Simulation of radioactivation and chlorination reaction behavior for Zircaloy-4 and Zirlo cladding hull wastes

Radioactivation of Zircaloy-4 (Zry-4) and Zirlo cladding hulls after 55 GWD/tU burn-up and 10 years of cooling was simulated using the ORIGEN-S code. The simulation results revealed that ¹²⁵Sb and ⁶⁰Co are major contributors of both radioactivity and decay heat in the case of the Zry-4 hulls. For the Zirlo hulls, ^93mNb and ¹²⁵Sb consisted 82.2% of radioactivity while ¹²⁵Sb and ⁶⁰Co emitted 77.9% of decay heat. Although the radioactivity between the Zry-4 (1.17 Ci for 1 kg of fresh Zry-4) and Zirlo (1.38 Ci for 1 kg of fresh Zirlo) hulls was not significantly different, decay heat of the activated Zry-4 hulls (8.58 mW) was much larger than 1.62 mW of the activated Zirlo hulls. This gap might have come from the different major constituents of Zry-4 (Zr, Sn, Fe, and Cr) and Zirlo (Zr, Sn, Nb, and Fe) resulting in different radioactive nuclides after radioactivation. Chlorination reaction behavior of the activated Zry-4 and Zirlo hulls was performed using the HSC chemistry code. Constituents of recovered ZrCl₄ were investigated via changes of Gibbs free energy and boiling points of resulting chlorides. The calculation results suggested that radioactivity and decay heat might decrease by 49.0 and 81.8%, respectively, in the ZrCl₄ recovered from the activated Zry-4 hulls. In the case of Zirlo, it was expected that radioactivity and decay heat might decrease by 11.6 and 13.0%, respectively, after the chlorination reaction. Effect of cooling time on radioactivity and decay heat was also investigated.     

Purification of radiozirconium and the influence of accumulation of daughter radioactivity on the accuracy of its distribution measurements

The use of nuclide⁹⁵Zr as radiotracer is often unfavourably influenced by the continuous accumulation of the radioactive daughter nuclide⁹⁵Nb. The present paper gives a method showing how the daughter radioactivity can influence the value of the distribution coefficient of zirconium calculated from radioactivity measurements. A simple method of continuous purification of⁹⁵Zr, which yields a product of the required degree of purity, is also described.     

Systematic radiochemical separation for the determination of <Superscript>99</Superscript>Tc, <Superscript>90</Superscript>Sr, <Superscript>94</Superscript>Nb, <Superscript>55</Superscript>Fe and <Superscript>59,63</Superscript>Ni in low and intermediate radioactive waste samples

A simple and rapid separation procedure was systemized for the determination of ⁹⁹Tc, ⁹⁰Sr, ⁹⁴Nb, ⁵⁵Fe and ^59,63Ni in low and intermediate level radioactive wastes. The integrated procedure involves precipitation, anion exchange and extraction chromatography for the separation and purification of individual radionuclide from sample matrix elements and from other radionuclides. After separating Re (as a surrogate of ⁹⁹Tc) on an anion change resin column, Sr, Nb, Fe and Ni were sequentially separated as follows; Sr was separated as Sr (Ca-oxalate) co-precipitates from Nb, Fe and Ni followed by purification using Sr-Spec extraction chromatographic resin. Nb was separated from Fe and Ni by anion exchange chromatography. Fe was separated from Ni by anion exchange chromatography. Ni was separated as Ni-dimethylglyoxime precipitates after the removal of ^134,137Cs and ^110mAg by Cs-phosphotungstate and AgCl precipitation, respectively. Finally, the radionuclide sources were prepared by precipitation for their radioactivity measurements. The reliability of the procedure was evaluated by measuring the recovery of chemical carriers added to a synthetic radioactive waste solution.     

Development of a method for the determination of 93Zr and 94Nb in radioactive waste using TEVA® resin

The behaviour of ⁹⁵Zr and ⁹⁵Nb isotopes on TEVA^® resin column was studied. The influence of hydrofluoric, hydrochloric, oxalic and sulphuric acids on the separation and chemical yield of zirconium and niobium was tested. The method is suitable for the separation of ⁹³Zr and ⁹⁴Nb isotopes from hydrofluoric, hydrochloric and sulphuric acid by using different concentrations of the acid for the load or elutes solutions. Samples from reactor and fuel assemblies such as the control-rod connection rod, shielding/absorber parts of fuel rods, neutron in-core measurement channels, pressure vessel basic construction material and internal cladding, core barrel and reactor protection tube unit were analysed.     

