Degradation mechanism of check valves in nuclear power plants

A large amount of deposit was detected at a 6-in. check valve installed in a nuclear power plant. To identify the origin of the deposit, the chemical composition of the deposit was analyzed. In this paper, in order to find out the degradation mechanism of the 6-in. check valve, vibration and temperature monitoring of the check valve are carried out during plant heat up and standby conditions. And some degradation mechanisms of the check valve are investigated. Results show that the degradation was caused by valve chattering due to the acoustic resonance.     

核电站环境放射性监测

随着国家核电产业的发展,越来越多的核电厂将陆续建设,为了更好的保护环境、保护公众,判断核电厂对环境、对周围居民的影响,环境放射性监测是非常必要的。文章就核电厂环境放射性监测的目的,监测项目,监测方法等方面进行介绍。     

中美核电厂流出物监测与排放管理要求对比分析

对我国和美国核电厂流出物的监测和排放管理要求进行了对比分析,指出我国在法规标准方面需要进行修订和完善之处,提出参考借鉴美国的经验对我国核电厂流出物监测和排放管理要求进行规范的建议。     

An assessment of acoustic emission for nuclear pressure vessel monitoring

Recent research has greatly improved our understanding of the basic mechanisms of deformation and fracture that generate detectable acoustic emission signals in structural steels. A critical review of the application of acoustic emission (AE) to the fabrication, proof testing and in-service monitoring of nuclear pressure vessels is presented in the light of this improved understanding. The detectability of deformation and fracture processes in pressure vessel steels is discussed, and recommendations made for improving source location accuracy and the development of quantitative source assessment techniques.

Published data suggest that AE can make an important contribution to weld fabrication monitoring, and to the detection of defects in lower toughness materials during vessel proof testing. In high toughness materials, however, the signals generated during ductile crack growth may frequently be too weak for reliable detection. The feasibility of AE for continuous monitoring has not yet been adequately demonstrated because of high background noise levels and uncertainty about AE signal strengths from the defect growth processes that occur in service. In-service leak detection by AE shows considerable promise.

It is recommended that further tests are carried out with realistic defects, and under realistic conditions of loading (including thermal shock and fatigue) and of environment.     

On-line monitoring applications in nuclear power plants

The nuclear power industry is working to reduce generation costs by adopting condition-based maintenance strategies and automating testing activities. These developments have stimulated great interest in on-line monitoring (OLM) technologies and new diagnostic and prognostic methods to anticipate, identify, and resolve equipment and process problems and ensure plant safety, efficiency, and immunity to accidents. This paper provides examples of these technologies with particular emphasis on eight key OLM applications: detecting sensing-line blockages, testing the response time of pressure transmitters, monitoring the calibration of pressure transmitters on-line, cross-calibrating temperature sensors in situ, assessing equipment condition, performing predictive maintenance of reactor internals, monitoring fluid flow, and extending the life of neutron detectors. These applications are discussed in the following sections. Emphasis is placed on the principles of a core OLM method - noise analysis - and the technical requirements for an integrated OLM system are summarized.     

Acoustic emission surveillance for improving availability of nuclear power plants

An experimental study of advanced acoustic emission monitoring of BWR components is being performed at Philadelphia Electric Company's Peach Bottom Atomic Power Station. The study addresses the feasibility of using continuous acoustic emission monitoring for increasing availability of LWR power units. Here we present a summary of a “Valve Surveillance” program and we describe the installation and performance of AE instrumentation for the “Pipe Surveillance” program.     

Fatigue analysis for analytically overloaded piping components and valves in nuclear power plants

Lately, in connection with life extension aspects of power plants, an increasingly accurate determination of the lifetime of components in nuclear stations is being required. In order to assess reliably current fatigue levels in piping systems, variables such as pressure, temperature, and resultant force and moment transients as well as analytical methods which take into account the real operational history must be considered. This paper presents a method for analyzing the transient heat transfer between fluid and pipe wall in order to investigate effects which until now have been assumed conservatively to be caused by a sudden jump in temperature. Further, an example is given showing that the K_e factor approach in current design codes for performing simplified elastic-plastic fatigue analyses is conservative.     

浅析中美核电站环境监测的通用要求

分析了中美两国核电站环境监测的管理机制及监测方案的通用技术要求,针对当前我国核电站环境监测现状提出了相关建议,旨在借鉴国外先进经验,促进我国核电站环境监测管理水平的提高。     

A sensitivity study of seismic structure-soil-structure interaction problems for nuclear power plants

A sensitivity study for the interaction effects of adjacent structures of nuclear power plants caused by horizontal seismic excitation has been performed. The key structural and soil parameters for linear and for nonlinear behaviour were varied within their applicable bandwidth. It has been shown that the interaction phenomena can contribute to the response of structures to such a large extent that it cannot be disregarded.     

A trilinear base-isolator concept for nuclear power plants

A friction limited base-isolation concept for moderate seismicity areas is presented. The idea of the concept is to combine frictional damping with base-isolation. The aim of the design effort is to develop a system whose stiffness and damping characteristics are selected to optimize the operational properties of the isolator device for the given site conditions, so that most favourable combination of acceleration and displacement responses of the system is achieved.     

A study on physicochemical properties of epoxy coating system for nuclear power plants

In this work, the thermal properties of epoxy coating system on the liner plate in the containment structure have been investigated by irradiation dose rate and design basis accident (DBA) conditions. Also, the effect of immersion in hot water on adhesion strengths of epoxy coating system has been studied. The glass transition temperature (T_g) and thermal stability of the epoxy coating system after DBA tests were measured by differential scanning calorimeter (DSC) and thermogravimetric analyser (TGA) analyses, respectively. Contact angle measurements were used to determine the effect of immersion on the surface energetics of epoxy coating system, including surface free energy and work of adhesion. Adhesion tests were also executed to evaluate the adhesion strength at interfaces between carbon steel plate and epoxy resins. As a result, the DBA test led to the improvement of the internal structure in cured epoxy systems, resulting in significantly increasing the thermal stability, as well as the T_g. Also, the immersion in hot water had a role in the post curing of epoxy resins and increased the mechanical interlocking of the network system, resulting in increasing the adhesion strengths of the epoxy coating system.     

我国核电厂流出物监测和辐射环境监测标准体系研究

为了适应我国核电快速发展新形势下环境辐射安全监督管理要求,并更好地指导核电厂的流出物监测和辐射环境监测工作的开展,需要对现有监测标准体系进行梳理和分析,推动标准体系的完善。本文分析了目前我国核电厂流出物监测和辐射环境监测标准的技术要求,提出了我国现行标准体系需要补充和修订的标准清单及修订和完善的建议,为加强和完善我国核电厂流出物监测和辐射环境监测的监督管理提供参考借鉴。     

Application of remote gamma spectrometry in automated systems for monitoring emissions from nuclear power plants

Methodological questions concerning the application of remote gamma spectrometry for radiation monitoring of air emissions from nuclear power plants and detecting trans-boundary transport of products of an accident are examined for the example of the development and experimental operation of the components of the Spaider data-acquisition system produced by the KonverSia company. A system of collimated γ spectrometers arranged along the monitoring contour at the site boundary of a nuclear power plant makes it possible to increase the accuracy of the computational predictions and to obtain and accumulate, during normal operation of a nuclear power plant, emissions data for radioactive inert gases and iodine in a continual monitoring regime. Translated from Atomnaya énergiya, Vol. 106, No. 1, pp. 35–42, January, 2009.