Nuclear fuels and development of nuclear fuel elements

The importance of nuclear energy in meeting future energy demands has been well-recognised and a variety of nuclear reactor systems have been developed. Inherent characteristics of nuclear technology like neutron economy and neutron irradiation-induced degradation in properties of materials require stringent control of material purity and necessarily limit the choice of candidate materials. Hence safe, reliable and economic operation of nuclear fission reactors, the source of nuclear power at present, requires judicious choice, careful preparation and specialised fabrication procedures for fuels and fuel element structural materials. These aspects of nuclear fuels (uranium, plutonium and their oxides and carbides), fuel element technology and structural materials (aluminium, zircaloy, stainless steel etc.) are discussed with particular reference to research and power reactors in India, e.g. theDhruva research reactor atBarc, Trombay, the pressurised heavy water reactors (Phwr) at Rajasthan and Kalpakkam, and the Fast Breeder Test Reactor (Fbtr) at Kalpakkam. Other reactors like the gas-cooled reactors operating in UK are also mentioned. Because of the limited uranium resources, India has opted for a three-stage nuclear power programme aimed at the ultimate utilization of her abundant thorium resources. The first phase consists of natural uranium dioxide-fuelled, heavy water-moderated and cooledPhwr. The second phase was initiated with the attainment of criticality in theFbtr at Kalpakkam. Fast Breeder Reactors (Fbr) utilize the plutonium and uranium by-products of phase 1. Moreover,Fbr can convert thorium into fissile U-233. They produce more fuel than is consumed — hence, the name breeders. The fuel parameters of some of the operating or proposed fast reactors in the world are compared.Fbtr is unique in the choice of mixed carbides of plutonium and uranium as fuel. Factors affecting the fuel element performance and life in various reactors e.g. hydriding of zircaloys, fuel pellet-cladding interaction etc. inPhwr and void swelling, irradiation creep and helium embrittlement of fuel element structural materials inFbr are discussed along with measures to overcome some of these problems. Lecture presented at the Frontier Symposium of the Engineering Sciences Session of the 75th Indian Science Congress, Pune, January 9, 1988     

Microlens array structures designed to defeat automated photocopying of documents

A microlens array structure that prevents automated photocopying is presented. This copy defeat laminate (CDL) employs a cylindrical lens array structure in conjunction with a mask pattern to prevent at-normal viewing of the document. Image brightness perceived by the human eye is reviewed as well as basic radiometry. Equations for Lambertian and CDL image brightness are derived. The brighter-than-white appearance of a CDL covered document is explained. Designs for the full-page-defeat and full-page-view versions of the CDL are presented.     

A simple one-dimensional approach to modelling ceramic composite armour defeat

This work develops a simple set of models for the perforation of ceramic composite armour, which highlight the essential physical processes and illustrate approximately the dependency of ballistic resistance on physical properties and impact parameters. The major features of ceramic composite armour failure (viz. fracture conoid formation, dishing failure of thin backing plates, perforation of thick packing plates, and projectile erosion) are combined with a lumping of masses to treat material acceleration to produce simple models which allow computations on ceramic targets with both thin and thick metallic backings. Calculations are compared with a broad range of empirical data and are also used to discuss aspects of the interaction of penetrators with ceramic composite armours. The goos correlation of models with experiment demonstrates the usefulness of the present approach for studying ceramic composite armour defeat.     

Thermosetting resins for nuclear track detection

Several new thermosetting resins with a three dimensional network structure like CR-39 were polymerized to study their characteristics for use as nuclear track detectors. During the course of this study, thermosetting resins with good etching properties and various sensitivities have been obtained. The comparison of the molecular structures of these resins gives us an important clue for the development of highly sensitive polymeric track detectors. They will also be useful for observations of ultra-heavy cosmic rays and heavily ionizing particles at low energies.     

Thermometric detection of nuclear magnetic resonance

Nuclear magnetic resonance has been detected in nonmagnetic materials by observing the temperature rise in the sample. The experiments were performed at temperatures between 1 and 4 K, and results are presented for the²⁷Al resonance in aluminum metal and the¹⁹F resonance in a sample of doped CaF₂. The primary sources of noise have been identified and ways of improving the apparatus are discussed. The technique could prove useful in experiments that require a large range of frequencies to be swept and in experiments investigating the effects of strong rf fields.     

