Sarcophagus and Decommissioning of the Chernobyl NPP

 

The main goal of fundamental work on the Sarcophagus is aimed at reducing the probability of an accident arising.

Chernobyl Shelter Fund (CSF), managed by the European Bank for Reconstruction and Development (EBRD), was set up in December 1997 to help finance the Shelter Implementation Plan (SIP), which sets out the tasks to be executed for the successful covering of Chernobyl's unit 4. The SIP will transform the existing temporary structure into a secure and environmentally sound system.

The Chernobyl Shelter Fund was established to assist Ukraine in transforming the

"Sarcophagus ", built under emergency conditions after the 1986 accident, into a stable and environmentally safe system through implementation of the Shelter Implementation Plan (SIP).

Since 1998, when SIP activities started, some risks have been reduced: the two most critical structural repairs were completed in 1998 and 1999. Some of the risks are understood better than several years ago, contrary to statements which often appear in the press coinciding with the anniversary of the accident, monitoring and investigations suggest that the probability of a nuclear chain reaction is almost zero. However, the nuclear inventory of the "Sarcophagus " - almost 200 tons of molten nuclear fuel, dust and radioactive liquids - will continue to pose a serious environmental threat until the SIP is completed.

The technical solutions for the SIP have been devised and agreed with Ukraine. The stabilisation programme, approved by the Ukrainian authorities in 2001, is at the detailed design stage. The new, stable and environmentally safe structure will contain the remains of the reactor for at least 100 years, during which time an even longer-lasting solution to the Chernobyl problem must be found.

The new confinement when completed will isolate the "Sarcophagus" and its inventory from the environment. The structure will consist of a 100-meter- high steel arch with a span of about 250 meters. It will slide along rails into place over the old "Sarcophagus".  It will also create a safer working environment for future waste management operations.

The final shutdown of Chernobyl NPP in December 2000 was a significant event. However, the task of dealing with the nuclear waste and spent nuclear fuel generated during its operation and the consequences of the 1986 accident, remains unsolved. It will take years of effort by Ukraine to complete the ongoing projects.

Within the framework of the overall financial assistance to Ukraine, and in addition to their own bilateral programmes, the donor countries and the European Community have committed around ˆ 1 billion for Chernobyl through the Chernobyl Shelter Fund (CSF) and the Nuclear Safety Account (NSA) managed by the EBRD.

The Nuclear Safety Account finances the two major decommissioning facilities and associated infrastructure, including a state-of-the-art physical protection system. After completion, the interim spent fuel storage facility will safely store more than 20,000 spent nuclear fuel assemblies for up to one hundred years. This is the largest spent fuel store ever built in the world.

The Ukrainian cabinet of ministers has approved a U.S. Department of Energy project to build a replacement heat plant at Chernobyl to provide process and space heat needed to support shutdown and deactivation of the Chernobyl units.

     

Legal basis

Objectives and main stages

Strategy for Chernobyl NPP units 1,2 and 3

Strategy for Chernobyl NPP units 4, Shelter ("Sarcophagus ")

New facilities for waste management and storage

 

Legal basis

 

The "Complex Program" of Chernobyl NPP decommissioning is developed by Ukrainian authority on the basis of the Decision the Cabinet of Ministers of Ukraine from March 29, 2000 ¹ 598 " About the termination of Unit 3 operation and final Chernobyl NPP decommissioning ".

The decision on ChNNP decommissioning was made as a result of mutual obligations on Memorandum of Understanding between G 7 and the Government of Ukraine, the EC and EBRD on Chernobyl NPP Decommissioning of 20 December 1995.

Also pursuant to the international agreements, laws and legislation of Ukraine regulating activity on removal from operation Chernobyl NPP and transformation of object " Sarcophagus " into an ecologically safe system, and also maintenance of social protection of the Chernobyl NPP personnel and inhabitants of Slavutich city.

In particular, the program is based on such documents:

Law of Ukraine “ On Human Protection against Ionising Irradiation”

Law of Ukraine “ On Utilisation of Nuclear Energy and Radiation Safety ”

Law of Ukraine “ Handling of Radioactive Wastes” 

Law of Ukraine “ On Legal Status of the Territory Affected by Radioactive Contamination due to Chernobyl Accident”

This ”Complex Program” provides an overview on the planned decommissioning and waste management system for the Chernobyl units 1 – 3 including some specific decommissioning problems of the site in addition to the three units.

 

Objectives and main stages.

