Measurements of thermal-neutron capture cross-section and resonance integral of neptunium-237

The thermal-neutron capture cross-section (σ₀) and resonance integral (I₀) were measured for the ²³⁷Np(n,γ) ²³⁸Np reaction by an activation method. A method with a Gadolinium filter, which is similar to the Cadmium difference method, was used to measure the σ₀ with paying attention to the first resonance at 0.489 eV of ²³⁷Np, and a value of 0.133 eV was taken as a cut-off energy. Neptunium-237 samples were irradiated at the pneumatic tube of the Kyoto University Research Reactor in Institute for Integral Radiation and Nuclear Science, Kyoto University. Wires of Co/Al and Au/Al alloys were used as monitors to determine thermal-neutron fluxes and epi-thermal Westcott’s indices at an irradiation position. A γ-ray spectroscopy was used to measure activities of ²³⁷Np, ²³⁸Np and neutron monitors. On the basis of Westcott’s convention, the σ₀ and I₀ values were derived as 186.9 ± 6.2 barn, and 1009 ± 90 barn, respectively.     

Thermal-Neutron Capture Cross Section and Resonance Integral of Americium-241

The thermal-neutron capture cross section (σ_0;g) and the resonance integral (I _0,g) leading to the ground state of 242Am were measured by an activation method for neutron capture by²⁴¹ Am. A method with gadolinium, which was similar to the cadmium difference method, was used to measure the cross section σ_0;g with attention to resonances of²⁴¹ Am. Americium chloride samples containing²⁴¹ Am radioisotope were irradiated for 68 h in the long-irradiation plug of the Kyoto University Research Reactor, KUR. Wires of Co/Al and Au/Al alloys were used as monitors to determine thermal-neutron fluxes and epithermal Westcott's indexes at the irradiation positions. An α-ray spectrometer was used to measure the activity ratios of²⁴² Cm to²⁴¹ Am. On the basis of Westcott's convention, the σ_0;g and I _0,g values were determined as 628 ± 22 b and 3:5 ± 0:3 kb, respectively.     

Measurement of thermal neutron cross-sections and resonance integrals for Hf(n,γ)Hf and Hf(n,γ)Hf reactions at the Pohang neutron facility

The thermal-neutron cross-sections and the resonance integrals for the ¹⁷⁹Hf(n,γ)^180mHf and the ¹⁸⁰Hf(n,γ)¹⁸¹Hf reactions have been measured by the activation method. The high purity Hf and Au metallic foils within and without a Cd shield case were irradiated in a neutron field of the Pohang neutron facility. The gamma-ray spectra from the activated foils were measured with a calibrated p-type high-purity Ge detector.In the experimental procedure, the thermal neutron cross-sections, σ₀, and resonance integrals, I₀, for the ¹⁷⁹Hf(n,γ)^180mHf and the ¹⁸⁰Hf(n,γ)¹⁸¹Hf reactions have been determined relative to the reference values of the ¹⁹⁷Au(n,γ)¹⁹⁸Au reaction, with σ₀ = 98.65 ± 0.09 barn and I₀ = 1550 ± 28 barn. In order to improve the accuracy of the experimental results, the interfering reactions and necessary correction factors were taken into account in the determinations. The obtained thermal neutron cross-sections and resonance integrals were σ₀ = 0.424 ± 0.018 barn and I₀ = 6.35 ± 0.45 barn for the ¹⁷⁹Hf(n,γ)^180mHf reaction, and σ₀ = 12.87 ± 0.52 barn and I₀ = 32.91 ± 2.38 barn for the ¹⁸⁰Hf(n,γ)¹⁸¹Hf reaction. The present results are in good agreement with recent measurements.     

Measurement of Thermal Neutron Capture Cross Section and Resonance Integral of the Reaction 133Cs(n, γ)134m,134gCs

The measurements of the thermal neutron (2,200 m/s neutron) cross section (σ₀) and the resonance integral (I ₀) of the ¹³³Cs(n, γ;) reaction were performed by an activation method to obtain fundamental data for research on the transmutation of nuclear wastes. The cross sections for the formations of the isomeric state ^134mCs and the ground state ^134mCs were measured respectively by following the behavior of the γ-ray counting rate after the irradiation.

