Reactor Neutron Irradiation Research Articles

Uranium Content Measurements in Building Materials Using Track Detection

In order to use the wood building materials in dwelling construction, uranium content measurements were performed by one of the alpha or fission track methods. The investigated samples were tree and rush samples, collected from different Romanian sites, situated in the vicinity of zones with human radioactive activities, such as: Sapantza, Izvorul Izei (North Romania), Omer and Periprava (Danube River Delta). We have examined the U atom distributions in these samples in order to detect any U contamination due to radioactivity. For each analysed sample, two U track micromappings were obtained in the two track detectors which were put in intimate contact with the sample during reactor neutron irradiations. The obtained track micromappings were studied by optical microscopy. The U distribution and content measurement results are presented and interpreted according to the present norms referring to maximum permissible values of U in building materials in Romania.

A study on the radiation damage and recovery of neutron irradiated vessel steel using magnetic Barkhausen noise

The radiation damage and thermal recovery characteristic of neutron irradiated SA508-3 reactor pressure vessel steel specimens have been investigated. Two recovery stages were identified from the results of hardness measurements during isochronal annealing and the mechanism responsible for the two stages was explained by using the results of Barkhausen noise measurement on the basis of the interaction between radiation induced defects and the magnetic domain wall. The coercivity was not changed by neutron irradiation, whereas the maximum magnetic induction increased. Barkhausen noise parameters associated with the domain wall motion were decreased by neutron irradiation and recovered with subsequent heat treatments.

Irradiation effects on magnetic properties in neutron and proton irradiated reactor pressure vessel steel

The effects of neutron and proton dose on the magnetic properties of a reactor pressure vessel (RPV) steel were investigated. The coercivity and maximum induction increased in two stages with respect to neutron dose, being nearly constant up to a dose of 1.5/spl times/10/sup -7/ dpa, followed by a rapid increase up to a dose of 1.5/spl times/10/sup -5/ dpa. The coercivity and maximum induction in the proton irradiated specimens also showed a two stage variation with respect to proton dose, namely a rapid increase up to a dose of 0.2/spl times/10/sup -2/ dpa, then a decrease up to 1.2/spl times/10/sup -2/ dpa. The Barkhausen noise (BN) amplitude in neutron irradiated specimens also varied in two stages in a reverse manner, the transition at the same dose of 1.5/spl times/10/sup -7/ dpa. The BN amplitude in proton irradiated specimens decreased by 60% up to 0.2/spl times/10/sup -2/ dpa followed by an increase up to 1.2/spl times/10/sup -2/ dpa. The results were in good accord with the one dimensional domain wall model considering the density of defects and wall energy.

Study of the critical current in YBaCuO films under reactor-neutron irradiation in the low-temperature helium circuit in the 25–300 K range

Changes in the temperature and dose dependences of I-V characteristics and of the critical current jc of YBaCuO films on MgO and SrTiO3 substrates under neutron irradiation has been studied at 25–80 K. The transport properties of YBaCuO films on MgO (M1) and SrTiO3 (S1) substrates were found to behave differently. It is shown that the M1 films have granular structure, and their transport properties were considered within the concept of percolation over weak intergranular links. The S1 are single-crystal films, and their properties are analyzed within a resistive-state theory associated with thermal activation of Abrikosov vortices. It is shown that the degradation rate of the critical temperature Tc of S1 films is 3.5 times smaller than that of the M1 films. The dose dependence of jc has an exponential character, jc=jc(0)exp(−kΦ), where k is related to the number of displaced atoms per neutron and is the same for the M1 and S1 films, irrespective of the irradiation temperature. The pinning energy has been derived from the I-V characteristics and it has been found that the U/kT ratio lies within 20–25 and is independent of neutron flux. It is shown that the radiation-induced disorder changes the pinning mechanism, from pinning at the boundaries of misoriented crystals to that at spatial inhomogeneities, apparently radiation induced.

Small defects in YBCO single crystals: T c after neutron irradiation and annealing

Neutron irradiation of HTSs creates a wide spectrum of defect sizes. In this work, the influence of small defects on the critical temperature is investigated by sequential reactor neutron irradiation and annealing of a YBCO single crystal. The characteristic behaviour of T c under this treatment is satisfactorily explained by a theoretical model considering the creation, migration and annihilation of small defects in the oxygen sublattice.

