The topic of this doctoral thesis is the potential near field immobilization of the radionuclide ... more The topic of this doctoral thesis is the potential near field immobilization of the radionuclide 79 Se after intrusion of groundwater into a spent nuclear fuel canister in a repository. 79 Se is a non naturally occurring long lived selenium isotope formed as a result of fission in nuclear fuel. Given the long half life (~3 x 10 5 y) and that the oxyanions of selenium are expected to be highly mobile and potentially difficult to immobilize the isotope is of interest for the long term safety assessment of high level waste repositories. In this work the near field has been limited to the study of processes at or near the UO 2 surface of (simulated) spent nuclear fuel and to processes occurring at or near the surface of iron (canister material) corroding under anoxic conditions. Selenite (HSeO 3 2-) was found to adsorb onto palladium (simulated noble metal inclusion in spent nuclear fuel). Under hydrogen atmosphere selenite was reduced to elemental selenium with a rate constant of ~2 x 10-9 m s-1 (with respect to the Pd surface, 24 bar H 2) forming colloidal particles. The rate constant of selenite reduction was increased by about two orders of magnitude to ~2.5 x 10-7 m s-1 (with respect to the Pd surface, 10 bar H 2) for a UO 2 surface doped with Pd particles, indicating that UO 2 is an efficient co-catalyst to Pd. Selenate (SeO 4 2-) was neither adsorbed nor reduced in the presence of Pd, UO 2 and hydrogen. In the iron corrosion studies selenate was found to become reduced to predominantly elemental Se in the presence of a pristine iron surface. Iron covered by a corrosion layer of magnetite did however appear inert with respect to selenate whereas selenite was reduced. The reduction of dissolved uranyl into UO 2 by the corroding iron surfaces was found to significantly increase the removal rate of selenite as well as selenate. The uranyl was found to transiently transform the outer iron oxide layers on the iron, forming a reactive mixed Fe(II)/Fe(III) oxyhydroxide (Green rust). Exchanging the solution and increasing the carbonate content (from 2 mM to 20 mM NaHCO 3) only resulted in a minor, transient remobilization of uranium. Addition of H 2 O 2 did however result in a significant release of uranium as well as selenium from the iron oxide surfaces. An irradiation experiment was also performed confirming the one electron reduction barrier of selenate as an important factor in systems where selenate reduction would be thermodynamically favorable.
For a future deep repository for spent nuclear fuel, the rate and mechanism for dissolution of fi... more For a future deep repository for spent nuclear fuel, the rate and mechanism for dissolution of fission products and actinides from the fuel is a key parameter for the safety assessment of the disposal concept. Although the behavior of spent nuclear fuel under deep repository conditions has been studied extensively, studies of failed fuel are relatively scarce. However, at the Studsvik laboratory, aerated leaching tests of spent fuel started in the 1980s and two of these were finalized only recently. This provides an opportunity to investigate the effects of long-term contact with water under aerated conditions similar to wet interim storage conditions. In this study, surface investigations have been performed on two fuel pellet samples which have been exposed to leaching solutions for over 30 years. Furthermore, the fuel samples have been exposed to carbonate solutions in an effort to dissolve the secondary phases formed during the extended leaching time.
In 2018 thirteen Special Fuel Rods were transported from Brunsbüttel to the Swedish Hot Cell labo... more In 2018 thirteen Special Fuel Rods were transported from Brunsbüttel to the Swedish Hot Cell laboratory at Studsvik for a Post-Irradiation Examination (PIE). The reason for this was to gain more valuable measurement data information for the dry long-term storage database. The planning for the transport, performed by DAHER NT using their NCS-45 cask, started already in 2016. This paper gives a characterization of the Special Fuel Rods and describes the examination program. Twelve of the rods are failed from debris fretting and possible Pellet Clad Interaction (PCI). Therefore, topics such as ingress of water causing residual moisture in the rods, cladding embrittlement and radial reorientation of the hydride of the rods are presented. Moreover, a summary of the efforts is given for the handling (loading and transport) of the Special Fuel Rods and the numerous licenses that are required for such a project.