The main objectives of the decommissioning are:

 - to protect facility personnel, the public, future generations and the environment against hazardous impact of ionising radiation,

 - to achieve such conditions at the facility site which reduce any restriction on use of the site to the extent possible.

These objectives shall be achieved by a stage-by-stage transformation of the facility.

The single stages are as follows:

termination of operation       
This step is carried out within the framework of the licence for operation of the facility (nuclear fuel removal, clearing of the facility from liquid radioactive waste, partial removal of solid ones); however, for the realisation of this stage, an additional permission is required on the basis of:

- an operation termination and decommissioning strategy and program,

- a Safety Analysis Report,

- amendments to technological rules of operation of the facility.

The main objective of this stage is transformation of the facility into a nuclear safe state (The nuclear safe state in the Ukrainian legislation is defined as a condition characterised by the absence of nuclear fuel on the site or its location within the site only inside nuclear fuel storage facilities which are aimed at long-term storage).

final closure    
The goal of this step is to bring the facility into a condition which excludes any possibility of using it again for the purpose for which it was constructed. The work to be done is dismantling of systems and elements external to the nuclear unit, preservation of barriers preventing the release of radioactive substances into the environment.

preservation    
At this step the facility will be brought into an appropriate condition in order to safely store its own radioactive substances during the prolonged storage (see the definition below). The necessary work must include reliable insulation of non-being dismantled parts of the facility, tight closure of pipes, tightening of connections, creation of conditions for a controlled temporary storage of radioactive substances on the facility, collection and conditioning of radioactive waste generated at this stage.

prolonged storage       
At this stage the facility shall take benefit from the fact, that the decay of radionuclides reduces essentially the quantities of radioactive substances just present at the preserved facility. For this purpose the systems, ensuring a safe storage of radioactive substances at the preserved facility, periodic inspections of the preserved facility will be needed.

dismantling     
At this final stage radioactive sources will be removed out of the facility or placed at its site in radioactive waste storage facilities. Main work to be performed includes collecting and conditioning of the generated radioactive waste, radiation inspection of the components which are not subject to dismantling, procedures on termination of radiation monitoring previously required.

Action of the decommissioning licence begins only after the stage of termination of operation putting the facility into a nuclear safe state. Separate permissions are needed for each of the aforesaid stages of decommissioning.

The decommissioning strategy defines the sequence of decommissioning and therefore the consequences, the duration and the main actions of each decommissioning stage as well as the state of the facility after each stage.

According to the Ukrainian regulation final the decommissioning strategy should be defined as a result of the consideration of various decommissioning variants and by the choice of the optimum among them on the basis of "cost-benefit" analysis. This corresponds to the balanced contributions of the following major factors: safety requirements, physical state of the facility including the forecasting changes, required financial costs and their availability, social aspects.

The facility decommissioning have to be carried out according to a decommissioning programme that have to be approved by national authority. The main components of this decommissioning program are the decommissioning strategy, the measures of safety assurance (programme of radiation protection, minimising of the occupational exposure, the environment and general public impact, emergency response measures, measures on physical protection of nuclear installations), man power program, quality assurance measures.

According to the regulation the operating organisation is obliged to plan the future decommissioning of a facility as soon as possible at all stages of its life cycle.

Besides decommissioning planning and operation, also a waste management system has to be developed and implemented. The existing regulation is defining the requests to radioactive waste management system. A number of national legal documents and requirements  in this field have been  being developed, mostly in accordance with internationally accepted principles: 

 -  to deal with radioactive waste in a manner that protects human health and the environment now and in the future without imposing undue burdens on future generations.

 -  to include a pre-treatment (collection, segregation, chemical adjustment, decontamination), treatment (volume reduction, radionuclides removal, change of composition), conditioning (transform the waste into a form suitable for handling, transportation, storage and disposal), packaging, interim storage, and final disposal (emplacement of radioactive waste in a disposal facility with reasonably assurance for safety without the intention of retrieval and without reliance on long-term surveillance and maintenance).

Safety objectives for the management of radioactive waste arising from decommissioning operations are:

-  to keep the individual and collective doses as low as reasonably achievable,

-  to reduce the volume of material selected to be disposed of as radioactive waste, to reuse to the greatest possible extent exempted material and cleared installations,

-  to decontaminate material in order to increase the accessibility to the work area,

-  to minimise the amount of secondary waste that arises during decontamination and dismantling of installations and buildings.

