Many countries are now pursuing a “site end state” for historical and complex nuclear and naturally occurring radioactive materials (NORM) industry sites that are nearing completion of decommissioning and remediation activities. Often this requires the use of controls, such as land use restrictions, to manage residual hazards. Where controls are used, both long-term management and stewardship are needed to ensure ongoing protection of people and the environment. Environmental management provides the practical long-term activities such as monitoring and maintenance of the site. The role of a steward is broader and longer-lasting, perhaps in perpetuity, and it embodies the ethical imperative to “take good care of something.” Deciding on a site end state is challenging. While the steps in the process are generally simple, it is difficult to determine how to consider all the technical, social, environmental, and economic factors in a site end state decision. Where a site end state includes administrative and/or physical controls, its design must be cognizant of the associated management and stewardship requirements. Presentations in this session will explore the approaches, challenges, benefits, and innovations associated with the site end state decision-making process; information required for decision-making; technologies needed to support long-term management; regulatory challenges; challenges in transitioning from cleanup to long-term stewardship at sites; and stewardship programs.
Session Organizers: Kim Baines, International Atomic Energy Agency; Emerald Laija, U.S. Environmental Protection Agency; Stephanie Jacobs, Savannah River National Laboratory; Boris Faybishenko, Lawrence Berkeley National Laboratory
| 1:00 - 1:05 p.m. |
Opening Remarks __________________________________________________ |
|
1:05 - 1:25 p.m. Using Chernobyl Data for the Source Zone Assessment, Stewardship, and Remediation: 1. Groundwater Monitoring in the Near-Field Chernobyl Exclusion Zone Dmitri Bugai, Institute of Geological Sciences, Kyiv, Ukraine ► PRESENTATION PDF |
 The 1986 Chernobyl Nuclear Power Plant (ChNPP) accident resulted in a fallout of radionuclides, mainly 137Cs, 90Sr, and Pu isotopes, and caused a widespread contamination of soil, surface water and groundwater in the Chernobyl Exclusion Zone and surrounding areas. We present the results of the analysis of groundwater monitoring datasets, which have been collected by the “Ecocenter” radiation monitoring service in Chernobyl Exclusion zone (CEZ) for the period of 37 years. The statistical analysis of radionuclide concentrations in 73 monitoring wells showed that groundwater contamination has likely been influenced by downward migration of radionuclides, which were deposited in the topsoil, releases from multiple waste disposal dumps in the Chernobyl Exclusion Zone (such as buried “Red Forest”), and seepage of contaminated surface water, for example, from the Chernobyl Cooling Pond. Statistical analysis of trends using Mann-Kendall method revealed decreasing or stable trends of 137Cs and 90Sr in majority (>90%) of monitoring wells for the last two decades. The application of the PyLEnM framework (Meray et al., 2022), based on unsupervised ML algorithms, allowed for identification of distinct differences and similarities in spatio-temporal distribution of 90Sr and 137Cs in soil and groundwater, depending on the groundwater water level, land surface deposition of fallout radionuclides and monitoring borehole design characteristics. The observed trends can be explained by the processes of natural attenuation driven by gradual exhaustion of the fuel particle source-term (for 90Sr), fixation of mobile forms by clayey minerals (for 137Cs), geochemical evolution of groundwater downstream from waste dumps (decrease of ionic strength, and increase of pH), and radionuclide retention in near-surface soils due to absorption and bio-cycling. Remedial measures implemented during the last decade, including the drainage of the Chernobyl Cooling Pond and construction of the ‘New safe confinement’ over the destroyed Chernobyl Unit 4, also contributed to groundwater protection. The conducted computational analysis of the Chernobyl hydrogeochemical dataset can serve as a benchmark and offers further opportunities for testing and developing Big Data Analytics (BDA), artificial intelligence (AI), and machine learning (ML) methods, improving conceptual understanding and validating radionuclide migration models, and drawing lessons from experience in monitoring consequences of large-scale releases of radioactive contaminant into the environment. Coauthors: Sergey Kireev (Ecocenter, Chernobyl, Ukraine), Boris Fabyshenko (Lawrence Berkeley National Laboratory) __________________________________________________ |
