Estimation of burnup in the Oklo natural nuclear reactor from ruthenium isotopic composition

Estimation of burnup in the Oklo natural reactor was based on Ru isotopic abundances determined by thermal ionization mass spectrometry. Nearly all Ru in the samples is fissiogenic, and burnup values calculated from¹⁰¹Ru,¹⁰²Ru and¹⁰⁴Ru isotope abundances are in good agreement with each other. The conversion factor of²³⁸U to²³⁵U was also determined using Ru isotope abundances.     

Quantitative and isotopic analysis of released and retained krypton and xenon fission gases from irradiated metallic fuels

We quantitatively measured the amounts and isotopic distributions of the released and retained fission gases (Kr and Xe) from two irradiated metallic fuels (U–10Zr and U–10Zr–5Ce) at approximately 2.9 at.% burnup, using a gas chromatography and a quadrupole mass spectrometer. The obtained Xe/Kr ratios indicate that the released and retained fission gases from the irradiated metallic fuels came primarily from the fission of ²³⁵U, instead of that of heavy isotopes such as ²³⁹Pu and ²⁴¹Pu. The calculated (⁸³Kr + ⁸⁴Kr)/⁸⁶Kr and (¹³¹Xe + ¹³²Xe)/¹³⁴Xe ratios suggest that no fuel rods became defective during the irradiation process.     

Isotopenkorrelationen Mit Gammaaktiven Spaltprodukten für die Kernmaterialkontrolle von WWER-Brennstoff

Linear correlations between burnup, Pu/U- and U₅/U₀-ratios on the one hand and¹⁵⁴Eu/¹³⁷Cs or¹³⁴Cs/¹³⁷Cs ratios on the other hand have been proved to exist in the case of spent WWER fuel. The possibility of using such correlations for safeguards to determine the²³⁵U and Pu content of fuel assemblies has been demonstrated. The results agree well with theoretical calculations using the COFIP and COHN codes.      

Cumulative yields of short-lived ruthenium isotopes in the thermal neutron induced fission of233U,235U and239Pu

Cumulative yields of short-lived ruthenium isotopes in the thermal neutron induced fission of²³⁵U,²³⁵U and²³⁹Pu have been determined using a fast radiochemical separation technique followed by gamma spectrometry. The cumulative yields of¹⁰⁷Ru and¹⁰³Ru in²³³U (n_th, f) and¹⁰⁷Ru and¹⁰⁹Ru in²³⁹Pu (n_th, f) are determined for the first time. The measured cumulative yields are converted to chain yields assuming normal charge distribution systematics for comparison with the literature data on chain yields.     

Determining the isotopic compositions of uranium and fission products in radioactive environmental microsamples using laser ablation ICP–MS with multiple ion counters

This paper presents the application of a multicollector inductively coupled plasma mass spectrometer (MC–ICP–MS)—a Nu Plasma HR—equipped with three ion-counting multipliers and coupled to a laser ablation system (LA) for the rapid and sensitive determination of the ²³⁵U/²³⁸U, ²³⁶U/²³⁸U, ¹⁴⁵Nd/¹⁴³Nd, ¹⁴⁶Nd/¹⁴³Nd, ¹⁰¹Ru/(⁹⁹Ru+⁹⁹Tc) and ¹⁰²Ru/(⁹⁹Ru+⁹⁹Tc) isotope ratios in microsamples collected in the vicinity of Chernobyl. Microsamples with dimensions ranging from a hundred μm to about 1 mm and with surface alpha activities of 3–38 mBq were first identified using nuclear track radiography. U, Nd and Ru isotope systems were then measured sequentially for the same microsample by LA–MC–ICP–MS. The application of a zoom ion optic for aligning the ion beams into the ion counters allows fast switching between different isotope systems, which enables all of the abovementioned isotope ratios to be measured for the same microsample within a total analysis time of 15–20 min (excluding MC–ICP–MS optimization and calibration). The ¹⁰¹Ru/(⁹⁹Ru+⁹⁹Tc) and ¹⁰²Ru/(⁹⁹Ru+⁹⁹Tc) isotope ratios were measured for four microsamples and were found to be significantly lower than the natural ratios, indicating that the microsamples were contaminated with the corresponding fission products (Ru and Tc). A slight depletion in ¹⁴⁶Nd of about 3–5% was observed in the contaminated samples, but the Nd isotopic ratios measured in the contaminated samples coincided with natural isotopic composition within the measurement uncertainty, as most of the Nd in the analyzed samples originates from the natural soil load of this element. The ²³⁵U/²³⁸U and ²³⁶U/²³⁸U isotope ratios were the most sensitive indicators of irradiated uranium. The present work yielded a significant variation in uranium isotope ratios in microsamples, in contrast with previously published results from the bulk analysis of contaminated samples originating from the vicinity of Chernobyl. Thus, the ²³⁵U/²³⁸U ratios measured in ten microsamples varied in the range from 0.0073 (corresponding to the natural uranium isotopic composition) to 0.023 (corresponding to initial ²³⁵U enrichment in reactor fuel). An inverse correlation was observed between the ²³⁶U/²³⁸U and ²³⁵U/²³⁸U isotope ratios, except in the case of one sample with natural uranium. The heterogeneity of the uranium isotope composition is attributed to the different burn-up grades of uranium in the fuel rods from which the microsamples originated. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Non-destructive determination of nuclear fuel burn-up by measuring the gamma radiation of fission products in irradiated uranium oxide

