Licensing Information and Regulatory Engagement

On July 17, 2025, the University of Illinois Urbana-Champaign submitted an updated "Regulatory Engagement Plan for Submittal and Approval of an Application to Construct a new Research Reactor" to the NRC Office of Nuclear Reactor Regulation. This Regulatory Engagement Plan includes a project description, the proposed regulatory strategy, anticipated timeline, and provides information to satisfy the applicant information requirements of 10 CFR 50.33(a) – (e) and 10 CFR 50.34(a).

The applicant information requirements consist of general and technical information required in the contents of the application. The general information includes the applicant's name, address, description, and the class of license applied for. The University of Illinois is the applicant and is applying for a construction permit for a class 104c research reactor. The technical information describes the minimum requirements for the Preliminary Safety Analysis Report (PSAR). The PSAR describes the preliminary design and safety features of a proposed nuclear reactor facility and is required to obtain a construction permit. This document will be submitted separately at a later date.

The proposed regulatory strategy details the pre-application activities planned to be done by the University of Illinois and NANO. The University of Illinois and NANO expects to maintain open and frequent coordination and communication with NRC staff by participating in both public and private meetings and discussions throughout the licensing process, and will prepare documents for early submission and review by the NRC. These documents are summarized in this Pre-Application Activities section below this entry. The U of I will respond to requests for additional information from NRC staff on the content of the submittals. If other submittals, either as white papers or technical reports, are deemed to be necessary for the conduct of NRC’s pre-application review of the proposed project, they will be discussed and prepared for staff review. 

An important part of the licensing process is the review of site characteristics to verify the impact of reactor operation on the environment and vice versa. The University of Illinois is following Section 12.12, "The Environmental Report," of the Interim Staff Guidance to NUREG-1537 to develop the Environmental Report. The Environmental Report is required by the NRC to obtain a construction permit and describes the impacts of the proposed facility on the environment and how the facility meets all applicable environmental laws and regulations. From the Environmental Report the NRC will determine whether an Environmental Assessment or an Environmental Impact Statement is required based on impacts to the natural or human environment. The University of Illinois expects to work closely with the NRC staff during the pre-application phase to ensure all requirements for a complete environmental review are met.

Prior to submission, the U of I will engage with the USNRC staff to conduct a pre-application readiness assessment of both the safety and environmental aspects of the application. The results of the assessment will be used to finalize the application and assist USNRC staff with planning and resource allocation for the application review.

After submission, the University of Illinois will continue with post-submission engagement with the NRC staff. This engagement includes responding to requests for additional information in a timely manner and continuing to participate  in public meetings upon request by NRC project staff. 

The U of I plans to submit a Construction Permit Application in the first quarter of 2026.

The Regulatory Engagement Plan lays the foundation for regulatory, technical, and environmental readiness in a major step towards a formal construction permit application. 

On June 13, 2022, the University of Illinois submitted the White Paper, "Utilizing a Class 104(c) Licensing Pathway for the Proposed the UIUC Research & Test Reactor,” to the NRC which provides an overview and justification for the licensing approach for its advanced test reactor.

The University of Illinois intends to deploy a Research and Test Reactor (RTR) on the U of I's campus  advance the commercial readiness of advanced reactor technology through education, research, and at-scale demonstrations, and enable wide adoption of microreactor technology. The proposed KRONOS Micro Modular Reactor (MMR) will be designed, licensed, and constructed around two core missions: 

• Core Mission 1: Education - Research reactors on campuses have historically been a powerful driver of public engagement. Their low risk profile and variable operational posture make them accessible to the public, valuable to the communities in which they are embedded, and underpinned by trusted university researchers. In addition, there has been a recent unprecedented launch of next-generation reactor demonstrations. Licensing and operating advanced nuclear reactors will require training facilities representative of those technologies. Despite these two facts, no new university research reactors have been built in nearly 30 years. The Illinois Microreactor Demonstration Project aims to develop the future workforce needed for next generation reactor technologies to be successful while simultaneously enhancing public confidence and trust in nuclear power. 
• Core Mission 2: Research - The reactor is being designed as a research test-bed to further the viability of advanced reactor technology. Direct research with a microreactor includes instrumentation and monitoring systems, optimization of system components and performance, and many other research and development areas currently being considered in the project planning.
• Cross Cutting Mission: At-Scale Demonstration - Large U.S. university campuses are a microcosm of the national landscape of energy needs and source diversification. The commercial viability and applicability of advanced reactors can be demonstrated through interfacing with existing university-owned power generation and distribution infrastructure.

