Effect Of Neutron Flux Research Articles

Temperature and frequency dependence of electric conductivity in nano-grained SiO2 exposed to neutron irradiation

We studied electric properties of SiO2 nanoparticles exposed to continuous neutron irradiation (2×1013cm−2s−1 neutron flux) for different periods up to 20h and initial states. Electric properties of the samples before and after irradiation were studied in the 0.09Hz–2.3MHz frequency and 100–400K temperature range. In the experiments the samples have been irradiated by up to 20h. It has been shown that upon increasing irradiation period, electric conductivity of the samples increases. The formation of clusters in three different states and energies at low temperatures under the neutron flux effect has been revealed. In addition, activation energy was calculated from the temperature-dependent dielectric response data using the Arrhenius expression.

Effect of Neutron Flux on Magnetic Hysteresis in Neutron-Irradiated Pressure Vessel Steels

The effect of neutron flux on magnetic minor hysteresis loops has been investigated on nuclear reactor pressure vessel steels, which were irradiated to a fluence of 3.3 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">19</sup> n/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . A minor-loop coefficient, which is an indicator of internal stress, exhibits a local maximum at a fluence of ~1 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">19</sup> n/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , whose position shifts to a low-fluence regime with decreasing neutron flux. Introducing an effective fluence, used to correct the flux effect of irradiation hardening, the data obtained by different flux were found to almost fall on single curve for some alloys. This implies that the flux effect on magnetic property is dominated by efficiency of radiation-enhanced diffusion of solute atoms, such as Cu, as in the case of irradiation hardening.

A new method by steering kernel-based Richardson–Lucy algorithm for neutron imaging restoration

Motivated by industrial applications, neutron radiography has become a powerful tool for non-destructive investigation techniques. However, resulted from a combined effect of neutron flux, collimated beam, limited spatial resolution of detector and scattering, etc., the images made with neutrons are degraded severely by blur and noise. For dealing with it, by integrating steering kernel regression into Richardson–Lucy approach, we present a novel restoration method in this paper, which is capable of suppressing noise while restoring details of the blurred imaging result efficiently. Experimental results show that compared with the other methods, the proposed method can improve the restoration quality both visually and quantitatively.

Analysis of Relationship Between the Radiation Embrittlement Mechanisms and the Influence of Neutron Flux in Respect of WWER Reactor Pressure Vessel Materials

The paper addresses the effect of neutron flux for WWER reactor pressure vessel materials in the cases where various embrittlement mechanisms prevail. The data on shifts of critical brittleness temperatures, which were obtained within various surveillance specimen programs and research programs, are used. The authors have defined the embrittlement mechanisms for which the neutron flux has no effect and the ones for which its effect is significant. For the case where the phosphorus segregation mechanism dominates, the absence of the neutron flux effect has been substantiated from the standpoint of the theory of radiation-accelerated diffusion.

Confirmatory investigations on the flux effect and associated unstable matrix damage in RPV materials exposed to high neutron fluence

This paper provides additional experimental data on the neutron flux effect on RPV hardening and embrittlement and on the so-called unstable matrix damage that was suggested to occur at high flux. Six materials taken from the first irradiation surveillance capsules of Belgian PWRs with a fluence not exceeding about 1.5×1019n/cm2 were further irradiated in the BR2 high flux reactor to additional fluences ranging between about 1 and 1.5×1020n/cm2 at 290°C. Eight additional RPV materials were selected to investigate the flux effect on irradiation hardening. No statistically-significant difference in irradiation hardening for low and high flux could be evidenced from the null hypothesis test applied with the general linear model. This is confirmed by additional experiments where fourteen irradiated specimens of various RPV materials consisting of low to high Cu and Ni contents were annealed at 350°C for 5h to eventually reveal some recovery of the unstable matrix damage. The results did not show any recovery upon heat treatment, which indicates that unstable matrix defects did not appear in these materials during irradiation at high flux.

