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Drain Piping Inspection at Arizona Public Services' Palo Verde Nuclear Generating Station*

Author: Daniel Wittas,
Buried Piping Program Manager
Palo Verde Nuclear Generating Station (APS)

Co-Author: Rich Roberts,
Vice President and General Manager
Quest Integrity Group

Buried piping at nuclear power plants is complex in terms of their physical configuration. The complexity creates challenges for inspection and maintenance due to limited access, elevation changes and the variety of fittings that are present. Excavation of buried piping is an expensive option and typically provides access to only a small portion of the pipe’s length. Use of in-line intelligent pigging technology provides the benefit of quickly inspecting 100% of the piping's axial length, along with both interior and exterior surfaces for wall loss (e.g. corrosion, pitting, erosion) and deformation (e.g. denting, ovality, etc.). Ultrasonic-based in-line intelligent pigging is credited as a direct inspection for the Underground Piping and Tanks Integrity Initiative (NEI-09-14).

Each unit at the Palo Verde Nuclear Generating Station (PVNGS) has interconnected buried Radioactive Waste Drains (RD) from 3 large tanks in the Chemical and Volume Control (CH) system. These 4" and 6" diameter drains are located between the tanks and a pump house in the Radiological Controlled Area (RCA). Quest Integrity's InVista™ intelligent pigging technology was identified as a good technology for direct inspection of the RD/CH piping due to limited access between the tanks, depth of the drains and the presence of other buried commodities.

Prior to beginning the project, representatives from Palo Verde's ISI, RP, Operations and Underground Piping departments traveled to Quest Integrity Group's headquarters in Seattle, Washington to address concerns with FME, ease of decontamination and inspection capabilities of the InVista technology. At conclusion of the technology interrogation all parties involved were satisfied that InVista met or exceeded Palo Verde's expectations. Palo Verde elected to employ a full scale mockup of the RD/CH piping at the Palo Verde site to identify potential issues with deployment, retrieval, coverage and to confirm the NDE capabilities of Quest Integrity's InVista technology.

The lessons learned from the mockup will be incorporated into the actual RD/CH inspection (currently scheduled for February/March 2014).


*This abstract was presented at the EPRI BPIG Meeting February 18-20, 2014.

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