Canister designs for deep geological disposal of spent nuclear fuel typically involve large amoun... more Canister designs for deep geological disposal of spent nuclear fuel typically involve large amounts of iron. Canister failure will likely involve corrosion of the canister at the disposal depth several hundred meters underground, where conditions are typically anoxic. Spent nuclear fuel corrosion and dissolution will therefore likely proceed together with anoxic iron corrosion. The iron corrosion can suppress spent fuel corrosion by creation of strongly reducing conditions from Fe(II) formation and generation of large quantities of hydrogen. In an attempt to separate the effect of hydrogen from that of Fe(II) and iron corrosion products, two experiments were performed. In both cases, spent nuclear fuel powders were used in autoclaves filled with simplified granitic groundwater initially pressurized with argon. In the first experiment, the autoclave contained iron powder. Following the initial radionuclide release at start-up, the concentration of redox sensitive radionuclides decreased with uranium reaching UO 2 (am) solubility levels within months. Release of non-redox sensitive elements such as Cs ceased after 223 days. Continuous hydrogen generation was observed. XRD and Raman spectroscopy of the iron corrosion products identified magnetite. The second experiment was therefore performed starting with magnetite powder. In this case, the autoclave argon atmosphere remained constant. Radionuclide release was, however, continuous with uranium reaching > 2 × 10 −5 M after 275 days. The magnetite powder of the second experiment was analyzed and found to be composed of mainly magnetite with a small fraction of hematite. In the iron corrosion experiment, Mo, Tc and U where found to have high iron corrosion product affinities. However, in the magnetite experiment, U, Tc and Mo displayed weak affinity for the corrosion products, indicating presence in the higher oxidation state. The results thus point to hydrogen evolution being the main contributor to the apparent inhibition of radionuclide release in the iron corrosion experiment.
Leaching results to compare the dissolution behavior of a new type of fuel with additives (Advanc... more Leaching results to compare the dissolution behavior of a new type of fuel with additives (Advanced Doped Pellet Technology, ADOPT) with standard UO2 fuel are presented. Both fuels were irradiated in the same assembly of a commercial boiling water reactor to a local burnup of ∼58 MWd/kgU. Fuel fragments are leached in simplified groundwater in two autoclaves under hydrogen atmosphere, representing conditions in a canister failure scenario resulting in water intrusion for a spent nuclear fuel repository. Preliminary results indicate the uranium concentration decreased to 3-4x10-8 M after 421 days, slightly above the solubility of amorphous UO2. Xe has been detected in the gas phase of both autoclaves. The concentration of Cs and I seems to gradually approach constant values, yet the redox sensitive elements continue to slowly increase with time. The preliminary data obtained supports the hypothesis that there is no major difference in leaching behavior between the two fuels.
The release of radionuclides from spent nuclear fuel upon contact with water is a central issue f... more The release of radionuclides from spent nuclear fuel upon contact with water is a central issue for the assessment of the safety of geological disposal concepts. Several studies have been conducted aiming at understanding matrix dissolution as well as the rapid/instant release of radionuclides separated from the UO 2 matrix; there are however questions remaining regarding how higher burn-up affects the amount of fission products segregated to the fuel-cladding gap and grain boundaries. In this study we have performed aerated fuel corrosion and leaching experiments using spent nuclear fuels with a range of burnups, from~52 to~70 MWd/KgU. The samples have been prepared in different manners in order to investigate the release of the segregated fission products from the gap and the grain boundaries. Thus, the fuel samples are prepared either as segments with the cladding attached, as fragments without cladding, or as milled powder. The fuel samples are leached in aqueous solution in aerated conditions and the radionuclide release is monitored during several contact periods for up to five years total leaching time. The results from the leaching of fuel segments reveal congruent release of e.g. europium and neodymium whereas the release of those elements was lower than the U-238 release for the fragment samples. Potential explanations for this are discussed in the paper. The results show that the release rates of elements segregated from the fuel matrix were in general found to be lower from segments samples as compared to fragment samples, which can be attributed to the closed fuel-cladding gap inhibiting the exposure of the gap inventory to water for the high burnup fuels used in this study. Leaching of fuel powder (78 MWd/kgU local BU) by simultaneous grinding and leaching showed a fractional release of Cs-137 and I-129 of 1.5% and 1.8% respectively.
ABSTRACTLeaching results on fragments of high burnup (65 MWd/kgU) UO2 fuel from a commercial pres... more ABSTRACTLeaching results on fragments of high burnup (65 MWd/kgU) UO2 fuel from a commercial pressurized water reactor are presented. The experiment was performed in simplified granitic groundwater under a hydrogen pressure of up to 5 MPa, representing conditions in a water intrusion scenario for a Swedish KBS-3 design spent nuclear fuel repository. The freshly crushed fragments were pre-washed for 6 days to remove pre-oxidized matrix and part of the instant release fraction of the radionuclide inventory, and then transferred to an autoclave for leaching under hydrogen conditions. Following an initial release of U attributed to dissolution of a pre-oxidized fuel layer caused by the aerated handling mainly during the transfer from pre-washing to autoclave, the U concentration decreased with time to levels of 2-5x10-9 M, which corresponds, approximately, to the solubility of amorphous UO2. The release of radionuclides such as Cs and Sr gradually declined indicating a transition to inh...
