Utility Reactor Operations Support
Reactor operations involve the activities in operating the reactor between cold zero power (CZP) at startup to CZP at shutdown. The activities include heatup to hot zero power (HZP), startup and testing, operating at full power, mid-cycle power maneuvers planned and unplanned, mid-cycle downpowers and reduced power operation, mid-cycle shutdowns and restarts, coastdown, end-of-cycle testing, shutdown, and cooldown and depressurization. Prolonged reduced power operation deconditions the fuel, and rapid return to power can produce significant Xe oscillations with short-term nodal linear powers exceeding the steady-state full power level by several percent. ANATECH has assisted utilities in better understanding the impact of these various power history conditions on fuel performance and margins, and in the development of strategies to improve margins and reduce risk of fuel failure.
Nuclear Fuel Performance
ANATECH staff have assisted utility clients around the world in assuring the safe and reliable operation of their fuel. Specific areas of support are detailed below but include:
- Quality Assurance audits and surveillances of fuel and component fabrication,
- Design reviews considering nuclear, thermal hydraulic, mechanical, materials and safety aspects (including independent design analyses),
- Assessment of in-core performance of commercial and next generation designs, and
- Analysis of in-core performance including accident analyses.
Fuel Operational Guidelines
It is clearly the goal of utilities to operate their nuclear fuel such that reliability issues including fuel failures are minimized. In support of the nuclear industry’s 2010 goal of zero defects, ANATECH has played a key role in the development, under EPRI’s Fuel Reliability Program, of two guidelines documents. The first, providing guidance to nuclear plant operators in their development of pro-active fuel operating strategies to mitigate pellet-cladding interaction (PCI) and duty-related failures, had the ultimate goal of providing a very clear quantitative understanding of key fuel and plant operational characteristics to allow PCI failure assessment.
Fuel Reload Support
Using FALCON, developed by ANATECH under contract with EPRI, ANATECH has performed evaluations for multiple utilities to assess PCI risk due to plant operational changes and fuel design changes. These evaluations have included the development of alternative cycle start-up strategies (e.g., various power escalation rates, power levels for holds, duration of power holds) and the impact of plant operational conditions on resultant cladding stress levels. Utility cladding stress criteria and operational constraints have been implemented in the evaluations. The analyses have also considered the impacts of missing pellet surface-type (MPS) defects. Furthermore, FALCON has been used to evaluate the impacts of advanced fuel designs that implement higher uranium loading per assembly on PCI risk.
Power Uprate
There are three types of plant uprate depending on magnitude and plant modifications:
MUR = Measurement Uncertainty Recapture (generally less than 2%)
SPU = Stretch Power Uprate (up to 7%)
EPU = Extended Power Uprate (greater than SPU, but less than or equal to 20%)
Reference
ANATECH supports utilities in evaluating the impact of power uprates on fuel performance with tools such as FALCON and RETRIEV, ANATECH’s proprietary fuel rod power history reconstruction code. Physical changes in the core operating environment may mean increased coolant temperature (affecting corrosion and other thermally driven fuel behavior), flow rate (affecting the potential for flow-induced vibration (FIV) and grid-to-rod fretting (GTRF)), and increases in maximum nodal linear power or hot channel enthalpy.
The MUR uprate is not considered too significant, since its magnitude is on the order of uncertainties in power, and the reduction in power peaking of a few percent is relatively easy. On the other hand, stretch and extended power uprates can be challenging, particularly for high duty (high power density) plants. As a result, ANATECH has worked with utilities to reduce peaking factors for more efficient fuel utilization and/or add more margin to technical limits.
