Development of ultrasonic guided wave inspection methodology for steam generator tubes of prototype fast breeder reactor

The present paper describes and clarifies the main difficulties arising in the 3D numerical simulations using finite element method of the remote field eddy current effect in magnetic steam generator tubes. The 2D axisymmetric and full 3D simulations are compared with experimental results from outer discontinuities in Monju fast breeder reactor steam generator tubes. Very good agreements were obtained between measurements and 2D simulations. The influences of several parameters are evaluated by 3D simulations: convergence error of the iterative matrix solutions, pattern of the mesh discretization, the boundary limit and finite element interpolation order. The computational cost of the remote field 3D model in Monju steam generator tubes and the numerical aspects of the 3D simulations are discussed in detail in the paper.

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Influence of thermal expansion bend and tubesheet geometry on guided wave inspection of steam generator tubes of a fast breeder reactor

Structural Health Monitoring ◽

10.1177/1475921720983520 ◽

2021 ◽

pp. 147592172098352

Author(s):

MM Narayanan ◽

V Arjun ◽

Anish Kumar

Keyword(s):

Thermal Expansion ◽

Steam Generator ◽

Mode Conversion ◽

Guided Wave ◽

Test Facility ◽

Discrete Wavelet ◽

Correlation Technique ◽

Element Analysis ◽

Flexural Mode ◽

Steam Generator Tubes

Periodic assessment of steam generator tubes of a sodium-cooled nuclear reactor is very crucial for smooth operation of steam generators. To examine the integrity, an in-bore magnetostrictive transducer capable of launching and receiving longitudinal ultrasonic guided waves (L(0,2) mode) from the inner diameter side of a steam generator tube developed in-house is used. Preliminary tests conducted on defective steam generator tubes with thermal expansion bends (three successive bends) of the mockup steam generator test facility yield a good sensitivity of 20% wall thickness deep flaw (0.46-mm deep and 1-mm wide half-circumferential groove) and the location accuracy of 10 mm. In order to remove high noise, wavelet-based denoising using discrete wavelet transform is used which improves the signal-to-noise ratio by 5–10 dB. In addition, cross-correlation technique is also used to denoise and unambiguously identify the defect echoes amid noise and multiple reflections between the defects. Furthermore, influence of the thermal expansion bend and tubesheet–spigot structure on L(0,2) mode is studied using the finite element analysis. It is observed that in the thermal expansion (multiple) bend, axisymmetric L(0,2) mode becomes non-axisymmetric (maximum and minimum amplitudes at extrados and intrados, respectively) and undergoes mode conversion to a weak flexural mode F(1,3). The results are validated experimentally. In the tubesheet–spigot structure, L(0,2) mode is found to have ∼10% reflection from spigot–tubesheet transitions, and it is seen to mode convert to bulk waves in the tubesheet. In conclusion, thicker tubesheets are found to be better from the perspective of inspection.

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Optimisation of helical geometry of inspection probe for steam generator tubes of the PFBR

Insight - Non-Destructive Testing and Condition Monitoring ◽

10.1784/insi.2021.63.10.585 ◽

2021 ◽

Vol 63 (10) ◽

pp. 585-591

Author(s):

G Perumalsamy ◽

P Visweswaran ◽

D Jagadishan ◽

S Joseph Winston ◽

S Murugan

Keyword(s):

Steam Generator ◽

Structural Design ◽

Smooth Transition ◽

Fast Breeder Reactor ◽

Groove Design ◽

Helical Groove ◽

Helical Geometry ◽

Steam Generator Tubes ◽

Helical Grooves ◽

Service Inspection

The steam generator (SG) tubes of the prototype fast breeder reactor (PFBR) located in Kalpakkam, India, need to be periodically inspected using the remote field eddy current (RFEC) technique. During the pre-service inspection of the SG tubes, it was found that the RFEC probes experienced frequent mechanical breakages. To avoid these failures, changes in the existing structural design of the RFEC probe were required. A helical groove design was proposed to obtain a smooth transition in the variation of stress across the probe during the inspection. It was difficult to calculate the flexural stiffness of the proposed helical geometry probe due to the varying cross-section along its length. In this paper, the smearing approach adopted to calculate the stiffness of the RFEC probe and the sensitivity analysis carried out to determine the optimal design of the probe are discussed. A probe was fabricated based on the helical groove design and tested to qualify its suitability for the SG inspection. The RFEC probe with helical grooves was employed for the pre-service inspection of the SG tubes of the PFBR. More than 200 tubes have been inspected using the proposed design and no mechanical failure of the probe has been observed.

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