Isotope Recycling Research Articles

Gas- and plasma-driven hydrogen permeation behavior of stagnant eutectic-solid GaInSn/Fe double-layer structure

Gas-driven permeation (GDP) and plasma-driven permeation (PDP) of hydrogen gas through GaInSn/Fe are systematically investigated in this work. The permeation parameters of hydrogen through GaInSn/Fe, including diffusivity, Sieverts’ constant, permeability, and surface recombination coefficient are obtained. The permeation flux of hydrogen through GaInSn/Fe shows great dependence on external conditions such as temperature, hydrogen pressure, and thickness of liquid GaInSn. Furthermore, the hydrogen permeation behavior through GaInSn/Fe is well consistent with the multi-layer permeation theory. In PDP and GDP experiments, hydrogen through GaInSn/Fe satisfies the diffusion-limited regime. In addition, the permeation flux of PDP is greater than that of GDP. The increase of hydrogen plasma density hardly causes the hydrogen PDP flux to change within the test scope of this work, which is due to the dissolution saturation. These findings provide guidance for a comprehensive and systematic understanding of hydrogen isotope recycling, permeation, and retention in plasma-facing components under actual conditions.

Basalt Mo isotope evidence for crustal recycling in continental subduction zone

Highly variable molybdenum (Mo) isotope compositions are common in mafic arc magmas above oceanic subduction zones, but Mo isotopes of mafic magmas related to continental deep subduction have not yet been documented. Here, we report for the first time the Mo isotope composition of mafic igneous rocks above a typical continental subduction zone in east-central China, where the North China Block was subducted by the South China Block in the Triassic. Continental basalts of Early Cretaceous age show negative δ98Mo values of −0.98 to −0.16 ‰, significantly lower than the normal mantle value of −0.20 ± 0.01 ‰. These basalts also exhibit arc-like trace element compositions, high (87Sr/86Sr)i ratios of 0.7050 to 0.7058, negative εNd(t) values of −15.2 to −10.4, and negative εHf(t) values of −18.7 to −7.9. The light Mo isotope signatures are associated with enrichments in not only radiogenic Sr-Nd-Hf isotopes but also melt-mobile incompatible elements in the basalts. This indicates that the mantle source of these basalts would be generated by metasomatic reaction of the mantle wedge peridotite with felsic melts derived from partial melting of the deeply subducted continental crust. Given that continental crust usually exhibits heavy Mo isotope compositions, it would be dehydrated during its subduction to subarc depths. While the dehydration would have released isotopically heavy Mo fluids from the subducting crust, it leaves isotopically light Mo in the residual crust. The dehydrated continental crust underwent partial melting at subarc depths to produce felsic melts with low δ98Mo values, transferring the light Mo isotope signature into the mantle source of the basalts. Therefore, Mo isotopes in mafic igneous rocks are a powerful means to decipher the recycling of crustal components at convergent plate margins. Our study provides the first insight into Mo isotope recycling in continental subduction zones.

A study of hydrogen isotopes fuel control by wall effect in magnetic fusion devices

Determination of plasma density behavior in magnetic confinement system needs to study the plasma materials interaction in the facing components such as first wall, limiter and divertor. Recycling of hydrogen isotope is an effective parameter in plasma density rate and plasma fueling. Recycling coefficient over the long pulse operation, gets to the unity, so it has a significant effect on steady state in magnetic fusion devices. Typically, sputtered carbon atoms from the plasma facing components form hydrocarbons and they redeposit on the wall. In this case little rate of hydrogen loss occurs. In present work a zero dimensional particle equilibrium model has been represented to determine particles density rate in main plasma and wall inventory under recycling effect and codeposition of hydrogen in case of continues and discontinues fueling methods and effective parameters on the main plasma decay has been studied.