Analysis of a link of embrittlement mechanisms and neutron flux effect as applied to reactor pressure vessel materials of WWER

The effect of neutron flux on embrittlement of WWER RPV materials is analyzed for cases when different radiation defects prevail. Data bases on the ductile–brittle transition temperature shifts obtained in the surveillance specimens programs and the research programs are used. The material embrittlement mechanisms for which the flux effect is practically absent and for which the flux effect is remarkable are determined. For case when the phosphorus segregation mechanism dominates the theoretical justification of the absence of the flux effect is performed on the basis of the theory of radiation-enhanced diffusion.

Evaluation of the Neutron Flux Effect on the ITER VUV Diagnostic System in the Upper Port

Evaluation of the Neutron Flux Effect on the ITER VUV Diagnostic System in the Upper Port

Neutron flux and annealing effects on irradiation hardening of RPV materials

This paper aims to examine an eventual effect of neutron flux, sometimes referred to as dose rate effect, on irradiation hardening of a typical A533B reactor pressure vessel steel. Tensile tests on both low flux (reactor surveillance data) and high flux (BR2 reactor) were performed in a large fluence range. The obtained results indicate two features. First, the surveillance data exhibit a constant (∼90 MPa) higher yield strength than the high flux data. However, this difference cannot be explained from a flux effect but most probably from differences in the initial tensile properties. The hardening kinetic of both low and high flux is the same. Annealing at low temperature, 345 °C/40 h, to eventually reveal unstable matrix damage did not affect both BR2 and surveillance specimens. This is confirmed by other annealing experimental data including both tensile and hardness measurements and tensile data on A508 forging and weld. It is suggested that the absence of flux effect on the tensile properties while different radiation-induced microstructures can be attributed to thermal ageing effects.

Irradiation temperature, flux and spectrum effects

Although great progress has been made in understanding the irradiation behaviour of reactor pressure vessel (RPV) steels, many aspects are still not fully understood. A large amount of data has been generated for understanding the effects of different irradiation conditions on material properties. The data needed for the long term operation of RPVs is almost always created by accelerated irradiations in test reactors, and due to insufficient knowledge on the damage interaction between the material and the high energy neutrons the potential bias of the conclusions on material properties in non-accelerated irradiation conditions can not be excluded. Important parameters for the extrapolation of results from accelerated irradiations to typical power irradiation conditions are the irradiation temperature, the neutron flux and the neutron spectrum. In particular, the effect of neutron flux on embrittlement behaviour is considered a complex phenomenon, and it seems to be dependent on the alloy composition, the neutron fluence range and the irradiation temperature. This paper will present the current knowledge on temperature, flux and spectrum effects, based on a recent literature survey and other relevant publications on the subject. It will explore the implications these effects may have for the safety evaluation of aged RPVs, especially for those exposed to long irradiation periods.

Embrittlement Correlation Method for the Japanese Reactor Pressure Vessel Materials

Abstract A new embrittlement correlation method developed for the Japanese reactor pressure vessel (RPV) steels is presented. The Central Research Institute of Electric Power Industry and the Japanese electric utilities conducted a project to develop a new embrittlement correlation method for the Japanese RPV steels based on the understandings on the mechanisms of the RPV embrittlement. In addition to the information from the literatures, we generated new information by characterizing the microstructural changes in the surveillance materials of the Japanese commercial reactors. We found that in low Cu materials, solute atom clusters containing little or no Cu atoms are formed at relatively low fluence of 3×1019 n/cm2, E&amp;gt;1 MeV. The volume fraction of the solute atom clusters has a good correlation with the Charpy transition temperature shift regardless of the Cu content. We also found that the microstructure of the boiling water reactor surveillance material is different from that of the archive material irradiated in material testing reactor. The understandings on the RPV embrittlement mechanisms were formulated using a set of rate equations, and the coefficients of the equations were optimized using the ΔRTNDT values of the Japanese surveillance database. This method considers the effect of neutron flux. Only one set of coefficients was developed, and they are independent of the product form. Predictions of the new embrittlement correlation method were compared with those of the recent U.S. correlation method as well as the U.S. surveillance data. The comparison shows the characteristics of the present method.

