Nuclear Plant Maintenance Research Articles

A Study on the Problem and Improvement of Law System for Safety and Maintenance of Nuclear Plant

A Study on the Problem and Improvement of Law System for Safety and Maintenance of Nuclear Plant

Effect of Boric Acid Concentration on Viscosity of Slag and Property of Weld Metal Obtained from Underwater Wet Welding

Underwater wet welding is a crucial repair and maintenance technology for nuclear plant. A boric acid environment raises a new challenge for the underwater welding maintenance of nuclear plant. This paper places emphasis on studying the influence of a boric acid environment in nuclear plant on the underwater welding process. Several groups of underwater wet welding experiments have been conducted in boric acid aqueous solution with different concentration (0-35000 ppm). The viscosity of the welding slag and the mechanical properties of welds, such as the hardness, strength, and elongation, have been studied. The results show that with increasing boric acid concentration, the viscosity of the slag decreases first and then increases at a lower temperature (less than 1441 °C). However, when the temperature is above 1480 °C, the differences between the viscosity measurements become less pronounced, and the viscosity tends to a constant value. The hardness and ductility of the joints can be enhanced significantly, and the maximum strength of the weld metal can be reached at 2300 ppm.

Reaction forces identification of a quadruped robot with parallel-serial leg structure

Interactions between feet and environment influence the stability and mobility of legged robot. This paper proposes a model to indirectly identify 3 degrees of freedom feet reaction forces for a quadruped robot with parallel-serial legs. The research platform is called Baby-Elephant: a heavy-duty four-legged robot designed for nuclear plant maintenance and disaster relief purposes. Each leg has three hydraulic actuators. With the pressure data from pump and hydraulic actuators, a double-chamber model with experimental derived friction is used to obtain the actuated force. The reaction forces model, including joint and foot forces, is simplified into an explicit function. Comparison between CAD simulation and analytical results shows the effectiveness of the model. A walking experiment with load cells proves the model is validate in practical application. The proposed model is used to identify the foot contact phase and the zero momentum point during crawling gait walking.

J032033 流体温度変動による配管熱疲労に関する研究 : 配管熱疲労に関する等価応力振幅を用いた信頼性評価手法([J032-03]エネルギープラント安全に向けた構造/熱流体/材料の達成問題(3))

This paper deals with the high cycle thermal fatigue phenomenon at a T-junction. The case of the phenomenon is a turbulent mixing at a T-junction, where hot and cold temperature fluids are mixed, in a plant piping system. The current guideline for high cycle thermal fatigue at pipes published by the Japan Society of Mechanical Engineers does not provide any procedure to measure actual safety margins, although both design and maintenance of nuclear plants need quantification of safety margins. Therefore, this paper proposes a new reliability assessment method for thermal fatigue in piping which considers loading and strength uncertainties to quantify safety margin. Since the procedure of the method should be concise for practical use, the proposed method uses the new concept "equivalent stress amplitude" which makes the complicated loading easy to deal with. Due to its conciseness and low calculation cost, the proposed method can contribute to introducing reliability assessment to the guideline for thermal fatigue evaluation.

HAZMAP: A REMOTE DIGITAL MEASUREMENT SYSTEM FOR WORK IN HAZARDOUS ENVIRONMENTS

AbstractIn a continuing drive to reduce the radiation exposure of nuclear workers, many routine aspects of nuclear plant maintenance and refurbishment are increasingly undertaken by robotic or remote handling tools. Accurate “as built” documentation of plant records is vital to the successful planning and execution of such operations since an unexpected obstruction or undocumented site modification may result in a costly disruption or even failure of the intervention. In recognition of the importance of such documentation, a recent European Community† sponsored project has been directed towards the development of techniques for cost effective survey and modelling of such plant. This paper will detail the rationale behind the design of such a system and will describe typical results from a number of pilot projects.

Transportation of Shippingport Reactor Pressure Vessel

The Shippingport Atomic Power Station in western Pennsylvania is the first nuclear electric generating station to be decommissioned with the goal of restoring the site to a radiologically clean condition acceptable for unrestricted use. In February, 1989, the 921 ton (836 metric tons) reactor pressure vessel/neutron‐shield tank assembly was hauled from a storage area on the plant site to a barge slip; loaded onto an oceangoing barge; shipped from Pennsylvania to Hanford, Washington; and hauled overland to a burial site on the U.S. Department of Energy's Hanford Reservation. This paper reviews the engineering requirements for the land and marine transportation operations. Engineering criteria for the hauling equipment and marine vessels, testing requirements, and operational methodology employed during the multimodal transportation are examined. Recommendations are made for future work of this nature performed as a part of nuclear plant maintenance and decommissioning projects, with particular emphasis pla...

Flow-Induced Vibration Analysis of Tube Bundles—A Proposed Section III Appendix N Nonmandatory Code

This paper presents guidelines for flow-induced vibration analysis of tubes and tube bundles such as those commonly encountered in steam generators, heat exchangers, condensers and nuclear fuel bundles. It was proposed as a nonmandatory code to be included in Section III Appendix N (N-1300 series) of the American Society of Mechanical Engineers (ASME) Boiler Code. In preparing this code, the authors tried to limit themselves to the better-defined flow excitation mechanisms—vortex-induced vibration, fluid-elastic instability and turbulence-induced vibration—and include only the more-established methods. References are, however, given for other methods whenever justified. This guideline covers only design analysis. A companion guideline on the testing and data analysis of heat exchanger tube banks was proposed as part of the ASME Code on Operations and Maintenance of Nuclear Plants. The latter is not included in this paper.

Reducing Nuclear Plant Cost and Enhancing Safety by Reliability Based Maintenance

The nuclear power industry and the government agencies recognize that the growing maturity of nuclear plants, as well as concern for plant outages, necessitates attention to surveillance and maintenance. This paper provides an overview of reliability based maintenance which is available to reduce (optimize) plant costs while maintaining or enhancing plant safety. Categorization of the various types of nuclear plant maintenance is provided as a foundation for maintenance program definition. A technique for maintenance feasibility review is presented, using a decision logic tree to assist the engineering and maintenance staff.