The effectiveness of full actinide recycle as a nuclear waste management strategy when implemented over a limited timeframe – Part I: Uranium fuel cycle

Disposal of spent nuclear fuel is a major political and public-perception problem for nuclear energy. From a radiological standpoint, the long-lived component of spent nuclear fuel primarily consists of transuranic (TRU) isotopes. Full recycling of TRU isotopes can, in theory, lead to a reduction in repository radiotoxicity to reference levels corresponds to the radiotoxicity of the unburned natural U required to fuel a conventional LWR in as little as ∼500 years provided reprocessing and fuel fabrication losses are limited. This strategy forms part of many envisaged ‘sustainable’ nuclear fuel cycles. However, over a limited timeframe, 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. The importance of low reprocessing losses and minor actinide (MA) recycling is also dependent on the timeframe during which actinides are recycled. In this paper, the fuel cycle code ORION is used to model the recycle of light water reactor (LWR)-produced TRUs in LWRs and sodium-cooled fast reactors (SFRs) over 1–5 generations of reactors, which is sufficient to infer general conclusions for higher numbers of generations. Here, a generation is defined as a fleet of reactors operating for 60 years, before being retired and potentially replaced. Over up to ∼5 generations of full actinide recycle in SFR burners, the final core inventory tends to dominate over reprocessing losses, beyond which the radiotoxicity rapidly becomes sensitive to reprocessing losses. For a single generation of SFRs, there is little or no advantage to recycling MAs. However, for multiple generations, the reduction in repository radiotoxicity is severely limited without MA recycling, and repository radiotoxicity converges on equilibrium after around 3 generations of 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 – which appears challenging from an economic and energy security standpoint. TRU recycle in pressurized water reactors (PWRs) with zero net actinide production provides similar performance to low-enriched-uranium (LEU)-fueled LWRs in equilibrium with a fleet of burner SFRs. However, it is not possible to reduce the TRU inventory over multiple generations of PWRs. TRU recycle in break-even SFRs is much less effective from a point of view of reducing spent nuclear fuel radiotoxicity.

Retention behaviors of hydrogen isotope in boron film exposed to H–H discharge in LHD

Retention behaviors of hydrogen isotopes in boron film exposed to a H–H discharge in the LHD was evaluated by TDS and compared with that in the D2+ implanted one. D2 TDS spectrum for D2+ implanted LHD-boron film showed that desorption stages were consisted of B–X–B, B–X, B–O–X and B–C–X bonds (X: hydrogen isotope). The ratios for B–O–X and B–C–X bonds to hydrogen isotope retentions were reached up to 60% for the LHD-boron film by H–H discharge, although those for the D2+ implanted were about 35%. The atomic concentrations of impurities were increased after H–H discharge. Therefore, it is suggested that the impurities in plasma would be introduced to boron film dynamically during H–H discharge. The impurity concentration during the H–H discharge or ion implantation would have a large impact on the retention. The hydrogen isotope trapping by impurities should be refrained to enhance the recycling of hydrogen isotope and the impurity control will be one of critical issues in LHD.

Experimental studies of lithium-based surface chemistry for fusion plasma-facing materials applications

Lithium has enhanced the operational performance of fusion devices such as: TFTR, CDX-U, FTU, T-11 M, and NSTX. Lithium in the solid and liquid state has been studied extensively in laboratory experiments including its erosion and hydrogen-retaining properties. Reductions in physical sputtering up to 40–60% have been measured for deuterated solid and liquid lithium surfaces. Computational modeling indicates that up to a 1:1 deuterium volumetric retention in lithium is possible. This paper presents the results of systematic in situ laboratory experimental studies on the surface chemistry evolution of ATJ graphite under lithium deposition. Results are compared to post-mortem analysis of similar lithium surface coatings on graphite exposed to deuterium discharge plasmas in NSTX. Lithium coatings on plasma-facing components in NSTX have shown substantial reduction of hydrogenic recycling. Questions remain on the role lithium surface chemistry on a graphite substrate has on particle sputtering (physical and chemical) as well as hydrogen isotope recycling. This is particularly due to the lack of in situ measurements of plasma-surface interactions in tokamaks such as NSTX. Results suggest that the lithium bonding state on ATJ graphite is lithium peroxide and with sufficient exposure to ambient air conditions, lithium carbonate is generated. Correlation between both results is used to assess the role of lithium chemistry on the state of lithium bonding and implications on hydrogen pumping and lithium sputtering. In addition, reduction of factors between 10 and 30 reduction in physical sputtering from lithiated graphite compared to pure lithium or carbon is also measured.

