Remediation of radioactive waste storage sites resulting from the Chernobyl Accident situated in populated areas: Experiences and ‘lessons learned’ Dmitri Bugai, Ukrainian National Academy of Sciences ENVIRONET plenary meeting, IAEA, Vienna, 31 October 2018 1 Project background • The study was implemented in 2016-2017 through the “Instrument for Nuclear Safety Cooperation (INSC)” technical assistance program by the European Commission to Ukraine in the frame of the project U4.01/12, Part D (12D) • Beneficiary: State Agency for the Management of the Exclusion Zone - SAMEZ; End user: Ukrainian State Corporation “Radon” Project 12-D was completed by Consortium consisting of Brenk Systemplanung, Plejades, TÜV NORD and DMT (Germany) Project expert team: D.Bugai (team leader), J.Gebauer, C.Scior, S.Burness, A.Sizov, V.Rudko, N.Molitor 2 ENVIRONET plenary meeting, IAEA, Vienna, 31 October 2018 Contents • Background information on waste storage sites • ‘Safety ranking’ of radioactive legacy sites and resulting prioritization of remedial works • Remedial design for a ‘pilot’ contaminated site • Development of the end-state radiological criteria • Ongoing activities including ‘Roadmap’ for urgent risk mitigation measures • Conclusions and ‘lessons learned’ 3 ENVIRONET plenary meeting, IAEA, Vienna, 31 October 2018 1.1 Background information Clean-up operations in villages - The studied radioactive waste storage sites were created in 1986-89 during Chernobyl accident mitigation works in areas adjacent to Chernobyl Exclusion (~30 km) Zone - Decontamination waste storage sites (DWSF) are trench-type disposal sites (volume n*100 – n*1000 m3) congaing wastes from clean-up in villages (soil, dismantled roof materials, etc.) Decontamination of vehicles - Special decontamination stations (SDS) were created close to roads for decontamination of vehicles and equipment coming from Chernobyl site - In total: 53 legacy sites (47 DWSF, 6 SDS, total volume of waste 30600 m3) that are currently managed by the Ukr. State Corporation “Radon” 4 ENVIRONET plenary meeting, IAEA, Vienna, 31 October 2018 1.2 Map of the studied Chernobyl radioactive legacy sites in Kiev Region Regions with legacy waste sites 30 km zone 5 ENVIRONET plenary meeting, IAEA, Vienna, 31 October 2018 1.3 Design features of DWSF and SDS sites Example cross-section of DWSF site Surface dose rate distribution at SDS site (dose rates in Sv/hour) Hot spot Water body • Constructed without design documentation • Usually dug in in sandy soils without isolating liners • No inventory records • Sites do not conform to current safety standards 6 ENVIRONET plenary meeting, IAEA, Vienna, 31 October 2018 1.4 Photo illustrating current site conditions SDS „Rudnya-Shpylivs'ka “ DWSF „Tarasy“ DWSF „Novaya Markivka 1“ µSv/h • Fences and radiation danger signs are often gone • … and the waste sites can be hardly distinguished from the surrounding terrain 7 ENVIRONET plenary meeting, IAEA, Vienna, 31 October 2018 1.5 Activity inventory of legacy sites • Initially (April-May 1986) activity of Chernobyl fallout was Evolution in time (starting from 26.04.1986) of integral activity of - emitting radionuclides of Chernobyl fallout determined by ensemble of short-lived nuclides (Zr-95, Nb-95, Ru-103, Ru-106, Ce-141, Ce-144 etc.) • At present time main contaminant of concern is Cs-137 (range of activity 0.4-300 kBq/kg); In some cases waste contains also Sr-90 and Am-241 isotopes • Waste activity as a rule is above clearance (free release) levels for radioactive materials (0.1 Bq/g for Cs-137) • In some instances waste activity is above exemption criteria for radioactive waste (10 Bq/g for Cs-137) 8 ENVIRONET plenary meeting, IAEA, Vienna, 31 October 2018 1.6 Post-accident management • Surveillance of DWSF and SDS sites are within the responsibility of Ukr. State Corporation “Radon” (however these are not licensed waste storage sites). Due to lack of resources and wide geographic distribution, individual sites were surveyed once in 3-4 years or at even lesser frequency. • The National Radioactive Waste Management Program (2008) foresees retrieval of waste from all sites and disposal to the “Vector” engineered disposal facility in Chernobyl Zone. This decision was based on non-compliance with formal requirements to storage (disposal) of radioactive wastes (i.e. perspective of ‘planned exposure’ regulatory framework) • In view of unreliable inventory data the program of characterization of legacy sites was started in 2013 (as a preparation phase to remediation works). Analyses presented below are carried out on 17 sites (from total 53) that were characterized by 2016. 