State Scientific Center - Research Institute of Atomic Reactors

The discovery of a new chemical element with atomic number Z=117 is reported. The isotopes (293)117 and (294)117 were produced in fusion reactions between (48)Ca and (249)Bk. Decay chains involving 11 new nuclei were identified by means of the Dubna gas-filled recoil separator. The measured decay properties show a strong rise of stability for heavier isotopes with Z > or = 111, validating the concept of the long sought island of enhanced stability for superheavy nuclei.

Two years after the discovery of element 117, we undertook a second campaign using the (249)Bk+(48)Ca reaction for further investigations of the production and decay properties of the isotopes of element 117 on a larger number of events. The experiments were started in the end of April 2012 and are still under way. This Letter presents the results obtained in 1200 hours of an experimental run with the beam dose of (48)Ca of about 1.5×10(19) particles. The (249)Bk target was irradiated at two energies of (48)Ca that correspond to the maximum probability of the reaction channels with evaporation of three and four neutrons from the excited (297)117. In this experiment, two decay chains of (294)117 (3n) and five decay chains of (293)117 (4n) were detected. In the course of the long-term work, (249)Cf-the product of decay of (249)Bk (330 d)-is being accumulated in the target. Consequently, in the present experiment, we also detected a single decay of the known isotope (294)118 that was produced during 2002-2005 in the reaction (249)Cf((48)Ca,3n)(294)118. The obtained results are compared with the data from previous experiments. The experiments are carried out in the Flerov Laboratory of Nuclear Reactions, Joint Institute for Nuclear Research, using the heavy-ion cyclotron U400.

The Baksan Experiment on Sterile Transitions (BEST) was designed to investigate the deficit of electron neutrinos ${\ensuremath{\nu}}_{e}$ observed in previous gallium-based radiochemical measurements with high-intensity neutrino sources, commonly referred to as the ``gallium anomaly,'' which could be interpreted as evidence for oscillations between ${\ensuremath{\nu}}_{e}$ and sterile neutrino (${\ensuremath{\nu}}_{s}$) states. A 3.414-MCi $^{51}\mathrm{Cr}$ ${\ensuremath{\nu}}_{e}$ source was placed at the center of two nested Ga volumes and measurements were made of the production of $^{71}\mathrm{Ge}$ through the charged current reaction, $^{71}\mathrm{Ga}({\ensuremath{\nu}}_{e},{e}^{\ensuremath{-}})^{71}\mathrm{Ge}$, at two average distances. The measured production rates for the inner and the outer targets, respectively, are [${54.9}_{\ensuremath{-}2.4}^{+2.5}(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}1.4(\mathrm{syst})$] and [${55.6}_{\ensuremath{-}2.6}^{+2.7}(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}1.4(\mathrm{syst})$] atoms of $^{71}\mathrm{Ge}/d$. The ratio ($R$) of the measured rate of $^{71}\mathrm{Ge}$ production at each distance to the expected rate from the known cross section and experimental efficiencies are ${R}_{\mathrm{in}}=0.79\ifmmode\pm\else\textpm\fi{}0.05$ and ${R}_{\mathrm{out}}=0.77\ifmmode\pm\else\textpm\fi{}0.05$. The ratio of the outer to the inner result is $0.97\ifmmode\pm\else\textpm\fi{}0.07$, which is consistent with unity within uncertainty. The rates at each distance were found to be similar, but 20%--24% lower than expected, thus reaffirming the anomaly. These results are consistent with ${\ensuremath{\nu}}_{e}\ensuremath{\rightarrow}{\ensuremath{\nu}}_{s}$ oscillations with a relatively large $\mathrm{\ensuremath{\Delta}}{m}^{2}$ ($>0.5\text{ }\text{ }{\mathrm{eV}}^{2}$) and mixing ${\mathrm{sin}}^{2}2\ensuremath{\theta}$ ($\ensuremath{\approx}0.4$).

