Chernobyl - 30 years on

28 March 2016



Three decades on from the Chernobyl disaster work continues to clear and contain the site. Vince Novak*, director of nuclear safety at European Bank of Reconstruction and Development, tells NEI of the journey so far as the project ramps up.


The 30th anniversary of the Chernobyl accident is an opportune moment to take stock of the measures planned and implemented to make the site of the world's worst nuclear accident environmentally safe. The scale of the accident is well known: approximately 3% of the radionuclides accumulated in Unit 4 were released into the environment. Large areas of Ukraine, Belarus and the Russian Federation were contaminated - according to the Ukrainian authorities about five million people were affected - and radioactive plumes spread across Europe. At the Chernobyl site, the accident and accident recovery measures, including the construction of the shelter hastily built to cover the ruins of Unit 4, led to the immediate death of at least 30 people.

The number of long-term casualties among the general population and among "liquidators" that are attributable to the radioactive fallout from the accident is difficult to estimate and has been the topic of many studies and debates. The human suffering as a consequence of the accident and the evacuation has certainly been huge.

Today the first impression for a visitor approaching the site is of a skyline dominated by the huge arch-shaped structure of the New Safe Confinement (NSC). In 2014, the two halves of the arch were lifted to their full height of more than 100 metres and in 2015 were joined together at the assembly site some 300 metres away from the old shelter. The NSC is the largest movable structure ever built on land. When all the equipment has been installed, and before sliding the arch into its final position over the shelter, scheduled for late 2016, the weight of the NSC will exceed 35,000 tonnes. It will then provide a barrier against any radiological releases from the shelter and provide the equipment to deconstruct the shelter and manage its radioactive inventory.

While an impressive feat of engineering, the NSC is only the final step in an extremely complex process of research and engineering, and political and technical decisions, dating back to the early 90s. This article attempts to describe this process concisely and to provide you with information on the key parameters of the NSC and on the other projects essential to protecting the environment from the consequences of the Chernobyl accident.

The Chernobyl accident has dramatically raised awareness of the risks associated with the operation of first-generation Soviet-designed reactors, and has had a defining impact worldwide on the public acceptance of nuclear power. International cooperation to mitigate these risks intensified after the collapse of the Soviet Union with the adoption of the International Convention on Nuclear Safety as a key milestone.

An important International Atomic Energy Agency (IAEA) extra-budgetary programme helped gather and consolidate knowledge about Soviet-designed reactors, and the resulting 'issue books' provided the technical basis for subsequent cooperation programmes in this field. The G7 Action Plan to improve nuclear safety in Eastern Europe and the countries of the former Soviet Union was made public at the Munich G7 summit in 1992. Largely inspired by the Chernobyl accident, the focus of the action plan was on short-term safety upgrades of VVER 440-230 and RBMK plants and, subsequently, their early closures. A number of bilateral programmes - notably the European Commission's PHARE and TACIS programmes - as well as many other actions by individual governments were initiated to improve nuclear safety.

The G7 and European Commission invited the European Bank for Reconstruction and Development (EBRD) to set up a Nuclear Safety Account (NSA) - the first of the multilateral nuclear safety grant funds managed by the EBRD - with a specific mission to finance short-term upgrades in Bulgaria, Lithuania and the Russian Federation. Ukraine was added to the NSA portfolio after the Memorandum of Understanding on the closure of Chernobyl was signed between Ukraine and the G7/EU in 1995. The MoU also created the basis for the Chernobyl Shelter Fund (CSF) to finance the Shelter Implementation Plan (SIP), a programme of actions to guide the conversion of the Shelter into an environmentally safe state.

Making a plan

Many proposals for a long-term solution for the Shelter - hundreds, in fact - were made in the years following the accident. Important steps included a study by the Alliance consortium - a group of European engineering companies - and a follow-on study by an international group of experts, both financed by the EU TACIS programme. They developed and examined a number of scenarios attempting to elaborate a conceptual design for a solution.

