Distribution characteristics of fission gas along the axial direction for an irradiated fuel rod of a pressurized water reactor (PWR)

In this work, the fission gas distribution of an irradiated oxide fuel was investigated by measuring the fission gas release (FGR) and retained gas from and in an oxide fuel along the axial height of the fuel rod. In addition to the fission gas measurements, other destructive and non-destructive post irradiation examination tests such as gamma scanning, eddy current testing, density and oxide layer thickness measurements, and ceramography/metallography were conducted to review their impact on the FGR and gas retention. A lead rod was extracted from a lead test assembly, which was irradiated to 56.9 GWd/tU during three irradiation cycles for a total exposure of 1,406 effective full power days. Considering the water-side oxide layer thickness and local burnup of the fuel rod, the rod was sectioned into four positions along the axial height and four samples were prepared from these positions. A sample fragment of around 0.1–0.2 g was individually melted to measure its retained krypton and xenon concentration. According to the measurement results, the retained krypton and xenon concentration ranges were 0.114–0.139 cc/gU and 1.073–1.338 cc/gU, respectively, and their retention percentage after normalization of the sample local burnup showed a decreasing trend as the axial height of the fuel rod raised. The water-side oxide layer thickness scope of the tested fuels measured by an observation of the optical microscope images was 13–42 μm, and the thickness was increased along the axial height of the rod. The amount of released krypton and xenon into the rod-free volume was measured as 5.7 and 54.6 cc, respectively, by a rod puncturing/collection procedure, which corresponds to a 1.94 % fractional fission gas release referring to fission gas generation by a code calculation.     

The measurement of retained fission gas compositions and their isotopic distributions in an irradiated oxide fuel by inert gas fusion-mass spectrometric analysis

In this work, an easy, fast and reliable measurement technique for the quantitative determination of retained fission gases in an irradiated oxide fuel was developed. Many experiments were conducted to determine the optimum conditions for fusion of an oxide fuel, for the quantitative collection and measurements of the released gases. Ion implantation technology was applied to make a krypton or xenon references in a solid matrix. A fragment of oxide fuel, about 0.1 g of an unirradiated SIMFUEL, was completely fused with excess metallic fluxes, 1.0 g of nickel and 1.0 g of tin, in a graphite crucible of a helium atmosphere for 120 s at 850 A as a mixture of metals and alloys. About 96 ± 3 to 98 ± 4% of the krypton and xenon that were injected into the instrument using a standard gas mixture was reproducibly recovered by collecting the releasing gas through the instrument for 120 s. Using the same fusion and collection conditions, it was possible to recover about 97 ± 3% of the injected krypton and xenon by fusing a fragment of SIMFUEL which was wrapped with krypton or xenon implanted aluminum foils. The recovery test results of krypton and xenon using ion planted aluminum foils gave encouraging results suggesting their potential use as a reference specimen. It was confirmed that a fragment of irradiated oxide fuel, 0.051 g, with a code burn-up of 56.9 MWd/MtU, was completely fused as the mixture of metals and alloys through the fusion conditions and more than 99% of the retained fission gases were recovered during the first fusion. Since no cryogenic trap was needed, the collected gas could be measured directly and thus the analysis time could be further reduced. Approximately 7 min was sufficient to finish the measurement of retained fission gases in the irradiated oxide fuel using the developed procedure.     

Chemical and isotopic compositions of bottled waters sold in Korea: chemical enrichment and isotopic fractionation by desalination

A total of 54 Korean bottled waters were investigated to characterize their origins and types using elemental and isotopic composition, as well as to identify elemental and isotopic changes in desalinated marine water that arise due to desalination. The different types of bottled water displayed a wide pH range (3.42 to 7.21). The elemental compositions of still and sparkling waters were quite similar, whereas desalinated marine water was clearly distinguished by its high concentrations of Ca, Mg, B, and Cl. In addition, desalinated marine water had much higher isotope ratios of oxygen and hydrogen (-0.5 and -2‰, respectively) than still and sparkling waters (-8.4 and -57‰). The elemental composition of desalinated marine water was adjusted through post-treatment procedures; in particular, boron was greatly enriched during desalination processes. The carbon isotope compositions of dissolved inorganic carbon (δ(13)C(DIC) values) varied widely according to the origins of the bottled waters (-25.6 to -13.6‰ for still water, -31.2 to -26.7‰ for sparkling water, and -24.1 to -6.3‰ for desalinated marine water). This indicates that carbon isotopes in dissolved inorganic carbon are significantly fractionated by desalination processes and re-modified through post-treatment procedures. The results suggest that combined elemental and stable isotopic tracers are useful for identifying the origin of bottled water, verifying elemental and isotopic modifications during desalination processes, and characterizing various water types of bottled waters.     