Studies of superheavy nuclei produced in the ${}^{249}$Bk + ${}^{48}$Ca reaction were performed using the Dubna Gas Filled Recoil Separator. The cross section for the production of ${}^{293}$117 and ${}^{294}$117 isotopes was measured at five excitation energies of the ${}^{297}$117 compound nucleus ranging from 30 to 48 MeV and yielding maximum values of 1.1${}_{\ensuremath{-}0.6}^{+1.2}$ pb for the $3n$ and 2.4${}_{\ensuremath{-}1.4}^{+3.3}$ pb for the $4n$ reaction channels. Alpha emission from ${}^{281}$Rg competing with spontaneous fission ($\ensuremath{\alpha}$/SF decay probability 1:9) was observed for the first time leading to the identification of the new isotope ${}^{277}$Mt (${T}_{\mathrm{SF}}\ensuremath{\approx}5$ ms). The measured decay properties are in good agreement with those expected based on the properties of neighboring even-$Z$ and odd-$Z$ nuclei. The $\ensuremath{\alpha}$ energies and half-lives of odd-$Z$ isotopes observed in the ${}^{293}$117 and ${}^{294}$117 decay chains together with results obtained for lower-$Z$ superheavy nuclei demonstrate enhanced stability with increasing neutron number toward the predicted new magic number $N=184$.

The heaviest isotopes of elements $Z=117$ to $Z=105$, ${}^{294}117$, ${}^{293}117$, ${}^{290}115$, ${}^{289}115$, ${}^{286}113$, ${}^{285}113$, $^{282}\mathrm{Rg}$, $^{281}\mathrm{Rg}$, $^{278}\mathrm{Mt}$, $^{274}\mathrm{Bh}$, and $^{270}\mathrm{Db}$, were identified by means of the Dubna gas-filled recoil separator among the products of the $^{249}\mathrm{Bk}$ $+$ $^{48}\mathrm{Ca}$ reaction. The details of the observed six decay chains, indicating the production and decay of isotopes ${}^{293}117$ and ${}^{294}117$, are presented and discussed. The decay energies and resulting half-lives of these new nuclei show a strong rise of stability with increasing neutron number, validating the concept of the island of enhanced stability for superheavy nuclei [Oganessian et al., Phys. Rev. Lett. 104, 142502 (2010)].

The experiment Neutrino-4 started in 2014 with a detector model and continued with a full-scale detector in 2016--2021. In this article, we describe all the steps of the preparatory work on this experiment. We present all results of the Neutrino-4 experiment with increased statistical accuracy provided to date. The experimental setup is constructed to measure the flux and spectrum of the reactor antineutrinos as a function of distance to the center of the active zone of the SM-3 reactor (Dimitrovgrad, Russia) in the range of 6--12 meters. Using all the collected data, we performed a model-independent analysis to determine the oscillation parameters $\mathrm{\ensuremath{\Delta}}{\mathrm{m}}_{14}^{2}$ and ${\mathrm{sin}}^{2}2{\ensuremath{\theta}}_{14}$. The method of coherent summation of measurement results allows us to directly demonstrate the oscillation effect. We present the analysis of possible systematic errors and the MC model of the experiment, which considers the possibility of the effect manifestation at the present precision level. As a result of the analysis, we can conclude that at currently available statistical accuracy, we observe the oscillations at the $2.9\ensuremath{\sigma}$ level with the parameters $\mathrm{\ensuremath{\Delta}}{m}_{14}^{2}=(7.3\ifmmode\pm\else\textpm\fi{}{0.13}_{\mathrm{st}}\ifmmode\pm\else\textpm\fi{}{1.16}_{\mathrm{syst}})\text{ }\text{ }{\mathrm{eV}}^{2}=(7.3\ifmmode\pm\else\textpm\fi{}1.17)\text{ }\text{ }{\mathrm{eV}}^{2}$ and ${\mathrm{sin}}^{2}2\ensuremath{\theta}=0.36\ifmmode\pm\else\textpm\fi{}{0.12}_{\mathrm{stat}}(2.9\ensuremath{\sigma})$. Monte Carlo based statistical analysis gave an estimation of the confidence level at $2.7\ensuremath{\sigma}$. We plan to improve the currently working experimental setup and create a completely new setup in order to increase the accuracy of the experiment by 3 times. We also provide a brief analysis of the general experimental situation in the search for sterile neutrinos.