 

Strategy for Chernobyl NPP units 1,2 and 3

The decision on ChNNP decommissioning was made following to “Memorandum of Understanding between G 7 and the Government of Ukraine, the EC and EBRD on Chernobyl NPP Decommissioning” of 20 December 1995.

In compliance with this Memorandum:

Company “AEA Technology” prepared in 1996 in the frameworks of TACIS project “Chernobyl NPP-1, 2, 3 Decommissioning Plan”(hereinafter referred to as CDP) which complies with the IAEA safety recommendations. The Plan was accepted as a basis in financing and decommissioning of Chernobyl NPP by both European Community Commission and Ukraine. In accordance with CDP the variant of Chernobyl NPP decommissioning which provides for preservation of unit equipment in the existing structures for period not less than 30 years with performance of minimum required activities on dismantling and preservation of reactor installations, was recognised as the most expedient. CDP was put in the basis of “Concept on Chernobyl NPP Decommissioning”;

“Recommended Policy” was developed in 1996 in the frameworks of TACIS Project “Chornobyl-4, Short-Term and Long-Term Measures – Measures 2 + 4”. It is proposed in this Policy to develop potential short-term and long-term measures and complex of priority measures on transformation of the Shelter in an ecologically safe system.

The complex of preparatory work for assuring Chernobyl NPP decommissioning has been specified in the concept and programme developed by Kyiv Institute “Energoproekt” in 1992 in fulfilment of the Ordinance of Verkhovna Rada of Ukraine “On Urgent Measures Related to Chernobyl NPP Decommissioning” of 29 October 1991.

According to the requirements of “General Provisions on Safety Assurance in NPP and Research Reactor Decommissioning” the transformation process includes the following stages (for each Unit):

-         operation termination ;

-         final closure;

-         preservation;

-         cooling;

-         dismantling.

The duration of operation termination stage depends on the term of commissioning new storage facility for spent nuclear fuel (ISF‑2), rate of nuclear fuel reloading from Units to ISF-2 under unconditional observance of the regime limiting dose loads on the personnel in nuclear fuel transport and handling procedures. The duration of the stage takes 6 years for each Unit beginning from the moment when the permission of the Regulatory Authority is obtained for performance of such activities. At the stage of operation termination the following shall be performed:

-         construction and commissioning of RW management facilities;

-         creation of new infrastructure;

-         reconstruction of systems and equipment remaining in operation;

-         performance of the measures provided by regulatory documents on decommissioning as well.

Transition to the second stage “final closure” is carried out after the license for decommissioning and separate permission for this stage are received. At the stage of final closure the following activities shall be performed:

-         decommissioning of some process and auxiliary systems;

-         decommissioning of nonoperating buildings and structures;

-         activities on RW movement, treatment, storage, and disposal.

The duration of the stage of final closure depends on preparedness of RW management facilities. Boundaries of reactor installation preservation are specified and a complex of arrangement and technical measures on transformation of the installation in the preservation mode is performed at this stage.

Presently, Units are at different stages of preparedness to decommissioning. The time interval created in this case, which are related to removal of spent nuclear fuel from the Units, will impact on priority and duration of decommissioning stages on each Unit. Due to the fact that ISF-2 and other RW management facilities are not prepared the accurate date of transition to the stage of ChNPP Unit decommissioning has not been determined. Total duration of transition to the preservation stage will take 10 years taking into account the time delay of the beginning of decommissioning at each of three Units.

At the preservation stage the reactor installation is transferred to the mode of interim safe storage of radioactive substances stored during operation. Radioactive waste generated during decommissioning is subject to treatment, conditioning, transportation, storage, and disposal at RW management facilities. Subsequent impacts will be determined by the development level of techniques and technologies for long-term storage of preserved equipment.

Besides routine operation of RW management systems and facilities the activities aimed at transformation of NPP systems, buildings, and structures from the initial condition to a final stage are carried out at the stages of operation termination and final closure in order to assure safe preservation and long-term storage.

To perform this work preliminary development and agreement in the established order are required for appropriate documentation including safety substantiation for work at each stage.

General procedures at the stages of operation termination, final closure, and preservation includes the following:

-         preparatory procedures and decommissioning (final shut-down) of systems and equipment, in particular, removal of operational environment from the system circuits, equipment, and pipelines (LRW, combustible and chemically hazardous materials, oils, etc.);

-         decontamination of systems, equipment, pipelines, Unit premises;

-         preservation of separate equipment;
training and skill maintenance for top-management personnel, operational personnel, repair personnel, maintenance personnel, instructor personnel;

-         dismantling of systems, equipment and pipelines of the Units which are decommissioned and not intended for the use;

-         collection of RW generated in work at the decommissioning stage, assurance of its interim monitored storage at the Units, its transfer to RW management facilities.