|
1:25 - 1:45 p.m. Using Chornobyl Data for the Source Zone Assessment, Stewardship, and Remediation: 2. Radioactive Contamination of Groundwater in the Vicinity of the Destroyed 4th Unit of the Chornobyl NPP Mykola Panasiuk, Institute for Safety Problems of Nuclear Power Plants of the National Academy of Sciences of Ukraine ► Presentation PDF |
Radio-hydro-ecological monitoring around the destroyed Unit 4 of the Chornobyl NPP (also called the Shelter Object) has been carried out since 1996. Volumetric activity of 90Sr in groundwater has ranged from 1 to 400 and even to 3800 Bq/l. It was determined that the volumetric activity of 90Sr2+ increased when Ca2+ concentration increased from 0.5 to 2 mmol/l. At the same time, the volumetric activity of 90Sr increased by a factor of 10-60 to concentrations of 420-2500 Bq/l. When the ionic strength of groundwater increased to above 5 mmol/l, the concentration of 90Sr2+ increased 200-500 times to values of 550-700 Bq/l. Moreover, a significant increase in 90Sr2+ concentration occurred both in neutral and strongly alkaline environments with pH from 9.5 to 12. Coauthors: Ihor Kovalenko (Institute for Safety Problems of Nuclear Power Plants of the National Academy of Sciences of Ukraine), Natalya Sosonna (Institute for Safety Problems of Nuclear Power Plants of the National Academy of Sciences of Ukraine), Mykhailo Buzynnyi (The O. M. Marzieiev Institute of Public Health of the National Academy of Medical Sciences of Ukraine), Ihor Оnyshchenko (Radioecological Center of the National Academy of Sciences of Ukraine), Irina Koliabina (Institute of Geological Science of the National Academy of Sciences of Ukraine), Boris Faybishenko (Lawrence Berkeley National Laboratory) __________________________________________________ |
|
1:45 - 2:05 p.m. Using Chernobyl Data for the Source Zone Assessment, Stewardship, and Remediation: 3. Monitoring and Modeling of the Closure of the Chernobyl NPP's Cooling Pond Boris Faybishenko, Lawrence Berkeley National Laboratory ► Presentation PDF |
The Chernobyl Cooling Pond, an artificial lake maintained by pumping of water from the Prypiat River, was used for cooling the Chernobyl NPP’s reactors during their operations. It was heavily contaminated during and after the 1986 Chernobyl NPP accident. With the end of the NPP operations in 2000, there has been no need for maintaining the Cooling Pond. The decision-making on how to proceed with closure of the Chernobyl Cooling Pond was supported by the International Atomic Energy Agency (IAEA). As of mid-May 1986, the total activity of the water in the pond was ~104 Bq/L, and the total inventory of radionuclides in the system was estimated to be ~2000 TBq. Of that inventory, about 95% of the total 137Cs and 99% of the total 90Sr were accumulated in bottom sediments. After the cessation of water pumping from the Pripyat River to the Cooling Pond in May 2014, the water level in the Cooling Pond started to decline naturally due to seepage and evaporation. Despite concentrations of 137Cs and 90Sr in the pond water dropped by 2-3 orders of magnitude from 1986 to 2014, the water level drawdown led to the exposure of highly contaminated sediments, containing 137Cs, 90Sr and hot particles with Pu, to the atmosphere (i.e., to the oxidizing environment). The accumulation of radionuclides in the exposed bottom sediments appeared being highly spatially variable, depending on the thickness, topography and characteristics of bottom sediments (e.g., clay content), as well as a dissolution rate, mobility, bioavailability, and speciation of radionuclides. It was estimated that after completion of a drawdown, a period of establishment of a new aquatic ecosystem would last for 7-10 years. The period for long-term institutional control of this specific object is estimated to exceed 10 years. It has been demonstrated that the monitored natural evolution of the system vis-à-vis its radiological status is the most reasonable strategy for remediation and the near-term management of the Cooling Pond. Coauthors: Dmitri Bugai (Institute of Geological Sciences, Kyiv, Ukraine), Horst Monken-Fernandes (International Atomic Energy Agency, Vienna, Austria) __________________________________________________ |
| 2:05 - 2:45 p.m. |
Open Discussion __________________________________________________ |
| 2:45 - 3:15 p.m. |
Posters and Vendor Exhibit __________________________________________________ |
|
3:15 - 3:35 p.m. Technical Support for the Long-Term Stewardship of a Uranium-Contaminated Wetland Daniel Kaplan, University of Georgia ► PRESENTATION PDF |
