What are the key issues of environmental protection under conditions of nuclear power plants decommissioning?

(Based on feature ‘Ecological aspects of Chornobyl NPP decommissioning’ by B.Ia. Oskolkov , A.V.Nosovskii in Bulletin of ecological situation within the Exclusion Zone and Zone of the Absolute Resettlement. Issue 16, Chornobylinterinform, 2000.)

On December 15, 2000, the decision of Ukraine about final shutdown of Chornobyl NPP Unit 3 began a final stage of the life-cycle of probably the most famous NPP in the world. The Chornobyl NPP and especially the 1986 accident exerted a strong influence onto all vital aspects of the present-day human society, the natural environment, economic and industry, psychology and politics. Since the moment of the severest accident in the world’s nuclear industry, ChNPP is continuously under a steadfast, attentive eye of the world community. Therefore, the world perceived a long-expected decision about its early decommissioning with great satisfaction.

However, a mere shutdown does not mean disappearance of ChNPP and all its problems. While reducing an NPP operational risk, a stop of electric power generation does not take away potential environmental impact produced by ChNPP.

As any other large-scale industrial project, construction of an NPP crucially changes 
human environment within the area adjacent to the plant, changes natural elements and their interrelation forming local biogeoceonosis or ecosystem. The final decommissioning objective usually includes total dismantling of all NPP structures, reactor fuel unloading, and ultimate disposal of its fuel and all radwaste, in other words, actual termination of man-caused impact and perfect rehabilitation of the environment within the NPP area. Often, the final objective of an NPP decommissioning assumes bringing its industrial site to the state that would allow its use for any other purpose, i.e. only partial elimination of the man-caused (NPP-specific) environmental impact. While performing a set of the abovementioned activities, it is necessary to ensure public and environmental protection from the radioactive and non-radioactive hazards related to the nuclear facility shutdown processes; the problems for the future generations should be also reduced to a minimum.

An adverse impact of any industrial facility, including NPP, onto the environment and human health can be defined by the sum of all the impacts produced by the facility onto an ecosystem:

Σ I = Σ Iecc + Σ Iop – Σ Iben

where, Iop is an adverse operational effect (emissions, releases, resource consumption, etc.),
Iecc are potential detrimental environmental and human effects resulting from eventual emergency situations,
Iben is a positive environmental impact (yield profit, location area improvement, data access, improvement of human living conditions, etc.)

As a result of an NPP decommissioning, I , the total level of impact, decreases down to a value acceptable for a society, when a chance of emergency consequences development becomes negligibly small, operational impact stops, and positive impact remains as great as possible due to local natural recourses revival, positive psychological and emotional effect and accumulation of useful information.

As is well known, an NPP decommissioning is a long and multistage process [7] that should be implemented based on a specially developed Program. According to the effective rules and regulations, the Program should be prepared as early as at the design stage of construction and then it should be continuously revised during the whole period of an NPP operation. Herewith, while developing such a Program, a comprehensive analysis of the planned environmental activities and assessment of the environmental effects produced in the course of the project implementation should be carried out. In accordance with the international and national requirements (Laws of Ukraine ‘On Environmental Protection’, Clause 51 and ‘On the Uses of Nuclear Energy and Radiation Safety’, Clause 37), NPP Decommissioning Programs should include a separate section on ‘Environmental Impact Assessment’ (EIA).

The objective of this section in the Program is to describe the following: what environmental impact is anticipated as a result of the project implementation; how environmental protection aspects should be envisaged by financing, planning and implementation procedures of the project; what ecological results are anticipated and how they should be achieved. Identification and addressing of environmental problems at early stages of NPP decommissioning may help to avoid excessive expenditures and delays in the project progress caused by nature-preservation contingencies.

From the viewpoint of environmental protection, the following should be analyzed in the EIA section during the Chornobyl NPP Decommissioning Program development:

  • current situation at the plant and actual environmental impact of ChNPP in general (assessment of radiation and non-radiation factors’ impact on the local ecosystem), including separate assessments for major ecologically hazardous objects, such as the Shelter Object, cooling pond, contamination of the industrial site and groundwater;
  • carry out predictive risk assessments of an adverse effect on biosphere or its elements (critical elements): during the project progress; during operation; in the future, following decommissioning of the facilities required to attain the Program objectives.

The Program should clearly describe ecological safety goals and objectives (levels) for separate facilities and the ChNPP on the whole, which should be achieved during the project progress. It should also characterize the local ecological situation resulting from ChNPP decommissioning, i.e. ecological outcome of the project.