The detailed description of work scope for each Unit is presented in appropriate programmes for operation termination. Based on the programmes for operation termination of Unite-1, 2, and 3 the annual work schedule is developed for operation termination. This work schedule presents in details operation termination measures subject to fulfilment, and assesses the demands in financial resources. The work schedule is the basis for application as to introduction of the planned financial resources in draft Law of State Budget for the next year.

 

Strategy for Chernobyl NPP units 4, Shelter ("Sarcophagus ")

Chernobyl NPP decommissioning and transformation of the Shelter in an ecologically safe system are also related to the need for solving the following issues:

-         Shelter RW management, Exclusion zone and Ukraine as a whole in view of complex approach to selection and substantiation of optimum decisions;

-         water-protection strategy in Exclusion zone, at ChNPP site including the strategy for actions on cooling pond;

-         social protection for the personnel released because of ChNPP decommissioning, and social-economical development of Slavutich city.

That issues should be solved within the special national program directly associated with Chernobyl NPP decommissioning and other related problems.

In 1997 the “Shelter Implementation Plan” (hereinafter referred to as SIP) was developed by European Commission, USA, Ukraine, and other international experts.  SIP established general concept, in particular, series of steps intended for putting the Shelter in ecologically safe condition. Two main tasks were taken into account in development of the SIP: assurance of detailed work schedule development and elaboration of preliminary assessment of the cost sufficient for providing international financial support in implementation of two first phases of “Recommended Policy.

“Shelter Transformation Strategy” and “Shelter Stabilisation Strategy” have been developed based on the position of Ukraine in the issues on the Shelter transformation and taking “Recommended Policy” into account.

All tasks associated with Chernobyl NPP decommissioning and with transformation of the Shelter to an ecologically safe system could be solved only by close co-operation and support of international community.

 

New facilities for waste management and storage

The following facilities will be built and putting to operation as important parts of the decommissioning and waste management strategy.

Spent Fuel Interim Storage Facility (SFISF)

Fuel assemblies on the site need to be stored in a dedicated building to allow them to cool down and the fission products to decay under adequate containment. After the Chernobyl NPP units termination of operation, fuel assemblies will mainly be located in the RBMK reactor cores, in the reactor cooling ponds of the three units and in the existing SFISF-1 (KHOJAT-1) fuel storage pond. The limited remaining capacity and design life of that last storage facility requires a new storage building to be built.

This new facility will be divided into two parts: the first one to prepare and condition the fuel assemblies, the second one to store them.

Using the transfer flasks already present on the site, the fuel assemblies will be transported from their intermediate storage areas to a hot cell, where the upper and lower fuel bundles will be separated by dry-cutting. The fuel bundles will immediately be placed into cartridges, while the extension rods will be cut and prepared before transfer to the plant storage facility. Absorber rods will be placed into cartridges and stored in a special vault located next to the processing facility.

The cartridges will be welded shut, filled with argon gas, and then placed in the storage canisters. The inner space of the canisters will be filled with inert gas and closure lids sealed by automated welding. Canisters will then be transported to the dry storage vaults.

The required production rate will be 2500 fuel assemblies per year. It should allow processing all the spent fuel bundles and absorber rods over a ten years period. These fuel bundles will be placed in 256 storage casks, each stored in individual vaults.

A consortium led by France's Framatome was awarded a contract to build an interim spent fuel storage facility for 25,000 fuel assemblies and 3,000 absorber rods.

 

Liquid Radioactive Waste Treatment Plant (LRTP)

The liquid radioactive wastes are currently stored in five 5000 m3 and nine 1000 m3 tanks placed on the Chernobyl NPP site and in the Chernobyl NPP liquid and solid radwaste storage facility respectively. The major part of the wastes stored in these tanks is composed of low level and intermediate level liquid wastes.

The treatment of the liquid wastes will require retrieval, transfer and processing in a dedicated treatment facility. A few of these waste tanks contain also resins, pulp and sludge, which bring some complexity to the transfer and treatment operations.

Moreover, this treatment facility should ultimately process the decontamination effluents from Chernobyl NPP decommissioning. The amount of liquid wastes generated by these operations has not yet been precisely estimated.