A nuclear fuel fabrication facility released 43,500 kg of uranium into a riparian wetland located on the Savannah River Site between 1955 and 1988. Studies were undertaken to evaluate hydrological and geochemical processes influencing uranium accumulation in the wetland. Gamma-radiation-mapping surveys were conducted by systematically walking over the contaminated wetland with backpacks equipped with global positioning systems and NaI gamma detectors. Based on maps compiled from >700,000 gamma spectra and eight sediment uranium depth profiles, it was determined that 94% of the released uranium remained in the wetland >50 years after being released. The uranium in the wetland is concentrated in five multi-hectare areas along the stream, accounting for ~11% of the land area adjacent to the stream. While land type (upland or wetland) and topography provided a reasonable first approximation of where much of the uranium was deposited, hydrological watershed modeling revealed that the stream velocity was especially slow through many of the hot spots. Using autoradiography combined with SEM/EDX measurements of contaminated sediments, surprisingly few hot particles were detected. Instead, uranium was evenly distributed throughout the sampled sediment, suggesting that dissolved uranium had bound to sediment particles that became suspended and later deposited in low energy (low flow velocity) portions of the stream. EXAFS suggested that U atoms were present as individual ions in disordered complexes within the sediment. Furthermore, linear combination analyses suggested that the predominant component of the U(VI) was adsorbed to sediment minerals (~70%) and a minor component (~30%) was associated with organic matter phases. These studies show that wetlands can be extraordinarily effective at binding and retaining uranium, thereby providing a natural barrier to the transport of uranium out of a watershed. However, significant anthropogenic or climatic changes to wetlands, such as those associated with flooding, forest fires, or land use, may disrupt the complex hydrological and biogeochemical balance necessary to maintain long-term stewardship of this contaminated site. Coauthors: Connor J. Parker (Oak Ridge National Laboratory), Kimberly A. Roberts (Savannah River National Laboratory), Pieter Hazenberg (Florida International University), Juan Morales (Florida International University), Edward J. O’Loughlin (Argonne National Laboratory), Maxim I. Boyanov (Argonne National Laboratory, Bulgarian Academy of Sciences), Kenneth M. Kemner (Argonne National Laboratory), Brian A. Powell (Clemson University) __________________________________________________ |
|
3:35 - 3:55 p.m. Phosphate Amendments for Treatment of U and Tc-99 in the Hanford Site’s Central Plateau Hilary Emerson, Pacific Northwest National Laboratory ► PRESENTATION PDF |
Technologies are being evaluated for remediation potential in the 200-DV-1 operable unit (OU) and in other source OUs located on the Hanford Site’s Central Plateau, as part of a broader treatability study. Nine technologies were determined to not yet be readily implementable for field deployment, due to data gaps in treatability of relevant contaminants of concern (U and Tc-99) and the influence of secondary contaminants of concern (I-129, Sr-90, Cr, and NO3-). The focus of these laboratory experiments was to evaluate the potential effectiveness of the selected remediation technologies under site-specific conditions. Here, we will present a subset of the technologies evaluated, including three phosphate-based technologies. The three technologies include two liquid amendments that target the formation of apatite (calcium citrate phosphate, Ca-Cit-PO4, and polyphosphate, Poly-PO4) and one preformed Sn(II)-substituted apatite particulate amendment (tin apatite, Sn-PO4). These amendments aim to sequester U and Tc-99 through a combination of adsorption, reduction, precipitation, and coating processes. To address the need for a site-specific understanding of amendment efficacy, batch and column experiments were conducted with sediments from three different formations, including the Hanford formation which represents much of the vadose zone, perched-zone sands in the B Complex, and Cold Creek gravel from near the water table in areas of the Site. Ca-Cit-PO4 and Sn-PO4 were both effective for Tc-99 and U. However, Poly-PO4 was effective only for U and must be paired with a reductant (e.g., polysulfide solutions or zero valent iron) to be effective for Tc-99. Coauthors: Amanda R. Lawter (Pacific Northwest National Laboratory), Michelle M.V. Snyder (Pacific Northwest National Laboratory), James E. Szecsody (Pacific Northwest National Laboratory), Rob D. Mackley (Pacific Northwest National Laboratory), Nicolas Huerta (Pacific Northwest National Laboratory) __________________________________________________ |
