Radiation-Induced Change in the Properties of Isotropic Structural Graphite

Three types of samples of isotropic graphite with different grain density and size were irradiated in a BOR-60 reactor up to neutron fluence (1.7–2.8)·10²⁶ m^–2 (E > 0.18 MeV) at 360–400°C. After irradiation, the change in the dimensions, resistivity, linear thermal expansion coefficient and dynamic elastic modulus were investigated. It was determined that the density in the range 1.67–1.76 g/cm³ results in an increase of the maximum weight and depth of volume shrinkage of isotropic fine-grain graphite. An equation was proposed for fitting the temperature dependence of the critical neutron fluence in the range 380–780°C for the experimental graphite samples.     

Investigation of radiation creep of reactor graphite

The results of investigations of the radiation creep of GR-280 graphite under a high compression load (about 15 MPa) after irradiation in a BOR-60 reactor at 520°C to fast-neutron fluence 1.2·10²² cm⁻² are presented. It is shown that the fluence dependence of the creep deformation, calculated using the standard relation as the difference of the change in the dimensions of loaded and control samples, is anomalous. The linear thermal expansion coefficients of loaded and control samples are found as functions of the neutron fluence under the same conditions. It is noted that the linear thermal expansion coefficient of the samples irradiated under a load is much higher than that of the control samples. Simmons' theorem is used to take account of the effect of a load on the linear thermal expansion coefficient, and the dimensional changes of graphite exposed to radiation and the dependence of the true creep deformation on the neutron fluence are calculated. It is shown that these dependences are close to linear in the experimental fluence range (0.4–1.2)·10²² cm⁻². Translated from Atomnaya énergiya, Vol. 105, No. 2, pp. 83–87, August, 2008.     

Fluence dependence of the surface roughness of InP after bombardment

InP(1 0 0) surfaces were sputtered under ultrahigh vacuum conditions by 5 keV ions at an angle of incidence of 41° to the sample normal. The fluence, , used in this study, varied from 1 × 10¹⁴ to 5 × 10¹⁸ cm⁻². The surface topography was investigated using field emission scanning electron microscopy (FE-SEM) and atomic force microscopy (AFM). At the lower fluences ( 5 × 10¹⁶ cm⁻²) only conelike features appeared, similar in shape as was found for noble gas ion bombardment of InP. At the higher fluences, ripples also appeared on the surface. The bombardment-induced topography was quantified using the rms roughness. This parameter showed a linear relationship with the logarithm of the fluence. A model is presented to explain this relationship. The ripple wavelength was also determined using a Fourier transform method. These measurements as a function of fluence do not agree with the predictions of the Bradley–Harper theory.     

Influence of various catalysts on the radiation resistance and the mechanical properties of cyanate ester/epoxy insulation systems

Fiber reinforced composites impregnated with mixtures of various cyanate ester and epoxy resins demonstrated their excellent performance at the ITER design fluence and beyond. The insulation systems consist of a wrapped R-glass/Kapton reinforcement, vacuum impregnated with a cyanate ester/epoxy blend. For the fabrication of the insulation a long pot-life of the resin is of great importance, which is mainly determined by the amount and the composition of the catalyst needed for curing the resin. However, the catalyst, which amounts to 1–2% of the resin, may also affect the mechanical properties as well as the radiation hardness of the material. In order to investigate these effects, two different composites were fabricated using a Mn- and a Co-catalyst, respectively.The mechanical properties are characterized prior to and after irradiation to a fast neutron fluence of 1 × 10²² m⁻² (E > 0.1 MeV) in tension and interlaminar shear at 77 K.     

Effect of the nonuniformity of graphite samples on their shape change under irradiation

It is shown that the use of the initial characteristics of samples makes it possible to decrease substantially the variance and the bias in the determination of the critical neutron fluence for GR-280 RBMK graphite. It is recommended that a graphite model that includes neutron fluence and the initial value of the elastic modulus be used as an approximation for dimensional changes of graphite samples. 2 figures, 2 tables, 3 references. Russian Science Center “Kurchatov Insitute”. Translated from Atomnaya énergiya, Vol. 87, No. 1, pp. 28–33, July, 1999.     