Separation of zirconium,niobium, cerium and ruthenium on chitin and chitosan columns for the determination of cesium in nuclear fuel solutions

Nuclear fuel solutions atpH=2.5 can be passed through 7×1 cm chitin or chitosan columns to fix the Zr, Nb, Ce and Ru radioisotopes. This rapid and quantitative separation clears the γ-ray spectrum of the solution from the main activity contribution and leaves the¹³⁷Cs spectrum alone for accurate Cs determination. The process can be extended to radioactive waste waters.     

Experimental and FLUKA study relevant to the production of <Superscript>124</Superscript>I through <Superscript>nat</Superscript>Te(p,xn) reaction at a medium-sized cyclotron

A radiochemical methodology for the determination of ⁹⁴Nb in low-level radioactive wastes from nuclear power plant was proposed. Although ⁹⁴Nb is a strong gamma emitter, its concentration in radioactive waste samples is usually several orders of magnitude lower than that of other β–γ emitters, whose emissions interferes in the detection of the emission lines of ⁹⁴Nb. The procedure involves acid digestion, precipitation, cation exchange chromatography by using Amberlite IRA120 resin, extraction chromatography by using TEVA resin to isolate the Nb and the gamma spectrometry to its measurement. The chemical yield was 70% in average. Samples of evaporator concentrate and spent resin were analyzed. For the samples of the evaporator concentrate, the results obtained were below L _D = 9.59 × 10^?4 Bq g^?1. For the spent resin an average result of 1.54 × 10² Bq g^?1 was obtained.     

Effect of dry density on 125I diffusion in GMZ bentonite

Gaomiaozi(GMZ) bentonite is regarded as the favorable candidate backfilling material for a potential repository in China.It is important to understand the diffusion behavior of 125 I in GMZ bentonite and compare the diffusion behavior in GMZ and other types of bentonite like MX-80,Avonlea,etc.Therefore,through-and out-diffusion experiments were conducted to obtain the effective diffusion coefficient(D e) and distribution coefficient(K d).A computer code named Fitting for diffusion coefficient(FDP) was used for the experimental data processing and theoretical modeling.At the dry density of GMZ bentonite from 1600-2000 kg/m 3,the D e values of 125 I were(2.4-20.4) × 10-12 m 2 /s and K d values were constants.At dry density above 1800 kg/m 3,the diffusion behaviors were almost the same,indicating that the anion exclusion was ineffective.Out-diffusion results showed that the species of 125 I may be changed during the diffusion processing.It was probably caused by some organic matters or reducing substances in GMZ bentonite.Since the main composition of bentonite is montmorillonite,similar diffusion parameters were obtained in GMZ and other types of bentonite.The relationship of D e and accessible porosity(acc) could be described by Archie’s law with exponent n = 1.2-2.8 for 125 I diffusion in bentonite,whereas n = 2.0 in GMZ bentonite.Furthermore,bentonite with the dry density of 1800 kg/m 3 was proposed as the backfilling materials used in the construction of high level radioactivity waste repository.     

Study of the 137Cs adsorption performance of ion-eroded cement

For this study, ion-eroded cement was prepared from the cement required for construction of middle- and low-level radioactive waste repositories in caves. The properties for adsorption of ¹³⁷Cs on cement before and after ion erosion were investigated. XRF, XRD, SEM–EDS and BET were used to analyse various cement materials. The effects of reaction time, solid–liquid ratio, initial radioactivity and different ions on adsorption were studied by static batch experiments. When the initial radioactivity was 1114.5 Bq L^?1 and the solid–liquid ratio was 5 g L^?1, the adsorption equilibrium time was 12 h. Adsorption of ¹³⁷Cs on ion-eroded cement was more effective than that on untreated cement. The adsorption process was consistent with the pseudosecond-order kinetic model and the Freundlich isotherm model, and the process involved multilayer chemisorption. This study provides basic research data for construction of a disposal repository.

     

Determination of indium in metallic tin and cadmium by substoichiometric neutron activation analysis

The paper deseribes the determination of indium in metallic tin and cadmium metals by the direct method, which is a variant of substoichiometric radioactivation analysis. It is based on substoichiometric extraction of indium diethyldithiocarbamate into carbon tetrachloride. Indium in tin metal was determined by^116mIn (T=54 min), while^115mIn (T=4.5 h), formed by the reaction¹¹⁴Cd(n, γ)¹¹⁵Cd was used for cadmium samples. The irradiated sample was dissolved and the radioactivity of^116mIn or^115mIn, A, was measured. After the separation of indium from the matrix, a known amount of indium, m, was separated substoichiometrically and the radioactivity, a, was measured. Indium was calculated as M_x=m A/a. If a known amount of the element, M, is added to the irradiated sample in advance, the equation for calculation is given as M_x-m A/a−M. By this method, indium can be determined without any consideration of self-shielding and secondary nuclear reaction of the matrix.     

