Challenges for Enhancing Fukushima Environmental Resilience

Transcription

1 Challenges for Enhancing Fukushima Environmental Resilience KanameMIYAHARA, Kimiaki SAITO Fukushima Environmental Safety Center Japan Atomic Energy Agency (JAEA) IAEA Technical Meeting on Remediation Techniques and Strategies in Post-Accident Situations June 2016, IAEA Headquarters, Vienna, Austria 1

2 Fukushima Regional Contamination Initially concern focused on shortlived iodine and other isotopes in addition to radiocesium evacuation and restriction of consumption of some foodstuffs After decay of short-lived isotopes, now dominated by 134 Cs/ 137 Cswhich is the focus for off-site clean-up actions Cs tends to bind strongly to soil surface, especially clay Exposuredoses of inhabitants are mainly from external exposures, generally not high, and have continually reduced by decay of Cs, washoff/ soil mixing 2

3 Evacuation Order Areas Designationofevacuation areaswas completed just after the accident (Apr. 22, 2011) Specific Spots Recommendedfor Evacuation Switched from distance to a threshold radiation dose of 20 msv/y on Apr. 22 Protective Actions Food and water restrictions Regulatory limits for contaminated food and water based on <5 msv/y (March 20, 2011) <1 msv/y(april 1, 2012) Category Limit (Bq/kg) Drinking water 10 Milk 50 Rapidly expanded (3-km, 10-km, 20-km radius by Mar. 12) 20km General Foods 100 Infant Foods 50 3

4 Remedial Management Options Management options are designed to reduce: (i) external doses from surfaces contaminated by deposited radionuclides; Currently, the dominantpathway of public exposure (ii) ingestion doses from the consumption of contaminated foodstuffs and drinking water; Strict Food Restrictions; Government restrictions put into place after the Fukushima Daiichi accident kept mostcontaminated foodstuffs off of the market (IAEA, 2011) (iii) inhalation doses from resuspended material This route of exposure is of less significance and not considered further (UNSCEAR, 2013) To reduce external doses Decontamination(cleanup)* Restrictions on access to highly contaminated areas (such as the outer 20 m borders of forests adjacent to settlements ) Other measures relevant for individual lifestyle (e.g. commute route change) based on the personal dose data and understanding Cs behaviors in the environment *Dilution methods for soils such as plowing are included 4

5 Decontamination Pilot Project (DPP) by JAEA JAEA was chosen by the Government to conduct decontamination pilot projects (DPP) at 16 model sites in 11 municipalities, including evacuation order areas (Sept. 2011~June 2012) Main challenges to implement full-scale decontamination were lack of both real-world examples and also experience for planning and implementing decontamination technology appropriate to Japanese boundary conditions Therefore, the decontamination pilot projects played a key role to support drafting of guidelines and manuals that can be used by the national government and local municipalities to optimize regional remediation work Check the availability and efficacy of proven and new techniques Investigate cost, work period, workforce, waste generated, and radiation exposure of workers Establish waste management including volume reduction of wastes and treatment of the secondary waste Secure workers safety under radiation protection Establish optimal radiation monitoring Record the public communication Fukushima City Miharu Town Koriyama City Target Municipalities Date City Kusano area Base of Patrol Team for Iitate the Entire Iitate Village Village Planned evacuation area Kawamata Town Sakashita area Nihonmatsu City Tsushima area Katsurao Village Katsurao Municipal Office and surrounding area Ono Town Tamura City Restricted Area Deliberate Evacuation Area Decontamination Pilot Project implementation areas Soma City Dose rate classification Less than 5mSv/y Minami Soma City Restricted Area Kanabusa Elementary School and surrounding area Jikenjo area Kawauchi Village Gongendo area Namie Town Okuma Town Futaba Town Tomioka Daini Junior High School Kainosaka area Kamishigeoka area Iwaki City Okuma Municipal Office and surrounding area Tomioka Town Naraha Town Minami Industrial Complex Hirono Town Chuo-dai/Nawashirogae area * An examination conducted by a committee appointed by JAEA Fukushima Dai-ichi Ottozawa area Yonomori Park Futaba Town has advised us that they would not join the Decontamination Model Project as a target area. 5