Effect of irradiation by 140 Mev Ag ions on the optical and electrical properties of polypropylene/TiO2 composite

Changes in the optical, structural, dielectric properties and surface morphology of a polypropylene/TiO₂ composite due to swift heavy ion irradiation were studied by means of UV–visible spectroscopy, X-ray diffraction, impedance gain phase analyzer and atomic force microscopy. Samples were irradiated with 140 MeV Ag¹¹⁺ ions at fluences of 1 × 10¹¹ and 5 × 10¹² ions/cm². UV–visible absorption analysis reveals a decrease in optical direct band gap from 2.62 to 2.42 eV after a fluence of 5 × 10¹² ions/cm². X-ray diffractograms show an increase in crystallinity of the composite due to irradiation. The dielectric constants obey the Universal law given by ε α f ⁿ⁻¹, where n varies from 0.38 to 0.91. The dielectric constant and loss are observed to change significantly due to irradiation. Cole–cole diagrams have shown the frequency dependence of the complex impedance at different fluences. The average surface roughness of the composite decreases upon irradiation.     

Reactor pressure vessel design of the high temperature engineering test reactor

The reactor pressure vessel (RPV) of the HTTR is 5.5 m (inside diameter), 13.2 m (inside height), and 122 mm (shell thickness). The RPV contains core components, reactor internals, reactivity control system, etc.2 1/4Cr–1Mo steel is chosen as the material for RPV. The temperature reaches about 400 °C at normal operation. The fluence of the RPV is estimated to be less than 1 × 10¹⁷ n/cm² (E > 1 MeV) and so irradiation embrittlement is negligible, but temper embrittlement is not negligible. For the purpose of reducing embrittlement, content of some elements must be limited in the 2 1/4Cr–1Mo steel for the RPV; embrittlement parameters, J-factor and are used.In this paper, design and structure of the RPV are reviewed first. Fabrication procedure of the RPV and its special feature are described. Material data on the 2 1/4Cr–1Mo steel manufactured for the RPV, especially the embrittlement parameters, J-factor and , and nil-ductility transition temperatures, T_NDT, by drop weight tests, are shown. In-service inspection and results of R&Ds are also described.     

Experimental Study of the Radioactive Contamination of Graphite Masonry in the Commercial Reactors at the Siberian Chemical Combine

The graphite masonry from decommissioned commercial uranium–graphite reactors is contaminated with radionuclides and is a significant fraction of the radioactive wastes from the nuclear industry. Information about the composition and degree of contamination of the graphite is needed to choose methods and time periods for handling this graphite. The results of investigations performed on I-1, ÉI-2, and ADÉ-3 reactors at the Siberian Chemical Combine in 1996–2001 are presented in this paper. Analysis of a large number of samples made it possible to construct a detailed picture of the contamination of the masonry, study the distribution of the radionuclides of different origin in the masonry, construct schemes for making estimates, and estimate the content of certain radionuclides, including ¹⁴C, ³H, ⁹⁰Sr, ²⁴¹Am, ²⁴⁴Cm, ^238–241Pu, ^137,134Cs, and ⁶⁰Co.     

High yield antibiotic producing mutants of Streptomyces erythreus induced by low energy ion implantation

Conidia of Streptomyces erythreus, an industrial microbe, were implanted by nitrogen ions with energy of 40–60 keV and fluence from 1 × 10¹¹ to 5 × 10¹⁴ ions/cm². The logarithm value of survival fraction had good linear relationship with the logarithm value of fluence. Some mutants with a high yield of erythromycin were induced by ion implantation. The yield increment was correlated with the implantation fluence. Compared with the mutation results induced by ultraviolet rays, mutation effects of ion implantation were obvious having higher increasing erythromycin potency and wider mutation spectrum. The spores of Bacillus subtilis were implanted by arsenic ions with energy of 100 keV. The distribution of implanted ions was measured by Rutherford Backscattering Spectrometry (RBS) and calculated in theory. The mechanism of mutation induced by ion implantation was discussed.     

