Specificity of decontamination and remediation activities after accident

Transcription

1 Specificity of decontamination and remediation activities after accident Sergey Mikheykin D-R PMU, Kozloduy NPP site Workshop on development of specific decontamination techniques for RBMK dismantlement and/or highly active material from contaminated areas from accident conditions, Visaginas, Lithuania, International Atomic Energy Agency

2 Definition Any unintended event, including operating errors, equipment failures and other mishaps, the consequences or potential consequences of which are not negligible from the point of view of protection or safety. [ SAFETY GLOSSARY. TERMINOLOGY USED IN NUCLEAR SAFETY AND RADIATION PROTECTION EDITION] Workshop, Visaginas, Lithuania on August 20-24,

3 Accidents/INES Off Site Impact On Site Impact 3

4 Waste after accidents The main differences in waste management system in normal operation and after accident are wide spectrum of wastes (liquid, solid: soil, concrete, metals, debris, vegetation etc) and large volume of radioactive wastes. For severe accident and cleanup, waste volumes are expressed in tens thousands or even millions of m 3. Special RWM strategies needed to address accident and cleanup waste due to the very large volumes, range of activities, timeframe, etc. Workshop, Visaginas, Lithuania on August 20-24,

5 EXAMPLES Major accident (INES Level 7): Major accident (INES Level 7): Serious accident (INES Level 6) Accident with wider consequences (INES Level 5): Chernobyl NPP, Ukraine Fukushima Daiichi NPP, Japan Mayak Reprocessing plant Kyshtym USSR Three Mile Island TMI-2, USA 1986 The releases from Unit 4 continued for 10 days, and included radioactive gases, condensed aerosols and a large amount of fuel particles. Area of more than km Tepco estimates published in May 2012 showed a total of about 1020 PBq released to the atmosphere over March 2011 (after which very little was released). Apart from noble gases this comprised 500 PBq iodine-131, 10 PBq Cs-137 and 10 PBq Cs In iodine-131 equivalent terms this comes to = 940 PBq Iodine-131 released to atmosphere 1957 Some km2 received contamination higher than 3.7 kbq/m2 of Sr-90. This delineated an area of approximately 1000 km2 that became known as the East Urals Radioactive Trace Approximately 2500 m 3 of water with an activity of 1 TBq/m3 were released into the auxiliary building, fuel handling building, service building and diesel generator building. Experiences and Lessons Learned Worldwide in the Cleanup and Decommissioning of Nuclear Facilities in the Aftermath of Accidents, Nuclear Energy Series, No. NW-T-2.7 5

6 EXAMPLES Accident with local consequences (INES Level 4): Serious incident (INES Level 3) Incident (INES Level 2) Anomaly (INES Level 1): A-1 Jaslovské Bohunice, Slovakia THORP Reprocessing Plant Sellafield Ltd, UK Atucha NPP Argentina (Reactor) Mihama NPP Japan 1977 Fuel integrity was lost as a result of two fuel loading events resulting in extensive damage of fuel cladding and release of radioactivity Following plant mass balance calculations, a pool of 83 m3 of product liquor was discovered within the feed clarification cell of the THORP reprocessing plant. No liquor was lost to the environment and no persons were injured or contaminated following this event Overexposure of a worker at a power reactor exceeding the annual limit A water pipe in a turbine building adjoining the Mihama 3 reactor burst suddenly as workers prepared to conduct a routine safety inspection. Though no radiation was released, the steam explosion killed five plant workers and injured others. Experiences and Lessons Learned Worldwide in the Cleanup and Decommissioning of Nuclear Facilities in the Aftermath of Accidents, Nuclear Energy Series, No. NW-T-2.7 6

7 The principle events Event Plant Date Current Status Windscale 1957 Care and Maintenance / Safe Enclosure TMI Care and Maintenance / Safe Enclosure Chernobyl 1986 Post Accident Clean up / Safe Enclosure Fukushima 2011 Emergency Response / Stabilisation Kyshtym 1957 Site Remediation A1 Safe Enclosure / Decommissioning Workshop, Visaginas, Lithuania on August 20-24,

8 Differences ## D&D Emergency 1 Facility is under regulation control within all Lost control as result of accident operation time 2 Records keeping, good knowledge about site No records, lack of information about present status of contamination and infrastructure 3 Control to constructive materials, process and main equipment 4 Operations in according with licensed decontamination plan 5 Need development of Decontamination plan at 1-5 years before shutdown of facility No control, partially demolished constructions and shields Needs in quick responds, possibilities for untypical solutions Decontamination plan developing AFTER accident 6 Standard management approaches Emergency management under pressing of time, irradiation and unknowns, many surprises 7 Strong regulation control, strong implementation of safety standards for operations Possibility to change of safety limits 8 Work of professional teams (selected as result of competition/tender process) 9 D&D activity should provide the owner of the Facility Needs in well - skilled personnel (radiophobia) Owner may have no resources, needs in the Governmental or International support Workshop, Visaginas, Lithuania on August 20-24,