The Illinois microreactor project is required to meet the emerging education and research needs of the advanced reactor community. These education and research activities provide clear alignment with the purpose and definition outlined under section 31 of the Atomic Energy Act (AEA).

The NRC issues licenses to non-power and utilization facilities (nuclear reactors not designed or primarily used to produce plutonium  or uranium-233) through two typical pathways commonly referred to as Class 103 licenses and Class 104 Licenses. These pathways are described in Title 10, Part 50 of the Federal Code of Regulations (CFR) and are enabled by the Atomic Energy Act of 1954, as amended, the Nuclear Energy Innovation and Modernization Act (NEIMA). Class 103 licenses are described in 10 CFR 50.22, authorized by Section 103 of the AEA and provides for “Commercial Licenses” for utilization and production facilities for industrial or commercial purposes. Class 104(c) licenses are described in 10 CFR 50.21(c), authorized by Section 104 of the Atomic Energy Act (AEA) and authorizes “Research and Development” licenses for utilization and production facilities, in subsection c, that are “useful in the conduct of research and development activities of the types specified in section 31.” 

 The stated education and research activities align directly with four of the five permissible R&D activities defined in Section 31 of the AEA. The University of Illinois plans to conduct research and development related to:

• "nuclear processes" - R&D activities related to fission, fuel burnup, and long core life in context of advanced non-light-water reactors and their effects on the reactor system, system operation, and overall performance are central to the development and validation of computational tools and the planned research and educational mission.
• "the theory and production of atomic energy, including processes, materials, and devices related to such production" - Research in the operational performance of the facility can lead to technologies that advance reactor instrumentation design, control methodologies, system monitoring, and future operational processes, materials, and devices that enhance the safety or performance of the reactor system.
• "utilization of atomic energy entailed in the production of atomic energy for the demonstration of advances in the commercial or industrial application of atomic energy" - Integration of the reactor system within existing campus power generation infrastructure and additional technologies for process heat applications will target advancements in the reactor system, operations, and support components to advance the commercial and industrial effectiveness of advanced reactor technology deployments. 
• "the protection of health and the promotion of safety during research and production activities" - R&D activities aim to improve the state of modeling and simulation of reactor behavior, develop instrumentation and monitoring systems and processes, enhance regulatory body technical expertise, and provide a test bed for demonstrating new systems and components that can advance the safe operation of the technology for various market applications.

Section 106 of the NEIMA, titled “Encouraging Private Investment in Research and Test Reactors” amended Section 104c of the AEA to establish cost recovery requirements for the Class 104(c) licensing pathway. This added to existing cost expenditure requirements in 10 CFR 50.22. A production or utilization facility will be deemed to be for industrial or commercial purposes if licensee shall recover more than 75 percent of the annual costs from or if more than 50 percent of the annual cost of owning and operating the facility is devoted to, the production of materials, products, or energy for sale or commercial distribution, or to the sale of services, other than research and development or education or training.

No sales of energy are planned for the proposed University of Illinois RTR. If energy generated by the reactor is sold in a future expansion of the reactor’s mission, the university will remain within the limits of the Class 104(c) license stipulations.

The University of Illinois RTR will satisfy all applicable statutory and regulatory criteria to be licensed as a Class 104c utilization facility and therefore the University of Illinois’ intent is to pursue a Class 104(c) license for the deployment of a RTR on campus. 

On August 5, 2022, the University of Illinois submitted the White Paper, "Proposed Contents of PSAR Using NUREG-1537 Guidance for the Micro Modular Reactor", to the NRC for review. 

Federal regulation (10 CFR 50.34(a)) requires that a Preliminary Safety Analysis Report (PSAR) must be submitted in the application for a Construction Permit (CP) and details the information that must be included. The PSAR describes the preliminary reactor design, presents design criteria and bases, and discusses potential accident scenarios along with the design features and operational procedures that mitigate their consequences. 

