH recommends the resource is not eligible for NRHP inclusion, neither individually nor as a contributing resource to the proposed DNPS Unit 1 Historic District.

Unit 1 Reactor Building Site construction began on May 1, 1956, and Unit 1 began commercial operation on July 4, 1960 (Figure 11). The dual-cycle BWR/1 operated on site until it was permanently shut down on October 31, 1978 (Figure 12).

General Electric designed the 192 MWe reactor for ComEd of Chicago. The BWR/1 was housed within a spherical steel building 190-feet in diameter, contain[ing] the reactor, steam separating drum, secondary steam generators, pumps and other auxiliaries - constituting a steam generator package (US Atomic Energy Commission 1958:41).

Background research did not reveal information about the electricity supplied between 1960 and 1969. However, between 1970 and 1978, Unit 1 supplied 16.49 terawatt hours (TW.h) of electricity to northeastern Illinois (IAEA 2025). All commercial nuclear power plants in the United States use light water reactors, with water used for cooling and as a neutron moderator to control the chain reaction (USDOE 2021). A BWR generates power when:

Figure 11. Unit 1 Reactor Building, facing northwest.

August 2025 SEARCH Final Technical Report Architectural History Survey of Dresden Nuclear Power Station, Grundy County, Illinois Architectural History Results 26 (1) The core inside the reactor vessel creates heat; (2) A steam-water mixture is produced when very pure water (reactor coolant) moved upward through the core, absorbing heat; and (3) The steam line directs the steam to the main turbine, causing it to turn the turbine generator, which produces electricity. (NRC 2023)

Unit 1s reactor vessel was carbon steel lined with stainless steel and ranged in thickness from 13.65 cm (5.38 in) to 22.86 cm (9 in). The New York Shipbuilding Corporation manufactured the plants reactor vessel (AEC 1958). The reactor core housed 488 fuel assemblies, or groups of fuel rods consisting of metal tubes containing fissionable material; 80 control rods; and eight instrument nozzles. Each fuel element contained 36 round fuel rods in a square Zircaloy-2 can (AEC 1958: 44; Figure 13 and Figure 14). Each rod contained enriched uranium dioxide sintered pellets, totaling 4,000,000 pellets within the reactors core (AEC 1958). It was cooled indirectly by water drawn from the junction of the Kankakee and Des Plaines rivers.

Unit 1 was permanently retired on October 31, 1978.

Unit 1s spent fuel was transferred from the spent fuel pool and fuel transfer pool to on-site ISFSI pads (Humphrey 2024). An ISFSI is a facility that is designed and constructed for the interim storage of spent nuclear fuel. These facilities are licensed separately from a nuclear power plant (NRC 2024a).

Its spent fuel pool and fuel transfer pool were drained and coated with stainless steel. Chemical decontamination of Unit 1 was completed in 1984, and Unit 1 has remained in SAFSTOR since the 2007 spent fuel transfer to ISFSI (Humphrey 2004).

SAFSTOR is the long-term storage condition for a permanently shut down nuclear power plant. During SAFSTOR, radioactive contamination decreases substantially, making subsequent decontamination and demolition easier and reducing the amount of

[low-level radioactive waste] requiring disposal (NRC 2023).

Figure 13. Unit 1 Reactor Fuel Element Diagram (US Atomic Energy Commission 1958: 45).

Figure 12. Diagram of BWR power generation process (NRC 2023).

SEARCH August 2025 Architectural History Survey of Dresden Nuclear Power Station, Grundy County, Illinois Final Technical Report 27 Architectural History Results In October 1991, the American Nuclear Society (ANS) designated the Unit 1 containment building a Nuclear Historic Landmark (ANS 2025). The ANS Nuclear Historic Landmark award acknowledges a historic event or activity [which] successfully provided an essential contribution to, or basis for, the subsequent peaceful application of nuclear technology or nuclear energy, and been a first of a kind, or provided a signific new departure (ANS 2025). The award acknowledges Unit 1s status as the first commercially funded nuclear reactor.

Spherical containment buildings of Unit 1s type were among early containment building types constructed at commercial nuclear plants. Early containment buildings reflect this design not as an aesthetic expression, but because a spherical shape evenly distributes pressure across a surface. However, for BWR containment, these spheres were quickly replaced in the late 1960s and early 1970s in favor of the Mark type containment buildings, which provided increased interior workspace, reinforced concrete construction, and improved safety through increased wall thickness (ANS 2012). By 1970, BWRs were housed in Mark I containment buildings, as evidenced by DNPS Unit 2 reactor building. These successive types allowed more flexible shape selection and allowed for rational equipment placement... the space inside the containment vessel can be effectively utilized (Li 2024), as the spherical shape greatly limited interior operating space. In 1978, NRC issued criteria for reviewing the seismic resistance of US power plants (Newmark and Hall 1978). The report noted many of the early nuclear facilities were designed and constructed during the time when seismic design procedures for such specialized systems were beginning and determined pre-1968 plants required safety reviews (Newmark and Hall 1978: 1). For early plants like the DNPS, the report acknowledged:

It is well known that upgrading and retrofitting constitute expensive operations when they can be accomplished at all. In many cases it is economically, if not physically, impossible to carry our significant seismic upgrading improvements.

(Newmark and Hall 1978: 2)

Unit 1 seismic review determined the spherical building posed a safety risk in the event of an earthquake. Given the building shapes inherent space limitations, and nuclear plant constructions movement toward more seismically appropriate Mark models post-1970, updating the building to comply with these requirements was determined cost prohibitive. For these reasons, Unit 1 permanently shut down in October 1978 (NRC 1980).

Background research indicates Unit 1s spherical containment building was among four similar structures built between ca. 1954 and 1962. The earliest spherical containment structure in the US is the ca. 1954 D1G Ball at the Kenneth Kesselring Site (West Milton NY), which housed a prototype sodium-cooled nuclear reactor until its 1996 decommission (Harvey 2022). Two other spherical containment buildings were built during the period, the ca. 1960 Yankee Rowe Nuclear Power Station (Row, MA) reactor building; and the ca. 1962 Big Rock Point Nuclear Power Plant (Charlevoix, MI) reactor building (IAEA 2025). However, these were demolished ca. 2005 (NETR 2005, 2008).

The Unit 1 Reactor building represents the first commercially funded nuclear plant in the United States, and is significant under Criterion A for this association. Background research indicates the

August 2025 SEARCH Final Technical Report Architectural History Survey of Dresden Nuclear Power Station, Grundy County, Illinois Architectural History Results 28 resource lacks association with any person(s) significant in history, and is recommended not significant under Criterion B. Background research indicates the Unit 1 Reactor building is one of two extant spherical reactor buildings in the US, along with the ca. 1954 Kesselring Site sphere.

This type was replaced in the 1970s in favor of reinforced concrete cylindrical shapes. SEARCH recommends the resource is significant under Criterion C for its engineering significance and association with mid-twentieth century nuclear technology construction. The resource is not significant under Criterion D because it lacks the potential to yield further information of historical importance.

The Unit 1 Reactor Building is located within its original footprint as an interconnected facility within the DPNS Building and retains integrity of location and setting. Unit 1 was permanently retired on October 31, 1978, and its spent fuel was removed from within the facility. The containment building is utilitarian and was purpose-built to safely house a nuclear reactor. The facilitys significance under Criterion A is associated with its role as the first privately funded nuclear reactor building; and its significance under Criterion C is associated with its engineering value. Per SHPO consultation on May 30, 2025, changes to a buildings use over time does not diminish the buildings aspects of integrity. The building retains its integrity of design, workmanship, feeling, and association. The buildings fuel was removed after its 1978 retirement, and Unit 1 was placed in long-term SAFSTOR. The reactors spent fuel pool and fuel transfer pool were drained and coated with stainless steel. The building no longer retains its integrity of materials. Based on its significance under Criteria A and C and its overall integrity, SEARCH recommends the resource is eligible individually and as a contributing resource within the proposed DNPS Unit 1 Historic District.

SEARCH August 2025 Architectural History Survey of Dresden Nuclear Power Station, Grundy County, Illinois Final Technical Report 29 Architectural History Results Figure 14. Cross Section of Unit 1 Reactor Core Within its Pressure Vessel (US Atomic Energy Commission 1958:43).

August 2025 SEARCH Final Technical Report Architectural History Survey of Dresden Nuclear Power Station, Grundy County, Illinois Architectural History Results 30 Unit 2 and 3 Reactor Building The ca. 1970-1971 Unit 2 and 3 Reactor Building are centrally located within the DNPS Building, approximately 121 m (396.98 ft) southwest of the Unit 1 Reactor Building (Figure 15). Unit 2 began commercial operation on June 9, 1970; and Unit 3 began commercial operation on November 16, 1971.

Both Unit 2 and 3 are GE BWR/3 in Mark I containment buildings (see Figure 12). The Unit 2 and 3 reactors are located within a shared multi-level, Industrial Vernacular-style reinforced concrete building which provides nuclear containment, also known as a Mark I building. The building has a rectangular plan and is covered by a flat roof enclosed by a metal railing. The buildings upper elevations are clad with metal factory panel. The building rests on a raised concrete slab and possesses no fenestration. In addition to the two BWRs, the Unit 2 and 3 Reactor Building contains the reactor cleanup system, the reactor shutdown system, the reactor isolation condenser system, and the reactor control rod drive hydraulic system (ComEd 1965: I-4-5).

Unit 2 is a GE Type 3 BWR designed as a Single cycle, forced circulation, BWR... similar except for a modest increase in size and capability to the reactors recently authorized at... Oyster Creek Nuclear Power Plant [in Waretown, New Jersey]... and Nine Mile Point Nuclear Power Plant [in Oswego, New York]. (ComEd 1965: I-4-1)

The Unit 2 reactor vessel is constructed of steel clad with stainless steel on its interior. The reactors core has Modules of four fuel assembles set in the interstices of a cruciform control rod...

the fuel for the reactor core consists of uranium dioxide pellets contained in sealed Zircaloy-2 tubes. These fuel rods are assembled into individual fuel assemblies of 49 fuel rods each. (ComEd 1965: I-4-9)

Unit 3 is a GE Type 3 BWR designed as a single cycle, forced circulation BWR which for all practicable purposes [is] identical with Unit 2 (ComEd 1966:I-1-1). The reactor vessel has an interior height of approximately 10.73 m (68 ft), an approximate diameter of 6.40 m (21 ft). The vessel is welded to a steel skirt above a ring girder resting on a concrete slab foundation (ComEd 1966: V-2-4).

Figure 15. Unit 2 and 3 Reactor Building, facing north.

SEARCH August 2025 Architectural History Survey of Dresden Nuclear Power Station, Grundy County, Illinois Final Technical Report 31 Architectural History Results The Unit 2 and 3 Reactor Building is an example of a typical reactor building type constructed in the United States during the 1970s, which were modeled on earlier, existing reactor building types at nuclear plants elsewhere. The building is not associated with events that have made a significant contribution to the broad patterns of history, and is not significant under Criterion A.

Background research indicates the building lacks association with any person(s) significant in history, and is not significant under Criterion B. The building is a Mark I model containment building housing two BWRs. The building represents a common model found at early 1970s nuclear plants elsewhere in the US. The building is not the first of the type and does not represent a significant engineering advance. The building lacks architectural and engineering distinction, is not the work of a master, does not possess high artistic values, and therefore is not significant under Criterion C. The resource is not significant under Criterion D because it lacks the potential to yield further information of historical importance. SEARCH recommends the resource is not eligible for NRHP inclusion, neither individually nor as a contributing resource to the proposed DNPS Unit 1 Historic District.

Unit 1 Turbine Building The Unit 1 Turbine Building is a ca. 1960 Industrial Vernacular structural

steel, reinforced concrete, and metal factory panel building (Figure 16). The building is attached to the Unit 1 Reactor building on the upper elevation of its east facade; and attached to the Unit 2 Turbine Building on its west facade. The buildings foundation was obscured from view by the Off Gas Recombiner Room and adjacent ductwork and transformers. The buildings flat roof is covered with reinforced concrete. The building is utilitarian and lacks exterior ornamentation and fenestration.

The Unit 1 Turbine Building no longer serves in its original function as a main turbine building since the Unit 1 Reactors retirement in 1978. Unit 2 and 3s main control room and support systems extend across the dividing wallinto the Dresden Unit 1 Turbine Building. The Dresden Units 2 and 3 Prime Computer Room, Prime Computer Uninterrupted Power Supply (UPS) and associated battery are in the Dresden Unit 1 Turbine building (NRC 2024b: 2). The building is also used for a general tool room and machine shop for the plant (ComEd 1998: 5).

The Unit 1 Turbine Building was built to house Unit 1s main turbine generator. The Unit 1 Reactor represents the first commercially funded nuclear plant in the United States. The Unit 1 Turbine Building is significant under Criterion A for this association. Background research indicates that the resource lacks association with any person(s) significant in history, and it is recommended not significant under Criterion B. Background research indicates the building is utilitarian Figure 16. Unit 1 Turbine Building, center rear, facing south.

August 2025 SEARCH Final Technical Report Architectural History Survey of Dresden Nuclear Power Station, Grundy County, Illinois Architectural History Results 32 reinforced concrete and steel construction. The building lacks architectural and engineering distinction, is not the work of a master, does not possess high artistic values, and therefore is not significant under Criterion C. The resource is not significant under Criterion D because it lacks the potential to yield further information of historical importance.

The Unit 1 Turbine Building is located within its original footprint as an interconnected facility within the DPNS Building and retains integrity of location and setting. The ca. 1970 Unit 2 Turbine Building was constructed on the buildings east elevation, and Unit 2 and 3s control room and support systems are now partially located within the building. The turbine machinery was removed ca. 2011 (ComEd 1998). The building no longer retains integrity of design. Unit 1 was decommissioned on October 31, 1978, and its spent fuel was removed from within the facility.

The Unit 1 Turbine Building is utilitarian and was purpose-built to house Unit 1s main turbine generator. The buildings significance under Criterion A is associated with Unit 1s function as the first privately funded nuclear reactor building. Per SHPO consultation on May 30, 2025, changes to the buildings use over time do not diminish the buildings aspects of integrity. Though Unit 1 is no longer operational, the plant overall remains in operation. Therefore, the building retains its integrity of materials, workmanship, feeling or association. Therefore, SEARCH recommends the resource is eligible as a contributing resource within the proposed DNPS Unit 1 Historic District.