However, the absence of firm data on the shelter, coupled with the physical impossibility of collecting data given the high levels of radiation - meant their report of November 1996 failed to produce an optimal solution.

The SIP, developed in mid-1997, finally offered a way forward. Sponsored by TACIS and the US Department of Energy, a team of Ukrainian and international experts, drawing heavily on previous studies, devised a technical strategy and the programme logic for conversion of the shelter into an environmentally safe system.

The SIP identified five principal technical goals: reduce collapse probability - structural stabilisation of the shelter; reduce collapse accident consequences; improve nuclear safety (the risk of criticality and radioactive leaks was considered to be high); improve worker and environmental safety; and long-term Strategy and study for conversion to environmentally safe site (including the strategies for dealing with fuel-containing materials (FCM), for the safe confinement and for the implementation of the confinement to support deconstruction and FCM removal).

The SIP authors recognised 'there are numerous open items and questions' and 'that by resolving the open items, through detailed data gathering, investigation, and engineering analyses, key programmatic decisions can be made'. They also identified ten programmatic milestones. The three key milestones were the decisions on strategies for stabilisation and shielding, for confinement and for FCM removal. The results of these decisions - as the SIP authors correctly noted - were a prerequisite for establishing the scope, schedule and cost of the SIP.

The SIP document has fulfilled its purpose by providing a sound basis and logic for decisions that have now brought the SIP very close to completion. With the benefit of hindsight, it is now also easy to see where the SIP underestimated the technical and regulatory challenges of achieving the programmatic decisions and then converting them into approved designs for this one-of-a-kind-facility with a one-hundred-year design life. The institutional environment for the project, including nuclear legislation, nuclear insurance and indemnity, and a stable administrative and regulatory framework, remained below the radar of the SIP authors. It has, however, had a significant impact on implementation of the SIP.

SIP Implementation

Implementation of the SIP began at the end of 1998 after the establishment of the Project Management Unit (an integrated team composed of the Consortium of Bechtel, Battelle Memorial Institute and EDF, and of dedicated Chernobyl staff) and the mobilisation of four engineering consortia. The principal task of the first phase of the SIP was to carry out engineering studies leading to the programmatic decisions and, in parallel, to define the initial set of projects that could be implemented to mitigate the risks arising from the condition of the shelter.

The threat of imminent collapse of the shelter made emergency repairs of the structure an obvious priority. The repairs of the beams supporting the shelter roof, which were completed in 1999, and the stabilisation of the vent stack, whose collapse was threatening both the shelter and Unit 3 (the latter still operating at the time), revealed the site infrastructure, in the broadest possible definition, was non-existent or inadequate to meet even the minimum safety standards. It took until 2004 to build the necessary facilities, provide equipment, establish health and safety and radiation protection procedures - including a state-of- the-art biomedical protection and screening programme - and create the nuclear safety culture required for major construction activities in a heavily contaminated area.

The other key risks perceived at the time - the possibility that radioactive water present in the shelter basement would leak into the water table of the Dnipro basin, or act as moderator to the FCM and lead to a criticality excursion - were addressed during early stages of the work. The possibility of criticality was ruled out as a credible accident scenario. However, an integrated and automated monitoring system, which among other things monitors FCM behaviour, was commissioned in 2010. Additional boreholes have not detected any increase in radiation levels in the shelter surroundings. Once the shelter has been covered by the NSC the remaining water will dry out, which in turn will increase the quantity of radioactive dust. However, dust- management systems and procedures have been successfully implemented.

Reaching a consensus among multiple stakeholders on the three interrelated key programmatic decisions has been extremely demanding. The guidance of the International Advisory Group (an independent multidisciplinary team of experts advising the CSF donor governments and the EBRD) has been instrumental in a process which has scientific, technical and political dimensions.

The scope of the Shelter stabilisation received regulatory approval in July 2001. The analysis of the risks and benefits - primarily the collective radiation dose for workers and the probability and consequences of accidents - led to a set of measures that were substantially reduced compared to scope contemplated in earlier studies.