Results on research of templates from Kozloduy-1 reactor pressure vessel

The studies on the specimens manufactured from the templates cut out from the weld 4 of Kozloduy NPP Unit 1 reactor vessel have been conducted. The data on chemical composition of the weld metal have been obtained. Neutron fluence, mechanical properties, ductile to brittle transition temperature (DBTT) using mini Charpy samples have been determined. The phosphorus and copper content averaged over all templates is 0.046 and 0.1 wt.%, respectively. The fluence amounted up to 5×10¹⁸ n cm⁻² within 15–18 fuel cycles, and about 5×10¹⁹ n cm⁻² for the whole period of operation. These values agree well with calculated data. DBTT was determined after irradiation (T_k) to evaluate the vessel metal state at the present moment, then after heat treatment at the temperature of 475°C to simulate the vessel metal state after thermal annealing (T_an), and after heat treatment at 560°C to simulate the metal state in the initial state (T_k0). As a result of the tests the following values were obtained: T_k, +91.5°C; T_an, +63°C; and T_k0, 54°C. The values of T_k and T_an obtained by measurements were found to be considerably lower than those predicted in accordance with the conservative method accepted in Russia (177°C for T_k and 100°C for T_an). Thus, the obtained results allowed to make a conclusion that it is not necessary to anneal Kozloduy NPP Unit 1 reactor vessel for the second time. The fractographic and electron-microscopic research allowed to draw some conclusions on the embrittlement mechanism.     

Neutron embrittlement surveillance of the garigliano reactor vessel steel

The effects of neutron radiation on the pressure vessel of the Garigliano Nuclear Power Station have been analyzed on the basis of results of a reactor vessel material surveillance program of the plant. A high radiation embrittlement sensitivity was determined for the weld metal and for the A336 forging steel of the ring forging course just above the level of the fuel core. Both showed high copper and phosphorus contents, which accounted for the embrittlement sensitivity. The ring forging opposite the fuel core had a low copper and phosphorus content and revealed relatively low embrittlement. A neutron fluence of 6.3 × 10¹⁹n/cm² > 1 MeV was determined for the peak flux plane for 40yr of operation. However, the 40yr fluence for the ring forging at the top of the core level (3.5 × 10¹⁹n/cm² > 1 MeV) resulted in the highest final transition temperature because of the sensitivity of this steel. The measured Charpy-V shelf energy absorption values were plotted against yield stress values for comparable irradiations on the ratio analysis diagram (RAD). The analysis revealed that the pressure vessel steel properties would continue to degrade toward a condition of possible frangibility at the end of its life. This projection is based on an assumption of uniform embrittlement throughout the vessel wall thickness. Such uniformity does not exist; in fact, a sharp gradient exists in the steel such that ductility rises rapidly in the steel toward the outside wall as well as above and below the fuel core. Hence, because of this strong ductility gradient, the Garigliano reactor vessel should be able to operate safely over its intended design lifetime.     

Neutron Irradiation Induced Changes in the Structure and Properties of Glassy Carbon

The results of an investigation of SU-1300 and SU-2000 glassy carbon samples after irradiation in a BOR-60 reactor at 360–400°C are presented. It is established that substantial radiation compression of glassy carbon under irradiation remains up to neutron fluence 3.6·10²⁶ m^–2 (E > 0.18 MeV). It is shown that radiation shrinkage is caused by compaction of packets of graphite-like layers and decrease of molecular porosity. Increasing the production temperature of glassy carbon from 1300 to 2000°C decreases the graphitizability of the material under irradiation.     

