Development of a Technical Bases Document to Support the IAEA Regulations for Safe Transport of Radioactive Material

The International Atomic Energy Agency (IAEA) is entrusted by the Social and Economic Council of the United Nations with developing safety requirements for the safe transport of radioactive material. These requirements were first published as “Regulations for the Safe Transport of Radioactive Material”, Safety Series No. 6, 1961 edition (The Regulations). At the same time, the Director General of the IAEA indicated that these regulations would be revised at appropriate intervals, in consultation with Member States, and with input from other relevant organizations, as appropriate. After 50 years, over 10 revisions of the Regulations have been published. These revisions have been taking into account experiences in transport, newly identified issues, new technologies, best practices, the demand for safer transport, and harmonization. Problems, challenges, the demand for improvements, and the need to provide biennial inputs to international dangerous goods model transport regulations have driven the transport community and the IAEA in particular, to facilitate the regular review and revision of the Regulations. With the passage of time, the scientific and technical heritage of several decades of development in transport safety has begun to fade, and the requirement to capture valuable knowledge which needs to be preserved for future reference has become clear. In general, every requirement in the regulations was developed based on an appropriate technical basis. The technical basis exists in a decentralized manner in many Member States with mature nuclear programs. Easier access to the existing technical bases for the Regulations could lead to a more comprehensive understanding of the Regulations and could inform proposals for change that were previously considered but not accepted for various technical (or political) reasons. Knowledge capture and transfer can contribute to the development of and innovations in, transport safety. This paper provides an overview of the efforts to date that have been undertaken to develop a technical basis document for supporting the current transport regulations and will highlight the future plans for the development of this document.

Effect of Thickness Measurement Procedure on Stress Analysis of Pipes With Local Metal Loss

Fitness-For-Service (FFS) assessment using Finite Element Analysis (FEA) has been a problem in deciding yes-no which vary from evaluator to evaluator. The difference in decision making is caused by the degree of freedom in modeling a FEA model. In this study, burst pressures of pipes with local metal loss were calculated by using FEA in order to investigate the influence of thickness measurement intervals on FFS assessment. The analyzed pressures by FEA were verified by burst tests. A pipe specimen, which was thinned by corrosion under insulation in the actual plant, was used for the burst tests. Shape of the pipe specimen was measured by laser displacement meter and extracted at several types of interval. It is concluded that the analyzed pressures in various measurement intervals showed almost no difference, but were higher than the actual burst pressure of the specimen.

Efficient Probabilistic Calculation of a Thermal Transient on a 3D FE Model With Variable Heat Exchange Coefficient

Probabilistic calculations are often used to evaluate reliability in nuclear industry. One of their main difficulties is that failure probabilities are, in this domain, very low and therefore their computations are very long. The speed of the calculations depends on the probabilistic algorithm and the complexity of the physical problem (usually modeled by a finite element analysis). The optimization of the probabilistic algorithms benefits from a wealth of literature but the physical problem is often very simplified by a lot of approximations. This paper develops a methodology to avoid some approximations. The geometry of the problem is often brought back to a 1D or 2D problem. Here, large 3D mesh can still be used thanks to transfer functions. This requires the linearity of the problem and especially a constant heat transfer coefficient for a thermo-elastic analysis. This limitation has been removed. This article’s focus is on methodology but qualitative results of a probabilistic brittle fracture application of a reactor pressure vessel (RPV) in ferritic steel are given. Other kinds of analysis can benefit from similar methodology.

Latest Developments in Optimizing Reformer Tube Life Through Advanced Inspection and Remaining Life Assessment

Steam methane reformer tubes must withstand high temperature and pressures during operation and are made from centrifugally cast austenitic materials, typically HK-40, HP Modified, and Micro-Alloy materials. Since operating conditions can result in various forms of damage, the identification and quantification of damage is of vital importance if tube life is to be predicted accurately. This paper describes the recent developments in an integrated inspection system which uses multiple NDT techniques to provide a most comprehensive assessment of current tube condition. This system is coupled with a sophisticated remaining life assessment software model which predicts the remaining life of each tube in a furnace.

Nuclear Reactor Pressure Vessel Integrity Assessment: Enhancement Provided by 3D Modeling Flaw Stability Calculations

Structural integrity of the Reactor Pressure Vessel (RPV) is one of the main considerations regarding safety and lifetime of Nuclear Power Plants (NPP) since this component is considered as not reasonably replaceable. Brittle fracture risk associated with the embrittlement of RPV steel in irradiated areas is the main potential damage. In France, deterministic integrity assessment for RPV is based on the crack initiation stage. The stability of an under-clad postulated flaw in the core area is currently evaluated under a Pressurized Thermal Shock (PTS) through a fracture mechanics simplified method. One of the axes of EDF’s implemented strategy for NPP lifetime extension is the improvement of the deterministic approach with regards to the input data and methods so as to reduce conservatisms. In this context, 3D finite element elastic-plastic calculations with flaw modelling have been carried out recently in order to quantify the enhancement provided by a more realistic approach in the most severe events. The aim of this paper is to present both simplified and 3D modelling flaw stability evaluation methods and the results obtained by running a small break LOCA event.

