This background section describes NRC’s role and its processes for overseeing reactor safety, specifically the Reactor Oversight Process and the Traditional Enforcement Process. NRC is an independent agency of about 4,000 employees established by the Energy Reorganization Act of 1974 to license and regulate U.S. civilian—that is, commercial, industrial, academic, and medical—use of nuclear materials. NRC is headed by a five-member Commission. The President appoints these Commission members, who are confirmed by the Senate, and designates one of them to serve as the Chair and official spokesperson. NRC seeks to carry out its mission of ensuring safe operation of the 100 commercial nuclear power reactors currently operating in the United States from its headquarters office in Rockville, Maryland, its four regional offices—in King of Prussia, Pennsylvania (Region I); Atlanta, Georgia (Region II); Lisle, Illinois (Region III); and Arlington, Texas (Region IV)—and resident (on-site) inspectors’ offices located at 62 nuclear power plants in 31 states. (See fig. 1.) Appendix II provides a complete list of the commercial nuclear power reactors operating in the United States and additional information about each one. Under the Atomic Energy Act, as amended, NRC is responsible for issuing licenses to commercial nuclear reactors and conducting oversight of activities under such licenses to protect the health and safety of the public, among other things. NRC is authorized to conduct inspections and investigations, to enforce its requirements, such as by issuing orders and imposing civil (monetary) penalties, and to revoke licenses. To oversee the activities of licensed commercial reactors, NRC has established regulations, as well as guidance, including regulatory guides, standard review plans, and NRC’s Inspection Manual. These regulations and guidance, along with plant-specific licenses and technical specifications, form the basis by which NRC provides continuous oversight of reactor operations. NRC’s oversight of commercial nuclear reactors includes monitoring their performance in three strategic areas: (1) reactor safety, that is, avoiding accidents and reducing the consequences of accidents if they occur; (2) radiation safety, that is, ensuring safety from radiation for both plant workers and the public during routine operations; and (3) safeguards, that is, protecting of the plant against sabotage or other security threats. These areas comprise seven cornerstones of NRC’s oversight (see table 1). According to NRC, reactors’ satisfactory performance in these cornerstones provides reasonable assurance of safe operation. Our review focuses on NRC’s oversight of the safe operation of reactors; therefore, the physical security of plants (Physical Protection cornerstone) is outside the scope of this review. NRC also looks for systemic problems by monitoring reactors’ performance in three cross-cutting areas that extend across the cornerstones: Problem identification and resolution. The licensee (1) ensures that issues potentially affecting nuclear safety are promptly identified, fully evaluated, and addressed in a timely manner; (2) uses operating experience information to support plant safety; and (3) conducts performance assessments to identify areas for improvement. Human performance. The licensee (1) makes decisions demonstrating that nuclear safety is an overriding priority; (2) ensures that staff, equipment, procedures, and other resources are available and adequate to assure nuclear safety; (3) plans and coordinates work activities consistent with nuclear safety; and (4) uses work practices that support human performance. Safety-conscious work environment. The licensee maintains an environment in which employees feel free to raise safety concerns, both to their management and to NRC, without fear of retaliation and where such concerns are promptly reviewed, properly prioritized, and appropriately resolved. The Reactor Oversight Process (ROP) is the central component of NRC’s oversight efforts. Under the ROP, NRC undertakes four key actions: (1) reviewing key indicators of licensees’ performance; (2) physically inspecting reactors; (3) assessing whether any findings resulting from inspections are associated with any of the cross-cutting areas; and (4) determining what actions, if any, to take in response to signs of declining performance and any related violations of NRC requirements. NRC technical specialists located at its regional offices review licensee performance using quantitative measures or indicators of that performance. According to NRC documents, performance indicators are designed to illustrate a long-term view of a licensee’s performance—over multiple quarters. Currently, NRC uses 17 performance indicators it developed collaboratively with the industry to measure licensee performance. Each performance indicator is designed to help gauge a licensee’s performance within the different cornerstones outlined above. For example, a performance indicator under the “Initiating Events” cornerstone measures the number of unplanned reactor shutdowns during the previous four quarters. Appendix III provides a list of the safety-related (nonsecurity) performance indicators and related cornerstones. Each licensee voluntarily submits data quarterly for each performance indicator, and NRC measures licensee performance from these data against established numerical thresholds; assigning a color—green, white, yellow, or red—to reflect increasing risk to reactor safety based on these performance