Unit 1 Fuel Handling Building The Unit 1 Fuel Handling Building is a ca. 1960 Industrial Vernacular-style building located adjacent to and south of the Unit 1 Reactor Building (Figure 17). Additionally the building is connected to the Shop and Warehouse Building on its west facade. The building is structural steel and reinforced concrete construction. Its exterior is clad with metal factory panel, and its flat roof is covered with concrete and built-up material. The building rests on an elevated concrete slab foundation. Two garage bays on the south facade are enclosed by metal roll down garage doors. A louvered vent is also located on the south facades lower elevation.

The building is utilitarian in design and possesses no exterior ornamentation.

The Unit 1 Fuel Handling Building was constructed as a support building to house the fuel handling crane, to receive new fuel, and to remove spent fuel from the Unit 1 Reactor. The facilitys fuel handling bridge was replaced in 1994, and fuel handling crane was replaced in 1999 as part of the SAFSTOR process (ComEd 1998). The building no longer serves in its original function as a fuel handling building since the Unit 1 Reactors retirement in 1978, and SAFSTOR dormancy since then. All of Unit 1s spent fuel was removed from the DNPS Building to ISFSI.

Figure 17. Unit 1 Fuel Handling Building, facing west.

SEARCH August 2025 Architectural History Survey of Dresden Nuclear Power Station, Grundy County, Illinois Final Technical Report 33 Architectural History Results The Unit 1 Fuel Handling Building was built to move Unit 1s new and spent fuel assemblies. The Unit 1 Reactor represents the first commercially funded nuclear plant in the United States. The Unit 1 Fuel Handling Building is significant under Criterion A for this association. Background research indicates the resource lacks association with any person(s) significant in history, and it is recommended not significant under Criterion B. Background research indicates the building is utilitarian reinforced concrete and steel construction. The building lacks architectural and engineering distinction, is not the work of a master, does not possess high artistic values, and therefore is not significant under Criterion C. The resource is not significant under Criterion D because it lacks the potential to yield further information of historical importance.

The Unit 1 Fuel Handling Building is located within its original footprint as an interconnected facility within the DPNS Building and retains integrity of location and setting. The facilitys fuel handling bridge was replaced in 1994, and its fuel handling crane was replaced in 1999. Since Unit 1s 1978 retirement and SAFSTOR dormancy, the building no longer functions as the reactors fuel handling building. Unit 1 was retired on October 31, 1978, and its spent fuel was removed from within the facility. The Unit 1 Fuel Handling Building is utilitarian and purpose-built. The buildings significance under Criterion A is associated with Unit 1s function as the first privately funded nuclear reactor building. Per SHPO consultation on May 30, 2025, changes to the buildings use over time do not diminish the buildings aspects of integrity. Though Unit 1 is no longer operational, the plant overall remains in operation. Therefore, the building retains its integrity of design, materials, workmanship, feeling, and association. Therefore, SEARCH recommends the resource is eligible as a contributing resource within the proposed DNPS Unit 1 Historic District.

Unit 1 Station Chimney The Unit 1 Station Chimney is a ca. 1960 reinforced concrete structure located approximately 16 m (52 ft) northwest of the Unit 1 Reactor Building (Figure 18). The chimney is approximately 91 m (300 ft) in height and provided an elevated release path for gaseous effluents (Exelon Generation 2018: 3-18). The structure is utilitarian in design and possesses no style. The chimney has been abandoned in place and was not removed due to its foundations proximity to underground electrical ductwork used for Unit 2 and 3 (NRC 2024b).

The Unit 1 Station Chimney was built to release Unit 1s waste gases. The Unit 1 Reactor represents the first commercially funded nuclear plant in the United States.

The Unit 1 Station Chimney is significant under Criterion A for this association. Background research indicates that the resource lacks association with any person(s) significant in history, and it is recommended not Figure 18. Unit 1 Station Chimney (left);

Unit 2 and 3 Station Chimney (right rear),

facing west.

August 2025 SEARCH Final Technical Report Architectural History Survey of Dresden Nuclear Power Station, Grundy County, Illinois Architectural History Results 34 significant under Criterion B. The concrete chimney is similar to those found at both early nuclear plants, such as the ca. 1956 Vallecitos Nuclear Center, and other plants and factories throughout the US. The resource lacks architectural and engineering distinction, is not the work of a master, does not possess high artistic values, and therefore is not significant under Criterion C. The resource is not significant under Criterion D because it lacks the potential to yield further information of historical importance.

The Unit 1 Station Chimney is located within its original footprint adjacent to Unit 1 Reactor Building and retains integrity of location and setting. Since Unit 1s 1978 retirement the structure has been abandoned in place and retains its integrity of workmanship and materials. The structures significance under Criterion A is associated with Unit 1s function as the first privately funded nuclear reactor building. Per SHPO consultation on May 30, 2025, changes to a buildings use over time do not diminish the buildings aspects of integrity. Though Unit 1 is no longer operational, the plant overall remains in operation. Therefore, the building retains its integrity of design, feeling, and association. SEARCH recommends the resource is eligible as a contributing resource within the proposed DNPS Unit 1 Historic District.

Unit 2 Turbine Building The Unit 2 Turbine building is a ca. 1970 Industrial Vernacular structural

steel, reinforced concrete and metal factory panel building (Figure 19). The building is attached to the Unit 1 Turbine Building on its east facade; and attached to the Unit 3 Turbine Building on its west facade. The building has a rectangular plan and rests on a reinforced concrete slab foundation. The buildings flat roof is covered with reinforced concrete. A garage bay is centrally located on the south facade and enclosed by a roll down metal garage door. An EJE Railroad spur formerly terminated within the building through this garage bay, but the track has been infilled with concrete.

The Unit 2 Turbine Building is a support facility for Unit 2 Reactor operation. The building is not associated with events that have made a significant contribution to the broad patterns of history, and is not significant under Criterion A. Background research indicates the building lacks association with any person(s) significant in history and is not significant under Criterion B. The building lacks architectural and engineering distinction, is not the work of a master, does not possess high artistic values, and therefore is not significant under Criterion C. The resource is not significant under Criterion D because it lacks the potential to yield further information of historical importance. SEARCH recommends the resource is not eligible for NRHP inclusion, neither individually nor as a contributing resource to the proposed DNPS Unit 1 Historic District.

Figure 19. Unit 2 Turbine Building, center rear, facing north.

SEARCH August 2025 Architectural History Survey of Dresden Nuclear Power Station, Grundy County, Illinois Final Technical Report 35 Architectural History Results Unit 3 Turbine Building The Unit 3 Turbine Building is a ca. 1971 Industrial Vernacular structural

steel, reinforced concrete, and metal factory panel building (Figure 20). The building is attached to the Unit 2 Turbine Building on its east facade and to the Unit 2 and 3 Reactor Building on its south facade. The building has a rectangular plan and rests on a reinforced concrete slab foundation. The buildings exterior is clad with metal factory panel, and its flat roof is covered with reinforced concrete. Aerial imagery indicates a chimney is located at the southeast corner of the buildings flat roof, but the chimney and its materials were obscured from view during survey. A garage bay is located offset on the south facade and enclosed by a roll down metal garage door. An EJE Railroad spur formerly terminated within the building through this garage bay, but the track has been infilled with concrete. The lower elevation of the buildings south facade is enclosed by a modern chain link security fence.

The Unit 3 Turbine Building is a support facility for Unit 3 Reactor operation. The building is not associated with events that have made a significant contribution to the broad patterns of history and is not significant under Criterion A. Background research indicates the building lacks association with any person(s) significant in history and is not significant under Criterion B. The building lacks architectural and engineering distinction, is not the work of a master, does not possess high artistic values, and therefore is not significant under Criterion C. The resource is not significant under Criterion D because it lacks the potential to yield further information of historical importance. SEARCH recommends the resource is not eligible for NRHP inclusion, neither individually nor as a contributing resource to the proposed DNPS Unit 1 Historic District.

Unit 2 and 3 Station Chimney The Unit 2 and 3 Station Chimney is a ca. 1970 reinforced concrete structure located approximately 50 m (164 ft) north of the Unit 3 Turbine Building (Figure 21). The chimney is approximately 94 (310 ft) in height and provides an elevated release path for gaseous effluents (Exelon Generation 2018:3-18). The structure is utilitarian in design and possesses no style.

The Unit 2 and 3 Station Chimney is an ancillary facility not associated with events that have made a significant contribution to the broad patterns of history. SEARCH recommends the resource is not significant under Criterion A. Background research indicates the resource lacks association with any person(s) significant in history, and the resource is recommended not significant under Criterion B. The concrete chimney is similar to those found at both early nuclear plants, such as the ca. 1956 Vallecitos Nuclear Center, and other plants and factories throughout Figure 20. Unit 3 Turbine Building, facing northeast.

August 2025 SEARCH Final Technical Report Architectural History Survey of Dresden Nuclear Power Station, Grundy County, Illinois Architectural History Results 36 the US. The resource lacks architectural and engineering distinction, is not the work of a master, does not possess high artistic values, and therefore is not significant under Criterion C. The resource is not significant under Criterion D because it lacks the potential to yield further information of historical importance. SEARCH recommends the resource is not eligible for NRHP inclusion, neither individually nor as a contributing resource to the proposed DNPS Unit 1 Historic District.

Units 2 and 3 Radwaste Building The Units 2 and 3 Radwaste Building is a ca.

1970-1971 Industrial Vernacular reinforced concrete and metal factory panel building (Figure 22). The building is attached to Unit 2 and 3 Station Chimney at its northeast corner. Its flat roof is covered with reinforced concrete. The building is mostly obscured from view by the Units 2 and 3 Station Chimney and Water Sample Tanks.

The Units 2 and 3 Radwaste Building is a support facility for Unit 2 and 3 Reactor operations. The building is not associated with events that have made a significant contribution to the broad patterns of history and is not significant under Criterion A. Background research indicates the building lacks association with any person(s) significant in history and is not significant under Criterion B. The building lacks architectural and engineering distinction, is not the work of a master, does not possess high artistic values, and therefore is not significant under Criterion C. The resource is not significant under Criterion D because it lacks the potential to yield further information of historical importance. SEARCH recommends the resource is not eligible for NRHP inclusion, neither individually nor as a contributing resource to the proposed DNPS Unit 1 Historic District.

Shop & Warehouse Building The Shop and Warehouse Building is a ca. 1960 Industrial Vernacular building located south of the Unit 1 Reactor Building. The building has an irregular plan due to subsequent ca. 1970 additions on the south facade. The buildings exterior is clad with metal factory panel and rests on a concrete slab foundation. The flat roof is covered with reinforced concrete. The structure is Figure 21. Unit 2 and 3 Station Chimney, facing west.

Figure 22. Units 2 and 3 Radwaste Building, center rear, facing southeast.

SEARCH August 2025 Architectural History Survey of Dresden Nuclear Power Station, Grundy County, Illinois Final Technical Report 37 Architectural History Results utilitarian in design and possesses no style. Two garage bays on the south facade are enclosed by metal roll down garage windows. Fixed pane windows on the south facade are located below attached barrel awnings. The building is utilitarian and possesses no exterior ornamentation.

Security access restricted photographs of the building during survey.

The Shop and Warehouse Building is an ancillary building built to support Unit 1 and the DNPS general operation. The Unit 1 Reactor building represents the first commercially funded nuclear plant in the United States. The resource is significant under Criterion A for its association with Unit 1. Background research indicates that the resource lacks association with any person(s) significant in history, and it is recommended not significant under Criterion B. The buildings design is utilitarian and purpose-built and represents a common example of a prefabricated warehouse. It lacks architectural and engineering distinction, is not the work of a master, does not possess high artistic values, and therefore is not significant under Criterion C. The resource is not significant under Criterion D because it lacks the potential to yield further information of historical importance.

The Shop and Warehouse Building is located within its original footprint, functions as a warehouse, and retains integrity of location and setting. The building has two subsequent additions on its south elevation, and a nonhistoric addition on its west elevation. These additions have enclosed and/or encapsulated the buildings former exterior on those elevations. The building no longer retains integrity of design, materials, or workmanship. Per SHPO consultation on May 30, 2025, changes to a buildings use over time do not diminish the buildings aspects of integrity. Although the building was originally constructed to support Unit 1s operation, the building retains its integrity of feeling and association. However, due to a lack of physical and design integrity caused by the buildings subsequent additions, it no longer retains sufficient integrity to convey significance. SEARCH recommends the resource is not eligible for NRHP inclusion, neither individually nor as a contributing resource to the proposed DNPS Unit 1 Historic District.

Administration Building/Service Building The ca. 1970 Administration Building/Service Building is attached to the Technical Support Center on its south facade and to the Administration Building 2 via an elevated skywalk on its west facade (Figure 23). The Technical Support Centers construction enclosed the Administration Buildings former south facade, and its west facade remains its only exterior-facing side. A ca. 1990 addition on its north facade also enclosed and obscured its original exterior. The Industrial Vernacular style building is clad with metal factory panel on its west facade. The building has an irregular plan and its flat roof is covered with Figure 23. Administration Building/Service Building, facing northeast.

August 2025 SEARCH Final Technical Report Architectural History Survey of Dresden Nuclear Power Station, Grundy County, Illinois Architectural History Results 38 built-up composite material. An offset entrance on the west facade is located within a prefabricated metal vestibule-like projection and enclosed by a metal door with a small upper light. Fenestration consists of a narrow bank of casement clerestory windows. The building is utilitarian in design and possesses no exterior ornamentation.

The Administration Building is a support building associated with the Unit 1 Reactor operations, which was retired in 1978. The Unit 1 Reactor represents the first commercially funded nuclear plant in the United States. The Administration Building is significant under Criterion A for this association. Background research indicates the resource lacks association with any person(s) significant in history and is recommended not significant under Criterion B. The resource lacks architectural and engineering distinction, is not the work of a master, does not possess high artistic values, and therefore is not significant under Criterion C. The resource is not significant under Criterion D because it lacks the potential to yield further information of historical importance.

The Administration Building is located within its original footprint as an interconnected facility within the DPNS Building, and it retains integrity of location and setting. The buildings significance under Criterion A is associated with Unit 1s function as the first privately funded nuclear reactor building. The building has been altered throughout its history by additions and alterations to its north, south, and west facades. Ca. 1990 additions have altered and encapsulated the buildings original design and appearance. The building no longer retains integrity of design, materials, or workmanship. Per SHPO consultation on May 30, 2025, changes to a buildings use over time do not diminish the buildings aspects of integrity. Though Unit 1 is no longer operational, the plant overall remains in operation. The facility has been repurposed to support Unit 2 and 3 operations. Therefore, the building retains its integrity of feeling and association. However, due to a lack of physical and design integrity caused by the buildings subsequent additions, it no longer retains sufficient integrity to convey significance. SEARCH recommends the resource is not eligible for NRHP inclusion, neither individually nor as a contributing resource to the proposed DNPS Unit 1 Historic District.