Speciation and analysis of corrosion products in the primary coolant of pressurized water reactors

The procedure involves separate sampling and determination of the insoluble, cationic and anionic species of corrosion products (Fe, Ni, Cr, Mn, Co, Zn, Cu) in the primary coolant of pressurized water reactors (PWRs) with concentrations in the range 0–2000 mg l^?1 boron and 0–5 mg l^?1 lithium. Samples of coolant (0.2–1 l) are passed through packs consisting of one 0.45-μm filter paper, one cation-exchange membrane (Whatman SA-2) and one anion-exchange membrane (Whatman SB-2). The membranes are examined by wavelength-dispersive x-ray spectrometry. Selection of the ion-exchange membranes and the influence of the boron and lithium concentrations (and pH) on retention of soluble species are discussed. With sample volumes of 0.5 l, the detection limits are between 0.05 and 0.3 μg l^?1 for undissolved species and from 0.03 to 0.14 μg l^?1 for ions. Data collected during a PWR shutdown procedure are summarized.     

Characterization of corrosion products deposited on fuel rods in a boiling water reactor (BWR-6) plant using hydrogen water chemistry (HWC)

The objective of this paper was to characterize the corrosion products deposited on fuel cladding surfaces under hydrogen water chemistry (HWC) conditions in the boiling water reactor unit of a nuclear power plant. Inductively coupled plasma-optical emission spectroscopy and gamma spectrometry were used to determine the elemental composition and radioactivity along the fuel rods. Scanning electron microscopy/energy dispersive X-ray spectroscopy was used to evaluate crud morphology and X-ray diffraction analysis was employed to determine the crystalline phase. Most of the iron in the crud comprised irregular shapes and flakes, with a number of crystallites (e.g. small quantities of ferrites, MnFe₂O₄). The major constituent of the outer layer was a loosely attached, stable form of hematite (α-Fe₂O₃). The amount of deposition on the fuel rods following the fourth fuel cycle of HWC (~1.0 mg cm^?2) was significantly greater than after the third cycle, due to extended burn-up time. In addition, the radioactivity ratio of ⁵⁸Co to ⁶⁰Co was lower for EOC22 than for EOC21, due to a longer storage period in the spent fuel pool. No apparent changes were observed in the characteristics (composition or oxidizing nature) of crud in the fuel bundles. Finally, no direct negative impact was observed on the fuel cladding surfaces following four fuel cycles of HWC, compared with normal water chemistry conditions.     

Characterizing the origins of bottled water on the South Korean market using chemical and isotopic compositions

We analyzed the major elements and stable isotopes of oxygen, hydrogen, and carbon (dissolved inorganic carbon: DIC) in various types of bottled water (domestic and foreign) commercially available in South Korea to classify the water types and to identify their origins. Only marine waters and some sparkling waters could be discriminated by their physicochemical compositions. Oxygen and hydrogen isotopes made marine waters more distinguishable from other water types. The determination of the carbon isotope composition of DIC was clearly useful for distinguishing between naturally and artificially sparkling waters. In addition, statistical analysis also appeared to aid in the discrimination of bottled water types. Our results indicate that a method that combines chemical and stable isotope composition analysis with statistical analysis is the most useful for discriminating water types and characterizing the origins of bottled water.     

气体扩散层中聚四氟乙烯的分布对质子交换膜燃料电池水淹的影响

通过在不同真空度下进行碳纸的聚四氟乙烯（PTFE）浸渍处理,考察了PTFE在碳纸中的分布对燃料电池水淹情况的影响. 碳纸PTFE浸渍过程中,抽真空作用可以将碳纸微孔中存留的空气移除,使PTFE更均匀地扩散到内部微孔中. 碳纸的断面电镜照片显示真空浸渍可以改善PTFE的分布. 在总浸渍量相同时,由于真空浸渍使更多的PTFE进入到碳纸内部微孔,故其表面的PTFE比例减少. 实验进一步考察了碳纸中亲水孔和憎水孔的分布,结果表明真空浸渍处理的碳纸具有更高比例的憎水孔. 将不同处理方法的碳纸制备成膜电极,通过全尺寸电池考察其性能,结果表明PTFE的均匀分布可以改善电池性能,并且电化学阻抗分析表明其有利于改善水淹问题.     

Rough localization of defective PWR fuel rods on the basis of the concentration ratio134Cs/137Cs in the primary coolant

The search for fuel assemblies with defective fuel rods by sipping tests involves expensive prolongations of the refuelling periods in nuclear power plants. It is attempted to reduce the number of fuel assemblies to be checked by sipping during the refuelling periods by means of rough localization of the defects on the basis of the fission product concentration ratio¹³⁴Cs/¹³⁷Cs in the primary coolant already during reactor operation. First results obtained in two examples of application at VVER type reactors are encouraging. The burnup of the defective assemblies could be correctly predicted from the cesium ratio in these two cases, which was confirmed by sipping tests after reactor shutdown.     

