The Kozloduy nuclear power plant is located in northwestern Bulgaria on the banks of the river Danube and just 3.7 km from the border with Romania. Units 1-4 are VVER-440 reactors; they were shut down as a condition of Bulgaria’s accession to the European Union and are currently undergoing decommissioning. Two newer VVER-1000 reactors, Kozloduy 5&6, remain in operation and in 2013 accounted for around 30% of the Bulgaria’s electricity supply.

Kozloduy units 1&2 were commissioned in 1974 and 1975 and comprise VVER-440/V230 reactors with two independent safety trains. Units 3&4, which came online in 1980 and 1982, respectively, are slightly-upgraded models with three safety trains. Plant facilities include two reactor buildings, two auxiliary buildings and a common turbine hall for units 1-4.

The start of the decommissioning process for Kozloduy 1-4 was determined in 1999 by a memorandum signed between the Bulgarian Government and the European Commission to shut down and decommission the units. KNPP 1&2 were shut down on 31 December 2002, followed by units 3&4 on 31 December 2006; within the agreed deadlines.

Subsequently, by decision of the Council of Ministers, KNPP 1-4 were entrusted to the State Enterprise Radioactive Waste (SERAW), the Bulgarian national operator for management of radioactive waste. SERAW is responsible for managing the units in compliance with the national strategy for radioactive waste and spent nuclear fuel management, and with the relevant international practices.

Decommissioning strategy

A two-stage decommissioning strategy is proposed for Kozloduy NPP Units 1-4. It is a continuous dismantling strategy, without a long safe enclosure period, that plans to result in a brownfield site in 2030 (See timeline). The approach aims for a smooth, even and continuous utilisation of human and financial resources, as well as of waste management facilities.

Stage 1 involves immediate dismantling of equipment outside of the safe enclosure area, including the auxiliary buildings and stacks.

Stage 2 covers dismantling of the equipment in the safe enclosure area (the reactor buildings, parts of the sanitary buildings and interconnecting passageways) and release of the buildings for reuse.

The complete decommissioning process for units 1-4 is outlined in the general decommissioning plan. The plan takes into account the extensive decommissioning experience from projects internationally – particularly in UK and France – and also lessons learned in Germany, Spain, Italy, Hungary and Slovakia.

The decommissioning process will involve competent and qualified personnel who have previously worked on the Kozloduy site and have knowledge of Units 1-4 and their operational history. As such, a number of personnel have been transferred from KNPP Units 1-4 to SERAW, under the direction of the Council of Ministers.

The number of staff needed for the decommissioning project is expected to decrease in stages as activities progress. Around 700 SERAW employees are involved in the project today, and this is expected to fall to around 400 in the 2020s and to 275 in 2030.


Preparation for the decommissioning of KNPP Units 1-4 in Bulgaria led to changes in the:

  • Regulatory framework and the practical application of the legal framework
  • National infrastructure for management of radioactive waste
  • Condition of the units.

Pursuant to the changes in the regulatory framework, the Bulgarian Government declared units 1-4 of KNPP as facilities for radioactive management, and along with the necessary property they were entrusted to SERAW in 2008 (units 1&2) and 2012 (units 3&4).

Pre-decommissioning activities began in 2010 after SERAW obtained the licences for operation of Units 1&2 as facilities for radioactive waste management – subject to decommissioning, from the Bulgarian Nuclear Regulatory Agency (BNRA). Licences for Units 3&4 were granted in February 2013.

The terms of the licences issued by BNRA allow the dismantling of uncontaminated non-safety related structures, systems and components (SSC) in the turbine hall, as well as preparatory activities related to the decommissioning of Units 1-4.

The next step in the regulatory process will to obtain decommissioning licences for Units 1-4. In October 2013, the Bulgarian Ministry of Environment and Waters issue a positive decision on the Environmental Impact Assessment (EIA) for KNPP 1-4 decommissioning. The Bulgarian regulator is currently in the process of reviewing the applications for decommissioning licences for Units 1-4. The licences are expected to be granted in 2014 for units 1&2 and 2016 for units 3&4. They will be issued for up to ten years and will be renewed on the basis of a safety re-assessment to cover the period up to 2030.

Pre-decommissioning activities

The scope of this work, currently underway, includes:

  • Development of required decommissioning documentation
  • Evaluation of the material backlog and radiological inventory of Units 1-4
  • Removal of hazardous, toxic, flammable, and combustible materials, and treatment of asbestos waste backlog
  • Procurement of equipment for dismantling and decontamination
  • Dismantling of uncontaminated, non-safety related-SSC in the turbine hall
  • Radiological surveys and free release disposal
  • Implementation of projects related to design and construction of infrastructure for decommissioning and radioactive waste treatment, conditioning and storage.

An approved schedule for dismantling the turbine hall is summarised in Table 1. As part of this programme, cutting machines for size reduction, along with containers, transportation and lifting equipment, ventilation equipment and other handheld electric tools for dismantling activities have been delivered to the turbine hall.

