Fission Product Decay Research Articles

90Sr/137Cs ratios in soil of epicentral zones of «Experimental Field» testing site of Semipalatinsk Test Site

The paper presents the results of 90Sr/137Cs isotopic ratios in the soil surface layer in the venues of surface and atmospheric nuclear tests at the territory of the «Experimental Field » site of the Semipalatinsk Test Site. One of the main factors in the radiation impact of a nuclear explosion on the environment is the decay of fission products. The determination of 137Cs activity in soil is carried out by accurate, rapid and sufficiently cheap gamma-spectrometric method, while the existing methods of determining 90Sr activity are quite problematic: they either have sufficiently high detection limits or are time-consuming. As an alternative method, 90Sr activity can be determined using its correlation dependence with 137Cs activity. According to the literature, each test has its own fission product ratio, depending on the nuclear charge. As a result of the conducted research it was revealed that one epicenter is located at the technical site P-1, the ratio of 90Sr/137Cs is equal to 4,8; at the technical site P-3 - 2 epicenters, the ratio of 90Sr/137Cs is equal to 0,8 and 0,9; at the technical site P-5 - 6 epicenters, the ratio of 90Sr/137Cs is in the range of 0,9-2,1; at the technical sites P-2, P-7 - 19 epicenters, the ratio of 90Sr/137Cs is in the range of 0,6-2,1. It is assumed that the differences in the value of fission product ratios are due to different types and capacities of nuclear charges, as well as different explosion altitudes. The obtained ratios allow to calculate 90Sr by 137Cs activity in soil of the epicentral zones at the territory of the «Experimental Field » testing site by the computational method.

Summation Calculations for Reactor Antineutrino Spectra, Decay Heat and Delayed Neutron Fractions Involving New TAGS Data and Evaluated Databases

Three observables of interest for present and future reactors depend on the β decay properties of the fission products: antineutrinos from reactors, the reactor decay heat and delayed neutron emission. In these proceedings, we present new results from summation calculations of the first two quantities quoted above, performed with evolved independent yields coupled with fission product decay data, from various nuclear data bases or models. New TAGS results from the latest experiment of the TAGS collaboration at the JYFL facility of Jyväskylä will be displayed as well as their impact on the antineutrino spectra and the decay heat associated to fission pulses of the main actinides.

Thermal Stability of Glass with Simulators of Chloride Highly Radioactive Wastes

High temperature behavior of sodium–aluminum fluorophosphate glass—a potential matrix for immobilisation of waste salt electrolyte from pyrochemical reprocessing of irradiated nuclear fuel (INF) has been studied. The glass crystallizes between 430 and 640°C with formation of phosphate phases, which dissolve above 640°C leading to homogenization of the glass. Similar transformations of the glass matrix due to heating from the decay of short-lived fission products may have a negative effect on properties of vitrified radioactive chloride wastes during storage in a repository.

Modified Point-Kinetics Model for Neutron Precursors and Fission Product Behavior for Fluid-Fueled Molten Salt Reactors

Fluid-fueled nuclear reactors, such as molten salt reactors (MSRs), have recently gained significant interest. These advanced reactors represent a potential revolutionary shift in the implementation of nuclear power, and as a broad class of reactors, they have the potential to directly address many U.S. energy policy objectives. Fuel that is dissolved in the coolant requires methods to account for the birth, decay, and transport of fission products not only in the core but also throughout the loop and any auxiliary systems, such as off-gas, to which liquid fuel flows, gaseous products are carried, or solid particulates plate out. System models are particularly well suited to explore the wide range of phenomena that are associated with fluid-fueled systems, especially for safeguards analysis. However, before system dynamics can be explored, the compositions of fission products of the salt throughout the loop must be determined as they drive the dynamic behavior of a reactor.This paper describes the derivation of a modified point-kinetics model for obtaining a first-order approximation of the behavior of a salt-fueled system in which neutron precursors and fission products are born in the fuel-salt and transported outside the core. This paper also provides verification of the model using a steady-state analytic solution and provides additional cases exploring the response under transient cases. This model establishes a baseline model that can be used to explore the dynamic response of fluid-fueled reactors and to investigate important safeguards issues such as mass accountability of source terms. The model is implemented in the Oak Ridge National Laboratory–developed, Modelica-based TRANSFORM library that was developed to investigate various aspects of advanced energy systems.

