Steven R. Doctor

Implementation of a Real-Time Ultrasonic Saft System for Inspection of Nuclear Reactor Components

In recent years, the Pacific Northwest Laboratory has been developing the Synthetic Aperture Focusing Technique for Ultrasonic Testing (SAFT-UT) for the U.S. Nuclear Regulatory Commission (NRC). The program objective has been to develop and validate the SAFT-UT technology for inservice inspection of nuclear power plant components. This technique utilizes the full three-dimensional SAFT algorithm computed in the time domain. The project has included development of a field-usable, real-time SAFT-UT imaging system, and also enhancement of the SAFT-UT algorithm to achieve real-time rates. This paper discusses techniques that have been employed to achieve these goals, including a description of the system, system performance data, and a discussion of a real-time SAFT processor peripheral device for performing the computer-intensive SAFT algorithm computations. An overall view of the SAFT-UT system itself will also be discussed.

A system for high-resolution, nondestructive, ultrasonic imaging of weld grains

The purpose of nondestructive evaluation is to detect degradation so that corrective action can be taken before the degradation challenges the structural integrity of an industrial system or one of its components. Accurate characterization is required to distinguish progressive degradation from benign material conditions. In nondestructive evaluation, characterization includes quantification and description of location, dimensions, shape, orientation, and composition of an indication of degradation. An imaging system that uses synthetic aperture focusing is one choice for detection and characterization of degradation in welded assemblies. In this paper, the ultrasonic imaging of the intended weld microstructure is reported. New technology invented for this purpose is described. This paper reviews how an ultrasonic imaging system that uses a synthetic lens can have a resolution that approaches the diffraction limit. A constrained solution to the coherent summation problem is presented for near real-time performance in high-resolution synthetic aperture focusing. Data are included to show that nondestructive, ultrasonic imaging of weld grains is practical.

Developing a generalized flaw distribution for reactor pressure vessels

The US Nuclear Regulatory Commission (NRC) is re-evaluating the guidance and criteria in the code of federal regulations as it relates to reactor vessel integrity, specifically pressurized thermal shock (PTS). Recent ultrasonic examination of considerable vessel material at Pacific Northwest National Laboratory (PNNL) and industry experiences with Yankee Rowe have provided the NRC with a better understanding of PTS issues. The re-evaluation of PTS will consider a risk-informed approach to the PTS rule and also provide important benefits for licensees considering license renewal. Pressurized thermal shock transients can lead to reactor vessel failure. These transients have occurred at operating reactors but, to date, they have not resulted in vessel failure. To properly determine the potential or probability for vessel failure from a PTS event, an accurate estimate of fabrication flaws is necessary. The characteristics of the fabrication flaw are inputs to fracture mechanics structural calculations that will determine the probability of vessel failure during a PTS event. Also, the results will indicate the sizes and locations of flaws that are most likely to cause failures. This information is also an integral input to the overall pressure vessel safety program. In order to obtain an accurate estimate of fabrication flaws to address PTS events for all classes of reactors, a generic flaw distribution must be developed. An expert judgment process will be used in conjunction with empirical data from PNNL, reactor pressure vessel studies and modeling (RR- PRODIGAL Code) in developing generalized flaw distributions. This paper will demonstrate the important relationship between reactor vessel integrity and flaw distributions in reactor pressure vessel material, discuss the PNNL work to date on developing flaw density and distributions for domestic RPVs, and describe the expert judgment process that was used to verify that a generalized flaw distribution can be properly developed and then assist in developing a generalized flaw distribution.

Preliminary Assessment of NDE Methods on Inspection of HDPE Butt Fusion Piping Joints for Lack of Fusion

Studies at the Pacific Northwest National Laboratory in Richland, Washington, are being conducted to evaluate nondestructive examination approaches for inspecting butt fusion joints in high density polyethylene (HDPE) pipe for lack of fusion (LOF). The work provides information to the United States Nuclear Regulatory Commission on the effectiveness and need for volumetric inspection techniques of HDPE butt fusion joints in Section III, Division 1, Class 3, buried piping systems in nuclear power plants. This paper describes results from preliminary assessments using ultrasonic nondestructive techniques and high-speed tensile impact testing for determining joint integrity. A series of butt joints were fabricated in 3408, 12-inch IPS DR-11 material by varying the fusion parameters in attempts to provide good joints and joints containing LOF. These butt joints were visually examined and volumetrically examined with time-of-flight diffraction (TOFD) and phased-array (PA) ultrasound. A limited subset of pipe joint material was destructively analyzed by either slicing through the joint and visually examining the surface or by employing a standard high-speed tensile impact test. Initial correlation of the fusion parameters, nondestructive, and destructive evaluations have shown that areas with gross LOF were detected with both TOFD and PA ultrasound and that the tensile impact test showed a brittle failure at the joint. There is still some ambiguity in results from the less obvious LOF conditions. Current work is targeted on assessing the sensitivity of the ultrasonic volumetric examinations and validating the results with a destructive analysis. It is expected that on-going and future work will lead to quantifying the ultrasonic responses in terms of joint integrity.Copyright

