Electrical Power Systems Research
The U.S. Nuclear Regulatory Commission (NRC) Office of Nuclear Regulatory Research (RES) performs research to support regulatory activities regarding electrical systems in the U.S. nuclear industry. RES provides technical information to support licensing decisions, evaluates the safety implications of new designs, and coordinates research and development activities with other NRC offices and external stakeholders.
Electrical systems research by the Office of Research (RES) falls into the following categories:
Electrical Cables
RES has been engaging in studies and research activities dealing with medium voltage, low voltage power, and instrumentation cables and their ability to perform the intended safety functions. Of particular interest is the long-term operations (LTO) and effectiveness of aging management programs. The following illustration depicts various parameters, characteristics, material conditions, stressors, aging effects, environmental conditions, safety functions, and condition monitoring that could be attributed to electrical cables. All of these elements contribute to and are fundamental to an effective and reliable aging management program.
To address these concerns regarding cable aging management and LTO, RES adopted the program shown in the diagram below. RES addressed condition monitoring of electrical cables as well as some aspects of Environmental Qualification (EQ) in NUREG/CR 7300, published in 2023. RES also investigated Tan Delta testing of submerged cables, which forms the basis of most condition monitoring of inaccessible and underground medium voltage cables. RIL 2021-011 documents the results of this study.
Additionally, RES is currently pursuing two research activities as follows:
- Evaluate the knowledge gaps and uncertainties previously identified in Volume 5 of NUREG/CR 7153 based on recent findings and research performed by various organizations. The findings will enhance the current understandings on management of aging cables and will inform regulatory positions.
- Future focused research on innovative cable condition monitoring. The findings will enhance understanding of available and emerging tools for aging management of cable systems.
Table 1 contains a list of public documents related to RES’ research regarding electrical cables.
Table 1: Electrical Cables Documents
| ID |
Title |
ADAMS Accession Number |
Document Date |
| NUREG/CR 7300 |
Radiation Accident Dose and Simulated Loss-of-Coolant Accident Test of Low Voltage Cables |
ML23237B247 |
2023-08-31 |
| RIL 2021-11 |
Assessment of EPRI’s Tan Delta Approach to Manage Cables in Submerged Environments: Statistical Review of EPRI Data |
ML22019A007 |
2021-01-31 |
| NUREG/CR 7153, Vol. 5 |
Expanded Materials Degradation Assessment (EMDA): Aging of Cables and Cable Systems |
ML14279A461 |
2014-10-31 |
Power Systems Protection and Reliability
Nuclear power plants (NPPs) require both an onsite and offsite electric power system to support safety-related functions. RES supports NRC regulatory activities related to these power systems. Recent and ongoing research topics include the following:
-
Harmonic distortion effects on degraded and loss of voltage relays
The emergency buses at NPPs are equipped with degraded and low voltage relays that initiate transfer from the normal power supply to the standby (emergency) power supply. Harmonics are produced by various sources, and the distortion from harmonics could potentially affect safety functions. To address this potential, RES performed a study to investigate the effects of harmonic and subharmonic waveforms on degraded and low voltage relays.
The details and the results of the study are documented in the research information letter RIL-2023-09. “An Assessment of the Harmonics Effects on Undervoltage Relays in Nuclear Power Plants.”
-
Valve Regulated Lead Acid Batteries (VRLA)
The purpose of this research project is to assess the feasibility of determining how operational and environmental conditions (cycles, temperature, depth of discharge, seismic vibration), and failure mode mechanisms (positive plate grid corrosion, negative lug and strap failures, negative plate discharge, etc.) could affect the service life of VRLA batteries.
The findings from this research project could inform regulatory decisions regarding the suitability of VRLA batteries in safety-related and important-to-safety electrical equipment in operating reactors and in small modular reactors and advanced reactors.
-
Island Mode Operation (IMO)
The purpose of this research project is to determine possible challenges to on-site electrical power systems in NPPs during the transition, operation, and recovery from IMO. The findings and conclusions from this project could inform future regulatory decisions regarding the ability of NPPs to safely operate during IMO.
| ID |
Title |
ADAMS Accession Number |
Document Date |
| RG 1.30, Rev. 1 |
Installation, Inspection, and Testing for Class 1E Power, Instrumentation, and Control Equipment at Production and Utilization Facilities |
ML24040A161 |
2024-04-30 |
| RIL-2023-09 |
An Assessment of the Harmonics Effects on Undervoltage Relays in Nuclear Power Plants |
ML23352A256 |
2023-12-18 |
| TLR-RES/DE-2023-015 |
An Assessment of the Harmonics Effects on Undervoltage Relays in Nuclear Power Plants |
ML23264A152 |
2023-09-30 |