9 ENVIRONET plenary meeting, IAEA, Vienna, 31 October 2018 2.1 Safety ranking of Chernobyl Legacy Sites – Objectives, Regulatory Context and Criteria As specific regulation in Ukraine for “nuclear legacies” is lacking, project team reached a consensus with the Ukrainian Regulator that Project 12D analyses should refer to the IAEA framework for “existing exposure situations” (IAEA GSR Part 3 Section 5, 2014) Objectives of safety ranking: Assess the safety of studied legacy sites to population and define remediation priorities (i.e. the sequence of remedial works) Criteria 1: Accessibility of site by population Criteria 2: Comparison of site activity inventory with background contamination level by Chernobyl fallout Criteria 3: “Screening” dose assessment (for members of general public) 10 ENVIRONET plenary meeting, IAEA, Vienna, 31 October 2018 2.2 Scenarios considered in screening dose assessment • SC1: Regular visiting the site ( ‘most likely scenario’) Dose criteria justifying remedial action Main pathway: external exposure; time of exposure t=1000 • In accordance with recommendations of hours/year IAEA GSR Part 3 Section 5 for “existing exposure” situations the reference level of . SC2: Intrusion - Excavation of waste site 1 mSv/y was used as a dose criteria for (‘accidental exposure’) further considering of remedial actions Assumes intrusion to the waste site (e.g. by a scrap metal • The above reference level was hunter; exposure time t=20 hours/event) coordinated with the Ukr. radiation safety Calculation procedures described in IAEA TECDOC-1030 authority (SNRIU) . SC3: Residence on contaminated site (‘worst case’ scenario) Uses “reference scenarios” described in Ukr. NRBU-97/D- 2000 regulation for near-surface radwaste disposal 11 ENVIRONET plenary meeting, IAEA, Vienna, 31 October 2018 2.3 Results for Criteria 1: Accessibility of sites by population Sites inside the ZOR At 1-st step, 5 legacy sites located in the administrative “Zone of Obligatory Resettlement” were given lower priority due to restricted access of population to this zone Zone of Obligatory Resettlement (ZOR) was established in 1991, and represents a higher contaminated area adjacent to the Chernobyl Exclusion Zone. Permanent living inside is not allowed, and “normal” industrial and agricultural activities are prohibited. Within the Kiev Region, the ZOR area is fenced and access to it is restricted. 12 ENVIRONET plenary meeting, IAEA, Vienna, 31 October 2018 2.5 Results for Criteria 2: Comparison with background contamination by Chernobyl fallout 1000.0 Remediation was deemed to be not justified in case the Cs-137 specific activity ratio 100.0 {“site inventory” : “background”} < 10 10.0 This criteria is in line with the requirements of the Ukr. regulations NRBU-97 1.0 Ratio of Cs-137 activity"WasteCs-137 of Ratio Topsoil" / Site Higher inventory sites ENVIRONET plenary meeting, IAEA, Vienna, 31 October 2018 13 2.6 Results for Criteria 3: Screening dose assessment 100.000 Scenario 1 • The priority 4 sites with Scenario 3 estimated doses close to or 10.000 exceeding 1 mSv a-1 for SC1 and SC3 are the same ones as 1.000 identified using Criterion 2 • For 8 sites the estimated Dose, mSv/year doses are by order of 0.100 magnitude less than 1 mSv a-1 criterion 0.010 Higher risk sites 14 ENVIRONET plenary meeting, IAEA, Vienna, 31 October 2018 2.7 Summary of safety ranking of legacy waste storage sites • 4 priority (higher risk) sites were identified that may require remediation: SDS “Orane”, SDS “Rudnya Shpilivska”, SDS “Sydorovichy”, and DWSF “Pisky-1” • 8 sites are candidates for release from special surveillance program by SC “Radon”: • low activity inventory (comparable to background) • low estimated radiological impact (doses << 1 mSv/year) The recommended strategy is that managing organization (SC “Radon”) should focus their monitoring, maintenance and remediation works on relatively few higher risk sites; characterization of all sites should be concluded as soon as possible Remark: Several sites inside the “Zone Obligatory Resettlement” have lower priority because of the current restricted access, may need re-evaluation in case their administrative regime changes 15 ENVIRONET plenary meeting, IAEA, Vienna, 31 October 2018 3.1 Pilot Site for remedial design - DWSF “Pisky-1” Site Location map DWSF “Pisky-1” is chosen as the pilot site for developing a Highway Chernobyl - Ivankiv “standard” remedial design: • One of 4 identified higher risk sites, • Close to village (500 m), Village • Poor technical condition, • Best available characterization data, • Good reference for other legacy sites Pisky 1 Distance to Kiev ~ 70 km 16 ENVIRONET plenary meeting, IAEA, Vienna, 31 October 2018 3.2 Characteristics of Pilot site – DWSF “Pisky-1” • Area: 18 m x 11 m • Depth ~ 1.8 m • ~ 300 m³ of waste • Measured nuclides: - Cs-137 (max 53 Bq/g) - also Sr-90 and Am-241 • Waste composed of