In the context of safety assessment, the fraction of inventory that is expected to rapidly dissol... more In the context of safety assessment, the fraction of inventory that is expected to rapidly dissolve when water contacts the spent fuel is called the Instant Release Fraction (IRF). Conceptually, this fraction consists of radionuclides outside of the uranium dioxide matrix and therefore the fraction can be further divided into the radionuclides in the fuel/cladding gap and radionuclides in the grain boundaries. The relative importance of these two fractions is investigated here for two Swedish high burnup fuels through simultaneous grinding and leaching fuel fragments in simplified groundwater for a short period of time. The hypothesis is that this will expose grain boundaries to leaching solution and provide an estimate of the release of the grain boundary inventory upon contact with water. The studied fragments were used in previous leaching experiments and thus pre-washed to remove any pre-oxidized phases. The results showed a significant release of iodine, cesium and rubidium and...
Environmental Science: Processes & Impacts, 2015
The long-lived fission product79Se is tightly bound to the UO2lattice in spent nuclear fuel; it w... more The long-lived fission product79Se is tightly bound to the UO2lattice in spent nuclear fuel; it will thus be released only very slowly from a geological repository for radioactive waste.
Reductive precipitation of the radiotoxic nuclide 237 Np from nuclear waste on the surface of iro... more Reductive precipitation of the radiotoxic nuclide 237 Np from nuclear waste on the surface of iron canister material at simulated deep repository conditions was investigated. Pristine polished as well as pre-corroded iron specimens were interacted in a deoxygenated solution containing 10-100 µM Np(V), with 10 mM NaCl and 2 mM NaHCO 3 as background electrolytes. The reactivity of each of the two different systems was investigated by analyzing the temporal evolution of the Np concentration in the reservoir. It was observed that pre-oxidized iron specimen with a 40µm Fe 3 O 4 corrosion layer are considerably more reactive regarding the reduction and immobilization of aqueous Np(V) as compared to pristine polished Fe (0) surfaces. 237 Np immobilized by the reactive iron surfaces was characterized by scanning electron microscopy as well as synchrotron-based micro-X-ray fluorescence and X-ray absorption spectroscopy. At the end of experiments, a 5-8 µm thick Np-rich layer was observed to be formed ontop of the Fe 3 O 4 corrosion layer on the iron specimen. The findings from this work are significant in the context of performance assessments of deep geologic repositories using iron as HLW canister material and are of relevance regarding removing pollutants from contaminated soil or groundwater aquifer systems.
A trend in the operation of nuclear power reactors is the increase in discharge burnup of the fue... more A trend in the operation of nuclear power reactors is the increase in discharge burnup of the fuel. Intrusion of groundwater in a failed canister of a future deep repository is expected to occur in the presence of hydrogen, produced by the anoxic corrosion of iron and by radiolysis of water. Compelling evidence now exists that hydrogen inhibits oxidative dissolution of irradiated nuclear fuel or alpha doped UO2, however the number of studies involving high burnup fuel are limited. In the experiment PWR UO2 fuel with a burnup of ∼75 MWd/kgU was leached in simulated groundwater (10 mM NaCl, 2 mM NaHCO3) at room temperature under 5 MPa of hydrogen. Since the main objective was to investigate the fuel matrix dissolution, a fuel fraction that had previously been leached for over one year was reused. The U-238 and Tc-99 concentration was found to vary in the samples taken over 1100 days of leaching, depending on the degree of centrifugation. The erratic behavior of this autoclave experime...
The Swedish spent nuclear fuel canister design KBS-3 consists of a cylindrical copper shell surro... more The Swedish spent nuclear fuel canister design KBS-3 consists of a cylindrical copper shell surrounding an iron insert that holds the spent fuel. Like in most other canister designs the mass of iron constitutes the majority of the canister weight. In order for groundwater to access the spent fuel in a future repository the copper shell must fail and iron corrosion occur. Spent nuclear fuel dissolution will therefor likely proceed under conditions of simultaneous anoxic iron corrosion. The iron corrosion can likely suppress the spent fuel release by creation of strongly reducing conditions from Fe(II) formation and the generation of large quantities of hydrogen. Redox sensitive radionuclides may either be reductively precipitated by dissolved Fe(II) or from interaction with iron corrosion products such a magnetite or green rusts. The generated hydrogen (up to several MPa) may also inhibit the spent nuclear fuel dissolution at the surface of the fuel via the so called hydrogen effect....
