Experimental Testing and Applied R&D

Independent Process Qualification: Recently, a significant steam generator (SG) sleeving program was implemented by a non-US utility to extend the life of their SG fleet until systematic SG replacement could be performed. In support of local regulatory requirements, DEI performed independent analysis and qualification of the sleeving process. Specific assistance and insights provided by DEI included:

• Design and construction of a complex, custom autoclave test facility to meet unique technical requirements imposed by the regulator
• Design and fabrication of tube/sleeve mockups to represent stresses at the sleeving hydraulic expansion locations and at the rolled joint within the tubesheet
• Estimation of in-service life of sleeved tubes based on experimental testing of time-to-failure for mockups via ID and OD cracking mechanisms and comparison to FEA modeling and predictions

These technical justifications supported acceptance of the proposed sleeving process by the local nuclear safety regulator, and the process has been successfully applied without issue at a number of units within the non-US utility’s fleet.

Multi-physics Modeling & Experimental Validation: Some nuclear waste streams exhibit unusual rheological properties and/or contain abrasive minerals that challenge design and reliable operation of processing equipment. DEI has provided ongoing technical consulting for the Hanford waste treatment plant (WTP) to ensure that waste processing does not result in erosion/wear that exceeds allowances for processing equipment. DEI technical support provided in this project included:

• Development and qualification of a non-radioactive simulant that accurately represents the abrasivity and non-Newtonian rheological properties of the actual Hanford tank waste
• Experimental testing (at large and small scales) to establish dependences of erosion/wear rates on parameters such as impingement jet velocity and angle, solids concentration, and particle size, hardness, and distribution, and to validate CFD results
• CFD modeling of particulate trajectories during waste jet impingement and development of correlations to predict erosion/wear rates at different testing scales and in actual Hanford plant equipment (full scale)

These results were essential in technical issue closure for erosion/wear at the Hanford WTP.

Crevice Corrosion Modeling & Experimental Validation: When building a new reactor or pursuing license renewal, critical cabling, instrumentation and connectors used within the plant must be qualified or re-qualified to withstand accident conditions, even after thermal and radiation aging during normal plant operation. DEI was recently contracted to perform a root cause investigation when unexpected failure of a cable/connector assembly was observed in equipment qualification (EQ) testing. DEI technical consulting services included:

• Inspection of failed parts and identification of possible failure mechanisms
• Chemistry modeling to determine if a suspected root cause (crevice corrosion) was plausible
• Testing to validate crevice corrosion modeling and simulate the suspected failure mechanism
• Recommendation of design modifications and alternate material selection for the cabling sheath to prevent the issue from recurring

The design / material changes recommended by DEI were incorporated and facilitated successful qualification of the cabling/connector assembly. The component has since been incorporated into several new reactors and has operated without issue.

Accelerated Degradation Testing: To guide material selection for an advanced reactor component, DEI conducted slow strain rate testing (per ASTM G129) of candidate alloys on behalf of the reactor supplier. This accelerated testing method involves slowly straining (10^-4 to 10^-7/s) axially-loaded test specimens to failure in a test environment in order to evaluate susceptibility to environmentally-assisted cracking. DEI provided the following technical services in this project:

• Designed and built a custom autoclave facility with an integrated 5000-lb servo ball-screw actuator
• Conducted slow strain rate testing on test specimens cut from the actual component of interest over a range of strain rates and in a test environment simulating the primary circuit of a PWR reactor during normal operation
• Provided recommendations on material selection based on susceptibility to environmentally-assisted cracking observed in testing

DEI material consulting and testing assisted in finalizing and qualifying material selection for the component of interest, which has since been incorporated into the advanced reactor design.

Root Cause Failure Analysis and Metallurgical Examinations: Over the last 30 years, more than 10 steam pipe explosions have occurred within NYC’s underground steam system, which provides heating and cooling for buildings and businesses in Manhattan. Following an explosion near Grand Central Terminal in 2007, DEI served as a technical expert to evaluate the root cause. Specific DEI consulting services and insights provided as part of this project included:

• Thermal and fluidic analysis of possible contributing factors including clogging of steam traps by debris and corrosion products and hydraulic shock from water hammer events and other transients
• Finite element analysis (FEA) of welding residual stresses and operational stresses present within the piping system
• Materials analysis and expertise, including metallurgical examination (both macroscopic and microscopic) of the failed pipe to evaluate postulated material failure scenarios

DEI’s technical breadth and depth was essential for comprehensive support of the investigation process by a single organization, and helped identify the relevance and interplay between different engineering factors.