Effects of dung and urine amendments on the isotopic content of N(2)O released from grasslands

The temporal and diurnal changes in nitrous oxide (N(2)O) fluxes were measured between 29(th) September and 2(nd) November 1999 from urine and dung patches from cattle deposited on grazed grassland. The delta(15)N and delta(18)O values of the N(2)O emitted from soil from both treatments were examined on four occasions during this period. The diurnal fluxes of N(2)O were measured by a chamber technique that provides hourly measurement of N(2)O fluxes. The (15)N and (18)O analysis of N(2)O were determined by isotope ratio mass spectrometry. N(2)O fluxes from the excreta patches were large, with peak emissions up to 1893 ng N m(-2) s(-1) occurring after heavy precipitation, measured one month after the treatment applications. Emissions from the urine patches were significantly greater than from the dung. The results showed that excretal patches are an important source of atmospheric N(2)O. The flux pattern showed a strong diurnal variation with maximum fluxes generally occurring in late afternoon or early morning, and generally not in phase with the soil temperature changes. The isotopic content of (15)N and (18)O in the N(2)O showed a similar trend to that of the N(2)O flux. The (15)N and (18)O values of the N(2)O emitted from the soil indicated that denitrification was the major process involved. After heavy precipitation on the 6(th) October, the larger delta(15)N and delta(18)O values suggested a consumption of the N(2)O by total denitrification.     

Distribution of 14C and 3H in low level radioactive wastes generated by wet waste streams from pressurized water reactors

Summary It is impossible to detect ¹⁴C and ³H by direct methods such as γ-spectroscopy because they are pure b-emitters and thus they are classified as hard to measure nuclides (HTM). In this paper the analysis results of ¹⁴C and ³H in the low level radioactive wastes (LLWs), including spent ion exchange resin, evaporated bottom and sludge are presented. The LLWs were generated by three nuclear power plants (NPPs), in Korea all with pressurized water type reactors (PWRs). A simultaneous separation procedure for ¹⁴C and ³H in LLWs was established by wet oxidation-acid stripping. A liquid scintillation analyzer was used for the measurement of ¹⁴C and ³H. It was found that the recovery of ¹⁴C and ³H was 82-99 and 78-103%, respectively, by wet oxidation-acid stripping with diluted standard solutions. At the lowest injection of ¹⁴C and ³H, i.e., at 1.44 Bq for ¹⁴C and 1.22 Bq for ³H, the minimum detectable activity (MDA) of ¹⁴C and ³H was calculated as 0.88 and 0.78 Bq/g, respectively, for the minimum allowable sample weight, using wet oxidation and 16 wt% H₂SO₄ acid. By the wet oxidation-16 wt% H₂SO₄ stripping method no interfering nuclides were detected in the trapping solution of ¹⁴CO₂ and the distillate of ³H. The activity concentration range of ¹⁴C in the analyzed samples, i.e., spent ion exchange resin, evaporated bottom and sludge, was 0.17-110,000, 8.4-1380 and 0.1-10,006 Bq/g, respectively, and that of ³H in the same was from no detectable to 769, 134-14,383 and 0.7-4820 Bq/g, respectively.     

Evaluation on 14C emission patterns of various PWR types in South Korea and effectiveness of inventory reduction driving (IRD)

Journal of Radioanalytical and Nuclear Chemistry - In this research, we investigated to examine the emission characteristics of radioactive carbon emitted from three types of pressurized water...     

Photometric measurement of trace As(III) and As(V) in drinking water

A simple, fast and sensitive light-emitting diode (LED)-based photometric method for the differential determination of ppb-ppm levels of As(III) and As(V) in potable water in the presence of ppm levels of phosphate was developed. The detection chemistry is based on the well-known formation of arsenomolybdate, followed by reduction to heteropoly blue. The front-end of the measurement system is configured to selectively retain P(V) and As(V), based on the considerable difference of the pK(a) of the corresponding acids relative to As(III). Thus, it is As(III) that is injected into the medium, oxidized in-line with KBrO(3) to As(V) and forms Mo-blue that is detected by an LED-based detector. Only As(III) is measured if the sample is injected as such; if all As in the sample is prereduced to As(III) (by the addition of cysteine, in a provided in-line arrangement), the system measures As(V)+As(III). In the present form, limit of detection (LOD) (S/N=3) is less than 8 mug l(-1) As, and the linear range extends to 2.4 mg l(-1). Potential interference from dissolved silica and Fe(III) is eliminated by the addition of NaF to the sample.     