In this work we have studied the possible remobilization of U and Se reductively immobilized on i... more In this work we have studied the possible remobilization of U and Se reductively immobilized on iron oxide surfaces experimentally. Samples consisting of reductively immobilized U and ...
ABSTRACTIn a future Swedish deep repository for spent nuclear fuel, irradiated control rods from ... more ABSTRACTIn a future Swedish deep repository for spent nuclear fuel, irradiated control rods from PWR nuclear reactors are planned to be stored together with the spent fuel. The control rod absorber consists of an 80% Ag, 5% Cd, 15% In alloy with a steel cladding. Upon in-reactor irradiation108Ag is produced by neutron capture. Release of108Ag has been identified as a potential source term for release of radioactive substances from the deep repository.Under reducing deep repository conditions, the Ag corrosion rate is however expected to be low which would imply that the release rate of108Ag should be low under these conditions. The aim of this study is to investigate the dissolution of PWR control rod absorber material under conditions relevant to a future deep repository for spent nuclear fuel. The experiments include tests using irradiated control rod absorber material from Ringhals 2, Sweden. Furthermore, un-irradiated control rod absorber alloy has been tested for comparison. Th...
ABSTRACTIn many deep repository concepts spent nuclear fuel (SNF) will be disposed in canisters c... more ABSTRACTIn many deep repository concepts spent nuclear fuel (SNF) will be disposed in canisters containing large amounts of iron. Intrusion of groundwater in a failed canister may occur under the presence of hydrogen, expected to be produced by the anoxic corrosion of iron. Compelling evidence now exists that hydrogen inhibits oxidative dissolution of SNF, the mechanism is however not fully understood. Hydrogen generally requires a catalyst in order to operate as a reductant. The metallic inclusions (ε-particles) present in SNF are a likely catalyst for this process due to their noble metal content. There is also evidence that the SNF UO2 matrix or doping of the UO2 with fission products can activate hydrogen. In most spent fuel experiments carried out under hydrogen, a decrease in concentration of all redox sensitive nuclides originating from a pre-oxidized layer is observed. Given their low concentrations and abundance in the fuel, it has however been difficult to detect any reduc...
Journal of Radioanalytical and Nuclear Chemistry, 2009
To understand the fate of 79 Se in a repositorylike environment, the interactions between iron ca... more To understand the fate of 79 Se in a repositorylike environment, the interactions between iron canister surface with dissolved selenite (SeO 3 2-) and selenate (SeO 4 2-) in anaerobic solutions have been investigated. Se(IV) immobilization on iron surface was observed to be about 100 times faster than that of Se(VI) at same conditions. An iron surface coated with a FeCO 3 layer corrosion product is more reactive than a polished iron to immobilize Se(IV) and Se(VI). The reacted iron surfaces were analysed by scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS), X-ray diffraction (XRD), Raman spectrometry and micro-X-ray Absorption Spectroscopy (XAS). The result show that Se(IV) and Se(VI) were reduced and precipitated. The dominating phase was found to be FeSe 2.
