Treatment Of High-level Waste Research Articles

Reflective reviews on Japanese high-level waste (HLW) vitrification – Exploring the obstacles encountered in active tests at Rokkasho

Vitrification is currently the most widely used technology for the treatment of high-level waste (HLW) generated from spent nuclear fuel (SNF) reprocessing. Glasses for the solidification of HLW have been developed over half a century at different times in each country. Likewise in Japan, repeated system evaluations of borosilicate waste glass matrices and the liquid-fed joule-heated ceramic-lined melter (LFCM) process have been found to be applicable to a wide range of HLW compositions. The Rokkasho vitrification facility located in northern Japan encounters significant operational issues owing to the presence of sparsely soluble elements including noble metals (NMs) and separated phases, such as the yellow phases (YPs) constituents, in glass melts. These elements cause serious disruptions, jeopardizing the stable functioning of the LFCM. The active vitrification test was suspended because of the formation of YPs in the glass melts and subsequent sedimentation of NMs at the bottom of the melter. First, we analyzed the testing data to identify the fundamental causes behind the unstable LFCM operation. Our investigation revealed that the presence of significant amounts of Mo and S, along with NMs, specifically Ru, Rh, and Pd, in the Rokkasho HLW stream triggers the formation of molybdate and sulfate salt phases (YPs), which subsequently enabled the sedimentation of NMs at the bottom of the melter. Second, we selected eight major tasks related to difficulties of LFCM operation in the active tests and studied the findings in each task considering the preconditions of task success. Moreover, we strengthened our analysis by subjecting each task to 22 hypotheses tests in a systematic manner to minimize the risk of issues associated with generalizability. Third, we combined these findings and classified them into two categories based on the action system theory on management: variable system (Y) and actor’s system (X), assuming that the indirect or mechanism/environment factors of X should influence on the directly observed factors of Y. Our approach involved implementing a reflective actor’s system (X’) to improve the variable system for the controllable system (Y’), thereby mitigating unexpected events. We then summarized the main implications of this method to ensure predictable and reliable outcomes for the associated tasks. Finally, we concluded the potential effectiveness of strategic actions that could leverage organizational capabilities and processes to improve task performances in the context of a controllable system given the implications we identified.

Multi-group analysis of Minor Actinides transmutation in a Fusion Hybrid Reactor

New nuclear technologies are currently being study to face High Level Waste treatment and disposal issues. Generally, GEN-IV fission Fast Reactors (FR) are considered the waste-burners of the future. In fact, a fast flux turns out to be the best choice for actinides irradiation in critical reactors because of favorable cross section conditions. Differently, Fusion Fission Hybrid Reactors (FFHR) are futuristic devices based on the combination of fusion and fission systems and could represent an alternative to FRs. In such systems, the choice spectrum of the neutron flux that irradiates HLW may be non-obvious due to some operational constraints which have to be considered. To design and optimize these systems as waste-burners, one should fully understand the transmutation dynamics occurring into the fission region. A multi-energy-group analysis by FISPACT-II code has been set to analyze the conversion processes in scenarios characterized by different neutron energy spectra and fluences. The results of this study show that, despite fast fluxes are characterized by better behaviors in terms of radiotoxicity treatment, the difficulties of reaching high reaction yields may require solutions involving moderators or broadened neutron fluxes to increase the reactions probabilities and, consequently, actinides mass conversion yield.

Radiation stability of ceramic tubular membranes containing ammonium molybdophosphate (AMP) for the application of radio-cesium recovery from radioactive wastes

In order to develop radiation resistant membranes for the treatment of high level waste (HLW), ceramic tubular membranes were prepared by incorporating varying amounts of ammonium molybdophosphate (AMP), known for efficient Cs(I) uptake from acidic feeds, for the recovery of radio-caesium. The sorption of Cs(I) onto the membrane increased linearly with increasing the AMP content (10%–40%). Radiation stability of the membranes was evaluated by exposing them to gamma radiation obtained from a 60Co source. The composite ceramic material showed excellent radiation stability without any morphological change up to 1100 kGy, indicating its potential application in radioactive waste treatment. For 10% AMP loaded ceramic membrane, the Cs(I) sorption decreased linearly with radiation dose. However, Cs sorption was not altered up to 1100 kGy dose for 20% and 40% loaded AMP.

