Enhanced Performance of Nuclear Power Plants
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Environmental Degradation of Materials in Light Water Reactor (LWR)
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Risk-informed Design. In the early phases of advanced systems design, information is scarce. The technologies, components and processes to be used have not been specified adequately or are not well understood and uncertainties are very large. We are developing a methodology that assists the designers at these early phases. It is based on the Analytic-Deliberative Decision Making Process (ADP) which brings together Multi-Attribute Decision Theory with the Analytic Hierarchy Process to create a dialogue among stakeholders. ADP identifies and prioritizes attributes relevant to a decision problem and supports the formulation of metrics to measure the performance of different design options. It allows stakeholders to quickly identify crucial parameters and uncertainties, rank alternatives and provides the information necessary to work toward consensus. ADP is a scalable methodology that can be refined as a system evolves to incorporate information that is more detailed and stakeholder preferences that are better developed. This methodology has been applied to the selection of a technology for a decay heat removal system in a lead-cooled flexible conversion ratio reactor concept under study at MIT.
Direct Cycle SCO2 Gas Cooled Fast Reactor
- 2400MWt rating
- 47% net efficiency at 650C core outlet T
- UO2 inverted fuel with low core Δp
- Use of BeO as diluent and SCO2 reflector achieves negative coolant void worth and flat power distribution
- Hybrid Active/passive ECCS
Reliability of Passive Safety Systems. A comprehensive risk-informed methodology for passive safety system design and performance assessment has been completed and demonstrated on the Flexible Conversion Ratio Reactor. First, the methodology provides a framework for risk-informed design decisions and as an example two design options for a decay heat removal system are assessed and quantitatively compared. Next, the reliability of the system is assessed by quantifying the uncertainties related to system performance and propagating these uncertainties through a response surface using Monte Carlo simulation. Finally, a sensitivity study is performed to measure the relative effects of each parameter and to identify ways to maintain, improve, and monitor system performance.
Pipe Welding
- Welding Setup at EPRI NDE center (left) and Welded Pipe rings as received @ MIT (right).
The Effect of Thermal Aging Properties on Stainless Steel Weld Metals. The effect of thermal aging on the environmentally assisted crack growth is being explored by Professor Ballinger’s group. While the initial thrust of the program focused on static (stress corrosion crack growth) crack growth, the program has now added an additional task-exploration of a newly identified immerging issue that has been termed “environmental fracture”. This phenomenon, identified and formally characterized for the first time in Professor Ballinger’s laboratory, manifests itself as a large reduction in resistance to unstable crack propagation and fracture when a material is exposed in high temperature water (~300°C) for periods that exceed approximately 2000 hours. Factors of over 50% reduction in fracture toughness have been observed. The program is focused on environmental fracture of welds in the current program.
Cladding-Counter Distance Dependence
Environmental Degradation of Materials in Light Water Reactor (LWR)
Environments-Including Irradiation Effects. Professor Ballinger has become actively involved with the Idaho National Laboratory in the areas of LWR materials degradation. His group has initiated a joint project with the INL to develop capabilities for testing of materials in LWR environments and to include irradiated materials. Testing is being done (crack growth and fracture toughness) on high strength materials at MIT. Capability is being constructed for both unirradiated and irradiated materials at INL with the goal of performing irradiations at the Advanced Test Reactor (ATR) and then testing at the INL facilities. Professor Ballinger’s group is supplying engineering and software for the INL facilities.
MIT Reactor Irradiation Capabilities
- There are four in-core irradiation locations (~2” ID and 24” long)
Other Recent In-Core Experiments
- Light Water Reactor Chemistry
- PWR & BWR Coolant Chemistry Loops
- Irradiation-Assisted Stress Corrosion
Cracking Test Facility
- Actively loaded slow strain rate test
- Shadow Corrosion Investigations
- Two materials and one ECP test
- Fuel Irradiation Facility
- Prototype annular fuel rods (5% enriched VIPAC UO2, Zr cladding)
- High-Temperature Irradiation Facility
- SiC/SiC composites and surrogate TRISO particles 850°C to 1600°C
Advanced Materials Degradation Simulation. Professor Yip has maintained his industrial collaborations on materials simulation research with projects on steel, glass, and polymers.
