Corrosion Resistant Cladding by YAG Laser Welding in Underwater Environment

2002 ◽  
Author(s):  
Tsutomu Kochi ◽  
Toshio Kojima ◽  
Suemi Hirata ◽  
Ichiro Morita ◽  
Katsura Ohwaki
Keyword(s):  
Laser Welding ◽  
Water Level ◽  
Nuclear Power ◽  
Power Plants ◽  
Drainage Water ◽  
Yag Laser ◽  
Corrosion Resistant ◽  
Underwater Environment ◽  
Nickel Base ◽  
Cladding Layers

It is known that stress-corrosion cracking (SCC) will occur in nickel-base alloys used in Reactor Pressure Vessel (RPV) and Internals of nuclear power plants. A SCC sensitivity has been evaluated by IHI in each part of RPV and Internals. There are several water level instrumentation nozzles installed in domestic BWR RPV. In water level instrumentation nozzles, 182 type nickel-base alloys were used for the welding joint to RPV. It is estimated the SCC potential is high in this joint because of a higher residual stress than the yield strength (about 400MPa). This report will describe a preventive maintenance method to these nozzles Heat Affected Zone (HAZ) and welds by a corrosion resistant cladding (CRC) by YAG Laser in underwater environment (without draining a reactor water). There are many kinds of countermeasures for SCC, for example, Induction Heating Stress Improvement (IHSI), Mechanical Stress Improvement Process (MSIP) and so on. A YAG laser CRC is one of them. In this technology a laser beam is used for heat source and irradiated through an optical fiber to a base metal and SCC resistant material is used for welding wires. After cladding the HAZ and welds are coated by the corrosion resistant materials so their surfaces are improved. A CRC by gas tungsten arc welding (GTAW) in an airenvironment had been developed and already applied to a couple of operating plants (16 Nozzles). This method was of course good but it spent much time to perform because of an installation of some water-proof working boxes to make a TIG-weldability environment. CRC by YAG laser welding in underwater environment has superior features comparing to this conventional TIG method as follows. At the viewpoint of underwater environment, (1) an outage term reduction (no drainage water). (2) a radioactive exposure dose reduction for personnel. At that of YAG laser welding, (1) A narrower HAZ. (2) A smaller distortion. (3) A few cladding layers. A YAG laser CRC test in underwater environment was carried out in the different welding position, horizontal, vertical upward and downward. The soundness of cladding layers (about 3 mm) is confirmed in visual and penetration test, and cross section observation. In the application to the actual plants, it is preferable to reduce the start and end point numbers of beads with which a defect is easy to cause. Therefore a special welding equipment for a YAG laser CRC that could weld continuously was developed.

scholarly journals A hybrid PSO-PID approach for trajectory tracking application of a liquid level control process

2015 ◽  
Vol 5 (2) ◽  
pp. 63-73 ◽  
Author(s):  
Turker Tekin Erguzel
Keyword(s):  
Water Level ◽  
Pid Controller ◽  
Nuclear Power ◽  
Power Plants ◽  
Control Process ◽  
Nonlinear Process ◽  
Reference Trajectory ◽  
Proportional Integral Derivative ◽  
Level Control ◽  
Steam Generators

Water level control is a crucial step for steam generators (SG) which are widely used to control the temperature of nuclear power plants. The control process is therefore a challenging task to improve the performance of water level control system. The performance assessment is another consideration to underline. In this paper, in order to get better control of water level, the nonlinear process was first expressed in terms of a transfer function (TF), a proportional-integral-derivative (PID) controller was then attached to the model. The parameters of the PID controller was finally optimized using particle swarm optimization (PSO). Simulation results indicate that the proposed approach can make an effective tracking of a given level set or reference trajectory.