The burn-up of²³⁵U was determined in two uranium oxide samples (0.713 and 89.9%²³⁵U in mixture) irradiated simultaneously with a cobalt monitor, from the amounts of⁹⁵Zr,¹⁰³Ru,¹³⁷Cs,¹⁴⁰Ba and¹⁴⁴Ce obtained by measuring the intensities of the corresponding gamma radiations. The samples were irradiated for 23 days, and the fission products were measured after cooling for 100 days, nondestructively, by means of a Ge(Li) spectrometer. The integrated neutron flux was determined by measuring the produced⁶⁰Co in the cobalt monitor. The burn-up in both samples was determined by measuring the intensity of eight gamma energies (0.5–1.6 MeV). The determined values are in good agreement. The standard deviation of the mean value ( ) is 5%. The atom per cent fission of²³⁵U in both samples, calculated according to , differs by 1%. The measured σ _f for²³⁵U is in good agreement with the data reported in the literature.     

The determination of fission products in irradiated uranium by electrophoretic focussing of ions

Electrophoretic focussing of ions was applied to the separation of fission products present in solutions of nuclear uranium fuel irradiated in various European reactors. By combining two separation methods, all the long-lived fission products could be determined individually and quantitatively by counting with a NaI(T1) and a GM detector of known detection efficiency. Radiography and autoradiography were used for semi-quantitative purposes. The concentrations of²³⁵U and²³⁸U were determined from a short post-irradiation of the fuel solution and counting of¹⁴⁰Ba−¹⁴⁰La and²³⁹Np, respectively. An iterative calculus method is presented which allows calculation of the irradiation history of the fuel solution from the above analyses. without any a priori knowledge.     

Uranium series disequilibrium in the coastal surface sediments and sea water of the Arabian Sea

Nearshore surface sediments from various locations of the West Coast of India were leached by saturated ammonium carbonate solution for the extraction of uranium isotopes. The reagent chosen was found to have high efficiency for leaching uranium isotopes without attacking the mineral core of the sediment particle. The activity ratios of²³⁴U/²³⁸U are in the range of 1.11 to 1.14 and the activity ratios of²³⁵U/²³⁵U are in the range of 0.045 to 0.047. The respective activity ratios in leachates, and residues after removal of surface organic matter from the sediment particles by treatment with hydrogen peroxide and 0.05M HCl, revealed disequilibrium between²³⁸U and²³⁴U only in the surface organic matter. The activity ratios of²³⁴U/²³⁸U and²³⁵U/²³⁸U have also been determined in some seawater samples from the Arabian Sea.     

Determination of isotopic ratios of osmium and ruthenium in meteorites by pretreatment and radiochemical neutron activation analysis

The isotopic abundance ratios of¹⁹⁰Os/¹⁸⁴Os and⁹⁶Ru/¹⁰²Ru for the metal phases of the Jilin and Taonan stone meteorites were determined by pretreatment and radiochemical neutron activation analysis. All experimental factors affecting Os and Ru isotopic ratios were discussed, including sampling, standard, irradiation, separation and counting. The statistical errors of measurement for the¹⁹⁹Os/¹⁸⁴Os ratio can be controlled within 1%. The experimental results indicate that the statistically significant anomalies of the¹⁹⁰Os/¹⁸⁴Os and⁹⁶Ru/¹⁰²Ru ratios have not been found relative to the terrestrial Os and Ru standards.     