Spent nuclear fuel with a hybrid heat pipe for electricity generation and thermal management

The global warming resulting from the emission of the greenhouse gases has led to tightened restrictions on the use of fossil. Therefore, renewable energy for new energy sources is being widely investigated. However, renewable energy has limitations such as location, environmental conditions, and the potential construction of a new electricity grid. Spent nuclear fuel (SNF) is one of the potential new energy candidates that does not emit the greenhouse gases or suffer from limitations of other renewable energy sources. In this research, generating electricity by using SNF is suggested with a hybrid heat pipe system. Thermal energy from SNF worldwide is ∼750 MWth; however, this energy is not used as an energy source but just removed by chilling in water or in air in storage facilities. To achieve electricity generation from SNF, a dry storage cask with heat pipes and a Stirling engine (UCAN, UNIST CANister) are designed. Using a 1/10-scale test facility, the experimental test of heat transfer and electricity generation as the module of the storage system is conducted. The results yield good agreement with those predicted by the thermal resistance network model, and the electricity generation of the Stirling engine is in the range from 2.3% to 3.2% of the total heat load. The calculated temperature distributions are a good agreement, deviating within 12.2%, and the cooling efficiencies range from 17.51% to 26.33%. The results show the advantages of the use of SNF and its effects, focusing on thermal management and energy generation. The amount of SNF will gradually increase because of the continued operation of nuclear power plants. The usable heat from the SNF is generated due to the decay of fission products during at least several hundred years, which enables to use the SNF as one of the energy sources.

Revealing fine structure in the antineutrino spectra from a nuclear reactor

We calculate the Inverse Beta Decay (IBD) antineutrino spectrum generated by nuclear reactors using the summation method to understand deviations from the smooth Huber-Mueller model due to the decay of individual fission products, showing that plotting the ratio of two adjacent spectra points can effectively reveal these deviations. We obtained that for binning energies of 0.1 MeV or lower, abrupt changes in the spectra due to the jagged nature of the individual antineutrino spectra could be observed for highly precise experiments. Surprisingly, our calculations also reveal a peak-like feature in the adjacent points ratio plot at 4.5 MeV even with a 0.25 MeV binning interval, which we find is present in the IBD Daya Bay spectrum published in 2016. We show that this 4.5 MeV feature is caused by the contributions of just four fission products, 95Y, 98,101N and 102Tc. This would be the first evidence of the decay of a few fission products in the IBD antineutrino spectrum from a nuclear reactor.

Total absorption spectroscopy study of the β decay of Br86 and Rb91

The beta decays of $^{86}$Br and $^{91}$Rb have been studied using the total absorption spectroscopy technique. The radioactive nuclei were produced at the IGISOL facility in Jyv\"askyl\"a and further purified using the JYFLTRAP. $^{86}$Br and $^{91}$Rb are considered to be major contributors to the decay heat in reactors. In addition $^{91}$Rb was used as a normalization point in direct measurements of mean gamma energies released in the beta decay of fission products by Rudstam {\it et al.} assuming that this decay was well known from high-resolution measurements. Our results show that both decays were suffering from the {\it Pandemonium} effect and that the results of Rudstam {\it et al.} should be renormalized. The relative impact of the studied decays in the prediction of the decay heat and antineutrino spectrum from reactors has been evaluated.

On Cherenkov light production by irradiated nuclear fuel rods

Safeguards verification of irradiated nuclear fuel assemblies in wet storage is frequently done by measuring the Cherenkov light in the surrounding water produced due to radioactive decays of fission products in the fuel. This paper accounts for the physical processes behind the Cherenkov light production caused by a single fuel rod in wet storage, and simulations are presented that investigate to what extent various properties of the rod affect the Cherenkov light production. The results show that the fuel properties have a noticeable effect on the Cherenkov light production, and thus that the prediction models for Cherenkov light production which are used in the safeguards verifications could potentially be improved by considering these properties. It is concluded that the dominating source of the Cherenkov light is gamma-ray interactions with electrons in the surrounding water. Electrons created from beta decay may also exit the fuel and produce Cherenkov light, and e.g. Y-90 was identified as a possible contributor to significant levels of the measurable Cherenkov light in long-cooled fuel. The results also show that the cylindrical, elongated fuel rod geometry results in a non-isotropic Cherenkov light production, and the light component parallel to the rod's axis exhibits a dependence on gamma-ray energy that differs from the total intensity, which is of importance since the typical safeguards measurement situation observes the vertical light component. It is also concluded that the radial distributions of the radiation sources in a fuel rod will affect the Cherenkov light production.

