Topical Issue: Innovative Technologies for Characterization of Underground Piping

The subject of underground and embedded piping relates to more than the piping itself. Many directly related components include fittings, valves, instruments wall penetrations, and hangers. The subject area also includes components connected by piping, such as pumps, sample collection devices, sumps, compressors, and vessels.

Buried pipes transferring contaminated fluids between buildings or tanks were commonly used at nuclear facilities designed and operated in the 1960s and 1970s. However, often there were problems presented by their design features. Typical problems associated with the decontamination and dismantling of those pipes include:

• uncertainties on exact piping routes and system connections due to poor design and (as-built) construction records and modest inspection possibilities,

• inability to distinctly identify the radiological and chemical contaminants because of poor operational records and/or lengthy idle periods between operations or following final shutdown,

• poor accessibility making physical and radiological characterization difficult,

• difficult access to injection points for the use of various decontamination chemicals,

• presence of hard-to-decontaminate deposits, sludge or sediments often due to long dormancy periods and lack of proper maintenance,

• uncertainties on the physical state of the piping walls and the possibilities for ongoing leakage that could render aggressive decontamination undesirable,

• difficult access for disassembly, including preliminary removal of obstacles and removal of segmented pieces,

• harsh working environments due to the presence of tight spaces, likelihood for heat stress, and/or high radiation/contamination levels requiring the use of personal protective equipment,

• inadequate or poorly adaptable technologies for handling, treatment, conditioning and storage/disposal of waste system piping including the management of toxic material such as asbestos insulating materials,

• lack of clearance regulations and measurement technologies for release of decontaminated pipes, and

• possible contamination of nearby components/structures and the soil due to leaking pipes and uncertainties on the extent of peripheral remedial work that may be required.

It should be noted that most of these issues are also relevant to the decontamination and decommissioning of underground tanks and other underground/embedded components. Descriptions of a few innovative and emerging piping characterization technologies are given below. A number of these techniques were developed, deployed and optimized on actual decommissioning operations with funding from the US Department of Energy to cope with the enormous legacy of redundant nuclear facilities in the USA [6.5]-[6.7]. Specific technologies addressed contaminated piping. Costs of these technologies and results from their testing are given in Reference [6.8].

Pipe Explorer^tm

This device is intended for characterization of pipes/drains. It is a pneumatically operated tubular plastic membrane that transports various characterizing sensors (e.g. gamma detectors, beta detectors, video cameras, and pipe locators) into contaminated piping systems. Historically this activity has been attempted using hand-held surveying instrumentation, surveying only the accessible exterior portions of pipe systems (however, there is no way of checking for alpha and/or beta contaminants) or resorting to costly exploratory digging and removal. Various measuring difficulties, and in some cases the inability to measure threshold surface contamination values and worker exposure, and physical access constraints have limited the effectiveness of the traditional survey approaches. An area where Pipe Explorer has been particularly effective is the capability to demonstrate that buried pipes were not contaminated and, therefore, could be left in place or removed using standard removal or demolition techniques. Pipe Explorer was deployed at various decommissioning sites e.g. Mound, Trojan NPP, Crystal River NPP, Idaho National Engineering and Environmental Laboratory [6.9] and CP-5 Decommissioning Project at Argonne National Laboratory [6.10]. Figure 6-3 gives an overview of Pipe Explorer.

Pipe Crawler^tm

Pipe Crawler consists of a wheeled platform on which is mounted an array of thin Geiger-Müller detectors. Crawler is manually transported through pipes using flexible fibreglass rods. It was extensively tested at CP-5 Decommissioning Project [6.10] and Park Township Site. It is described in more detail in [6.11]. The development of a pipe crawler system and the results of a specific application at Savannah River Site are described in full detail in [6.12]. Further experience, costs, strengths and limitations of this system are given in [6.13], [6.14]. Figure 6-4 provides a photo of Pipe Crawler.

Alpha contamination measurements

Direct measurement of alpha contamination inside pipes is difficult because alpha particles have such a short travel range (alpha particles can only travel a few centimetres in air and only a few microns in materials such as aluminum). Therefore, indirect methods are used to measure alpha-emitting radionuclides. The IonSens monitors were used at the United States Department of Energy’s Savannah

River Site in a fuel fabrication facility in late 1998 to measure alpha contamination in pipes that have inaccessible surfaces [6.15]. Detectors based on the Long Range Alpha Detector (LRAD) technology have been developed at the Los Alamos National Laboratory in the USA. The LRAD technology measures alpha contamination by detecting the ions produced in a gaseous medium by alpha particles rather than by detecting the alpha particles themselves. The advantage of LRAD technology is that, unlike conventional detectors, LRAD-based instruments do not need to be in close proximity to the alpha sources to provide a sensitive measurement. Monitors were designed and built especially to detect contamination in pipes [6.16], [6.17].

Figure 6-3: Pipe Explorer^tm Overview (source http://tech.inel.gov/tech-detail.asp?id=67)

Figure 6-4: Pipe Crawler^tm

(source http://www.netl.doe.gov/dd/images/photos/html/technologies/characterization/bb11097.htm)

Subsurface contamination measurements

A typical problem with radiological characterization of underground pipes is the possibility that pipes had leaked and contaminated the surrounding soil. An interesting application of innovative technologies to solve this problem is given in [6.18]. During operation of the Brookhaven Graphite Research Reactor, the below grade exhaust air ducts provided passage of the cooling air flowing through the graphite reactor pile to the exhaust stack. Following reactor shutdown, the ducts collected water and were a potential source of contamination to the soils beneath the facility. Thorough subsurface soil characterization was required to determine the location and extent of potential contamination to facilitate appropriate remedial action planning for the below grade facilities and surrounding soils. The innovative technologies included the use of a small Geoprobe to install sampling ports in the soil and beneath the buildings. Components included gas tracers to define the leak pathways, 3-D visualization tools to investigate the data, the In-Situ Object Counting System (ISOCS) for rapid field gamma surveys of soil samples, and BetaScint, for beta surveying of soil samples.