Fused pyridine derivatives Fused pyridine derivatives R 0450 Samarium-Promoted Coupling of 1,10-P... more Fused pyridine derivatives Fused pyridine derivatives R 0450 Samarium-Promoted Coupling of 1,10-Phenanthroline with Carbonyl Compounds for Synthesis of New Ligands.-A methodology for the synthesis of a wide variety of phenanthroline ligands is now available. 1,10-Phenanthroline (I) readily undergoes coupling with aliphatic carbonyl compounds (II) or (VIII) in the presence of SmI2 to afford 2-(hydroxyalkyl)-substituted phenanthrolines in moderate to good yields. The reaction outcome strongly depends on the order of addition of reagents, since aliphatic aldehydes (VIII) only undergo reaction if they are mixed with phenanthroline (I) prior to addition of SmI2. Aromatic carbonyl compounds are not reactive under the presented reaction conditions. Further functionalization of the side chain is achieved by O-alkylation or O-acylation and subsequent deoxygenation reactions.-(WEITGENANT,
The topic of this doctoral thesis is the potential near field immobilization of the radionuclide ... more The topic of this doctoral thesis is the potential near field immobilization of the radionuclide 79 Se after intrusion of groundwater into a spent nuclear fuel canister in a repository. 79 Se is a non naturally occurring long lived selenium isotope formed as a result of fission in nuclear fuel. Given the long half life (~3 x 10 5 y) and that the oxyanions of selenium are expected to be highly mobile and potentially difficult to immobilize the isotope is of interest for the long term safety assessment of high level waste repositories. In this work the near field has been limited to the study of processes at or near the UO 2 surface of (simulated) spent nuclear fuel and to processes occurring at or near the surface of iron (canister material) corroding under anoxic conditions. Selenite (HSeO 3 2-) was found to adsorb onto palladium (simulated noble metal inclusion in spent nuclear fuel). Under hydrogen atmosphere selenite was reduced to elemental selenium with a rate constant of ~2 x 10-9 m s-1 (with respect to the Pd surface, 24 bar H 2) forming colloidal particles. The rate constant of selenite reduction was increased by about two orders of magnitude to ~2.5 x 10-7 m s-1 (with respect to the Pd surface, 10 bar H 2) for a UO 2 surface doped with Pd particles, indicating that UO 2 is an efficient co-catalyst to Pd. Selenate (SeO 4 2-) was neither adsorbed nor reduced in the presence of Pd, UO 2 and hydrogen. In the iron corrosion studies selenate was found to become reduced to predominantly elemental Se in the presence of a pristine iron surface. Iron covered by a corrosion layer of magnetite did however appear inert with respect to selenate whereas selenite was reduced. The reduction of dissolved uranyl into UO 2 by the corroding iron surfaces was found to significantly increase the removal rate of selenite as well as selenate. The uranyl was found to transiently transform the outer iron oxide layers on the iron, forming a reactive mixed Fe(II)/Fe(III) oxyhydroxide (Green rust). Exchanging the solution and increasing the carbonate content (from 2 mM to 20 mM NaHCO 3) only resulted in a minor, transient remobilization of uranium. Addition of H 2 O 2 did however result in a significant release of uranium as well as selenium from the iron oxide surfaces. An irradiation experiment was also performed confirming the one electron reduction barrier of selenate as an important factor in systems where selenate reduction would be thermodynamically favorable.
For a future deep repository for spent nuclear fuel, the rate and mechanism for dissolution of fi... more For a future deep repository for spent nuclear fuel, the rate and mechanism for dissolution of fission products and actinides from the fuel is a key parameter for the safety assessment of the disposal concept. Although the behavior of spent nuclear fuel under deep repository conditions has been studied extensively, studies of failed fuel are relatively scarce. However, at the Studsvik laboratory, aerated leaching tests of spent fuel started in the 1980s and two of these were finalized only recently. This provides an opportunity to investigate the effects of long-term contact with water under aerated conditions similar to wet interim storage conditions. In this study, surface investigations have been performed on two fuel pellet samples which have been exposed to leaching solutions for over 30 years. Furthermore, the fuel samples have been exposed to carbonate solutions in an effort to dissolve the secondary phases formed during the extended leaching time.
In 2018 thirteen Special Fuel Rods were transported from Brunsbüttel to the Swedish Hot Cell labo... more In 2018 thirteen Special Fuel Rods were transported from Brunsbüttel to the Swedish Hot Cell laboratory at Studsvik for a Post-Irradiation Examination (PIE). The reason for this was to gain more valuable measurement data information for the dry long-term storage database. The planning for the transport, performed by DAHER NT using their NCS-45 cask, started already in 2016. This paper gives a characterization of the Special Fuel Rods and describes the examination program. Twelve of the rods are failed from debris fretting and possible Pellet Clad Interaction (PCI). Therefore, topics such as ingress of water causing residual moisture in the rods, cladding embrittlement and radial reorientation of the hydride of the rods are presented. Moreover, a summary of the efforts is given for the handling (loading and transport) of the Special Fuel Rods and the numerous licenses that are required for such a project.
