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Soil Sampling for the NEI Buired Pipe and Tank Initiative
Posted on April 4th, 2013

RSCS has recently completed Phase 1 of a soil sampling and analysis campaign to support subsurface assessment of corrosive conditions proximal to subsurface pipes, systems, and tanks that contain, or may contain licensed radioactive material at a commercial nuclear power plant in the northeastern region of the United States.

The soil sampling campaign completed by RSCS, to assess subsurface corrosive conditions, is part of a wider nuclear power industry initiative known as the NEI 09-14: Underground Piping and Tanks Integrity Initiative.  The purpose of this initiative is to provide reasonable assurance of structural and leak integrity of underground piping and tanks.  The program focuses emphasis on components that contain or may contain licensed material.

The Initiative uses a variety of assessment techniques to directly and indirectly inspect and assess in-scope components.  These assessment tools include, but are not limited to, direct inspection of outside diameter (OD) pipe/tank conditions and assessment of OD pipe coatings, inside diameter (ID) inspection by means of robotic inspection using various non-destructive evaluation (NDE) methods, pressure testing, and indirect evaluation methods such as the in-situ soil conditions proximal to in-scope components.

Certain soil conditions and characteristics increase the risk of inducing corrosive conditions and/or promoting corrosion rates higher than tolerable design limits.  Some of these characteristics include:

  • Soil Texture
  • Electrical Resistance
  • Pipe-to-Soil Electric Potential 
  • pH
  • Moisture Content
  • Microbial Community Types and Activity
  • Reduction-Oxidation Potential
  • Soil Chemistry
    • Extractable Cations (Na, Ca, K, Mg)
    • Extractable Anions (Cl, SO4)

Combined, the analytical results of these characteristics can provide plant engineering with a relative measure of corrosive conditions within soil proximal to components of interest.

RSCS developed procedures and sample plans necessary to collect soil samples and deploy instrumentation in the field necessary to assess the soil characteristics discussed above.  One of the major challenges of the project was to collect soil and in-situ measurements proximal to components in the subsurface without creating large excavations, especially in areas below the water table.  Large excavations are costly and take up a large footprint, which have the potential to disrupt normal plant operations.

To limit costs and disruption to site operations, RSCS employed direct push soil sampling and boring techniques to first collect samples, and then send instrumentation down the boring to measure in-situ pipe-to-soil potential.

Direct push soil sampling uses mechanical down-force and percussion to drive a soil sampling device into the subsurface.  To satisfy the initiative objective to collect discrete soil samples proximal to components, and perform in-situ measurements, dual tube soil sampling tooling was used to advance each boring to the specified depth and collect soil samples.  The dual tube sampling system allows the sampler to advance continuously into the subsurface within a protective outer steel casing.  The sampler can be retrieved from the leading section of casing with a retrieval rod within the casing, which is connected to the down-hole sample tube.  Once the sample tube is removed, the steel casing can temporarily be left in the ground, which is open on the bottom.  This allows for in-situ measurements and/or equipment installation through the open casing.  The opening also allows operators to use “hand utility clearance” methods through the steel casing, such as small diameter hand augers, to avoid potential subsurface obstructions as the tooling is advanced. 

This method was used safely and successfully to collect 14 precision soil samples and conduct in-situ measurements without causing disruption to site operations, while also minimizing costs relative to open excavation sampling methods.  RSCS will re-mobilize to the site in the fall of 2013 to conduct a follow-up campaign of soil sampling and in-situ measurements to compare the spring 2013 results to samples recently collected in the spring of 2013.  The follow-up samples will be used to assess potential corrosion effects associated with annual fluctuations in the groundwater table and winter salt application used for deicing. 

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