The thermal neutron capture cross sections and the resonance integrals of the ¹³³Cs(n, γ) reaction were determined to be 2.70±0.13 b and 23.2±1.8 b for the formation of the isomeric state ^134mCs, and 26.3±1.0 b and 275±16 b for the formation of the ground state of ^134gCs. The results for the reaction ¹³³Cs(n, γ)^134m+gCs were 29.0±l.0 b and 298±16 b, respectively. As for the thermal neutron capture cross section for the formation of ^134m+gCs, the evaluated value (29.00 b) of JENDL-3.2 agreed with the present result. The reported value by Baerg et al. was in good agreement with the present result within the limits of error on the thermal neutron capture cross section for ^134mCs. On the other hand, the resonance integral for ^134m+g Cs was 32% smaller than the experimental value by Steinnes et al.     

Investigation of excitation functions of alpha induced reactions on Xe: Production of the therapeutic radioisotope Cs

Excitation functions were measured for alpha-particle induced nuclear reactions on natural xenon leading to the formation of the radionuclides ^{129m(rel),129g,131m,131mg,133m,135m,137m,139cum}Ba and ^{129cum,130mg,132,134m,135m,136mg,138mg}Cs from the respective thresholds up to 40 MeV. No earlier experimental cross section data were found in the literature. The experimental data were compared to and analyzed with the results of the theoretical model code ALICE-IPPE. The feasibility of the production of the therapeutic radioisotope ¹³¹Cs by using gas target technology was investigated. Comparison of reactor and cyclotron production routes of ¹³¹Cs was given.     

Neutron Resonance Parameters of Ba-135, Ba-137 and Ba-138

Neutron transmission measurements were carried out on the separated isotopes of Ba at the JAERI electron linac. Resonance energies and neutron widths were determined for a large number of resonances in the neutron energy range from 400 eV to 4.6 keV for ¹³⁵Ba, 15 keV for ¹³⁷Ba and 63 keV for ¹³⁸Ba. Many of these resonances were newly observed in this experiment. The s-wave strength functions obtained are S ₀= (1.33±0.22) x ^10-4 for ¹³⁵Ba, and S ₀= (0.51±0.12) x ^10-4 for ¹³⁷Ba. An apparent energy dependence of the strength function was observed for ¹³⁵Ba. New resonance parameters of ¹³⁸Ba were also obtained for several weak P-wave levels.     

Measurement of Resonance Activation Integral of 55Mn

The resonance activation integral of ⁵⁵Mn was measured relatively to that of ¹⁹⁷Au by absolute counting on ⁵⁶Mn and ¹⁹⁸Au: ⁵⁶Mn was measured with a Ge(Li) counter whose detecting efficiency for γ-rays had been previously determined by a set of IAEA calibrated γ-sources, while ¹⁹⁸Au was measured with a 4πβ-γ coincidence counter. The neutron spectrum was determined by p ₁ calculation and was verified by time-of-flight method.

The ratio I _1/v/I _res was obtained experimentally making use of boron filters of three different thicknesses.

The results were I _total= 14.1±0.6 barn and I _1/v/I _res =0.57±0.06, for a cutoff energy of 0. 63 eV.     

Analysis of cesium isotope compositions in environmental samples by thermal ionization mass spectrometry – 1. A preliminary study for source analysis of radioactive contamination in Fukushima prefecture

Cesium was recovered from plant samples obtained from Fukushima prefecture. The isotopic ratios of ¹³⁴Cs/¹³⁷Cs and ¹³⁵Cs/¹³⁷Cs were analyzed by thermal ionization mass spectrometry with a single filament method using a TaO activator. Samples containing 5 Bq of ¹³⁷Cs were analyzed with typical analytical errors of approximately 0.5% for ¹³⁴Cs/¹³⁷Cs and approximately 0.1% for ¹³⁵Cs/¹³⁷Cs. Measurements of both ratios showed profiles that were characteristic of the measurements of among other environmental samples reported in the literature. The results showed the isotopic ratios of ¹³⁴Cs/¹³⁷Cs and ¹³⁵Cs/¹³⁷Cs were applicable for the source analysis of radioactive Cs in Fukushima prefecture.     