Technical Support Center The ca. 1975-1979 Technical Support Center Building A is attached to the Administration Building/Service Building on its north facade (Figure 24). The Industrial Vernacular style building is clad with brick masonry veneer. The building has a rectangular plan and its flat roof is covered with reinforced concrete. An offset entrance on the south facade is enclosed by a solid metal door. The buildings west facade is located below the adjacent Administration Buildings enclosed skywalk. The building is utilitarian in design and lacks exterior ornamentation and fenestration.

The Technical Support Center is an ancillary building which supports the operation of Units 2 and

3. The building is not associated with events that have made a significant contribution to the broad patterns of history. SEARCH recommends the building is not significant under Criterion A.

Background research indicates the resource lacks association with any person(s) significant in history, and the resource is recommended not significant under Criterion B. The buildings design

SEARCH August 2025 Architectural History Survey of Dresden Nuclear Power Station, Grundy County, Illinois Final Technical Report 39 Architectural History Results is utilitarian and purpose-built. It lacks architectural and engineering distinction, is not the work of a master, does not possess high artistic values, and therefore is not significant under Criterion C. The resource is not significant under Criterion D because it lacks the potential to yield further information of historical importance. SEARCH recommends the resource is not eligible for NRHP inclusion, neither individually nor as a contributing resource to the proposed DNPS Unit 1 Historic District.

High Radiation Sampling Building A The ca. 1975-1979 High Radiation Sample Building A is located adjacent to and southeast of the Unit 2 and 3 Reactor Building (Figure 25). The Industrial Vernacular-style building is reinforced concrete construction and rests on a concrete slab foundation. The building has a square plan and its flat roof is covered with reinforced concrete. The building is utilitarian in design and lacks exterior ornamentation and fenestration.

The High Radiation Sample Building A is an ancillary building which supports the operation of Units 2 and 3. The building is not associated with events that have made a significant contribution to the broad patterns of history. SEARCH recommends the building is not significant under Criterion A. Background research indicates the resource lacks association with any person(s) significant in history, and the resource is recommended not significant under Criterion B. The concrete and steel buildings design is utilitarian. It lacks engineering and architectural distinction, is not the work of a master, does not possess high artistic values, and therefore is not significant under Criterion C. The resource is not significant under Criterion D because it lacks the potential to yield further information of historical importance. SEARCH recommends the resource is not eligible for NRHP inclusion, neither individually nor as a contributing resource to the proposed DNPS Unit 1 Historic District.

HPCI and Diesel Generator Building The ca. 1970-1971 HPCI and Diesel Generator Building is attached to the Unit 2 and 3 Reactor Building on its north facade (Figure 26). The Industrial Vernacular style building is reinforced Figure 25. High Radiation Sampling Building A, far right, facing north.

Figure 24. Technical Support Center, facing northeast.

August 2025 SEARCH Final Technical Report Architectural History Survey of Dresden Nuclear Power Station, Grundy County, Illinois Architectural History Results 40 concrete construction and rests on a concrete slab foundation. The building has a rectangular plan, and its flat roof is covered with reinforced concrete. Two cylinder tanks partially obscure the resources south facade. The building is utilitarian in design and lacks exterior ornamentation and fenestration.

The HPCI and Diesel Generator Building is an ancillary building which supports the operation of Units 2 and 3. The building is not associated with events that have made a significant contribution to the broad patterns of history. SEARCH recommends the building is not significant under Criterion A. Background research indicates the resource lacks association with any person(s) significant in history, and the resource is recommended not significant under Criterion B. The concrete buildings design is utilitarian. It lacks architectural and engineering distinction, is not the work of a master, does not possess high artistic values, and therefore is not significant under Criterion C. The resource is not significant under Criterion D because it lacks the potential to yield further information of historical importance. SEARCH recommends the resource is not eligible for NRHP inclusion, neither individually nor as a contributing resource to the proposed DNPS Unit 1 Historic District.

High Radiation Sampling Building B The ca. 1975-1979 High Radiation Sampling Building B is Industrial Vernacular in style and located 51 m (168 ft) south of the Unit 3 Turbine Building. This facility is situated off a paved road but is within a gravel lot. This one-story building rests on a concrete slab foundation and its exterior is reinforced concrete construction (Figure 27). Built-up materials cover the flat, staggered roof. A single-leaf steel door is recessed into the south end of the east facade with a slightly elevated concrete sidewalk leading to the entrance. No other fenestration is visible on the building.

This structure is utilitarian in design and lacks exterior ornamentation.

High Radiation Sampling Building B is an ancillary building that supports the operation of Units 2 and 3. The building is not associated with events that have made a significant contribution to the broad patterns of history. SEARCH recommends the building is not significant under Criterion A.

Figure 26. HPCI and Diesel Generator Building, center rear behind cylinders, facing northwest.

Figure 27. High Radiation Sampling Building, facing west.

SEARCH August 2025 Architectural History Survey of Dresden Nuclear Power Station, Grundy County, Illinois Final Technical Report 41 Architectural History Results Background research indicates the resource lacks association with any person(s) significant in history, and the resource is recommended not significant under Criterion B. The concrete buildings design is utilitarian. It lacks architectural and engineering distinction, is not the work of a master, does not possess high artistic values, and therefore is not significant under Criterion C. The resource is not significant under Criterion D because it lacks the potential to yield further information of historical importance. SEARCH recommends the resource is not eligible for NRHP inclusion, neither individually nor as a contributing resource to the proposed DNPS Unit 1 Historic District.

Off Gas Recombiner Room A The ca. 1970-1971 Off Gas Recombiner Room A is attached to the Unit 3 Reactor Building on its south facade (Figure 28). The multi-story Industrial Vernacular-style building is reinforced concrete construction and rests on a concrete slab foundation. The building has a rectangular plan and its flat roof is covered with reinforced concrete. The buildings exterior is clad with metal factory panel. The building is utilitarian in design and possesses no exterior ornamentation or fenestration.

The Off Gas Recombiner Room A is an ancillary building that supports the operation of the Unit 3 Reactor. The building is not associated with events that have made a significant contribution to the broad patterns of history. SEARCH recommends the building is not significant under Criterion A. Background research indicates the resource lacks association with any person(s) significant in history, and the resource is recommended not significant under Criterion B. The concrete and steel buildings design is utilitarian. It lacks architectural and engineering distinction, is not the work of a master, does not possess high artistic values, and therefore is not significant under Criterion C. The resource is not significant under Criterion D because it lacks the potential to yield further information of historical importance. SEARCH recommends the resource is not eligible for NRHP inclusion, neither individually nor as a contributing resource to the proposed DNPS Unit 1 Historic District.

Off Gas Recombiner Room B The ca. 1970-1971 Off Gas Recombiner Room B is attached to the Unit 2 Reactor Building on its south facade (Figure 29). The multi-story Industrial Vernacular-style building is reinforced concrete construction and rests on a concrete slab foundation. The building has a rectangular plan and its flat roof is covered with reinforced concrete. The buildings north facade and the upper portions of its east and west facades are clad with metal factory panel. The building is utilitarian in design and possesses no exterior ornamentation or fenestration.

Figure 28. Off Gas Recombiner Room A, far right rear indicated with arrow, facing southwest.

August 2025 SEARCH Final Technical Report Architectural History Survey of Dresden Nuclear Power Station, Grundy County, Illinois Architectural History Results 42 The Off Gas Recombiner Room B is an ancillary building that supports the operation of the Unit 2 Reactor. The building is not associated with events that have made a significant contribution to the broad patterns of history.

SEARCH recommends the building is not significant under Criterion A. Background research indicates the resource lacks association with any person(s) significant in history, and the resource is recommended not significant under Criterion B. The concrete and steel buildings design is utilitarian. It lacks architectural and engineering distinction, is not the work of a master, does not possess high artistic values, and therefore is not significant under Criterion C. The resource is not significant under Criterion D because it lacks the potential to yield further information of historical importance. SEARCH recommends the resource is not eligible for NRHP inclusion, neither individually nor as a contributing resource to the proposed DNPS Unit 1 Historic District.

Max Recycle Radwaste Building The Max Recycle Radwaste Building is a ca. 1970-1971 Industrial Vernacular-style building located 24 m (77 ft) north of the Unit 2 Turbine Building off a paved road.

This one-story facility rests on a concrete slab foundation, and its exterior is of reinforced concrete construction (Figure 30). There is no fenestration visible on the building, though a metal roll-up door is located on the north end of the east facade. Another former entrance was located on the north facade but has been enclosed with concrete block. Built-up materials cover the buildings flat roof.

This structure is utilitarian in design and lacks exterior ornamentation.

The Max Recycle Radwaste Building is an ancillary building that supports the operation of the Unit 2 and 3 Reactors. The building is not associated with events that have made a significant contribution to the broad patterns of history. SEARCH recommends the building is not significant under Criterion A. Background research indicates the resource lacks association with any person(s) significant in history, and the resource is recommended not significant under Criterion B. The concrete buildings design is utilitarian. It lacks architectural and engineering distinction, Figure 29. Off Gas Recombiner Room B, center rear, facing southwest.

Figure 30. Max Recycle Radwaste Building, facing southeast.

SEARCH August 2025 Architectural History Survey of Dresden Nuclear Power Station, Grundy County, Illinois Final Technical Report 43 Architectural History Results is not the work of a master, does not possess high artistic values, and therefore is not significant under Criterion C. The resource is not significant under Criterion D because it lacks the potential to yield further information of historical importance. SEARCH recommends the resource is not eligible for NRHP inclusion, neither individually nor as a contributing resource to the proposed DNPS Unit 1 Historic District.

Waste Sample Tanks The Waste Sample Tanks are ca. 1970 tanks with no architectural style, located 47 m (154 ft) north of the Unit 3 Turbine Building off a paved road. Six welded steel tanks are contained within a

concrete half wall (Figure 31). The northwest tank is the largest tank, and the remaining five tanks are smaller in size. These tanks serve as settling tanks for wastewater.

Per Constellation communication dated July 3, 2025, the tanks were built to support the operations of Units 2 and 3. Therefore, the structure is not associated with events that have made a significant contribution to the broad patterns of history. SEARCH recommends the resource is not significant under Criterion A.

Background research indicates the tanks lack association with any person(s) significant in history, and they are recommended not significant under Criterion B. The metal tanks design is utilitarian. They lack architectural and engineering distinction, are not the work of a master, do not possess high artistic values, and therefore are not significant under Criterion C. The tanks are not significant under Criterion D because they lack the potential to yield further information of historical importance. SEARCH recommends the resource is not eligible for NRHP inclusion, neither individually nor as a contributing resource to the proposed DNPS Unit 1 Historic District.

Heating Boiler House The Heating Boiler House is a ca. 1970 Industrial Vernacular-style building located 37 m (122 ft) north of the Unit 3 Turbine Building off a paved road. This one-story facility rests on a concrete slab foundation and is a prefabricated metal building with a tall, welded metal chimney constructed on the flat metal roof (Figure 32). A smaller prefabricated metal building with a shed roof is constructed on this facilitys west facade and a vent is directly south of this addition. No fenestration was visible on the north or west facades. This structure is utilitarian in design and lacks exterior ornamentation.

Per Constellation communication dated July 3, 2025, the Heating Boiler House was built to support the operations of Units 2 and 3. Therefore, the building is not associated with events that have made a significant contribution to the broad patterns of history. SEARCH recommends the Figure 31. Water Sample Tanks, facing southeast.

August 2025 SEARCH Final Technical Report Architectural History Survey of Dresden Nuclear Power Station, Grundy County, Illinois Architectural History Results 44 building is not significant under Criterion A.

Background research indicates the resource lacks association with any person(s) significant in history, and the resource is recommended not significant under Criterion B. The resources design is utilitarian. It lacks architectural and engineering distinction, is not the work of a master, does not possess high artistic values, and therefore is not significant under Criterion C. The resource is not significant under Criterion D because it lacks the potential to yield further information of historical importance. SEARCH recommends the resource is not eligible for NRHP inclusion, neither individually nor as a contributing resource to the proposed DNPS Unit 1 Historic District.

Floor Drain Surge Tank The Floor Drain Surge Tank is a ca. 1974 ancillary building with no architectural style, located 19 m (63 ft) south of the Unit 3 Turbine Building off a paved road. This two-story facility rests on a concrete slab foundation, and its exterior is reinforced concrete construction (Figure 33). Concrete also comprises the flat roof. No fenestration is visible on the north, west, and south facades. A small concrete addition with a flat roof and a vent is constructed on the east side of the north facade. A metal ladder providing roof access is attached to the north facade. This structure is utilitarian in design and lacks exterior ornamentation.

The Floor Drain Surge Tank is a support facility for Unit 2 and 3 operations. The building is not associated with events that have made a significant contribution to the broad patterns of history and is not significant under Criterion A. Background research indicates the resource lacks association with any person(s) significant in history, and the resource is recommended not significant under Criterion B. The concrete buildings design is utilitarian. It lacks architectural and engineering distinction, is not the work of a master, does not possess high artistic values, and therefore is not significant under Criterion C. The resource is not significant under Criterion D because it lacks the potential to yield further information of historical importance. SEARCH recommends the resource is not eligible for NRHP inclusion, neither individually nor as a contributing resource to the proposed DNPS Unit 1 Historic District.

Figure 32. Heating Boiler House, facing east.

Figure 33. Floor Drain Surge Tank, facing east.

SEARCH August 2025 Architectural History Survey of Dresden Nuclear Power Station, Grundy County, Illinois Final Technical Report 45 Architectural History Results Unit 1 Crib House The ca. 1960 Unit 1 Crib House is located 48 m (156 ft) northwest of the Unit 1 Reactor building at the terminus of the Unit 1 Intake Canal (Figure 34). The resources aboveground components and superstructure were removed ca. 2008 (NETR 2007, 2009). A capped slab, access doors, and modern concrete risers and railings remain in the former buildings footprint. The slab is enclosed by modern bollards. The access doors lead to the crib houses below-grade pumps, which draw water from the Unit 1 Intake Canal for use in the DNPS fire suppression system.

The Unit 1 Crib House is associated with the Unit 1 Reactor buildings ca. 1960 operations, and it is recommended significant under Criterion A for this association. Background research indicates the building lacks association with any person(s) significant in history, and it is recommended not significant under Criterion B. The building lacks architectural or engineering distinction and is recommended not significant under Criterion C. The building is recommended not significant under Criterion D because it lacks the potential to yield further information of historical importance.