Research of Technology for Repair of Heat Exchangers of Nuclear Power Plants by Laser Welding

2021 ◽  
Vol 313 ◽  
pp. 94-105
Author(s):  
A. Bernatskyi ◽  
V. Sydorets ◽  
O.M. Berdnikova ◽  
I. Krivtsun ◽  
O. Kushnarova
Keyword(s):  
Service Life ◽  
Laser Welding ◽  
Welded Joints ◽  
Heat Exchangers ◽  
Nuclear Power ◽  
Power Plants ◽  
Nuclear Power Plants ◽  
Mechanical Test ◽  
Austenitic Steels ◽  
Depth Of Penetration

Extending the lifetime of energy facilities is extremely important today. This is especially true of nuclear power plants, the closure (or modernization) of which poses enormous financial and environmental problems. High-quality repair of reactors can significantly extend their service life. One of the critical parts is heat exchangers, the tubes of which quite often fail. Sealing, as a type of repair of heat exchanger tubes by the plugs, is promising provided that the joint quality is high. Practical experience in the use of welding to solve this problem has shown the need to search technological solutions associated with increasing the depth of penetration and reducing the area of thermal effect. The aim of the work was to develop a highly efficient technology for repair and extension of service life of heat exchangers of nuclear power plants based on the results of studying the technological features of laser welding of joints of dissimilar austenitic steels AISI 321 and AISI 316Ti in the vertical spatial position. Based on the results of the analysis of mechanical test data, visual and radiographic control, impermeability tests and metallographic studies of welded joints, the appropriate modes of laser welding of plugs have been determined. The principal causes of defects during laser welding of annular welded joints of dissimilar stainless steels are determined and techniques for their elimination and prevention of their formation are proposed. Based on the results of the research, technological recommendations for laser welding of plugs in the heat exchange tube of the collector are formulated, which significantly improves the technology of repair of steam generators of nuclear power plants and extends the service life of reactors.

Numerical Analysis of Unsteady Flow Field in the RWT for the Prediction of the Potential for Air Ingression Into the ECC Supply Lines During the SBLOCA at the KSNPs

2007 ◽  
Author(s):  
Jong Chull Jo ◽  
Seon Oh Yu
Keyword(s):  
Flow Field ◽  
Unsteady Flow ◽  
Water Level ◽  
Nuclear Power ◽  
Power Plants ◽  
Nuclear Power Plants ◽  
Vortex Flow ◽  
Air Entrainment ◽  
Water Tank ◽  
Outlet Valve

This paper addresses the three-dimensional analysis of unsteady flow in the RWT (Refueling Water Tank) for the prediction of the potential for air ingression into the ECC (Emergency Core Cooling) pump during the SBLOCA (Small Break Loss Of Coolant Accident) at KSNPs (Korean Standard Nuclear Power plants). Upon the receipt of RAS (Recirculation Actuation Signal) by the occurrence of SBLOCA, the RWT outlet valve is designed to be isolated manually. At the nuclear power plants without the provision of automatic isolation operation of the valve on the downstream of the RWT line, the refueling water begins to discharge from the RWT, which may result in forming and developing the vortex flow in the RWT, under the condition of the minimum pressure of containment and minimum water level of containment recirculation sump during the phase of RAS. Due to the vortex flow, when the water level is below the critical height, a dip starts to develop, causing air ingression before the refueling water drains fully. Hence it can be surmised that there is a possibility of ECC pump failure due to air ingression into the ECC supply line even before the RWT is fully drained. Therefore, in this work, when the RAS is actuated followed by the SBLOCA occurrence, a quantitative evaluation for the maximum limiting allowable time for the manual closing of RWT outlet valve is carried out to eliminate the possibility of air ingression into the ECC pump from the RWT. To do this, the unsteady flow field in the RWT including the drain pit with the connected discharge piping in the process of SBLOCA is analyzed using a CFD (Computational Fluid Dynamics) code. In addition, the transient flow behavior accompanying air entrainment resulting from the dip formation due to vortex flow at the upper part of RWT is examined and the applicable limiting time of the isolation valve closing for preventing air ingression is assessed.

scholarly journals Application of Fuzzy Control in Ocean Nuclear Power Plant Control

