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By Steve Blankinship, Associate Editor
A 3-D laser measurement and imaging technology used for years in fossil and nuclear plants could be an effective means to assess the ability of emergency core cooling systems to provide long-term core cooling in the event of a loss of cooling accident in pressurized water reactor (PWR) nuclear plants.
Based on a risk assessment program that began in 1998, the Nuclear Regulatory Commission (NRC) issued General Safety Issue 191 (GSI-191) requiring nuclear power plant operators to asses the impact on PWR sump performance posed by potential debris accumulation and determine precisely how much debris could accumulate. The requirement applies to 70 of the more than 100 utility power reactors in the United States. In a related action, the NRC in 2004 issued Generic Letter 2004-02: Potential Impact of Debris Blockage on Emergency Recirculation During Design Basis Accidents at Pressurized Water Reactors. This requires that all corrective actions addressing this concern be implemented by December 31, 2007.
Issuance of GSI-191 stemmed from concerns that in the event of a high energy line break (HELB) or loss of coolant accident (LOCA), fluid leaked from the system and the debris generated by the accident could flow first to the emergency core cooling system (ECCS) sumps and/or the containment spray system (CSS). The objective of GSI-191 and GL2004-02 is to ensure that debris will not impede or prevent operation of emergency cooling and containment spray systems in recirculation mode at PWRs following LOCA or HELB accidents for which sump recirculation is required.
To comply, the zone of influence (ZOI) must be identified. The ZOI is the area affected by the accident in which everything is assumed to be dislodged by a LOCA or HELB. The ZOI is the basis for analyzing the sump system to ensure it remains unblocked. Many plants are currently doing walk downs or trying to recreate models to determine the ZOI. This traditional approach is costly, time-consuming and can cause radiation exposure issues.
The 3-D laser measurement and imaging technology developed by Pittsburgh-based Quantapoint allows a plant to be “digitized” to help ensure that any modifications performed and any equipment used in making the needed modification will fit into the area and that construction will be “clash-free.” Over the past year, Quantapoint has worked at more than a dozen U.S. nuclear plants where it has conducted life extension and power uprate modifications.
“This process can help our clients improve project performance and reduce risk by providing a single, consistent and up-to-date source of as-exists conditions created using a 3-D laser technology,” says James McGill, vice president of marketing for Quantapoint. “The system captures high-resolution dimensional data in 80 percent less time and with half the personnel of traditional techniques that use digital cameras, plumb bobs and tape measures.” He says this ensures that radiation exposure is kept as low as possible while data is being gathered. The result is a digitized plant that includes interactive 3-D laser models that resemble CAD models.
Project planners can use the 3-D laser models during design, fabrication and construction planning to ensure they are interference and clash free. Laser scanners can also be operated remotely if work must be conducted in irradiated or hard-to-access areas.
Quantapoint 3-D laser models can be used to support NRC GSI-191. During the first phase, the 3-D laser models can be “clashed” against the ZOI to determine the volume of debris that would be generated in an accident. During the second phase, the 3-D laser models can be used as a basis for creating a computational fluid dynamic (CFD) model, improving accuracy and detail and eliminating additional field trips. If modifications to the ECCS system are required, the 3-D laser models can support the project by helping improve engineering design efficiency, reduce construction schedules, improve safety and reduce rework. Finally, the 3-D laser models can be useful to departments such as engineering, maintenance, training and operations to support other projects or activities where more accurate and complete information is required.