Analysis of cesium isotope compositions in environmental samples by thermal ionization mass spectrometry-3

Cesium was recovered from soil samples obtained in Fukushima prefecture. Isotopic analysis of Cs was performed by γ-spectrometry to determine the activity ratio of ¹³⁴Cs/¹³⁷Cs and thermal ionization mass spectrometry was used to determine the isotopic ratios of ¹³³Cs/¹³⁷Cs and ¹³⁵Cs/¹³⁷Cs. The analytical results showed that both the activity ratio of ¹³⁴Cs/¹³⁷Cs and the isotopic ratio of ¹³⁵Cs/¹³⁷Cs were within the expected values for the Fukushima Daiichi Nuclear Power Plant estimated using the ORIGEN-II code, suggesting that most of the radioactive Cs in the soil sample originated from the Fukushima Daiichi Nuclear Power Plant. The concentration of ¹³⁷Cs and the contribution of radioactive Cs from global fallout were correlated to the distance from the Fukushima Daiichi Nuclear Power Plant, while the contribution of radioactive Cs from each reactor did not show any similar distance dependence.     

Determination of 79Se and 135Cs in Spent Nuclear Fuel for Inventory Estimation of High-Level Radioactive Wastes

⁷⁹Se and ¹³⁵Cs are long-lived fission products and are found in high-level radioactive waste (HLW). The estimation of their inventories in HLW is essential for the safety assessment of geological disposal, owing to their mobility in the strata. In this study, the amounts of ⁷⁹Se and ¹³⁵Cs in a spent nuclear fuel solution were measured. About 5 g of irradiated UO₂ fuel discharged from a commercial Japanese pressurized water reactor (PWR) with a burn-up of 44.9 GWd/t was sampled and dissolved with 50mL of 4M nitric acid in a hot cell for 2 h. After Se and Cs were chemically separated, the amounts of ⁷⁹Se and ¹³⁵Cs in the spent nuclear fuel solution were measured by inductively coupled plasma quadrupole mass spectrometry (ICP-QMS). The amounts of ⁷⁹Se and 135Cs were 5:2 ± 1:5 and 447 ± 40 g/MTU, respectively. The results presented in this study, which are the first postirradiation experimental data in Japan, showed good agreement with those obtained by the ORIGEN2 code using the data library of JENDL-3.3.     

Radiochemical Application of “Iron Ferrocyanide-Anion Exchange Resin”

Preparation of iron ferrocyanide-anion exchange resin and adsorption of ¹³⁷Cs on the resin are described.

The resin was found to effectively adsorb ¹³⁷Cs from concentrated nitric acid solution, contrast to the negative results previously obtained with copper ferrocyanide-anion exchange resin.

A discussion is given of the possibility of applying the iron resin to the removal of ¹³⁷Cs from fuel reprocessing waste solution.

Fission products were effectively separated from each other with a column of this resin, utilizing the properties possessed by it of both iron ferrocyanide and the parent ion exchange resin.     

Measurement of Thermal Neutron Capture Cross Section and Resonance Integral of the 237Np(n, γ)238Np Reaction

The thermal neutron capture cross section (σ₀) and the resonance integral (I ₀)of ²³⁷Np have been measured by an activation method to supply basic data for the study of transmutation of nuclear waste. The neutron irradiation of ²³⁷Np samples have been done at the Research Reactor Institute, Kyoto University (KUR). Samples of ²³⁷Np were irradiated between two Cd sheets or without a Cd sheet. Since ²³⁷Np has a strong resonance at the energy of 0.49 eV, the Cd cutoff energy was adjusted at 0.358 eV (thickness of the Cd sheets: 0.125 mm). A high purity Ge detector was employed for activity measurement. The reaction rate to produce ²³⁸Np from ²³⁷Np was analyzed by the Westcott's convention. Results obtained were 141.7±5.4 barns for σ₀ and 862±51 barns for I ₀ above 0.358 eV of ²⁷³Np. By setting the Cd cut-off energy at 0.358 eV considering the resonance at 0.49 eV, a smaller value of σ₀ was obtained in this work than the values reported by the previous authors.     