6 Recommended Clean-up Technologies Residential area Large structure Land use classification Roof floor Forest Farmland Roof Gutter Wall Topsoil Rubble Turf Garden tree Interlocking block Concrete and Mortar surface Comprehensive evaluation Removal of leaf litter and humus layers (on flat ground and slopes), 〇 Removalof leaf litter, humus layers and topsoil (on flat ground), Trunk washing, 〇 Branch trimming in the lower part (evergreen tree) Machine that strips off surface of soils, 〇 Backhoe(stripping off depth of 5 cm of the soil), Reversal tillage (by tractor and plough), 〇 Ploughing to replace surface soil with subsoil (by backhoe) High pressure water, 〇 Brushing, 〇 Wiping, Apply a remover High pressure water, 〇 Wiping 〇 Brushing 〇 Removal of topsoil 〇 Washing of the rubble, 〇 Removal of the rubble 〇 Removal of the Turf Clipping a garden tree High pressure water Sanding machine with the dust-collection (Plane which scrapes concrete), 〇 Ultrahigh pressure water (Over 150MPa), 〇 High pressure water (10-20MPa), 〇 Iron shot blasting Concrete surface 〇 High pressure water (including brushing) Waterproof coating surface 〇 High pressure water (including brushing) Downpipe 〇 High pressure water(maximum 50MPa) Playing field 〇 Strips off surface of soils (Large mower+sweeper), 〇 Strips off surface of soils (Road planers), 〇 Strips off surface of soils(motor grader), 〇 Ploughing to replace surface soil with subsoil Swimming pool Turf Paved road 〇 High pressure water 〇 Turf stripper Road cleaners + Riding style road sweepers, High pressure water (About 15MPa)+Brushing, Car of a functional recovery drainage pavement, 〇 Ultrahigh pressure water (120~240MPa), Iron shot blasting, TS Road planers :highly effective, :effective, :moderately effective, :limited effect 6

7 Accident Recovery The Act on Special Measures Concerning the Handling of Radioactive Pollution(August 2011) Special decontamination areas; the Restricted Area + the Deliberate Evacuation Area Further subdivided into three areas(august 2013) Area 1:<20 msv ready to be lifted Area 2:20-50 msv ordered to remain evacuated Area 3: >50 msv not expected to drop below 20 msv/y within 5 years Intensive contamination survey areas; all other contaminated areas (1 msv/y ~20 msv) Decontamination of these areas involves the cleaning of structures and removal of contaminated soil Removed soil and other contaminated wastes are being stored at remediation locations or at temporary sites Contaminated soil and waste are to be gathered and placed into interim storage facilities until transferred to a long-term disposal site outside of the Fukushima area 100 msv/y Special decontamination areas The national government implements decontamination work 20 msv/y Intensive contamination survey areas Municipalities implement decontamination work funded by the government 1 msv/y Principles set by ICRP Emergency exposure situation Aiming at 20 msv/y or less Existing exposure situation Long-term objectives Additional dose to be 1 msv/y 7

8 Waste Management Challenges Cs removed or reduced materials Reuse Soils & wastes Volume (Mm 3 ) 16~22Mm 3 current estimation Mm Mm 3 Below 8kBq/kg Volume Reduction Cs accumulated materials Contaminated soil and wastes Over 8kBq/kg below 100kBq/kg Contaminated soil and wastes Incinerated ash 0.01Mm Mm Mm 3 Over 100kBq/kg Incinerated ash over 100kBq/kg Final disposal Waste in countermeasure area over 100kBq/kg Wet particle-size separation Chemical treatment Heat treatment Clean-up efforts are generating huge volumes of contaminated soil and waste, which must be managed in a safe and costeffective manner, wherever possible implementing waste volume reduction Future reuse of soil for construction purposes is an important option, if constraints in terms of allowable organic and clay content can be managed 8