Neutron irradiation effects on optical absorption of KU1 and KS-4V quartz glasses and Infrasil 301

In this work we have compared the effects of neutron (10²¹–10²² n/m² fluences) and gamma irradiation (23.8 MGy dose) on the IR–vis–UV optical absorption spectra of high purity silica with different OH content: KU1 (800 ppm), KS-4V (<0.2 ppm), and commercial silica Infrasil 301 (<8 ppm). The results show that the UV–vis optical degradation of the silica, after neutron irradiation at the highest fluence is similar for the three grades studied, while gamma-induced optical absorption depends on the material grade (KS-4V shows the lowest optical absorption). The effects of both types of radiation on the IR band related with the hydroxyl group (3650 cm⁻¹) depend on the silica grade. For KU1, the shape of this band changes with neutron fluence. For Infrasil 301 gamma and neutron irradiated, this band height increases, possibly due to free molecular or hydrogen atoms. The shift to lower energies observed for the 2260 cm⁻¹ band in the three neutron irradiated silica grades, reflects the changes induced by neutrons in the lattice bonding angle distribution.     

Influence of the neutron flux density on the radiation embrittlement of VVér-440/213 vessel materials

In work on minisamples of the fifth complex of the No. 3 unit of the Kola nuclear power plant it is shown that for neutron fluence 410²³ m^–2 (operation for approximately 10 yr), neutron flux density 310¹⁵ sec^–1m^–2 and copper content 0.03% and 0.09% in the metal the shifts of the cold-brittleness temperature are 50 and 120°C, respectively. Under the same irradiation conditions but with neutron flux density 310¹⁶ sec^–1m^–2, this shift for standard samples is 50°C. These results attest to the state of the vessel material at a given moment in time.Translated from Atomnaya Énergiya, Vol. 97, No. 3, pp. 177–182, September, 2004.     

The radiation change in the coefficient of linear thermal expansion of carbon materials

Conclusion Hence, the thermal coefficient of volume expansion of graphite is related exponentially to the height of the crystals and the density of the material and depends on the specific surface of the structure and micropores. The coefficient of linear thermal expansion of graphite is inversely proportional to the dynamic modulus of elasticity. The negative change in α of graphite on neutron irradiation: changes nonmonotonically with the neutron fluence and the radiation temperature — initially it increases, reaches a maximum, then falls and again increases; is inversely proportional to the power 1/3 of its initial value, to the rate of steady radiation creep and the neutron fluence; is determined by the degree of perfection of the crystal structure and the concentration of spherolites (carboids) of the elements of the microstructure. Their increase facilitates a fall in α below its initial value; it does not recover completely on thermal annealing to 2300 K. The relative change in α of carbon-carbon composition materials when irradiated to a neutron fluence of 3·10²⁰ cm⁻² and a temperature from 320 K to 2100 K does not exceed 10%. The complex nature of the radiation change makes it difficult to calculate the value of α, and hence it has to be determined in experiments up to the resource dose. Graphite Scientific Research Institute. Translated from Atomnaya énergiya, Vol. 82, No. 6, pp. 417–424, June, 1997.     

Investigation of the Effect of Radiation and High-Temperature Treatment on the x-Ray Luminescence of Quartz Glasses

The x-ray luminescence of KI, KV, and KU-1 quartz glasses, irradiated with and n– radiation in the dose range 10²–10⁷ Gy and neutron fluence range 10¹⁵–10¹⁷ cm^–2 and subjected to high-temperature annealing in air at 450 and 900°C is investigated. It is shown that the spectra of the nonirradiated and the and n– irradiated glasses of the first two types are a superposition of bands with _max = 410 and 460 nm, which are due to an impurity center initially present in the glasses (_max = 410 nm) and the initial and radiation-generated with dose 10⁶ Gy and fluence 10¹⁶ cm^–2 E' centers (_max = 460 nm). X-Ray luminescence is not observed in nonirradiated KU-1 glasses; a band with _max = 460–470 nm, due to radiation-generated E' centers, appears in the spectra of and n– irradiated glasses. As the radiation dose and the neutron fluence increase, the number of impurity centers decreases and the number of E' centers increases. It is established that the 410 nm band is due to the component of the n– radiation. High-temperature annealing in air at 900°C induces in the spectra new bands with _max = 470 and 520–540 nm, which are believed to be due to interstitial defects of the type O^– and O₂ ^–, formed when oxygen from air diffuses into the glass and localizes in interstices. 6 figures, 7 references.     