Recent progress in the RF low activation structural materials R&D road map towards DEMO via the FBR tests (BOR-60, BN-600, BN-800) and the TBM tests in ITER is overviewed. The properties of the RAFMS RUSFER-EK-181 (Fe?12Cr?2W?Ta?V?B?C) and the V?4Ti?4Cr alloys are presented. The next important steps include further studies on the influence of high dose and high-temperature irradiation on the properties of base structural materials and joints. Activation, transmutation and radiation damage of the materials in BN-600 and DEMO-RF (Kurchatov Institute project) neutron spectra are calculated. The results of the application of the internal friction (ultrasonic) non-destructive method to research the DBTT are in good agreement with the results of the destructive impact method. The important influence of boron on the heat resistance of materials and the He concentration level under irradiation are calculated. The new special regimes of the heat treatments of the alloys are suggested to widen the temperature windows of the applications. The results of the BOR-60 examinations of RUSFER-EK-181 (irradiation temperature 320?340??C and doses up to 15?dpa) are presented. The BN-600 projects for the high dose and high-temperature irradiation tests of manufactured alloys are presented.

Production and decay of the isotopes of Hs were studied in the ${}^{226}$Ra+${}^{48}$Ca reaction at beam energies ${E}_{\mathrm{lab}}=229$, 234, and 241 MeV. At the ${E}_{\mathrm{lab}}=234$ MeV energy, the maximum of the 4$n$-evaporation channel of the reaction, six identical $\ensuremath{\alpha}$-SF decay chains of the nucleus ${}^{270}$Hs were detected corresponding to a cross section of ${\ensuremath{\sigma}}_{4n}={16}_{\ensuremath{-}7}^{+13}$ pb. At the other ${}^{48}$Ca energies, no Hs isotopes were observed. Nuclei of ${}^{270}$Hs undergo $\ensuremath{\alpha}$ decay with a ${Q}_{\ensuremath{\alpha}}=9.15\ifmmode\pm\else\textpm\fi{}0.08$ MeV and the half-life of the daughter spontaneous fission (SF) isotope ${}^{266}$Sg is 0.28${}_{\ensuremath{-}0.08}^{+0.19}$ s, in good agreement with the data previously observed in the ${}^{248}$Cm(${}^{26}$Mg,4$n$)${}^{270}$Hs reaction. The partial $\ensuremath{\alpha}$-decay half-life of ${}^{270}$Hs was measured for the first time: ${T}_{\ensuremath{\alpha}}=7.{6}_{\ensuremath{-}2.2}^{+4.9}$ s. For the spontaneous fission, we determined a lower limit ${T}_{\mathrm{SF}}\ensuremath{\geqslant}10$ s. Decay properties of ${}^{270}$Hs corroborate theoretical predictions of its relatively high stability caused by the effect of the deformed shells at $Z=108$ and $N=162$.

First results from the BEST Collaboration searching for short-baseline neutrino oscillations to sterile neutrinos with a high-intensity ${}^{51}$Cr monoenergetic neutrino source reaffirm that the so-called gallium anomaly, a deficit in electron neutrinos, persists. $4\ensuremath{\sigma}$ deficits were observed in the ${}^{71}$Ge production rates at two different distance scales, which could be interpreted as oscillations between an electron neutrino and a hypothetical sterile neutrino. The results are consistent with oscillations with a mass squared difference above about 0.5 eV${}^{2}$ and a large mixing angle ${\mathrm{sin}}^{2}\phantom{\rule{0.167em}{0ex}}2\ensuremath{\theta}\ensuremath{\approx}0.4$.