Canister designs for deep geological disposal of spent nuclear fuel typically involve large amoun... more Canister designs for deep geological disposal of spent nuclear fuel typically involve large amounts of iron. Canister failure will likely involve corrosion of the canister at the disposal depth several hundred meters underground, where conditions are typically anoxic. Spent nuclear fuel corrosion and dissolution will therefore likely proceed together with anoxic iron corrosion. The iron corrosion can suppress spent fuel corrosion by creation of strongly reducing conditions from Fe(II) formation and generation of large quantities of hydrogen. In an attempt to separate the effect of hydrogen from that of Fe(II) and iron corrosion products, two experiments were performed. In both cases, spent nuclear fuel powders were used in autoclaves filled with simplified granitic groundwater initially pressurized with argon. In the first experiment, the autoclave contained iron powder. Following the initial radionuclide release at start-up, the concentration of redox sensitive radionuclides decreased with uranium reaching UO 2 (am) solubility levels within months. Release of non-redox sensitive elements such as Cs ceased after 223 days. Continuous hydrogen generation was observed. XRD and Raman spectroscopy of the iron corrosion products identified magnetite. The second experiment was therefore performed starting with magnetite powder. In this case, the autoclave argon atmosphere remained constant. Radionuclide release was, however, continuous with uranium reaching > 2 × 10 −5 M after 275 days. The magnetite powder of the second experiment was analyzed and found to be composed of mainly magnetite with a small fraction of hematite. In the iron corrosion experiment, Mo, Tc and U where found to have high iron corrosion product affinities. However, in the magnetite experiment, U, Tc and Mo displayed weak affinity for the corrosion products, indicating presence in the higher oxidation state. The results thus point to hydrogen evolution being the main contributor to the apparent inhibition of radionuclide release in the iron corrosion experiment.
Leaching results to compare the dissolution behavior of a new type of fuel with additives (Advanc... more Leaching results to compare the dissolution behavior of a new type of fuel with additives (Advanced Doped Pellet Technology, ADOPT) with standard UO2 fuel are presented. Both fuels were irradiated in the same assembly of a commercial boiling water reactor to a local burnup of ∼58 MWd/kgU. Fuel fragments are leached in simplified groundwater in two autoclaves under hydrogen atmosphere, representing conditions in a canister failure scenario resulting in water intrusion for a spent nuclear fuel repository. Preliminary results indicate the uranium concentration decreased to 3-4x10-8 M after 421 days, slightly above the solubility of amorphous UO2. Xe has been detected in the gas phase of both autoclaves. The concentration of Cs and I seems to gradually approach constant values, yet the redox sensitive elements continue to slowly increase with time. The preliminary data obtained supports the hypothesis that there is no major difference in leaching behavior between the two fuels.
The release of radionuclides from spent nuclear fuel upon contact with water is a central issue f... more The release of radionuclides from spent nuclear fuel upon contact with water is a central issue for the assessment of the safety of geological disposal concepts. Several studies have been conducted aiming at understanding matrix dissolution as well as the rapid/instant release of radionuclides separated from the UO 2 matrix; there are however questions remaining regarding how higher burn-up affects the amount of fission products segregated to the fuel-cladding gap and grain boundaries. In this study we have performed aerated fuel corrosion and leaching experiments using spent nuclear fuels with a range of burnups, from~52 to~70 MWd/KgU. The samples have been prepared in different manners in order to investigate the release of the segregated fission products from the gap and the grain boundaries. Thus, the fuel samples are prepared either as segments with the cladding attached, as fragments without cladding, or as milled powder. The fuel samples are leached in aqueous solution in aerated conditions and the radionuclide release is monitored during several contact periods for up to five years total leaching time. The results from the leaching of fuel segments reveal congruent release of e.g. europium and neodymium whereas the release of those elements was lower than the U-238 release for the fragment samples. Potential explanations for this are discussed in the paper. The results show that the release rates of elements segregated from the fuel matrix were in general found to be lower from segments samples as compared to fragment samples, which can be attributed to the closed fuel-cladding gap inhibiting the exposure of the gap inventory to water for the high burnup fuels used in this study. Leaching of fuel powder (78 MWd/kgU local BU) by simultaneous grinding and leaching showed a fractional release of Cs-137 and I-129 of 1.5% and 1.8% respectively.
ABSTRACTLeaching results on fragments of high burnup (65 MWd/kgU) UO2 fuel from a commercial pres... more ABSTRACTLeaching results on fragments of high burnup (65 MWd/kgU) UO2 fuel from a commercial pressurized water reactor are presented. The experiment was performed in simplified granitic groundwater under a hydrogen pressure of up to 5 MPa, representing conditions in a water intrusion scenario for a Swedish KBS-3 design spent nuclear fuel repository. The freshly crushed fragments were pre-washed for 6 days to remove pre-oxidized matrix and part of the instant release fraction of the radionuclide inventory, and then transferred to an autoclave for leaching under hydrogen conditions. Following an initial release of U attributed to dissolution of a pre-oxidized fuel layer caused by the aerated handling mainly during the transfer from pre-washing to autoclave, the U concentration decreased with time to levels of 2-5x10-9 M, which corresponds, approximately, to the solubility of amorphous UO2. The release of radionuclides such as Cs and Sr gradually declined indicating a transition to inh...