2021 ◽  
Vol 2076 (1) ◽  
pp. 012010
Author(s):  
Chunhui Dai ◽  
Ping Song ◽  
Lie Chen ◽  
Xingsheng Lao ◽  
Kelong Zhang
Keyword(s):  
Mathematical Model ◽  
Power Plant ◽  
Nuclear Power Plant ◽  
Fuzzy Control ◽  
Water Level ◽  
Nuclear Power ◽  
Power Plants ◽  
Nuclear Power Plants ◽  
Fuzzy Controller ◽  
Good Control

Abstract In marine nuclear power plants based on molten salt reactors, the complexity of core nuclear reactions, fuel fluidity, and the “false” water level characteristics of the steam generator water level make it unrealistic to establish an accurate mathematical model, so it is difficult to implement traditional PID control methods. This has increased substantially. The fuzzy control has a good solution to this feature. Therefore, combined with the fuzzy control that does not depend on the precise mathematical model of the controlled object, the fuzzy controller of the nuclear power plant is designed, and the control research of the core power is obtained respectively through MATLAB/Simulink simulation. It shows that the designed fuzzy controller can achieve good control of nuclear power plants.

Remote-Controlled Inspection Robot for Nuclear Facilities in Underwater Environment

2009 ◽  
Author(s):  
Harunobu Okihana ◽  
Keiji Iwata ◽  
Yasuhiro Miwa
Keyword(s):  
Radiation Exposure ◽  
Nuclear Power ◽  
Power Plants ◽  
Ccd Camera ◽  
High Dose ◽  
Nuclear Facilities ◽  
Original Design ◽  
Inspection Robot ◽  
Manual Inspection ◽  
Underwater Environment

A remote-controlled inspection robot for nuclear facilities in underwater environment was developed. The Array system of Eddy Current Testing (Array-ECT) is installed on the existing robot that consists of the driving unit and the inspection unit with enlarged Charge-Coupled Device (CCD) camera. It can swim in the tank, crawl on the inner surface of the tank, stay on the inspection area and by its two devices, Array-ECT and enlarged CCD camera, start inspection. Array-ECT can record the color contour image, and also can display oscillograph. This technology had been developed in order to reduce worker’s radiation exposure and improve inspection-ability in nuclear power plants for some Radioactive Waste (RW) tanks. With conventional manual inspection, RW tanks must be examined with the sequence of (a) full drainage and decontamination, (b) scaffolding set-up with workers under high dose, and (c) manual inspection. As such, the inspection is time consuming and workers should have high radiation exposure. With the original robot that has only enlarged CCD camera, inspection can be performed without tank drainage and with minimum worker’s radiation exposure. However, it needs experienced inspector for interpretation of visual examination using enlarged CCD camera. Newly developed robot with Array-ECT and enlarged CCD camera can achieve the same performance using the original robot and an experienced inspector for visual inspection using enlarged CCD camera. The new feature added to the original design (i.e. Array-ECT) eliminates the need for an experienced inspector.

Study on Flushing Phenomena by Microwave Heating

2013 ◽  
Author(s):  
Tatsunori Yamaki ◽  
Akiko Kaneko ◽  
Yutaka Abe ◽  
Tomoomi Segawa ◽  
Koichi Kawaguchi ◽  
...  
Keyword(s):  
Water Level ◽  
Microwave Heating ◽  
Nuclear Fuel ◽  
Nuclear Power ◽  
Power Plants ◽  
Nuclear Power Plants ◽  
Nitrate Solution ◽  
Vessel Diameter ◽  
Initial Water ◽  
Liquid Superheat