The preliminary FCM strategy, which deferred FCM removal for several decades, served as one of the main inputs for the decision on the NSC. The option of the lightweight arch was chosen as the result of a consensus view that it is 'structurally efficient and [the] most versatile option to cope with the many uncertainties associated with the future FCM removal and dismantling of the existing shelter'. The confinement decision was approved by a decree signed by the Prime Minister of Ukraine in April 2001, but it took more than a year to overcome bureaucratic obstacles to the commencement of the concept designs which finally received formal approval in July 2004. The set of SIP decisions was converted into a large and complex project that would face many uncertainties and challenges in the ensuing stages of procurement, design and construction.

The contract for the design and construction of the NSC was signed between the Chernobyl Nuclear Power Plant and NOVARKA (a consortium of Vinci and Bouygues) in September 2007, after a protracted procurement procedure that included independent technical and legal assessments and a thorough pre-contract analysis of the design basis for the concept design. The key conclusion was agreement on the need to develop a concept-design safety document to bring together the functional specification, the design safety criteria and the contractor's proposed concept design.

It took until mid-2009 to develop this document, to receive regulatory approvals and to agree on the resolution of regulatory comments. Accommodating requirements for the NSC's resistance to the impact of seismic events of a magnitude of level 6, to tornado class 3 and to heavy wind and snow loads was a particular design challenge for both the main arch structure and cladding. The preliminary design also identified the need to change the design of the main crane: instead of a telescopic mast as foreseen in the technical specification, the crane would be equipped with a tensile truss platform. Discussions about this unique crane to be used for dismantling the shelter and for waste management operations inside the NSC continued for many years until its new technical specification received formal regulatory approval in late 2015, when the crane had already been delivered to the Chernobyl site.

The design was divided into five packages. The three licensing packages were to allow for an early start on the site preparation, for NSC erection and for transfer-zone foundations. The removal of the Unit 3 and Unit 4 ventilation stack, another activity not foreseen in the SIP, was implemented under a separate contract. The NSC design had two licensing steps: the first one (LP 5), including structural design of the arch and the foundations the cladding the main crane system and the preliminary safety analysis, was to allow for the start of manufacturing and erection of the arch steel structures. The second step (LP 6) was defined as the integrated NSC design including the auxiliary buildings and systems, the safety analysis report and the environmental impact assessment.

As the design evolved, concerns were raised about the increased complexity and cost of systems such as the main crane, cladding and corrosion protection. Corrosion control for the 100-year design life had a defining impact on decisions such as the steel grade, coatings and ventilation and humidity control systems. Multiple requirements on the cladding system, including its resistance to tornado class 3 loads, required substantive research before the final solution was adopted.

The most significant design decision at variance with the concept design was the humidity-controlled over-pressurisation of the arch annulus (less than 40% relative humidity to prevent corrosion). Performance requirements on the main crane system made it almost three times more expensive than anticipated in the concept design. Design and cost optimisation have been a constant feature of the NSC design process, but only the detailed design of the cladding and sealing, of the technological and operational systems and of auxiliary facilities revealed the full extent of the design challenges of this first-of-a-kind project. Major design efforts continued until the licensing package (LP 6) for the integrated NSC design received formal concurrence from the regulatory authorities in April 2013.

Site preparatory works were largely completed in 2011. After the removal of contaminated soil the concrete NSC assembly platform was built in the erection zone as a barrier against surface contamination. The 'clean area' allowed simplified access, significantly reduced the need for radiation protection measures for workers and was a prerequisite for the arch-assembly work which commenced in April 2012.

Work on permanent arch foundations required considerable re-design of piling, and occasionally, spectacular radioactive-waste management operations, as both high-level waste and a wide array of contaminated objects buried after the 1986 accident were being discovered.

New Safe Confinement and SIP projects today

All of the SIP tasks, except those directly supporting the NSC construction, commissioning and early deconstruction, have been completed. Stabilisation of the shelter, which began in 2004, was completed in 2008, when 80% of the roof load on the western wall of the shelter was transferred to the new supporting structure. Structural and seismic monitoring became part of the integrated monitoring system. Stabilisation has significantly reduced the probability of collapse and has allowed the work on the NSC to proceed. The shelter's design life has been extended by 15 years, to 2023.