Proactive Management of Materials Degradation for nuclear power plant systems

There are approximately 440 operating reactors in the global nuclear power plant (NPP) fleet that have an average age greater than 20 years and design lives of 30 or 40 years. The United States is currently implementing license extensions of 20 years on many plants, and consideration is now being given to the concept of ldquolife-beyond-60,rdquo a further period of license extension from 60 to 80 years and potentially longer. In almost all countries with NPPs, authorities are looking at some form of license renewal program. There is a growing urgency as a number of plants face either approvals for license renewal or shut down, which will require deployment of new power plants. In support of NPP license renewal over the past decade, various national and international programs have been initiated. This paper reports part of the work performed in support of the U.S. Nuclear Regulatory Commissionpsilas (NRCpsilas) Proactive Management of Materials Degradation (PMMD) program. The paper concisely explains the basic principles of PMMD and its relationship to advanced diagnostics and prognostics and provides an assessment of some the technical gaps in PMMD and prognostics that need to be addressed.

Distributions of Fabrication Flaws in Reactor Pressure Vessels for Structural Integrity Evaluations

To reduce uncertainties in flaw-related inputs for probabilistic fracture mechanics (PFM) evaluations, the U.S. Nuclear Regulatory Commission (USNRC) has supported research at Pacific Northwest National Laboratory (PNNL) involving nondestructive and destructive examinations for fabrication flaws in reactor pressure vessel (RPV) material. Using these data, statistical distributions have been developed to characterize the flaws in regions of a RPV. The regions include the main seam welds, repair welds, base metal, and the cladding at the inner surface of the vessel. This paper summarizes the available data and describes the treatment of these data to estimate flaw densities, flaw depth distributions, and flaw aspect ratio distributions. The methodology has generated flaw-related inputs for PFM calculations that have been part of an effort to update pressurized thermal shock (PTS) regulations. Statistical treatments of uncertainties in the parameters of the flaw distribution functions are part of the inputs to the PFM calculations. The paper concludes with a presentation of some example input files that have supported evaluations by USNRC of the risk of vessel failures caused by PTS events.Copyright

Measurement Challenges Associated With Irradiated Reactor Components

Nuclear reactor components are known to degrade as reactors age. The reactor pressure vessel and the reactor internals are subjected to the highest radiation fields and thus, age faster. Some boiling water reactors are experiencing extensive cracking of the core shroud and some pressurized water reactors are experiencing a reduction in their fracture toughness. This paper provides background information on reactor pressure vessel materials, fabrication, and construction practices. It identifies some of the challenges that are associated with the nondestructive measurement of changes in material properties associated with these components. The inspection environment, surface conditions and designs are also discussed.

Development and validation of a real-time SAFT-UT system for inservice inspection of LWRs

Abstract A three-year program is in progress at the Pacific Northwest Laboratory to evolve the synthetic aperture focusing technique for ultrasonic testing (SAFT-UT) from the laboratory into the field for inspection of light water reactor components. This paper reports on the second years activities and highlights work on a time variable gain amplifier, laboratory work to develop tandem SAFT (TSAFT), attempts at reducing processing time, envelope detection techniques, and field trips to Dresden and Vermont Yankee nuclear power plants.

Development of Generic In-Service Inspection Priorities for Pressure Boundary Systems

This paper reports on, to provide a technical basis for improved in-service inspection (ISI) plans, Pacific Northwest Laboratory (PNL) developed and applied a method that uses results of probabilistic risk assessment to establish piping system ISI priorities. In the PNL program, the feasibility of generic ISI guidances is being conducted in two phases. Phase I identifies and prioritizes the systems most relevant to plant safety. These evaluations lead to the development of comprehensive ISI guidances for pressure boundary systems and components that take place in Phase II.

Integration of Nondestructive Examination Reliability and Fracture Mechanics

A multi-year program on the Integration of Nondestructive Examination and Fracture Mechanics (NDE/FM) has been funded by the U.S. Nuclear Regulatory Commission at the Pacific Northwest Laboratory. Many activities are being pursued under this program. This paper highlights some of the activities: input to the NRC Pipe Crack Task Group, an evaluation of manual ultrasonic testing of centrifugally cast stainless steel, interaction matrix, advanced UT technique evaluation, qualification document, evaluation of crack characterization techniques, international NDE reliability work, siamese imaging technique for imaging planar-type radial defects in reactor piping, fracture mechanics analysis for PTS-type flaws and piping reliability, and a position paper on piping ISI.