In the context of safety assessment, the fraction of inventory that is expected to rapidly dissol... more In the context of safety assessment, the fraction of inventory that is expected to rapidly dissolve when water contacts the spent fuel is called the Instant Release Fraction (IRF). Conceptually, this fraction consists of radionuclides outside of the uranium dioxide matrix and therefore the fraction can be further divided into the radionuclides in the fuel/cladding gap and radionuclides in the grain boundaries. The relative importance of these two fractions is investigated here for two Swedish high burnup fuels through simultaneous grinding and leaching fuel fragments in simplified groundwater for a short period of time. The hypothesis is that this will expose grain boundaries to leaching solution and provide an estimate of the release of the grain boundary inventory upon contact with water. The studied fragments were used in previous leaching experiments and thus pre-washed to remove any pre-oxidized phases. The results showed a significant release of iodine, cesium and rubidium and...
Environmental Science: Processes & Impacts, 2015
The long-lived fission product79Se is tightly bound to the UO2lattice in spent nuclear fuel; it w... more The long-lived fission product79Se is tightly bound to the UO2lattice in spent nuclear fuel; it will thus be released only very slowly from a geological repository for radioactive waste.
Reductive precipitation of the radiotoxic nuclide 237 Np from nuclear waste on the surface of iro... more Reductive precipitation of the radiotoxic nuclide 237 Np from nuclear waste on the surface of iron canister material at simulated deep repository conditions was investigated. Pristine polished as well as pre-corroded iron specimens were interacted in a deoxygenated solution containing 10-100 µM Np(V), with 10 mM NaCl and 2 mM NaHCO 3 as background electrolytes. The reactivity of each of the two different systems was investigated by analyzing the temporal evolution of the Np concentration in the reservoir. It was observed that pre-oxidized iron specimen with a 40µm Fe 3 O 4 corrosion layer are considerably more reactive regarding the reduction and immobilization of aqueous Np(V) as compared to pristine polished Fe (0) surfaces. 237 Np immobilized by the reactive iron surfaces was characterized by scanning electron microscopy as well as synchrotron-based micro-X-ray fluorescence and X-ray absorption spectroscopy. At the end of experiments, a 5-8 µm thick Np-rich layer was observed to be formed ontop of the Fe 3 O 4 corrosion layer on the iron specimen. The findings from this work are significant in the context of performance assessments of deep geologic repositories using iron as HLW canister material and are of relevance regarding removing pollutants from contaminated soil or groundwater aquifer systems.
A trend in the operation of nuclear power reactors is the increase in discharge burnup of the fue... more A trend in the operation of nuclear power reactors is the increase in discharge burnup of the fuel. Intrusion of groundwater in a failed canister of a future deep repository is expected to occur in the presence of hydrogen, produced by the anoxic corrosion of iron and by radiolysis of water. Compelling evidence now exists that hydrogen inhibits oxidative dissolution of irradiated nuclear fuel or alpha doped UO2, however the number of studies involving high burnup fuel are limited. In the experiment PWR UO2 fuel with a burnup of ∼75 MWd/kgU was leached in simulated groundwater (10 mM NaCl, 2 mM NaHCO3) at room temperature under 5 MPa of hydrogen. Since the main objective was to investigate the fuel matrix dissolution, a fuel fraction that had previously been leached for over one year was reused. The U-238 and Tc-99 concentration was found to vary in the samples taken over 1100 days of leaching, depending on the degree of centrifugation. The erratic behavior of this autoclave experime...
The Swedish spent nuclear fuel canister design KBS-3 consists of a cylindrical copper shell surro... more The Swedish spent nuclear fuel canister design KBS-3 consists of a cylindrical copper shell surrounding an iron insert that holds the spent fuel. Like in most other canister designs the mass of iron constitutes the majority of the canister weight. In order for groundwater to access the spent fuel in a future repository the copper shell must fail and iron corrosion occur. Spent nuclear fuel dissolution will therefor likely proceed under conditions of simultaneous anoxic iron corrosion. The iron corrosion can likely suppress the spent fuel release by creation of strongly reducing conditions from Fe(II) formation and the generation of large quantities of hydrogen. Redox sensitive radionuclides may either be reductively precipitated by dissolved Fe(II) or from interaction with iron corrosion products such a magnetite or green rusts. The generated hydrogen (up to several MPa) may also inhibit the spent nuclear fuel dissolution at the surface of the fuel via the so called hydrogen effect....