Magnetic properties and critical currents in Tl-based high-Tcsuperconducting single crystals

${\mathrm{Tl}}_{2}$${\mathrm{Ca}}_{2}$${\mathrm{Ba}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{10}$ (Tl-2223) and (TlPb)(SrBa${)}_{2}$${\mathrm{Ca}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{8}$ (Tl-1223) single crystals were investigated by superconducting quantum interference device magnetometry in fields up to 8 T (H\ensuremath{\parallel}c axis). The samples were subjected to sequential reactor neutron irradiation up to a fluence of 24\ifmmode\times\else\texttimes\fi{}${10}^{21}$ ${\mathrm{m}}^{\mathrm{\ensuremath{-}}2}$ (E>0.1 MeV). The superconducting transition temperature ${\mathrm{T}}_{\mathrm{c}}$, the magnetization, and the irreversibility lines were measured before and after each irradiation step. Because of the wide range of magnetic fields and temperatures, where the magnetization is totally reversible, especially in Tl-2223, the basic mixed-state parameters, such as the critical magnetic fields and the characteristic lengths, could be evaluated. In the irreversible range, the critical current densities were calculated from the hysteresis loops using an extended Bean model. We find that ${\mathrm{J}}_{\mathrm{c}}$ is strongly enhanced by the radiation-induced defects, e.g., by a factor of 52 in Tl-2223 at 40 K and 1 T. The irreversibility lines are shifted to higher fields and temperatures, but remain always below those of unirradiated Tl-1223, even at the highest neutron fluence. In Tl-1223, the critical current densities are moderately enhanced. The irreversibility line is at the same position or even higher than that of Y-123 and is moderately shifted to higher fields and temperatures after irradiation. The experimental results are discussed in terms of flux pinning and dimensionality.

Evaluation of thermal recovery of neutron-irradiated SA508-3 steel using magnetic property measurements

The Vickers microhardness and magnetic properties have been used to investigate irradiation effects and thermal recovery characteristics of neutron-irradiated SA508-3 reactor pressure vessel steel specimens irradiated to a neutron fluence of 5.5×1017 n cm-2 (E>1 MeV) at 70°C. Two recovery stages were identified from the hardness results during isochronal annealing and the mechanism responsible for the two stages was explained using the results of Barkhausen noise on the basis of the interaction between radiation-induced defects and the magnetic domain wall. The neutron irradiation caused the coercivity to decrease, whereas the maximum magnetic induction increased. Barkhausen noise parameters associated with the domain-wall motion were decreased by neutron irradiation and recovered with subsequent heat treatments. From the sensitive changes in the Barkhausen noise upon annealing heat treatment, it is suggested that the Barkhausen noise measurements may be used as a useful tool for monitoring the early stage of the thermal recovery behaviour of neutron-irradiated reactor pressure vessel steels.

Thermal recovery characteristics of neutron-irradiated high-copper weld (Linde 80)

The recovery activation energy, the order of reaction and the characteristic recovery rate constant were determined by isochronal (573–823 K) and isothermal (723 K and 775 K) annealing experiments on specimens made from a broken half of a surveillance weld specimen (fluence: 1.21 × 10 23 n/m 2, E ≥ 1 MeV, Cu: 0.29 wt%) to investigate the recovery characteristics of a high copper weld of neutron-irradiated reactor pressure vessel (RPV). Vickers microhardness tests were conducted to trace the recovery behavior after heat treatments. The results were analyzed in terms of recovery stages, behavior of responsible defects and recovery kinetics. It was shown that recovery occurred through two annealing stages (stage I: 673–753 K, stage II: 753–823 K) with recovery activation energies of 2.68 eV and 2.83 eV for stage I and II, respectively. The isothermal hardness recovery at 723 K and 775 K coincided with the ratio of the characteristic rate constant for each recovery stage. The order of reaction was 2 for both recovery stages. The recovery activation energies of present specimens are approximately equal to that of copper diffusion in α-iron in the presence of vacancies, suggesting that recovery may occur through the diffusion of copper atoms. The present results strongly support the copper precipitate coarsening model.

