WWR-M Reactor Research Articles

Small-angle neutron scattering study of radiation defects in synthetic quartz

The superatomic structure of synthetic quartz single crystals with dislocation densities ρ = 54 and 570 cm−2 was studied in the initial state and after irradiation with fast neutrons with energies E n > 0.1 MeV in a WWRM reactor (St. Petersburg Nuclear Physics Institute) in the fluence range F = 0.2 × 1017−5.0 × 1018 neutrons/cm2. Weak irradiation with F = 0.2 × 1017 neutrons/cm2 causes only slight structural changes, whereas appreciable generation of defects with radii of gyration r g ∼ 1–2 nm and R G ∼ 40–50 nm occurs at F = 7.7 × 1017−5.0 × 1018 neutrons/cm2. As the fluence increases further, the number and volume fraction of point defects, as well as extended (channels ∼2 nm in radius) and globular (amorphous phase nuclei) defects, increase.

The Size Distribution of Defect Clusters in n-Si (FZ, Cz), Irradiated by Fast Neutrons

The dependence of concentration of defects on doping level for average cluster in n-Si was calculated. It was shown that in the framework of the Gossick's model the concentration of defects for the average cluster is in inverse proportion to the square of a cluster radius. One obtains the size distribution of defect clusters created by fast neutrons of WWR-M reactor, by the transformation of energy spectrum of the primary knock-on atom in n-Si (FZ, Cz). Threshold energy of defect clusters formation 4.7 keV by comparing n-Si crystals irradiated by deuterons and fast-pile neutrons was calculated.

Measurement of thermal neutron radiative capture cross-sections of the 14N and 19F by in-beam γ-spectroscopy method with reactor neutrons

The cross-sections of the 14N(n ,γ) 15N and 19F(n ,γ) 20F reactions were measured by γ-spectroscopy method with the target placed at the end of a neutron guide of the WWR-M reactor (PNPI, Gatchina). The neutron spectrum was measured by the TOF method. The maximum of the spectrum is located at 0.028(2) eV and FWHM is about 0.03 eV. Cross-section of radiative neutron capture in aluminium and absolute γ-intensities of the 1779 and 1633 keV γ-lines from beta decay of the 28Al and 20F, respectively, and the prompt 1678 and 1885 keV γ-lines from the 14N(n, γ) 15N reaction were taken as standards. The thermal neutron radiative cross-sections of the 14N and 19F were measured to be 0.0795(13) and 0.00950(15)b, respectively. New value of the γ-intensity of the 1678 keV γ-line from the 14N(n, γ) 15N reaction has been proposed.

Neutron diffraction and optics in noncentrosymmetric crystals: New feasibility of a search for neutron EDM

Recently strong electric fields (up to 10 9 V/cm) have been discovered, which affect the neutrons moving in noncentrosymmetric crystals. Such fields allow for new polarization phenomena in the neutron diffraction and in the optics and provide, for instance, a new method of a search for the neutron electric dipole moment (EDM). A strong interplanar electric field of the crystal and a sufficiently long time for the neutron passage through the crystal for Bragg angle close to π/2 in the case of Laue diffraction make it possible to exceed the sensitivity achieved with the magnetic resonance method using ultra cold neutrons (UCN method). The pilot setup has been created and mounted at the neutron beam at the WWR-M reactor in Gatchina. It allows to study the optics and the dynamical diffraction of polarized neutrons in thick (1–10 cm) crystals, using the direct diffraction beam and Bragg angles close to 90°. The first experimental results are discussed on observing new effects in both the Laue diffraction and the optics of cold neutrons. These results confirm the opportunity to increase more than by an order of magnitude the sensitivity of the method to neutron EDM, using the diffraction angles close to 90° and give a real prospect to exceed the sensitivity of the UCN method.

The effect of large irradiation doses on polarizing and non-polarizing supermirrors

In order to study radiation stability of the neutron supermirror coatings, the effect of large irradiation doses on polarizing (FeCoV/TiZr) and non-polarizing (NiMo/Ti and Ni/Ti) supermirrors has been studied. The samples were irradiated at the WWR-M reactor (Gatchina) inside a vertical channel behind the Be reflector, where the flux of thermal neutrons and neutrons with energies exceeding 1 MeV was, respectively, (0.6–1)×10 13 and 2×10 11 cm −2 s −1 . During irradiation the temperature of the samples did not exceed 70°C. The data obtained at the reflectometer RPN-2M (PNPI) for FeCoV/TiZr and NiMo/Ti supermirrors (produced in PNPI) and for Ni/Ti supermirrors (produced in PSI), irradiated with different doses, are presented. The polarizing efficiency and the reflectivity of the supermirrors sputtered onto float-glass substrates have not revealed significant changes for the fluences up to 10 19 cm −2 .