This work included, in August 2013, the installation of a band saw machines for cutting the dismantled equipment. Personnel have already received training on the machines, and diamond-wire saw cutting is currently being used to dismantle heavy and complex reinforced concrete structures to facilitate transportation and storage.

Materials from the turbine hall undergo radiological investigation before dismantling, after dismantling and before removal from the turbine hall.

During 2010-2013 more than 4500 tons of equipment was dismantled from the turbine hall of Units 1&2. This is just a small proportion of the 70,000 tons that is expected to arise from decommissioning. After processing, the materials will be classified in three categories, depending on the level of the radioactive contamination: materials that are free of contamination (category I); potentially- contaminated materials (category II) and contaminated materials (category III). An important goal of the dismantling work is to achieve maximum reuse and recycling of dismantled materials, especially metals.

Other key projects that are currently underway are profiled in the boxes.

Radioactive waste management

Management of radioactive waste in Bulgaria is carried out by SERAW, which operates several waste-management facilities through its four specialised divisions (SD), depending on the origin of the waste.

Two streams of radwaste are generated in Bulgaria: low and intermediate level radwaste from nuclear applications, and from Kozloduy nuclear power plant.

SD Radioactive Waste – Kozloduy is responsible for the management of operational waste from Kozloduy NPP.

SD Decommissioning – Kozloduy is engaged with managing KNPP Units 1-4 as facilities for radwaste management subject to decommissioning.
These organisations are responsible for managing the entire cycle from generation of radwaste through to preliminary treatment, processing, transportation, transformation into a condition that is suitable for temporary storage and subsequent disposal.

SD Novi Han is responsible for managing radioactive waste from nuclear applications. SD National Repository for Disposal of Low and Intermediate Level RAW – Kozloduy will be responsible for long-term safe storage of all radioactive waste in Bulgaria.

On the Kozloduy site, radioactive waste is managed in three main installations: a RAW processing shop, a storage facility for radioactive waste and a lime storage facility.

The RAW processing shop includes solid and liquid radioactive waste processing lines and a facility for decontamination of metal waste. The solid radioactive waste line is used for sorting and treating (pressing) the solid RAW to reduce the volume and prepare the waste for the subsequent conditioning. It can treat up to 1300 m3 of solid waste per year.

The liquid radioactive waste processing line includes facilities for retrieval of the liquid waste, transport, collection into tanks, evaporation, cementation and packing, and has a capacity of 450 m3 per year.

The processing shop also includes a modular facility for decontaminating metal waste, with capacity of 25 tons per year. The type of treatment depends on the waste.

The storage facility for conditioned RAW (SFCRAW) is a modern over-ground facility with capacity for temporary storage of 1920 reinforced concrete containers. All operations are performed remotely.

Additional radwaste facilities include a movable modular system ‘Danube’ for decontamination of low-level liquid waste generated by floor drain water, hot showers and laundry.

Repository plans

In 2013, SERAW started a project to build a national repository for the disposal of low- and medium-level radioactive waste generated from nuclear facilities and other nuclear applications.

The national repository is of significant importance for the implementation of continuous dismantling at Kozloduy nuclear power plant. The construction of the facility will provide stable and reliable isolation of radwaste that is currently in temporary storage at the site.

The repository will be a surface-based, trench-type facility with multiple-barrier protection for permanent storage of treated waste packaged in concrete containers.

It will be located in the radiation-protected area of the Kozloduy site and will have capacity for 138,200 m3 of radwaste.

Construction of the repository has been designated as ‘high priority’ over the next year. Construction is expected to be completed in 2020, and the facility will have an anticipated operational life of 60 years.

Funding for decommissioning

The total decommissioning costs for KNPP Units 1-4 over the period 2003-2030 are estimated at €1.1 billion.

The financing of activities for decommissioning units 1-4 is carried out by the Kozloduy International Decommissioning Support Fund (KIDSF), administered by the European Bank for Reconstruction and Development (EBRD), as well as two Bulgarian national funds: the Radioactive Waste Fund (RWF) and the Fund for Decommissioning of Nuclear Facilities (FDNF).

KIDSF contributed €592 million – or 85% of the total funds – for KNPP Units 1-4 decommissioning from 2003 to 2013, with state funds financing the remaining €97 million.

EU funding via the KIDSF is available to support pre-decommissioning activities such as the construction of the infrastructure for management, treatment and conditioning of radioactive waste.

Path ahead

The ultimate goal is to realize safe and effective decommissioning and to minimise the costs and environmental impact of decommissioning Kozloduy NPP.
One of the main challenges being faced at this stage relates to the selection of the appropriate technology, methods and tools for the dismantling of activated components like the reactor and its internals. Another challenge is to preserve knowledge and engage appropriately-qualified personnel for the work.
SERAW’s stakeholder engagement plan includes a number of activities aimed at ensuring public support during the decommissioning process.

About the author

Denitsa Dishkova, International Project Management Division, State Enterprise "Radioactive Waste", Bulgaria. This article is based on a presentation made at the European Nuclear Congress held in Marseille, France 11-14 May, 2014.