Recently, the number of nuclear power plants has been increased in many countries. In contrast, uranium fuels used in nuclear power plants are exhaustible resources. Therefore, it is required to exploit uranium resources effectively, and reprocessing of spent fuel is indispensable. To use recovered uranium and plutonium as raw material of nuclear fuel, reprocessing solution (uranium and plutonium mixed nitrate solution) of the spent nuclear fuel is converted to uranium and plutonium mixed oxide (MOX) powder. Microwave heating direct denitration method (MH method) is one of such methods to convert nitrate solution to MOX powder. The cylindrical denitration vessel can be expected to realize high-speed and high-capacity processing against traditional shallow vessel. However, flushing and overflow phenomena of solution have been confirmed in cylindrical vessel. Thus, the safety and the optimization of the vessel shape during microwave heating. In the present study, the purpose of this paper is to clarify generation conditions and generation mechanism of flushing phenomena that is not fully understood. In experiment, flushing phenomena was observed and the liquid temperature was measured using microwave heating device. The main parameters are the vessel diameter, initial water level and the magnetron power. There was tendency of flushing in the case of short vessel diameter and high initial water level when magnetron power was constant. There was also tendency of flushing in the case of large magnetron power when vessel diameter and initial water level was constant. From visualization, it was clarified that generation of singular bubble triggers flushing. If flushing occurs, the liquid is blown up at a burst, and the vessel become almost empty. From temperature measurement results, it was clarified that the liquid had over 10 °C superheat just before flushing. Therefore, it was suggested that the liquid superheat affected flushing significantly. Generation conditions of flushing are different with the vessel diameter, initial water level and the magnetron power because it is considered that these characteristics have influence on the liquid superheat.

scholarly journals Risk Assessment of Extreme Weather Conditions for Nuclear Power Plants at Tidal Rivers

2010 ◽  
Vol 13 (1) ◽  
pp. 41-52 ◽  
Author(s):  
Heinz-Peter Berg ◽  
Matias Krauß
Keyword(s):  
Risk Assessment ◽  
Power Plant ◽  
Nuclear Power Plant ◽  
Water Level ◽  
Nuclear Power ◽  
Power Plants ◽  
Nuclear Power Plants ◽  
Weather Conditions ◽  
Extreme Weather ◽  
Tidal Rivers

Risk Assessment of Extreme Weather Conditions for Nuclear Power Plants at Tidal RiversThe effects of flooding on a nuclear power plant site may have a major bearing on the safety of the plant and may result in a common cause failure for safety related systems, such as the emergency power supply systems. For river sites with tidal influences, an extreme flood event - tide combined with storm water level set-up - must be assumed. A storm-tide must be covered with an exceeding frequency of 10-4/a. However, the risk assessment regarding the availability of systems and components of a nuclear power plant also includes the situation of extreme low water level of rivers, i. e. below the minimum water level necessary for the supply of the nuclear power plants with cooling water.

Development of Underwater Laser Cladding and Underwater Laser Seal Welding Techniques for Reactor Components (III)

2008 ◽  
Author(s):  
Masataka Tamura ◽  
Yoshinobu Makino ◽  
Takehisa Hino ◽  
Shohei Kawano ◽  
Wataru Kouno ◽  
...  
Keyword(s):  
Laser Welding ◽  
Laser Cladding ◽  
Stress Corrosion Cracking ◽  
Nuclear Power ◽  
Power Plants ◽  
Water Environment ◽  
High Exposure ◽  
Maintenance And Repair ◽  
Underwater Laser ◽  
Repair Techniques

Recently, stress corrosion cracking (SCC) has been observed at aged components of nuclear power plants under water environment and high exposure of radiation. Toshiba has been developing both an underwater laser welding directly onto surface of the aged components as maintenance and repair techniques. This paper reports underwater laser cladding and seal welding using INCONEL 52/52M.

lnvestigation of β-Emission Methods of Monitoring Coolant Water Level in Nuclear Power Plants

Atomic Energy ◽  
2017 ◽  
Vol 122 (3) ◽  
pp. 207-212
Author(s):  
S. I. Aleksandrov ◽  
A. A. Bol’shov ◽  
A. V. Kornienko ◽  
I. V Novikov ◽  
V. V. Postnikov ◽  
...  
Keyword(s):  
Water Level ◽  
Nuclear Power ◽  
Power Plants ◽  
Nuclear Power Plants ◽  
Coolant Water
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