9 Role Decontamination and remediation starting with the start of post-accidental works. The role of these actions are reduction of risk for personnel from irradiation/inhalation and protection of environment from the distribution of radioactive substances with natural factors as wind and water streams (rain, snow melting, groundwater streams). Decommissioning and site remediation after accident are under strong pressure of irradiation, absence of full information about present status of accidental site, time pressure, absence of well skilled decontamination team etc. Workshop, Visaginas, Lithuania on August 20-24,

10 Phases of planning of post-accident cleanup projects. Planning Phases for INES Scale 1-4 Planning Phases for INES Scale 5-7 Post- Post-Accident Cleanup Post-Accident Cleanup Activities Restore/ Stabilize Accident Completion Stabilize Operate Early Final After Cleanup Reactor control/source Control X X Decay heat removal NA X Gain access & information for X X stabilization Characterization O X O X X X Facility condition assessment X O X Fuel/Source condition X X X assessment Enclosure Structures (large) NA X Water storage If applies X O O Gas and air processing and If applies X release Water processing If applies X X O Decontamination for access X X Damaged fuel/source removal X X Damaged fuel/source storage X X Waste shipping & disposal X O O X O O Decontamination for operation X NA Return to operation X NA Waste storage If applies X 10? Decontamination for cleanup X X

11 Criteria Subjects 1. Structural and Boundary Integrity List of operations Criteria Statements Structural and boundary integrity will be such that: 1) inspection personnel are safe, 2) contamination or hazardous materials remaining in the facility are contained, and 3) intrusion by unauthorized personnel, as well as animals and plants, are prevented. 1. Nuclear Materials Nuclear fuel and debris will be removed to the extent practical. Residual fissile material must be reduced to a level such that criticality cannot occur. 1. Hazardous Materials Hazardous materials and chemicals will be removed in accordance with environmental regulations. Fixed in place hazardous materials remaining in the facility will be contained in limited areas or stabilized to prevent release. The amount and location of remaining hazardous materials will be documented. 1. Process Systems and Equipment 1. Service and Utility Systems and Equipment Process systems and equipment have been abandoned in place, isolated or sealed off for safety of future personnel, or removed where there is a compelling reason to do so. Only systems required to support the monitored storage state and maintain the stable condition are operational. Other utility systems will be abandoned in place, isolated or sealed off for safety of personnel, or removed where there is a compelling reason to do so. 1. Personnel Safety Inspection personnel are safeguarded by stable conditions, postings, and written procedures that have been established in accordance with standard procedures for radiological protection and industrial safety practice. 1. Waste and Liquid Effluents Waste will have been removed to the extent practical. Waste may remain if removal is with extreme difficulty. The only liquids remaining are minor quantities that cannot be readily removed with installed equipment. 1. Radiation Protection Established in accordance with standard procedures. In particular, the periodic inspection path will be subjected to ALARA review. Contamination remaining in the facility will be contained in limited areas or stabilized to prevent release. 1. Housekeeping & Miscellaneous Materials Valuable materials will be removed. Trash and non-contaminated furniture, loose equipment, etc. will be removed. Workshop, Visaginas, Lithuania on August 20-24,

12 Specificity of RWM 12

13 Approaches Chernobyl Decontamination ASAP Fukushima Decontamination ASAR TMI-2 Removal of the fuel debris Workshop, Visaginas, Lithuania on August 20-24,

14 Specificity of decontamination Much of the past decontamination experience at nuclear facilities relates to the cleanup of buildings, equipment and paved surfaces in or adjacent to nuclear reactors and other facilities during normal operations or decommissioning. Decontamination experience ranges from the cleanup of highly active components or buildings in reprocessing plants or in other facilities after a serious accident, to operations on slightly contaminated equipment or buildings being released for unrestricted use. Dynamics of self-decontamination of the region of the Fukushima-1 NPP contaminated by radioactive substances can predict that the maximum dose rate in the region of contamination will decrease to the background level in approximately 200 years. Workshop, Visaginas, Lithuania on August 20-24,

15 Preparation works Characterization/monitoring Development of decontamination strategy Installation of safety barriers and ventilation Equipment Organization of waste and personnel routes Team creation, training Workshop, Visaginas, Lithuania on August 20-24,