Effect of lithium PFC coatings on NSTX density control

Lithium coatings on the graphite plasma facing components (PFCs) in NSTX are being investigated as a tool for density profile control and reducing the recycling of hydrogen isotopes. Repeated lithium pellet injection into Center Stack Limited and Lower Single Null ohmic helium discharges were used to coat graphite surfaces that had been pre-conditioned with ohmic helium discharges of the same shape to reduce their contribution to hydrogen isotope recycling. The following deuterium NBI reference discharges exhibited a reduction in density by a factor of about 3 for limited and 2 for diverted plasmas, respectively, and peaked density profiles. Recently, a lithium evaporator has been used to apply thin coatings on conditioned and unconditioned PFCs. Effects on the plasma density and the impurities were obtained by pre-conditioning the PFCs with ohmic helium discharges, and performing the first deuterium NBI discharge as soon as possible after applying the lithium coating.

PSI issues at plasma facing surfaces of blankets in fusion reactors

Important PSI issues for the first wall of blankets in fusion reactors are reviewed. Present understandings and remaining issues for particle loads (fast neutral, thermal ions, and energetic alpha particle ripple losses), and evaluation of low-activation structural materials (RAF, V-alloys, and SiC f/SiC) and tungsten as first-wall armor (including the effect on tritium breeding ratio of blankets) are explained. If the characteristics of particle load to the first-wall evaluated for ITER-FEAT is similar to DEMO and future reactors, erosion rates of the blanket first-wall made by low-activation materials are not acceptable considering their thickness. For this case, armor materials such as W or some protection methods such as in-situ coatings of low Z materials could be needed. Blistering and H/He embrittlement are also important issues to consider. Possible effects of the first wall on core plasma performance are briefly discussed in terms of hydrogen isotope recycling and reflection of synchrotron radiation.

Experimental Simulation of Hydrogen Recycling at Plasma-Facing Metal-Hydride for Fusion Reactors

In this paper we consider the possibility of using a hydride-forming Zr-V alloy as a first-wall material for fusion devices. Theoretical and experimental studies of the Zr-V hydride irradiation with flows of high-energy plasma particles have been performed. It is shown that the use of these materials allows the reduction of erosion of the first wall and also a better control of the hydrogen isotope recycling.

Impact of duration of infusion and choice of isotope label on isotope recycling in glucose homeostasis.

The purposes of this study were to quantify the impact of the duration of infusion and choice of stable isotope of glucose on measures of glucose rate of appearance (glucose R(a)) and to determine whether the differences observed were due to tracer recycling via the glycogen pool (direct pathway) or gluconeogenesis (indirect pathway). Six healthy adult volunteers were studied on four occasions in the postabsorptive state during infusions of [1-(13)C]glucose and [6,6-(2)H(2)]glucose: 2.5-h infusion of both (A), and 2.5-h infusion of one (B) and 14.5-h infusion of the other isotope (C), and 5-h infusion of [6,6-(2)H(2)]glucose and 2.5-h infusion of [1-(13)C]glucose (D). Infusion of both isotopes for 2.5 h resulted in similar glucose R(a) values. When compared with a 14.5-h infusion, the 2.5-h glucose tracer infusion overestimated glucose R(a) by 26-35%. Glucose (13)C recycled via the Cori cycle, resulting in slower decay from the plasma pool and longer half-life of [1-(13)C]glucose compared with [6,6-(2)H(2)]glucose. There was no detectable release of [(13)C]glucose or [(2)H(2)]glucose tracer into the plasma pool after administration of glucagon. These data demonstrate that glucose R(a) varies not as a result of isotope cycling but as a result of differences in duration of isotope infusion regardless of the isotope used. This is most likely due to incomplete isotope and substrate equilibration with the 2.5-h infusion. The potential error was reduced by nearly 80% using a 5-h infusion of [6,6-(2)H(2)]glucose. These studies demonstrate that the duration of isotope infusion has significantly greater impact on quantitation of glucose R(a) than does the selection of isotope.