The global sensitivity analysis of a complex numerical model often calls for the estimation of variance-based importance measures, named Sobol' indices. Metamodel-based techniques have been developed in order to replace the CPU time-expensive computer code with an inexpensive mathematical function, which predicts the computer code output. The common metamodel-based sensitivity analysis methods are well suited for computer codes with scalar outputs. However, in the environmental domain, as in many areas of application, the numerical model outputs are often spatial maps, which may also vary with time. In this paper, we introduce an innovative method to obtain a spatial map of Sobol' indices with a minimal number of numerical model computations. It is based upon the functional decomposition of the spatial output onto a wavelet basis and the metamodeling of the wavelet coefficients by the Gaussian process. An analytical example is presented to clarify the various steps of our methodology. This technique is then applied to a real hydrogeological case: for each model input variable, a spatial map of Sobol' indices is thus obtained. Copyright © 2010 John Wiley & Sons, Ltd.

Studied were evolution of dislocation structure, phase, and element composition of binary alloys Zr-1Nb and Zr-2.5Nb and multicomponent alloys Zr-1Nb-1.2Sn-0.4Fe and Zr-1.2Sn-0.4Fe under neutron irradiation. The investigations were carried out using cladding and pressure tubes before and after irradiation to a fluence of ∼1026 n/m2 (E ≥ 0.1 MeV) in experimental and commercial reactors at 300 to 350°C using TEM, EDX, and XRD. In most cases, irradiation-induced defects are in the form of dislocation loops with Burgers vector 1/3 ⟨1120⟩. The density of dislocations with a ⟨c⟩ component is less than 2 × 1014 m-2. A higher fluence or the presence of strain results in the ordering of the dislocation structure of ⟨c⟩ component and ⟨a⟩-type dislocation loops. Before irradiation, the multicomponent alloys contain fine precipitates of Zr-Nb-Fe composition, and the matrix is depleted in Fe. Under irradiation, recrystallization proceeds intensively (as distinct from Zr-Nb alloys), changes take place in size, distribution, and composition of precipitates (with a relative decrease of Fe content compared to Nb), and the Fecontent of α-Zr matrix is increased. None of the materials studied showed any significant evidence of secondary phase particle amorphization. The density of dislocations with ⟨a⟩ and ⟨c⟩ components and irradiation-induced defects, their mean size, the extent of ordering, and the planes of their occurrence were determined. A comparison was made between irradiation-induced evolutions of microstructures of the different alloys.

Complex oxides of the pyrochlore (space groups Fd3m, [8]A2 [6]B2O7) and garnet (Ia3d, [8]A3 [6]B2 [4]T3O12) structures (“A” = Ca2+, Ln3+/4+, An3+/4+; “B” = (Ti, Sn, Hf, and Zr)4+ in pyrochlore, and Al3+, Ga3+, and Fe3+ in garnet alone; “T” = (Al3+, Ga3+, and Fe3+) are promising matrices for actinide-bearing wastes. In order to identify optimal compositions of these phases, their isomorphic capacity with respect to REE, actinides, and other components of wastes was examined. The long-term behavior of the matrix at a repository was predicted based on data obtained on the behavior of pyrochlores and garnets under ion irradiation and 244Cm decay and on the determined leaching rates of REE from the matrices because of their interaction with aqueous solutions, including that after amorphization. In order to propose efficient synthesis techniques, samples prepared with the use of various methods were studied. The possibility of incorporating long-lived decay products of 99Tc into the crystalline matrices was analyzed.

Extraction efficiencies of Pd(ii), Rh(iii), and Ru(iii) from HNO3(aq) to [Hbet][Tf2N] were demonstrated, i.e., Pd(ii) is the most extractable, Rh(iii) is medium extractable, and Ru(iii) is the least extractable. The extraction seems to proceed through coordination of betaine to the metal ions and the cation exchange of the formed complex with H(+).