NUREG-1537, "Guidelines for Preparing and Reviewing Application for the licensing of Non-Power Reactors", provides detailed guidance on the content in a license application for a non-power reactor, as well as the standard review plan and acceptable criteria used by the NRC staff. While conforming to NUREG-1537 is not required, it is strongly recommended to ensure completeness of the application, simplify the NRC review, reduce need for requests for additional information (RAIs), and shorten overall review time. The guidance in NUREG-1537 is primarily designed for light-water cooled non-power reactors, the KRONOS Micro Modular Reactor (MMR) design is a High-Temperature Gas Cooled Reactor (HTGR) non-power reactor and therefore some guidance are not applicable to the KRONOS MMR design. In addition to the PSAR which is required for the CP, there is also the Final Safety Analysis Report (FSAR) which is required later for the Operating License. NUREG-1537 provides guidance for Safety Analysis Reports (SARs) and allows for some content in the PSAR to be deferred to the FSAR as long as the deviations do not compromise the NRC’s ability to adequately review and approve the CP application. 

This White Paper summarizes the contents that must be included in the PSAR and identifies differences from the content recommended in NUREG-1537 that is either due to features of the MMR design not covered under the guidance, or may not be included in the PSAR for authorization to proceed with construction, but will be incorporated into the FSAR. The University of Illinois intends to follow the suggested framing for the license application in NUREG-1537, as 18 chapters addressing the following topics: 

1. The Facility - Parameters such as expected operating life, power level, and power cycling as well as details on the MMR facility, shared and independent infrastructure and structures, systems, and components (SSCs) required for reactor safety. 
2. Site Characteristics - Includes the precise location of the site, previous uses for the site, and seismic and regional weather as well as the impacts of potential accidents at the nearby sites on reactor operation.
3. Design of Structures, Systems, and Components - Defines the principal design criteria (PDC) and design bases of SSCs.
4. Reactor Description -  Includes an overview of the core nuclear design including descriptions of the fuel design, the preliminary design for biological shielding to protect plant workers from radiological exposure, and the Quality Assurance Program (QAP)
5. Reactor Coolant Systems - Describes and provides design bases for the heat transfer system (HTS) and the secondary circuit including the molten salt coolant.
6. Engineering Safety Features - Describes the proposed functional containment strategy for protecting against radiological release. 
7. Instrumentation and Control Systems - Describes and provides criteria and bases for the Reactivity Control System (RCS), Reactor Protection System (RPS), and Radiological Monitoring System (RMS).
8. Electrical Power Systems - Describes the normal electrical system including offsite power source, major system equipment, and design parameters 

9. Auxiliary Systems - Describes the reactor building heating, ventilation, and air conditioning (HVAC) system major components and functions, fire protection system (FPS), and communication system during normal and emergency conditions. 

10. Experimental Facilities and Utilization - The MMR will not contain experimental facilities for irradiation testing or isotope production making this section not applicable.

11. Radiation Protection Program and Waste Management - Contains details of the radiation protection program including administrative controls and procedures, organizational structure, interfaces with other safety-related systems, and training programs.

12. Conduct of Operations - Provides a high level chart depicting the organizational structure of the facility within the University of Illinois hierarchy, as well as the operating organization charged with operation and utilization of the RTR.

13.  Accident Analyses - Identifies and describes potential accident initiating events and scenarios. For each accident category, plausible events that could affect the MMR facility will be identified and categorized by significance. 
14. Technical Specifications - Identifies variables and conditions that are expected to be controlled by technical specifications 
15. Financial Qualifications - Provides reasonable assurance that the University of Illinois will have the financial ability to construct, operate, and decommission the reactor facility and estimates of the total construction cost.
16. Other License Considerations - The MMR will not utilize used SSCs or be used to generate medical isotopes or perform radiation therapy making this section of the PSAR not applicable. 

17. Decommissioning and Possession-only License Amendments - Decommissioning does not need to be discussed in detail in the PSAR. 

18. Highly Enriched to Low-Enriched Uranium Conversions - The MMR will use high-assay low enriched uranium (HALEU) as its fuel, so there is no need for conversion. This section is not applicable. 

The PSAR will follow this structure and provide the most up-to-date information and plans for each chapter. The PSAR does not need to address non-application content in detail, but adequate justification for why it does not apply to the MMR design will be included to facilitate the NRC staff review. Most of the required information for the PSAR is discussed in other Pre-Application Activities, this white paper along with the other Pre-Application documents make the writing and review of the PSAR simpler and smoother. 

