Industry Leaders in Plant-Specific Neutron Fluence Evaluations
Neutron Fluence for Licensing Applications
Neutron Fluence in Nuclear Power Plant License Renewal Applications: 60-Year, 80-Year, and Beyond
Neutron fluence—the cumulative neutron exposure experienced by reactor materials over time—is a critical parameter in evaluating radiation-induced degradation, particularly for the reactor pressure vessel (RPV) and other neutron-exposed components. In license renewal applications for extending commercial power reactor operation to 60 years (initial renewal), 80 years (subsequent license renewal, SLR), and beyond, neutron fluence calculations and projections support aging management programs and time-limited aging analyses (TLAAs) are required under NRC regulations. These assessments ensure that safety margins are maintained and degradation mechanisms are understood and managed throughout extended operation.
The TransWare Advantage
At TransWare, fluence is our passion. We’ve spent more than 30 years developing and innovating this crucial area of plant support and operation. We are the principal developers of the RAMA Fluence Methodology; a three-dimensional, deterministic particle transport code, approved for use in RPV and internal component fluence calculations by the U. S. Nuclear Regulatory Commission.
Whether you’re performing a plant life extension, P-T curve analysis, component flaw evaluation, or equipment qualification, fluence will be a critical part of your project, and we have the tools and expertise to help you. Contact us to get a free quote on your next neutron fluence analysis!
Regulatory Framework
GALL/GALL-SLR Reports (NUREG 1801/NUREG 2191)
The GALL reports (Generic Aging Lessons Learned) provide the NRC's generic technical basis for aging management during license renewal to ensure safe operation during the period of extended operation. NUREG 1801 (GALL) addresses requirements during the first license renewal (40 -> 60 years) and NUREG 2191 (GALL-SLR) addresses requirements during the subsequent licensing renewal (60+).
10CFR54
The U.S. Nuclear Regulatory Commission’s license renewal rule is codified in Title 10 of the Code of Federal Regulations (10 CFR) Part 54. It establishes requirements for renewing nuclear power plant operating licenses for additional 20-year periods, focusing on the aging of structures and components important to safety. A renewed license may be subsequently renewed for further periods under the same regulatory framework.
Specifically, and as it relates to neutron fluence and aging component management and analysis, 10 CFR 54.21(c) allows for three different disposition paths for a Time-Limited Aging Analysis (TLAA). A licensee must show that a TLAA is:
- Valid for the period of extended operation, or
- Projected to remain within established limits for the period of extended operation, or
- Managed by an Aging Management Program (AMP)
TLAAs
Time-limited aging analyses are design-basis calculations or analyses that account for aging effects over a defined time period. TLAAs must be re-evaluated to account for extended operation. This includes plant-specific neutron fluence analyses.
AMPs
Aging Management Programs (AMPs) consist of an organized set of activities used to identify, monitor, and control the effects of aging on nuclear power plant systems, structures, components, and repair components to ensure they perform their intended functions throughout the licensed period of plant operation.
To conceptualize the difference between TLAAs and AMPs, attempt to think of it this way. A TLAA will question whether the design analysis is still valid after 40 years, and will it remain valid at 60 or 80 years? An AMP will question what is being watched, how often, and what will happen if degradation appears? Because of these distinct, but related, discrepancies, the NRC requires TLAAs to be bounding or re-calculated under changing operating conditions and AMPs to be monitored and implement necessary corrective actions when degradation is identified.
Neutron Fluence
Neutron fluence contributes to material degradation and embrittlement that cannot be measured within the plant; instead, it must be calculated. Neutron fluence calculations will be used to help address long-term degradation mechanisms such as:
- Metal fatigue
- Stress corrosion cracking
- Thermal aging
- Radiation embrittlement
- Concrete degradation
- Crack growth rates
- Voiding, swelling, and creep
- Stress relaxation
Under varying plant operating conditions, it is up to the licensee to determine their method of compliance with 10 CFR 54.