The Unit 1 Crib House is located within its original footprint and retains integrity of location and setting. The buildings aboveground elements were removed ca. 2008, leaving a capped concrete slab and the below-grade pump system. The building no longer retains its integrity of design, workmanship, or materials or feeling. Since the Unit 1 Reactor Buildings retirement, the Unit 1 Crib House draws water from the Unit 1 Intake Canal for use in the plants fire suppression system. The resource no longer functions as part of reactor buildings operations. Due to its partial dismantlement, the resource no longer retains sufficient integrity to convey its significance under Criterion A. SEARCH recommends the resource is not eligible for NRHP inclusion, neither individually nor as a contributing resource to the proposed DNPS Unit 1 Historic District.

Unit 2 & 3 Crib House The ca. 1971 Unit 2 and 3 Crib House is located at the terminus of the Unit 2 and 3 Intake Canal 47 m (154 ft) north of the Unit 2 Turbine Building (Figure 35). The aboveground portion of the facility consists of adjoined one-and two-story wings with a flat, staggered roofline. The Industrial Vernacular-style building is concrete block masonry construction on a concrete slab foundation.

Fenestration on the northeast facade includes paired, aluminum frame casement windows above concrete sills. Fenestration on the northwest facade includes double solid metal doors and an elevated garage bay enclosed by double factory metal panel doors. A ceiling trolley track extends Figure 34. Unit 1 Crib House slab, facing northeast.

August 2025 SEARCH Final Technical Report Architectural History Survey of Dresden Nuclear Power Station, Grundy County, Illinois Architectural History Results 46 above the garage bay outward from the northwest facade. An exterior trolley track system is also fixed along the roofline along the buildings northeast facade. Fenestration on the southwest facade consists of grouped aluminum frame casement windows. The below-grade portion of the facility houses water pumps that supply cooling water to Units 2 and 3. Water from the Unit 2 and 3 Intake Canal is drawn through a trash rack, stoplogs, and traveling screens into service water pumps.

From there, water passes through strainers and into circulating water pumps before moving to Units 2 and 3. The below-grade construction is concrete block masonry and reinforced concrete.

The building is utilitarian in design and lacks exterior ornamentation.

The Unit 2 and 3 Crib House is an ancillary building which supports the operation of Units 2 and

3. The building is not associated with events that have made a significant contribution to the broad patterns of history. SEARCH recommends the building is not significant under Criterion A.

Background research indicates the resource lacks association with any person(s) significant in history, and the resource is recommended not significant under Criterion B. The buildings design is utilitarian concrete block masonry construction, and representative of late-twentieth century crib houses at plants throughout the US. It lacks architectural and engineering distinction, is not the work of a master, does not possess high artistic values, and therefore is not significant under Criterion C. The resource is not significant under Criterion D because it lacks the potential to yield further information of historical importance. SEARCH recommends the resource is not eligible for NRHP inclusion, neither individually nor as a contributing resource to the proposed DNPS Unit 1 Historic District.

Intake and Discharge Canals Unit 1 Intake Canal The ca. 1960 Unit 1 Intake Canal extends east from the Unit 1 Crib House north of Unit 1 Reactor Building (Figure 36). The canal is approximately 0.61 km (0.38 mi) in length. Its width ranges between approximately 13 m (43 ft) to 30 m (98 ft), with its widest point located at its terminus above the Unit 1 Crib House. The canal was originally built to draw cooling water for the Unit 1 Reactor from the Kankakee River. Following Unit 1s retirement in 1978 and the removal of the Unit 1 Crib House, the canal functions in support of the DNPS fire pump and fire protection system.

The Unit 1 Intake Canal was built to provide cooling water from the Kankakee River for the Unit 1 Reactor. The Unit 1 Reactor represents the first commercially funded nuclear plant in the United States. The Unit 1 Intake Canal is significant under Criterion A for this association.

Figure 35. Unit 2 and 3 Crib House, facing southeast.

SEARCH August 2025 Architectural History Survey of Dresden Nuclear Power Station, Grundy County, Illinois Final Technical Report 47 Architectural History Results Background research indicates that the resource lacks association with any person(s) significant in history, and it is recommended not significant under Criterion B. The resource lacks engineering distinction, is not the work of a master, does not possess high artistic values, and therefore is not significant under Criterion C. The resource is not significant under Criterion D because it lacks the potential to yield further information of historical importance.

The Unit 1 Intake Canal is located within its original footprint north of the Unit 1 Reactor Building, and retains integrity of location, setting, materials, and workmanship. Since Unit 1s 1978 retirement the structure has supported the DNPS fire protection system. The Unit 1 Intake Canal is utilitarian and typical of twentieth century canal construction. The structures significance under Criterion A is associated with Unit 1s function as the first privately funded nuclear reactor building. Per SHPO consultation on May 30, 2025, changes to this facilitys use over time do not diminish the structures aspects of integrity. Though Unit 1 is no longer operational, the plant overall remains in operation and the canal supports the fire system. The structure retains its integrity of design, feeling, and association. Therefore, SEARCH recommends the resource is eligible as a contributing resource within the proposed DNPS Unit 1 Historic District.

Unit 2 and 3 Intake Canal The ca. 1970-1971 Unit 2 and 3 Intake Canal extends east from the Unit 2 and 3 Crib House north of the Unit 2 Turbine Building (Figure 37). The earthen canal is approximately 0.7 km (0.4 mi) in length. Its width ranges between approximately 17 m (56 ft) to 50 m (164 ft), with its widest point located at its terminus above the Unit 2 and 3 Crib House. The canal was built to draw cooling water for the Unit 2 and 3 Reactors from the Kankakee River.

The Unit 2 and 3 Intake Canal is a support facility for Unit 2 and 3 reactor operations and is not associated with events that have made a significant contribution to the broad patterns of history. SEARCH recommends the resource is not significant under Criterion A. Background research indicates the resource lacks Figure 36. Unit 1 Intake Canal, facing northwest.

Figure 37. Unit 2 and 3 Intake Canal, facing northwest.

August 2025 SEARCH Final Technical Report Architectural History Survey of Dresden Nuclear Power Station, Grundy County, Illinois Architectural History Results 48 association with any person(s) significant in history, and the resource is recommended not significant under Criterion B. The resource is utilitarian and representative of twentieth century canal construction. The resource lacks engineering distinction, is not the work of a master, does not possess high artistic values, and therefore is not significant under Criterion C. The resource is not significant under Criterion D because it lacks the potential to yield further information of historical importance. SEARCH recommends the resource is not eligible for NRHP inclusion, neither individually nor as a contributing resource to the proposed DNPS Unit 1 Historic District.

Unit 2 and 3 Discharge Canals The ca. 1970 Unit 2 and 3 Discharge Canals form a water cooling system that supports Unit 2 and 3 Reactor operation (Figure 38). A hot canal leads from the Unit 2 and 3 Reactor Buildings from a discharge point 82 m (269 ft) north of the Unit 3 Turbine Building. The earthen canal forks 127 m (417 ft) north of this discharge point. The east fork is 0.58 km (0.36 mi) in length, passes through the Flow Regulation Station, and discharges into the Illinois River. The west fork is 3.53 km (2.19 mi) in length and terminates at the Dresden Cooling Lakes Lift Station. Heated water passes along this fork into the Dresden Cooling Lake where it cools while circulating in a clockwise motion before entering the cold canal through the Spillway. Cooled water then passes in a northward direction through the cold canal to the Flow Regulating Station. The Flow Regulating Station then sends the cooled water to the Illinois River discharge fork or back to the Unit 2 and 3 Crib House to be used again as cooling water within the reactors. The canals range in width from 13 m (43ft) to 40 m (131 ft). The canals were initially built as spray canals with fountain-like spray modules installed along the length of the hot and cold canals to speed cooling, but these modules are no longer extant (ComEd 1973: 3-1).

The Unit 2 and 3 Discharge Canals constitute a support facility for Unit 2 and 3 Reactor operations and are not associated with events that have made a significant contribution to the broad patterns of history. SEARCH recommends the resource is not significant under Criterion A.

Background research indicates the resource lacks association with any person(s) significant in history, and the resource is recommended not significant under Criterion B. The resource is utilitarian and representative of twentieth century canal construction. The resource lacks architectural and engineering distinction, is not the work of a master, does not possess high artistic values, and therefore is not significant under Criterion C. The resource is not significant under Criterion D because it lacks the potential to yield further information of historical importance. SEARCH recommends the resource is not eligible for NRHP inclusion, neither individually nor as a contributing resource to the proposed DNPS Unit 1 Historic District.

Figure 38. Unit 2 and 3 Discharge Canal, cold canal (far left) and hot canal (center), facing northwest from Lift Station.

SEARCH August 2025 Architectural History Survey of Dresden Nuclear Power Station, Grundy County, Illinois Final Technical Report 49 Architectural History Results Flow Regulation Station The ca. 1970 Flow Regulation Station controls the flow of water through the Unit 2 and 3 Discharge Canals (Figure 39). The structure is located 0.30 km (0.19 mi) north of the Unit 3 Turbine Building. The station consists of three reinforced concrete construction spillways with metal hydraulic gates. The gates lift or drop to direct water flow through the discharge canals north toward the Illinois River; southwest into the hot canal for movement into the Dresden Cooling Lake; or southeast back toward the Unit 2 and 3 Crib House to reuse as cooling water for the Unit 2 and 3 Reactors. The structure is utilitarian in design and lacks exterior ornamentation.

The Flow Regulation Station is a support facility for Unit 2 and 3 reactor operations and is not associated with events that have made a significant contribution to the broad patterns of history.

SEARCH recommends the resource is not significant under Criterion A. Background research indicates the resource lacks association with any person(s) significant in history, and the resource is recommended not significant under Criterion B. The resource is a utilitarian example of twentieth century canal and water management construction. The resource lacks architectural and engineering distinction, is not the work of a master, does not possess high artistic values, and therefore is not significant under Criterion C. The resource is not significant under Criterion D because it lacks the potential to yield further information of historical importance. SEARCH recommends the resource is not eligible for NRHP inclusion, neither individually nor as a contributing resource to the proposed DNPS Unit 1 Historic District.

Dresden Cooling Lake The ca. 1971 Dresden Cooling Lake is at the Survey Areas southern boundary along E. Pine Bluff Road/Lorenzo Road. The lake is 515.97 ha (1275 ac) in total, and the Grundy County-Will County boundary divides the lake on a north-south orientation 1.64 km (1.02 mi) east of N Dresden Road (Figure 40). The lakes five pools link to DNPS via intake and discharge canals north of the lake.

The lake is enclosed by an 10.67 km-long (6.62 mi-long) earthen berm around most of its perimeter. The berm tapers and terminates at a short shoreline at the lakes southeast corner 0.50 km (0.31 mi) west of the intersection of Lorenzo Road and Cottage Road. Dikes within the lake divide it into five pools which induce a clockwise flow maximizing the residence time of the water in the lake (AEC 1973:3-11). The lakes average depth is 3.05 m (10 ft), and contains approximately 4 billion gallons of water with a recirculation time of about 2.5 days (AEC 1973:75).

Figure 39. Flow Regulation Station, facing north.

August 2025 SEARCH Final Technical Report Architectural History Survey of Dresden Nuclear Power Station, Grundy County, Illinois Architectural History Results 50 Sargent and Lundy Engineers Inc. designed the lake for DNPS and completed construction in October 1971. The lake occupies former agricultural land. The lakes dike construction required removal of all topsoil from the footprint and used silty clay local to the area for the lakebed. During construction, builders determined that an abandoned mid-nineteenth century coal mine is located below the cooling lake, though they determined this would not affect the lake. In October 1972, a 15.24 m (50 ft) section of the enclosing berm failed, resulting in slight damage to public property (AEC 1973:5-6) and additional testing to identify areas of potential failure. Driven sheet pilings were added along lengths of the berm to reinforce its construction. Public access is restricted by a perimeter fence.

The Dresden Cooling Lake is an ancillary structure that supports the operation of Units 2 and 3.

The lake was completed in October 1971 prior to Unit 3s November 1971 commission date. The resource is not associated with events that have made a significant contribution to the broad patterns of history. SEARCH recommends the structure is not significant under Criterion A.

Background research indicates the resource lacks association with any person(s) significant in history, and the resource is recommended not significant under Criterion B. The resources design as a reservoir is utilitarian, and it is not used for recreation or other activities. It lacks architectural and engineering distinction, is not the work of a master, does not possess high artistic values, and therefore is not significant under Criterion C. The resource is not significant under Criterion D because it lacks the potential to yield further information of historical importance. SEARCH recommends the resource is not eligible for NRHP inclusion, neither individually nor as a contributing resource to the proposed DNPS Unit 1 Historic District.

Spillway The ca. 1974 Spillway is located 2.86 km (1.78 mi) southeast of the DNPS Building on Dresden Cooling Lakes northwest corner (Figure 41). The Spillway is a low reinforced concrete dam with lake discharge weir gates. The gates control the flow of cooled water from the Dresden Cooling Lake into the Unit 2 and 3 cold canal. The spillway has a reinforced concrete wingwall, sidewall, and headwall built into the lakes berm on its southwest end and into the lakes earthen dike on the northeast end. The structure is utilitarian in design and lacks exterior ornamentation.

The Spillway is an ancillary structure that supports the operation of Units 2 and 3. It is not associated with events that have made a significant contribution to the broad patterns of history.

SEARCH recommends the resource is not significant under Criterion A. Background research indicates the resource lacks association with any person(s) significant in history, and the resource is recommended not significant under Criterion B. The resources design is utilitarian and Figure 40. Dresden Cooling Lake south of cooling lake bridge, facing southeast.

SEARCH August 2025 Architectural History Survey of Dresden Nuclear Power Station, Grundy County, Illinois Final Technical Report 51 Architectural History Results common to twentieth-century water management construction.

It lacks architectural and engineering distinction, is not the work of a master, does not possess high artistic values, and therefore is not significant under Criterion C. The resource is not significant under Criterion D because it lacks the potential to yield further information of historical importance. SEARCH recommends the resource is not eligible for NRHP inclusion, neither individually nor as a contributing resource to the proposed DNPS Unit 1 Historic District.

Lift Station The ca. 1970 Lift Station is located 2.86 km (1.78 mi) southeast of the DNPS building on the Dresden Cooling Lakes northwest corner (Figure 42). The Lift Station is a metal factory panel-clad two-story facility that houses the lakes six pumps. The building has louvered vents on the upper portion of the northwest facade. Its flat roof is covered with metal factory panel. The Lift Station has reinforced concrete wing walls and sidewalls further clad with metal panel walls. The structure is utilitarian in design and lacks exterior ornamentation.