Neptunium distribution in a high acid first cycle Purex Process

This work deals with the extraction behavior of neptunium in a high acid Purex Process. The composition of PWR fuel type with 3.2% enrichment, 500 MWd/t burn-up and 100 d cooling time was considered. Two consecutive cold runs were performed in a mock-up facility at IPEN-CNEN/SP with simulated feed solutions containing: 3M HNO₃; 1M U; 455 g²³⁷Np labeled with²³⁹Np; 15 mg Zr l^–1, 12 mg Ce l^–1, 7 mg Ru l^–1 and 13 mg Mo l^–1 traced with active isotopes⁹⁵Zr,¹⁴¹Ce,¹⁰³Ru and⁹⁹Mo as FP. A 30 vol% TBP/n-dodecane was used as solvent. Countercurrent experiments were carried out using two 16 stages plexiglass mixer-settlers, at 25°C, during 21 h continuous operation, with O/A ratio of 2 in the extraction section and 9 and 13 in the 1st and 2nd scrubbing sections, respectively. For a 65% organic loading, ca. 77% of neptunium remains in the waste stream, without any Np valence adjustment.     

Uncertainty of decay heat calculations originating from errors in the nuclear data and the yields of individual fission products

The calculation of the abundance pattern of the fission products with due account taken of feeding from the fission of²³⁵U,²³⁸U, and²³⁹Pu, from the decay of parent nuclei, from neutron capture, and from delayed-neutron emission is described. By means of the abundances and the average beta and gamma energies the decay heat in nuclear fuel is evaluated along with its error derived from the uncertainties of fission yields and nuclear properties of the individual fission products.     

Combined gamma and passive X-ray fluorescent measurement of235U enrichment and U-total concentration

A new combined single step gamma-spectrometric and passive X-ray fluorescent measurement method and a corresponding procedure have been developed. Only one gamma-X-ray spectrometric measurement is required in order to determine both²³⁵U enrichment and U-total concentration of the measured sample. In this way, if the sample is homogeneous and weighted, the total quantities of U-total and²³⁵U can be determined. The main advantages of this approach over the enrichment measurement method used are: (1) the U-concentration of the measured material is determined; (2) the²³⁵U enrichment is determined more reliably and accurately. The matrix of the material, which influences the enrichment measurement, is also determined and taken into account.     

Anomalous behaviour of uranium isotopes in backwater sediments of Zuari river

The surface leaching of the labile component of uranium has been carried out in estuarine sediments of Zuari river in Goa. The measurements of alpha activities of²³⁸U,²³⁵U and²³⁴U in the leachates indicated a remarkable anomaly between the activities of²³⁸U and²³⁴U. The activity ratios of²³⁴U/²³⁸U in these leachates have been found to be in the range of 1.10 to 1.14. However, the activity ratios of²³⁵U/²³⁸U have been found to be 0.045 which is close to that in natural uranium. It has also been observed that the anomaly between²³⁸U and²³⁴U exists only on the surface organic layers of the backwater sediments of the Zuari river.     

Determination of234U/238U and235U/238U ratios from commercially available uranium compounds by α-spectrometry

The²³⁴U/²³⁸U and²³⁵U/²³⁸U ratios from uranium compounds by -spectrometry technique have been obtained. Ten commercially available uranium reagents were analyzed. The well-separated peaks corresponding to uranium isotopes are evident, providing an energy spectrum of the -particles of uranium isotopes. It was found that some commerical uranium salts were depleted in²³⁴U and²³⁵U.     

