[en] Several institutions in Europe, including the Joint Research Centre (JRC) have capabilities to deal with several of the problems posed by the ageing of structural components and their structural integrity assessment. These institutions and the JRC have developed cooperative programmes now organised in Networks. They are utilities, engineering companies, R and D laboratories and Regulatory Bodies. Networks are organised and managed like the PISC programme: the Institute for Advanced Materials of JRC plays the role of Operating Agent and Manager of these Networks: ENIQ, AMES, NESC, each of them dealing with a specific aspect of fitness for purpose of materials in structural components. There is a good complementarity between these Networks and other working groups of the EC. (authors). 2 refs., 1 fig

[en] United Kingdom safety legislation places absolute liability on the licensee for the safe design and operation of nuclear installations. The approach taken by the UK regulatory body HM Nuclear Installations Inspectorate (NII) in assessing the structural integrity safety case for the reactor pressure vessel and other incredible failure components is outlined. Attention is focused on ultrasonic inspection proposals, which must satisfy the NII Safety Assessment principles in terms of the 'Special Case Procedure', the setting of realistic inspection goals, the extent of redundancy, diversity, validation to be built into the inspection programme and the avoidance of common mode effects. In order to pass a judgement on the inspection proposals, it has been necessary to investigate the performance of various teams in the international inspection trials. The results of these trials yielded valuable information on inspection capability for a range of defect types. It is argued that the above safety principles should be incorporated into international codes and standards. These measures may appear excessive but the increase in safety far outweighs the initial costs. (author). 3 refs

[en] The United Kingdom safety legislation places absolute liability on the licensee as regards the safe design and operation of nuclear installations. In this paper, the approach taken by HM Nuclear Installations Inspectorate (NII) in assessing the structural integrity safety case for the Sizewell B PWR reactor pressure vessel and the other incredible failure components is described. Attention is focused on the ultrasonic inspection proposals which must satisfy the NII Safety Principles in terms of the Special Case Procedure, appropriate inspection standards, the setting of realistic inspection goals, the extent of the validation, redundancy and diversity to be built into the inspection programme and the avoidance of common mode effects. It is argued that these safety concepts should be incorporated into the appropriate codes and standards and whilst these measures may appear excessive when compared with past practice, the increase in safety and the ease of in-service inspection in later years, for outweight the initial costs. (orig.)

[en] Controlled experiments such as those carried out in the PISC programme have yielded information which can assist a regulatory authority to make a measured judgement on the adequacies of inspection proposals. In this paper a comparison is made between the inspection targets set in the UK LWRSG reports and the performances of various teams in the PISC II inspection trials. While the teams that carried out a procedure in strict adherence to ASME Section X1 failed to meet these inspection targets, there were a number of successful teams whose performances reached the required standard and they included teams using procedures of the type planned for use on the Sizewell 'B' PWR contract. The wide variation of team performance suggests that there are areas of uncertainty requiring further study. In particular, attention is drawn to the failure of teams to detect and accurately size smooth faced planar defects located in the near surface region. (author)

[en] The paper presents comments by H.M. Nuclear Installations Inspectorate on the Programme for the Inspection of Steel Components PISC II, and the results of international ultrasonic inspection trials. A description is given of the United Kingdom safety legislation, the importance of non-destructive examination and inspection reliability. Sources of information on inspection reliability are described, along with an evaluation of the PISC II results and their possible impact on future in-service inspection policy. (U.K.)

[en] An investigation has been undertaken to determine the magnitude of any reduction in properties which may occur in cast duplex stainless steels and weldments during long term exposure to reactor operating conditions. Test panels were fabricated in CF3 stainless steel by a manual metal arc (MMA) process using 19.9.L (Type 308L) consumables. The mechanical properties and intergranular corrosion resistance of parent material and weldments were measured following accelerated ageing at 375⁰ and 400⁰C for up to 10,000 hours. Both the impact energy and J/sub R/ fracture toughness properties of the cast austenitic/ferritic stainless steel were reduced following aging at 400⁰C for 10,000 hours, whereas austenitic stainless steel MMA weld metals exhibited a reduction in J/sub R/ fracture toughness but no change in impact energy. Even in the unaged state, MMA weld metals were shown to have a much lower resistance to stable crack growth than the parent cast steel, and, following aging, there is a further reduction in the ductile tearing resistance of such weld metals. Therefore, in any assessment of the structural integrity of the reactor coolant pump bowl for a pressurized water reactor (PWR), the weld metal fracture properties during service are likely to be of considerable importance

[en] NESC was launched in 1993 to address questions concerning the reliability of the entire structural integrity assessment procedure for steel components. The first international project (NESC 1) is a spinning cylinder, pressurized thermal shock (PTS) experiment. The main objective of the project is to validate the non-destructive evaluation and structural mechanics procedures for PWR reactor pressure vessels under pressurized thermal shock conditions, which presents the greatest threat to the vessel integrity, especially when the material of construction is aged by the effects of irradiation. This paper describes the structure and operation of the NESC Network, the progress of the NESC 1 project to date achieved through the synergistic interaction between the five disciplinary Task Groups, and finally the topics presently under consideration as candidates for future NESC projects

[en] Examples are given of the wide variety of structural integrity assessments of nuclear plant carried out by the United Kingdom Nuclear Installations Inspectorate (NII) and the consequent need for a flexible approach within the framework provided by the Safety Assessment Principles. The paper describes the use of the Special Case Procedure and draws the distinction between the assessment of incredibility of failure of components and components whose failures are considered within the design basis. Assessment examples provided are the Sizewell B reactor pressure vessel, Magnox reactor pressure vessels, the Prototype Fast Reactor core support structure, Advanced Gas-cooled Reactor steam plant, Thermal Oxide Reprocessing Plant (THORP) vessels, and Steam Generating Heavy Water Reactor pressure tubes. (author)

[en] The paper on the inspection proposals for primary circuit components of Sizewell-B reactor was presented to the conference on 'Non-destructive testing in the fitness-for-purpose assessment of welded constructions', London, 1984. The background to the assessment of inspection techniques for nuclear reactors is summarized for the period 1971-84. A review and commentary on the Sizewell-B inspection proposals is given, including: an in-process inspection of the reactor pressure vessel (RPV), in-service inspection of the RVP, and inspection of austenitic components. The authors conclude that the Sizewell-B RPV will be manufactured and inspected to very high standards which are in keeping with a component whose failure without forewarning is deemed incredible. (UK)

[en] Slow strain rate stress corrosion tests have been performed on specimens cut from four separate heats of alloy 600 (Inconel 600) steam generator tubing. The material was tested in the mill-annealed and thermally-stabilised conditions and after various low temperature ageing treatments. Only limited cracking was observed, even for tests at 340⁰C, but the initiation of intergranular cracking was easier on the inner than on the outer surfaces on the tubing. Polarization data has been obtained in high-temperature water and in saturated boric acid and saturated lithium hydroxide at the atmospheric boiling points, and slow strain tests were performed at controlled potentials in these environments. Again, only very short cracks formed during the slow strain rate tests which were performed at a strain rate of about 10^-6 s^-1. The data is discussed in terms of the probable crack tip strain rates that would exist in these tests and at other strain rates. It is argued that if cracking occurs, the main role of very slow strain rate tests is to provide time for initiation and crack growth, so that cyclic loading or intermittent loading long term tests are likely to be more successful in sustaining crack growth in this alloy. (orig./HP)