9 Current Status 避難指示区域 (2011 年 11 月 25 日 ) not expected to drop below 20 msv/y within 5 years ordered to remain evacuated ready to be lifted Evacuation order areas (2015/9/5) Various situations exist Areas where people regain ordinary daily life Areas where the evacuation order was lifted * Lifted on April 1, 2014 Lifted on Oct. 1, 2014 Lifted on Sept. 5, 2015 Areas where the evacuation order will be lifted no later than March 2017 Areas where the prospects for lifting the evacuation orders are not in sight *Exposure dose reduced to the evacuation standard of 20 msv y -1 or less 9

10 How to Enhance Fukushima Environmental Resilience Address the needs for better scientific and technological capabilities to assess, predict, and minimize the impact of radiological contamination Enhance the understanding of radiation and associated risks in the public Kai Vetter, 2015 The concept of Resilience; The ability to recover from or more successfully adapt to adverse events 10

11 Development of a Technical Basis for Enhancing Fukushima Environmental Resilience Regional scale distribution Deposition of Radiocaesium[Bq/m 2 ] Forest Transport and accumulation in a river basin Dam Individual external doses in living areas River/Floodplain 11

12 Evolution of Air Dose Rate Distribution Analysis of repeated survey results clarified the trends in airdose rate reduction for different conditions due to radioactive decay, decontamination and natural weathering processes Dose rate maps derived from carborne surveys Average air dose rate (relative) Roads (car survey) Physical decay & Forest Elapsed me since June 2011 Flat fields 12

13 Development of a Predictive Model by an Empirical Approach Air dose rate (relative) Evacuated zone(20-50 µsv/y)except forests Elapsed time after the accident(y) Air dose rate Air dose rate (µsvh -1 ) (µsvh -1 ) years after 30 years after An empirical approach was employed to predict the dose rate distribution based on statistical analyses of large-scale environmental monitoring data accumulates since the accident The time-dependent decrease of air dose rate in any specific setting can be approximated by a combination of two exponential functions, representing fast and slow reduction rates Analysis linked to geostatisticaldata shows that the air dose rate reduction clearly depends on land use 13

14 Empirical Prediction of Air Dose Rate Distribution Area more than 3.8 µsv/h will decrease in 30 years after to as much as 5% of such area in 5 years after the accident. After 5 y After 30 y Corresponding to the evacuation standard of 20 µsvy -1 * air dose rate (μsv/h) *based on the assumption that people spend 8 hours a day outdoors and 16 hours a day indoors, for the latter considering a dose reduction factor of 0.4 air dose rate (μsv/h) 14

15 Development of a Technical Basis for Enhancing Fukushima Environmental Resilience Regional scale distribution Deposition of Radiocaesium[Bq/m 2 ] Forest Transport and accumulation in a river basin Dam Individual external doses in living areas River/Floodplain 15

16 Natural Processes Causing Mobilazation of Radiocaesium transport from tree crowns to litter Cs tends to bind strongly to surface soil, especially clay Deposition of Cs-loaded suspended particles removal of litter/soil by runoff Normal flow conditions During heavy rainfall Transport / accumulation in a river system Soil loss by runoff Transport by ocean currents 16

17 Cs Transport in the Forest Currently, most of Cs deposited on tree crowns has transported to forest floor Cumulative amount of 137 Cs (kbq/m 2 ) Mature Japanese cedar Fallen leaves Stemflow Throughfall FY Elapsed time after the accident(d) Evolution of cumulative Cs due to transport from tree crowns to forest floor (Onda et al., 2016) 放射性セシウム濃度 Cs concentration (Bq/L) (Bq/L) /4/1 KA-1 Japanese cedar forest in Kawauchi village 年度 2013/5/ /7/ /8/ /10/18 Throughfall 2013/12/7 137 Cs 134 Cs Evolution of Cs concentration in stemflow(bq/l) 2014/1/ /3/ /5/6 Stemflow Fallen leaves 2014/6/25 Cs-134 Cs /8/ /10/3 17