Data are given on Zr alloy E635 (Zr-l.2Sn-lNb-0.4Fe), developed in Russia as a fuel rod cladding and other component material for use in cores of VVER and RBMK types. The alloy is much superior to binary alloys with 1.0 and 2.5% Nb and Zircaloys in terms of its resistance to irradiation-induced creep and growth and nodular corrosion. The creep rate of the alloy is slightly dependent on irradiation temperature, stress, neutron fluence, and neutron density. The alloy is subject to substantial irradiation hardening while retaining its high-percent elongation. Corrosion, creep, and growth resistances are slightly dependent on the structure of components (alloy, final product). Based on the previously studied influence of impurities, structure, heat treatment, and working schedules, the technological processes were designed and mastered commercially for fabrication of tubes, bars, strips, and fuel rod claddings from this alloy. Components are produced commercially. Fuel assemblies with fuel rods clad in the E635 alloy were successfully tested in the RBMK reactor at the Leningrad NPP as well as in experimental reactors under VVER-1000 conditions. Today, the E635 alloy is recommended as a promising material for use in cores of VVER-1000 and VVER of new generations as well as RBMK-type reactors having a longer fuel cycle.

First experimental results of a chemical investigation of element 113 independently confirm the synthesis of the new elements 115 and 113 in the nuclear fusion reaction of <sup>48</sup>Ca + <sup>243</sup>Am and indicate a chemical behaviour resembling a species with a high volatility, a weak interaction with inert surfaces and an enhanced reactivity towards gold surfaces.

Abstract On account of the search for the optimal composition and structure-phase state of Zr alloys much attention is paid to upgrade the E110 (Zr-1 %Nb) and E635 (Zr-1 %Nb-0.35 %Fe-1.2 %Sn) alloys that have proved well in terms of irradiation-induced creep and growth, high strength characteristics, and corrosion. The difference between the alloy properties is determined by their states related to their compositions. The structure-phase state of the Zr-Nb and Zr-Nb-Fe-Sn systems has been studied after heat treatment in the α-- and α + β- regions and its influence on the irradiation-induced growth (IIG) during BOR-60 irradiation at T =315–350 °C was investigated. A substantial difference has been shown in the deformation effected by IIG of those alloys, it is less for Zr-Nb-Fe-Sn alloys in dissimilar structure-phase states. The incubation period of the accelerated growth stage is determined by the α-matrix composition, the phase state and the initial dislocation structure. Neutron irradiation leads to a redistribution of alloying elements between the matrix and the precipitates, and to changes in the α-solid solution composition. These changes affect accumulation and mobility of irradiation defects, anisotropy and formation of vacancy c-component dislocation loops. The appearance of c-loops usually correlates with an axial direction acceleration of the IIG of tubes conforming to their texture. The basic regularities of the phase transformation have been established: a) β-Nb precipitates in Zr-Nb alloys are altered in composition to reduce the Nb content from 85–90 % to ∼ 50 %, fine precipitates likely enriched in Nb are formed; b) β-Zr precipitates are subject to irradiation-stimulated decomposition; c) Laves phase precipitates change composition (the content of Fe decreases) and crystal structure, HCP to BCC (β-Nb); d) (Zr,Nb)2Fe precipitates having the FCC lattice retain their composition and crystal structure; e) no amorphization of any secondary phase precipitates is observable under the given conditions of irradiation (T = 315–350 °C). Based on the dpa, the results were compared pertaining to Zr-alloy IIG deformation vs. fluence in various reactors at different energies of fast neutrons. The presented graphs enable comparison between the results of numerous experiments and enable predictions of Zr-material behavior in long-term operation and at high burn-up in commercial reactors.