Influence of a Variable in Time Heat Transfer Coefficient on Stresses in Model of Power Plant Components

The paper discusses the issue of modelling of strains and stresses resulting from heating and cooling processes of components in power plants. The main purpose of the work is to determine the mechanical behaviour of power plant components operating under mechanical and thermal loading. Finite element method (FEM) has been used to evaluate the temperature and stresses changes in components as a function of time. Temperature fields in the components of power plants are dependent, among parameters, on variable heat-transfer conditions between components and the fluid medium, which may change its condition, flowing inside them. For this reason, evaluation of the temperature field and the consequent stress fields requires the use of heat-transfer coefficients as time-dependent variables and techniques for determining appropriate values for these coefficients should be used. The methodology of combining computer modelling of the temperature fields with its measurements performed at selected points of the pipelines may be used in this case. The graphs of stress changes as a function of time have been determined for the chosen plant components. The influence of the heat transfer conditions on the temperature fields and mechanical behaviour of components have been discussed.

Study on the Relief Capacity and Safety Integrity of Multiple Relief Valves of Charge Gas Pipe in Ethylene-Cracking Plant

The shutdown of charge gas compressor in large-scale ethylene-cracking plant always involves emergency pressure relief of charge gas through multiple safety valves. The emergency relief capacity plays an important role on the safety of the overall plant. In this paper, by studying the difference between the configuration of the pressure relief system of two 1000 KTA ethylene-cracking plants (the inner diameters of the charge gas pipeline in both plants are 2m, while the number of same-sized relief valves are 28 and 19, respectively), the relief capacity of multiple relief valves is studied and compared with empirical calculation and numerical analysis. It is found that, due to the interruption of fluid flow when compressor is emergency shutdown, the upstream pressure of each relief valve increase steadily with the continuously make-up of the charge gas, but the difference between the inlet pressure of all relief valves can be neglected. With the increase of the upstream pressure, the opening of relief valves is determined mainly by the set pressure. In multiple valves pressure relief scenario, normally the downstream valves have greater relief capacity than those upstream valves if both relief valves have the same back pressure. Also, by analysis it is noted that the pressure relief capacities of multiple relief valves in both plants are sufficient. The minimum number of relief valves required for process safety is obtained. The maximum achievable Safety Integrity Level (SIL) of pressure relief system is determined by calculation of the reliability of the redundant relief valves. The analysis is used for determination of the SIL of the pressure relief system. The finding is also significant for determination of the required capacity of multiple relief valves.

Assessment of Weld Overlay Defects in a Hydrocracking Unit Reactor

Asset Performance Management is a key element of operational excellence. It refers to the management systems, strategies and activities aimed at maintaining the integrity of plant assets for their desired life. The safe operation of the assets is to be ensured at any cost. The objective of this paper is to offer one of the most critical assets in a refinery, namely the Hydrocracking Unit (HCU) reactor, as a case study addressing assessment of defects found in the weld overlay. The reactor was built in 1978 according to ASME Sec. VIII Div. 2 and has been in operation since then. The reactor is constructed of Chromium-Molybdenum (Cr-Mo) base material (SA 336 F21) with thickness of 266 mm and corrosion resistant stainless steel (TP-347 with thickness of 3.2 mm) weld overlay. The very high operating temperature and pressure of the reactor in hydrogen rich hydrocarbon service and the resulting thermal stress and material degradation caused disbonding and cracks in the stainless steel weld overlay. This paper will address the approach that was used to alleviate such type of defects. Also, various considerations that go into the assessment are discussed and recommendations are suggested.

Mitigating Failures in Ferritic-Austenitic Dissimilar Metal Joints in Petrochemical Industry

There are several failure mechanisms that might affect ferritic-austenitic dissimilar metal welds (DMWs) in petrochemical plants and refineries. Examples are cracking due to creep, stress corrosion cracking (SCC), sulphide SSC, thermal fatigue, brittle fracture, pitting corrosion, and hydrogen embrittlement. Of these, creep, SCC, and hydrogen embrittlement are perhaps of greater interest. Industry has many lessons learned; however, still experiences high consequence failures. This work describes the most common failure mechanisms in dissimilar ferritic-austenitic welds and summarizes a guidance to prepare welding procedures and reduce the likelihood of failures. This guidance is based on a literature review and industry experience. The metallurgical characteristics of the damage observed in both service and laboratory test samples indicate that creep rupture is the dominant failure mode for Dissimilar Metal Welds (DMW) in some high temperature service conditions. However, it has also been observed that temperature cycling contributes significantly to damage and can cause failure even when primary stress levels are relatively low. Therefore, a creep-fatigue assessment procedure is required as part of a remaining life calculation. API 579-1/ASME FFS-1 2007 Fitness-For-Service standard includes a compendium of consensus methods for reliable assessment of the structural integrity of equipment containing identified flaws or damage. Part 10 of API 579-1 includes a method for protection against failure from creep-fatigue. In the assessment of DMW, a creep-fatigue interaction equation is provided to evaluate damage caused by thermal mismatch, sustained primary stresses, and cyclic secondary loads [Ref.1]. Failures due to hydrogen embrittlement cracking (HEC) mechanisms are not uncommon and are also described in this paper [Ref. 2]. Finally, a case history of a DMW failure in a steam methane furnace, which is common in the petrochemical industry, is described and shown as an example of a failure mitigation approach.

Change Gasket: Overview and Recent Developments

The paper discusses the development of sealing technology within the organisation with particular emphasis on the novel gasket (NG) referred to as Change. The paper will introduce the concept and product; it will discuss the series of tests including comparison with four other gasket styles commonly used in the sealing industry. A brief summary of product development is under taken and sealing industry gasket constants and calculations are used to highlight the benefits of novel technology.