The objective of the abovementioned analysis is to coordinate basic ecological and health criteria, safety criteria, actions to remediate existing environmental conditions and a program for their improvement (Environmental Management Plan). Also monitoring and reporting requirements should be identified. An Environmental Management Section (EMS) of EIA should include major problems, measures taken to appropriately address them, schedule, and cost-estimate for corresponding expenditures. Some of the measures may be urgent, in particular, those imposing a substantial risk to human health and safety in case requirements and permissions of regulatory bodies are not observed. The EMS also concerns the issues requiring a long-term or step-by-step approach, such as observation of the regulatory bodies’ prospective requirements, including comparability with the European Union’s standards or other international legal acts, standards and practice (for example, the Convention on the environmental impact assessment in a transboundary context).

While decommissioning the Chornobyl NPP, it is necessary to consider not only ecological requirements and legislation, but also adherence to the requirements stated in the Concept of the Chornobyl Exclusion Zone within The Territory of Ukraine (1995) and Draft Concept of the Chornobyl Exclusion Zone and radiationally hazardous lands within the territory of Ukraine.

The EIA Section of the Program should also set out an assessment of a potential negative environmental impact emerging while performing some large-scale activities, appropriate efforts to prevent and mitigate such an impact, predictive estimates of a potential damage to human health and environment from the radiation risk viewpoint (assessments of radiation burden for personnel and environment) during:

  • implementation (carrying out engineering work at each stage of the activities);
  • further operation of some facilities (RAW processing plants, RAW storage facilities, etc.) both now and in the far future; also, it is required to present predictive estimates for the future human (personnel) radiation burden during decommissioning these facilities.

The NPP Decommissioning Program should also take account of its obligatory expert assessment during the agreement and approval process. According to Laws of Ukraine ‘On the Uses of Nuclear Energy and Radiation Safety’, Clause 40, and ‘On the Environmental Protection’, Clause 27, the compulsory ecological expert assessment of the projects that may produce a negative impact on the environment is required. Moreover, being a large-scale investment project, the NPP Decommissioning Program also comes under the state investment expert assessment, including environmental one, as per Law of Ukraine ‘On the Investment Activity’, Clauses 8 & 15, and Resolution of the Cabinet of Ministers of Ukraine ‘On Approval of Investment Programs and Projects, Carrying out the State Expert Assessment of Investments’ No.473 of August 15, 1992.

Decommissioning is an ordinary stage of any NPP operational life. However, it is quite different at the Chornobyl NPP due to its early shutdown and the 1986 accident consequences.

The ahead-of-schedule closure has not allowed timely and full-scope fulfillment of all the required procedures (incl. the NPP decommissioning program development, financial assets accumulation, etc.)

The accident consequences, including the problems of the territory radioactive contamination, cooling pond and certainly the Shelter Object, significantly increase complexity and scope of the activities required to eliminate the adverse environmental impacts.

Among major consequences of the 1986 accident is a total radioactive contamination of all the equipment located in the buildings and structures of the ChNPP industrial site; as a result, non-radioactive waste is practically absent at ChNPP. Therewith, extremely various characteristics (specific activity, radionuclide composition, physicochemical properties and location) of the radwaste accumulated at the ChNPP should be considered. Based on assessments, an approximate total volume of the ChNPP radwaste subject to processing and disposal during ChNPP decommissioning, including the Shelter Object and the industrial site area, is 3.2 million tons. Processing and subsequent disposal of such a volume of the radwaste is a complex technical and ecological problem. Currently, there are no solutions on high-level radwaste disposal and ultimate storage of the spent nuclear fuel.

The Shelter Object, which in reality is a non-decommissioned nuclear power Unit 4, by no means may and should be excluded out of the program for ChNPP decommissioning activities. In the Statement on regulatory policy regarding the Shelter Object nuclear and radiation safety issued by the SSE Chornobyl NPP (approved by Order No 49 of April 8, 1998 issued by the Ministry of Environmental Protection of Ukraine) the wording of the Shelter Object status is as following: the Shelter Object is Chornobyl NPP Unit 4 destroyed as a result of the beyond-the-design-basis accident, which has lost all operational properties of a power unit, where the first-priority actions to mitigate the accident consequences have been performed and the works to ensure its nuclear and radiation safety are in progress. Consequently, being a part of the Chornobyl NPP, the Shelter Object should be decommissioned in accordance with the abovementioned requirements of the environmental legislation. However, none of the effective documents regarding the SO includes comprehensive activities focused on environmental safety achievement as well as clearly specified ecological objectives. The strategy of works to be performed at the Shelter Object is described in the following effective documents: “Principal directions of the activity for the Shelter Object safety assurance during 1995 – 2000”, 1995; “Prospective Program of the Shelter Object transformation into ecologically safe system”, 1996; “Shelter Object Stabilization Plan”, 1996; “Shelter Object Transformation Strategy”, 1997. The latter provides for “a removal of fuel-containing materials from the Shelter Object, their conditioning, conversion into a safe condition by way of relocation inside the protective barriers and controlled storage in RAW storage facilities…” (‘The Shelter Object Transformation Strategy”, i. 4.3.1). Unfortunately, the following have not been considered anywhere yet: what ecological outcome should be obtained as a result of performing the works above; what ecological criteria should be met by the results; and what environmental impact the process of this strategy implementation will have. So far, this problem is actually shifted on the shoulders of our offspring.

