Thermal treatment technologies for off-site radioactively contaminated wastes

Transcription

1 WM2016 Panel /03/2016 Thermal treatment technologies for off-site radioactively contaminated wastes Hidetoshi Kuramochi Center for Material Cycles and Waste Management Research National Institute for Environmental Studies 1

2 2 Outline Off-site contaminated wastes Incineration of contaminated municipal solid waste (CMSW) Incineration of contaminated vegetation waste (CVW) Interim Storage Facility (ISF) Thermal treatment technologies required for ISF

3 Spread of radioactive materials by the accident of Fukushima Dai-ichi nuclear power plant Miyagi pref. Iwate pref. Deposition amount of Cs-134&137 Fukushima pref. FDNPP Gunma pref. Tochigi pref. Ibaraki pref. Special Decontamination Area Chiba pref. 3

4 Off-site contaminated wastes (1) Examples (Pretreatment requirement) Disaster waste Bulky waste Vegetation waste (VW) At temporal cites, rough separation of combustible materials (2) Examples (No requirement) Municipal solid waste (MSW) 1) Slices and chips 2) Wrapping with flexible containers Sludge Transport by packer vehicles Transport in closed flexible containers 4

5 5 Classification on the contaminated waste (in case of Fukushima pref.) 8,000Bq/kg: based on 1mSv/y of human exposure risk level in the waste management Municipal and industrial waste (Incineration residue, sewage sludge, etc.) Decontamination work Over 8,000Bq/kg? No Specified municipal and industrial solid waste Yes Specified waste which MOE is responsible for. Designated waste waste from special decontamination area in Fukushima Pref. Contaminated vegetation waste (CVW) Contaminated soil Ordinary disposal which are municipality and private sector responsible for. Over 100,000Bq/kg? Yes No Landfill disposal with special control Interim storage facility (ISF)

6 6 Classification on the contaminated waste (in case of prefectures except for Fukushima) Municipal and industrial waste (Incineration residue, sewage sludge, etc.) Over 8,000Bq/kg? No Yes Designated waste which MOE is responsible for Decontamination work Specified municipal and industrial solid waste Landfill disposal with special control CVW Contaminated soil Ordinary disposal which are municipality and private sector responsible for Under discussion

7 Thermal treatment of contaminated municipal solid waste (CMSW) FY ,620 thousands 100% MSW 20 thousands At-home disposal Citizen s group collection&recycling 2,640thousands 6.2% 1.3% 79.8% 13.9% 5.0% Thermal treatment plant (Incineration + melting) Intermediate treatment without incineration Direct resource recovery MSW treatment in Japan 11.2% Final disposal site 10.6% 15.6% 9.9% Resource Recovery 20.5% 7

8 Thermal treatment methods for MSW MSW Baghouse FA FA FA MSW MSW MSW Fly Ash (FA) 1400 C 1650 C Bottom Ash (BA) Stoker-type incinerator (73%) Incombustibles Fluidized-bed-type incinerator (17%) Fe and Al Slag Gasificationmelting furnace Slag (Total number <10%) Metal Shaft-type melting furnace Incineration (>850 C) Melting process ( C) 8

9 CMSW incineration (Radioactivity enrichment to ash) Radioactivity In FA (Bq/kg) 3000 Stoker Fluidized bed Gasification melting Ash melting Oguchi, NIES Technical Report, 2013 CMSW Fly Ash (FA) Bottom Ash (BA) Estimated Radioactivity in CMSW (Bq/kg) Radioactivity; FA (30 times higher) >> CMSW (Stocker-type, FA > BA (4.6 times higher) > CMSW) 9

10 Seasonal change in radioactive Cs (r-cs) concentration in FA from CMSW incineration Relative radioactivity ( = 1.0) ごみ Cs 濃度 (2011-7=1 とした相対値 ) Average 平均値 Median 中央値 25%ile /75%ile %ile 値 /75%ile 値 10%ile/90%ile Spring Spring Winter Winter 10%ile 値 /90%ile 値 Time (Month) Oguchi, NIES,

