Category Archives: Materials’ ageing and degradation in. light water reactors

Management techniques for reactor internals

Materials used for PWR internals include ferritic steel, wrought austenitic stainless steel, cast stainless steel (CASS) and Ni alloys. The internals main­tain the soundness of the geometrical core. The core consists of the upper core structure, core baffle/former/barrel, thermal shield and lower core sup­port structure. The factors which influence degradation of these parts are: thermal plant transient, flow-induced vibration, radiation, […]

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Basic design features of the VVER-1000

The VVER-1000 model exists in several versions. The ‘small series’ plants could be considered as pioneers of this model. The VVER-1000/320 is the large series version of the design. Developed after 1975, VVER-1000/320 type plants are operated in Bulgaria, the Czech Republic, Russia, Ukraine and China. Modernized versions of VVER-1000 plants are under construc­tion in five countries (Bulgaria, China, India, […]

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A complex picture of ensuring and justification of LTO of VVER plants has been given in this chapter. The VVER-440/213 model especially is discussed in detail. In VVER operating countries, proper regulatory frameworks and compre­hensive plant lifetime management systems have been developed to ensure the safety of LTO of VVER-440 and VVER-1000 type plants. Detailed stud­ies and already approved cases […]

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Radiation damage

High energy neutron exposure results in accumulation of many defects like point defects (vacancies and interstitials) and dislocations, and causes redistribution in the chemistry (phase change or radiation-induced segre­gation (RIS)) in the materials. These modifications lead to deterioration in mechanical and corrosion properties of the exposed materials. The micro­scopic defects produced in materials due to irradiation are referred to as […]

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Management techniques for steam generator tubes

Degradation management in steam generators is possible with the help of research and development or a technical support programme. Strategies can be established by supplementing inspection and repair programmes based on operating experience in power plants. Management of ageing can be divided into the understanding, prevention, detection, monitoring and mitigation of ageing. A measure to systematically combine the management strategies […]

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Review and validation of the time-limited ageing analyses

TLAAs and their role in the justification of LTO Although the wording is sometimes different, the term ‘time-limited ageing analyses’ is understood by the VVER operators in a very similar way to its definition in 10CFR54.3 (Requirements for Renewal of Operating Licenses for Nuclear Power Plants). The role of the review and revalidation of the TLAAs in the justification of […]

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