Thermal fatigue crack nucleation in ferritic–martensitic steels before and after neutron irradiation

Thermal fatigue behaviour of the ferritic–martensitic steels MANET-II, 12Cr–1.5NiMo and F82H-mod. have been investigated in the temperature range from 50°C to 350°C and total strain range ⩽0.33%. Crack appearance has been checked after 3×103, 6×103 and 104 cycles and has been successively detected in these steels. The thermal fatigue cracks have a transgranular character; sometimes, intergranular cracks are observed in the F82H-mod. steel. A certain correlation of grain size and ferrite content with the thermal fatigue crack peculiarities has been noted. Specimens of MANET-II and 12Cr–1.5NiMo have been irradiated in a WWR-M reactor with a fluence of 1×1025 n m−2 at a temperature of 300°C and then subjected to thermocyclic loading. It has been established that the neutron irradiation does not significantly affect fatigue crack nucleation in both materials.

The k0 and Q0 Values for the Zr-Isotopes: A Re-Investigation

The k0 and Q0 values for 94Zr(n,γ)95Zr(Eγ = 724.2+756.7 keV) and 96Zr(n,γ)97Zr(β−) 97mNb (Eγ = 743.4 keV) were re-investigated. The aim was to further improve the reliability of the neutron spectrum characterization (f and α monitoring) in k0-NAA, based on "bare monitor" methods with the use of these Zr radionuclides. So as to achieve this goal, experimental determinations were performed in three reactor centers: KFKI AEKI, Budapest (WWR-M reactor); INW, Gent (THETIS reactor); SCK·CEN, Mol (BR1 reactor). The results were: Q0(94Zr) = 5.306; Q0(96Zr) = 251.6; k0(95Zr, 724.2+756.7 keV) = 2.000E-4; k0(97Zr/97mNb, 743.4 keV) = 1.237E-5. This means that the newly evaluated k0-values are about 4.7% lower than the formerly reported ones. It is also emphasized that the 97Zr half-life is 16.74 hours, contrary to the ∼1% higher values usually reported.

WWR-M celebrates 40 years

December 29, 1999 marked the 40th anniversary of the WWR-M reactor in Gatchina—one of the oldest research reactors in existence.

A re-evaluation of k0 and related nuclear data for the 555.8 keV gamma-line emitted by the 104mRh- 104Rh mother–daughter pair for use in NAA

A re-evaluation is made of the k 0-factor and related nuclear data for the 555.8 keV gamma-ray of the 104mRh- 104Rh mother–daughter pair that are important in neutron activation analysis (NAA). This study considers that the relevant level is also fed by the 4.34 min 104mRh mother (with an absolute gamma-ray emission probability γ 2=0.13%) and not only, as assumed in former work, by the 42.3 s 104Rh daughter isotope (with γ 3=2.0%). In view of this, generalised equations were developed for both the experimental determination and the analytical use of the k 0-factor and of the associated parameters k 0(m)/ k 0(g), Q 0(m) and Q 0(g) [(m): 104mRh; (g): 104Rh], requiring the introduction of the γ 2 and γ 3 data and also of the 104mRh→ 104Rh fractional decay factor F 2(=0.9987). The experimental determinations were based on irradiations performed in the BR1 reactor in Mol and the WWR-M reactor in Budapest. Furthermore, considering the special formation of the 555.8 keV gamma-ray, the procedure for true-coincidence correction was revised as well. All this led to the compilation and recommendation of a new set of ‘ k 0-NAA’ data.

On the yield of cold and ultracold neutrons for liquid hydrogen at low temperatures near the melting point

The neutron scattering cross sections for liquid hydrogen in the temperature range from the melting point to the boiling point are calculated. It is shown that lowering the temperature results in a significant increase in the yield of cold neutrons: for instance, a 44% increase for an incident neutron energy of 19.4 meV. The major cause of this increment is the para-to-ortho transition of a hydrogen molecule though accompanied by an appreciable increase in the density. The results of the cold- and ultracold-neutron yields are discussed in connection with the experimental results of Altarev et al. at the WWR-M reactor.

Design and experience of HEU and LEU fuel for WWR-M reactors

Thin-walled WWR-M5 fuel elements were designed and manufactured and have been used successfully for 16 years; they contain twice as much uranium-235 as the WWR-M2 and WWR-M3 fuel elements. The fuel elements have been optimized with regard to their neutron physics and thermal-hydraulic parameters and fuel consumption has been minimized. The mean specific power in the core of the WWR-M reactor was raised to 230 kW l −1, the measured maximum volume thermal specific power was 900±100 kW l −1 and the surface specific power was 136±15 W cm −2. The WWR-M5 fuel elements enable the power of the WWR-M pooltype reactor to be raised to 30 MW while simultaneously increasing the number of cells in the core available for experimentation by a factor of approximately two and reducing fuel element consumption. Reactor tests of WWR-M fuel elements with reduced fuel enrichment (36 and 21%) were carried out for a meat uranium density up to 2–3 g cm −3. Conversion of WWR-SM-type reactors to these fuel elements did not lead to a loss in reactivity and enabled their power to be increased to 20–30 MW.