The prefabricated metal Lift Station is an ancillary structure that supports the operation of Units 2 and 3. It is not associated with events that have made a significant contribution to the broad patterns of history. SEARCH recommends the resource is not significant under Criterion A.

Background research indicates the resource lacks association with any person(s) significant in history, and the resource is recommended not significant under Criterion B. The resources design is utilitarian and common to twentieth century water management construction. It lacks architectural and engineering distinction, is not the work of a master, does not possess high artistic values, and therefore is not significant under Criterion C. The resource is not significant under Criterion D because it lacks the potential to yield further information of historical importance. SEARCH recommends the resource is not eligible for NRHP inclusion, neither individually nor as a contributing resource to the proposed DNPS Unit 1 Historic District.

Figure 41. Spillway, right rear indicated with arrow, facing southwest.

Figure 42. Lift Station, center rear, facing southwest.

August 2025 SEARCH Final Technical Report Architectural History Survey of Dresden Nuclear Power Station, Grundy County, Illinois Architectural History Results 52 Wastewater Treatment Facility A The ca. 1975-1979 Wastewater Treatment Facility A is located 98 m (321.5 ft) northwest of the Unit 3 Turbine Building (Figure 43). The Wastewater Treatment Facility A is a one-story prefabricated metal building clad with metal factory panel. Its low-slope, gabled roof is covered with metal factory panel. The building has a rectangular plan and rests on a concrete slab foundation. Two entrances on the south facade are enclosed with solid metal doors, and a central garage bay is enclosed by a metal roll down garage door. The structure is utilitarian in design and lacks exterior ornamentation.

The Wastewater Treatment Facility A is an ancillary structure that supports the operation of Units 2 and 3. It is not associated with events that have made a significant contribution to the broad patterns of history. SEARCH recommends the resource is not significant under Criterion A.

Background research indicates the resource lacks association with any person(s) significant in history, and is recommended not significant under Criterion B. The resources design is minimal, and representative of a late-twentieth century prefabricated warehouse. It lacks architectural and engineering distinction, is not the work of a master, does not possess high artistic values, and therefore is not significant under Criterion C. The resource is not significant under Criterion D because it lacks the potential to yield further information of historical importance. SEARCH recommends the resource is not eligible for NRHP inclusion, neither individually nor as a contributing resource to the proposed DNPS Unit 1 Historic District.

Fuel Oil Storage Tank and Berm The ca. 1960-1970 Fuel Oil Storage Tank is located 61 m (200.13 ft) east of the Wastewater Treatment Facility A

(Figure 44). The cylindrical tank is steel and rests on a concrete slab foundation. A low rockfill berm encircles the tank.

The structure is utilitarian in design, has no style, and lacks exterior ornamentation.

Per Constellation communication dated July 3, 2025, the resource was built to support the operations of Units 2 and 3.

Therefore, the structure is not associated Figure 44. Fuel Oil Storage Tank, facing northeast.

Figure 43. Wastewater Treatment Facility A, center rear, facing southwest.

SEARCH August 2025 Architectural History Survey of Dresden Nuclear Power Station, Grundy County, Illinois Final Technical Report 53 Architectural History Results with events that have made a significant contribution to the broad patterns of history. SEARCH recommends the resource is not significant under Criterion A. Background research indicates the resource lacks association with any person(s) significant in history, and the resource is recommended not significant under Criterion B. The structure is a utilitarian welded tank. It lacks architectural and engineering distinction, is not the work of a master, does not possess high artistic values, and therefore is not significant under Criterion C. The resource is not significant under Criterion D because it lacks the potential to yield further information of historical importance. SEARCH recommends the resource is not eligible for NRHP inclusion, neither individually nor as a contributing resource to the proposed DNPS Unit 1 Historic District.

Off Gas Filter Building The ca. 1970 Off Gas Filter Building is located 64 m (210 ft) east of the Fuel Oil Tank (Figure 45). The Industrial Vernacular-style prefabricated metal building has an L-shaped plan and rests on a concrete slab foundation. Its exterior is clad with factory metal panel. The buildings flat roof is also covered with factory metal panel. An entrance on the south facade is enclosed by a solid metal door. The building is utilitarian in design and possesses no exterior ornamentation.

The Off Gas Filter Building is an ancillary structure that supports the operation of Units 2 and 3.

It is not associated with events that have made a significant contribution to the broad patterns of history. SEARCH recommends the resource is not significant under Criterion A. Background research indicates the resource lacks association with any person(s) significant in history, and is recommended not significant under Criterion B. The resources design is minimal, and representative of a late-twentieth century prefabricated warehouse. It lacks architectural and engineering distinction, is not the work of a master, does not possess high artistic values, and therefore is not significant under Criterion C. The resource is not significant under Criterion D because it lacks the potential to yield further information of historical importance. SEARCH recommends the resource is not eligible for NRHP inclusion, neither individually nor as a contributing resource to the proposed DNPS Unit 1 Historic District.

Warehouse 5 The ca. 1970 Warehouse 5 is a one-story Industrial Vernacular-style building located 52 m (170.6 ft) east of the Unit 3 Turbine Building (Figure 46). The ancillary building has a rectangular plan and a low-pitched gable roof covered with factory metal panel. It rests on a concrete foundation.

The buildings exterior is clad with factory metal panel. The building has a flush metal door with a single upper light offset on the south facade; and a full-height garage bay enclosed by a metal Figure 45. Off Gas Filter Building, facing northeast.

August 2025 SEARCH Final Technical Report Architectural History Survey of Dresden Nuclear Power Station, Grundy County, Illinois Architectural History Results 54 roll down door centered on the south facade. The building is utilitarian in design and has no ornamentation or additional fenestration. The building supports the auxiliary storage needs for the DNPS.

Warehouse 5 is an ancillary building that supports the operation of Units 2 and 3. It is not associated with events that have made a significant contribution to the broad patterns of history.

SEARCH recommends the resource is not significant under Criterion A. Background research indicates the resource lacks association with any person(s) significant in history, and is recommended not significant under Criterion B. The resources design is minimal, and representative of a late-twentieth century prefabricated warehouse. It lacks architectural and engineering distinction, is not the work of a master, does not possess high artistic values, and therefore is not significant under Criterion C. The resource is not significant under Criterion D because it lacks the potential to yield further information of historical importance.

SEARCH recommends the resource is not eligible for NRHP inclusion, neither individually nor as a contributing resource to the proposed DNPS Unit 1 Historic District.

Safe Shutdown Warehouse The Safe Shutdown Warehouse building is a ca. 1970 one-story Industrial Vernacular-style prefabricated warehouse located 91 m (299 ft) south of Warehouse 5 (Figure 47).

The ancillary building has a rectangular plan with a low-pitched, gable roof covered with factory metal panel and rests on a concrete foundation. The buildings exterior is clad with factory metal panel. The building has a full-height garage bay enclosed by a rolling metal door centered on the north facade. A metal air duct and hood are fixed to the north facade adjacent to the garage bay. The building is utilitarian in design and possesses no ornamentation or additional fenestration. The building supports the auxiliary storage needs of the DNPS.

Figure 46. Warehouse 5, facing northwest.

Figure 47. Safe Shutdown Warehouse, facing southwest.

SEARCH August 2025 Architectural History Survey of Dresden Nuclear Power Station, Grundy County, Illinois Final Technical Report 55 Architectural History Results The Safe Shutdown Warehouse is an ancillary building that supports the operation of Units 2 and

3. It is not associated with events that have made a significant contribution to the broad patterns of history. SEARCH recommends the resource is not significant under Criterion A. Background research indicates the resource lacks association with any person(s) significant in history, and is recommended not significant under Criterion B. The resources design is minimal, and representative of a late-twentieth century prefabricated warehouse. It lacks architectural and engineering distinction, is not the work of a master, does not possess high artistic values, and therefore is not significant under Criterion C. The resource is not significant under Criterion D because it lacks the potential to yield further information of historical importance. SEARCH recommends the resource is not eligible for NRHP inclusion, neither individually nor as a contributing resource to the proposed DNPS Unit 1 Historic District.

Administration Building 2 Administration Building 2 is a ca. 1975-1979 two story Industrial Vernacular-style building located adjacent to the NRC Office (Figure 48).

The building consists of a ca. 1975-1983 main wing and a non-historic addition on the buildings northwest facade. The building has an irregular plan and rests on a concrete slab foundation. Its flat roof is covered with built-up roof material. The buildings exterior is clad with smooth concrete stucco. Fenestration consists of aluminum frame single and grouped fixed pane windows on upper stories of all elevations. The main entrance of the building is offset on the non-historic additions northeast facade and enclosed by glazed double doors within aluminum frame fixed pane surrounds and transoms leading to an interior vestibule. There are two additional entries on the southwest facade. An enclosed prefabricated metal skybridge on the additions north facade connects the building to the Technical Support Center and the Administration Building/Service Building. The skybridge is clad with factory metal panel and supported by pairs of girder beams.

The building possesses minimal exterior ornamentation.

Administration Building 2 is an ancillary structure that supports the operation of Units 2 and 3. It is not associated with events that have made a significant contribution to the broad patterns of history. SEARCH recommends the resource is not significant under Criterion A. Background research indicates the resource lacks association with any person(s) significant in history, and is recommended not significant under Criterion B. It lacks architectural and engineering distinction, is not the work of a master, does not possess high artistic values, and therefore is not significant under Criterion C. The resource is not significant under Criterion D because it lacks the potential to yield further information of historical importance. SEARCH recommends the resource is not eligible for NRHP inclusion, neither individually nor as a contributing resource to the proposed DNPS Unit 1 Historic District.

Figure 48. Administration Building 2, facing west.

August 2025 SEARCH Final Technical Report Architectural History Survey of Dresden Nuclear Power Station, Grundy County, Illinois Architectural History Results 56 Gatehouse/Main Access Facility The Main Access Facility/Gatehouse is a two-story ca. 1975-1979 Industrial Vernacular-style building located southeast of the NRC Office. The building has a rectangular plan with a flat roof covered with factory metal panel. The building rests on a raised concrete slab foundation. The building is concrete block construction. The buildings main entrance is located on the east facade and is enclosed by a single solid metal door. There is no visible fenestration. The building is utilitarian in design and lacks exterior ornamentation. Security access restricted photographs of the building during survey.

The Main Access Facility/Gatehouse is not associated with events that have made a significant contribution to the broad patterns of history, and is recommended not significant under Criterion A. Background research indicates the resource lacks association with any person(s) significant in history, and the resource is recommended not significant under Criterion B. The resources lacks architectural and engineering distinction and is recommended not significant under Criterion C.

The resource is recommended not significant under Criterion D because it lacks the potential to yield further information of historical importance. SEARCH recommends the resource is not eligible for NRHP inclusion, neither individually nor as a contributing resource to the proposed DNPS Unit 1 Historic District.

Visitors Center/NRC Office The NRC Office building is a one-story ca.

1975-1979 Industrial Vernacular-style building located south of the Technical Support Center and formerly served at the Visitors Center (Figure 49). The building has a rectangular plan and rests on a concrete slab foundation. The buildings original mass is covered by a flat roof; and its addition is covered by a low-sloped gable roof covered by factory metal panel. The buildings exterior is clad with brick masonry veneer in a stack bond. Fenestration on the east facade consists of two bays: a single pane stationary casement picture window left, and a pair of single pane stationary casement windows right. Both windows have visible aprons.

The building has a recessed entry located within an incised porch below a deep overhang, with a single steel flush door on the east facade. The building is utilitarian in design and lacks exterior ornamentation.

The Visitors Center/NRC Office is not associated with events that have made a significant contribution to the broad patterns of history, and it is recommended not significant under Criterion A. Background research indicates the resource lacks association with any person(s)

Figure 49. Visitor's Center/NRC Office, facing northwest.

SEARCH August 2025 Architectural History Survey of Dresden Nuclear Power Station, Grundy County, Illinois Final Technical Report 57 Architectural History Results significant in history, and the resource is recommended not significant under Criterion B. The resource is a Masonry Vernacular office building. It lacks architectural and engineering distinction, is not the work of a master, does not possess high artistic values, and therefore is not significant under Criterion C. The resource is recommended not significant under Criterion D because it lacks the potential to yield further information of historical importance. SEARCH recommends the resource is not eligible for NRHP inclusion, neither individually nor as a contributing resource to the proposed DNPS Unit 1 Historic District.

Security/Diesel Generator Building The Security/Diesel Generator Building is a one-story ca. 1975-1979 Industrial Vernacular-style building located east of the Storeroom. The concrete block masonry construction building rests on an elevated concrete slab foundation. The building has a flat roof covered with composite roof material. The building is minimal and utilitarian in design and lacks exterior ornamentation. The building currently acts as the location for security clearance and formerly housed a diesel generator. DNPS security restricted photographs of the building during survey.

The Security/Diesel Generator Building is not associated with events that have made a significant contribution to the broad patterns of history, and is recommended not significant under Criterion A. Background research indicates the resource lacks association with any person(s) significant in history, and the resource is recommended not significant under Criterion B. The resource is a vernacular concrete block masonry building. It lacks architectural and engineering distinction, is not the work of a master, does not possess high artistic values, and therefore is not significant under Criterion C. The resource is recommended not significant under Criterion D because it lacks the potential to yield further information of historical importance. SEARCH recommends the resource is not eligible for NRHP inclusion, neither individually nor as a contributing resource to the proposed DNPS Unit 1 Historic District.

Storeroom The Storeroom is a ca. 1975-1979 Industrial Vernacular-style building located east of the Security/Diesel Generator Building (Figure 50). The building consists of a one-story concrete wing on the west end and a lofted prefabricated metal warehouse wing on the east end. The building has an irregular plan with a low-pitched gable roof above the warehouse wing; and a flat roof covered with built-up roof material above the one-story concrete wing. The building rests on an elevated concrete slab foundation. The buildings exterior is clad with factory metal panel and smooth concrete stucco. The building has a single pane stationary casement picture window with an awning left on the north facade. Off-center on the west facade are three fixed pane windows below fixed barrel awnings. The main entrance is off-center on the one-story wings north facade and is enclosed by a half-glass door below a fixed barrel awning. A low sloped, modern concrete ramp with metal handrails leads to the main entrance. A secondary entrance on the east facade is enclosed by a flush steel door. There are two loading bays enclosed with metal roll down doors on the south facade. The building supports the auxiliary storage needs for the facility, is utilitarian in design, and lacks exterior ornamentation.