We report Neutrino-4 experiment results of measurements of reactor antineutrinos flux and spectrum dependence on the distance in range 6–12 m from the center of the reactor core. The fit of experimental dependence with the law 1/L2, where L is the distance from the reactor center, gave satisfactory result with goodness of fit 81%. However, we discovered that the experimental neutrino spectrum is different from the calculated one. Using experimental spectrum, we performed the model independent analysis of restrictions on oscillation parameters Δm 14 2 and sin2 2θ14. The results of this analysis exclude area of reactor and gallium anomaly at CL more than 99.7% (>3σ) for values Δm 14 2 < 3 eV2 and sin2 2θ14 > 0.1. However, we observed an oscillation effect at CL 2.8σ in vicinity of Δm 14 2 Δm 14 2 ≈ 7.3 eV2 and sin2 2θ14 ≈ 0.39. The method of coherent addition of results of measurements, which allows us to directly observe the effect of oscillations, is proposed. The analysis of that effect is presented. In general, it seems that the effect predicted in gallium and reactor experiments is being confirmed but at sufficiently large value of Δm 14 2 . Future prospects of the experiment are discussed.

Abstract In the search for more optimal core materials for a water cooled reactor at extended burnup, much attention is paid to alloys of the Zr-Nb and Zr-Nb-Fe-Sn systems. E110 and E635 alloys are two such. In the current VVER fuel cycle, the E110 alloy is used as fuel cladding and in SG components. The E635 alloy is under development as a fuel cladding and for fuel assembly structural elements for water cooled reactors of the VVER and RBMK types. E110, while having a unique corrosion resistance in pressurized water reactors, is subject to noticeable disadvantages in terms of corrosion resistance under conditions of boiling and higher coolant oxygen contents as well as in deformation stability under stresses and irradiation. Currently, the E635 alloy has passed the most important steps of qualification and is being introduced into cores as a material for guide thimbles, central tubes, and stiff frame angles in VVER-1000 FAA and FA-2. Properties of alloys are governed by their compositions and microstructure and even small changes in composition (Nb, Fe, Sn) and processing (heating in the α or the α+β regions) lead to substantial changes in properties as a result of changes in second phase precipitates and matrix composition. ATEM was used to study structure—phase states of a series of alloys Zr-(0.6–1.2) Nb-(0–0.6) Fe-(0–1.5) Sn (% weight), to determine the microstructural characteristics of recrystallized cladding tubes and the temperature stability regions of β-Nb, β-Zr, Zr(Nb,Fe)2, and (Zr,Nb)2Fe second phase precipitates. An increase in the relative content of iron R=Fe/(Fe+Nb) results in a larger volume fraction of (Zr,Nb)2 Fe precipitates. β-Nb and Zr(Nb,Fe)2 particles are completely dissolved at ⩽750°C, the (Zr,Nb)2Fe phase at ⩽800°C. Autoclave corrosion tests revealed that the corrosion resistance of the materials depends on alloy composition. The content of tin lowered down to 0.8 % reduces weight gains in water, water containing Li, and particularly in steam. The content of Nb reduced to 0.6 % results in lower weight gains in water and steam and higher weight gains in Li containing water. The optimal content of iron in Zr-Nb-Fe-Sn alloys for corrosion resistance depends on the R ratio and makes up 0.2–0.4 %. Tests of samples produced from tubes of the above alloys and irradiated in BOR-60 at 315–345°C show that alloying Zr-Nb alloys with iron and tin improves their resistance to irradiation growth and creep. Sn and a higher Fe content in solid solution effected by transfer of Fe from the Laves phase precipitates to the matrix under irradiation strengthens the alloys. The influence of irradiation on phase compositions was established using irradiated samples (gas filled and unstressed) of cladding tubes: β-Nb (85-90 % Nb) precipitates become depleted in niobium (or enriched in zirconium) to 50-60 % Nb and finely dispersed irradiation induced second particles (IIPs) enriched in niobium are formed. The Laves phase becomes depleted in iron and alters its crystal structure from hcp to bcc of the β-Nb type. The fcc (Zr,Nb)2Fe precipitates retain on the whole their composition and structure, but the peripheries of particles reveal structural features, possibly related to niobium redistribution. No amorphization of any of the precipitates was identified. Alloy composition and applied stress under irradiation influence density and distribution of dislocation loops and IIP precipitates. Proceeding from results of out-of-pile and from post-irradiation examinations of the structure and properties of E110 and E635 type cladding tubes, compositions of alloys having improved corrosion and irradiation resistances are proposed. E110 type (Zr-1Nb-0.1Fe-0.1O) alloy features enhanced strength characteristics as a result of iron transfer from Laves phase precipitates to the matrix under irradiation, lower irradiation induced growth strain, and irradiation-thermal creep. An E635 type alloy (tin and niobium content lowered down to &amp;lt;0.8 %) has a higher corrosion resistance and comparable creep and growth resistance as compared to the standard E635 alloy.