Addressing the cooling pond problem requires special consideration within the framework of ChNPP decommissioning. The ChNPP cooling pond is a unique artificial water body having become a natural radwaste storage reservoir after the accident. On the one hand, it is a radiationally hazardous reservoir comprising a significant bulk of radwaste, which state is scarcely known and storage conditions do not meet the requirements established by standards and regulations. On the other hand, it is an engineering facility supplying the Chornobyl NPP with service water, though its operational functions will be changed because of the NPP decommissioning. Besides, from the viewpoint of the radiobiology the cooling pond is one of the largest and unique water bodies in the local ecosystem. The solutions related to the cooling pond should take account of all the three aspects of the problem.

In addition to the aforesaid large-scale and quite evident problems that determine the ChNPP decommissioning specificity, there also exists a problem of the groundwater contamination.

As is well known, there is a water exchange zone within the bounds of the ChNPP industrial site. And radioactive contamination of groundwater may occur in the zone including the two aquifers deemed to be Quaternary and Eocene sediments. The aquifer in Quaternary sediments is spread within the whole territory of the ChNPP site. Analysis of the data obtained during long-term observations indicates an existence of a quite spread streak of radioactively contaminated groundwater within the limits of the ChNP industrial site. Currently, 137Cs average concentration in ChNPP groundwater is in the range of 1-5 Bq/litre. The most significant increase of 137Cs concentration in the groundwater (within the range from 10-40 1-5 Bq/litre up to 313 Bq/litre) is observed within Level II area. Distribution of 90Sr concentrations indicates that the groundwater contain a well-marked increased concentration (>100 Bq/litre) aureole stretching from South-West to North-East and also spread under Level II area. At the Shelter Object site, 90Sr average concentrations are 3 – 650 Bq/litre. There are local plots with increased 90Sr concentration ranging from 80-100 Bq/litre and even up to 3600 Bq/litre. The trend towards an increase of radionuclides specific concentration is observed in the industrial site groundwater, in the wells located within the maximum surface contamination areas. Although, the contaminated groundwater is not used for practical purposes and no possible contamination of the aquifer being a source of drinking water supply is registered now, the fact of its radioactive contamination requires the most careful ecological analysis in the case of making a long-term future forecasts and is undoubtedly among ChNPP ecological problems.

While developing the Chornobyl NPP Decommissioning Program, it is necessary to consider all real ecological conditions of its existence. And an attainable and appropriate end result, in other words an ultimate environmental objective, should be defined taking into account economic capacities.

Ecological results of ChNPP decommissioning may be defined reasoning from the following principles:

  • the level of environmental safety resulting from the activities should be as maximum as reasonably achievable with due regard to economic and social factors, it also should be generally acceptable for the society;
  • ChNPP decommissioning processes should not result in irreversible changes of the ecosystem’s natural elements (divestment of lands, loss of species, changes in litho and aqua spheres);
  • natural processes of the Chornobyl Exclusion Zone biogeocenosis self-recovery should not be disturbed;
  • ChNPP decommissioning activities should result in the 1986 accident consequences mitigation;
  • implementation of the activities should not bring additional problems for future generations;
  • public and personnel exposure during the working progress should not exceed the levels fixed in the national standards;
  • predicted public and environmental exposure should not exceed the levels stated in National Standards NRBU-97/D-2000.

From an ecological perspective, the Chornobyl NPP decommissioning stages are generally the same as at any other NPP. However, starting with one of the most complicated and large-scale stages, i.e. RAW processing and disposal, the factors resulting from the accident become critically important at the Chornobyl NPP.

Unfortunately, the conceptual and program documents for ChNPP decommissioning developed to date do not provide answers to many ecological questions.