Some aspects of radioactive contamination after Chernobyl accident in Romania

After the Chernobyl disaster, the radioactive cloud passage over Romania beginning with the April 30th, 1986 caused fall-out of different intensities in different regions.. The principal contributors to the radioactive exposure during the month of May and rest of 1986 were the short and medium half-live radionuclides: ¹³²Te+¹³²I, ¹³¹I, ¹⁴⁰Ba+¹⁴⁰La, ¹⁰³Ru+¹⁰³Rh, ¹⁰⁶Ru+¹⁰⁶Rh, ⁹⁵Zr+⁹⁵Nb, ¹³⁶Cs, ¹³⁴Cs, ¹⁴¹Ce, ¹⁴⁴Ce and ¹²⁵Sb. After four-five years only ¹³⁷Cs and ⁹⁰Sr remained significant radioactive contaminants. During May 1986 the grass was the mostly affected component of the environment and it contaminated rapidly the majority of foods. Measurements made on the daily gathered pollen samples and eggs during May 1986 clearly indicated that these samples can be used as bioindicators of radioactive contamination of the atmospheric air and, respectively, for soil and grass. Regarding soil contamination, the higher ^134+137Cs deposits in Romania following the northeast-southwest direction were measured, some of these being above 80 kBq/m². This direction is the same with the cloud passage over Romania during the first week of May 1986 and it was confirmed by measurements in the former Yugoslavia, Albania, Greece, and south of Italy.     

Alpha particle induced reactions on zirconium

Target foil stacks of zirconium were bombarded with beams of alpha particles at incident energies ≤55.0 MeV. Excitation functions for the production of^99mMo,⁹⁰Mo,^97gNb,⁹⁰Nb,⁹⁵Zr,⁹²Y,^90mY and⁸⁶Y were determined. On the basis of the cross sections, the thick target yields and saturation production rates of⁹⁵Zr have been evaluated. This work was partially supported by the International Atomic Energy Agency     

Sequential separation of <Superscript>99</Superscript>Tc, <Superscript>94</Superscript>Nb, <Superscript>55</Superscript>Fe, <Superscript>90</Superscript>Sr and <Superscript>59/63</Superscript>Ni from radioactive wastes

A sequential separation procedure has been developed for the determination of ⁹⁹Tc, ⁹⁴Nb, ⁵⁵Fe, ⁹⁰Sr and ^59/63Ni in various radioactive wastes generated from nuclear power plants. Ion exchange and extraction chromatography were adopted for individual separation of the radionuclides. Precipitation was supplementarily utilized for both purification of the individual radionuclides and preparation of the radionuclide sources for use in a radioactivity measurement. The chromatographic separation behavior of the radionuclides both from the sample matrix metals and from one another was investigated using stable metals, Re (as a surrogate of ⁹⁹Tc), Nb, Fe, Sr and Ni. The validity of the procedure for reliability and applicability was evaluated by measuring the recovery of the metal carriers added to synthetic radioactive waste solutions. The recoveries by the chromatographic separation were in the range of 84.8 to 102.2% with 2s of less than 8.6%, the recoveries by the precipitation being in the range of 84.3 to 97.3% with 2s of less than 10.9%.     

Determination of 94Nb in radioactive waste using ion exchange chromatography

This paper describes a rapid method of ⁹⁴Nb pre-concentration, separation and purification by using cation and anion exchange resins. The method is suitable for analyzing highly contaminated radioactive waste samples in a relatively short time and high decontamination factors. The use and effectiveness of the method was successfully tested by analysis of samples from nuclear reactor parts such as control rod drive shaft, shielding cassettes, neutron in-core measurement channels (KNI), pressure vessel construction material and fuel cassette construction material samples.     

Study of the state of95Zr+95Nb in aqueous solutions

The adsorption on paraffine and polyethylene and the paper chromatography in aqueous solutions in the pH range of 2–12 were used for the study of the behaviour of⁹⁵Zr and⁹⁵Nb. The effect of complexing ions (SO ₄ ^2? and CO ₃ ^2? ) was studied in the same pH range. The constants of hydrolysis and the composition of hydrolytic species of⁹⁵Zr in the solution containing sulphate ions were determined in the pH range of 1–2. The paper chromatography was used for the control of the purity of⁹⁵Zr after an extractive separation from⁹⁵Nb with α-benzoinoxime. The possibility of studying the extraction processes of Zr (without its previous separation from Nb) by reversed phase chromatography is shown. Conditions for the formation of polynuclear compounds of Zr and Nb and their influence on the extraction separation in nitrate media were studied.     

