Frequently Asked Questions About Fire-Induced Circuit Faults
On this page:
- What is the NRC’s goal regarding the protection of circuits nuclear power plants (NPPs)?
- What is a circuit fault?
- How do licensees prevent fire-induced circuit faults from affecting safe shutdown?
- Do all plants have separation in accordance with the regulation?
- What does it mean to say that there is enforcement discretion for circuit failure issues?
What is the NRC’s goal regarding the protection of circuits nuclear power plants (NPPs)?
The main goal of the U.S. Nuclear Regulatory Commission (NRC) is safety. The NRC achieves this goal partly through the use of the defense-in-depth concept. As indicated in Appendix R to Title 10, Part 50, of the Code of Federal Regulations (10 CFR Part 50), the fire protection program extends the concept of defense-in-depth to fire protection with the following objectives: (1) prevent fires from starting; (2) detect rapidly, control, and extinguish those fires that do occur; and (3) provide protection for structures, systems, and components important to safety so that a fire that is not promptly extinguished by the fire suppression activities will not prevent the safe shutdown of the plant. Protection of circuits is an important tool in achieving the third objective above.
What is a circuit fault?
Circuit faults are failures within plant electrical systems where wires come into contact with other wires or other equipment in a way that is outside the plant design. These faults are described in the rule as hot shorts, shorts to ground, or open circuits. The circuit faults of interest are the ones that have the potential to prevent operation or cause maloperation of plant equipment that is important to safe shutdown.
How do licensees prevent fire-induced circuit faults from affecting safe shutdown?
Nuclear power plants are designed with redundant safe shutdown systems. Plants have been designed to separate these redundant safe shutdown systems either to be installed in separate plant areas or to have separation within individual fire areas. Therefore, circuit faults would not affect more than one safe-shutdown system.
Do all plants have separation in accordance with the regulation?
The Browns Ferry fire occurred after many plants were designed and, therefore, the separation features were not originally built into all plants. Consequently, plants were subsequently modified to provide adequate separation. In some cases, separation in accordance with the requirements was not necessary to achieve safety, because the plants were adequately safe without fully implementing all requirements. In those cases, licensees submitted deviations from the requirements to the NRC for review and approval in accordance with NRC requirements.
What does it mean to say that there is enforcement discretion for circuit failure issues?
In 1998, the NRC identified inconsistency between the industry and NRC positions regarding the regulations concerning fire-induced circuit failures. Therefore, until the issue is clarified, the NRC instituted enforcement discretion, which allows licensees that had implemented compensatory measures, such as staging fire watches, for identified circuit failure issues to avoid enforcement for non-compliances. This means that when either the NRC or a licensee identifies a fire-induced circuit failure issue, violations and fines will not be imposed on those licensees that have instituted compensatory measures. This enforcement discretion is not permanent and is expected to end when the issue is clarified.