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DOE OSTI2020

Criticality Consideration for Geologic Disposal of DOE-Owned Spent Nuclear Fuels - 20255

Decisions must be made relative to packaging spent nuclear fuel (SNF) for storage, transportation, and eventual disposal. This paper evaluates potential criticality-related loading and packaging considerations for Department of Energy (DOE)-owned SNF that could be impacted favorably or unfavorably by disposal uncertainties and proposes approaches to minimize such impacts. Using Al-Based SNF as an example and drawing on analyses performed in support of the Yucca Mountain Repository License Application (LA), this paper explores the role of natural barriers, engineered barriers, and waste form characteristics relative to reducing the potential for postclosure criticality. Several parameters important to postclosure criticality are considered in order to determine which are useful discriminators to support packaging decisions. Using these parameters, a qualitative assessment is performed relative to three options for managing DOE-owned SNFs. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗

DOE OSTI2022

Waste Control Specialists Technical Review Team Report

1. Modeling of Drum 68660 and the WCS Drums: A calibrated model of Los Alamos National Laboratory (LANL) Drum 68660 indicates that pressurization of the drum by restriction of drum venting could have led to the thermal runaway reaction at the Waste Isolation Pilot Plant (WIPP) in 2014, supporting the hypothesis that the contents of the drum were not fundamentally different from the overall remediated nitrate salt (RNS) waste stream. 2. Nitric Acid Reactions and Aging of the Waste: The stability of the WCS RNS waste with respect to autocatalytic thermal runaway due to nitric acid chemistry should increase over time as the nitric acid is depleted from chemical reactions in the drum. However, this cannot be confirmed because of the lack of long-term experimental data on the impact of aging on the reactivity of RNS waste. The calibrated model indicates that the waste drums retain most of their reactive components, metal nitrate salts and sWheat Scoop ® , even after eight years. 3. Pressure Effects and Runaway Reactions: The calibrated model indicates that if the drums and standard waste boxes (SWBs) are not allowed to pressurize during transport or storage and they are stored at historical WIPP repository temperatures, then an autocatalytic thermal runaway event is not expected to occur. Since the cause of Drum 68660 pressurization is not known, decision makers are not able to tailor mitigating strategies to the initiating event. Consequently, mitigating strategies must consider all feasible internal and external events that could lead to the pressurization of the drums. 4. Temperature Effects and Runaway Reactions: Temperature also has a strong influence on the stability of the waste. The calibrated model indicates that cooling the drums or SWBs can reduce the possibility of autocatalytic thermal runaway reactions. Simulations suggest that for a drum with a plugged vent, the probability of thermal runaway may be reduced or eliminated if wastes are maintained at or below 43 °F through active cooling measures from the initiation of transport until emplacement at WIPP.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗

DOE OSTI2016

Future German R and D on HLW Disposal - 16519

In 2009, after the General elections, the new German Government showed a relatively positive attitude towards a prolonged use of nuclear power. Power plant shutdown was planned for the year 2032. Nuclear power was considered as a sort of transition energy technology until the energy supply would take place by the use of renewable energy sources. This was in line with the legal framework and the political strategy of the energy turnaround. Then, 17 nuclear power plants (NPP) were operational. The Fukushima incident heralded the sound of drastic changes in the German energy policy: Besides an intermediate stop of operation of reactors until a so-called stress test was accomplished, the general political decision was to phase-out nuclear earlier than planned and to implement faster the decisions regarding the energy transition policy. The shut-down of the last German nuclear power plant will occur in 2022. Accordingly, all the necessary legal changes were made. A consensus about the appropriate waste management strategy for heat generating waste (spent nuclear fuel (SNF) and vitrified waste (HLW)) was still pending at this time. Public and political discussions on this subject continued as in the years before. In July 2013, after intensive discussions, most of the parties represented in the German parliament agreed to eventually tackle the challenge of finding a repository by a consensual, transparent and science-based approach. This was to be codified in a law. In July 2013, the Site Selection Act passed the parliament. This law should pave the way for a new holistic process that addresses social, political, and scientific aspects of siting and the site selection process. The basics for this process should be provided by the 'Commission Storage of Radioactive Waste Materials' which was established according this law. Against this background discussions showed that scientific-technical R and D activities should be mirrored accordingly and R and D has to deal both with the future challenges of radioactive waste HLW disposal and related aspects. Considering this the Federal Ministry for Economic Affairs and Energy (BMWi), which is responsible for non-site specific R and D, created the new Research Concept 'Research for the management of radioactive waste', being fundamental and the frame for non-site specific R and D projects funded by BMWi. Key changes - mirroring the new requirements and different aspects - touch the issues: host rock research, i.e. all potential host rocks available in Germany are equally addressed and there is no prioritization, consideration of consequences of prolonged storage at NPP sites, alternative waste management strategies compared to direct disposal in a mined repository, and involvement of socio-technical aspects.This paper intends to highlight the key changes, its consequences, and will give a brief overview on first initiated R and D activities. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗

DOE OSTI2015

Effectiveness of actinide management in fast reactors over a finite recycling period - 15123

Long-lived nuclear waste primarily consists of transuranic (TRU) isotopes. Full recycling of TRU isotopes can, in theory, lead to a reduction in repository radiotoxicity to reference levels in as little as ∼500 years provided reprocessing and fuel fabrication losses are limited. However, over a limited time frame, the radiotoxicity of the 'final' core can dominate over reprocessing losses, leading to a much lower reduction in radiotoxicity compared to that achievable at equilibrium. In this paper, the fuel cycle code ORION is used to model the recycle of light water reactor (LWR)-produced TRUs in sodium-cooled fast reactors (SFRs). With full actinide recycling, at least 6 generations of SFRs are required in a gradual phase-out of nuclear power to achieve transmutation performance approaching the theoretical equilibrium performance. Break-even SFRs are much less effective from a point of view of reducing waste radiotoxicity. Thorium (Th)-burner fuel cycles are found to result in slightly lower radiotoxicity than U-burner fuel cycles for the same number of generations. Closed break-even Th fuel cycles require ∼3 generations of operation before their waste radiotoxicity benefits result in decay to the reference level in ∼1000 years, provided that Pa is recycled. While this is a very long time frame, it is substantially better than the time frame required by other strategies. The integrated decay heat over the scenario time frame is substantially higher for break-even Th-SFRs than break-even U-SFRs as a result of much higher {sup 90}Sr production. As decay heat affects repository sizing, this weakens the argument for the Th cycle. (authors)

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗

DOE OSTI2015

Development of a backfill material for LILW and HLW disposal galleries in the current Belgian geological disposal concept - 15374

In Belgium, it is planned to dispose of long-lived and high-level waste in an underground facility. After disposal of the waste, the galleries will be backfilled to provide stability to the galleries and to limit the amount of voids in the repository. To achieve those goals, the backfill material has to have a good flowability, a negligible bleeding, and a limited shrinkage. A limited grain size is also required to allow the injection of the backfill material. Despite the fact that the backfill supports the gallery lining, its strength must be low enough to enable the retrieval of the waste packages. The backfill material has to be chemically compatible with the Boom Clay and the waste packages. This means that it should not unduly perturb the clay or disposal packages. The thermal conductivity of the backfill material in the galleries containing high-level and thus heat-generating waste must be high enough to allow sufficient dissipation of the decay heat into the surrounding clay. Based on these objectives, material requirements were specified and the development of a backfill mixture was carried out. Initially, the mix composition was optimized in the laboratory. Thereafter, the backfill process of a gallery section was simulated. The investigations illustrate that this mixture can be transported via pipelines through the shaft and drifts and would fill completely the backfill sections in the galleries. Measurements of the porosity, the pore solution composition, the thermal material properties, and the strength illustrate the compliancies with the requirements and the feasibility of backfilling the disposal galleries. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗

DOE OSTI2015

FY15 Report on Thermomechanical Testing

Sandia is participating in the third phase of a United States (US)-German Joint Project that compares constitutive models and simulation procedures on the basis of model calculations of the thermomechanical behavior and healing of rock salt (Salzer et al. 2015). The first goal of the project is to evaluate the ability of numerical modeling tools to correctly describe the relevant deformation phenomena in rock salt under various influences. Among the numerical modeling tools required to address this are constitutive models that are used in computer simulations for the description of the thermal, mechanical, and hydraulic behavior of the host rock under various influences and for the long-term prediction of this behavior. Achieving this goal will lead to increased confidence in the results of numerical simulations related to the secure disposal of radioactive wastes in rock salt. Results of the Joint Project may ultimately be used to make various assertions regarding stability analysis of an underground repository in salt during the operating phase as well as long-term integrity of the geological barrier in the post-operating phase A primary evaluation of constitutive model capabilities comes by way of predicting large-scale field tests. The Joint Project partners decided to model Waste Isolation Pilot Plant (WIPP) Rooms B & D which are full-scale rooms having the same dimensions. Room D deformed under natural, ambient conditions while Room B was thermally driven by an array of waste-simulating heaters (Munson et al. 1988; 1990). Existing laboratory test data for WIPP salt were carefully scrutinized and the partners decided that additional testing would be needed to help evaluate advanced features of the constitutive models. The German partners performed over 140 laboratory tests on WIPP salt at no charge to the US Department of Energy (DOE).

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗

DOE OSTI2016

A New Consolidated Storage Facility for Used Nuclear Fuel in Andrews County, Texas - 16418

On February 6, 2015, Waste Control Specialists LLC (WCS) announced its plan to file a license application with the U.S. Nuclear Regulatory Commission (NRC) to construct and operate a Consolidated Interim Storage Facility (CISF). Upon issuance of the license, WCS would be authorized to receive Used Nuclear Fuel (UNF) and reactor related Greater Than Class C Low Level Radioactive Waste (referred hence forth as UNF) at the CISF in late 2020. WCS based its decision to license a CISF based on strong support from the State of Texas and the local community's willingness to host such a facility in Andrews County, Texas. WCS' decision to license a CISF in a supportive community is consistent with the consent-based licensing approach recommended by the Blue Ribbon Commission on America's Nuclear Future. WCS intends to use existing technology developed by AREVA and NAC International that have already been approved by the NRC to transport UNF from existing commercial nuclear reactors across the nation for interim storage at its 14,000 acre site in Andrew County, Texas. In the pre-application licensing meetings held with the NRC, WCS underscored that UNF would be removed first from the shutdown decommissioned reactor sites and transported to the CISF. Approximately eighty percent of the UNF currently residing at the shutdown decommissioned reactor sites can be safely placed into the storage systems developed by AREVA and NAC International that are currently licensed by the NRC. WCS plans to store up to 40,000 Metric Tons of Heavy Metal (MTHM) at the CISF that would be constructed in eight phases over the next 20 years. WCS intends to submit its license application for the CISF to the NRC by April 2016. The license application will request authorization to possess up to 5,000 MTHM of UNF for Phase One which can accommodate storing the fuel located at over ten shutdown decommissioned reactor sites. As discussed with the NRC, the license application will be developed following NRC regulatory guidance to comply with the technical requirements specified in Title 10 of the Code of Federal Regulations (CFR) Part 72, Licensing Requirements for the Independent Storage of Spent Nuclear Fuel, High-Level Radioactive Waste, and Reactor-Related Greater Than Class C Waste. In addition, to filing the license application, WCS is also seeking legislative changes to the Nuclear Waste Policy Act of 1982 requiring the U.S. Department of Energy (DOE) to take title of the UNF at the commercial nuclear reactor sites. Under such legislative changes, the DOE would also be responsible for the transport of UNF to the CISF. In addition to preparing the CISF License Application, WCS and its partners AREVA and NAC International are prepared to work with DOE to facilitate the development of the UNF transportation infrastructure in the timeframe needed to support CISF operations. The WCS site and technical approach give it several advantages which uniquely position it to become the first successful commercial CISF in the U.S. These advantages include: broad consent-based support at the local, state, and Congressional level; an operating waste disposal site with an existing transportation infrastructure; and the use of already licensed systems to address 80% of the UNF currently in dry storage at shutdown sites in the U.S. WCS firmly believes this initiative will provide an economically viable option for consolidated interim storage of UNF until a permanent geologic repository becomes available. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗

DOE OSTI2018

Experience by BAM in the Transport Package Safety Assessment of German Waste Containers - 18469

Transport and storage containers for low and mid-level radioactive waste are getting more and more of relevance due to the nuclear phase out decision in 2011. For higher activities Type B(U) approved waste containers will be needed for the shut down and dismantling phases of NPPs. It is expected that large quantities are required in the near future. German waste containers are generally approved for transport and interim storage and are also intended for the final disposal in the Konrad repository. BAM is involved in the authority licensing of transport package designs in Germany. In this context, BAM is responsible for the assessment of safe containment, mechanical, thermal and quality management issues. BAM also operates test facilities and performs drop as well as thermal tests during package licensing procedures. This paper summarizes our experience in the transport package design assessment of Type B(U) waste containers. A general overview of the approval process, the requirements and approaches BAM applies are described. Some examples are used to illustrate different aspects and technical issues we are addressing during the package assessment. In the first part of the paper the specific design aspects of German waste containers are described. Here, a general overview is given e.g. about closure systems, impact limiter designs, and the handling concepts. Furthermore, the wide range of radioactive content and their physical behavior including the impact on the packages assessment are described. The second part is focused on questions about the licensing and assessment process of German waste containers from the BAM authority point of view. The general approaches for the strategy of demonstration are outlined on the basis of the test conditions according to IAEA Regulations SSR-6. Furthermore, particular issues of the mechanical and thermal assessment with respect to the specific test conditions are discussed. For accident conditions of transport, aspects to be mentioned are e.g. the assessment of the lid bolts, the axial gap applied between content and lid, and the thermal behavior of the wood filled impact limiter after the fire test. However, issues of the assessment for routine and normal conditions of transport are addressed in this paper, too. The intention of this paper is introduce recent approval procedure experience in Germany, describing technical evaluation issues and so reduce rounds of questions during applications. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗

DOE OSTI2015

The Cires facility in Morvilliers: from a VLL waste disposal facility to the development of industrial activities - 15252

The disposal facility of CIRES for very low level wastes was designed to provide safe and cost effective services to waste generators, in particular for decommissioning works. The facility could significantly increase waste annual deliveries to meet waste generators' needs and accommodate large disused components as PWR steam generators after decontamination. However an anticipated saturation of its capacity is foreseen as needs for disposal has doubled since its start-up. The geometry of the cells was optimized and the technical capacity of the repository is presently by 40% above its licensed capacity. Saturation has been delayed; however a new facility will be necessary by 2030 and other waste management options are to be considered as recycling of metallic wastes or crushed concrete rubble. CIRES facility also became Andra's industrial platform for the management of institutional wastes. A grouping and a storage facility have been built and a new processing facility should start up in 2016. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗

DOE OSTI2015

Development of three-dimensional models for WIPP performance assessment using PFLOTRAN - 15073

The Waste Isolation Pilot Plant (WIPP), located in southeastern New Mexico, has been developed by the U.S. Department of Energy (DOE) for the deep geologic disposal of transuranic (TRU) waste. WIPP performance assessment (PA) calculations estimate the probability and consequence of potential radionuclide releases from the repository to the accessible environment for a regulatory period of 10,000 years after facility closure. To date, WIPP PA calculations have employed multiple 2D numerical models requiring simplification of the mesh and processes. Introducing 3D numerical models within WIPP PA enables increasingly realistic representations of the WIPP subsurface domain and improved flexibility for incorporating relevant features. Furthermore, the increased computing capacity afforded by modern hardware architectures enables this 3D modeling. Modeling in 3D will be more flexible because less homogenization is required and better accuracy of the results can be obtained by making fewer assumptions and/or simplifications. The use of PFLOTRAN, a state-of-art massively parallel subsurface flow and reactive transport code, will enable this 3D modeling, and eliminate the need for multiple related, but decoupled 2D models. However, there are capabilities that PFLOTRAN must be demonstrated in order to fulfill requirements for WIPP PA. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗

DOE OSTI2017

Sorption Behavior of Iodide Ions on Calcium Silicate Hydrate Formed under the Condition Saturated with Saline Water - 17069

The sorption behavior of iodide ions on calcium-silicate-hydrate (CSH gel) under the condition saturated with saline water was examined by using a Raman spectroscopy and ICP-AES, without drying process. In the sorption experiments, I-127 is a stable isotope was used as an alternative of I-129. CSH gel was synthesized with mixing CaO, SiO{sub 2}, and NaCl solution. The Ca/Si molar ratios of CSH gel were set to 0.4, 0.8, 1.2 and 1.6, and the concentration of NaCl solution was set to 0.6 M for simulating the condition of saline groundwater. The liquid/solid weight ratios of CSH gel were set to 10, 13, 15, 17, and 20, and the total weight of solid phase was 1.5 g. Furthermore, at the preparation of CSH gel, the substance of iodide ions in each sample was adjusted to 15 μmol. The synthesis procedure for all samples was conducted in a glove bag filled with nitrogen gas. The curing period was 7, 14, 30, and 60 days at a room temperature (298 K) with shaking at 120 strokes/min. The results of the sorption experiments, iodide ions adsorbed on CSH gel regardless of the high concentration of NaCl. The concentration of iodide ions in liquid phase was equal to the initial one under all experimental conditions. Moreover, the distribution coefficients, K{sub d}, were kept constant (K{sub d} = 1 mL/g) after 14 days. In the results of Raman analysis, the structure of CSH gel was scarcely influenced by incorporating iodide ions from the viewpoint of the silicate chain. These results suggest that iodide ions will be incorporated into CSH gel with the hydration water without changing its structure. Such effect of CSH gel formed with leaching cementitious constituents around the repository may retard the migration of radionuclide (I-129) in the natural barrier of the radioactive waste disposal system. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗

DOE OSTI2023

Application of Particle Accelerators to Mitigate Energy and Climate Change Problems Facing America

Reliable CO 2 -free baseload power is needed to address ever-increasing demands for electricity while minimizing adverse climate change. Diversified power supply provided by solar, wind, geothermal, and nuclear reactors can displace the use of fossil fuels. The United States (U.S.) is taking a new look at nuclear power as a source of electrical energy and the nuclear industry is proposing new approaches which may minimize capital costs. However, nuclear power comes with a variety of technical problems. Chief among those is managing the used fuel from nuclear reactors. No long-term, practicable solution to this problem is available. The lack of progress on a comprehensive waste management strategy restricts growth in the nuclear power industry and minimizes the role that nuclear energy may serve as part of a zero-carbon future (Bahr, 2021). According to the Nuclear Waste Policy Act of 1982, as amended, the U.S. Government has possession of the used reactor fuel and incurs large annual storage fees paid to utilities to store and safeguard the accumulated used fuel. In effect, short term on-site storage of nuclear waste is the current waste management plan. The amount of used reactor fuel in the U.S. is approximately 80,000 metric tons. While no geologic repository exists within the U.S., the potential site at Yucca Mountain, NV would accommodate 70,000 metric tons, which fails to meet current and future needs. Given the technical and political challenges associated with establishing a single geological storage site, it is necessary for the U.S. to implement technologies that improve the suitability of geological storage by reducing the volume and radiotoxicity of stored material. No extant technology meets this need. Accelerator driven waste burners have been proposed as a scalable method to process used nuclear fuel, however considerable technical challenges remain which impede commercialization. Innovations in design require investigation of novel materials, development of accurate models and simulations, and a comprehensive assessment of safety and performance. This proposal elaborates how LANL is uniquely positioned to make key contributions to this area of research.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗

DOE OSTI2021

ORNL Input to GDSA Repository Systems Analysis FY21

This document satisfies the M3 milestone M3SF-21OR010304082 titled “ORNL Input to GDSA Repository Systems.” This document describes the current status of Oak Ridge National Laboratory’s (ORNL’s) efforts related to analyses of dual-purpose canister (DPC) disposal in unsaturated alluvium with a focus on thermal hydrological constraints on criticality timing and power output. This analysis updates previous analyses of thermal hydrological constraints on timing and power output of a potential criticality event in Dual-Purpose Canisters (DPCs) in a hypothetical repository in unsaturated alluvium using a more realistic representation of heat transport inside dry DPCs. PFLOTRAN was used for the simulations of multiphase thermal hydrology near a single DPC. The scenario considers a DPC failure at 9000 years, allowing water to enter and eventually fill the DPC. Once the DPC is filled to a level that could support a criticality event, different values for criticality power output were added to the decay heat. The main objective is to bound the power output that could be produced by a criticality event without driving water out of the package. For the conditions analyzed here, following a package breach, the alluvial formation could supply enough water to allow enough accumulation in the DPC to support a criticality event. However, the power output that would be generated is limited to modest values by loss of water moderator due to evaporation and vapor diffusion. In the reference case scenario, the DPC would not start to fill with water until about 16,000 years post closure and would not fill to a level that allows a criticality event until approximately 25,000 years post closure. The long-term average power output that could be sustained without driving off the water and terminating the criticality event is limited to approximately 100 W. Sensitivity to assumed conditions and parameters in the reference case, especially the deep percolation rate, need to be addressed but could not be undertaken because of numerical failures of the PFLOTRAN code running in general mode in the dry conditions of an unsaturated alluvium repository

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗

DOE OSTI2020

Nuclear Criticality Safety Assessment of Criticality Control Containers without Moderation Control at the Waste Isolation Pilot Plant

The Waste Isolation Pilot Plant (WIPP) provides for safe, permanent disposal of government-owned transuranic (TRU) and TRU mixed wastes. Receipt and disposal of waste at the WIPP site began in March 1999. The Sandia report, Consideration of Nuclear Criticality When Disposing of Transuranic Waste at the Waste Isolation Pilot Plant, addressed potential nuclear criticality safety issues based on the projected inventory characteristics known at the time [1]. As designs for inventory, waste forms, and disposal packages have changed, new analyses have been performed, and updates have been made to address any potential effects to the WIPP safety basis. New analyses performed include Saylor 2017 [2] and Brickner 2019 [3], which address certain waste containers with specified loadings under post-closure conditions. Both examined several hypothetical scenarios and included analyses to bound (from a criticality potential standpoint) credible configurations that could occur at WIPP during the repository regulatory post-closure disposal time period for feature, event, and process (FEP) considerations—10,000 years. During this post-closure period at WIPP, the screening of FEPs is governed by the risk-based standards and implementing regulations of the US Environmental Protection Agency (EPA) (i.e., 40 CFR 191 and 40 CFR 194, respectively) [4,5]. An FEP screening can be based on either a low-consequence or low-probability rationale. A low-probability rationale includes either (a) a qualitative rationale that the FEP is not credible or (b) a quantitative demonstration that the probability is less than 10-4 in 104 years. In this evaluation, a qualitative lowprobability rationale of not credible is used by demonstrating that bounding configurations of the waste are not critical. The demonstration of subcriticality is through quantitative calculations, but a probability of criticality is not evaluated. Rather, the rationale for this evaluation is that bounding configurations with an effective neutron multiplication factor (keff) well below the upper subcriticality limit (USL) make criticality incredible. Reference [2] documented a nuclear criticality assessment of the WIPP repository for disposal of dilute surplus plutonium materials using the Dilute and Dispose Approach and packaging in criticality control overpacks (CCOs). The CCO is the waste disposal container recently designed to allow for up to 380 fissile gram equivalent (FGE) 239 Pu per drum, which is a higher fissile loading than typical waste containers. The CCO consists of a criticality control container (CCC) positioned by upper and lower plywood spacers within a standard 55 gal drum. The CCC is used to establish a geometry control for fissile materials during transportation and WIPP emplacement operations. The current WIPP waste acceptance criteria for CCO payloads limit beryllium to less than or equal to 1% by weight of the waste contents and require the waste form to be non-machine compacted. Reference [2] considered two scenario progressions—room closure from salt creep, hereafter referred to as the reconfigured dry scenario, and flooding with brine, hereafter referred to as the reconfigured wet scenario. The subsequent drying out of the reconfigured wet scenarios was also considered. For all scenarios, subcriticality was maintained when 50 g of B 4 C (acting as a neutron absorber) per CCC was intermixed within the plutonium disposition waste form. The analysis used a waste form description that limits the amount of moderation that could be present within the waste form (i.e., it limits the amount of water and polyethylene that could be present based on planned processing conditions). This analysis to evaluate increased limits on the amount of moderation that could be present was performed as a companion to Reference [2] to address concerns associated with verifying moisture and/or plastic contents of waste materials following packaging of dilute surplus plutonium in the CCO. To that end, this analysis used the models and methods from Reference [2] to evaluate a more generic base waste form consisting of water and polyethylene that is more similar (and nearly identical) to the generic waste forms utilized in other models/analyses supporting the TRU Package Transporter Model II (TRUPACTII) safety analysis [6] (all are without moderation controls). The waste form in this analysis uses a base mixture of 75% water and 25% polyethylene, the total amount of which is varied to determine the optimum moderation to fissile material (H/Pu) ratio. The fissile loading is maintained at up to 380 FGE 239 Pu (modeled as PuO 2 ) per CCO with an additional 545 g of beryllium (to bound the 1% by weight contents restriction) and 50 g of B 4 C intermixed per CCO. The beryllium content (1% by weight) is based on the total allowed waste weight (this does not include packaging and container weights). Figures ES-1 and ES-2 display summary results, showing that with this model including 50 g of B 4 C per CCO, the system keff remains under 0.85 for all moderator amounts and provides a significant margin against post-closure criticality under postulated bounding conditions for compaction. Figure ES-1 compares an infinite model with a room model at the initial emplacement spacing and under full radial compaction. Full radial compaction places each CCC in direct contact and does not credit any anticipated spacing associated with current post-closure geomechanical modeling of the repository [7]. The effects of variations in the H/Pu ratio were evaluated by varying the amount of the water/polyethylene component of the waste model, with fissile loading maintained at 380 239 Pu FGE. Similarly, Figure ES-2 illustrates how various amounts of B 4 C per CCO influence k eff at different radial compactions, all at the H/Pu ratio of 200 (in the room array model). Therefore, while the results from Saylor 2017 [2] modeled more realistic process limits associated with packaging of dilute surplus plutonium, this analysis demonstrates that limits on moderation (plastic and water content) are not necessary to ensure subcriticality in the WIPP repository, provided the requisite B 4 C absorber is present.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗

DOE OSTI2015

Charge-Coupled Substituted Garnets (Y 3-x Ca 0.5x M 0.5x )Fe 5 O 12 (M = Ce, Th): Structure and Stability as Crystalline Nuclear Waste Forms

The garnet structure has been proposed as a potential crystalline nuclear waste form for accommodation of actinide elements, especially uranium (U). In this study, yttrium iron garnet (YIG) as a model garnet host was studied for the incorporation of U analogs, cerium (Ce) and thorium (Th), incorporated by a charge-coupled substitution with calcium (Ca) for yttrium (Y) in YIG, namely, 2Y 3+ = Ca 2+ + M 4+ , where M 4+ = Ce 4+ or Th 4+ . Single-phase garnets Y 3–x Ca 0.5x M 0.5x Fe 5 O 12 (x = 0.1–0.7) were synthesized by the citrate–nitrate combustion method. Ce was confirmed to be tetravalent by X-ray absorption spectroscopy and X-ray photoelectron spectroscopy. X-ray diffraction and 57 Fe–Mössbauer spectroscopy indicated that M 4+ and Ca 2+ cations are restricted to the c site, and the local environments of both the tetrahedral and the octahedral Fe 3+ are systematically affected by the extent of substitution. The charge-coupled substitution has advantages in incorporating Ce/Th and in stabilizing the substituted phases compared to a single substitution strategy. Enthalpies of formation of garnets were obtained by high temperature oxide melt solution calorimetry, and the enthalpies of substitution of Ce and Th were determined. The thermodynamic analysis demonstrates that the substituted garnets are entropically rather than energetically stabilized. This suggests that such garnets may form and persist in repositories at high temperature but might decompose near room temperature.