New method for precise determination of neutron beam polarization

We report the realization of a new method for precise determination of neutron beam polarization. The analyzing system utilizes two analyzers connected by a neutron guide which contains a spin flipper. The entire device can be rotated by 180°, thereby reversing the neutron trajectories through the device. The method has also been used to measure the neutron spin depolarization in the two analyzers. The depolarization is consistent with zero within an uncertainty of 10 −3. As a consequence of this, two additional measurements, made with the device, yield values for the neutron polarization. The observed consistency of the three results suggests an accuracy for the method of 0.2%. We have used this technique to measure the polarization of the 50 × 100 mm 2 cold neutron beam at the vertical channel of the WWR-M reactor with an accuracy of 0.2%.

Neutron induced prompt gamma ray method in the quantitative elemental analysis of materials and compounds determination of antimony in Bi-Pb-Cu-Sr-Ca-Sb-O high temperature superconducting ceramics

The in-beam neutron induced prompt γ-ray method of quantitative elemental analysis of materials and compounds used in Neutron Research Department (NRD) of PNPI and experimental arrangement installed on the horizontal channel of WWR-M reactor are described. The results of measurements of antimony concentration in the antimony doped sample of HTSC ceramics after two stages of annealing are reported.

Influence of helium upon the structure, the strength, and the plasticity of alloys with high nickel content

Results are presented of a combined investigation of the influence of helium on the structure, strength, and plasticity of the following nigh-nickel steels--03Kh20N45M4BCh, 0Kh16N15M3B, and 03Kh20N45M4BRTs--after alpha particle irradiation at the Institute for Nuclear Physics cyclotron and neutron irradiation in a WWR-M reactor. Mechanical test procedures are described as are possible nuclear reaction scenarios in the steels. The purpose of the investigation is to assess the viability of these steels for reactor materials.

Applicability of the 1/E1+α epithermal spectrum representation and the effective resonance energy $$\bar E_r$$ in NAA

The practical applicability of the 1/E1+α epithermal spectrum representation and of the effective resonance energy\(\bar E_r\) in NAA is investigated. Attention is paid to fundamental considerations such as definitions and approximations, error propagation functions, uncertainty statements, reliability of nuclear data and formal dimensioning problems. As to the latter, it is concluded that the applicability of the\(\bar E_r\)-concept is not dependent on the choice of a reference energy. The usefulness of the parameters α and\(\bar E_r\) in NAA is demonstrated by new experimental evidence obtained from α and Q0 determinations in three different reactors: the WWR-M reactor (Budapest, Hungary), the THETIS reactor (Gent, Belgium) and the DR-3 reactor (Riso, Denmark).

The accuracy and precision of the experimental α-determination in the 1/E1+α epithermal reactor-neutron spectrum

Some methods for the experimental α-determination in the 1/E1+α epithermal reactorneutron spetrum are critically compared with respect to their accuracy and precision. The analysis is based on the error propagation theory. Besides the general formulae numerical examples are elaborated for specific conditions in the Thetis reactor (Gent) and the WWR-M reactor (Budapest).

Five-metre neutron polarizing guide-tube at the Leningrad nuclear physics institute

A 8.5 × 60 mm 2 5 m neutron polarizing guide-tube based on 60% Co−40% Fe mirrors with a 85% Ti−15% Gd absorbing underlayer is described. The design of the neutron guide-tube and the test results on the WWR-M reactor at the LNPI are presented. The average flux at the exit of the neutron guide-tube was 1.5 × 10 6 n/cm 2 s for a 15 MW reactor, the peak of the exit spectrum lies at the wavelength of 2.2 Å, and the polarization averaged over the whole spectrum was no less than 96%.

Supressing background and increasing luminosity of a β-spectrometer of internal target type for an investigation of the ( n, e) reaction

A method for reducing background and increasing transmission and luminosity of the β-spectrometer of internal target type for an investigation of the (n, e) reaction is proposed. The electron background of such spectrometers is shown to come mainly from scattering of the electrons which are produced outside the target by the target itself. This component of the electron background can be cancelled with the aid of an appropriate magnetic field. Using the method proposed, the β-spectrometer at the WWR-M reactor in Gatchina has been successfully modernized. The spectrometer in its present form incorporates a transport solenoid (instead of a lense) for guiding electrons away from the target situated in a tangential channel near the reactor core and for focusing them onto a magnetic shield slit, which is an electron source for a 45 cm radius double focusing iron-core magnet-analyser. Sensitivity of the β-spectrometer with the transport solenoid compared with that of the β-spectrometer with the lense is increased 7 times. Correspondingly, the time need for obtaining the same statistical accuracy as before is decreased by a factor of 49. Using the β-spectrometer, conversion electron spectra from the 115In(n, e) 116In, 133Cs(n, e) 134Cs and 121Sb(n, e) 122Sb reactions have been measured. Some of them are presented.