Flux of secondary neutrons produced by 660 MeV protons in shielding

With the help of a set of threshold and resonance detectors, measurements were made of the spatial and energy distribution of secondary neutrons in graphite and nickel blocks. Absolute values of the neutron flux as a function of depth in an infinite slab were obtained for a plane, monodireetionat proton source. The energy distribution of the secondary neutrons in the energy range 2.5·10^–8 to 6.6·10² Mev was represented by seven groups. The magnitude of the dose behind plane nickel and graphite shielding as a function of thickness was also determined. The results are discussed.Translated from Atomnaya Énergiya, Vol. 18, No. 6, pp. 573–578, June, 1965     

Radiation Characteristics of Graphite in the Commercial Uranium–Graphite Reactors at the Mayak Industrial Association

The results of investigations of the radiation characteristics of graphite samples taken from the masonry in two commercial uranium–graphite reactors at the Mayak Industrial Association are presented. The specific activity of , , and emitters present in the graphite in different parts of the masonry, including cells located next to the damaged cell, is determined. The specific activity of the main product of activation ⁶⁰Co is 10²–10⁴ Bq/g. The concentration of ¹³⁷Cs in the graphite is higher than that of any other fission product (the specific activity in the cells located next to the damaged cell is 10⁴–10⁶ Bq/g). ²⁴⁴Cm makes the largest contribution to the total activity of transuranium elements; its activity in one sample was 2·10⁷Bq/g. More than 90% of the activity of the masonry graphite is due to ¹⁴C. The outer and inner surfaces of the graphite bricks are most highly contaminated with radionuclides. The results obtined are the basis for the high estimated content of radionuclides in the entire graphite masonry for each reactor.     

Investigation of radioactive contamination of graphite samples from the AM reactor

The world’s first nuclear power plant operated for almost 48 years. Over this period of time, the neutron fluence on the graphite masonry reached ∼10²² cm⁻², which resulted in activation of the impurities present in the graphite. During operation, incidents occurred with loss of seal and sometimes loss of integrity of the fuel-element claddings in some cells and particles of the fuel and steam-water mixture entered the graphite masonry. This resulted in radiation contamination with a complex radionuclide composition. Experimental information about the content and distribution of radionuclides in the spent nuclear graphite is needed in order to plan methods and periods of time for disassembly and salvaging of the graphite masonry of the stopped reactor taking account of the dose loads on the workers and the ecological safety norms. The problems which can be solved on the basis of the present work included the determination of the ¹⁴C and ³H contents by liquid-scintillation β spectrometry, analysis of the actinide content by direct γ spectrometry, and neutron-activation analysis followed by γ spectrometry. These investigation yielded new data on the content of fission products and activation impurities in graphite. __________ Translated from Atomnaya énergiya, Vol. 101, No. 5, pp. 358–364, November, 2006.     

Monitoring the Fast-Neutron Flux Density and Fluence in a RBMK Core using a Threshold Fission Chamber in a Screen-Absorber

A new method for measuring the flux density and fluence of fast neutrons in a RBMK core, using a threshold ionization fission chamber with a ²³⁸U radiator, and a computational-experimental method based on threshold chambers for fissioning of ²³⁸U with enrichment at least 99.999% are proposed. A method is proposed for taking account of the correction factors for the change in sensitivity of threshold fission chambers with and without screens on the basis of RBMK-1000 fast-neutron spectra determined experimentally by the activation method.__________Translated from Atomnaya Energiya, Vol. 98, No. 4, pp. 260–267, April, 2005.