18 Cs Transport from Forest Areas by Runoff 137 Cs transport rates by surface-soil erosion A monitoring plot to measure erosion rates of surface soil Measurement at a monitoring plot in Kawauchi village (2013/11/19 ~2014/10/20) A: Erosion rate of surface soi kg/m 2 /y B: 137 Cs concentration in eroded soil C: 137 Cs transport rate by erosion(a B) D: 137 Cs deposition in surface soil Ratio of annual 137 Cs lossto 137 Cs deposition in surface soil(c/d) (FY 2013) 137 Cs transport rate by erosion Ratio of annual 137 Cs lossto 137 Cs deposition in surface soil 16 kbq/kg 0.19 kbq/m 2 /y 770 kbq/m %/y 1.2 kbq/m 2 /y 0.15%/y Measurement of accumulated 137 Cs in stream sediments in Kawauchi Village (2014/6/27~ 2014/9/30) A: Erosion rate of surface soil B: 137 Cs concentration in eroded soil C: 137 Cs transport rate by erosion [A B 4 / 54,000 m 2 ] 4.9 kg/3months 64 kbq/kg kbq/m 2 /y A sampling point of stream sediments 18

19 Cs Transport by River Flow (dissolved/particulate-bound Cs) Concentration of suspended substances (mg/l) 土砂濃度 (mg/l) >60 um 3-60 um um (0.6) 11 (1.4) 16 (1.8) 流量 (m 3 /s)( 水位 (m)) Flow rate (m 3 /s) (Water level (m)) 137 Cs concentration Ukedo riv. Takase riv. water flow 2 m 3 /s 16 m 3 /s Dissolved 137 Cs (A) 0.3Bq/L 0.3Bq/L Particulate-bound 137 Cs (B) Ogaki dam Normal flow High river flow 0.1 Bq/L 2.2 Bq/L (A)+(B) 0.6 Bq/L 3.3 Bq/L 19

20 Simulation of Sediment inflow due to a flood event (Deposition of sand, silt, and clay 120 hrafter the event) Observed Cs concentration in the sediment of dam lake Sand Silt Clay St.2 Activity conc. (kbq/kg) ,000 0 Depth (cm) St.5 Depth (cm) St.7 Depth (cm) Cs Accumulation in the Sediment of Dam Lake St.2 134Cs 137Cs Cs Activity conc. (kbq/kg) ,000 St.5 134Cs 137Cs Cs Activity conc.(kbq/kg) ,000 1,500 2,000 St.7 134Cs 137Cs Cs Ogaki dam Water level Concentration of 137 Cs (Bq/L) Elevation: 140 m (Current water level) Measured Simulated Concentration of 137 Cs in Flow at the exit of the reservoir More than 90% of inflow sediment and 137 Cs deposited in the reservoir during and after heavy rainfall events Elevation: 170 m * Ratio of silt outflow 4.5% 1.6% Ratio of clay outflow 54% 34% Ratio of 137 Cs outflow 9.0% 3.5% Ratio of silt-bound 137 Cs 40% 18% Ratio of clay-bound 137 Cs 60% 82% *Operational water level before the accidents 20

21 Overview of 137 Cs Flux from Each Catchment of Ukedo River Basin Annual transportrate of 137 Cs of the forest topsoil is around 0.1% More than 90% of radiocaesium flowing into the Ogaki dam lake was sedimentedin the lake Ukedo riv. Ogaki-dam outflow 0.07 TBq/y Takase riv. Total flux to the ocean 1TBq/y 3 km Inventory Discharge 21

