Decommissioning of Nuclear Installations

Transcription

1 Decommissioning of Nuclear Installations

2 Definition of Decommissioning The administrative and technical actions taken to allow the removal of some or all of the regulatory controls from a nuclear facility (except for a repository or for certain nuclear facilities used for the disposal of residues from the mining and processing of radioactive material, which are closed and not decommissioned ). The two main objectives of decommissioning are to render the site permanently safe and to recover it, as far as practicable, for reuse

3 Present situation of NPPs and other installations 435 NPPs operating (as of February 2015) 31 countries, total of MWe capacity 70 reactors are being built 240 research reactors in 56 countries 180 reactors on ships/submarines

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5 Situation of shut-down and/or decommissioned nuclear installations About 100 mines, about 110 commercial power reactors, 46 experimental or prototype reactors, over 250 research reactors and a number of fuel cycle facilities, have been retired from operation. Some of these have been fully dismantled. Most parts of a nuclear power plant do not become radioactive, or are contaminated at only very low levels. Most of the metal can be recycled. Proven techniques and equipment are available to dismantle nuclear facilities safely and these have now been well demonstrated in several parts of the world. Decommissioning costs for nuclear power plants, including disposal of associated wastes, are reducing and contribute only a small fraction of the total cost of electricity generation.

6 Experience France: Chinon, Bugey and St: partial dismantling and postponed final dismantling and demolition for 50 years. A recycling plant for steel from dismantled nuclear facilities is at Marcoule, in France. This metal will contain some activation products, but it can be recycled for other nuclear plants. UK: 29 reactors, 25 of them early Magnox types with graphite moderators. One of the first was Berkeley nuclear power station (2 x 138 MWe), The reactor buildings are in an extended Safstor period. E: Vandellos 1, a 480 MWe gas-graphite reactor, was closed down in After 30 years Safestor, when activity levels have diminished by 95%, the remainder of the plant will be removed. Germany: Eleven of Germany s 19 decommissioned units are subject to immediate dismantling. (EUR 30 billion set aside for decommissioning and waste disposal.) Germany chose immediate dismantling over safe enclosure for the closed Greifswald nuclear power station in the former East Germany, where five reactors had been operating. Similarly, the site of the 100 MWe Niederaichbach nuclear power plant in Bavaria was declared fit for unrestricted agricultural use in mid The 250 MWe Gundremmingen A unit was Germany's first commercial nuclear reactor, operating Decommissioning work started in 1983, and moved to the more contaminated parts in 1990, using underwater cutting techniques. This project demonstrated that decommissioning could be undertaken safely and economically without long delays, and recycling most of the metal.

7 Experience Japan's Tokai 1 reactor, a 160 MWe UK Magnox design, is being decommissioned Experience in the USA has varied, but 13 power reactors are using the Safestor approach, while 16 mostly single-unit plants are using, or have used, Decon. Procedures are set by the Nuclear Regulatory Commission (NRC), and considerable experience has now been gained. A total of 32 power reactors have been closed and decommissioned. NRC requires that the operating license of a closed reactor be terminated and decommissioning activities be completed within 60 years Rancho Seco (single 913 MWe, PWR) was closed in 1989, and in 1995 NRC approved a Safestor plan for it. However, the utility subsequently decided upon incremental dismantling and this was completed in 2009, leaving about 3 ha still under NRC licence for waste storage. About 32 ha has been released for unrestricted use. Thus, after 14 years of comprehensive clean-up activities, including the removal of fuel, debris and water from the 1979 accident, Three Mile Island 2 was placed in Post-Defuelling Monitored Storage (Safstor) until the operating licence of Unit 1expires, so that both units can be dismantled together. San Onofre 1, which closed in 1992, was put into Safestor until licences for Units 2 and 3 expired in The cost of fully decommissioning them is estimated at $4 billion. A US Decon project was the 60 MWe Shippingport reactor, which operated commercially from 1957 to It was used to demonstrate the safe and costeffective dismantling of a commercial scale nuclear power plant and the early release of the site. Defuelling was completed in two years, and five years later the site was released for use without any restrictions. Because of its size, the pressure vessel could be removed and disposed of intact