In this work we have studied the possible remobilization of U and Se reductively immobilized on i... more In this work we have studied the possible remobilization of U and Se reductively immobilized on iron oxide surfaces experimentally. Samples consisting of reductively immobilized U and ...
ABSTRACTIn a future Swedish deep repository for spent nuclear fuel, irradiated control rods from ... more ABSTRACTIn a future Swedish deep repository for spent nuclear fuel, irradiated control rods from PWR nuclear reactors are planned to be stored together with the spent fuel. The control rod absorber consists of an 80% Ag, 5% Cd, 15% In alloy with a steel cladding. Upon in-reactor irradiation108Ag is produced by neutron capture. Release of108Ag has been identified as a potential source term for release of radioactive substances from the deep repository.Under reducing deep repository conditions, the Ag corrosion rate is however expected to be low which would imply that the release rate of108Ag should be low under these conditions. The aim of this study is to investigate the dissolution of PWR control rod absorber material under conditions relevant to a future deep repository for spent nuclear fuel. The experiments include tests using irradiated control rod absorber material from Ringhals 2, Sweden. Furthermore, un-irradiated control rod absorber alloy has been tested for comparison. Th...
ABSTRACTIn many deep repository concepts spent nuclear fuel (SNF) will be disposed in canisters c... more ABSTRACTIn many deep repository concepts spent nuclear fuel (SNF) will be disposed in canisters containing large amounts of iron. Intrusion of groundwater in a failed canister may occur under the presence of hydrogen, expected to be produced by the anoxic corrosion of iron. Compelling evidence now exists that hydrogen inhibits oxidative dissolution of SNF, the mechanism is however not fully understood. Hydrogen generally requires a catalyst in order to operate as a reductant. The metallic inclusions (ε-particles) present in SNF are a likely catalyst for this process due to their noble metal content. There is also evidence that the SNF UO2 matrix or doping of the UO2 with fission products can activate hydrogen. In most spent fuel experiments carried out under hydrogen, a decrease in concentration of all redox sensitive nuclides originating from a pre-oxidized layer is observed. Given their low concentrations and abundance in the fuel, it has however been difficult to detect any reduc...
Journal of Radioanalytical and Nuclear Chemistry, 2009
To understand the fate of 79 Se in a repositorylike environment, the interactions between iron ca... more To understand the fate of 79 Se in a repositorylike environment, the interactions between iron canister surface with dissolved selenite (SeO 3 2-) and selenate (SeO 4 2-) in anaerobic solutions have been investigated. Se(IV) immobilization on iron surface was observed to be about 100 times faster than that of Se(VI) at same conditions. An iron surface coated with a FeCO 3 layer corrosion product is more reactive than a polished iron to immobilize Se(IV) and Se(VI). The reacted iron surfaces were analysed by scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS), X-ray diffraction (XRD), Raman spectrometry and micro-X-ray Absorption Spectroscopy (XAS). The result show that Se(IV) and Se(VI) were reduced and precipitated. The dominating phase was found to be FeSe 2.
Fused pyridine derivatives Fused pyridine derivatives R 0450 Samarium-Promoted Coupling of 1,10-P... more Fused pyridine derivatives Fused pyridine derivatives R 0450 Samarium-Promoted Coupling of 1,10-Phenanthroline with Carbonyl Compounds for Synthesis of New Ligands.-A methodology for the synthesis of a wide variety of phenanthroline ligands is now available. 1,10-Phenanthroline (I) readily undergoes coupling with aliphatic carbonyl compounds (II) or (VIII) in the presence of SmI2 to afford 2-(hydroxyalkyl)-substituted phenanthrolines in moderate to good yields. The reaction outcome strongly depends on the order of addition of reagents, since aliphatic aldehydes (VIII) only undergo reaction if they are mixed with phenanthroline (I) prior to addition of SmI2. Aromatic carbonyl compounds are not reactive under the presented reaction conditions. Further functionalization of the side chain is achieved by O-alkylation or O-acylation and subsequent deoxygenation reactions.-(WEITGENANT,
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Papers by Anders Puranen