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The report 'Probability of Defect Detection of Posiva's electron beam weld' describes POD curves of four NDT methods radiographic testing, ultrasonic testing, eddy current testing and visual testing. POD-curves are based on the artificial defects in reference blocks. The results are devoted to the demonstration of suitability of the methods for EB weld testing. Report describes methodology and procedure applied by BAM.
Report creates a link from the assessment of the reliability and inspection performance to the risk assessment process of the canister final disposal project. Report ensures the confirmation of the basic quality of the NDT methods and their capability to describe the quality of the EB-weld.
The probability of detection curves are determined based on the MIL-1823 standard and it's reliability guidelines. The MIL-1823 standard was developed for the determination of integrity of gas turbine engines for the US military.
In the POD-process there are determined as a key parameter for the defect detectability the a90/95 magnitudes, i.e. the size measure a of the defect, for which the lower 95 % confidence band crosses the 90 % POD level. By this way can be confirmed that defects with a size of a90/95 will be detected with 90 % probability. In case the experiment will be repeated 5 % might fall outside this confidence limit.
This report describes the progress in understanding and describing the detectability of the ultrasonic inspection technique developed by SKB for the inspection of copper tubes used for the final disposal of the Swedish spent nuclear fuel. In former research activities dedicated to the different parts of the canister, the probability of detection (POD) evaluation technique, as developed for thin aircraft components, was further developed for the application on complex hick-walled components. The result of this development was the introduction of a “multi-parameter” POD framework. In contrast to taking only the defect size into consideration (as for aircraft components) additional influencing factors, relevant for thick components, such as depth position, orientation and part geometry, were included. Furthermore, the variation of ultrasonic attenuation due to various material properties was included.
This report describes the methodology of the reliability investigation performed on the ultrasonic
phased array NDT system, developed by SKB in collaboration with Posiva, for inspection of the
canisters for permanent storage of nuclear spent fuel.
The canister is composed of a cast iron insert surrounded by a copper shell. The shell is composed
of the tube and the lid/base which are welded to the tube after the fuel has been place, in the
tube. The manufacturing process of the canister parts and the welding process are described.
Possible defects, which might arise in the canister components during the manufacturing
or in the weld during the welding, are indentified.
The number of real defects in manufactured components have been limited. Therefore the reliability
of the NDT system has been determined using a number of test objects with artifical defects.
The reliability analysis is based on the signal response analysis. The conventional signal response
analysis is adopted and further developed before applied on the modern ultrasonic phased-array
NDT system. The concept of multi-parameter a, where the response of the NDT system is dependent
on more than just one parameter, is introduced. The weakness of use of the peak signal response
in the analysis is demonstrated and integration of the amplitudes in the C-scan is proposed as an
alternative. The calculation of the volume POD, when the part is inspected with more configurations,
is also presented. The reliability analysis is supported by the ultrasonic simulation based on the
point source synthesis method.