Stevenson & Associates (S&A) have been pioneers in developing the methodology, design and licensing of High Density Polyethylene (HDPE) piping to replace buried low carbon steel ASME Class 2 and 3 piping.  Due to the cost and durability advantages, it was concluded that ASME code inclusion of HDPE piping was logical.  The Electric Power Research Institute (EPRI) retained Stevenson & Associates to research and develop an analysis method for HDPE piping in nuclear power plants. The methods comply with ASME Power Piping Code, B31.1-2004 and Section III of the ASME Boiler and Pressure Vessel Code. Extensive use was made of data and experience gained from the more than 40 years that HDPE piping has been in use.

S&A then designed and implemented a strength and fatigue testing program of HDPE components to supplement the existing body of data.  The test plan met the requirements of ASME III Appendix XXIII. Testing included the development of full range stress-strain properties of the HDPE piping at four temperatures for both new and thermally aged conditions. Fatigue testing of fusion butt welded HDPE pipe and 5 segment miter elbow joints was also conducted. Stress intensification factors (SIFs) for fusion butt joints were developed in accordance with the ASME Boiler and Pressure Vessel Code, Section III, Division 1, Appendix II, Article II - 2000.  Also developed was a S-N curve that can be used for ASME BPVC, Section III, Division 1 fatigue checks.

S&A designed and implemented a vibration monitoring system for Main Steam piping at a commercial nuclear power plant. A 32 channel data acquisition system was used to continuously sample operating vibration during the first Method Uncertainty Recapture (MUR) power uprate ascension. The data samples are also being used to design a new piping support scheme, one that will feature energy absorbing viscous dampers in place of rigid pipe supports. The redesign will address flow conditions for future Extended Power Uprate (EPU) operation.

S&A is developing piping models to predict vibration levels for the EPU conditions. The models are first validated with the measured vibration data, including operating vibration levels and structural-acoustic natural mode signatures.

Viscous damper (VD) schemes are widely used in Europe and Asia and are now being adopted at US industrial/power plants. S&A has partnered with international VD designers and is at the forefront of the effort to implement the VD system in the US.

 

 

 

The Mixed Oxide (MOX) Fuel Fabrication Facility, currently under construction at the DOE Savannah River Site, will demilitarize surplus plutonium. Plutonium oxide is blended with uranium oxide powder and made into small pellets about the size of a pencil eraser. The pellets are pressed into shape, sintered (baked at high temperatures), ground to the required dimensions and loaded into fuel rods. The rods are bundled together to form fuel assemblies, which are then ready for shipment to a commercial power plant. Most of the process is fully automated and, to protect workers, is contained within confinement structures (“gloveboxes”).

S&A performed seismic analysis, stress analysis and overall structural qualification of gloveboxes, pressure vessels and piping. Analyses included development of detailed, 3-dimensional finite element models. S&A also developed design criteria and performed generic seismic ruggedness studies. The pressure vessel analysis addressed pressure integrity, criticality safety and shielding.

 

 

 

Since 9-11 nuclear plants have upgraded their security facilities even further to meet new and more demanding regulator-postulated design basis threat scenarios. S&A has provided analysis and design engineering services to improve numerous nuclear plant defenses including:

• Blast analysis of existing facilities
• Bullet and blast-resistant enclosures and barriers
• Bunkers, hardened communication facilities and surveillance posts
• Navigable waterway and sea barriers
• Hardened building armor
• Retractable crash barriers and gates
• Permanent barrier and obstacle design
• On-site construction management and oversight

As part of on-site Independent Spent Fuel Storage Installation (ISFSI), many utilities have significantly increased the dimensions and weights of the dry casks used to transfer spent fuel. Facility upgrades performed for US nuclear plants include:

• Modification to spent fuel pool cranes and crane supporting structures
• Modification to existing structures used to decontaminate, seal and maintain casks.
• Analysis and design of final storage facilities and foundation pads
• Soil-structure interaction analysis to establish seimic demand for ISFSI casks
• Analysis and design of ISFSI casks for terrorist threats
• Design of roadway and track transportation facilities for increased loads

The University of Albany constructed a large cleanroom building to support R&D for the microelectronics and nanotech industries. To ensure optimum tool performance, facility requirements included strict limits on floor vibration. S&A/VEC was retained by architect CDM to provide expertise in vibration control. We performed on-site vibration testing, finite element modeling, and dynamic analysis. Our design recommendations addressed foundation stiffness, elevated floor slab design, lateral bracing, and vibration isolation of tools. The location is a deep-soil site and long, heavy piles were employed to shield critical areas from ground vibration. The vibration-controlled elevated slab is a reinforced concrete open waffle braced by internal shear walls. The favorable stiffness and damping properties of the structure quiet the response to mechanical vibration sources.