Review of a non-probabilistic sampler versus a Vezin sampler on low weight percent solids slurries

Author Summary: The Hanford Tank Operations Contractor (TOC) and the Hanford Waste Treatment and Immobilization Plant (WTP) contractor are both engaged in demonstrating mixing, sampling, and transfer system capability using simulated Hanford High-Level Radioactive Waste (HLW) formulations. This work represents one of the remaining technical issues with the high-level waste treatment mission at Hanford – the TOC’s ability to adequately sample high-level waste feed to meet the Waste Treatment and Immobilization Plant (WTP) Waste Acceptance Criteria Data Quality Objectives. A full-scale sampling loop was used at a cold test facility to evaluate sampler capability. The sampler under investigation for deployment is non-probabilistic but radioactive environment friendly. A Vezin sampler (probabilistic) was used to obtain reference samples and accurately characterize the simulant as it flowed through the test loop. The two samplers are located in series, allowing for multiple samples to be taken from both samplers over the same time period (sample pairs) and direct sample comparison. The Vezin sampler was modified to minimize material build up allowing for steady state operation. This report discusses modifications made to the Vezin sampler and the results of sampler comparison.

Amides of heterocyclic carboxylic acids as novel extractants for high-level waste treatment

Extraction properties of various heterocyclic carboxylic acid amides are considered. The extraction properties of heterocyclic dicarboxylic acid diamides are determined by two major factors: diamide structure and kind of diluent. Among heterocyclic (di)carboxylic acid amides and diamides, the most promising extractants for separating actinides and lanthanides are tri- and tetradentate extractants: diamides of dipicolinic, bipyridinedicarboxylic, and phenanthrolinedicarboxylic acids, which can be used for recovering metals from acid solutions.

Recovery of Uranium, Plutonium, and Neptunium from High-Level Waste Solutions prior to Actinide Partitioning

AbstractThe prior removal of uranium along with plutonium and neptunium from high-level waste (HLW) can simplify the subsequent actinide partitioning steps. In this context, extraction and stripping behavior of uranium, plutonium, and neptunium was investigated employing 1.1-M solutions of tri-n-butyl phosphate (TBP) and N,N-dihexyl octanamide (DHOA) dissolved in n-dodecane as extractants in the presence of 6 g/L U relevant to pressurized heavy-water reactor (PHWR) high-level waste (HLW) conditions. Reductants such as acetohydroxamic acid (AHA) and hydroxyurea (HU) were evaluated for selective stripping of plutonium and neptunium over uranium from the loaded organic phases. These studies indicated the possibility of quantitative recovery of U(VI), Pu(IV), and Np(IV) from HLW solution employing either DHOA or TBP as extractant. Integration of this step in the minor actinide partitioning simplifies the treatment of HLW with the specially designed extractants like octyl(phenyl)- N, N-diisobutyl carbamoyl me...

Methods to Avoid Post-Filtration Precipitation in Treatment of High-Level Waste

The Hanford Tank Waste Treatment and Immobilization Plant, currently under construction for treating high level waste at the Hanford Site, will rely on ultrafiltration to provide solids/liquid separation as a core part of the treatment process. A series of bench-scale simulant tests have been performed to evaluate the potential for post-filtration precipitation. These tests focused on identifying precipitation from a range of potential feed compositions and providing the data required to evaluate mitigation options. This data is also important to the Savannah River Site as they are also attempting to dissolve saltcake from their tanks. Inadvertent solids formation after saltcake dissolution, either within a staging tank or in transfer piping can have serious repercussions on the eventual retrieval and transfer of the waste. A series of tests were performed using a variety of simulant samples. These tests identified the expected extent of supersaturation that develops under normal operations and identified and characterized the solids phases that are expected to form when the filtrate solutions are stored. In addition, tests identified the potential to mitigate the formation of these solids through both dilution and the application of increased temperature.

Radiation chemical effects on radiochemistry: A review of examples important to nuclear power

Radiochemistry deals with the chemistry of the radioactive elements. In the nuclear industry successful fuel reprocessing, high-level waste treatment, and long-term storage of spent fuel depend on an understanding of the radiochemistry of actinides and fission products in these settings. Radiation chemistry is concerned with the chemical effects of ionizing radiation, with the most common types of radiation encountered by the radiochemist being low linear energy transfer (LET) β- and γ radiation, and higher LET α radiation. These radiations can have profound and important effects on radiochemistry, including changes in metal oxidation states and degradation of the organic ligands designed to complex radioelements. This may occur by direct action of the incident radiation on compounds present with high abundance or by reaction with radiolytically produced reactive species for trace components, such as the complexing agents. This review examines the role of reactive species created in irradiated aqueous and organic solution and their effects on radiochemistry. The sources and nature of these reactive species are discussed. Examples of radiation chemical effects are provided related to solvent extraction of the actinides from acidic solution, metal complexation and technetium redox chemistry in alkaline tank waste, and the corrosion of spent fuel stored in repository brine.

