This section provides some examples of recent programmes that are being implemented to improve performance and reliability across a span of the reactors that are currently opera­ting, see IAEA-TECDOC-1175 (2000). In some cases, the improvements are also being incorporated for safety reasons; the resulting better performance is an additional bonus.

In Central Europe, various safety upgrades and reliability improvements have been made on the earlier VVER-440/230 reactors that are still operating. For example, in the Bohunice Units 1 and 2 in Slovakia, the emergency core cooling systems and electrical systems have been reconstructed to achieve better separation redundancy and independence. On each plant, the instrumentation and control (I & C) system has also been reconstructed and an emergency feed water system (EFWS) has been added. Other significant improvements include annealing of the reactor pressure vessels and better seismic qualification.

The improvements for these earlier VVER-440/230s are to ensure safe and economic operation for only a relatively short period of operation; most will be decommissioned within the next few years. Improvements are being carried out on the newer VVER — 440/213 reactors to ensure operation for one or possibly two decades into the future.

There have been major modernisation and upgrading programmes on the Dukovany plants in the Czech Republic. Achievement of improved economics by increasing the power rating of each unit by as much as 20 MWe may be possible via an improved evaluation of the operating margins. Modernisation activities include better fire protection, improved I & C systems, modification of the EFWS and better hydrogen control under accident conditions. The Paks plants in Hungary are undergoing similar enhancements.

In Japan, there has been an active programme to establish the necessary inspection and maintenance activities to be done as countermeasures against ageing. There are ambitious targets to extend the life of some of the older plants out to 60 years.

The most modern plants are already incorporating technical features in their design for better practice, improved operation and better maintenance. The latest advanced boiling water reactor (ABWR) plants (Kashiwazaki-Kariwa Units 6 & 7) that entered operation in Japan in the last decade have the largest capacity, yet shortest outage times. This is seen to be due to national component testing programmes to verify their performance for Japanese ABWR operation, even if previous international experience exists elsewhere. Further, during the initial outages, there were rigorous overhauls and inspections of new design features (reactor pumps, advanced control drive mechanisms, high-efficiency steam turbines). There have also been full-scale training programmes for reactor maintenance staff.

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