Basic Study of 137Cs Sorption on Soil

Abstract

The sorption of ¹³⁷Cs by soil simulated from its main compositions of clay (Ca-saturated bentonite), organic matter (humic acid) and sand, as well as their relative contributions have been studied. All these sorbents revealed linear sorption isotherm under the initial concentration ranging from 10^?12 to 10^?10 mol/l of ¹³⁷Cs. Therefore, surface phenomena, adsorption and/or ion exchange, dominate the sorption of ¹³⁷Cs on soil.

In the experiments of mixed sorbents, humic acid was added to a mixture of bentonite and standard sand. It was found that distribution coefficient K _d decreased nonlinearly with the weight fraction of humic acid. The conclusion was that some sorption sites of bentonite were blocked by humic acid. A model using a block function with an exponential form was proposed as a means to explain the phenomena observed in this experiment. Such phenomena should be taken into account when assessing or selecting the disposal site of radwaste.     

Validation of 134Cs, 137Cs and 154Eu single ratios as burnup monitors for ultra-high burnup UO2 fuel

A measurement station has been built for the non-destructive investigation of burnt fuel rod segments through high-resolution gamma spectrometry. Four UO₂ pressurised water reactor fuel rod segments with different burnup levels between 50 and >100 GWd/t and ⩽10 year cooling time have been experimentally characterised using gamma-ray spectrometry to determine ¹³⁴Cs, ¹³⁷Cs and ¹⁵⁴Eu and their corresponding concentration ratios. Experimental errors of ∼2% (1σ) for the ¹³⁴Cs/¹³⁷Cs ratio were obtained for most of the segments. In parallel, pin cell depletion calculations have been performed for each segment using the deterministic code CASMO-4. Measured and calculated ratios have then been compared with the purpose of deriving and validating pin-averaged single-ratio burnup indicators for very high burnups. It is shown that the ¹³⁴Cs/¹³⁷Cs ratio, frequently used as a burnup monitor, is considerably less precise for values exceeding 50 GWd/t; discrepancies of ∼16% are found between measured and calculated values, increasing with burnup up to ∼23%. The ratios built with the ¹⁵⁴Eu concentration show even much larger discrepancies, essentially because this isotope is rather poorly predicted as revealed by just using different basic cross section data.     

Assessment of <Superscript>137</Superscript>Cs decontamination of concrete by the reagent method

The particulars of radioactive contamination of concrete wastes by ¹³⁷Cs were studied. x-Ray phase analysis and chemical analysis show that clayey materials, including Al₂O₃, Fe₂O₃, K₂O, and MgO, on which ¹³⁷Cs sorption is possible, were present in the concrete wastes. The content and form in which ¹³⁷Cs was found in radioactive concrete wastes from nuclear power facilities as well as in model samples were determined. When the wastes were treated with nitric acid the binder dissolved and a polydisperse suspension formed. The suspension consisted of three phases: solution, fine suspension, and rapidly settling precipitate of heavy filler particles. x-Ray phase analysis was performed and the ¹³⁷Cs mass ratio and distribution in the phases were determined. The possibility of decontaminating the concrete by a reagent method was evaluated.     

