Reducing the radioactive doses of liquid samples taken from reprocessing plant vessels by volume reduction

Size reduction is attractive because it should enable a solution to be analysed by much more direct, and therefore faster and simpler, methods. For instance if the traditional 7 ml vials used in reprocessing plants can be replaced by vessels containing less than 1 μl, it should be possible to analyse the non-diluted solutions in gloveboxes. These vessels would be electro-mechanical, so the term MEMS might be appropriate.This paper determines a conservative estimate for the dose reduction that would be obtained if microlitre samples were extracted from an input accountancy tank at a reprocessing plant, in which the spent fuel is dissolved in nitric acid. This estimate has to take into account the self-shielding effect, that varies for different low-energy and high-energy gamma-emitting isotopes. The typical composition of the solution from an input accountancy tank in a reprocessing plant is first derived by means of a burn-up code. Eight different spent fuel cases are considered to cover the range of fission products, that can emit low and high energy gamma's. The neutron and gamma fluxes emitted from the classical 7 ml vial and from a vessel with less than a microlitre solution are calculated by means of Monte Carlo simulations. The resulting doses are calculated and compared in average and in distribution for different cases of spent fuel composition. For a volume size reduction of 6300 an averaged conservative dose reduction of 6000 is obtained.     

Transport of radioactive sources in Africa: the Nigerian experience

Abstract

In his plenary presentation at PATRAM 2010, Professor Shamsideen Elegba of the Nigerian Nuclear Regulatory Authority, Abuja, Nigeria, reviewed the regulatory framework for transport of radioactive materials in Africa.     

Effect of External Stress on the Behavior of Oxide Scales on 9Cr-1Mo Steel

Tensile specimens of 9Cr-1Mo steel weresubjected to oxidation in air at a temperature of 973 Kfor periods of 25, 47, 70, 97, 120, and 140 hr. Theintegrity of the oxide scale was examined by an in-situ technique which involved the recording of theacoustic-emission activity associated with the breakingof the scale. Specimens were also subjected to oxidationfor the same times after subjecting them to an external stress of 40 MPa. The applicationof the external stress was found to alter the integrityof the scale. Spalling of the scale occurred to a lesserextent when external stress was applied due to partial release of growth stresses becauseof the elongation of the specimen. The scale buckledbefore spalling when no external stress was applied. Onthe other hand, the scale developed wedge-type cracks before spalling when subjected toexternal stress during oxidation. Postoxidationexamination of the stressed specimen revealedsubstantial segregation of silicon and chromium at thegrain boundaries (oxide ridges). The specimens, which wereoxidized without external stress, revealed a reductionin the concentration of chromium on the surface. Thisbehavior was attributed to enhanced spalling in the case of the latter specimen compared to theformer.     

The Role of Scale Stresses in the Sulfidation of Steels

Several high-temperature processes in chemical,petrochemical, and energy-processing industry arecharacterized by H₂S-containing atmospheres,confronting engineers with severe corrosion attack ofthe metallic components. Sulfidation is observed onmaterials used for heat exchangers within theheat-recovery zones. The damage is originated not onlyby the relatively fast growth rates of the sulfidescales, but is also due to the loss of their limitedprotective effect by cracking. Scale failure, as aconsequence of stresses generated during scale growthand by temperature changes, was investigated on a carbon steel, a low-chromium steel (1Cr-0.4Mo, T12),a ferritic-chromium steel (12Cr-1Mo), and on austeniticsteel (18Cr-9Ni, AISI 321). The experiments in thetemperature range 400-600°C (700°C), withsubsequent cooling to ambient temperature, wereaccompanied by acoustic-emission measurements in orderto detect scale cracking. Critical parameters for scalefailure are presented.     

Using a modified CINDER90 routine in MCNPX 2.6.0 for the prediction of helium production in minor actinide targets

Fast reactors containing heterogeneous minor actinide (MA) target rods are now being modeled. When studying transmutation in these rods, helium production from α-decay must be considered since it is produced in substantial quantities. This research utilized an innovative method to calculate gas production by modifying the CINDER90 depletion code used by MCNPX 2.6.0 to include helium production from α-decay. The modified CINDER90 code was verified using the ORIGEN-ARP module of SCALE6. It was tested using the Sodium-Cooled Heterogeneous Innovative Burner Reactor model created at the University of South Carolina. It is recommended that the modified version of the cinder.dat file be distributed in subsequent MCNPX 2.6.0 releases for use in fast reactor calculations using heterogeneous MA target rods since it includes helium production otherwise not available from the current version.     