|
3:55 - 4:15 p.m. Determination of Site End States for Complex Sites in the UK Vicky Newling, Quintessa Limited ► PRESENTATION PDF |
In the UK, “Guidance on Requirements for Release from Radioactive Substances Regulation” (GRR) has been issued by the environment agencies, providing the potential for some radioactive waste and/or radioactively contaminated ground to remain on-site at the end of the decommissioning process. This guidance requires that the Site End State is clearly optimised, considering all credible on and off-site disposal options and is based upon the principles of BAT (Best Available Techniques) or Best Practicable Means (BPM) assessment. Sites with a clear time frame for cessation of operations or which are nearing completion of decommissioning and remediation activities, can face a complex decision-making process for determining a Site End State within the context of GRR. However, this process can become even more challenging where potential End Uses may not be clear, for example, a complex site with a prolonged period of closure, or an operational site which does not have clear visibility on when operations will cease or how their business will evolve over time. Similarly, some UK sites also have co-located operators at opposite ends of the development and decommissioning life-cycle, creating challenging interfaces for Site End State decision making. This presents unique challenges in determining the level of remediation required now and provides a fine line for prevention of foreclosure of options for future use. The complexities of co-located and developing sites for End State definitions are examined using decision-critical technical, social, environmental, and economic factors. Capturing the changing priorities and significance of key factors as the level of site complexity increases is key to developing a coherent End State decision-making strategy. Coauthors: Alan Paulley (Quintessa Limited) |
|
4:15 - 4:35 p.m. Challenges in Transition from Cleanup to Long-Term Stewardship at Sites Emerald Laija, United States Environmental Protection Agency ► PRESENTATION PDF |
 The transition from cleanup to long-term stewardship at legacy sites poses unique challenges for the Department of Energy (DOE) Office of Legacy Management (LM) and U.S. Environmental Protection Agency (EPA) Federal Facilities Restoration and Reuse Office. This presentation explores these challenges and strategies to address them effectively including the use of lessons learned from past site transitions. LM understands that long-term stewardship successes are built from a strong foundation of a consensus-driven end-state vision formulated during site clean-up. Remedies and stewardship plans need to be adaptable, to address the challenges associated with evolving remedies, including instances of remedy failure. Collaboration between DOE, EPA, and stakeholders in forming the vision and then addressing these situations is crucial. The presentation will underscore the commitment to transparency, community engagement, workforce retention and preservation of institutional knowledge throughout transition. The presentation will discuss the importance of pre-planning and collaboration with cleanup organizations and their stakeholders to facilitate a smooth transition. It will address the duration of the transition period and consider the size and complexity of each site. Lessons learned from previous transfers including the Fernald, Mound and Weldon Spring sites will be shared to enhance understanding and guide future efforts. Moreover, the presentation will delve into the complexities encountered during the transition process and identify key factors that influence stewardship continuity and successful outcomes. The importance of active maintenance, surveillance, record-keeping, and ongoing engagement with regulators, stakeholders, and community organizations will be highlighted as vital components of post-transfer long-term site management. Attendees will gain valuable insights on the complexities of transitioning from cleanup to long-term stewardship at legacy sites. The information will aid site managers, regulators, and stakeholders in understanding the challenges involved and developing effective strategies to ensure the successful long-term care and protection of these sites for future generations. Coauthors: Cliff Carpenter (Department of Energy Legacy Management), Kathleen Whysner (Department of Energy Legacy Management), Tiffany Drake (Department of Energy Legacy Management), Melissa Lutz (Department of Energy Legacy Management) __________________________________________________ |
|
4:35 - 5:00 p.m. |
Open Discussion and Closing Remarks __________________________________________________ |