Separation of Precipitate-forming Elements during High Level Waste Treatment Using Acidic Zirconium Salt of Dibutyl Phosphoric Acid

Iron extraction and the limits of iron dibutyl phosphate precipitation were investigated for use in TPE/RE recovery and partitioning with the use of the acidic Zr salt of dibutyl phosphoric acid (ZS HDBP, Zr:HDBP = 1:9), dissolved in 30% TBP with Isopar-L. The presence of Mo and the solvent loading with RE affected the Fe extraction in the opposite ways. Slow kinetics and process irreversibility were found for the Fe extraction with the ZS HDBP solution. To increase acceptable Fe concentration in a HLW, reduction of Fe(III) by ascorbic acid (AA) was studied to be carried out continuously in the feed flow, just before entering the head contactor of the partitioning extraction cycle. The Mo extraction is of the same order as that of TPE and RE; so its selective stripping prior to the TPE/RE separation is required. This can be done using the DTPA or H2O2 solution in diluted nitric acid. The effectiveness of the process was verified by laboratory scale trials on the centrifugal contactor rig using simulated HLW. The Zr-to-HDBP ratio of 1:6 was found to be useful to decrease the Fe and Mo extractability for their better backwashing with complexants.

Separation of Precipitate-forming Elements during High Level Waste Treatment Using Acidic Zirconium Salt of Dibutyl Phosphoric Acid

Separation of Precipitate-forming Elements during High Level Waste Treatment Using Acidic Zirconium Salt of Dibutyl Phosphoric Acid

Maximizing Production Capacity from an Ultrafiltration Process at the Hanford Department of Energy Waste Treatment Facility

The Department of Energy has contracted Bechtel National, Inc. to design, construct, and commission a Waste Treatment and Immobilization Plant (WTP) to treat radioactive slurry currently stored in underground waste storage tanks. A critical element of the waste treatment capacity for the WTP is the proper operation of an ultrafiltration process (UFP). The UFP separates supernate solution from radioactive solids. The solution and solid phases are separately immobilized. An oversight review of the UFP design and operation has identified several methods to improve the capacity of the ultrafiltration process, which will also improve the capacity of the WTP. Areas explored were the basis of design, an analysis of the WTP capacity, process chemistry within the UFP, and UFP process control. This article discusses some of the findings of this oversight review in terms of sodium and solid production, which supports the treatment of low activity waste (LAW) associated with the facility, and solid production, which supports the treatment of high level waste (HLW) associated with the facility.

Mechanisms of Strontium and Uranium Removal from High-Level Radioactive Waste Simulant Solutions by the Sorbent Monosodium Titanate

High-level waste (HLW) is a waste associated with the dissolution of spent nuclear fuel for the recovery of weapons-grade material. It is the priority problem for the U.S. Department of Energy's Environmental Management Program. Current HLW treatment processes at the Savannah River Site (Aiken, SC) include the use of monosodium titanate (MST, with a similar stoichiometry to NaTi2O5 x xH2O) to concentrate strontium (Sr) and actinides. The high affinity of MST for Sr and actinides in HLW solutions rich in Na+ is poorly understood. Mechanistic information about the nature of radionuclide uptake will provide insight about MST treatment reliability. Our study characterized the morphology of MST and the chemistry of sorbed Sr2+ and uranium [U(VI)] as uranyl ion, UO2(2+), on MST, which were added (individually) from stock solutions of Sr and 238U(VI) with spectroscopic and transmission electron microscopic techniques. The local structure of sorbed U varied with loading, but the local structure of Sr did not vary with loading. Sorbed Sr exhibited specific adsorption as partially hydrated species whereas sorbed U exhibited specific adsorption as monomeric and dimeric U(VI)-carbonate complexes. Sorption proved site specific. These differences in site specificity and sorption mechanism may account forthe difficulties associated with predicting Sr and U loading and removal kinetics using MST.