Effect of Hf Additions on the Isothermal-Oxidation Behavior of TiAl at High Temperatures

The isothermal-oxidation behavior of TiAlcoupons containing Hf of up to 5.2 mass % has beenstudied in the temperature range 1100-1400 K in a flowof purified oxygen under atmospheric pressure. Theaddition of 0.2% Hf is very effective to decrease theoxidation rate at 1200 and 1300 K. Metallographicexamination using conventional methods revealed that theinitially-formed Al₂O₃ scale ismaintained very sound by the addition. However, further additions ofHf result in a slight enhancement of oxidation at 1200K and a gradual decrease of the effect at 1300 K.Finally, there is almost no effect by the addition of 5.2% Hf at 1300 K. Excess amounts of Hf leadto the formation of oxide mounds on theAl₂O₃ scale. They grow in size andnumber during subsequent oxidation until the wholespecimen surface is covered with a thick scale. Such a scale is notprotective having a structure often reported in theliterature. The effect of the addition of 0.2% Hfbecomes small at 1350 K and at 1400 K it is inverted.Possible mechanisms for the improvement attained by thesuitable addition are discussed.     

Segregation at the Al2O3-FeCrAl Interface During High-Temperature Oxidation

Impurity segregation at theAl₂O₃-metal interface of Fe-Cr-Aland Fe-Cr-Al-Y alloys oxidized at 1100°C was studiedusing Auger electron spectroscopy (AES). A strong sulfursegregation of the order of a monolayer was found at the contactoxide-metal interface on the yttrium-free alloy, whilealmost no sulfur was detected at the interface on theyttrium-containing alloy. These results are in agreement with the AES studies of surface segregation onthe same alloys during heating at 900°C inultra-high vacuum. It is suggested that stresses in thealumina scale and underlying metal during oxidation may provide the driving force for impuritysegregation at the contact oxide-metalinterface.     

核数据对球床式高温气冷堆燃料元件中子学特性的影响

球床式高温气冷堆采用了球形燃料元件,燃料区域由石墨基体和弥散在其中的包覆燃料颗粒构成,其外有与石墨基体相同材料的包壳;燃料球堆叠成填充率约为0.61的球床式堆芯活性区。在堆芯物理计算中,必须考虑其特殊的双重非均匀性结构对共振计算的影响。此外,由于石墨起到了中子慢化和结构材料的重要作用,其截面参数的准确性对共振计算和临界计算均有很大影响。本文采用蒙特卡罗中子输运计算程序SCALE/KENO-Ⅵ和Serpent-2,对比分析了ENDF/B Ⅶ.0和ENDF/B Ⅶ.1版本核数据库对不同燃料模型的有效增殖因数(keff)及反应率的影响,并进一步比较了不同双重非均匀性处理方法对计算结果的影响。结果表明,由于石墨吸收率增大,使用ENDF/B Ⅶ.1版本核数据库所得keff小于使用ENDF/B Ⅶ.0版本核数据库的结果,且计算模型中石墨材料越多,计算结果相差越大:对于包覆颗粒模型差别约为200pcm,对于燃料元件约为700pcm,对于堆芯单元约为1 600pcm。SCALE/KENO-Ⅵ程序使用DOUBLEHET模型进行多群蒙特卡罗计算所得结果与连续能量模型计算结果吻合良好,且计算效率高,对燃料球模型而言可节省约85%的计算时间。     

Recycling of steel plant mill scale via iron ore pelletisation process

Abstract

Mill scale is an iron oxide waste generated during steelmaking, casting and rolling. Total generation of mill scale at JSWSL is around 150 t/day and contains 60–70%FeO and 30–35%Fe₂O₃. To recover the iron, the mill scale must be smelted in a blast furnace or other reduction furnace; however, it is usually too fine to use without previous agglomeration such as via pellet or sinter mix. JSWSL operates a 4·2 Mtpa pellet plant to produce pellets for Corex and BF ironmaking units. The aim of this study is to determine the effect of mill scale on pellet properties. Detailed laboratory basket trials were conducted using up to 40% of mill scale in the pellet mix. The addition of mill scale up to 10% is considered to provide the optimum balance of chemical, physical and metallurgical properties of the pellet.