On March 15, 2024, the University of Illinois submitted the Topical Report, "University of Illinois Urbana-Champaign High Temperature Gas-cooled Research Reactor: Applicability of Nuclear Regulatory Commission Regulations," Release 04 to the NRC for review.

Current NRC regulations are primarily designed for light-water reactors. As a high-temperature, gas-cooled research reactor and a class 104 non-commercial and non-power reactor, the KRONOS Micro Modular Reactor (MMR) has fundamental design differences from light-water reactors. Therefore, typical NRC regulations are not applicable or require modification. On a case-to-case basis, the NRC may grant specific exemptions from the requirements of the NRC regulation in Part 50 when the exemptions are authorized by law, will not present an undue risk to the public health and safety, and are consistent with the common defense and security; and special circumstances are present. 

To support licensing actions, the University of Illinois has reviewed the NRC’s regulations to identify requirements prior to submission of a formal license application in order to support a more efficient and timely review. Aligned with the NRC approval of KAIROS (KP-TR-004-NP) as well as NRC white papers, the University of Illinois has developed eight different regulatory applicability groups to categorize regulations with respect to relevance considering the entry conditions or other plain language included in the regulation as described below. 

1. Not Applicable - technology differs in a fundamentally different law than that of an Light-Water Reactor. The capability, system, or feature is not required, making the regulation not applicable.
2. Not Applicable to Non-Power Production or Utilization Facilities - The regulation is stated to be not applicable to Class 104c research reactor facilities.
3. Applicable as is - Regulation applies, although there may be sub-paragraphs that have their own specific entry conditions as noted.
   • 3(a). Modified/Partial - Regulation applies, with some specific limitations or modifications, which are not considered to be significant deviations. 
   • 3(b). Meets Intent -  Regulation applies and the underlying safety basis is relevant, but means of implementation are subject to interpretation. The University of Illinois approach is considered to meet the intent of the regulation. 
   • 3(c). Administrative - Applies but does not affect design or technical requirements.
   • 3(d). NRC, not Applicant - Regulation applies only to NRC activities, not relevant to an applicant or licensee.
4. Request Exemption -  The University of Illinois may request an exemption from the regulation.

In the Safety Evaluation for the Technical Report dated July 25, 2024, the NRC Staff determined that the technical report identified a generally acceptable list of applicable regulatory requirements for use in developing a license application for the described KRONOS MMR research rector. 

This safety evaluation establishes how NRC regulations apply to the KRONOS MMR and will be directly applied to in forthcoming license applications and sets a clear path forward for microreactor deployments. 

On February 20, 2023, the University of Illinois  submitted a Plan entitled, "UIUC Safeguards Information-Modified Handling (SGI-M) Protection Plan" to the U.S. Nuclear Regulatory Commission (NRC) for review to determine if the University of Illinois had provided sufficient assurance that it will protect SGI-M that it produces, receives, or acquires from unauthorized disclosure in accordance with the requirements of 10 CFR 73.21, “Protection of Safeguards Information: Performance Requirements,” and 73.23, “Protection of Safeguards Information-Modified Handling: Specific Requirements.”  This plan was withheld from public disclosure due to containing security-related information under federal regulation.

Information and material that the NRC determines are safeguards information must be protected from unauthorized disclosure. “Safeguards Information-Modified Handling” (SGI-M) is used as the distinguishing marking for certain materials that are determined by the NRC to require a more rigorous level of protection. Information deemed SGI-M is information that if disclosed could reasonably be expected to have a significant adverse effect on the health and safety of the public or common defense and security and significantly increase the likelihood of theft, division, or sabotage of materials or facilities subject to NRC jurisdiction. The overall measure for considering SGI-M is the usefulness of the information (security or otherwise) to an adversary in planning or attempting a malevolent act. While SGI-M is considered to be sensitive unclassified information, its handling and protection more closely resemble the handling of classified/confidential information than other sensitive unclassified information. 

Access to SGI-M beyond the initial recipients of the order is governed by the background check requirements imposed by the order. Access must include both an appropriate need-to-know determination and a determination concerning the trustworthiness of individuals having access to the information. Need-to-know is defined as a determination by a person having responsibility for protecting SGI-M that a proposed recipient’s access to SGI-M is necessary in the performance of official, contractual, or licensee duties of employment.