Study on the LLFPs transmutation in a super-critical water-cooled fast reactor

The performance of the super-critical water-cooled fast reactor (Super FR) for the transmutation treatment of long-lived fission products (LLFPs) was evaluated. Two regions with the soft neutron spectrum, which is of great benefit to the LLFPs transmutation, can be utilized in the Super FR. First region is in the blanket assembly due to the ZrH_1.7 layer which was utilized to slow down the fast neutrons to achieve a negative void reactivity. Second region is in the reflector region of core like other metal-cooled fast reactors. The LLFPs selected in the transmutation analysis include ⁹⁹Tc, ¹²⁹I and ¹³⁵Cs discharged from LWR or fast reactor. Their isotopes, such as ¹²⁷I, ¹³³Cs, ¹³⁴Cs and ¹³⁷Cs were also considered to avoid the separation. By loading the isotopes (⁹⁹Tc or ¹²⁷I and ¹²⁹I) in the blanket assembly and the reflector region simultaneously, the transmutation rates of 5.36%/GWe year and 2.79%/GWe year can be obtained for ⁹⁹Tc and ¹²⁹I, respectively. The transmuted amounts of ⁹⁹Tc and ¹²⁹I are equal to the yields from 11.8 and 6.2 1000 MWe-class PWRs. Because of the very low capture cross section of ¹³⁵Cs and the effect of other cesium isotopes, ¹³⁵Cs was loaded with three rings of assemblies in the reflector region to make the transmuted amount be larger than the yields of two 1000 MWe-class PWRs.Based on these results, ⁹⁹Tc and ¹²⁹I can be transmuted conveniently and higher transmutation performance can be obtained in the Super FR. However, the transmutation of ¹³⁵Cs is very difficult and the transmuted amount is less than that produced by the Super FR. It turns out that the transmutation of ¹³⁵Cs is a challenge not only for the Super FR but also for other commercial fast reactors.     

Estimation of the inventory of the radioactive wastes in Fukushima Daiichi NPS with a radionuclide transport model in the contaminated water

Quantification of the radioactive waste inventory remaining inside the reactors at Fukushima Daiichi NPS is necessary to effectively plan their recovery, treatment, and disposal. Analysis of radionuclide concentrations and secondary wastes in the contaminated water treatment system can provide a means to estimate the radioactive waste inventory, which is not possible by more direct methods due to problems of accessibility and high levels of radiation. A predictive model has therefore been developed to estimate the radioactive waste inventory from the radionuclide concentrations and throughputs in the contaminated water. Model fitting has enabled the estimation of the key parameters, such as the initial radionuclide concentration C₀, the continuous release rate F, and inventory of source of continuous release I_S0. An estimated one-third of the total ¹³⁷Cs inventory has already made its way into the water treatment system as secondary wastes, whereas half still remains inside the damaged reactors as of 13 March 2014.     

Estimation of Total Amounts of Anthropogenic Radionuclides in the Japan Sea

We estimated the total amounts of anthropogenic radionuclides, consisting of ⁹⁰Sr, ¹³⁷Cs, and ^239+240 Pu, in the Japan Sea for the first time based on experimental data on their concentrations in seawater and seabed sediment. The radionuclide inventories in seawater and seabed sediment at each sampling site varied depending on the water depth, with total inventories for ⁹⁰Sr, ¹³⁷Cs, and ^239+240Pu in the range of 0.52–2.8 kBq m^?2, 0.64--4.1 kBqm^?2, and 27-122Bqm^?2, respectively. Based on the relationship between the inventories and the water depths, the total amounts in the Japan Sea were estimated to be about 1:2 ± 0:4PBq for ⁹⁰Sr, 1:8 ± 0:7PBq for ¹³⁷Cs, and 69 ± 14TBq for ^239+240Pu, respectively; the amount ratio, ⁹⁰Sr:¹³⁷Cs:^239+240Pu, was 1.0:1.6:0.059. The amounts of ⁹⁰Sr and ¹³⁷Cs in the Japan Sea were in balance with those supplied from global fallout, whereas the amount of ^239+240Pu exceeded that supplied by fallout by nearly 40%. These results suggest a preferential accumulation of the plutonium isotopes. The data used in this study were obtained through a wide-area research project, named the “Japan Sea expeditions (phase I),” covering the Japanese and Russian exclusive economic zones.     

Measurement of the thermal-neutron-induced fission cross-section of 238U

The thermal-neutron-induced fission cross-section of ²³⁸U was measured at an intense and very clean thermal-neutron beam of the Grenoble high-flux reactor. The best ²³⁸U sample material used contained only 12 ppb of ²³⁵U. The fission fragments were detected with surface barrier detectors. Relative to a thermal fission cross-section of 587.6 barn for ²³⁵U, a value of (11 ± 2) μbarn was obtained for the ²³⁸U fission cross-section. By comparing this result with ²³⁸U(n, f) measurements in the resonance region, the existence of a negative resonance or resonances in ²³⁹U is demonstrated.