11 Distribution of r-cs between FA and BA (combustibles or slag) Distribution to ash / - Cs transfer ratio / stoker 1 stoker 2 stoker 3 stoker 4 fluidized bed FA from melting process melting furnace FA from melting process melting furnace R-Cs distribution between FA and BA (incombustilbles or slag) Ref: Kuramochi H., Journal of Society for Remediation of Radioactive Contamination in Environment, 2(2), 71-84(2014) :Abe et al., The 1st International Symposium on Remediation of Radioactive Contamination in the Environment.(2012), :Harada et al., Toshiseisou (2014) :FA :BA :incombustible :slag Distribution of r-cs to FA: Melting process Fluidized-bed >> Stoker R-Cs activity in FA: Melting process > Stoker > Fluidized-bed 11

12 Leachability of r-cs from BA and FA Water soluble CsCl on fly ash Leachability of r-cs (%) Maximum and minimum values Water-insoluble CsAlSi 2 O 6 or slag CMSW-BA CMSW-FA FA from incineration of sewage sludge Leaching test of r-cs for various incineration ashes Leachability from FA depends on type of wastes to be incinerated! 12

13 Safety of flue gas: Removal efficiency of r-cs from flue gas using bag filters (BF)? 13 *BF:Bag filter, EP:Electric precipitator ** MOE: Ministry of the Environment, NIES : National Institute for Environmental Studies, A: a private company Radioactivity of stack gas level << the regulation of the air environment (( 134 Cs conc.)/20+( 137 Cs conc.)/30 1) BF unit is highly effective for removal of r-cs (>99.9%). Safe!

14 High dose locations inside the furnace due to accumulation of r-cs into refractory material With refractory Without refractory Air dose rate(μsv/h) 487 C 920 C 426 C Radioactive Cs Air dose rate 248 C 159 C 149 C Radioactive Cs in ash on wall (Bq/kg) Upstream Bottom Middle Top Combustion Chamber Inlet of GCT1 Outlet Preheat of GCT1 for Air Inlet of GC2 Outlet of GC2 Downstream Sampling points Radioactivity of ash on wall and air dose rate inside of furnace (GCT: gas cooling tower, GC: gas cooler, BH: baghouse) BH With refractory: Low radioactive ash, but high dose rate. r-cs accumulates into refractory Without refractory : High radioactive ash, but low dose rate = ambient dose rate. 14

15 Incineration of contaminated vegetation waste (CVW) from decontamination activity 15 CVW is combusted by newly-constructed temporary incinerators within SDA. Just now, CVW, household-cleaning waste, and disaster waste are incinerated in several cities. A temporary incinerator

16 16 Differences between CVW and CMSW incinerations(i) Radioactivity of Cs In FA (Bq/kg) Radioactivity of Cs in BA (Bq/kg) FA vs BA in terms of radioactivity Radioactivity in ash: CVW-FA CVW-BA Radioactivity ratio of FA to BA: CVW CMSW

17 17 Differences between CVW and CMSW incinerations (II) Distribution of r-cs between BA and FA Distribution to BA / % Distribution to FA % CMSW CVW 76, 85 15, 24 Leachability of r-cs from BA and FA Leachability from BA / % Leachability from FA / % CMSW <8.2, 5.6, 2.5, < CVW <0.03, < , 07 R-Cs form in CVW-FA that in CMSW-FA R-Cs behavior during incineration of CVW is much different

18 Interim Storage Facility (ISF) Fukushima Dai-ichi NPP Soil storage type I Soil Storage type IIA Soil Storage Type IIB Wastes storage Acceptation, selection, vol reduction Additional for administrative, research, info. Screening Parking Water treatment Buffering Boundary of interim site Administrative boundary MOE HP 18

19 Several facilities at ISF Temporary storage sites Transportation Soil storage facility Receiving/sorting facility Volume reduction facility (incineration) Waste storage facility Other facilities ( screening, wastewater treatment, stockyard, laboratory, information, etc.) 19

20 Estimation for the amount of contaminated soil and wastes transported to ISF Municipal and industrial waste (Incineration residue, sewage sludge, etc.) Decontamination work Over 8,000Bq/kg? No Specified municipal and industrial solid waste Ordinary disposal Yes Specified waste Designated waste waste from special decontamination area in Fukushima Pref. Over 100,000Bq/kg? No Contaminated waste Contaminated soil Incineration ash 1,550,000 m 3 <8,000Bq/kg 10,060,000 m 3 8,000Bq/kg< 10,360,000 m 3 Landfill disposal Yes Incineration ash 20,000 m 3 ISF 20

