Fire Protection Activities for Fuel Cycle Facilities
As part of its fire protection program for fuel cycle facilities, the U.S. Nuclear Regulatory Commission (NRC) engages in a variety of regulatory, guidance, licensing, and oversight activities. These activities involve studying the behavior, suppression, and investigation of fire and related emergencies; conducting research (including reliability assessments and modeling); and producing, testing, and implementing systems to prevent and detect fires and mitigate their consequences. For details regarding the NRC's ongoing activities, see the following topics on this page:
Fire Events Database
The NRC is developing and maintaining a database, containing approximately 20 years of fire events data. This database has the following purposes:
- Identify trends that indicate weaknesses in the NRC's review/inspection procedures.
- Identify trends that indicate weaknesses in the NRC's regulations.
- Identify trends that may indicate aging effects on components.
- Reveal weaknesses in a licensee's fire protection program or design.
- Determine initiating events that should be considered in the integrated safety analyses (ISAs).
- Provide a population of site-specific fire events for use in estimating fire frequency.
- Formulate a methodology for using failure data to better estimate the reliability of fire protection measures, including both administrative and engineered controls, as well as items relied on for safety (IROFS).
Reliability of Fire Protection Controls
Determination of reasonable reliability estimates for fire protection measures (including both administrative and engineered controls) has historically been an area of uncertainty in the preparation and review of Integrated Safety Analyses (ISAs). Presently, licensees and applicants make "best estimates" of reliability using operational data (where available), and then use management measures (such as tests and surveillances) to maintain the estimated reliability. At present, the greatest uncertainty is associated with the reliability of fire suppression systems (other than wet pipe sprinkler systems), manual suppression measures, and combustible material control measures.
Reliability of Dynamic Confinement During Fires
For the proposed mixed-oxide (MOX) fuel fabrication facility, the NRC has established additional fire protection measures to augment the usual active engineered controls for fuel cycle facilities. Specifically, these additional measures include "dynamic confinement" systems, equipped with high-efficiency particulate air (HEPA) filters. These systems provide an important level of added protection because the MOX facility is designed to produce light-water reactor fuel by recycling plutonium that has been secured through international nuclear disarmament agreements.
In the event of a fire, the proposed MOX facility relies on dynamic confinement to ensure that potential doses to the facility workers and the public will remain as low as reasonably achievable (ALARA) and will not exceed the threshold limits established in Title 10, Part 70, of the Code of Federal Regulations (10 CFR Part 70). In addition, the MOX facility relies on dynamic confinement to mitigate other internal release scenarios and prevent some types of accidents.
Nonetheless, maintaining dynamic confinement systems poses certain challenges for fire protection. In particular, these challenges include ensuring adequate separation and protection between redundant power and control trains, preventing the collection of soot (which may be sufficient to block the filters), and protecting the filters from fire-induced heat loads.
Modeling of Explosions from Natural Gas Line Ruptures
Most fuel cycle facilities use natural gas in their heating, drying, or incineration processes. As a result, these facilities are often located in close proximity to natural gas lines, which are capable being breached and creating the potential for explosion and/or fire hazards. The present methods used to evaluate these hazards often combine probabilistic estimates of breach occurrence with deterministic assumptions for explosion modeling. Consequently, the NRC considers it desirable to develop a more risk-based methodology for use in evaluating the explosion/fire hazards associated with natural gas lines.
Facility Aging Issues Relative to Fire Protection
Many of the existing fuel cycle facilities are still operating after 50 years of service. In particular, these include the Honeywell uranium conversion facility in Metropolis, Illinois; and several fuel fabrication facilities throughout the United States. In addition, numerous facilities are requesting license renewals for up to 40 additional years.
These realities raise concerns regarding the aging of components (particularly in electrical and fire protection systems), as well as corrosion in confinement systems. Thus far, the major aging concerns for fuel cycle and other nuclear materials facilities involve the operability of wet pipe sprinkler system heads, the buildup of sediment in sprinkler branch piping, and leaks in underground distribution system piping . As noted above, the Fire Events Database is expected to yield additional information regarding trends that may indicate aging effects on components.