Flux dependence of cluster formation in neutron-irradiated weld material

The effect of neutron flux on the formation of irradiation-induced clusters in reactorpressure vessel (RPV) steels is an unresolved issue. Small-angle neutron scattering wasmeasured for a neutron-irradiated RPV weld material containing 0.22 wt% impurity Cu.The experiment was focused on the influence of neutron flux on the formation ofirradiation-induced clusters at fixed fluence. The aim was to separate and tentativelyinterpret the effect of flux on the characteristics of the cluster size distribution. Wehave observed a pronounced effect of neutron flux on cluster size, whereas thetotal volume fraction of irradiation-induced clusters is insensitive to the level offlux. The result is compatible with a rate theory model according to which therange of applied fluxes covers the transition from a flux-independent regime atlower fluxes to a regime of decelerating cluster growth. The results are confrontedwith measured irradiation-induced changes of mechanical properties. Despitethe observed flux effect on cluster size, both yield stress increase and transitiontemperature shift turned out to be independent of flux. This is in agreement with thevolume fraction of irradiation-induced clusters being insensitive to the level of flux.

Radiation Embrittlement of Cr–Ni–Mo and Cr–Mo RPV Steels

Abstract Radiation embrittlement kinetics of Cr–Mo and Cr–Ni–Mo steels, used for manufacturing VVER-440 and VVER-1000 RPV steels, respectively, are under consideration. Radiation embrittlement of VVER-440 and VVER-1000 RPV steels exposed to irradiation for 17–22 years is analyzed. Extremely high levels of thermal aging of VVER-1000 RPV steels at 320°C is pointed out. The neutron flux effect problem and the problem of accelerated radiation embrittlement of welds with high nickel contents are emphasized. The effect of phosphorus, copper, silicon, manganese, and nickel contents on radiation embrittlement of VVER-440 and VVER-1000 RPV steels is studied using the Russian surveillance database and representative results of research programs. The trend curves for VVER-440 and VVER-1000 RPV steels are proposed. The mechanisms of radiation embrittlement of Cr–Ni–Mo and Cr–Mo RPV steels are supposed.

Neutron Flux Effect on the Irradiation Hardening of Type 304 Stainless Steel

Abstract In order to investigate the neutron flux effect on the irradiation hardening of type 304 stainless steel, microstructure observation, tensile test, and micro Vickers hardness test were performed on the type 304 stainless steel irradiated to 1.6 × 1024−1.4 × 1026 n/m2 in LWRs, (flux 3.4 × 1015−5.6 × 1017 n/m2/s). The tensile test was carried out in air at 288°C, and the hardness test was also carried out in air, but at room temperature. The amount of irradiation hardening increased with increasing neutron flux. The amount of irradiation hardening was proportional to the 0.25th power of neutron flux. Dislocation loop density increased with increasing neutron flux, and mean diameter had hardly any dependence on neutron flux. From the above, the neutron flux dependence of dislocation loop density could be said to be the main factor controlling irradiation hardening under LWR irradiation conditions. The amount of irradiation hardening of type 304 stainless steel used in LWR is expected to be lower than the predicted amount from higher flux irradiated materials.

The Effect of Neutron Flux on Radiation-Induced Embrittlement in Reactor Pressure Vessel Steels

Abstract The effect of neutron flux level is a longstanding concern for determining the applicability of test reactor data or high lead-factor surveillance data to the prediction of embrittlement in commercial reactor pressure vessels (RPV). However, as operating reactors reach higher fluences, the question of flux effects is becoming increasingly relevant for situations such as embrittlement attenuation through the (RPV) and the comparison of boiling and pressurized reactor RPVs. In spite of its technological importance and extensive experimental and theoretical investigation, the issue of neutron flux effects on radiation-induced embrittlement in RPV steels remains unresolved. For neutron fluxes much greater than RPV operating conditions (&amp;gt;100 times higher), a regime exists in which the effects of flux are well defined experimentally and are well predicted by current models. These same models predict that the effect of flux should be relatively weak for values near those obtained in commercial RPVs, but may increase at lower fluxes. However, it is difficult to obtain sufficient data at low to intermediate fluxes to unambiguously determine the effects of flux since the time required to reach the desired fluences is necessarily long. In order to demonstrate the potential effects of flux on RPV embrittlement, and to help interpret the available experiments, a kinetic embrittlement model has been used in an analysis of the primary variables involved. The results of the analysis are consistent with a modest effect of flux on embrittlement for fluxes near those typical of commercial RPVs.