A radioactive tracer dilution method to determine the mass of molten salt

A new technique for molten salt mass determination, termed radioactive tracer dilution, that uses ²²Na as a tracer was validated at bench scale. It has been a challenging problem to determine the mass of molten salt in irregularly shaped containers, where a highly radioactive, high-temperature molten salt was used to process nuclear spent/used fuel during electrochemical recycling (pyro-processing) or for coolant/fuel salt from molten salt reactors. A radioactive source with known activity is dissolved into the salt. After a complete mixture, a small amount of the salt is sampled and measured in terms of its mass and radioactivity. By finding the ratio of the mass to radioactivity, the unknown salt mass in the original container can be precisely determined.

     

Cross-sections for formation of <Superscript>178m2</Superscript>Hf and <Superscript>179m2</Superscript>Hf through reactions on natural hafnium at neutron energy 14.8 ± 0.2 MeV

The cross sections for formation of metastable state of ¹⁷⁸Hf (^178m2Hf, 574.215 keV, 31 y) and ¹⁷⁹Hf (^179m2Hf, 362.55 keV, 25.05 d) through reactions induced by 14.8 ± 0.2 MeV neutrons on natural hafnium were measured for the first time. The monoenergetic neutron beam was produced via the ³H(d, n)⁴He reaction on ZF-300-II Intense Neutron Generator at Lanzhou University. Induced gamma activities were measured by a gamma-ray spectrometer with high-purity germanium (HPGe) detector. Measurements were corrected for gamma-ray attenuations, random coincidence (pile-up), dead time and fluctuation of neutron flux. The neutron fluence were determined by the cross section of ⁹³Nb(n, 2n)^92mNb reaction. The neutron energy in the measurement were by the cross section ratios of ⁹⁰Zr(n, 2n)^89m+gZr and ⁹³Nb(n, 2n)^92mNb reactions.     

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.     

Gamma-spektroskopisches Verfahren Zur Verfolgung von Zr−Hf-Trennungen

A quantitative γ-spectroscopic method for the persecution of Zr-Hf separation is described. The nuclides⁹⁵Zr and^175+181Hf are used as tracer. Difficulties caused by the presence of the radioactive daughter⁹⁵Nb are avoided by the application of a Ge(Li) detector. The simultaneous determination of Zr and Hf is possible over a wide range of concentration.      

Some problems of parametric neutron activation analysis based on the use of radioactive daughters of longer-lived mothers with low mother/daughter half-life ratios

The theoretical and practical aspects of the use of radioactive daughters originated from the decay of longer-lived radioactive mothers in parametric activation analysis, when the ratio: mother half-life to daughter half-life is less than 10, are discussed. The mother-daughter relationships: ⁴⁷Ca/⁴⁷Sc; ⁹⁵Zr/⁹⁵Nb; ¹⁴⁰Ba/¹⁴⁰La; ⁹⁹Mo/^99mTc and ¹¹⁵Cd/^115mIn are selected as models for the study. The cases when the radionuclide of interest is formed through both direct and indirect routes are also analyzed. As illustrative example, the direct reaction and the reaction chain: ⁴⁷Ti(n,p)⁴⁷Sc/⁴⁶Ca(n,γ)⁴⁷Ca(β⁻)⁴⁷Sc are evaluated with respect to the determination of the elements involved and their reciprocal interferences.     

New possibilities in isotope correlation analysis of spent nuclear fuel

Isotopic correlation analysis is believed to make possible quick and accurate determinations of nuclear fuel parameters for reactor operation, reprocessing, fuel management and nuclear safeguards. Correlation dependencies have been found between ratios of fission products on the one hand and isotope ratios of the heavy elements on the other hand. The use of the¹⁵⁴Eu/¹⁵⁵Eu ratio in correlation analysis was proposed by SMULEK. The scope of useful applications of this isotopic ratio has been further investigated. A quick and time-saving method to measure the¹⁵⁴Eu/¹⁵⁵Eu ratio has been elaborated. The atomic ratios have been found by internal calibration using the computer programme ABSINT. Beside this the atomic ratios of¹⁵⁴Eu/¹⁵⁵Eu as a function of nuclear fuel burn-up have been calculated using the computer programme ISOTOP. The correlation between the¹⁵⁴Eu/¹⁵⁵Eu ratio and nuclear fuel burn-up is best approximated by a quadratic function. Up to a burn-up of 1% fima a linear function can be used.