Complete β -decay pattern for the high-priority decay-heat isotopes I137 and Xe137 determined using total absorption spectroscopy

Background: An assessment done under the auspices of the Nuclear Energy Agency in 2007 suggested that the $\ensuremath{\beta}$ decays of abundant fission products in nuclear reactors may be incomplete. Many of the nuclei are potentially affected by the so called pandemonium effect and their $\ensuremath{\beta}\text{\ensuremath{-}}\ensuremath{\gamma}$ decay heat should be restudied using the total absorption technique. The fission products $^{137}\mathrm{I}$ and $^{137}\mathrm{Xe}$ were assigned highest priority for restudy due to their large cumulative fission branching fractions. In addition, measuring $\ensuremath{\beta}$-delayed neutron emission probabilities is challenging and any new technique for measuring the $\ensuremath{\beta}$-neutron spectrum and the $\ensuremath{\beta}$-delayed neutron emission probabilities is an important addition to nuclear physics experimental techniques.Purpose: To obtain the complete $\ensuremath{\beta}$-decay pattern of $^{137}\mathrm{I}$ and $^{137}\mathrm{Xe}$ and determine their consequences for reactor decay heat and ${\overline{\ensuremath{\nu}}}_{e}$ emission. Complete $\ensuremath{\beta}$-decay feeding includes ground state to ground state $\ensuremath{\beta}$ feeding with no associated $\ensuremath{\gamma}$ rays, ground state to excited states $\ensuremath{\beta}$ transitions followed by $\ensuremath{\gamma}$ transitions to the daughter nucleus ground state, and $\ensuremath{\beta}$-delayed neutron emission from the daughter nucleus in the case of $^{137}\mathrm{I}$.Method: We measured the complete $\ensuremath{\beta}$-decay intensities of $^{137}\mathrm{I}$ and $^{137}\mathrm{Xe}$ with the Modular Total Absorption Spectrometer at Oak Ridge National Laboratory. We describe a technique for measuring the $\ensuremath{\beta}$-delayed neutron energy spectrum, which also provides a measurement of the $\ensuremath{\beta}$-neutron branching ratio, ${P}_{n}$.Results: We validate the current Evaluated Nuclear Structure Data File (ENSDF) evaluation of $^{137}\mathrm{Xe}\phantom{\rule{4pt}{0ex}}\ensuremath{\beta}$ decay. We find that major changes to the current ENSDF assessment of $^{137}\mathrm{I}\ensuremath{\beta}$-decay intensity are required. The average $\ensuremath{\gamma}$ energy per $\ensuremath{\beta}$ decay for $^{137}\mathrm{I}\ensuremath{\beta}$ decay ($\ensuremath{\gamma}$ decay heat) increases by 19%, from 1050--1250 keV, which increases the average $\ensuremath{\gamma}$ energy per $^{235}\mathrm{U}$ fission by $0.11%$. We measure a $\ensuremath{\beta}$-delayed neutron branching fraction for $^{137}\mathrm{I}\ensuremath{\beta}$ decay of $7.9\ifmmode\pm\else\textpm\fi{}0.2(\mathrm{fit})\ifmmode\pm\else\textpm\fi{}0.4(\mathrm{sys})%$ and we provide a $\ensuremath{\beta}$-neutron energy spectrum.Conclusions: The Modular Total Absorption Spectrometer measurements of $^{137}\mathrm{I}$ and $^{137}\mathrm{Xe}$ demonstrate the importance of revisiting and remeasuring complex $\ensuremath{\beta}$-decaying fission products with total absorption spectroscopy. We demonstrate the ability of the Modular Total Absorption Spectrometer to measure $\ensuremath{\beta}$-delayed neutron energy spectra.

Automated generation of burnup chain for reactor analysis applications

Abstract This paper presents the development of an automated generation of burnup chain for reactor analysis applications. Algorithms are proposed to reevaluate decay modes, branching ratios and effective fission product (FP) cumulative yields of a given list of important FPs taking into account intermediate reactions. A new burnup chain is generated using the updated data sources taken from the JENDL FP decay data file 2011 and Fission yields data file 2011. The new burnup chain is output according to the format for the SRAC code system. Verification has been performed to evaluate the accuracy of the new burnup chain. The results show that the new burnup chain reproduces well the results of a reference one with 193 fission products used in SRAC. Burnup calculations using the new burnup chain have also been performed based on UO2 and MOX fuel pin cells and compared with a reference chain th2cm6fp193bp6T.