Radiation damage and the recovery of neutron-irradiated TiAl studied by positron lifetime spectrometry

Abstract Radiation damage and the recovery of neutron-irradiated γ-TiAl (Ti 44 Al 56 ) have been studied using positron annihilation lifetime spectrometry. The recovering process of the neutron-irradiated TiAl can be divided into two stages. The first stage, below 660 K, is ascribed to the migration of point defects and the second stage, above 660 K, is due to the dissolution of secondary defects formed at the former stage. The major defect induced by reactor neutron-irradiation is collapsed planar aggregates of point defects. Although some non-collapsed vacancy clusters are also induced, they consist of only a few vacancies each, seldom grow into larger voids during the subsequent annealing, and almost disappear below 700 K. Neutron-irradiated Ti 44 Al 56 recovers to the fully annealed state below 960 K. γ-TiAl has good tolerance for radiation.

Damage calculation in compound materials under neutron and ion irradiation

A method for displacement damage rate calculations in compound materials under neutron and ion accelerator irradiation is proposed. The method is especially suitable for materials with significantly different masses of species. Range and damage depth profiles in HTSC ceramics for different He-ion projectile energies were calculated. Partial contributions of each species to displacement damage and spectral-averaged partial damage cross sections for two neutron irradiation conditions were also calculated. The developed code provides a quick and reliable way of comparison of the displacement damage under neutron and ion irradiation. Helium ion doses equivalent by dpa to neutron irradiation in ORR and YAYOI reactors were obtained.

Neutron Damage in Reactor Pressure-Vessel Steel Examined with Positron Annihilation Lifetime Spectroscopy

AbstractWe have used positron annihilation lifetime spectroscopy to study the development of damage and annealing behavior of neutron-irradiated reactor pressure-vessel steels. We irradiated samples of ASTM A508 nuclear reactor pressure-vessel steel to fast neutron 172 fluences of up to 1017 n/cm2, and we examined these samples using positron annihilation lifetime spectroscopy (PALS) to study the effects of neutron damage in the steels on positron lifetimes. Non-irradiated samples show two positron lifetimes: a 110 ps component corresponding to annihilations in the bulk material, and a 165 ps lifetime corresponding to annihilations in dislocation defects. The irradiated samples show an additional lifetime component of 300 ps in the PAL spectra and an increase in the proportion of annihilations with a 165 ps lifetime, suggesting that vacancies and vacancy clusters are present in the material after room temperature irradiation. The samples were then annealed to temperatures ranging from 210° C to 450° C. The positron lifetimes introduced by neutron damage disappear after annealing the samples at 280° C.

A low wall-loading DEMO reactor design with high priority for early and reliable realization of a tokamak fusion reactor over the cost performance

Based on scientific databases adopted for designing ITER plasmas and on the advancement of fusion nuclear technology from the recent R&D program, a low wall-loading DEMO fusion reactor has been designed, where high priority has been given to the early and reliable realization of a tokamak fusion plasma over the cost performance. Since the major radius of this DEMO reactor is chosen to be 10 m, plasma ignition is achievable with a low fusion power of 0.8 GW and an operation period of 4–5 hours is available only with inductive current drive. The low ignition power makes it possible to adopt a first wall with an austenitic stainless steel, for which significant databases and operating experience exists, due to its use in the presence of neutron irradiation in fission reactors. In step with development of advanced materials, a step-wise increase of the fusion power seems to be feasible and realistic, because this DEMO reactor has the potential to produce a fusion power of ∼5 GW.

Mechanisms of radiation damages formation in gadolinium gallium garnet (GGG) single crystals

Abstract The influence of γ-, electrons and reactor neutrons irradiation on the optical and electrophysical properties of Gd3 Ga5 O12 single crystals is investigated. Experimental data and theoretical estimations of radiation defect concentration are compared.

Influence of fast neutron irradiation on tensile properties of mild steel

Abstract An investigation has been made on the influence of reactor neutron irradiation on tensile properties of mild steel at ambient temperature. Flat tensile specimens with gauge section 15.5 mm × 2.9 mm × 2.5 mm were exposed to neutron irradiation (E > 0.1 MeV) to three different fluences of 0.6 × 1018, 1.2 × 1018 and 4.8 × 10.18 n/cm2. The irradiated specimens were tested in tension at room temperature. It was observed that while there was marked increase in the yield strength, there was relatively less increase in the ultimate tensile strength and the work hardening of the material was considerably reduced to due to neutron irradiation. Further, the ductility was also reduced progressively with the increasing fluence of neutron.