data. Specifically, a green indicator reflects performance within an expected range, but white, yellow, and red represent decreasing levels of a licensee’s performance (see table 2). Physical inspections are one of the main tools NRC uses to oversee licensee performance. During these inspections, NRC inspectors are to verify the accuracy of the quarterly data for each performance indicator supplied by the licensee and to assess aspects of licensee performance that are not directly measured by the performance indicator data—for example, confirming that fire protection equipment is in place and that certain maintenance operations have occurred. These inspections cover a wide variety of major systems and technical areas of nuclear power reactors that NRC considers most critical to meeting the overall agency mission of ensuring nuclear power plant safety. NRC currently has 52 different inspection procedures, and they are divided into three broad types of inspections—baseline (46), supplemental (3), and reactive (3)— that vary by depth and objective. Appendix IV provides a list of inspection procedures. Baseline inspections. Baseline inspections are the minimum level of inspections performed at all nuclear power reactors, regardless of performance, and are designed to detect declining safety performance in each of the cornerstones and to review licensee effectiveness at identifying and resolving safety problems. NRC resident inspectors, who are located at each plant, and regional technical specialists, who travel to each plant from NRC regional offices, conduct 46 baseline inspection procedures both as needed and at intervals ranging from quarterly to triennially, involving physical observations of licensee activities and plant performance, reviewing and verifying licensee reports, and interviewing licensee personnel. Each of the baseline procedures specifies a range of sample activities to inspect. Within the scope and requirements of each procedure, inspectors select the type and number of activities to review on the basis of factors, such as the sample activities available; their risk significance; and the amount of time since a particular system or component was last inspected. NRC assesses any issues of concern and determines whether to elevate them to a finding based on certain criteria. To determine whether an issue of concern constitutes a finding, inspectors must first decide whether it is associated with a performance deficiency, which NRC guidance defines as “an issue that is the result of a licensee not meeting a requirement or standard where the cause was reasonably within the licensee’s ability to foresee and correct, and therefore should have been prevented.” NRC guidance defines a finding as an issue of concern associated with a performance deficiency that inspectors or regional officials then determine to be more than minor. NRC then assesses—through its ROP Significance Determination Process—the finding’s risk significance. Similar to performance indicators, NRC assigns the finding one of four colors to reflect increasing risk to reactor safety. Green findings—also called nonescalated findings—equate to very low risk significance, while white, yellow, and red findings—considered to be escalated findings—represent increasing levels of risk (see table 3). Appendix V provides select examples of NRC findings and related information that illustrate the varying levels of risk significance. Supplemental inspections. When NRC identifies one or more escalated findings or a performance indicator exceeding the green threshold at a reactor, regional officials conduct supplemental inspections, which expand the scope beyond baseline inspection procedures and focus on diagnosing the cause of the finding. There are three levels of supplemental inspections that increase in breadth and depth of analysis, depending on the number and type of performance problems identified. The first and lowest level of supplemental inspection assesses the licensee’s corrective actions to ensure they were sufficient in both correcting the problem and addressing the root and contributing causes to prevent recurrence. The second level of supplemental inspection has an increased scope that includes independently assessing the extent of the condition for both the specific and any broader performance problems. The third and highest level of supplemental inspection is more comprehensive and includes determining whether the reactor can continue to operate and whether additional regulatory actions are necessary. The highest level of supplemental inspection is usually conducted by a multidisciplinary team of NRC inspectors and may take place over several months. Also, as a part of this inspection, NRC inspectors assess the adequacy of the licensee’s overall programs for identifying, evaluating, and correcting performance issues. Reactive inspections. NRC conducts reactive inspections of licensee performance when specific events occur that are of particular interest to NRC because of their potential safety significance or because of potential generic safety concerns important to multiple licensees. Reactive inspections determine the cause of the event and assess the licensee’s response to the event. Reactive inspections have three levels that are normally determined by an event’s safety, or risk significance. According to NRC officials, recent reactive inspections have focused on issues such as an automatic reactor shutdown following a loss of offsite power, and a flaw discovered in a weld on a reactor component.