The existing concept and Program of ChNPP Units Decommissioning [1-5] provide for fuel unloading, processing of the accumulated RAW with subsequent decontamination and dismantling of low-level structures and further conservation of the reactor facilities in the available engineering structures for a period of at least 30 years. What’s next? These documents do not provide an answer. At the same time, it is implied that an environmental impact of such disused installations is insignificant; economic activities are no longer implemented within their location area that is not used by people (useless). It is scarcely possible to completely agree with such a solution. Firstly, the fundamental provision on a complete termination of the facility’s environmental impact is not observed and no land rehabilitation is assumed. Secondly, there is no justification of the decision taken. Finally, the ecological objective of ChNPP decommissioning including the Shelter Object is not clearly defined (there is only a slogan ‘environmentally safe system’). It is not specified what safety and ecological impact criteria should be met by a future system of the Shelter.

As noted above, the final objective of an NPP decommissioning, from an ecological point of view, is to cease its adverse impact on the local ecosystem and renew natural conditions to the initial level, i.e. the one registered ‘before an NPP construction’ (for example, ‘green field’), or to the level currently acceptable for the society, taking into account minimization of the problems faced by future generations. Such a result is practically unachievable for the Chornobyl NPP. In reality, recovery of the local ecosystem’s elements to their initial condition is practically impossible because of the post-accident contamination.

The mere recovery of the pre-accidental characteristics of the soil contamination level would require enormous financial expenses, huge scope of decontamination activities, which would be accompanied by significant additional exposure of personnel, formation of large radwaste quantities, and would have a greater, not less, negative impact on the environment. Therefore, it makes sense to determine ecological results of ChNPP decommissioning from a bit different point of view.

We usually consider rehabilitation of a territory from the human point of view only, i.e. if absolute and unlimited use of natural recourses by a man is possible within a territory, then a recovery goal was achieved . We acknowledge an independent value of nature; though for some reason while speaking about results of definite territory rehabilitation we often mean an opportunity to use it exactly by a man. We assess radiation factor only based on a value of human radiation burden; we examine a territory from the viewpoint of its fitness for agricultural activity or permanent residence of people. Though, it’s wrong. Recovery of natural conditions within a territory is not a renewal of industrial system. These notions are different.

How should we assess a natural biogeosystem? Probably, if all presently known ecological laws and standards hold true in an ecosystem, i.e. all biocenosis in the system develop without a human interference, if the system does not degrade, then this is a natural ecosystem.

If we consider the Chornobyl Exclusion Zone emerged after the accident from the viewpoint of natural recourses development, then we should state that it is not a territory of ‘the greatest ecological catastrophe’ as is often called by the media. Local environmental landscapes are still developing; active processes of natural biocenocis succession and rehabilitation are in progress. The territory becomes ‘a catastrophe’ only when admitting the fact that unlimited human use of this area is unsafe for a man’s life and health. Objective data on an ecological catastrophe are absent.

Taking into account the thoughts above, rehabilitation of the Exclusion Zone will have a bit different form. And the activities, including ChNPP decommissioning, should be performed there based on the principles of minimization of human interference and industrial impact on natural resources, i.e. elimination of the human activity aftermaths within the territory under consideration and exclusion of any hazardous impact of the Exclusion Zone on the national public health.

These results may be obtained as a result of implementing the set of activities provided by the abovementioned programs, that is removal and reliable disposal of spent fuel, operational RAW, and the Shelter Object fuel-containing materials (FCM). Herewith, new RAW processing and disposal facilities should be constructed completely conformant to the requirements of the effective standards (in particular, potential public exposure should be assessed taking NRBU-97/D-2000 into account); all the environmental requirements relating to contaminants discharge and emission should be also observed.

It is required to envisage the measures to ensure maximum possible removal of radioactivity or maximal fixation of radioactivity in case the removal is not possible from economic point of view. What does it mean? The Program should specify a level for the structures’ maximum allowable residual radioactive contamination, in which case they should not be disposed as RAW. An average level of radioactivity content in soils of the near zone (0-5cm surface layer) should become a decision criterion. All the material, structures, etc. characterized by a higher level of radionuclides content are to be processed and disposed as RAW. This point refers to not only the structures of the formerly operated units, but also to the Shelter Object. Some structures may be left in situ, in case stable fixation of radioactive contamination and impossibility for radionuclides migration into the environment under any probable impact during the plant and Exclusion Zone conservation term are proved. All items that are movable and which activity is higher than the allowable levels should be processed and disposed.

A special consideration is required for the issue of the industrial site post-accident contamination with the high-level reactor elements thrown out during the accident and further covered with concrete or soil during the consequences elimination and the “sarcophagus” construction. Thus, it is necessary to carry out a comparative assessment of the ecological consequences caused by search and removal of such residues and preservation of their current state.