基于高斯模型的核探测机器人寻找核辐射源方法

针对核泄露后核放射源准确定位的问题,提出了用核探测机器人自主寻找核辐射源的方法.该方法利用高斯模型描述核泄漏事故发生后周围大气中放射性核素云团的扩散,估测地面上放射性核素水平,并利用小型核探测机器人搭载核辐射探测仪,实时探测核辐射水平;根据建立的核污染扩散模型,采用模拟退火算法,自主寻找地面放射性核素辐射浓度最高的区域;通过基于超声模糊避障控制系统,保证机器人在执行任务中无碰撞.模拟核辐射源泄漏事故实验结果表明,该方法可以帮助机器人自主寻找到地面核素辐射水平最高区域.     

核磁共振技术检测钚复合构件

该文仿真计算在不同外磁感应强度下,钢铍钚复合构件各球壳静磁场分布及缺陷样品磁场分布情况。结果表明:不同的磁场强度和磁导率对复杂金属结构的磁场分布不一样,总的来说,磁感应强度越大,磁导率越小,则各球壳层磁场强度越大。外磁场能够深入钚复合构件多层结构且保持一定强度和均匀性,满足声-核磁共振无损检测系统的要求。最后对无缺陷和有缺陷的样品进行磁场分布模拟,对比结果表明:钚复合构件中气泡、裂纹等缺陷可通过探测磁场分布进行定性判断,为下一步声核磁共振检测技术奠定理论基础。     

Spontaneous nuclear ferromagnetic ordering of in nuclei in AuIn2 Part I. Nuclear specific heat and nuclear susceptibility

We have measured the nuclear specific heat C_n and nuclear susceptibility _n of In nuclei (I=9/2, =5.5 _n) in the cubic intermetallic compound AuIn₂ (Korringa constant =0.11 Ksec) in the normal conducting state at 30K10mK and 2mTB115 mT. Our data show a positive nuclear Weiss temperature =+ 43 K and that the In nuclei undergo a nuclear ferromagnetic transition at T_c=35 K. The In nuclei experience an internal field of about 10 mT (obtained from C_n at T>T_c ). The nuclear ordering temperature T_c and the internal field increase with applied magnetic field. From the data we deduce exchange constants for the investigated system. The critical entropy reduction S(T_c)/S_max=8.6% and critical enthalpy E=0.28 RT_c are in reasonable agreement with the measured ordering temperature T_c,applying the Heisenberg model for a simple cubic I=9/2 spin system. The nuclear spin relaxation time calculated from the real and imaginary parts of _n is 10 msec at T>50 K, but drops to <1msec at T_c.This is the first observation of a spontaneous nuclear magnetic ordering transition in a not-hyperfine-enhanced metal at thermal equilibrium, i.e. at T _nuclear =T _electron .     

Special nuclear material detection with a mobile multi-detector system

The detection of special nuclear material has been studied with a mobile inspection system used both as a high sensitivity passive neutron/gamma spectroscopic tool and as an active inspection device using tagged neutrons. The detection of plutonium samples seems to be possible with passive interrogation, even for small samples, thanks to the yield of gamma ray and neutrons. Moreover the gamma ray spectrum shows clear signatures related to ²³⁹Pu. The passive detection of uranium is much more difficult because of the low neutron yield and of the easiness of shielding the gamma ray yield of highly enriched U samples. However, we show that active interrogation with tagged neutrons is able to provide signatures for the discrimination of uranium against other heavy metals.     

Probabilistic interpretation of command and control signals: Bayesian updating of the probability of nuclear attack

A warning system such as the Command, Control, Communication, and Intelligence system (C³I) for the United States nuclear forces operates on the basis of various sources of information among which are signals from sensors. A fundamental problem in the use of such signals is that these sensors provide only imperfect information. Bayesian probability, defined as a degree of belief in the possibility of each event, is therefore a key concept in the logical treatment of the signals. However, the base of evidence for estimation of these probabilities may be small and, therefore, the results of the updating (posterior probabilities of attack) may also be uncertain. In this paper, we examine the case where uncertainties hinge upon the existence of several possible underlying hypotheses (or models), and where the decision-maker attributes a different probability of attack to each of these fundamental hypotheses. We present a two-stage Bayesian updating process, first of the probabilities of the fundamental hypotheses, then of the probabilities of attack conditional on each hypothesis, given a positive signal from the C³I. We illustrate the method in the discrete case where there are only two possible fundamental hypotheses, and in the case of a continuous set of hypotheses. We discuss briefly the implications of the results for decision-making. The method can be generalized to other warning systems with imperfect signals, when the prior probability of the event of interest is uncertain.     