August 2025 SEARCH Final Technical Report Architectural History Survey of Dresden Nuclear Power Station, Grundy County, Illinois Architectural History Results 58 The Storeroom is not associated with events that have made a significant contribution to the broad patterns of history, and is recommended not significant under Criterion A. Background research indicates the resource lacks association with any person(s) significant in history, and the resource is recommended not significant under Criterion B. The resources is a utilitarian prefabricated metal warehouse. It lacks architectural and engineering distinction, is not the work of a master, does not possess high artistic values, and therefore is not significant under Criterion C.

The resource is recommended not significant under Criterion D because it lacks the potential to yield further information of historical importance. SEARCH recommends the resource is not eligible for NRHP inclusion, neither individually nor as a contributing resource to the proposed DNPS Unit 1 Historic District.

Storeroom Secondary Warehouse The Storeroom Secondary Warehouse is a ca.

1975-1979 Industrial Vernacular-style building located south of the Storeroom (Figure 51) The ancillary building has a rectangular plan with a medium-pitched, gable roof covered by factory metal panel and rests on a concrete foundation. Its exterior is clad with metal factory panel. The building has a flush door and a garage bay enclosed by a metal roll down door off center on the north facade. The building supports the auxiliary storage needs for the facility.

The building is utilitarian in design and lacks ornamentation or additional fenestration.

The Storeroom Secondary Warehouse is not associated with events that have made a significant contribution to the broad patterns of history, and is recommended not significant under Criterion A. Background research indicates the resource lacks association with any person(s) significant in history, and the resource is recommended not significant under Criterion B. The resources is a utilitarian prefabricated metal warehouse. It lacks architectural and engineering distinction, is not the work of a master, does not possess high artistic values, and therefore is not significant under Criterion C. The resource is recommended not significant under Criterion D because it lacks the potential to yield further information of historical importance. SEARCH recommends the Figure 50. Storeroom, facing southeast.

Figure 51. Storeroom Secondary Warehouse, facing southwest.

SEARCH August 2025 Architectural History Survey of Dresden Nuclear Power Station, Grundy County, Illinois Final Technical Report 59 Architectural History Results resource is not eligible for NRHP inclusion, neither individually nor as a contributing resource to the proposed DNPS Unit 1 Historic District.

Maintenance Warehouse The ca. 1975-1979 Maintenance Warehouse is an Industrial Vernacular-style building located approximately 0.2 km (0.1 mi) southeast of the Unit 1 Reactor Building. The one-story building rests on a concrete slab foundation and its exterior is clad with pencil seam sheet metal (Figure 52). The buildings low-pitched front gabled roof is also clad in pencil seam sheet metal. Fenestration on the southwest facade includes a single-leaf metal door with a sign that reads Storeroom Steel Building, as well as a metal roll-up door. A non-historic addition was constructed on the south side of the warehouse between 1983 and 1994 (NETR 1983, 1994). This structure is utilitarian in design and lacks exterior ornamentation.

The Maintenance Warehouse is an ancillary facility not associated with events that have made a significant contribution to the broad patterns of history. SEARCH recommends the building is not significant under Criterion A. Background research indicates the resource lacks association with any person(s) significant in history, and the resource is recommended not significant under Criterion B. The resources is a utilitarian prefabricated metal warehouse. It lacks architectural and engineering distinction, is not the work of a master, does not possess high artistic values, and therefore is not significant under Criterion C. The resource is recommended not significant under Criterion D because it lacks the potential to yield further information of historical importance. SEARCH recommends the resource is not eligible for NRHP inclusion, neither individually nor as a contributing resource to the proposed DNPS Unit 1 Historic District.

Wastewater Treatment Facility B The ca. 1975-1979 Wastewater Treatment Facility B is Industrial Vernacular in style and located 81 m (264 ft) east of the Unit 1 Reactor Building. The two-story building rests on a concrete slab foundation and its exterior is clad with metal factory panel (Figure 53). Built-up materials cover the buildings flat roof. Fenestration on the south facade includes three single-leaf metal doors and a metal roll-up door. One entrance is located on the second floor and can be accessed via a metal staircase. Two additional metal roll-up doors and another single-leaf metal door are on the east facade. A sign on one of the doors reads Unit 1 Chemical Cleaning Building. A non-historic addition clad in reinforced concrete was constructed on the northeast corner of this facility between 1983 and 1994 (NETR 1983, 1994). This structure is utilitarian in design and lacks exterior ornamentation.

Figure 52. Maintenance Warehouse, facing northeast.

August 2025 SEARCH Final Technical Report Architectural History Survey of Dresden Nuclear Power Station, Grundy County, Illinois Architectural History Results 60 The Wastewater Treatment Facility B is an ancillary structure that supports the operation of Units 2 and 3. It is not associated with events that have made a

significant contribution to the broad patterns of history.

SEARCH recommends the resource is not significant under Criterion A. Background research indicates the resource lacks association with any person(s) significant in history, and is recommended not significant under Criterion B. The resources design is minimal, and representative of a late-twentieth century prefabricated warehouse. It lacks architectural and engineering distinction, is not the work of a master, does not possess high artistic values, and therefore is not significant under Criterion C. The resource is not significant under Criterion D because it lacks the potential to yield further information of historical importance. SEARCH recommends the resource is not eligible for NRHP inclusion, neither individually nor as a contributing resource to the proposed DNPS Unit 1 Historic District.

Diesel Generator and HPCI Building/Station Blackout Building The ca. 1978 Diesel Generator and HPCI Building/Station Blackout (SBO) Building is an Industrial Vernacular-style building located 46 m (150 ft) east of the Unit 1 Reactor Building.

Aerial photographs indicate the building replaced an earlier building associated with Unit 1 by 1983 (NETR 1974, 1983). The two-story building rests on a concrete slab foundation and its exterior is clad with reinforced concrete (Figure 54). Built-up materials cover this buildings flat roof. The main entrances to the facility are obscured by concrete projections located on the east and west facades. A metal roll-up door encloses a garage bay on the west facade. A metal ladder is attached to the west facade that leads to the roof. The north end of the roof features a metal balustrade lining its perimeter, and an additional projection with louvered vents is centrally located on the roof. This building is utilitarian in design and possesses no exterior ornamentation. This facility serves as the Unit 2 and 3 SBO (Exelon Generation 2018:3-23).

The Diesel Generator and HPCI Building/SBO Building is an ancillary facility not associated with events that have made a significant contribution to the broad patterns of history. SEARCH Figure 53. Wastewater Treatment Facility B, facing east.

Figure 54. Station Blackout (SBO) Building, facing southwest.

SEARCH August 2025 Architectural History Survey of Dresden Nuclear Power Station, Grundy County, Illinois Final Technical Report 61 Architectural History Results recommends the building is not significant under Criterion A. Background research indicates the resource lacks association with any person(s) significant in history, and the resource is recommended not significant under Criterion B. The concrete resources design is utilitarian. It lacks architectural and engineering distinction, is not the work of a master, does not possess high artistic values, and therefore is not significant under Criterion C. The resource is not significant under Criterion D because it lacks the potential to yield further information of historical importance. SEARCH recommends the resource is not eligible for NRHP inclusion, neither individually nor as a contributing resource to the proposed DNPS Unit 1 Historic District.

Radwaste Building The ca. 1974 Radwaste Building Unit 1A is Industrial Vernacular in style and located 84 m (275 ft) southeast of the Unit 1 Reactor Building and 6 m (19 ft) east of the Radwaste Building Unit 1B. The one-and-a-half story building rests on a concrete slab foundation (Figure 55). The first story elevations are reinforced concrete construction, while the second story is covered in factory metal panel.

The main entrance is located on the upper portion of the west facade; it can be accessed via a metal staircase and is partially sheltered by a metal shed-roofed awning. An additional former entrance was located on the first storys east wall, but it has been enclosed with sheet metal. A square vent is also located on the east walls second floor. The flat roof is covered with factory metal panel and concrete and supports an exhaust stack. This structure is utilitarian in design and lacks exterior ornamentation.

The Radwaste Building is an ancillary structure that supports the operation of Units 2 and 3. It is not associated with events that have made a significant contribution to the broad patterns of history. SEARCH recommends the building is not significant under Criterion A. Background research indicates the resource lacks association with any person(s) significant in history, and the resource is recommended not significant under Criterion B. The resource is a utilitarian concrete and steel warehouse. It lacks architectural and engineering distinction, is not the work of a master, does not possess high artistic values, and therefore is not significant under Criterion C.

The resource is recommended not significant under Criterion D because it lacks the potential to yield further information of historical importance. SEARCH recommends the resource is not eligible for NRHP inclusion, neither individually nor as a contributing resource to the proposed DNPS Unit 1 Historic District.

Figure 55. Radwaste Building, facing west.

August 2025 SEARCH Final Technical Report Architectural History Survey of Dresden Nuclear Power Station, Grundy County, Illinois Architectural History Results 62 Radwaste Building Unit 1 The ca. 1960 Radwaste Building Unit 1 is Industrial Vernacular in style and located 67 m (219 ft) southeast of the Unit 1 Reactor Building and 6 m (19 ft) west of the Radwaste Building Unit 1A. This one-story building rests on a concrete slab foundation and its exterior is clad with factory metal panel (Figure 56).

The main entrance on the north or west facade is obscured. A metal hatch and ladder are located on the west facade. The building has a flat metal roof, is utilitarian in design, and lacks exterior ornamentation.

The Radwaste Building Unit 1 is significant under Criterion A as this building is associated with Unit 1 operation. Background research indicates that the resource lacks association with any person(s) significant in history, and the resource is recommended not significant under Criterion B. The resource is a utilitarian concrete and steel warehouse. It lacks architectural and engineering distinction, is not the work of a master, does not possess high artistic values, and therefore is not significant under Criterion C.

The resource is recommended not significant under Criterion D because it lacks the potential to yield further information of historical importance.

The Radwaste Building Unit 1 is located within its original footprint and retains integrity of location and setting. The structures significance under Criterion A is associated with Unit 1s function as the first privately funded nuclear reactor building. Per SHPO consultation on May 30, 2025, changes to a buildings use over time do not diminish the buildings aspects of integrity.

Though Unit 1 is no longer operational, the plant overall remains in operation. The building retains its integrity of design, materials, workmanship, feeling, and association. Therefore, SEARCH recommends the resource is eligible as a contributing resource within the proposed DNPS Unit 1 Historic District.

345 kV Switchyard The ca. 1960-1970 345 kV Switchyard has no architectural style and is located approximately 0.5 km (0.3 mi) west of the Unit 1 Reactor Building. Aerial imagery indicates the switchyard has not expanded since it was originally constructed and comprises approximately 6.2 ha (15.4 ac; NETR 1973, 2021). The switchyard is located off a gravel road parallel to the Unit 2 and 3 Intake cold canal. This resource is set back on a maintained gravel fill lot and enclosed by a chain link and barbed wire perimeter fence (Figure 57). The switchyard contains transmission and distribution lines, switchgears, bus pipes, and other infrastructure, in addition to a non-historic prefabricated ancillary building and the Switchyard Maintenance Building.

Figure 56. Radwaste Building Unit 1, facing west.

SEARCH August 2025 Architectural History Survey of Dresden Nuclear Power Station, Grundy County, Illinois Final Technical Report 63 Architectural History Results Per Constellation communication dated July 3, 2025, the resource was built to support the operations of Units 2 and 3. Therefore, the structure is not associated with events that have made a significant contribution to the broad patterns of history.

SEARCH recommends the resource is not significant under Criterion A.

Background research indicates the resource lacks association with any person(s) significant in history and is recommended not significant under Criterion B. The resource lacks architectural and engineering distinction, is not the work of a master, does not possess high artistic values, and therefore is not significant under Criterion C. The resource is not significant under Criterion D because it lacks the potential to yield further information of historical importance. SEARCH recommends the resource is not eligible for NRHP inclusion, neither individually nor as a contributing resource to the proposed DNPS Unit 1 Historic District.

Switchyard Maintenance Building The ca. 1975-1979 Switchyard Maintenance Building is Industrial Vernacular in style and located approximately 0.5 km (0.3 mi) west of the Unit 1 Reactor Building. This facility is situated off a gravel road and is in the southeast corner of the 345 kV Switchyard. A concrete driveway is constructed south of this resource. This one-story maintenance building rests on a concrete slab foundation and its exterior is clad in metal factory panel (Figure 58). Metal also covers the low-pitched gabled roof. The fenestration on the south wall consists of a single-leaf metal door with an upper square light and a metal roll-up door. A sliding window is located on the east facade. The north facade possesses a sliding window and metal roll-up door enclosing a garage bay. An identical metal roll-up door also encloses a garage bay on the south facade. This structure is utilitarian in design and lacks exterior ornamentation.

The Switchyard Maintenance Building is an ancillary facility not associated with events that have made a significant contribution to the broad patterns of history. SEARCH recommends the building is not significant under Criterion A. Background research indicates the resource lacks association with any person(s) significant in history, and the resource is recommended not significant under Criterion B. The resources design is utilitarian prefabricated warehouse. It lacks Figure 57. 345 kV Switchyard, facing west.

Figure 58. Switchyard Maintenance Building, facing northwest.

August 2025 SEARCH Final Technical Report Architectural History Survey of Dresden Nuclear Power Station, Grundy County, Illinois Architectural History Results 64 architectural and engineering distinction, is not the work of a master, does not possess high artistic values, and therefore is not significant under Criterion C. The resource is recommended not significant under Criterion D because it lacks the potential to yield further information of historical importance. SEARCH recommends the resource is not eligible for NRHP inclusion, neither individually nor as a contributing resource to the proposed DNPS Unit 1 Historic District.

138 kV Switchyard The ca. 1960 135 kV Switchyard has no architectural style and is 131 m (429 ft) northwest of the Unit 1 Reactor Building. Aerial imagery indicates the switchyard has not expanded since it was originally constructed and comprises approximately 1 ha (2.4 ac; NETR 1961, 2021). The switchyard is located off a paved road north of and parallel to the Unit 2 and 3 Intake Canal. This resource is set back on a maintained gravel fill lot and enclosed by a chain link and barbed wire perimeter fence (Figure 59). The switchyard contains transmission and distribution lines, switchgears, bus pipes, and other infrastructure, in addition to two non-historic buildings and the 138 kV Relay House. Per Constellation communication dated July 3, 2025, the resource is owned by Exelon.

The 138 kV Switchyard is a support facility associated with the Unit 1 Reactor operations, which was retired in 1978. The Unit 1 Reactor represents the first commercially funded nuclear plant in the United States. The 138 kV Switchyard is significant under Criterion A for this association.

Background research indicates the resource lacks association with any person(s) significant in history and is recommended not significant under Criterion B. The resource lacks architectural and engineering distinction, is not the work of a master, does not possess high artistic values, and therefore is not significant under Criterion C. The resource is not significant under Criterion D because it lacks the potential to yield further information of historical importance.