21 R&D on volume reduction technologies Contaminated soil and incineration ash Main technologies Volume reduction and separation of r-cs Large amount of much lower r-cs level material Small amount of much higher r-cs level material 1. Wet sieving/washing treatment Radioactivity level of soil depends on its size. Utilization Final disposal 土壌分級装置 2.Chemical treatment Decomposition using heating and reagents. 3.Thermal treatment Evaporation of r-cs by a high-temperature treatment such as sintering and melting. 昇華装置内部 Revised MOE s material 21

22 Status of R&D on thermal treatment technologies (I) Sintering technology (Demonstration phase) Sintering -> decontamination Construction materials MSW Incinerator ash Kiln furnace Removal ratio = >99.9% Clean materials Concrete MSW Sewage sludge Forest Pruned branch By-product Filling, aggregate, etc School Rice straw ISF Shielding container Different products Farmland Different wastes Stripping land Soil 22

23 Status of R&D on thermal treatment technologies (II) 23 Comparison among three technologies Technology Temp. (C) Reagents Removal efficiency /% Utilization of treated material Cost (Guesstimate) Thermochemical treatment < (soil), 96 (BA) Filling, aggregate and earthen cover Low Sintering process 1300 > 99.9 Filling, aggregate and earthen cover, roadbeds Middle Melting process* > 1350 < 99.9 Filling, aggregate and earthen cover, roadbeds High *: Possibility to recover reagents for thermal treatment Currently, cannot determine which one is the best!

24 24 Future subjects Current target is contaminated soil only. No large-scale test plant for new methods No regulation on radioactivity level for recycling Optimization in terms of safety, cost, etc. Method for maintenance and demolition

25 Thank you for your kind attention! 25

26 2014/7/16 26 Finer ash particles can pass through a bag filter? Bag filter Particle penetration ratio Anaoka&Makino, Hajimeteno shujingijutsu, 2013 Aerodynamic diameter (nm) Finer ash particles cannot pass through the bag filter.

27 27 Evaporated Cs in combustion gas Evaporated Cs chemicals are condensed as a solid of CsCl and forms on surface of dust during cooling flue gas. Evaporated Cs Condensation Temperature decreases less than 200 ºC at bag filter. CsCl: bt = 1300ºC, mt = 646 ºC Vapor pressure: 1 npa at 200 ºC (Estimation) Fly ash having average size of 10s μm Osako, NIES, 2013

28 Gas cleaning for r-cs in flue gas? 28 A conventional gas cleaning is valid for removal of r-cs? Ash cake layer Precoating layer Bag filter In a baghouse Dust = fly ash with Cs In a baghouse, dusts are removed. As a result, r-cs chemicals solidified on the dust during gas cooling are also removed. The presence of ash cake layer and precoating layer enables bag filter to remove finer dusts. Flue gas Cleaning gas

29 Permeation and accumulation of r-cs gas into refractory? Cut to thin layers Cut into thin layers Inside Outside (550~650 C) Measurement of radioactivity for individual layers (850~900 C) Inside furnace Outside furnace Inside Depth from the surface (= inner wall of furnace) (Ba/kg) Outside R-Cs chemicals permeate and accumulate into refractory. This behavior may depend on temperature condition. 18

30 30 Difference in r-cs behavior between CVW and CMSW incinerations Contaminated Vegetation Waste Contaminated Municipal Solid Waste Cs Cs Cs Cs Cs Cl Cs Cl Cs Cs Cs Cl Fly ash Cs Cl Cs Cs Cs Cl cooling Cs Cl Blowing up Volatile Cs Cs Cs Bottom ash Bottom ash

31 Soil storage facility type I Low land Cs < 8 kbq/kg Rain drain Cover soil Monitoring Soil storage facility type IIA Hill Cs > 8 kbq/kg Rain drain Gas leakage Cover & water shielding soil Monitoring Permeable layer Soil storage facility type IIB Hill Cs > 8 kbq/kg Rain drain Drainage layer Cover & water shielding soil Monitoring Drainage layer Protecting soil Water tight sheet Ground water pipe Wastes storage facility Hill Cs > 100 kbq/kg Durable shielding storage container Inspection corridor Water treatment Concrete wall for radiation shielding Monitoring Water shielding layer Ground water pipe Water treatment MOE HP 31