Evaluation of thermal annealing behavior of neutron-irradiated reactor pressure vessel steels using nondestructive test methods

Evaluation of thermal annealing behavior of neutron-irradiated reactor pressure vessel steels using nondestructive test methods

Evaluation of thermal annealing behavior of neutron-irradiated reactor pressure vessel steels using nondestructive test methods

Evaluation of thermal annealing behavior of neutron-irradiated reactor pressure vessel steels using nondestructive test methods

Radiation induced carrier enhancement and intrinsic defect transformation in n-GaAs

Gallium arsenide grown by the metallorganic chemical vapor deposition method and n doped with silicon to a concentration of 1015 cm−3 was exposed to reactor neutron irradiation in the 1012 to 3×1014 cm−2 1 MeV equivalent fluence range. Studies of the defects through deep level transient spectroscopy (DLTS), photoluminescence (PL), and transport measurements on this material indicate correlation between the nature and density of defects, and some of the transport parameters. Contrary to the general perception of degradation of electronic properties of semiconductors on nuclear irradiation, we observe enhancement in some of the electrical/optical properties of GaAs on irradiation at lower fluence levels. These properties degrade on irradiation at higher fluences. The PL intensity of irradiated GaAs increases over the 1×1012 to 1×1013 cm−2 fluence range. At 1×1013 cm−2, the increase in the signal from different PL peaks ranges from 25% to 200%. Similarly, the carrier density of irradiated GaAs, as determined by transport measurements, increases by about 25% on irradiation at 3×1012 cm−2, before decreasing at and above 3×1013 cm−2 fluence. The density of the EL2 trap as determined through the DLTS technique, remains constant with fluence and that of the EL12 trap at 780 meV below the conduction band decreases at an injection ratio of −0.5±0.3 cm−1 up to ≂1×1014 cm−2 fluence. The EL6 trap at 0.38 meV below the conduction band is introduced at a rate of 0.30±0.04 cm−1. Thus, neutron irradiation restructures the deep levels, with the consequence that the carrier density goes through a maximum at low fluence levels. Through PL measurements, the maximum in carrier density corresponds to a fluence level of (1.0±0.2)×1013 cm−2. At fluences above 1014 cm−2, we observe the introduction of a deep level at 260±85 meV below the conduction band (EL14) at a rate of 1.7±0.4 cm−1. Above 1014 cm−2, we observe an increase in carrier depletion in GaAs through PL and transport measurements.

X-ray line broadening in neutron irradiated silicon carbide

X-ray line broadening in reaction-sintered β-SiC after neutron irradiation in fast breeder reactors at temperatures around 370–620°C to fluences of 3.0×10 24 to 1.7×10 27 n/m 2 (E>0.1 MeV) has been investigated. Broadening occurred after neutron irradiation for all specimens and appreciable broadening was present for specimens irradiated to ≥3.2×10 26 n/m 2 . At neutron fluences below 1.5×10 26 n/m 2 observed broadening could be attributed mainly to the crystallite size effect but a strain contribution was significant above 3.2×10 26 n/m 2 . Fairly large interstitial dislocation loops were observed with TEM in the latter specimens. The calculated crystallite size was in close agreement with the spacing of the dislocation loops.

Radiation effects in PLZT and PSN ceramics

Abstract Comprehensive studies of radiation effects on the optical and dielectric properties of PLZT X/65/35 and PSN ceramics have been made. The samples have been exposed to gamma, electron and reactor neutron irradiation. With regard to the optical properties, a maximum in the absorption difference with respect to the pre-irradiated state, appears in samples of PLZT 8-11/65/35 at wavelength of 380 nm, irrespective of the type of radiation. With regard to dielectric properties, the radiation-induced effects have been found to be strongly dependent on the sample composition, especially their La-content as well on the state of polarization of the sample during irradiation. Those samples, which are characterized by a slim hysteresis loop, show linear correlations between the 380 nm-maximum of the optical density difference, which is presumably proportional to the defect concentration, and the change of polarization in the neutronirradiated state.

Radiation effects on physical properties of PLZT ceramics

Abstract Comprehensive studies of radiation effects on the optical and dielectric properties of PLZT X/65/35 ceramics have been made. The samples have been exposed to gamma-electron and reactor neutron irradiation.