As for rehabilitation of the territories occupied with the ChNPP buildings and constructions, including those of Level 3 subjected to conservation in 1987, it is expedient to abandon them and let natural destruction to take place based on economic analyses and taking into account the principle of minimizing human activity within the Exclusion Zone. Though, a control of destruction processes safety should be ensured. The Program may include a list of facilities and areas, which territory may be potentially rehabilitated in terms of the Exclusion Zone conditions. In other words, some objects can be completely dismantled, and the soil stratum with the radioactive contamination levels not exceeding the ‘near zone’ average values or lower may be rehabilitated within this territory.

As noted above, the cooling pond, an artificially created water body, which existence is ensured by the annual inflow of 130 million m 3 of water from the Prypyat River, requires special attention. There are over 5,000 Ci of radioactive agents contained in the pond bottom sediments (4 500 Ci of 137Cs and 950 Ci of 90Sr, according to the 1991 assessments). The cooling pond cannot be liquidated without a thorough ecological analysis. As it appears from the recent detailed analyses of the information on the cooling pond [6], there is a lack of data required to take reasonable decisions, i.e. there are no complete data on quantity and distribution of radioactivity in the pond, its physicochemical characteristics, as well as the data required to forecast the radioactivity behavior in the future and assess a risk of its impact onto public health and the environment.

In view of the ChNPP Decommissioning Program absence, the problem of fire-safety and service water supply to the power units, Shelter Object and facilities being under construction has not been addressed to date.

A comprehensive analysis of the cooling pond’s ecological importance for the local ecosystem and the world is not available. Stretching over an area of 22 km2, the world’s largest radioactive water body characterized by an abundant and varied flora and fauna (more than 41 fish species, over 120 algae species) is a unique radiobiological laboratory. Conservation of this pond as an element of the local ecosystem is crucially important and its potential use may be of greater benefit than the costs required for its maintenance and decontamination.

Previously proposed cooling pond management options are poorly justified, including economic apects, and do not cover all aspects of the problem.

A detailed mapping of radionuclides distribution (1:10 000 general maps and 1:5 000- 1:2 000 maps of the most contaminated areas), research of physicochemical characteristics of the fuel particles producing the pond radioactive contamination seem necessary with the objective to address the problem on a scientifically justified basis. The following is required: development of technical proposals on water supply to the ChNPP power units subject to decommissioning, Shelter Object, and facilities under the construction; experimental and theoretical modeling of radionuclides migration from the pond; and seismic and radiological risk assessment. It is possible to conduct these activities during Stages1& 2 of the ChNPP decommissioning process (2-3 years after Unit 3 shutdown [7]).The cost-benefit analysis is a must for all options of the pond management.

Many ecological aspects of the ChNPP decommissioning problem, especially RAW management and groundwater radioactive contamination, cannot be solved appart of the Chornobyl zone problems and general nuclear requirements in Ukraine. Detailed designs of all new facilities under construction including ‘Vector’ Waste Disposal Complex, the Liquid Radioactive Waste Treatment Plant, the Spent Fuel Storage Facility (ISF-2), the new ChNPP Replacement Heat Plant, contain EIA sections developed in line with the requirements of the Ukrainian legislation. However, the authors of the article would like to emphasize that the general complexity of the problem requires a scientifically justified analysis of all its aspects and a comprehensive system approach to their solving.  Many tasks related to the Chornobyl Zone and the Chornobyl NPP ecology may be addressed within the framework of the ChNPP Decommissioning Program.

References:

  1. Concept of the ChNPP Units 1,2&3 Decommissioning . VNIPIET, 1990.
  2. Concept of the Chornobyl NPP Decommissioning , Kiev Institute ‘Energoproject’, 1992.
  3. Action Plan of the Chornobyl NPP Decommissioning , Kiev Institute ‘Energoproject’, 1992.
  4. Draft ‘Preparation for Decommissioning the Chornobyl NPP RMBK Reactors 1,2, &3’ developed by the AЕ A Technology (UK) under КЕС UR / 028 contract within the framework of TAС IS Program.
  5. Comprehensive Program of the Chornobyl NPP Decommissioning . Kyiv Institute ‘Energoproject’. 1997
  6. Collection and Analysis of Information and Data related to the Contamination of the Chornobyl Cooling Pond. Study contract B7-5350/99/6241/MAR/C2, 2000.
  7. A.V. Nosovskiy., O.Ye .Skripov, V.K. Tolstonogov. Preparation of the ChNPP for Decommissioning . Issue15, 2000.