Determination of U/U atom ratio in uranium samples using liquid scintillation counting (LSC)

A correlation has been developed for the determination of ²³⁵U/²³⁸U atom ratio in uranium samples using liquid scintillation counting (LSC). The ²³⁵U/²³⁸U atom ratio determined by thermal ionization mass spectrometry (TIMS) was correlated to the ratio of (i) α-count rate and (ii) Cerenkov count rate due to ^234mPa in the sample; both measured by LSC. This correlation is linear over the range of ²³⁵U/²³⁸U atom ratio encountered in the nuclear fuel samples, i.e. the low enriched uranium (LEU) samples with ²³⁵U < 20 atom%. The methodology based on this correlation will be useful for the quick determination and verification of ²³⁵U/²³⁸U atom ratios in fuel samples using cost effective technique of LSC.     

Determination of the balance of the nuclear reactor fuel burn-out process by gamma-spectrometry of fission products III

The possibility for the determination of heavy water reactor fuel burn-up on the basis of gamma-spectrometric measurements of the activity quotients¹⁰⁶Ru/¹³⁷Cs and¹³⁴Cs/¹³⁷Cs has been experimentally investigated. The investigation has been carried out on the non-enriched uranium metal fuel of the Czechoslovak Nuclear Power Plant Al. A spectrometer with germanium detector has been used for spectrum analysis of the irradiated fuel gamm-radiation. Burn-up has been determined (1) by the applied here procedure, and (2) from the results of mass-spectrometric determination of the isotopic composition and content of U, Pu and Nd. Two groups of the values obtained have been compared and the influence of the errors of the measured activity quotients on the established deviations has been evaluated.     

Anomalous behaviours of protactinium in the acid-leaching experiments on pitchblende

A series of leaching experiments with H₂O, HCl, HNO₂ and HF were carried out on a sample of pitchblende from Africa. Anomalously high²³¹Pa/²³⁵U ratios, which were not accompanied by similar enhancements of²³⁴U/²³⁸U and²³⁵U/²³⁸U ratios, were observed in some uranium fractions. The observed²³¹Pa/²³⁵U ratios varied between the values of 0.035±0.005 and 2,000±300 (Ci/Ci). These results are interpreted as due, primarily, to the difference in the chemical properties of protactinium and uranium, rather than to the alpha-recoil effects.     

Limit of the INAA procedure for copper determination based on the64Cu 511 keV line

The²³⁵U/²³⁸U ratio is determined by neutron activation analysis counting the ϕ-rays of short half-lives fission products and²³⁹U. The effect of the neutron spectrum hardening using a⁶LiD converter is also demonstrated. The²³⁵U/²³⁸U ratio is determined using short irradiation, waiting and counting times.     

Importance of double neutron-capture as a second-order reaction interference in NAA

In order to estimate gut absorption by determining tracer concentration in plasma, a technique based on the administration of two stable isotopes of the same element was combined with proton activation analysis. The optimization for the determination of Zr isotopes in biological samples is presented together with the results of a preliminary study on Zr biokinetics in animals. (p,n) reactions on⁹⁰Zr and⁹⁶Zr resulted the most convenient. The obtained minimum detectable quantities are 3 and 2 ng/ml plasma, respectively, for⁹⁰Zr and⁹⁶Zr. Zr plasma clearance and Zr response to a simple oral test were studied separately in different subjects by using the natural Zr solution. The data analysis was performed measuring the concentration of⁹⁰Zr to obtain indication on the time behavior and fractional level of Zr appearance in plasma depending on the administration routes. Two rabbits were intravenously injected 50 g⁹⁰Zr and a third rabbit was orally given 2.5 mg of⁹⁰Zr. Concentration in plasma samples of intravenously and orally given Zr isotopes are reported, as a function of time after administration. The injected tracer concentration relative to the first two rabbits were fitted simultaneously to obtain clearance parameters. Zr intestinal absorption is evaluated to be less than 0.2%. The work confirms that proton activation is a powerful tool for biokinetic studies with stable isotopes.     

Uranium fallout from the nuclear-powered satellites and volcanic eruptions

Increasing trends of the concentrations of²³⁴U,²³⁵U and²³⁸U in rain observed during the period between April 1984 and June 1985 at Fayetteville (36°N, 94°W), Arkansas, and peak concentrations of²³⁴U and²³⁵U observed in a number of rain samples collected during the months of May and June 1985 appear to be the effects of delayed fallout from the 1982 eruption of El Chichón volcano and the 1983 fall of the nuclear-powered satellite Cosmos-1402, respectively.This investigation was supported by the National Science Foundation under Grant ATM 84-07618.