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.     

Room temperature, high-resolution X-ray spectroscopy with silicondrift chambers

The development of detectors for high resolution room temperature X-ray spectroscopy represents a relevant progress in many fields of application, mainly in out-of-laboratory environments. A new type of silicon detector, the semiconductor drift chamber (SDC), allows one to obtain at room temperature, or with a moderate cooling, a resolution comparable to that obtained at liquid nitrogen temperature with traditional detectors of the same active area. The key feature of the SDC's is the very low output capacitance (about 100 fF) independent of the active area of the device. This feature, together with a good capacitive matching between the detector and the first stage of amplification, leads to high values of the resolution at short shaping times. We tested a simple 6-mm² cylindrical SDC at room temperature and at -20°C (easily obtainable with electrical cooling), by using a specifically designed, low capacitance, JFET as the input transistor of the preamplifier. With a ⁵⁵Fe source, we measured an equivalent noise charge (ENC) of 34 e^- RMS and 27 e^- RMS at room temperature and at -20°C respectively. To our knowledge these are presently the best values obtained for the same active area near room temperature     

Tokamak reactor concepts using high temperature,high-field superconductors

Tokamak ETR and demo reactor design concepts using high-temperature, high-field oxide superconductors are described. Current densities in recently developed oxide superconductors appear at present to be very low, and it is not clear whether practical magnets for fusion applications can be developed. However, if this development occurs the potential impact on tokamak design appears large. Significant reductions in cost, complexity, and physics extrapolation could be possible by the combination of very high fields and liquid nitrogen operation. Illustrative parameters are given for an ETR device that has about the same plasma volume as TFTR. Parameters are also given for a demo device with approximately the same plasma volume as JET. If practical oxide superconducting magnets cannot be developed, a significant degree of the improvement due to high-field operation might in fact still be realized using existing superconducting materials such as Nb₃Sn (Ta, Ti).This work performed under D.O.E. Contract #DOE-AC02-78ET-51013. Reproduction, translation, publication, use and disposal, in whole or in part, by or for the United States government is permitted.This work performed under appointment to the Magnetic Fusion Energy Technology Fellowship which is administered for the U.S. Department of Energy by Oak Ridge Associated Universities.     

SNR-300, strategy and state of the elevated temperature design

This paper describes the procedure for the elevated-temperature structural analysis of the SNR-300. The preliminary analysis based on elastic calculations will be followed by detailed inelastic analysis, if required to provide assurance against all failure modes. In coherence with the progress of the project, experimental work is being done as a first phase of preparation to the elevated temperature design. On the one hand material data will be established and on the other hand analytical work for computer codes and design criteria will be done. The first inelastic investigations are running. Changes in the geometry of the components and/or the planned operating conditions can be considered in case the structural adequacy cannot be demonstrated even through detailed inealstic analysis.     

Collision cascade temperature

Interaction of a projectile with a solid has been considered in detail. It has been found that any collision cascade generated by a projectile can be characterized by the average kinetic energy of cascade atoms that represents an “instantaneous temperature” of the cascade during its very short lifetime (10⁻¹² s). We refer to this value as the “dynamic temperature” in order to emphasize the fact that cascade atoms are in a dynamic equilibrium and have a definite energy distribution. The dynamic temperature defines the electron distribution in the cascade area and, hence, the ionization probability of sputtered atoms. The energy distribution of cascade atoms and, as a consequence, the dynamic temperature can be found experimentally by measuring the energy distribution of sputtered atoms. The calculated dynamic temperature has been found to be in good agreement with the experimental data on ion formation in the case of cesium and oxygen ion sputtering of silicon. Based on the developed model we suggest an experimental technique for a radical improvement of the existing cascade sputtering models.     