8 Why have the plants been shut down? Country Reactor Type MWe net Years operating Shut down reason Germany Greifswald 5 VVER-440/V /1989 Partial core melt Gundremmingen A BWR /1977 Botched shutdown Japan Fukushima Daiichi 1 BWR /2011 Core melt from cooling loss Fukushima Daiichi 2 BWR /2011 Core melt from cooling loss Fukushima Daiichi 3 BWR /2011 Core melt from cooling loss Fukushima Daiichi 4 BWR /2011 Damage from hydrogen explosion Slovakia Bohunice A1 Prot GCHWR Core damage from fuelling error Spain Vandellos 1 GCR mid 1990 Turbine fire Switzerland St Lucens Exp GCHWR Core Melt Ukraine Chernobyl 4 RBMK LWGR /1986 Fire and meltdown USA Three Mile Island 2 PWR /1979 Partial core melt

9 IAEA documents

10 What are the main phases of decommissioning?

11 The critical tasks / The process Initial characterization of the plant Fuel removal Containment maintenance and modification Decontamination Dismantling Final radiological survey

12 Initial characterization of the installation A survey of radiological and non-radiological hazards is an important input for the safety assessment and for implementing a safe approach A characterization report should be prepared which documents the information and data obtained during the characterization process. An adequate number of radiation and contamination surveys should be conducted to determine the radionuclides, maximum and average dose rates, and contamination levels of inner and outer surfaces of structures or components throughout the reactor installation. For completeness, contamination in shielded or self-shielded components, such as inside pipes and pumps, should be characterized. Results of such surveys will aid in the preparation of radiation and contamination maps.

13 Characterization before dismantling : a difficult job but a lot of possibilities Before dismantling: by direct measurement on site by sampling & measurement (lab or radiochemistry) by remote monitoring (e.g. ISOCS) by calculation (improvements in activation codes and even contamination models)

14 Containment maintenance and modification Containment is an important element of defence in depth to prevent the movement of residual radionuclides. Containment systems should remain intact as long as necessary and feasible. However, the containment may require changes during decommissioning as radioactive materials (spent fuel and operational waste) are removed from the installations or as the installation is modified, for example, in order to increase accessibility. When containment related barriers or devices are removed or altered in the course of dismantling, acceptable confinement of residual radioactive material should be planned and demonstrated by the operating organization. Similarly, adequate containment should be planned and demonstrated when cutting and dismantling operations are carried out which may give rise to airborne contamination.

15 Decontamination A broad range of activities directed to the removal or reduction of radioactive contamination in or on materials, structures and equipment at a nuclear installation. Decommissioning of a reactor may be aided at certain stages by partial or total decontamination. Decontamination may be applied to internal or external surfaces of components and systems, structural surfaces and the tools employed in decommissioning. The objectives of decontamination include: (a) a reduction of exposures during decommissioning activities; (b) a minimization of the volume of the categories of material to be classified or disposed of as solid radioactive waste; and (c) the increase of the possibility of recycle and reuse of equipment, materials or premises.

16 Dismantling There are many available dismantling techniques applicable to reactor decommissioning. Each technique carries some advantages as well as some disadvantages. Selection of methods and techniques to be used in safe dismantling should take into account such aspects as: the types and characteristics (e.g. size, shape and accessibility) of materials, equipment and systems to be dismantled; the availability of proven equipment; the radiation hazards to the worker and the general public, e.g. level of activation and surface contamination, production of aerosols and dose rates; the environmental conditions of the workplace, e.g. temperature, humidity and atmosphere; the radioactive waste and secondary waste produced; the non-radioactive waste produced; and the requirement for development work.

17 Characterization & measurement during D&D: a hard job Some measurements have to be carried out during the dismantling to allow sorting the material or defining the route to follow

18 Final radiological survey At the completion of the decontamination or dismantling activities, a survey of the residual radionuclides at the reactor site should be performed to demonstrate that the residual activity complies with the criteria set by the national regulatory authority and the decommissioning objectives have been fulfilled. The survey may be carried out in phases, as decommissioning work is completed, to enable parts of the site to be released from regulatory control.

19 Characterization after decommissioning: an important step For radwaste management or material free release, the needs for characterization are important! Gross gamma counting Gamma spectrometry Alpha spectrometry Use of isotopic vector...

20 Time requirements The time period to the decommissioning activities for nuclear power plants and research reactors may typically range from a few years to decades (for example, to allow for radioactive decay). As a consequence, decommissioning may be carried out in one continuous operation following shutdown or in a series of discrete operations over time (i.e. phased decommissioning) Subject to national legal and regulatory requirements, a nuclear installation or its remaining parts may also be considered decommissioned if incorporated into a new or existing facility, or even if the site at which it is located is still under regulatory or other institutional control. This could apply, for example, to the decommissioning of a nuclear installation located on a multifacility site.