Technical Issues on the Control of Plasma-Wall Interactions in Steady-State Magnetic Fusion Devices. 2. Plasma Wall Interactions Database and Related Computer Codes. Modeling of Hydrogen Isotope Recycling from Graphite, and the Data Needs for Diffusion and Recombination Coefficients.

For the purpose of evaluating transient recycling of hydrogen at plasma-facing materials, mass balance equations for mobile and trapped hydrogen atoms have been proposed, in which the elementary processes leading to re-emission, such as diffusion, detrapping, (re)trapping, and local molecular recombination are taken into account. Under appropriate conditions, it was demonstrated that the concentrations of mobile and trapped species can be analytically solved as functions of depth, time, or ion flux, and that the thermal desorption spectrum can be calculated from the time dependence of the concentration of trapped hydrogen atoms. It was also shown that by using the analytical solutions, the diffusion constant and the rate constant of effective local molecular recombinations can be determined experimentally. The experimental data on the diffusion coefficient and the molecular recombination rate are summarized and critically discussed using the solution of the mass balance equations.

Isotope recycling in lactating dogs (Canis familiaris).

Isotope-based techniques for the measurement of water turnover, energy expenditure, and milk intake often assume that there is no recycling of isotopes once they have left the labeled animal. In experiments involving lactating females or their suckling offspring, there are several possible routes of isotope recycling. These include the consumption of labeled milk by offspring, the ingestion of labeled excreta, and the rebreathing of exhaled labeled CO(2) or water vapor by both mother and offspring. Isotope recycling might be especially important during lactation because the offspring are in close contact with each other and their mother for prolonged periods. We show here in 24- to 30-day-old domestic dog Canis familiaris puppies that there was no detectable transfer of (18)O or (2)H from labeled to unlabeled pups in two litters (16 pups, 8 labeled, 8 unlabeled) that were weaned early and independent of their mother. However, there was a significant transfer of both isotopes from labeled to unlabeled pups and from labeled pups to their mothers in nine equivalent nursing litters of the same age (27 labeled, 26 unlabeled pups). The increases in enrichment of isotopes in unlabeled offspring were greater than the increases in enrichment of the mothers. This indicates that maternal ingestion of offspring excreta and subsequent transfer of isotope in milk is not the sole pathway of recycling. Additional routes must also be important, such as exchange of isotope between pups on saliva-coated nipples and perhaps direct ingestion of excreta by unweaned young. Recycling is unlikely to be an important factor when determining maternal metabolic rate during peak lactation in domestic dogs. However, experiments that are designed to assess the energy demands of pups and isotope-based estimates of water turnover in offspring may need to take into account any effects of isotope recycling. In a theoretical example, removing the effects of recycling increased the measured energy expenditure in pups by up to 7% and increased the calculated elimination rates of both isotopes by up to 11.1% in (18)oxygen and 10.9% in (2)hydrogen.

Tritium recycling and retention in JET

JET's 1997 Deuterium Tritium Experiment (DTE1) allows a detailed study of hydrogenic isotope recycling and retention in a pumped divertor configuration relevant to ITER. There appear to be two distinct forms of retained tritium. (1) A dynamic inventory which controls the fueling behaviour of a single discharge, and in particular determines the isotopic composition. This is shown to be consistent with neutral particle implantation over the whole vessel surface area. (2) A continually growing inventory, which plays a small role in the particle balance of a single discharge, but ultimately dominates the hydrogenic inventory for an experimental campaign comprising thousands of pulses. This will be the dominant retention mechanism in long-pulse devices like ITER. The JET retention scaled-up to ITER proportions suggests that ITER may reach its tritium inventory limit in less than 100 pulses.

Wall Conditioning to Control Impurity and Hydrogen Isotope Recycling in JT-60U.

Wall conditioning can control impurity and hydrogen isotope. So various methods of wall conditioning have been adopted in JT-60U. After the vacuum vessel is closed and pumping system works, tokamak discharges can be obtained within a week. The conditioning can also make a good condition that recycled particles are so low as to correspond to injected NB particles. An equivalent QDT up to 1.25 can be transiently achieved in reversed shear plasmas because of both optimization of wall conditioning and improved confinement. Wall conditioning in JT-60U is discussed in this paper.