Mass and charge distribution in the fission of 238U

The mass and charge distribution in the fission of ²³⁸U by protons of 15·6 MeV have been determined using Ge(Li) spectroscopy. The total fission cross section was found to be 1005 mb. For 10 shielded or quasi-shielded nuclides, correlation with a Gaussian charge dispersion was investigated using various mass formulae and charge distribution hypotheses. The postulate of minimum potential energy using a shell-effected mass equation was found to best correlate the data.     

Role of membranes and membrane reactors in the hydrogen supply of fuel cells

Production, storage and supply of high-purity hydrogen as a clean and efficient fuel is a key point for the development of fuel cell technology, in particular in vehicle traction. Presently, technologies for handling liquefied or gaseous hydrogen in transports are not available so that various alternative fuels are considered with the aim of in-situ generation of hydrogen through catalytic processes. The concept of integrated membrane reactors (MRs) can greatly benefit to these technologies. Particular emphasis is put on inorganic membranes and their role in MR performance for H₂ production.     

Ammonium uranyl carbonate (AUC) based process of simultaneous partitioning and reconversion for uranium and plutonium in fast breeder reactors (FBRs) fuel reprocessing

Ammonium uranyl carbonate (AUC) based process of simultaneous partitioning and reconversion for uranium and plutonium is developed for the recovery of uranium and plutonium present in spent fuel of fast breeder reactors (FBRs). Effect of pH on the solubility of carbonates of uranium and plutonium in ammonium carbonate medium is studied. Effect of mole ratios of uranium and plutonium as a function of uranium and plutonium concentration at pH 8.0–8.5 for effective separation of uranium and plutonium to each other is studied. Feasibility of reconversion of plutonium in carbonate medium is also studied. The studies indicate that uranium is selectively precipitated as AUC at pH 8.0–8.5 by adding ammonium carbonate solution leaving plutonium in the filtrate. Plutonium in the filtrate after acidified with concentrated nitric acid could also be precipitated as carbonate at pH 6.5–7.0 by adding ammonium carbonate solution. A flow sheet is proposed and evaluated for partitioning and reconversion of uranium and plutonium simultaneously in the FBR fuel reprocessing.     

A one-year study of the total air-borne14C effluents from two Swedish light-water reactors,one boiling water- and one pressurized water reactor

The results of a one-year study of the total air-borne¹⁴C effluents from two Swedish light-water reactors, one boiling water reactor (BWR) at Forsmark and one pressurized water reactor (PWR) at Ringhals, are presented. Air emitted from the stacks has been collected continuously over two-week periods and the¹⁴C content in the samples has been analysed using accelerator mass spectrometry (AMS). The¹⁴C activity concentration in the air issuing from the stack of the PWR varied between 2 and 1132 Bq/m³ with a mean value of 200 Bq/m³, while from the BWR the activity concentration varied between 4 and 146 Bq/m³, with a mean value of 95 Bq/m³. The corresponding¹⁴C release rate was 0.27 TBq/GW_el·year for the PWR and 0.48 TBq/GW_el·year for the BWR. During the same period of time, for comparison, the¹⁴C activity in continuously collected air from the stack of the PWR was also measured by liquid scintillation counting. In most cases the results of these measurements were in fair agreement with the corresponding AMS results.     

Multiresidue analysis of four pesticide residues in water dropwort (Oenanthe javanica) via pressurized liquid extraction, supercritical fluid extraction, and liquid-liquid extraction and gas chromatographic determination

The primary objective of this study was to simultaneously analyze the residues of the most commonly used pesticides, chlorpyrifos-methyl, endosulfan, EPN, and iprodione in the water dropwort, via accelerated solvent extraction (ASE), supercritical fluid extraction (SFE), and conventional solvent extraction (LLE) techniques. Residue levels were determined using GC with electron-capture detection (GC-ECD). The confirmation of pesticide identity was performed by GC-MS in a selected ion-monitoring (SIM) mode. In none of the ASE and SFE techniques were the extraction conditions optimized. Rather, the experimental variables were predicated on the author's experience. The ECD response for all pesticides was linear in the studied range of concentrations of 0.005-5.0 ppm, with correlation coefficients in excess of 0.9991. At each of the two studied fortification levels, the pesticides yielded recoveries in excess of 72% with RSDs between 1 and 19%. The LODs were achieved at a range of levels from 0.001 to 0.063 ppm, depending on the pesticide utilized. The LOQs, which ranged from 0.003 to 0.188 ppm, were lower than the maximum residue limits (MRLs) authorized by the Korean Food and Drug Administration (KFDA). All of the methods were applied successfully to the determination of pesticide residues in the real samples. It could, therefore, be concluded that any of the techniques utilized in this investigation might prove successful, given that the applied extraction conditions are wisely chosen.