A unified model to describe the anisotropic viscoplastic behaviour of zircaloy-4 cladding tubes between 320 °C and 400 °C from an unirradiated state to high fluence and under fast neutron flux

This paper proposes a damaged viscoplastic model to simulate, for different isotherms (320, 350, 380, 400 and 420°C), the out-of-flux anisotropic mechanical behavior of Zircaloy-4 claddings in a stress relieved state over the fluence range 0-85.10 24 nm -2 (E>lMeV). The model, identified from uni and biaxial tests conducted at 350 and 400°C, is validated from tests made at 320, 380 and 420°C. This model is able to simulate strain hardening under an internal pressure followed by a stress relaxation period, since the loading produces an interaction between the pellet and the cladding (thermal creep). Both the integration of a scalar state variable, characterizing the damage caused by a bombardment with neutrons, and the modification of the static recovery law allowed us to simulate the fast neutron flux effect (irradiation creep).

On the Effect of Neutron Flux and Composition on Hardening of Reactor Pressure Vessel Steels and Model Alloys

ABSTRACTSingle variable experiments on a set of reactor pressure vessel and model alloys with a range of controlled compositions show a systematic effect of neutron flux (ϕ) on hardening in the intermediate fluence (ϕt) regime. The data suggest that high ϕ and enhanced recombination by vacancy trapping by solutes delays the onset of radiation-enhanced precipitation hardening.

Effect of neutron flux on low temperature irradiation embrittlement of reactor pressure vessel steel

Miniature Charpy V-notch impact test specimens of commercial reactor pressure vessel (RPV) steels having high and low copper contents were irradiated at the different irradiation positions with neutron flux levels of ∼6 × 10 14, ∼7 × 10 15, and ∼8 × 10 16 n m −2 s −1 ( E > 1 MeV) to fluence levels ranging from ∼6 × 10 21 to ∼7 × 10 22 n m −2 ( E > 1 MeV) at temperatures of about 50°C to 150°C in the Japan Materials Testing Reactor (JMTR). The results showed that the radiation-induced increases in ductile-to-brittle transition temperature (ΔDBTT) at a neutron flux level of ∼6 × 10 14 n m −2s −1 were greater than those for neutron flux level of ∼7 × 10 15 n m −2 s −1. The neutron flux effect on embrittlement tended to be more pronounced in the lower neutron fluence range of ∼6 × 10 21–∼1 × 10 22 n m −2 than in the higher fluence level of ∼7 × 10 22 n m −2, and also to be larger for the low copper steel than for the high copper steel, although the ΔDBTT for the high copper steel was larger than that for the low copper steel regardless of neutron fluence or flux. The displacement dose rate effect identified by the data converted to the ΔDBTT for the full size Charpy specimens from those for the miniature Charpy specimens was consistent with that based on the comparison of the results in the literature.

Determination of platinum in enviromental and geological samples by radiochemical neutron activation analysis

A radiochemical neutron activation analysis technique was developed for the determination of traces of platinum in environmental and geological samples via the indicator radionuclide 199Au, based on the separation of gold on polyurethane foam from 1 M HCl. In the determination of platinum at the ng g −1 level in the presence of antimony at concentrations higher than about 5 μg g −1, owing to a slight co-retention of antimony, further decontamination of the indicator radionuclide fraction was necessary. The effect of neutron flux and irradiation time on the extent of the second-order interfering reaction 197Au(n,γ) 198Au(n,γ) 199Au and the effect of the gold content on the limit of detection of platinum are considered in detail. The feasibility of this technique was tested by the analysis of environmental and geological samples, and the results obtained were compared with those of other methods.