22 Recovery of the Coastal Marine Environment Number of samples Statistics on fish samples >100Bq/kg <100Bq/kg Excess ratio グラフタイトル Apr.-Jun. Oct.-Dec. Apr.-Jun. Oct.-Dec. Apr.-Jun. Oct.-Dec. Apr.-Jun. Oct.-Dec. Apr.-Jun. Oct.-Dec. Jul.-Sep. Jan.-Mar. Jul.-Sep. Jan.-Mar. Jul.-Sep. Jan.-Mar. Jul.-Sep. Jan.-Mar. Jul.-Sep. Jan.-Feb 系列 系列 系列 3 Excess ratio % Fisheries Agency of Japan (2015) **Otosaka and Kobayashi (2013) + Updated 22

23 Development of a Technical Basis for Enhancing Fukushima Environmental Resilience Regional scale distribution Deposition of Radiocaesium[Bq/m 2 ] Forest Transport and accumulation in a river basin Dam Individual external doses in living areas River/Floodplain 23

24 Individual doses estimated from air dose rates Currently applied simple method results in larger uncertainties. D(p) and t(p) are not realistically considered in estimate. E= Σ c D(p) t(p) E: total effective dose C: conversion coefficient from air dose to effective dose D(p) : airdose rateatlocation p t(p) : residence time at location p t(p) varies according to individual D(p) varies according to location Difference of lifestyle Indoors Outdoors (Location-specific external exposure) pavement ground Amount of time spent indoors or outdoors depending on occupation Variations in working places depending on the type and location of work Dose reduction factor depending on house type and surrounding conditions Distribution of Cs deposition on the surface (ground, pavement etc.) Weathering effects 24

25 Realistic estimates of Individual doses Communicate with evacuees who wish to return to their homes Interview to evacuees Man-borne survey 経路 / 場所 ID 地点 ( 部屋 ) 移動手段 開始時刻 終了時刻 1 自宅 ( 寝室 ) 0:00 5:30 2 自宅 ( リビング ) 5:30 8:00 3 徒歩 8:00 8:05 4 裏山 8:05 11:55 3 徒歩 11:55 12:00 2 自宅 ( リビング ) 12:00 13:00 5 徒歩 13:00 13:05 6 畑 13:05 13:50 7 徒歩 13:50 14:00 8 畑 14:00 14:50 7 徒歩 14:50 15:00 2 自宅 ( リビング ) 15:00 16:00 9 車 16:00 16:10 10 銭湯 16:10 17:50 9 車 17:50 18:00 2 自宅 18:00 0:00 Detailed data acquisition by interview to know how much time will be spent along individual s daily route after evacuees return to their homes Measurement of air dose rates according to the individual s daily route Realistic estimates of individual doses according to individual s daily route Air dose rate (μsv/h) Time Estimated external cumulative radiation doses Field 2 Indoor Field 1 Hill Walking on roads 25

26 Knowledge and experience gained for Enhancing Fukushima Environmental Resilience Cleanup Navi The Cleanup-naviCommunication Platform provides an overview of regional contamination due to the accident and approaches to remediation. It also includes background information on the nature of ionising radiation and its health effects to allow the user to make informed judgements as to the value of the remediation actions that are being undertaken. DPP reports Part 1 summarises the Decontamination Pilot Project, providing the background required to put this work in context for an international audience. In Part 2, the subsequent application of output from this project to regional remediation is discussed, along with a status update on such work (including radioactivity monitoring), an overview of JAEA s associated R&D and international input to / review of regional environmental decontamination in Fukushima. Lessons learned report This report provides a concise overview of knowledge and experience gained from the activities for environmental remediation after the Fukushima Daiichi accident. It is specifically tailored for international use, to establish or refine the technical basis for strategic, off-site response to nuclear incidents. 26

27 Thank you for your attention