螺旋管式直流蒸汽发生器的准稳态数学模型

为了满足模拟机实时仿真核电站一、二回路工况的需要,根据流体的质量、动量和能量守恒原理,建立了适合模拟机要求的螺旋管式直流蒸汽发生器的准稳态数学模型.该模型将蒸汽发生器作为单管模型处理,并根据水的状态将蒸汽发生器分为单相水段、两相段和过热段三大段,每大段又细分若干小段.该数学模型方程采用变步长四阶龙格库塔法联立求解一、二...     

Flow behaviour of autoclaved, 20% cold worked, Zr-2.5Nb alloy pressure tube material in the temperature range of room temperature to 800 °C

Pressure tube material of Indian Heavy Water Reactors is 20% cold-worked and stress relieved Zr-2.5Nb alloy. Inherent variability in the process parameters during the fabrication stages of pressure tube and also along the length of component have their effect on micro-structural and texture properties of the material, which in turn affect its strength parameters (yield strength and ultimate tensile strength) and flow characteristics. Data of tensile tests carried out in the temperature range from room temperature to 800 °C using the samples taken out from a single pressure tube have been used to develop correlations for characterizing the strength parameters’ variation as a function of axial location along length of the tube and the test temperature. Applicability of Ramberg-Osgood, Holloman and Voce’s correlations for defining the post yield behaviour of the material has been investigated. Effect of strain rate change on the deformation behaviour has also been studied.     

High temperature component design

High temperature component design requires the consideration of constructive aspects prior to design and dimensioning work. In the high temperature range of more than 800°C special importance is attached to the failure modes “creep fatigue”, “ratcheting” and “creep buckling”. Comprehensive examinations of existing design rules considering these failure modes with regard to possible applicability for HTR-conditions have been completed. Corresponding calculations have pointed out that there is a promising potential for safe component design even for extreme temperature load conditions. These results have additionally confirmed that available elastic methods often cannot be used and would lead to very conservative approximations. Thus the improvement of simplified verification methods as well as the improvement of relevant constitutive equations is required in view of further development work in the field of high temperature component design.     

Nuclear plant temperature instrumentation

Most critical process temperatures in nuclear power plants are measured using resistance temperature detectors (RTDs) and thermocouples. In addition to excellent reliability and accident survivability, nuclear safety-related RTDs are expected to have good calibration and fast dynamic response time, as these characteristics are important to plant safety and economy. In plants where RTDs are installed in thermowells in the primary coolant pipes, response-time requirements have a range of 4.0-8.0 s versus the direct-immersion RTDs installed in bypass loops which have a required response range of 1.0-3.0 s. The variety of problems that can affect the accuracy and response time of RTDs is extensive: dynamic response problems, failure of extension leads, low-insulation resistance, premature failure, wrong calibration tables, loose or bad connections, large EMF effects, open elements, thinning of the platinum wire, lead-wire imbalance, seeping of chemicals from the connection head into the thermowell, cracking of the thermowell, and erroneous indication. The causes of core-exit thermocouples failure can take the form of large calibration shifts, erratic and noisy output, saturated output, accidental reverse connections, and response-time degradation. Several effective methods for detecting RTD and thermocouple performance failure while the plant is operating are available. To detect accuracy problems, the cross-calibration technique is effective for both RTDs and core-exit thermocouples. It involves recording the readings of redundant online RTDs, averaging these readings, and calculating the deviation of each RTD from the average, less any outliers. To detect response time degradation online, the loop current step response (LCSR) test is the most accurate method. However, the noise analysis technique remains the most popular for detecting response time degradation in core-exit thermocouples.     

SHTV,as a technique for core calculation using spatial homogenization and temperature variation

The accuracy of static neutronic parameters in the nuclear reactors depends upon the determination of group constants of the diffusion equation in the desired geometry. Although several methods have been proposed for calculating these parameters, there is still the need for more reliable methods. In this paper a powerful and innovative method based on Spatial Homogenization and Temperature Variation (SHTV) of physical properties of a WWER-1000 nuclear reactor core for calculating the relative power distribution of Fuel Assemblies (FA) and the hot fuel rod, is presented. The method is based on replacing the heterogeneous lattices of materials with different properties by an equivalent homogeneous mixture of these material for determining the few group constants, while the effect of temperature variation in the fuel and coolant density along the axial core direction is considered. All calculations are performed using WIMS and CITATION codes. The obtained results are compared with the results of Final Safety Analysis Report (FSAR) prepared by the designer, and good agreement between the two results is shown.     