21 Options Immediate Dismantling (or Early Site Release/'Decon' in the US): This option allows for the facility to be removed from regulatory control relatively soon after shutdown or termination of regulated activities. Final dismantling or decontamination activities can begin within a few months or years, depending on the facility. Following removal from regulatory control, the site is then available for re-use. Safe Enclosure ('Safstor') or deferred dismantling: This option postpones the final removal of controls for a longer period, usually in the order of 40 to 60 years. The facility is placed into a safe storage configuration until the eventual dismantling and decontamination activities occur after residual radioactivity has decayed. Entombment (or 'Entomb'): This option entails placing the facility into a condition that will allow the remaining on-site radioactive material to remain on-site without ever removing it totally. This option usually involves reducing the size of the area where the radioactive material is located and then encasing the facility in a long-lived structure such as concrete, that will last for a period of time to ensure the remaining radioactivity is no longer of concern.

22 Options A specific decommissioning option will, among other things, define the timing and the sequencing of decommissioning activities. Decommissioning options can range from immediate dismantling and removal of all radioactive materials from the site, allowing unrestricted release, to an option of in situ disposal involving encapsulation of the reactor and subsequent restriction of access An intermediate option consists of a minimum degree of early dismantling and of conversion of the plant to safe enclosure, before eventual dismantling. Similarly, options can include the dismantling of some parts of the plant, usually externally accessible areas, while placing others, particularly the reactor core, into a safe enclosure mode. Most options consider the safe removal of the fuel and operational waste early in the decommissioning phase in order to obtain a significant reduction in the hazard associated with the installation

23 The selection of a safe enclosure option for a defined period of time is known as deferred dismantling. If the chosen option is deferred dismantling, studies of appropriate methods and approaches should still be conducted in preparation for the eventual dismantling.

24 Examples for techniques

25 Building wall clearance through ISOCS (Vandellos NPP, Spain)

26 The Vaporsphere at ANL, USA, a former nuclear facility, now a warehouse

27 Journalists watching decommissionin g activities at Vandellos NPP, Spain

28 Handheld mechanical cutting equipment for small contaminated pipes (decommissioning with limited resources)

29 A1 NPP Slovakia, Aladin gamma camera

30 A1 Slovakia Graphic simulation (IGRIP)

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32 Development of the technology Eg. the US has carried out many times the one piece removal of RPV...

33 Is technology mature? Current technology is able to carry out most decommissioning activities and operations Nevertheless, improvements can be done for improving the operations The incentives to improve technology are rather important: reduce the costs limit the waste production reduce operator exposure reduce contamination hazard improve the industrial safety reduce the industrial and financial risk be able to react to unforeseen situations

34 Decontamination: this concept covers a very broad spectrum of activities Metal decontamination: before dismantling after dismantling Concrete decontamination Site or soil decontamination

35 Greifswald Networks/IDN/idnfiles/CuttingTechniqueWkp- Germany2011/EWN_Dismantling_of_the_reactors_o n_the_greifswald_nuclear_power_plant_site.pdf

36 Example of application of thorough chemical decontamination: the Medoc workshop at BR3

37 Material after decontamination

38 Another example: Projection of CO 2 ice or water ice CO 2 ice pellets are projected at high speed against the surface The CO 2 pellets evaporate and remove the contamination The operator works in ventilated suit inside a ventilated room to remove CO 2 and contamination Needs some decontamination tests before selecting the process (not efficient for deep contamination)

39 New techniques are currently developed to improve the efficiency and reduce the effluents Methods based on laser ablation Increasing the pressure of the water jetting New chemical or electrochemical methods; new effluents treatment methods Other methods... But they are still under development!

40 Examples of Hand scabbling (labour intensive) Courtesy from Belgoprocess

41 Automatic wall shaver Close up view of the machine Use on a reprocessing cell wall Courtesy from Belgoprocess

42 Remote controlled jackhammer Courtesy from Belgoprocess

43 Some other shots... Brokk and jackhammer Diamond centerless saw Shaver

44 Some views of the very large number of processes Explosive Cutting Pipe cutter Laser Cutting Plasma Cutting

45 The cut pieces must match the material handling and removal requirements Output dismantling = Input material management e.g. Belgian standard : 400-l drum