Overall, the NSC construction work has made outstanding progress since assembly of the arch structure began in April 2012. A particular achievement is the excellent health and safety record. Health and safety is central to every activity undertaken on the SIP, with a rigorous industrial and radiation safety programme in place and enforced. There has not been a single incident of a worker on the New Safe Confinement project exceeding international radiation-dose control limits.

The rolling cumulative rate of lost work incidents (lost-time incidents per 200,000 hours) for all SIP projects from 2010-15 is 0.096. This is significantly lower than the incident rate averages in US industry. The construction of the New Safe Confinement is in its final stage. The primary structural work on the arch is complete and almost 90% of cladding has been installed. The ongoing installation of the main crane system is scheduled for completion in June 2016. Pre-commissioning testing will start at the end of May and all the systems in the arch will be installed by October. Finalising as many of the testing activities as possible while the arch is in the 'clean area' is of crucial importance for keeping the collective radiation dose as low as possible.

Work on the technological building in the vicinity of the shelter - which will contain electrical and control systems for the NSC - is being carried out behind a temporary shielding wall. From the radiation protection and health and safety perspective, the most demanding activity is the construction of the NSC-enclosing perimeter walls inside the turbine hall of Units 3 and 4, which are necessary to ensure the confinement function of the NSC. The sealing surfaces, where an elastic membrane interfaces with the existing structures of Unit 3, must be ready before the NSC is slid into its final position. The work on the perimeter walls is making good progress in difficult post-accident conditions and is on track.

The sliding of the arch into its final position is now very ambitiously targeted for November 2016, more than six months earlier than was planned less than a year ago. This is a unique task in which a total weight of more than 35,000 tonnes will be pushed over 300 metres on a rail system by 116 remote- controlled synchronised jacks. The sliding operation at a speed of 10 mph is expected to take two days.

The sealing operations, interconnections between the NSC and the Shelter and the commissioning testing are scheduled for completion by November 2017. At that juncture the safety objectives of the SIP will be met. The overall cost of the NSC is projected to be in the region of €1.5 billion and of the entire SIP approximately €2.1 billion. More than 40 governments and the EBRD have provided the finances to convert the site into an environmentally safe state.

Chernobyl Nuclear Power Plant staff will play a major role in the testing and commissioning of the NSC and its ensuing long-term operation. Their first major task after the operational licence has been granted will be to deconstruct the most unstable elements of the old shelter before its licence expires in 2023. Over the 100-year lifetime of the NSC, the operators, scientists and authorities of Ukraine will have to find a solution for the FCM in the context of a national strategy for high-level radioactive waste. Studies, notably carried out by the Kurchatov Institute in the past and within one of the SIP tasks, concluded that no degradation of the FCM could be observed. Neutron and radiation monitoring systems, as part of the integrated monitoring system, are in place.

The SIP has provided the principal tools for long-term deconstruction and waste management to commence once conditions permit. The challenges of future tasks should not be underestimated but, thanks to the SIP, and for the first time since the Chernobyl accident, a clear path for the long-term future at Chernobyl has been established.

 


*Vince Novak is director of the Nuclear Safety Department at the EBRD. He supports the bank's nuclear safety projects and the seven international multilateral grant funds established at the EBRD. He joined the EBRD in 1997 as the head of the Chernobyl Shelter Fund (CSF). He began his career in the nuclear sector in 1978 after holding numerous positions at major nuclear projects across Europe

Chernobyl
Chernobyl Items left behind in Pripyat following the disaster and evacuation
Chernobyl Power plant control room
Chernobyl
Chernobyl The first stage of the arch being moved into position
Chernobyl The western wall of the shelter
Chernobyl The Safe Confinement zone under construction
Chernobyl
Chernobyl
Chernobyl


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