The high temperature gas-cooled reactor as a source of high temperature process heat

The nuclear reactor has established itself as a future major supplier of electrical energy. The industrial market for other forms of energy, however, is almost as large and represents a new potential for the use of nuclear reactors. The high temperature gas-cooled reactor (HTGR) has been developed for commercial application in the electric power generation field. Since the HTGR is capable of delivering process heat in the temperature range of 1000–1500°F, it has many applications that would not be possible at the lower operating temperatures of water-cooled reactors. This paper briefly summarizes the development of the HTGR and outlines its salient technical features. Modifications to the reactor that enable it to be used as a process heat source are discussed. Specific applications are developed for coal gasification, steelmaking, and hydrogen production.     

气压、气温、风速对室内氡气传输影响的三维瞬态数值模拟

利用数值差分方法,模拟了室内氡气传输的三维瞬态过程,定量讨论了气压、气温、风速对室内氡气传输的影响。结果表明:室内氡浓度随高度增加逐渐减小,室外气压、气温、风速的变化,将引起室内压差的变化,从而引起室内氡浓度的变化,其相位差大于180°。计算值与实验值符合得很好。     

Thermal conductivity degradation of ceramic materials due to low temperature, low dose neutron irradiation

The thermal conductivity degradation due to low-temperature neutron irradiation is studied and quantified in terms of thermal resistance terms. Neutron irradiation is assumed to have no effect on umklapp scattering. A theoretical model is presented to quantify the relative phonon-scattering effectiveness of the three dominant defect types produced by neutron irradiation: point defects, dislocation loops and voids. Several commercial ceramics have been irradiated with fission reactor fast neutrons at low temperatures to produce defects. Materials include silicon carbide, sapphire, polycrystalline alumina, aluminum nitride, silicon nitride, beryllium oxide, and a carbon fiber composite. The neutron dose corresponded to 0.001 and 0.01 displacements per atom (dpa) for a 60 °C irradiation and 0.01 and 0.1 dpa for a 300 °C irradiation. Substantial thermal conductivity degradation occurred in all of the materials except BeO following irradiation at 60 °C to a dose of only 0.001 dpa. The data are discussed in terms of the effective increase in thermal resistance caused by the different irradiation conditions. Evidence for significant point defect mobility during irradiation at 60 and 300 °C was obtained for all of the ceramics. The thermal stability of the radiation defects was investigated by isochronal annealing up to 1050 °C.     

Synergistic effects of hydrogen plasma exposure,pulsed laser heating and temperature on rhodium surfaces

The combined effect of hydrogen plasma exposure and surface heating, either continuous or by short laser pulses (5 ns), on the surface morphology of rhodium layers has been studied. Investigations were performed by reflectivity measurements, scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and atomic force microscope (AFM). While surfaces exposed at room temperature exhibit little modifications, strong surface changes are observed for surface temperatures higher than 250 °C. At 500 °C, the plasma exposed surface exhibits a nanoscale structure (50–100 nm) with a high level of porosity and a low reflectivity. Additional laser irradiation of the surface strongly enhances the observed surface damage. Localized surface melting is observed with craters extending deep into the substrate together with a dense network of voids.     