Low temperature embrittlement of LWR RPV support structures

The results of the High Flux Isotope Reactor (HFIR) Surveillance Programme have attracted considerable interest amongst regulators and utilities because of their implications for, in particular, light water reactor (LWR) support structures operating at temperatures below 100°C. The cause of concern was the apparently higher rate of embrittlement encountered in this programme at near ambient temperatures and at an apparently modest, by reactor pressure vessel (RPV) standards, neutron fluence. This was originally interpreted as a neutron flux effect. Because of these concerns the authors have undertaken a comprehensive review of the scientific literature on radiation embrittlement of RPV and structural steels in order to assess the potential impact on the integrity of the LWR/boiling water reactor support structures. Two main issues have been identified in this review. The first of these, the effect of neutron spectrum, relates specifically to the possibly unique character of the HFIR environment. The second relates to the nature of the embrittlement processes at low temperatures, in particular the occurrence or otherwise of the copper effect, which is known to be important at normal RPV temperatures of 150°C and above. Wilth respect to the effect of the neutron spectrum, it is now widely accepted that the highly thermalised neutron environment in HFIR played an important part in promoting the apparently higher embrittlement of the HFIR materials. It has been proposed that the lower energy recoils produced by thermal neutron ( n − γ) reactions are about 10 times more efficient in creating displacement damage than the high energy neutrons (E > 1 MeV), which normally account for most of the radiation damage in RPV and core components. This conclusion is firmly based on theoretical studies of displacement cascades and can be inferred from detailed studies of irradiation effects such as radiation induced segregation in different radiation environments. A major issue concerning the relevance of the HFIR results to RPV support structure embrittlement therefore centres on the nature of the neutron spectrum. To enable this issue to be resolved it is recommended that an effort be made to obtain more comprehensive and reliable dosimetry for RPV supports, particularly in relation to the thermal neutron component of the neutron spectrum. The literature survey has also demonstrated the confused situation that exists concerning the possible role of Cu in low temperature irradiation embrittlement. The only direct evidence concerning the role of Cu appears to be that of Russian workers who observed pronounced embrittlement in both commercial steels and model Fe/Cu/Ti alloys at 50°C. In the latter work a direct link to Cu content was identified at levels consistent with the predictions of models proposed for higher temperature embrittlement. However, the results also suggest a possibly strong inhibiting effect of interstitial elements such that embrittlement was only observed in alloys containing scavenging additions such as V and Ti. One analysis of the HFIR surveillance data has identified the possible effect of Cu and this can be shown to be consistent with the recent Shippingport neutron shield tank results. Similar analysis of other data from the literature appears to demonstrate a pattern of behaviour consistent with an undiminished copper embrittlement at low temperatures and reinforces the original concerns about RPV support structures raised by the HFIR surveillance results. The concerns are further reinforced by the fact that the support structures of many plant are manufactured from steels containing high (0·2-0·4% wt) Cu levels. It is concluded that there is a need to resolve the issues of neutron spectrum and low temperature Cu embrittlement effects, so that the structural integrity of RPV support structures in many operating nuclear plants may be better assessed.

Improved specific activity of reactor produced 117mSn with the Szilard-Chalmers process

We report an investigation of the application of the Szilard-Chalmers process to improve the specific activity of reactor produced 117mSn. The radiopharmaceutical 117mSn 4+DTPA is a promising agent for relieving bone pain in breast and prostate cancer patients. Preliminary studies in these patients have given very encouraging results. For this application high specific activity 117mSn is required to minimize the quantity of administered DTPA. Using a tetraphenyltin target we have investigated solvent extraction and ion exchange techniques to enrich the radioactive atom concentration. Other variables studied include the effect of neutron flux, total neutron fluence and sample mass. The enrichment factor was comparable for both solvent extraction and ion exchange techniques, but solvent extraction was more convenient. For 1 h irradiations the enrichment factor averaged ∼ 70 but declined to ∼ 2 after 24 h irradiation due to accumulated radiation damage. The enrichment factor also declined with increasing neutron energy. An isotope effect on the Szilard-Chalmers process was observed as the enrichment factor for 113Sn was consistently higher than for 117mSn.