Nutrition and growth of suckling black bears (Ursus americanus) during their mothers' winter fast.

In black bears the last 6-8 weeks of gestation and the first 10-12 weeks of lactation occur in winter while the mother is in a dormant state, and reportedly does not eat, drink, urinate or defaecate. Measurements were made of the body composition and organ weights of cubs, of the composition of milk, and of milk intake (by dilution of 2H2O), in the first 3 months after birth. Additional milk samples were collected until 10 months postpartum. Bear cubs were small at birth, only 3.7 g/kg maternal weight, and chemically immature, as indicated by the high concentration of water (840 g/kg) in their bodies. Organ weights at birth were similar to those of puppies. In the first month after birth cubs gained 22 g/d or 0.23 g/g milk consumed; the milk was high in fat (220 g/kg) and low in water (670 g/kg). About 30% of the ingested energy and 51% of the ingested N were retained in the body. Over the entire 12-week period bear cubs required about 11 kg milk, containing (kg) water 7, fat 2.5, protein 0.8 and total sugar 0.25, to achieve a 2.5 kg weight gain. The birth of immature young and the production of high-fat, low-carbohydrate milk seem to be maternal adaptations to limit the utilization of glucogenic substrates during a long fast. Isotope recycling indicates that mothers may also recover most of the water (and perhaps much of the N) exported in milk by ingesting the excreta of the cubs. Lactation represents another aspect of the profound metabolic economy of the fasting bear in its winter den.

Glucose isotope, carbon recycling, and gluconeogenesis using [U-13C]glucose and mass isotopomer analysis

Experimental determinations of glucose carbon recycling using 14C or 13C glucose tracer often underestimate true Cori cycle activity because of dilution and exchange of isotope tracer through the tricarboxylic acid (TCA) cycle. The term glucose isotope recycling therefore is used to distinguish recycling of isotope from recycling of glucose carbon, the actual quantity of circulating glucose recycled. Recently, per-labeled glucose ([U-13C6]glucose) has been used to estimate glucose appearance rate and glucose isotope recycling. Chemical structural information determined by mass isotopomer analysis has been used to correct for dilution of isotope through the TCA cycle. In this report, we present experiments in the study of glucose turnover and recycling using [U-13C6]glucose. Methods of single injection and continuous infusion of [U-13C6]glucose are compared. A formula for the calculation of a dilution factor using TCA cycle parameters is derived. In this study of six rabbits, glucose turnover rate ranged from 3.4 to 8.8 mg/kg/min, and glucose m + 3 mass isotopomer recycling from 7 to 12%. The rate of pyruvate carboxylation (Y) was comparable to that of citrate synthetase, having an average relative flux of 0.89. Applying the correction factor for tracer dilution to the observed mass isotopomer recycling, we determined glucose carbon recycling (or Cori cycle activity) to be 22-35% of hepatic glucose output.

Isotopic Measurement of Glucose and Lactate Kinetics

A variety of isotopic tracers can be used to quantitate glucose kinetics in vivo. Using the standard approach to calculate the rate of appearance (Ra) of glucose from kinetic data, different rates of Ra glucose are obtained depending on the nature and position of the label in glucose. If total glucose production is considered to be all glycogen breakdown and gluconeogenesis, then that value can be calculated using the following stable isotopic tracers, or, in most cases their radioactive counterparts: 6, 6-2H-glucose; 1-13C, 6-13C; and U-13C-glucose. In the case of the 13C-labeled glucose, account must be taken of the extent of recycling of labeled carbons. If U-13C-glucose is used and recycling of isotope not quantitated, the resulting calculated value for Ra glucose will represent the rate of production from non-recycled carbons, plus some recycled carbons, due to potential dilution of 13C in the oxaloacetate pool and some loss of 13C in the PEPCK reaction. Traditional calculation of Ra glucose using 2-2H-glucose will include the rate of total glucose production and the contribution from the glucose cycle, and use of 3-2H-glucose will include the rate of total glucose production and contribution of the fructose cycle. The traditional methodology used to measure lactate production, in contrast to glucose, has a major conceptual flaw. It requires the assumption that there is no isotopic exchange between lactate and other compounds, yet experimental evidence indicates that lactate and pyruvate are in rapid equilibrium. Consequently, this approach will overestimate the true rate of net lactate production, possibly by as much as 400%.