Study of the $\beta $ Decay of Fission Products with the DTAS Detector

Study of the $\beta $ Decay of Fission Products with the DTAS Detector

TAGS measurements of 100Nb ground and isomeric states and 140Cs for neutrino physics with the new DTAS detector

In this work we report on total absorption γ-ray spectroscopy measurements of the β decay of fission products that are important contributors to the antineutrino spectrum. The experiment was performed at IGISOL as a part of a campaign of measurements with the new DTAS spectrometer. Preliminary results of the analysis of the β decay of ¹⁰⁰Nb, ¹⁰⁰Nb and ¹⁴⁰Cs are presented.

Effect of carbon impurity in irradiated mixed uranium–plutonium nitride on the phase composition upon β−-decay of fission products

As shown by thermodynamic modeling, accumulation of fission products in the course of irradiation of mixed uranium–plutonium nitride containing 0.25 wt % C impurity leads to the formation of a multicomponent carbonitride solid solution containing U, Pu, Am, Np, Zr, Y, lanthanides, and also separate carbide (UMoC2, U2RuC2, URu3C0,7, BaC2, SrC2) and nitride (U2N3) phases and intermetallic compounds U(Ru, Rh, Pd)3. The β−-decay of metallic radionuclides in separate carbide phases of spent nuclear fuel leads to changes in their chemical compositions. The transformation kinetics of separate dicarbide (89SrC2 → 89YC2, 90SrC2 → 90YC2 → 90ZrC + C, 140BaC2 → 140LaC2 → 140CeC2) and complex carbide (U99MoC2 → UC2 + 99Tc) phases was calculated.

Effect of the β decay of metallic fission products on the chemical and phase compositions of the uranium–plutonium nitride nuclear fuel irradiated by fast neutrons

Thermodynamic analysis of the chemical and phase compositions of uranium–plutonium nitride (U0.8Pu0.2)N0.995 irradiated by fast neutrons to a burn-up fraction of 14% shows that a structure, which consists of a solid solution based on uranium and plutonium nitrides and containing some elements (americium, neptunium, zirconium, yttrium, lanthanides), individual condensed phases (U2N3, CeRu2, Ba3N2, CsI, Sr3N2, LaSe), metallic molybdenum and technetium, and U(Ru, Rh, Pd)3 intermetallics, forms due to the accumulation of metallic fission products. The contents and compositions of these phases are calculated. The change in the chemical and phase compositions of the irradiated uranium–plutonium nitride during the β decay of metallic radioactive fission products is studied. The kinetics of the transformations of 95Nb41N, 143Pr59N, 151Sm62N, and 147NdN into 95Mo42 + Ns.s., 143Nd60N, 151Eu63N, and 147SmN, respectively, is calculated.

Measurements of extinct fission products in nuclear bomb debris: Determination of the yield of the Trinity nuclear test 70 y later

This paper describes an approach to measuring extinct fission products that would allow for the characterization of a nuclear test at any time. The isotopic composition of molybdenum in five samples of glassy debris from the 1945 Trinity nuclear test has been measured. Nonnatural molybdenum isotopic compositions were observed, reflecting an input from the decay of the short-lived fission products (95)Zr and (97)Zr. By measuring both the perturbation of the (95)Mo/(96)Mo and (97)Mo/(96)Mo isotopic ratios and the total amount of molybdenum in the Trinity nuclear debris samples, it is possible to calculate the original concentrations of the (95)Zr and (97)Zr isotopes formed in the nuclear detonation. Together with a determination of the amount of plutonium in the debris, these measurements of extinct fission products allow for new estimates of the efficiency and yield of the historic Trinity test.

