EPRI NDE CENTRE HELPS US UTILITIES WITH RULE CHANGE
At the end of 1997 the US Nuclear Regulatory Commission (NRC) focused attention on the issue of qualification of inspection procedures, equipment, and personnel when it published a proposed rulemaking that would adopt Appendix VIII to ASME Section XI into US federal law.
Appendix VIII requires demonstration of performance of ultrasonic inspection procedures and personnel using realistic mock-ups containing defects that must be detected and correctly characterised. The proposed rule contains modifications to the ASME Code that would affect implementation by utilities. For example, one of the proposed modifications changes the requirements for the kinds of defects that can be used in qualification test pieces. EPRI and its member utilities are organising public responses to the proposed rule with the objective of minimising the economic impact of these modifications and other requirements of the rule.
Some years ago in response to the issuance of Appendix VIII, American utilities formed what is called the Performance Demonstration Initiative (PDI) to develop the mockups and to implement the requirements of the Appendix. This was well in advance of the rule change which is only now taking place and will not become law until January 1999 at the earliest.
EPRI provides technical and administrative support to PDI and as utilities in the US and other countries that use ASME Section XI are preparing to implement Appendix VIII, the NDE programme at the EPRI NDE Center, Charlotte, NC, provides the tools for success.
Qualification begins with a thorough evaluation of the procedure to ensure that it defines essential variables and provides step-by-step guidance for inspection personnel. Personnel are then presented with sequences of test specimens containing intentional defects of well known sizes and locations for examination. The intentional defects were designed to meet the technical requirements of the applicable codes and were produced to tightly controlled tolerances. Each defect was examined carefully to ensure that it produced realistic ultrasonic responses. Each qualification is closely monitored by expert staff who verify that the key decisions made by operators are as defined in the procedure and that all results are explained. This process provides high confidence that the results of the qualification are technically sound and greatly reduces the likelihood that acceptable results could be obtained by chance.
Complex geometrical components such as nozzles require an additional basis for effective qualification. Computer modelling is used to assess the essential parameters of the procedure such as the angle between the flaw plane and the beam axis. This misorientation angle is a key parameter for assessing the flaw detection capability of the procedure over its full application range. Without a tool such as modelling, assessment of performance would require a very extensive set of experimental trials to fully explore the capability of the procedure.
EPRI and phased-array
The performance demonstration efforts are just a part of EPRI’s NDE programme, which strives to increase the value of and lower the costs of inspections performed in member utility plants. The EPRI NDE Center has developed a comprehensive programme of R&D coupled closely with technology transfer and commercialisation efforts to ensure that proven technology is delivered into the hands of commercial service providers. The EPRI NDE programme encompasses all key plant components, including piping, pressure vessels, containment structures, heat exchangers, turbine/generators, bolting, and reactor internals.
Phased-array ultrasonics is the largest single component of the EPRI R&D programme. With this technology, ultrasonic beams can be rapidly generated, steered, and focused electronically, greatly increasing speed and capability relative to conventional fixed multiple probe technology. Along with the increased examination speed, improved examination coverage and inspection accuracy are likely. EPRI’s first target applications include piping, reactor internals, pressure vessels, and turbine-generator components. A “for the record” reactor internals inspection using phased-array is scheduled for March.
The immediate benefits of phased-array are reduced inspection costs, lower radiation exposure, and improved examination coverage in difficult access conditions. EPRI is developing and qualifying technologies in a broad international programme that includes close co-operation with commercial service providers to encourage adoption of this cost-saving technology.
MULTI-NATIONAL PROJECT PROMOTES phased-array
R/D Tech of Canada is heading a two year R&D project started in early 1997 which aims to improve the state-of-the-art of ultrasonic NDT in the nuclear power industry using phased-array technology. The project is sponsored by eight leading nuclear inspection companies, EPRI, and a major European nuclear utility. The countries represented in the project are France, Germany, Belgium, Sweden, Switzerland, Japan, the USA, and Canada.
R/D Tech has already applied phased-array technology to the inspection of the complex geometry of turbine disks in France. The method, jointly developed with SGS Qualitest, has allowed the accurate depth measurement of cracks in anti-rotation keys, a particularly difficult problem. This type of inspection has been routinely performed in France since 1996.
Another application of phased-array technology is being developed with Ontario Hydro. Here the goal is to perform the inspection of the turbine blade roots without removing the blade from the turbine disk, thereby dramatically decreasing the inspection time. A paper was presented on this subject at the 1997 EPRI steam turbine generator meeting and improvements to the technique will be discussed in a paper to be presented at the European Conference on NDT to be held in Copenhagen this May.
R/D Tech expects that phased-array ultrasonics will play an increasing role in the NDT of power plant components, including pipe welds, reactor pressure vessels welds, nozzle welds, turbine shafts and turbine disks.
The company points out that phased-array, which provides electronically adjustable ultrasound beam angle and focal distance, is widely used in the medical field. It can greatly reduce the size of probe arrays in multi-transducer applications, allows the inspection of components with very complex geometry and also greatly reduces inspection time.
TECNATOM TO SUPPLY EC LABORATORY
Tecnatom of Spain has recently been awarded a contract to supply a complete system for ultrasonic inspection to the Institute for Advanced Materials of the European Commission Joint Research Center in Petten.
The system will be used in the development of inspection techniques including the harmonisation of certification/validation methodology for non-destructive testing in the European Union countries.
The supply includes an ultrasonic multichannel data acquisition system (SUMIAD), a data evaluation system (MASERA), and a mechanical manipulator (PIPE), with its computerised controller (SIROCO).
MAKING VISUAL INSPECTION MORE INTELLIGENT
R Brooks Associates has been awarded a $250 000 cost sharing contract by the New York State Energy Research & Development Authority (NYSERDA) for design and development of an Intelligent Visual Inspection System (IVIS) for steam generators.
The system would be capable of quantifying the results of visual inspections. Brooks, in co-operation with the Rochester Institute of Technology Research Corp, expects during the 18 month project to develop and demonstrate equipment that will accurately measure sludge loading, crack size, and quatrefoil blockage. Brooks will also use the system to predict sludge accumulation rates, thereby assisting utilities in formulating proactive approaches to steam generator maintenance.
LOOKING INTO THE PERIPHERAL LANE
A remote visual inspection device has been developed by SRA SAVAC of France to obtain visual data from the peripheral tube lane of steam generators. Such visual inspection is of vital importance in assessing the condition of a steam generator. It is performed after sludge lancing to check the effectiveness of the process.
Compared with existing devices, SRA SAVAC’s new machine is very light and quick to set up, reducing doses to operators. It enables sludge deposits and foreign objects to be detected in the peripheral tube lane, in the three first intertubes over the whole periphery and also between tube bundle and wrapper.
Inserted through an existing handhole, the self propelled robot can inspect the peripheral tube lane quarter by quarter.
Once the robot is installed, it can move over the tubesheet using four wheels coupled to two motors. The front camera tilts vertically over 180 degrees, inspecting from the tubesheet upwards. The rear camera rotates horizontally over 270 degrees, to inspect from shell to in-bundle.
Colour visual inspection results are recorded on videotapes. The system is remotely controlled from a computerised operation station that can be located 15 m away from the steam generators, in a low dose area. The equipment is designed to operate on Framatome Model 51 and 47/22 steam generators in 900 MWe units as well as Framatome Model 68/19 steam generators in 1300 MWe units.
The system is designed to assure retrievability under all conditions and is currently being qualified by EDF.