Lactation in the tammar wallaby (Macropus eugenii). I. Milk consumption and the algebraic description of the lactation curve

The milk intake of suckling tammar wallabies (Macropus eugenii) was estimated between 213 and 339 days of age using a double‐isotope procedure in which tritiated water (TOH) was injected into the dams and deuterium oxide (D2O) injected into the offspring. Recycling of isotopes between mothers and offspring was shown not to be a significant source of error. Estimates of body water (isotope dilution space) in the mothers or offspring, as a proportion of their body weight, were similar to values obtained with other macropodids and with placental mammals (0.73–0.75). Total water inflow in the offspring increased throughout the period, but the proportion of this contributed by milk fell in sigmoid fashion from 95.6% at 213 d to 3.7% at 340 d. Milk intakes reached a peak of about 86 ml/d, which was low compared with placental species. Before the peak, intakes were more closely related to body weight than age. Peak milk intake corresponded with the period of emergence from the pouch. Milk intakes were also in excellent agreement with published data obtained earlier in lactation, in animals drawn from the same population. These data were therefore combined to provide estimates of intake for the whole of lactation in the tammar wallaby, and algebraic models fitted to describe the pattern of milk intake in relation to body weight or age. With body weight, the pattern of milk intake was well described by a rising linear phase to a peak intake of about 86 ml/d near 1110 g body weight, followed by a gradual exponential decline. When related to age, the pattern was well described by a rising logistic phase (peak at 251 d) followed by a sharp exponential decline. It is shown that this latter pattern is markedly similar to the shape of the functions describing the energy requirements for the sum of pregnancy and lactation in a placental species, the sheep.

Recent progress in wall material development and of surface technology for fusion devices at the Japan Atomic Energy Research Institute

The research and development of materials and material processes associated with the plasma–wall interaction in magnetically confined fusion devices includes current and near-term problems which must be solved to advance plasma confinement research. The major elements to be considered for the materials and processes are (a) impurity release and surface modification; (b) hydrogen isotope recycling, retention, and permeation; (c) high heat flux removal and thermomechanical response; and (d) the effects of plasma disruptions. The development of wall materials and processes and the associated plasma–wall interaction study at the Japan Atomic Energy Research Institute have been carried out primarily from the device-oriented standpoint. The weight is laid on the development and performance tests of new materials and processes for plasma-interactive components. In the JT-60 tokamak, TiC-coated molybdenum and TiC-coated Inconel tiles are currently used as most plasma-interactive components. The JAERI coating program also includes the development of in situ coating techniques for TiC and C. For the near-term devices, actively cooled components will be developed. The major technical issues are to improve ceramic materials and to develop ceramic–metal bondings which satisfy the requirements specific to fusion devices.

A computer-simulated analysis of errors associated with a two-pool compartmental model for estimating protein turnover rates in chickens.

An analysis on the extent of underestimation in fractional rates of protein turnover was conducted by using computer simulation with a two-pool compartmental model in chickens. The extent of underestimation in calculated values for fractional synthesis rates, which was 148 Japan. Poultry Sci., 24(3), 1987 introduced by ignoring isotope recycling, was compared in terms of three isotope administration methods, i.e., pulse injection, continuous infusion and primed infusion. Also tested were the effects on the underestimation of the length of easurement period, varying the fractional rate of protein synthesis per se, and of relative pool size of protein to free amino acid (R).It was shown that the longer the measurement period, the larger the underestimation resulted in. There was a similar extent of underestimation between the three administration methods within half an hour, while the difference was evident at 6 hours. When fractional rates of protein synthesis per se were high, the extent of underestimation became so large that the effect of isotope recycling was no longer ignorable, especially by the continuous and primed infusion methods at the end of 6-hour measurement period. The R value had a most remarkable effect on the extent of underestimation, which was drastically increased particularly when the R value was low.The present results suggest that the calculation of fractional rates of protein turnover without consideriog isotope recycling would be underestimated to the extent as large as 70%, depending on the condition employed.