Guo, Xiaofeng↗

DOE OSTI2017

Conceptual Design of the Package Handling System for the Deep Borehole Engineering Demonstration - 17064

Deep borehole disposal involves drilling one or more boreholes into crystalline basement rock to a depth of about 5 km, emplacing waste packages in the lower 2 km of the borehole, and sealing and plugging the upper 3 km. These depths are several times deeper than for typical mined repositories. A deep borehole field test (DBFT) is proposed to confirm the safety and feasibility of the deep borehole concept. The primary goals are to demonstrate the construction and characterization of deep boreholes, demonstrate the equipment and operations used for safe waste handling and emplacement downhole, study geologic controls on waste form stability and isolation, and evaluate the overall safety and practicality of the concept. The test will be conducted using simulated waste packages; no radioactive wastes will be handled at the deep borehole field test site. A key component of the DBFT is an engineering demonstration of the equipment and operations needed to transport waste packages to the site, move packages between the transportation and emplacement systems, and lower or retrieve packages into or out of the borehole. This paper describes the conceptualization of test package handling, from transportation and receipt through the interface with the borehole. It also describes the use of an integrated test facility to check out equipment prior to deployment at the DBFT site, and performance of the engineering demonstration at the DBFT site. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗

DOE OSTI2014

Delayed Gamma-ray Spectroscopy for Non-Destructive Assay of Nuclear Materials

This project addresses the need for improved non-destructive assay techniques for quantifying the actinide composition of spent nuclear fuel and for the independent verification of declared quantities of special nuclear materials at key stages of the fuel cycle. High-energy delayed gamma-ray spectroscopy following neutron irradiation is a potential technique for directly assaying spent fuel assemblies and achieving the safeguards goal of quantifying nuclear material inventories for spent fuel handling, interim storage, reprocessing facilities, repository sites, and final disposal. Other potential applications include determination of MOX fuel composition, characterization of nuclear waste packages, and challenges in homeland security and arms control verification.

98 NUCLEAR DISARMAMENT, SAFEGUARDS, AND PHYSICAL P↗

DOE OSTI2015

Delayed Gamma-Ray Spectroscopy for Non-Destructive Assay of Nuclear Materials

High-energy, beta-delayed gamma-ray spectroscopy is a potential, non-destructive assay techniques for the independent verification of declared quantities of special nuclear materials at key stages of the fuel cycle and for directly assaying nuclear material inventories for spent fuel handling, interim storage, reprocessing facilities, repository sites, and final disposal. Other potential applications include determination of MOX fuel composition, characterization of nuclear waste packages, and challenges in homeland security and arms control verification. Experimental measurements were performed to evaluate fission fragment yields, to test methods for determining isotopic fractions, and to benchmark the modeling code package. Experimental measurement campaigns were carried out at the IAC using a photo-neutron source and at OSU using a thermal neutron beam from the TRIGA reactor to characterize the emission of high-energy delayed gamma rays from 235 U, 239 Pu, and 241 Pu targets following neutron induced fission. Data were collected for pure and combined targets for several irradiation/spectroscopy cycle times ranging from 10/10 seconds to 15/30 minutes.The delayed gamma-ray signature of 241 Pu, a significant fissile constituent in spent fuel, was measured and compared to 239 Pu. The 241 Pu/ 239 Pu ratios varied between 0.5 and 1.2 for ten prominent lines in the 2700-3600 keV energy range. Such significant differences in relative peak intensities make it possible to determine relative fractions of these isotopes in a mixed sample. A method for determining fission product yields by fitting the energy and time dependence of the delayed gamma-ray emission was developed and demonstrated on a limited 235 U data set. De-convolution methods for determining fissile fractions were developed and tested on the experimental data. The use of high count-rate LaBr 3 detectors was investigated as a potential alternative to HPGe detectors. Modeling capabilities were added to an existing framework and codes were adapted as needed for analyzing experiments and assessing application-specific assay concepts. A de-convolution analysis of the delayed gamma-ray response spectra modeled for spent fuel assemblies was performed using the same method that was applied to the experimental spectra.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