Lignin-based formulations to prevent pesticides pollution

The pesticides isoproturon, imidacloprid and cyromazine, identified as groundwater pollutants, were incorporated in lignin-based formulations to obtain controlled release (CR) properties. The formulations were prepared by mixing the pesticide with a commercially available pine kraft lignin under melting conditions. A high efficiency of the preparations was therefore reached; it oscillated between 93.36% and 98.20% for the cyromazine and the isoproturon formulations. Kinetic-release experiments carried out in water showed that the release rate of isoproturon, imidacloprid and cyromazine from CR granules diminished in all cases in relation to the technical products. From the analysis of the time taken for 50% of the active ingredient to be released into water (T₅₀), it can be deduced that the release rates were much higher in cyromazine CR formulations than in those prepared with isoproturon. However, imidacloprid showed an intermediate release rate. The obtained linear regression between T₅₀ values and granule size can be suitable to select the most appropriate formulation to avoid the isoproturon, imidacloprid and ciromazine tendency to leach.     

Nuclear power plant sensor fault detection using singular value decomposition-based method

In a nuclear power plant, periodic sensor calibration is necessary to ensure the correctness of measurements. Those sensors which have gone out of calibration can lead to malfunction of the plant, possibly causing a loss in revenue or damage to equipment. Continuous sensor status monitoring is desirable to assure smooth running of the plant and reduce maintenance costs associated with unnecessary manual sensor calibrations. In this paper, a method is proposed to detect and identify any degradation of sensor performance. The validation process consists of two steps: (i) residual generation and (ii) fault detection by residual evaluation. Singular value decomposition (SVD) and Euclidean distance (ED) methods are used to generate the residual and evaluate the fault on the residual space, respectively. This paper claims that SVD-based fault detection method is better than the well-known principal component analysis-based method. The method is validated using data from fast breeder test reactor.     

Resistance of self-consolidating concrete to ammonium sulphate attack

With the growing use of self-consolidating concrete (SCC) in various infrastructure applications, it has become necessary to establish reliable data on its long-term durability since its mixture design, rheology and consolidation are different than that of normal concrete. Several applications of SCC involve its exposure to chemical attack, particularly to sulphate-rich media such as wastewater treatment facilities, industrial and agricultural zones which also encompass ammonium cations. Thereby, this study aims at investigating the resistance of a wide scope of SCC mixture designs to ammonium sulphate attack. Specimens from 23 SCC mixtures were continuously immersed in a high concentration ammonium sulphate solution with controlled pH (6.0?C8.0) up to 54?weeks. The main test variables included the type of binder (single, binary, ternary and quaternary), air-entrainment, sand-to-total aggregates mass ratio, and the inclusion of fibre reinforcement (single and hybrid). The SCC specimens showed variable degrees of deterioration after 54?weeks, indicating different modes of degradation. The study highlights the role of ternary and quaternary binders in improving the resistance of SCC to ammonium sulphate attack. It is also emphasized that multiple performance indicators are needed to achieve a reliable assessment of cement-based materials under ammonium sulphate attack.     

Photoelectronic properties of HgI2 crystals for nuclear radiation detection

Photoelectronic properties of red mercuric iodide single crystals, grown from its saturated solution in tetrahydrofuran, have been studied for the wavelength range 450–700 nm at temperatures 80,110, 175, 235 and 300 K. Various aspects of the optical generation of charge carriers have been discussed. The computer simulation of the room temperature photoconductivity has generated the optimized values of the mobility-lifetime products μ_eτ_e = 5.67 × 10⁻⁵ cm²/V, μ_hτ_h = 0.18 × 10⁻⁵ cm²/V), and surface recombination velocities (S_e = 3.2 × 10⁵ cm/s, S_h = 4.5 × 10⁵ cm/s) of the charge carriers in these crystals. The estimated values of the electron and hole drift lengths for typical electric fields suggest that, under the negative electrode illumination, THF α-HgI₂ crystals have high potential as regards to their use as photodetectors in most of the scintillation spectrometers.