Each person who produces, receives, or acquires SGI-M shall ensure that it is protected against unauthorized disclosure. To meet this requirement, licensees and persons shall establish and maintain an information protection system that includes the measures specified below. 

• Protection While in Use - While in use, SGI-M shall be under the control of an authorized individual. The primary consideration is limiting access to those who have a need-to-know. Some examples would be alarm stations, guard posts and guard ready rooms, engineering or drafting areas, plant maintenance offices, or administrative offices if visitors are escorted and information is not clearly visible. 

• Protection While in Storage - While unattended, SGI-M shall be stored in a locked file drawer or container. Knowledge of lock combinations or access to keys protecting SGI-M shall be limited to a minimum number of personnel for operating purposes who have a "need-to-know" and are otherwise authorized access to SGI-M in accordance with these requirements. Access to lock combinations or keys shall be strictly controlled so as to prevent disclosure to an unauthorized individual.

• Transportation of Documents and Other Matter - Documents containing SGI-M when transmitted outside an authorized place of use or storage shall be enclosed in two sealed envelopes or wrappers. SGI-M may be transported by any commercial delivery company that provides nationwide overnight service with computer tracking features, US first class, registered, express, or certified mail, or by any individual authorized access pursuant to these requirements.

• Preparation and Marking of Documents - All documents or other matter containing SGI-M in use or in storage shall be marked and each item of correspondence that contains SGI-M shall, by marking or other means, clearly indicating which portions (e.g., paragraphs, pages, or appendices) contain SGI-M and which do not. 

• Reproduction of Matter Containing SGI-M - SGI-M may be reproduced to the minimum extent necessary consistent with need without the permission of the originator. If the copier is retaining SGI-M information in memory, the copier cannot be connected to a network. It should also be placed in a location that is cleared and controlled for the authorized processing of SGI-M information.

• Telecommunications - SGI-M may not be transmitted by unprotected telecommunications circuits except under emergency or extraordinary conditions.

• Destruction - Documents containing SGI-M should be destroyed when no longer needed.

At a minimum, the University of Illinois Safeguards Information-Modified Handling (SGI-M) Protection Plan will contain a detailed description of how University of Illinois' plans to fulfill these requirements. 

On December 4, 2024, University of Illinois submitted the Topical Report, "University of Illinois Urbana-Champaign High Temperature Gas-cooled Research Reactor: Fuel Qualification Methodology" to the NRC for review. The qualification of nuclear fuel is the process by which a fuel is certified for use in a specific reactor design by ensuring the fuel will perform as intended. The Fuel Qualification Methodology described in this technical report outlines the planned testing, modeling, and acceptance criteria in order to qualify the fuel for use in the KRONOS Micro Modular Reactor (MMR) research reactor. Qualification of the fuel is required in order to receive an operating license. 

The KRONOS MMR fuel consists of Uranium Oxycarbide (UCO) tristructural isotropic (TRISO) coated particles, which are each no larger than a poppy seed. Uranium Oxycarbide is one of two common fuels used in reactors, and resides in the center of the fuel particle; this is referred to as the kernel. Tristructural isoptriopic (TRISO) is a series of 3 coatings over the kernel that help retain fission products and radionuclides (unstable isotopes of elements that emit radiation as they decay) inside the kernel. The inner and outer coatings are pyrolytic carbon (PyC) with slightly different characteristics between the inner and outer layers, and the inner layer is Silicon Carbide (SiC), which is the most effective barrier to the release of radioactivity from TRISO particles. These TRISO particles are then embedded into an additional cylindrical ceramic matrix to form a Fully Ceramic Micro-encapsulated (FCM) annular fuel pellet. These layers provide Defense-In-Depth and are key to the functional containment. The FCM fuel form is designed to provide excellent fission product retention under normal operating and accident conditions. 

The KRONOS MMR FCM fuel particle design and specifications are based on the fuel particle specifications from the "Advanced Gas Reactor Fuel Development and Quantification Program" (AGR). AGR is a 2002 program by the DOE to establish U.S. capacity to fabricate high-quality UCO TRISO fuel and demonstrate its performance.  The NRC has developed a performance-based fuel qualification approach for advanced reactors. NUREG-2246, "Fuel Qualification for Advanced Reactors" provides a fuel qualification assessment framework (FQAF) systematically  identifies fuel safety criteria in a top down approach, composed of a series of subgoals. The University of Illinois Fuel Qualification Methodology is based on the AGR and designed to meet the requirements set by the fuel qualification assessment framework. Key performance metrics are radionuclide retention and pellet integrity during normal operation and accident conditions.  