The 138 kV Switchyard is within its original footprint and retains integrity of location and setting.

The resources significance under Criterion A is associated with Unit 1s function as the first privately funded nuclear reactor building. Per SHPO consultation on May 30, 2025, changes to this buildings use over time do not diminish the buildings aspects of integrity. Though Unit 1 is no longer operational, the plant overall remains in operation. The resource retains its integrity of design, materials, workmanship, feeling, and association. Therefore, SEARCH recommends the resource is eligible as a contributing resource within the proposed DNPS Unit 1 Historic District.

Figure 59. 138 kV Switchyard, facing northwest.

SEARCH August 2025 Architectural History Survey of Dresden Nuclear Power Station, Grundy County, Illinois Final Technical Report 65 Architectural History Results 138 kV Relay House The ca. 1960 138 kV Relay House is Industrial Vernacular in style building and located 125 m (411 ft) northwest of the Unit 1 Reactor Building.

This facility is situated off a paved road and is in the southeast corner of the 345 kV Switchyard perimeter.

This one-story building is constructed above grade on a concrete slab foundation and its exterior is clad in corrugated sheet metal (Figure 60). Metal also covers the flat roof. A single-leaf metal door is set on both the east and west facades.

No other fenestration is visible. The doors are accessed via concrete steps. This structure is utilitarian in design and lacks exterior ornamentation.

The 138 kV Relay House is a support facility associated with the Unit 1 Reactor operations, which was retired in 1978. The Unit 1 Reactor represents the first commercially funded nuclear plant in the United States. The 138 kV Relay House is significant under Criterion A for this association.

Background research indicates the resource lacks association with any person(s) significant in history and is recommended not significant under Criterion B. The resource lacks architectural and engineering distinction, is not the work of a master, does not possess high artistic values, and therefore is not significant under Criterion C. The resource is not significant under Criterion D because it lacks the potential to yield further information of historical importance.

The 138 kV Relay House is located within its original footprint and retains integrity of location and setting. The buildings significance under Criterion A is associated with Unit 1s function as the first privately funded nuclear reactor building. Per SHPO consultation on May 30, 2025, changes to a buildings use over time do not diminish the buildings aspects of integrity. Though Unit 1 is no longer operational, the plant overall remains in operation. The building retains its integrity of design, materials, workmanship, feeling and association. Therefore, SEARCH recommends the resource is eligible as a contributing resource within the proposed DNPS Unit 1 Historic District.

Substation The ca. 1975-1979 Substation has no architectural style and is located approximately 1.5 km (0.9 mi) northwest of the Unit 1 Reactor Building. Aerial imagery indicates that the Substation has not expanded since it was originally constructed and comprises approximately 0.7 ha (1.8 ac; NETR 1983, 2021). The Substation is located off a gravel road. This resource is setback on a maintained gravel fill lot and enclosed by a chain link and barbed wire perimeter fence (Figure 61). The Substation contains various metal structures and suspended powerlines are constructed Figure 60. 138 kV Relay House, facing northeast.

August 2025 SEARCH Final Technical Report Architectural History Survey of Dresden Nuclear Power Station, Grundy County, Illinois Architectural History Results 66 throughout the substation in addition to one brick masonry veneer utility building set on a concrete slab foundation.

The Substation is an ancillary facility which supports the operation of Units 2 and 3. It is not associated with events that have made a significant contribution to the broad patterns of history. SEARCH recommends the building is not significant under Criterion A. Background research indicates the resource lacks association with any person(s) significant in history, and the resource is recommended not significant under Criterion B. The resources design is utilitarian and purpose-built. It lacks architectural and engineering distinction, is not the work of a master, does not possess high artistic values, and therefore is not significant under Criterion C. The resource is recommended not significant under Criterion D because it lacks the potential to yield further information of historical importance. SEARCH recommends the resource is not eligible for NRHP inclusion, neither individually nor as a contributing resource to the proposed DNPS Unit 1 Historic District.

Elgin, Joliet and Eastern Railroad Spur The ca. 1956 EJE Railroad Spur alignment formerly linked the DNPS Gatehouse and Reactor Building with the EJE main line 2.2 km (1.4 mi) west of the Reactor Building (Figure 62). The mainline is depicted on the earliest topographic quadrangle map of the area, 1897 Morris, IL (USGS 1897). The resource is a minor spur track built to facilitate DNPS construction between 1956 and 1971.

The spur is first depicted on 1973 aerial photographs of the area, and on 1974 Minooka, IL USGS topographic quadrangle map (USGS 1974).

The EJE was a regional Class II railroad colloquially known as the Chicago Outer Belt Line or the J (American Rails 2025). The 282 km (175 mi) railroad linked regional lines in northeast Indiana with similar regional lines north of Chicago. In 1886, Chicago businessman Philip Shumway founded the Joliet, Aurora and Northern, a precursor to the EJE Railroad, which operated between Joliet and Aurora, Illinois. In 1888, J.P.

Morgan invested in the railroads expansion. Shumway chartered the EJE Railroad and incorporated several small local lines to provide service between southeast Indiana and Elgin, Illinois. By 1889, service expanded further to northern Indiana and Waukegan, Illinois.

Figure 62. EJE Spur south of Unit 1 Reactor Building, facing north.

Figure 61. Substation, facing northeast.

SEARCH August 2025 Architectural History Survey of Dresden Nuclear Power Station, Grundy County, Illinois Final Technical Report 67 Architectural History Results Between 1889 and 1907, the EJE Railroad operated dedicated passenger trains (Shaw Local 2018). Morning and evening passenger service completed trips between Aurora and Joliet six days a week. The railroad switched to mixed passenger and freight trains after 1907 and ended passenger service ca. 1910 (American Rails 2025). Between 1937 and 1949, EJE replaced its steam engine fleet with diesel-electric locomotives.

In the late nineteenth and early twentieth centuries, the EJE Railroad primarily transported steel industry products, including iron ore, coke, and coal to steel mills along the alignment. The railroad also transported steel products and limestone throughout the region with the benefit of avoiding congested Chicago railways (American Rails 2025). The railroad and its East Joliet Rail Yard remained one of the regions largest employers throughout the late nineteenth and twentieth centuries and attracted many working-class families to the Chicago suburbs and exurbs (Joliet Museum n.d.). In 2009, Canadian National purchased the EJE Railroad and merged it with Wisconsin Central Limited. Canadian National freight lines remain in service on the EJE alignment (Joliet Museum n.d.).

Within the Study Area, the spur forks are.67 km (.42 mi) east of the DNPS western boundary. The north fork continues into the DNPS complex, and the south fork continues south terminating at an industrial facility outside the Survey Area. A railroad bridge carries the track across the canals approximately 0.25 km (0.15 mi) southwest of Administration Building 2. The track forks again 0.13 km (0.08 mi) east of the railroad bridge. A short track segment remains in its alignment terminating at the Unit 2 and 3 Reactor Building and is used to move equipment short distances in combination with other hauling equipment.

Segments west of the Administration/Service building and south of Unit 1 Reactor Building have been mostly removed and infilled with concrete, and the spur now terminates at a security barrier 71 m (234 ft) southwest of Administration Building 2. SEARCH observed other track segments within the parcel boundary adjacent to the Meteorological Tower (Figure 63). These segments also appear disused and are partially infilled with gravel.

The track represents a minor spur track built for DNPS construction between 1956 and 1971. The resource is associated with DNPSs construction via regional transportation link. SEARCH recommends the resource is significant under Criterion A for this association. Background research indicates that the resource lacks association with any person(s) significant in history, and the resource is recommended not significant under Criterion B. The resources design is minimal, utilitarian, generally lacks architectural or engineering distinction and is recommended not significant under Criterion C. The resource is recommended not significant under Criterion D because it lacks the potential to yield further information of historical importance.

Figure 63. EJE Spur track adjacent to the Meteorological Tower, abandoned in place and partially infilled with gravel, facing

August 2025 SEARCH Final Technical Report Architectural History Survey of Dresden Nuclear Power Station, Grundy County, Illinois Architectural History Results 68 Within the Survey Area, the resource consists of discontinuous track segments which no longer link the DNPS with the EJE Railroad main line. The remaining track segments have been removed and infilled with concrete or abandoned in place and infilled with gravel. The resource no longer retains its integrity of location, design, setting, workmanship or materials. The resource does not function as an industrial or freight spur track in support of DNPS Unit 1 operation and no longer retains its integrity of feeling or association. The resource has been considerably physically altered and no longer retains sufficient physical or design integrity to convey its significance under Criterion A. SEARCH recommends the resource is not eligible for NRHP inclusion, neither individually nor as a contributing resource to the proposed DNPS Unit 1 Historic District.

Railroad Bridge The ca. 1970 Railroad Bridge is located 0.26 km (0.16 mi) west of the DNPS Buildings Administration Building facility. The small concrete beam bridge carried the EJE spur track within the Survey Area across the Unit 2 and 3 Discharge hot and cold canals west of the DNPS Building.

The bridge in its entirety is 51 m (68 ft) in length with an east-west orientation, and approximately 6 m (20 ft) in width. The bridge has a concrete deck built on a concrete superstructure. The bridges railroad ties and track remain in place, though the alignment is infilled with gravel and concrete. The bridge is enclosed on the north and south sides by a galvanized guardrail. The resource appears disused and abandoned in place. A security barrier and perimeter fence located west of the railroad bridge obstructs access to the resource. The resource is utilitarian in design and lacks exterior ornamentation. Security access restricted any photographs or survey within the security barrier.

The railroad bridge carried a minor EJE spur track across the Unit 2 and 3 Discharge Canals. The resource is associated with DNPSs construction via regional transportation link. SEARCH recommends the resource is significant under Criterion A for this association. Background research indicates that the resource lacks association with any person(s) significant in history, and the resource is recommended not significant under Criterion B. The resource constitutes a small, vernacular concrete beam bridge. It lacks architectural and engineering distinction, is not the work of a master, does not possess high artistic values, and therefore is not significant under Criterion C. The resource is recommended not significant under Criterion D because it lacks the potential to yield further information of historical importance.

The Railroad Bridge retains its substructure, ties, and track, though its alignment is infilled with concrete and gravel. The resource retains its integrity of location and materials. The resource is disused, no longer links the DNPS Building or EJE mainline, and no longer carries rail traffic across the hot and cold canals. The spur track is further obstructed west of the railroad bridge by a security barrier and perimeter fence. The resource no longer retains integrity of setting, design, workmanship, feeling, or association. The resource no longer retains sufficient integrity to convey its significance under Criterion A. SEARCH recommends the resource is not eligible for NRHP inclusion, neither individually nor as a contributing resource to the proposed DNPS Unit 1 Historic District.

SEARCH August 2025 Architectural History Survey of Dresden Nuclear Power Station, Grundy County, Illinois Final Technical Report 69 Architectural History Results Meteorological Tower The ca. 1960 Meteorological Tower is 0.5 km (0.3 mi) east of Dock Road and.5 km (0.3 mi) north of E Collins Road (Figure 64). The three-level aluminum tower is located on low terrain 0.9 km (0.6 mi) west of the DNPS building. The tower is 100 m (328 ft) in height and provides data such as wind speed, wind direction, and temperature. The structure is utilitarian in design and lacks exterior ornamentation.

The Meteorological Tower is a support facility associated with the Unit 1 Reactor operations, which was retired in 1978. The Unit 1 Reactor represents the first commercially funded nuclear plant in the United States. The resource is significant under Criterion A for this association. Background research indicates the resource lacks association with any person(s) significant in history and is recommended not significant under Criterion B. The resource is a typical aluminum data collection tower. It lacks architectural and engineering distinction, is not the work of a master, does not possess high artistic values, and therefore is not significant under Criterion C. The resource is not significant under Criterion D because it lacks the potential to yield further information of historical importance.

The Meteorological Tower is located within its original footprint and retains integrity of location and setting. The facilitys significance under Criterion A is associated with Unit 1s function as the first privately funded nuclear reactor building. Per SHPO consultation on May 30, 2025, changes to a buildings use over time do not diminish the buildings aspects of integrity. Though Unit 1 is no longer operational, the plant overall remains in operation. The facility retains its integrity of design, materials, workmanship, feeling and association. Therefore, SEARCH recommends the resource is eligible as a contributing resource within the proposed DNPS Unit 1 Historic District.

Storage Barn The ca. 1940-1950 Storage Barn is located within the Survey Area 117 m (385 ft) northeast of the intersection of E. Collins Road and Lock Road (Figure 65). The Vernacular barn is first depicted on 1954 Minooka, IL USGS topographic quadrangle map adjacent to, and northwest of, a residence that is no longer extant (USGS 1954). The adjacent residence was demolished by 1973 (NETR 1952, 1973). The Storage Barn is wood frame construction on a continuous concrete foundation.

Its exterior is clad with wood lap siding and metal factory panel, though most of the cladding is no longer extant. The buildings side gabled roof is covered with corrugated metal panel. A single track door is located at the south end of the buildings east facade and enclosed by a sliding door.

Any additional fenestration that may have been present is no longer discernable due to its deteriorated condition. The building is utilitarian in design and has no exterior ornamentation.

The building appears disused and in poor condition.

Figure 64. Meteorological Tower, facing west.

August 2025 SEARCH Final Technical Report Architectural History Survey of Dresden Nuclear Power Station, Grundy County, Illinois Architectural History Results 70 The Vernacular Storage Barn represents mid-twentieth century rural development, and the residence formerly associated with it was demolished by 1973. Although located within the Survey Area boundary, the ca. 1940-1950 resource predates DNPS construction and is not associated with its operation. The resource is not significant under Criterion A as it is not associated with events that have made a significant contribution to the broad patterns of our history. The resource is not significant under Criterion B as it lacks association with any person(s) significant in history. The building lacks architectural distinction, is not the work of a master, does not possess high artistic values, and therefore is not significant under Criterion C. The resource is not significant under Criterion D because it lacks the potential to yield further information of historical importance. SEARCH recommends the resource is not eligible for NRHP inclusion, neither individually nor as a contributing resource to the proposed DNPS Unit 1 Historic District.

DNPS Unit 1 Historic District The proposed DNPS Unit 1 Historic District is bounded roughly by the Unit 1 Intake Canal to the east and northeast, the 138 kV Switchyard to the north, the service road south of the DNPS Building to the south, and the 345 kV Switchyard and Meteorological Tower to the west and northwest. Within the boundary, SEARCH recommends there are 9 contributing resources and 33 non-contributing resources (Table 3; Appendix B). Full resource descriptions, NRHP evaluations, and integrity recommendations are outlined for each individual resources in the NRHP Evaluations section above.

