Temper bead welding (TBW) is one effective repair welding method for the large-scale nuclear power plants instead of post weld heat treatment (PWHT). Consistent Layer (CSL) technique is the theoretically most authoritative method among the five temper bead welding techniques. For TBW, toughness is the key criteria to evaluate the tempering effect. A neural network-based method for toughness prediction in heat affected zone (HAZ) of low-alloy steel has been investigated to evaluate the tempering effect...
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Prediction of Toughness in HAZ produced by Temper Bead Welding of Consistent Layer Technique

Japanese code for ultrasonic testing in-service inspection, named JEAC 4207, allows inspection through weld metal, in case that some factors, such as weld crown or other structures, disturb scanning. The applicability of through weld metal inspection had been reported with BWR piping. This paper will be technical basis of applicability of through weld metal inspection for PWR piping, which is thicker and has factor hardens inspection. The data successfully shows the capability for detection and sizing...
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Result of UT Verification Test for Stainless Steel through Weld Deposit (2nd Report)

In 1999, NEL developed the transmit-receive type ECT array probe for steam generator (SG) tubing, called “X-probe”, in cooperation with foreign firms. Recently NEL has developed the advanced ECT array probe, “Smart Array Probe”, characterized with a significantly improved resolution for circumferential cracks. The doubled channels in the circumferential mode have greatly improved the circumferential resolution of Smart Array Probe. With all the circumferential mode channels on the same circle, there i...
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Development and Field Practical Performance of Smart Array Probe

In Japan, the preventive maintenance task of the 600 series nickel basis alloy weld of the reactor vessel (RV) and the steam generator (S/G) safe end weld are pushed forward sequentially, and a defect sizing using the ultrasonic testing (UT) from the inside of the safe end is carried out when the defect was dete cted by surface inspection prior to the work. Some defects are recognized on the S/G safe end and the R/V safe end in Japan, and these defects have occurred in the axial direction of the safe end w...
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Development of Advanced Defect Sizing Technique Using Ultrasonic Testing for Nozzle Welding

In this study, a predictive simulation model coupling weld bead formation and thermal conduction was developed for construction of the method of predicting or evaluating the temperature distribution during temper bead welding. Welding parameters used in the analysis were estimated from experimental welding conditions based on the thermal conduction theory and numerical simulations of previous works. The simulation results were compared with the experimental results under the same welding conditions to ...
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Predictive Simulation Model of Bead Shape and Temperature Distribution during Temper Bead Welding

Recently, preventive maintenance tasks for welding of safe-end nozzles of reactor vessels and steam generators of PWRs in Japan had been carried out sequentially. Before the maintenance tasks, inspection services were carried out and several crack indications were found by eddy current testing (ECT). These indications were found in the welding which made b y 600 series nickel base alloy and evaluated as stress corrosion cracks which were oriented to the axial direction of the nozzle. Then investigations to...
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Development of the advanced phased array UT technique for accurate sizing of cracks in the nozzlewelding

Japanese government has recently addressed a policy to increase capacity factor of existing nuclear PPs to achieve the goal to decrease the emission of CO2. Numerous preventive measures have taken in nuclear power plants to minimize the risk of unexpected long shutdown. Newly developed mitigation measures or repair methods need to be qualified to satisfy regulatory standards, before it is implemented to nuclear power plants. The qualification process needs to comply regulatory standards though it may consum...
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R/D and implement of temper bead welding as newly developed maintenance technique in nuclear power plant

Abstract For the last couple of years, issue of defects in Alloy 600 weld lowered the capacity factor of nuclear power plants. To apply newly developed repair technique, like temper-bead welding that has not been prescribed in technical standards, it is necessary to evaluate its technical applicability to the requirement. In the previous cases, this process has been completed by issuance of no action letter for specific area and condition, utilizing implementation process, such as confirm testing by J...
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Study on implementing newly developed repair welding technique within a limited time frame for nuclear power plant

Primary water stress corrosion cracking (PWSCC) has been concerned in Bottom Mounted Instrumentation (BMI) of Reactor Pressure Vessel with alloy 600 for the last two decades. Generally the Rules on Fitness for Service for Nuclear Power Plants of JSME are applied for flaw evaluation after detecting defects in the operating nuclear plants. However in the case that a crack is detected in a complex configuration area such as J-groove weld, it is needed to perform a fracture mechanics approach using FE ana...
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Approach for Improvement of maintenance technology of BMI

In order to reutilize nuclear power generation and maintain their presence, it is important to take actions based on assumptions beyond "safety myth". For example, in the field of SCC, long term reliability may be further assured based on evaluation under severer condition than the usual operating environment. Since such severe conditions cannot be reasonably simulated by the experiment in the laboratory, it is effective to utilize numerical simulation as reported in the previous paper. This paper rep...
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Development of an evaluation method utilizing numerical simulation to assure long-term reliability of residual stress improvement by surface treatment