The Fuel Qualification Methodology includes:

• Development of fuel product specifications for FCM pellets and TRISO particles, and demonstration of manufacturing and quality control processes capable of consistently meeting fuel product specifications.
• Testing and characterization of unirradiated fuel and materials
• Fuel pellet irradiation tests, post-irradiation high temperature testing to simulate accident scenario conditions, and post-irradiation examination (PIE) and characterization of tested specimens to determine irradiated fuel performance.
• Fuel performance modeling calculations in support of fuel qualification 

Two types of irradiation tests are planned, steady-state long-term tests and short-duration failure tests. Steady-state long-term test will be performed at the High Flux Reactor (HFR) in Petten, Netherlands and will be used to represent normal operations. Short-duration failure tests will be performed at the Massachusetts Institute of Technology Nuclear Research Reactor (MITR) and will be performed to represent accident level irradiation conditions. High-temperature furnace testing of specimens will occur following the planned irradiation testing, as part of planned post-irradition testing. The planned irradiation testing aims to bolster and confirm the radionuclide retention performance of TRISO particles demonstrated under the AGR program and to demonstrate that differences in pellet/compact manufacturing between the AGR fuel and the planned FCM fuel will not negatively impact radionuclide retention performance. 

The NRC approved the proposed Fuel Qualification Methodology in a Safety Evaluation (SE) on April 1, 2025. The NRC staff concluded that the proposed fuel qualification methodology provides an acceptable methodology to support qualification of the described FCM fuel product for use in the KRONOS MMR. It is important to note, however, that approval of the fuel qualification methodology does not constitute qualification of the fuel itself. All results of testing, analysis, and modeling activities and methodology described in this technical report will be provided to the NRC in future regulatory reports and undergo the appropriate regulatory review as required prior to the qualification of the fuel and receipt of the Operating License.

The Fuel Qualification Methodology is a key portion of the Preliminary Safety Analysis Report (PSAR), required for the receipt of the Construction Permit. The timely approval of the Fuel Qualification Methodology sets a clear pathway to the qualification of the FCM fuel for use in the KRONOS MMR, and is a pivotal step in the Operating License process.

On February 28, 2024, the University of Illinois submitted the Topical Report, "University of Illinois Urbana-Champaign High Temperature Gas-cooled Research Reactor: Event Sequence Identification and SSC Safety Classification Methodology" to the NRC for review. 

This topical report describes the methodology to identify possible event sequences and the methodology to classify Structures, Systems, and Components (SSCs) as either required for safety or not required for safety. The event sequence methodology is a process used to identify and assess Postulated Initiating Events (PIEs) throughout the development of the KRONOS Micro Modular Reactor (MMR) design, screen the identified PIEs and define and group resulting sequences. A Postulated Initiating Event (PIE) is an event identified in the design phase of a nuclear reactor capable of leading to disruptions of normal function of the reactor or accident conditions. The event sequence identification methodology begins with PIE identification, which is a three step process.

• Initial Phase - The initial PIE list is developed using historical information, regulatory documents, and engineering judgment. Some of the historical and regulatory sources considered and assessed against the MMR design to identify applicable PIEs include the Safety Analysis Report from Fort St. Vrain, a high-temperature gas reactor that operated in northern Colorado  from 1979 until 1989, as well as other publications from the Canadian Nuclear Safety Commission (CNSC), International Atomic Energy Agency (IAEA), and the United States Nuclear Regulatory Commission (NRC). 
• Top-Down Phase - As the design becomes more mature, the top-down phase uses master logic diagrams (MLDs) to analyze three high level fundamental safety functions: reactivity control, reactor heat removal, and control of release of radioactive material that could exceed public dose limits. By analyzing challenges to these functions, the PIEs identified during the initial phase can be confirmed or extended. Given the increased design maturity, specific initiating events can be identified. This process starts with the effect and determines a cause.
• Bottom-Up Phase - In this phase it is possible to follow a “bottow-up” approach where the design is now defined in sufficient detail such that failures can more easily be determined. This phase verifies and expands on the details that resulted from the top-down phase using unique methodologies for each type of PIE identified. The PIE types include piping system breaches, transients, and internal and external hazards. 