The DNPS Unit 1 Reactor was the first full-scale, privately financed nuclear plant in the US (Constellation 2025). Unit 1 remained in operation between 1960 and 1978. SEARCH recommends the proposed DNPS Unit 1 Historic District is NRHP eligible for its statewide significance under Criterion A (Industry) for its association with Unit 1, the USs first privately funded reactor, and under Criterion C (Engineering) for Unit 1s ca. 1960 spherical containment building.

Unit 1s spherical reactor building is representative of a type built at early BWR nuclear plants in the US (Figure 66). Background research identified three additional spherical reactor buildings at US plants built between 1955 and 1962: the ca. 1955 Kenneth Kesselring site (West Milton, NY),

the ca. 1960 Yankee Rowe Nuclear Power Station (Rowe, MA) reactor building, and the ca. 1962 Big Rock Point Nuclear Power Plant (Charlevoix, MI) reactor building (IAEA 2025). Of these three, the Keith Kesselring site is the only that remains extant. Engineers determined the spherical design was too limiting and inappropriate for optimal interior machinery layouts. This design was Figure 65. Storage Barn, facing northwest.

SEARCH August 2025 Architectural History Survey of Dresden Nuclear Power Station, Grundy County, Illinois Final Technical Report 71 Architectural History Results replaced by the Mark I and II model containment buildings in the late 1960s to house BWRs, and later by the Mark III model. By the time of Unit 2s construction in 1970, the Mark I building was the BWR containment standard. Therefore, SEARCH recommends the Period of Significance for the proposed DNPS Unit 1 Historic District is 1960-1969.

SEARCH recommends the ca. 1960 Unit 1 Reactor Building is eligible as a contributing resource within the proposed DNPS Unit 1 Historic District for its significance under Criterion A and C.

SEARCH recommends the 8 additional contributing resources within the proposed DNPS Unit 1 Historic District are associated with Unit 1s construction as the first privately financed reactor, and are significant for this association under Criterion A. These buildings were constructed within the recommended 1960-1969 Period of Significance (see Table 3). Additionally, SEARCH recommends these buildings retain sufficient integrity to convey their significance under Criterion A.

Of the 33 noncontributing resources within the proposed DNPS Unit 1 Historic District boundary, SEARCH recommends 28 resources are not eligible for NRHP inclusion due to a lack of historic significance, and most were constructed outside the recommended 1960-1969 Period of Significance. Five resources are significant under Criterion A and/or C for their association with Unit 1s construction as the first privately funded reactor in the US, but no longer retain sufficient integrity to convey that significance (see Table 3). Full resource descriptions, NRHP evaluations, and integrity recommendations for these resources are included above in the NRHP Evaluations section.

Table 3. DNPS Unit 1 Historic District Contributing and Noncontributing Resources.

Resource Name Date NRHP Recommendation Note Unit 1 Reactor Building ca. 1960 Eligible Individually (Criterion C);

and as Contributing Resource (Criterion A)

Criterion A, C Unit 1 Turbine Building ca. 1960 Eligible as Contributing Resource Criterion A Unit 1 Fuel Handling Building ca. 1960 Eligible as Contributing Resource Criterion A Figure 66. DNPS Building, facing north (left); DNPS Building, facing west.

August 2025 SEARCH Final Technical Report Architectural History Survey of Dresden Nuclear Power Station, Grundy County, Illinois Architectural History Results 72 Table 3. DNPS Unit 1 Historic District Contributing and Noncontributing Resources.

Resource Name Date NRHP Recommendation Note Unit 1 Station Chimney ca. 1960 Eligible as Contributing Resource Criterion A Shop & Warehouse Building ca. 1960 Not Eligible, Noncontributing No longer retains sufficient integrity to convey its significance under Criterion A.

Administration Building/Service Building ca. 1960 Not Eligible, Noncontributing No longer retains sufficient integrity to convey its significance under Criterion A.

Waste Sample Tanks ca. 1970 Not Eligible, Noncontributing Not eligible due to lack of significance Heating Boiler House ca. 1970 Not Eligible, Noncontributing Not eligible due to lack of significance Unit 1 Intake Canal ca. 1960 Eligible as Contributing Resource Criterion A Fuel Oil Storage Tank and Berm ca. 1960-1970 Not Eligible, Noncontributing Not eligible due to lack of significance Radwaste Building Unit 1 ca. 1960 Eligible as Contributing Resource Criterion A 345 kV Switchyard ca. 1960 Not Eligible, Noncontributing Not eligible due to lack of significance 138 kV Switchyard ca. 1960 Eligible as Contributing Resource Criterion A 138 kV Relay House ca. 1960 Eligible as Contributing Resource Criterion A Meteorological Tower ca. 1960 Eligible as Contributing Resource Criterion A DNPS Building ca. 1960-1979 Not Eligible, Noncontributing No longer retains sufficient integrity to convey its significance under Criteria A or C.

Elgin, Joliet and Eastern Railroad Spur ca. 1956 Not Eligible, Noncontributing No longer retains sufficient integrity to convey its significance under Criterion A.

Unit 1 Crib House ca. 1960 Not Eligible, Noncontributing No longer retains sufficient integrity to convey its significance under Criterion A.

Unit 2 and 3 Intake Canal ca. 1970-1971 Not Eligible, Noncontributing Not eligible due to lack of significance Unit 2 and 3 Discharge Canals ca. 1970-1971 Not Eligible, Noncontributing Not eligible due to lack of significance Wastewater Treatment Facility A ca. 1975-1979 Not Eligible, Noncontributing Not eligible due to lack of significance Wastewater Treatment Facility B ca. 1975-1979 Not Eligible, Noncontributing Not eligible due to lack of significance Off Gas Filter Building ca. 1970 Not Eligible, Noncontributing Not eligible due to lack of significance Unit 2 and 3 Crib House ca. 1970 Not Eligible, Noncontributing Not eligible due to lack of significance Switchyard Maintenance Building ca. 1975-1979 Not Eligible, Noncontributing Not eligible due to lack of significance Warehouse 5 ca. 1970 Not Eligible, Noncontributing Not eligible due to lack of significance Maintenance Warehouse ca. 1975-1979 Not Eligible, Noncontributing Not eligible due to lack of significance

SEARCH August 2025 Architectural History Survey of Dresden Nuclear Power Station, Grundy County, Illinois Final Technical Report 73 Architectural History Results Table 3. DNPS Unit 1 Historic District Contributing and Noncontributing Resources.

Resource Name Date NRHP Recommendation Note Diesel Generator & HPCI Building/SBO Building ca. 1978 Not Eligible, Noncontributing Not eligible due to lack of significance Radwaste Building ca. 1970 Not Eligible, Noncontributing Not eligible due to lack of significance Technical Support Center ca. 1975-1979 Not Eligible, Noncontributing Not eligible due to lack of significance Unit 2 Turbine Building ca. 1970 Not Eligible, Noncontributing Not eligible due to lack of significance Unit 3 Turbine Building ca. 1971 Not Eligible, Noncontributing Not eligible due to lack of significance High Radiation Sampling Building A ca. 1975-1979 Not Eligible, Noncontributing Not eligible due to lack of significance High Radiation Sampling Building B ca. 1975-1979 Not Eligible, Noncontributing Not eligible due to lack of significance HPCI & Diesel Generator Building ca. 1970-1971 Not Eligible, Noncontributing Not eligible due to lack of significance Off Gas Recombiner Room A ca. 1970-1971 Not Eligible, Noncontributing Not eligible due to lack of significance Off Gas Recombiner Room B ca. 1970-1971 Not Eligible, Noncontributing Not eligible due to lack of significance Unit 2 and 3 Reactor Building ca. 1970-1971 Not Eligible, Noncontributing Not eligible due to lack of significance Unit 2 and 3 Station Chimney ca. 1970-1971 Not Eligible, Noncontributing Not eligible due to lack of significance Units 2 and 3 Radwaste Building ca. 1970-1971 Not Eligible, Noncontributing Not eligible due to lack of significance Max Recycle Radwaste Building ca. 1970-1971 Not Eligible, Noncontributing Not eligible due to lack of significance Floor Drain Surge Tank ca. 1974 Not Eligible, Noncontributing Not eligible due to lack of significance The DNPS as a whole represents a mid-twentieth-century nuclear plant with BWRs used for power generation. Its sequential construction and site plan does not indicate a unified landscape plan, but rather a collection of support facilities constructed, adapted, or demolished throughout its history to address the plants changing needs. Historic aerial photographs indicate construction expanded within the Survey Area throughout the 1980s and 1990s as necessary.

Other facilities were demolished or replaced throughout the DNPS history of use.

SEARCH recommends the proposed project, a subsequent License Renewal application to the NRC, does not possess the potential for adverse effects to the proposed DNPS Unit 1 Historic District or to its 9 contributing resources (see Table 3).

August 2025 SEARCH Final Technical Report Architectural History Survey of Dresden Nuclear Power Station, Grundy County, Illinois Architectural History Results 74 This page intentionally left blank.

SEARCH August 2025 Architectural History Survey of Dresden Nuclear Power Station, Grundy County, Illinois Final Technical Report 75 Conclusions and Recommendations CONCLUSIONS AND RECOMMENDATIONS SEARCH conducted intensive architectural history survey of the DNPS Survey Area in Grundy County, Illinois, on March 11 and 12, 2025. The Survey Area includes the entire DNPS: an approximately 385.67 ha (953 ac) area bounded by the Illinois River to the north, the Kankakee River to the east, Pine Bluff Road to the south, and E Collins Road and private parcels to the west.

SEARCH identified 57 historic-age resources in the Survey Area, including 38 buildings, 18 structures, and the proposed DNPS Unit 1 Historic District. One resource, the DNPS Building, consists of 21 interconnected historic age facilities.

SEARCH recommends the proposed DNPS Unit 1 Historic District is NRHP eligible for its significance under Criteria A and C and recommends 9 surveyed resources are eligible as contributing resources to the proposed district. The remaining 47 resources are recommended not eligible for NRHP inclusion, neither individually nor as a contributing resource to the proposed DNPS Unit 1 Historic District. SEARCH recommends the proposed project, a subsequent License Renewal application to the NRC, does not possess the potential for adverse effects to the proposed DNPS Unit 1 Historic District, or to its 9 contributing resources. No additional architectural history work is recommended.

August 2025 SEARCH Final Technical Report Architectural History Survey of Dresden Nuclear Power Station, Grundy County, Illinois Conclusions and Recommendations 76 This page intentionally left blank.

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APPENDIX A.

IL SHPO CORRESPONDENCE (PROVIDED JUNE 10, 2025)

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1 Various Counties Morris License Renewal, Dresden Nuclear Power Station 6500 N. Dresden Rd.

Goose Lake Prairie State Natural Area State Park - Country Road 5000 E White & Companys Goose Lake Stoneware Manufactury - 5010 N. Jugtown Rd. NRHP listed 8/6/1998 White & Companys Goose Lake Tile Works - 5010 N. Jugtown Rd. NRHP listed 8/6/1998 Dresden Nuclear Power Station - 6500 N. Dresden Rd., b.ca.1960-1979 SHPO Log #012103124 June 10, 2025 Allison Stalker Constellation Energy 200 Energy Way Kennett Square, PA 19348 We have reviewed the information provided for the above referenced project. Our review is required by Section 106 of the National Historic Preservation Act of 1966, as amended, and its implementing regulations, 36 CFR 800: "Protection of Historic Properties."

At this level of the undertaking, SHPO is only reviewing the "Generic Environmental Impact Statement for License Renewal of Nuclear Power Plants, Supplement 17, Second Renewal: Draft Report for Comment" that was submitted to our office on May 22, 2025.

Our office does not concur with the determination of eligibility presented in the architectural survey that found none of the structures to be individually eligible for the National Register of Historic Places. We would ask for additional consideration of the facility as a "...pioneering facility in the history of the nuclear power in the U.S.," as stated in your report (p. 5).

Page 29 of the report states that, "In October 1991, the American Nuclear Society (ANS) designated the Unit 1 containment building a Nuclear Historic Landmark (ANS 2025), [which] acknowledges a historic event or activity [which] successfully provided an essential contribution to, or basis for, the subsequent peaceful application of nuclear technology or nuclear energy, and been a first of a kind, or provided a signific new departure (ANS 2025). The award acknowledges Unit 1s status as the first commercially funded nuclear reactor. Page 31 says, The Unit 1 Reactor building represents the first commercially funded nuclear plant in the United States, and is significant under Criterion A for this association, and, The facilitys significance under Criterion A is specifically associated with its function as the first privately funded nuclear reactor building.

We do not agree with the finding that appears later in the report that the facility is not significant under Criterion C, as explained by the idea that it, 1) "...was not the first containment building constructed in the United States..." and that its 2) "... spherical shape also represents a containment building type popular

2 among nuclear facilities constructed in the 1960s and 1970s...," 3) was replaced, "... in favor of reinforced concrete cylindrical shapes...," and 4) "lacks engineering distinction, is not the work of a master, does not possess high artistic values," and 5) is "... therefore is not significant under Criterion C.

Though the facility is not the first of its kind, it is significant as the first to be commercially funded. Though other spherical containment buildings were built in the 1960s and 70s, Dresden was built in 1960, before the others; engineering distinction is asserted at the beginning of the report.

The American Nuclear Society expressed its significance for over 35 years, and though we do not consider the facility to be the work of a master or hold high artistic value, Dresden, according to Criterion C, Embod[ies]

distinctive characteristics of a type, period, or method of construction. The spherical shape, even though later was discarded in favor of other shapes, remains significant (as many historic resources represent a form that has been abandoned or changed in favor of something more modern).

Additionally, despite the facility no longer operating in its original capacity, it remains significant as would a water tower, gas station, or other functional building or structure that derives significance but no longer functions as it once had. Despite the abandoned, removed, and/or repurposed components, we do not find a lack of integrity for the Unit 1 Reactor Building.

Finally, we consider the facility to hold national, state, and local significance, which is evidenced by the American Nuclear Society's designation of it as a Nuclear Historic Landmark, as a model for privately financed nuclear power, as a contributor to power grid stability, and as foundation of the state and local economies.

SHPO proposes that the draft be re-reviewed and the site is evaluated as a possible historic district.

If you have any further questions, please contact Rita Baker, Cultural Resources Manager, at (217) 785-4998 or at Rita.E.Baker@illinois.gov.

Sincerely, Carey L. Mayer, AIA Deputy State Historic Preservation Officer c: Jennifer Davis, United States Nuclear Regulatory Commission