European consortium upgrades Bulgaria’s Kozloduy 5 and 6 plants

The Kozloduy nuclear power plant in Bulgaria consists of six units equipped with Russian-designed pressurised water reactors, VVERs. Units 1 to 4 are VVER-440s, with a gross electrical output of 440 MW each, and are of the first generation, 230 type. They were put into operation between 1974 and 1982. Units 5 and 6 are third generation VVER-1000s, of the 320 type. They were connected to the grid in the period 1988 and 1993. With a capacity of 1000 MWe each, these units are the most powerful blocks in the Bulgarian electrical grid.

Ranking safety issues

At the beginning of the 1990s, international expert groups carried out a number of investigations on the safety status of VVER nuclear power plants. In parallel, at around this time, the Russian state safety authority released a new set of improved basic safety standards. All of these sources, together with conclusions from further safety missions and from international conferences, formed the basis on which the International Atomic Energy Agency (IAEA) compiled its assessment of safety issues and their ranking for VVERs. These were issued separately for each of the VVER reactor types. The results of the IAEA reports suggested there were no fundamental safety deficiencies in the case of the second and third generation VVER units. It was recommended that feasible safety improvements could be carried out in order to reach a safety level in principle similar to current international levels.

Besides the identified safety issues – determined by comparison with the international IAEA standards and with Western nuclear power plants of similar vintage – it also turned out that the operational performance of VVERs, especially the large VVER-1000 units, showed that some improvements were needed.

Development of the Kozloduy 5 and 6 programme

In addition to an internationally supported set of activities for preservation and safety enhancement of the old Kozloduy plants, units 1 to 4, the Bulgarian national electricity utility launched a project with the aim of preserving the long term operability of the larger and more modern units at the site, namely Kozloduy 5 and 6. The aim of the project was to achieve full compliance with international safety standards, as well as to upgrade the plants to achieve improved performance.

In 1994/95, a comprehensive modernisation programme for Kozloduy units 5 and 6 was established jointly by the Bulgarian national utility, by the nuclear power plant staff and by Bulgarian organisations, supported by the French utility EDF and by Russian design institutes, in a grouping called MOHT. Due to the support of EDF and MOHT, the technical content of the programme was such that the safety enhancement would bring the plants in line with current Russian and international requirements and practice for operating plants. The proposed set of operational improvements reflected the in-depth knowledge of the VVER’s main design organisations on one hand, and the operational experience of a large PWR-based utility on the other hand, ie EDF. EDF was also involved in the budget estimations for the original programme.

Further relevant sources of insights to inform the modernisation programme were operational experience of the Kozloduy power plant staff, the Kozloduy staff’s own studies, as well as investigations by Bulgarian design institutes. In addition, feedback from other VVER-1000 plants was also taken on board.

The modernisation programme was investigated by IAEA review missions, in order to find out whether the relevant IAEA safety issues were addressed.

Subsequently, in support of the Bulgarian safety regulator, there was an assessment by Riskaudit, a joint venture of German and French safety consultants. The conclusions of this exercise were also taken into account.

The resulting Kozloduy 5 and 6 modernisation programme includes about 200 separate measures, which are structured mainly in four groups:

Design-related safety upgrading measures.

Additional studies and analyses of safety-related items.

Availability enhancement measures without direct impact on safety features.

Measures to improve operating conditions.

European Consortium Kozloduy (ECK)

After the issuance of the terms of reference of the modernisation programme in 1996, Siemens and Framatome, which had already been involved in the definition phase of the project – in the drawing up of technical solutions and budget estimations – decided to form the European Consortium Kozloduy (ECK) with the Russian nuclear plant export organisation, Atomenergoexport, in order to be able to offer a way of financing the full range of measures that had been identified. Major sources of financing were a Euratom loan proposal, submitted by the Western European partners, and a Russian state export credit.

From the technical point of view, this consortium combines the capabilities of the original VVER designers with those of leading Western European companies having broad experience of both Western safety upgrade practice and previous VVER upgrade projects.

The ECK is the first east–west consortium of its kind to work on a big project in the nuclear energy field.

Early in 1997 framework contracts were concluded. The major part of the modernisation project, about 120 work items, was awarded to the European Consortium Kozloduy, with Siemens taking the lead role. In the autumn of 1998 the first steps in actual implementation of the modernisation project were taken by the Consortium. Among these first steps were:

Implementation (currently underway) of very urgent measures to:

modernise the non-interruptible electri cal power supply (by replacement of major portions of the system);

replace the existing boron meters with systems of a new type;

replace the moisture separators in the secondary circuit.

Carrying out of the “basic engineering phase” (the “BEP Contract”), which includes around 50 measures out of the total ECK scope. The goal of this basic engineering phase was to develop basic designs for the modernisation projects and to carry out studies in support of safety relevant measures and/or measures where the scope of hardware modifications was such that their justification needed further investigation or analyses. This work was done between winter 1998 and spring 2000.

The main contract

The ECK contract for the major implementation phase (the “Main Contract”) was signed in mid-1999. This contract contains a “definitely defined” portion and a “preliminarily defined” portion, the latter being mainly those items of work to be further justified in the basic engineering phase.

For the main contract, the financing agreement between the nuclear power plant and Euratom has recently been signed. The financing scheme envisages that 50 per cent of the overall project funding will come from Euratom and 30 per cent from Roseximbank of Russia. At the end of the basic engineering phase, in spring 2000, the final technical documentation was accepted by the client and the prices for implementation of the related work items were re-investigated and recalculated. Based on these results, negotiations will be carried out shortly on the “preliminarily defined” part of the main contract, and the outcome of these may have an influence on the final scope of measures carried out in the modernisation project as a whole.

Realisation of the main body of the project is planned to start this coming autumn. The overall duration will be about four years. It is planned that physical modifications to the plant will be done during the annual outages of the units, which may be prolonged to some extent. But the plan is to avoid a dedicated major long-term reconstruction shutdown. This requires optimised scheduling and logistics planning of the work items – an essential element of the project.

Another key element is involvement of local organisations, with major participation by Bulgarian design institutes, manufacturers and building companies.

Main items of the Kozloduy 5 and 6 modernisation project

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