The two sets of storage tanks are connected by transfer pipelines, which run in a transfer gallery. Transfer of the wastes from the tanks to the treatment facility will require installation of retrieval systems and specific connections between the retrieval equipment and the pipelines to move them from the tanks into the transfer gallery and between the pipelines and the treatment facility. The retrieval system will be composed of agitation devices and pumping systems.

After receipt in the LRTP, the volume of the wastes will, where possible, be reduced prior to the treatment process. Particular wastes such as spent resin and perlite pulp will have to be processed too in this facility. The final process in the LRTP prior to the packaging of the product will be a cementation process in order to immobilise the treated wastes in a matrix.

The final conditioning of these packages will depend on the acceptance criteria of the near surface disposal centre. So, it will probably be necessary to build intermediate buffer storage areas in order to receive these packages before a final solution is reached for disposal of every type of packages.

The consortium led by Belgatom won a contract to design and build a liquid radioactive waste processing plant at the site. Over 10 years, the plant is expected to process approximately 35,000 cubic meters of liquid waste.

 

Low and Intermediate Level solid Waste Retrieval Facility (LILWRF)

Low and intermediate level solid wastes are currently stored on the Chernobyl NPP site in an above ground concrete shielded structure, separated into three compartments categorised according to the types of wastes. Their volumes are respectively 1087 m3, 1000 m3 and 1884 m3. The two first compartments are 98% and 92% full respectively and the third one, which is reserved for higher level solid wastes, is 18% full. Access to the compartments can be carried out via hatches of various sizes. The solid wastes are composed of ” technological wastes ” and are in the form of metal, concrete, plastics, wood, paper etc. The content of two of these compartments has been covered with a layer of concrete approximately 1 m thick.

Options for retrieval of the wastes include a mechanical grabber and an overhead crane retrieving waste from above, or using a digger and penetrating equipment to retrieve wastes through the side of the tanks. The retrieval equipment should be capable of breaking and retrieving the concrete cap that has been placed over the top of the stored active wastes and it should be designed to be mobile, so that it can be used to retrieve successively wastes from the three compartments.

Wastes will be put in containers and transported to a sorting and conditioning facility. The retrieval rate should be about 3 m3 per day.

It is to be noted that wastes stored in the three compartments are not suitably identified and thus presence of high level radioactive wastes will have to be envisaged during the retrieval.

 

Low and Intermediate Level solid Waste Processing Facility (LILWPF)

The LILWPF will be designed in a first step to process the wastes issuing from the retrieval facility. It could be adapted to the treatment of wastes from decommissioning of Chernobyl NPP reactors.

The facility will be also equipped with an incinerator to burn contaminated oil coming from the turbines of the reactor units (about 300 m3).

The solid wastes from the retrieval facility will be transferred to a sorting bay in the LILWPF, where they will be sorted out and categorised in four types :

-         compactable wastes for compaction,

-         non-compactable wastes for packaging and grouting,

-         combustible organic wastes for incineration,

-         long-lived wastes for interim storage;

Compacted wastes and non-compactable wastes will be overpacked into containers approved for final disposal in an engineered near surface facility. Wastes will be grouted into these containers using a facility whose production rate should be approximately 10 m3 grout per day, allowing typically 20 m3 of packaged wastes to be grouted.

Some of the wastes retrieved from the solid waste compartments may be too large and bulky to be dispatched directly to an appropriate treatment process. They will require size reduction before compaction or direct packaging.

A part of the retrieved wastes will not be suitable for near surface disposal due to radiological and, maybe, chemical contents. Therefore, it will be placed into dedicated containers and sealed. These containers will be designed for long-term storage.

It is to be noted that categorisation of wastes has not been definitively set up by the Ukrainian government. This could be a major problem to design the waste processing facility and the subsequent near surface disposal area.

 

Low and Intermediate Level Waste engineered near Surface disposal Facility (LILWSF)

The LILWSF will receive packages containing LILW immobilised in a cement matrix, for final disposal. The packages will be of an approved design, meeting acceptance criteria set up by the disposal facility. All their characteristics will be recorded and filed when arriving on the site.

The design of this disposal will be based on an engineered near surface trench concept. The first phase of the construction will consist of one trench. The following ones will be built according to the waste packages production. Each of them will be capped as it becomes filled. Capping material will be selected so that it will assist in evacuating rainwater towards a surrounding drainage system.

This near surface disposal will be built in the Chernobyl restricted area.