The identification of PIEs is the first stage in the safety classification methodology of structures, systems, and components (SSCs) followed by the identification of limiting event sequences. An event sequence is defined as a PIE or combination of PIEs that initially perturbs the plant, the resulting response following the PIE, or the resulting well defined end state. In addition, the worst case failure of any active component is assumed when defining event sequences. SSCs are split into safety-required and non-safety-required by the safety classification methodology. Any SSCs that are required to mitigate the consequences of event sequences or  have an impact on safety and are relied upon to remain functional to meet at least one of the three fundamental safety functions during and following all event sequences that are part of the plant design basis are considered safety-required. The three fundamental safety functions for safety-required SSCs

• Control of reactivity (including reactor shutdown)

• Removal of heat from the reactor

• Control of release of radioactive material that could exceed public dose limits. 

Any remaining SSCs are classified as non-safety-required. 

In a Safety Evaluation issued on March 7, 2024,  the NRC staff concluded that the University of Illinois Event Sequence Identification and SSC Safety Classification Methodology provides acceptable methodologies to identify PIEs and limiting event sequences. Specifically, the staff determined that the methodologies described in the TR represent a well-defined approach that could reasonably be expected to be implemented in a manner that would align with the intent regulatory guidelines and consistent with the requirements of applicable of federal regulation.

On April 10, 2024, the University of Illinois submitted the Topical Report, "University of Illinois Urbana-Champaign High Temperature Gas-cooled Research Reactor: Micro Modular Reactor (MMR) Principal Design Criteria " to the NRC for review. 

Each application for a construction permit is required by NRC regulation 10 CFR 50.34a to include principal design criteria (PDC). The principal design criteria define the necessary design, fabrication, construction, testing, and performance requirements for structures, systems, and components (SSCs) that are crucial for safety.  They ensure that nuclear power plants can be operated safely with no undue risk to the health and safety of the public. To assist non-light-water reactor designers, applicants, and licensees to develop principal design criteria for any non-light-water reactor designs, the NRC developed a regulatory guide titled "Guidance for Developing Principal Design Criteria for Non-Light-Water Reactors". The regulatory guide also describes the NRC’s proposed guidance for modifying and supplementing the general design criteria to develop principal design criteria that address two specific non-light-water reactor design concepts: sodium-cooled fast reactors, and modular high temperature gas-cooled reactors. The principal design criteria described in this topical report were developed based on this regulatory guide with adjustments made to eight principal design criteria in order to reflect certain specific aspects of the reactor design. 

The University of Illinois determined that 17 principal design criteria suggested in the regulatory guide were not applicable to the University of Illinois microreactor design. The NRC staff reviewed each of these criteria and found that the exclusion of each is appropriate. The remaining eight deviations from the regulatory guide principal design criteria were made to either change the language to improve clarity and organization or resolve conflicts in definitions, or removed certain requirements to reflect the technology of the University of Illinois microreactor. One example is the removal of the requirement for emergency electrical power because the reactor is designed to not require coolant, electricity, or an operator to safely shut down the reactor in case of emergency. The NRC staff found that this change in principal design criteria meets the intent of NUREG-1537 Part 2 section 8.2 which states that emergency electrical power is required when “assuring power is required to maintain safe reactor shutdown … to support operation of a required engineering safety feature … or protect the public from release of radioactive effluents”. The NRC staff determined these principal design criteria warranted specific evaluation regarding their applicability resulting from differences in verbiage that the NRC staff considered more than minimal departures. 

In the Safety Evaluation issued on July 25, 2024, the NRC staff concluded that the principal design criteria listed in the technical report describe an acceptable list of principal design criteria that can be used to meet the requirements of 10 CFR 50.34a in support of future licensing actions associated with the construction and operation of the proposed University of Illinois microreactor. This approval clears regulatory uncertainty about how the NRC determines that a design can achieve adequate protection of the public.

Application of the approved Principal Design Criteria will provide assurance that the University of Illinois design process satisfies the NRC’s rigorous regulatory requirements and reduces risk in subsequent license applications.