16 Decontamination in Chernobyl Area During large-scaled decontamination campaign in about one thousand of settlements were treated, tens of thousand inhabited and social buildings, more than thousand of agricultural farms. Depending of decontamination technologies the dose rate over different plots was decreased by a factor of 1.5 to 15. Actual effectiveness of the annual external dose decrease after upper soil layer removal usually was 10 to 20% for average population ranging from about 30% for children visiting kindergarten and schools to less than 10% for outdoor workers (herders, foresters, etc.). Workshop, Visaginas, Lithuania on August 20-24,

17 Decontamination in Chernobyl Area 1. Removal of the upper 5-20 cm layer of soil (it depends on the activity distribution in depth) in courtyards in front of residential buildings, around public buildings, schools and kindergartens, from roadsides inside a settlement. The removed most contaminated layer of soil gets placed into the holes specially dug on the territory of a private homestead land or on the territory of a settlement when decontaminating the settlement as a whole. At that the clean soil (sand) from the dug holes gets used for covering decontaminated areas. Such technology excludes the formation of special burials of radioactive waste. Workshop, Visaginas, Lithuania on August 20-24,

18 Decontamination in Chernobyl Area 2. Deep ploughing of private fruit gardens territories or removal of the upper 5-10 cm layer of the soil. If vegetable gardens have been ploughed up many times, and in this case the activity distribution in soil will be uniform in the layer cm deep 3. Covering the decontaminated parts with a layer of «clean sand/soil», or, where possible, with a layer of gravel to attenuate residual radiation (see item 1). 4. Cleaning the roofs or their replacement (the roof decontamination should be done before decontaminating the under spread surface). Workshop, Visaginas, Lithuania on August 20-24,

19 Achievable Decontamination Factors for Various Urban Surfaces. Workshop, Visaginas, Lithuania on August 20-24,

20 Decontamination

21 Decontamination

22 Fukushima - Land decontamination House and garden (to reduce airborne dose rate) Lots of radioactivity has washed out from roofs. Dirt in ditch, moss and weed in surrounding area have a higher radioactivity. Road and street (to reduce airborne dose rate) Lots of radioactivity has washed out from the pavement. Dirt and grass on a side soil and in ditch is effective. Workshop, Visaginas, Lithuania on August 20-24,

23 Fukushima - Land decontamination Farmland (to reduce the radioactivity) 5,000 Bq/kg is the upper limit for agricultural utilization. Soft remediation method, i.e. plowing, rotary harrowing, is applied to relatively low contaminated area. Strong remediation method, i.e. top soil removal, replacement by fresh soil, Workshop, Visaginas, Lithuania on August 20-24,

24 Soil treatment Specially designed removal equipment 24

25 Demonstration test results for Remediation Technologies by MAFF* *: Ministry of Agriculture, Forestry and Fishers Remediation Technology Test Condition Reduction of Cs Concentration [Bq/kg] Surface soil removal Removal depth = ~4cm 10,370 2,599 DF=4.0 Chemical fixation & Surface soil removal Surface soil removal with Grass & Weed Harrowing & muddy water drainage Fixative = Mg compound Removal depth = ~3cm 9,090 1,671 DF=5.4 Removal depth = ~3cm 13, DF=42 15,254 9,689 DF=1.6 Applicable Contamination Level [Bq/kg] 10,000-25,000 > 25,000 > 25,000 5,000-10,000 Phytoremediation Plant = Sunflower Soil = 7,715 Stem=52, Root= in Japanese Farmland contaminated more than 5,000Bq/kg = 83km 2 3.0million tons of waste are generated by 5cm soil removal. 25

26 Urban decontamination Decontamination of settlements is one of the main countermeasures to be applied to reduce external exposure of the public and clean-up workers during the initial stage of the response to a severe nuclear emergency. 26

27 Decontamination of Houses 27

28 Waste disposal Workshop, Visaginas, Lithuania on August 20-24,

29 Radioactive waste management flow sheets after accidents International Atomic Energy Agency

30 Contaminated Soil Removing from surface Radiometric sorting Reuse Reuse Decontamination (optionally) Solidification (optionally) Packaging Storage Workshop, Visaginas, Lithuania on August 20-24, 2015

31 Concrete Decontamination (scrabbling etc.) Crushing Reuse Radiometric separation Reuse Solidification (optionally) Packaging Storage

32 Metals Decontamination Fragmentation Reuse Melting (optionally) Reuse Packaging Storage

33 Sediments Decontamination or purification Reuse Solidification Packaging Storage Workshop, Visaginas, Lithuania on August 20-24, 2015

34 Water Purification Pure Water Reuse Sediments, resins, sorbents Reuse Solidification Packaging Storage

35 Debris Sorting Wood, organics Plastic, Protection clothes Cables Incineration Solidification Packaging Compaction Packaging Storage

36 Thank you! 36