A highly emissive copper(I) complex bearing (4R,5R)-(-)-4,5-bis(diphenylphosphinomethyl)-2,2-dimethyl-1,3-dioxolane (diop) and 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (dmpp), [Cu(dmpp)(diop)]PF6 (1·PF6), was newly synthesized. The quantum yield of the luminescence of 1·PF6 in degassed dichloromethane is 0.38, which is one of the highest values among all copper(I) complexes bearing two bidentate ligands, diimine and diphosphine, under the same conditions. The long lifetime (26 μs) and high intensity of the emission come from the small non-radiative decay rate of the excited states. The TD-DFT study indicates that the charge transfer transition from both copper and diphosphine to diimine orbitals plays an important role in the photophysical properties. Photophysics of [Cu(dmp)(diop)]PF6 (2·PF6, dmp = 2,9-dimethyl-1,10-phenanthroline) was also studied in order to reveal the effects of the introduction of the phenyl group at 4- and 7-positions of phenanthroline.

The studies of the dislocation structure, phase, and microchemical compositions of alloy Zr-1Nb-1.2Sn-0.35Fe (E635) and its modifications containing Fe from 0.15 to 0.65% were carried out before and after research reactor irradiation at ∼350°C to maximal fluence of ∼1027 m-2 (E &amp;gt; 0.1 MeV) and at ∼60°C. The size and concentration of the &amp;lt;a&amp;gt;-type loops depend on the alloy composition and fluence and saturate even at low doses (&amp;lt;1 dpa). The evolution of the &amp;lt;c&amp;gt;-component dislocation structure in recrystallized alloys of E365 type is determined by the chemical and phase compositions of alloys specifically, by the Fe/Nb ratio and the threshold dose, and is consistent with the irradiation growth strain acceleration. In E635 alloy containing 0.15%Fe the accelerated growth is observed after the dose of 15 dpa and is attended with the evolution of the &amp;lt;c&amp;gt; dislocation structure which is similar to Zr-1Nb (E110) alloy behavior. The irradiation induced growth of E635 type alloy containing 0.65% Fe is similar to that of E635 having the normal composition; no &amp;lt;c&amp;gt; dislocations are observed up to the dose of 20 dpa. E635 alloy contains precipitates Zr(Nb1-xFex)2 (HCP) as the basic excess phase and individual (Zr,Nb)2Fe (FCC) precipitates; in 0.15%Fe alloy aside from Zr(Nb,Fe)2 also β-Nb (BCC) particles precipitate, while 0.65%Fe alloy contains Zr(Nb,Fe)2 and (Zr,Nb)2Fe particles. Irradiation at 330 –350 °C does not effect an amorphization of β-Nb or Zr(Nb,Fe)2 precipitates; however, at higher fluences the β-Nb phase becomes depleted in Nb and Zr(Nb,Fe)2 in Fe. Irradiation at 60°C leads to the amorphization of Zr(Nb,Fe)2 in E635. The analysis revealed that the key factors promoting a delay in the accelerated irradiation growth in Zr-Nb-Fe-Sn alloys are the composition of (Nb,Fe,Sn) solid solution and the Fe/Nb ratio in alloys.