モンテカルロ法による放射線量の簡易計算法

Large amounts of fission products (FP) were released at the Fukushima Daiichi Nuclear Power Plant of Tokyo Electricity Power Company due to the accident, initiated by the tsunami that was triggered by the East Japan Great Earthquake on March 11, 2011. It has been more than five years since the disaster occurred. The radioactivity owing to FP deposited on the grounds, houses, forests and so on have been decreasing steadily by the decay of FP, soil infiltration, weathering effect and the planned decontamination. As a result, the residence restriction areas have been re-organized as areas prepared for evacuation cancellation and it has been allowed for the residents to return to their homes. The conscious surveys for residents showed that they were worrying about the influence of radioactivity to human body. Therefore, it is necessary to let them know sufficient detailed information and knowledge. The decrease of radiation dose depends considerably on the density of the building construction materials, so that it would be desirable for indoor radiation dose rate to be estimated by taking account of housing types and floor plans. This paper deals with a novel method for calculating radiation dose rate within a building and around its surroundings. We employed the Monte Carlo method to calculate gamma ray penetration through various shield configurations and the absorption within an object positioned at an evaluation point. The gamma rays shifted to lower energy levels caused by the Compton scattering, i.e. buildup fluxes, were simply treated using the buildup factor as a function of the mean free path of photons. RADAR-γ code which has been developed on the basis of this study was benchmarked for a simplified geometry case with Cesium 137 deposited on the ground surface. The results were compared with the point-kernel integration code QAD-CGGP-A, which has been widely used in radiative physics analyses to calculate operational exposures and gamma radiation fields through shielding. The results of both methods were in good agreement. It was confirmed that the proposed method could be used for predicting radiation dose rate in the area where FP have been deposited.

Ruthenium Release from Thermally Overheated Nitric Acid Solution Containing Ruthenium Nitrosyl Nitrate and Sodium Nitrate to Solidify

Radioactive ruthenium (Ru) is one of the dominant elemental species released into the environment from a fuel reprocessing plant in a hypothetical design accident due to its relatively higher fission yield and longer half-life. After the hypothetical accident assuming the loss of all electric power and cooling functions, high-level liquid waste (HLLW) may be overheated by the energetic decays of many fission products in it, and Ru may be oxidized to the volatile tetroxide, RuO4, which is released through the off-gas pathway. At a reprocessing plant in Japan, alkaline solution from the solvent scrubbing stream is sometimes mixed with the HLLW followed by vitrification, which can be influenced by the addition of sodium nitrate to a simulated HLLW containing ruthenium nitrosyl nitrate that was experimentally evaluated on a small scale using the overheated nitric acid solution of 2mol dm−3, which was kept at 180°C in a glass evaporator placed in a thermostatic bath. The release fraction of Ru increased by approximately 30% by the addition of sodium nitrate. This may be partially explained by the existence of relatively highly concentrated nitrate ions in the liquid phase that oxidize the ruthenium species to RuO4 during the drying process.

Total Absorption Spectroscopy of Fission Fragments Relevant for Reactor Antineutrino Spectra and Decay Heat Calculations

Beta decay of fission products is at the origin of decay heat and antineutrino emission in nuclear reactors. Decay heat represents about 7% of the reactor power during operation and strongly impacts reactor safety. Reactor antineutrino detection is used in several fundamental neutrino physics experiments and it can also be used for reactor monitoring and non-proliferation purposes. 92,93 Rb are two fission products of importance in reactor antineutrino spectra and decay heat, but their β -decay properties are not well known. New measurements of 92,93 Rb β -decay properties have been performed at the IGISOL facility (Jyvaskyla, Finland) using Total Absorption Spectroscopy (TAS). TAS is complementary to techniques based on Germanium detectors. It implies the use of a calorimeter to measure the total gamma intensity de-exciting each level in the daughter nucleus providing a direct measurement of the beta feeding. In these proceedings we present preliminary results for 93 Rb, our measured beta feedings for 92 Rb and we show the impact of these results on reactor antineutrino spectra and decay heat calculations.

The preparation of non-radioactive glassy surrogate nuclear explosion debris (SNED) loaded with isotopically altered Xe

The measurement of Kr and Xe isotope ratios in nuclear explosion debris can be performed requiring little sample preparation. Fragments of debris are simply crushed or heated to release trapped gases Kr and Xe arising from fission product decay. As a suitable test material for this measurement, we have been investigating a method to incorporate isotopically enriched 129Xe in glassy materials that mimic nuclear explosion debris. The approach used to prepare these materials will be described along with some of the example results obtained.

Actinide, Activation Product and Fission Product Decay Data for Reactor-based Applications

The UK Activation Product Decay Data Library was first released in September 1977 as UK-PADD1, to be followed by regular improvements on an almost yearly basis up to the assembly of UKPADD6.12 in March 2013. Similarly, the UK Heavy Element and Actinide Decay Data Library followed in December 1981 as UKHEDD1, with the implementation of various modifications leading to UKHEDD2.6, February 2008. Both the data content and evaluation procedures are defined, and the most recent evaluations are described in terms of specific radionuclides and the resulting consistency of their recommended decay-data files. New versions of the UKPADD and UKHEDD libraries are regularly submitted to the NEA Data Bank for possible inclusion in the JEFF library.