Annealing study of gold,zinc and germanium alloyed aluminum neutron-irradiated at liquid nitrogen temperature

A study of the recovery of the electrical resistivity of the dilute aluminum alloys Al-Au (0.02–0.25 at % Au), Al-Zn (0.05–1.0 at % Zn) and Al-Ge (0.02–0.5 at % Ge) after neutron-irradiation at a total dose of 9 × 10¹⁸n/cm²at 78 K was undertaken. The annealing spectra of Al-Au and Al-Zn alloys showed two distinct substages in stage II, while in Al-Ge alloys a five-peak structure was apparent. At the low-temperature side of the main peak of stage III a shoulder is definitely apparent in the three alloy systems. After stage III, Al-Ge alloys appear to have two doublets and a reverse recovery resistivity, which can be attributed to the formation of Guinier-Preston zones. The break-up of interstitials from impurity atoms or their clusters and the trapping of vacancy-type defects during their migration in stage III, are the mechanisms which can explain stages II and III respectively. The activation energy for the main peak of stage III was in all cases found to be 0.60 eV, and the peak obeys second-order kinetics.     

Influence of temperature, strain rate and specimen geometry on the microscopic cleavage fracture stress

The aim of this work is to determine the influence of temperature, strain rate and specimen geometry on the microscopic cleavage fracture stress σ_f*. Besides, the dependence of the initiation temperature for shear fracture T_i and the temperature for general yield T_gy on strain rate is investigated. Finally, the local values of stress triaxiality and equivalent plastic strain at the occurrence of cleavage fracture for several steels and specimen types are compared with the failure curve for ductile fracture to check the validity of the theory of stress controlled cleavage fracture and the strain/triaxiality controlled shear fracture in the transition region. Based on experimental tests, the results are obtained by finite element analyses. The investigation shows, that σ_f* is dependent on temperature and strain rate and increases with decreasing test temperature and increasing strain rate. The transition temperatures T_i and T_gy increase with increasing strain rate. The theories of stress controlled cleavage fracture and of shear fracture controlled by equivalent plastic strain and stress triaxiality seem to be valid. That fracture mechanism occurs for which the critical condition is reached first.     

Comparison between the low temperature thermoluminescence spectra in annealed LiF:Mg,Cu, LiF:Mg,Cu,P and LiF:Mg,Cu,Si

Two strong thermal peaks in the wavelength range 220-420 nm have been detected at 128 and 140 K in LiF:Mg,Cu, at 123 and 135 K in LiF:Mg,Cu,P and at 125 and 133 K in LiF:Mg,Cu,Si, respectively. The origin of these main TL peaks is discussed in terms of defect perturbed H-F and V_K-e type recombination, respectively. The relative intensity between the two peaks in each sample and the emission spectra are dependent on the dopants.Annealing at 240-390 °C can modify the low temperature TL features, especially in those samples doped with three impurities. The low temperature data give some clues to select most favourable dopants for future LiF-type dosimeters.     

Effect of the temperature,pressure, and inorganic gas impurities on the radiolysis efficiency of water and carbon dioxide

I. V. Kurchatov Institute of Atomic Energy. Translated from Atomnaya Énergiya, Vol. 72, No. 1, pp. 54–59, January, 1992.     

Indicator to estimate temperature sensitivity of resonance in temperature measurement by neutron resonance spectroscopy

Through series of simplification and simulation, we find that it is the ratio of z (=Δ/Γ) and σ₀ (cross-section at the exact resonance energy in the absence of temperature broadening) that contains the most information of temperature sensitivity for a resonance. We consequently define a factor h called the effective fitness indicator to represent the lower limit of temperature error for each resonance. h bears succinct forms and is tested against numerical simulations as well as gathered experimental data. Our further analysis and simulation justify the use of h at high temperatures (above several hundreds degrees centigrade). When the transmission of a resonance is free from suffering a flat-bottom (without ntσ₀ ? 1), h can be used to estimate the temperature sensitivity of individual resonance with an analytic formula constructed from fitting, telling a relation between the temperature error and h. Moreover, spread of emission time caused by the moderator, phosphorescent decay of the scintillator, and background fraction are all included in numerical simulations to reveal their influences.