Site map

AEC Kozlodui AEC Kozlodui
AEC Kozlodui AEC Kozlodui
About the Plant Current Information Generation Safety Information Center Careers For kids Culture, Sport, Recreation Useful links Gallery
Home » About the Plant » Modernizations

In order to guarantee safe electricity generation from the nuclear facilities Kozloduy NPP has been making everything needed to maintain these units in compliance with the world trends strictly following the modern safety and reliability requirements.


For the last 15 years of operation of these units continuous improvements have been made, aimed at improving the design of the 440 MW units in compliance with the increasing world standards and technological development of nuclear industry. Within the period 1991 – 2002 three large-scope modernizations were implemented, as the first two were for Units 1–4, and the third – for units 3 and 4, with a view to the political decision made for the closure of Units 1 and 2 at the end of 2002. Within the first two modernization programs numerous improvements of the design of these units to the total amount of USD 245 M were made. Within the period 2000 – 2002 a number of additional modernizations amounting to USD 66 M were implemented at units 3 and 4. By the end of 2005, when the modernizations for improvement of units 3 and 4 safety, in accordance with the long-term licenses for operation, more projects amounting to €14,3 M were implemented.

Assessments of international expert missions
Kozloduy NPP is a subject to detailed review of safety from the most competent international authorities in the area of nuclear power engineering.
In June 2002 an IAEA mission was conducted in order to review the results from the units modernization. In accordance with the results from this review, all IAEA recommendations on design, operation and seismic security of units 3 and 4 are completely addressed, and that in many cases the scope implemented goes beyond these requirements.
In the summer of 2003 a peer review was held in Kozloduy NPP by the World Association of Nuclear Operators (WANO). The aim of this peer review was to get another independent assessment of the operational status of Units 3 and 4. The review concluded that Kozloduy NPP has achieved significant improvements for the last years and has competent staff available that will ensure the good performance of the plant in the future.
In November 2003 11 experts from different countries members of the Atomic Questions Group (AQG) by the European Council held a peer review in Kozloduy NPP, that was agreed by the Bulgarian Government in the course of the negotiations for the accession of Bulgaria to the EU and closing of chapter 14-Energy. The following conclusions were made in the official report of this mission:

  • All AQG recommendations to Bulgaria from 2001 and 2002 have been adequately addressed and implemented. Further monitoring activity on the recommendations of the AQG/WPNS are not considered to be necessary.
  • Kozloduy NPP has performed excellent engineering activities in terms of the Accident Localization System, in full compliance with the western approaches and good practices.
  • The safety of reactors 3 and 4 is ensured by a significant safety margin till the end of the terms of their licenses issued by NRA.
  • As regards the Severe Accident Management, the activities implemented go beyond the AQG scope of recommendations.
  • Kozloduy NPP has highly qualified, competent and motivated personnel.
  • An adequate licensing regime is established and is maintained as well as the existing good cooperation between the Operator and Regulator

Installation of a Jet Vortex Condenser at Unit 3, 2002


Almost immediately after the commissioning of units 5 and 6, the implementation of a number of modifications started, that lead to the significant improvement of the units’ operation.
The idea for a large-scope modernization programme at these units dates back since the beginning of the 90-ies and it was implemented through the Modernization Programme developed for units 5 and 6 of Kozloduy NPP.
The modernization program for units 5 and 6 of the Bulgarian nuclear power plant is the first and at present the only program in the world, through which the full scope of the recommendations for improvement was implemented at 1000 MW units of WWER type.
Ensuring the transparency of the whole process of the Program implementation and taking into consideration the expert opinion of the best specialist in nuclear power engineering, Kozloduy NPP Plc has achieved a guarantee for the international acceptance of the safe operation of those units.
The program includes 212 measures and is aimed at the implementation of a large-scope improvement of the 1000 MW units of Kozloduy NPP. It was finalized successfully in 2008. The funding of the project was ensured by the plant own resources according to the investment programme of Kozloduy NPP and credits from different international financial and bank institutions (Euratom, Rosseximbank, Citibank).

International reviews
The program was reviewed in 1995 and twice in 2000 by the International Atomic Energy Agency (IAEA) for adequacy and completeness of the measures determined. The project is assessed also independently in 1997 by Risk Audit – an organization including specialists from institutes assisting the regulatory authorities of France and Germany, (IPSN and GRS Int).
The expert mission of IAEA conducted in 2000 concluded that “there isn’t any problem area in terms of safety without partially or completely implemented or started measures, directed to the solution of the corresponding safety problems in order to meet the IAEA guidelines”.

Replacement of Condenser Tubes, Unit 6, 2003