Melting attack of solid plates by a high temperature liquid jet — effect of crust formation

When a molten UO₂ jet impinges on a steel structure in a reactor vessel during a severe accident, the erosion rate of the steel by the molten UO₂ jet is expected to be limited considerably by a UO₂ crust layer forming on a molten steel substrate at the jet/steel plate interface. A series of simulation experiments was performed to study the melting behavior of solid plates by high temperature liquid jets and the effects of crust forming at jet/structure interface. In the first series of experiments, salt (NaCl) was selected as the jet material and tin (Sn) as the solid structure. The experiments were conducted with varying the jet diameter (10 30 mm) and jet temperature (900 1100°C). The jets were accelerated to a range of 3 5 m/s at the nozzle outlet by gravitational force and impinged perpendicularly to the solid plate underneath. Furthermore, to check the effects of the thermo-physical properties on the erosion behaviors, preliminary experiments were performed by using a molten Al₂O₃ jet ( 2200°C) impinging on stainless steel plate at room temperature. The erosion rates obtained in the present experiments were far less than the values predicted by an analytical solution that neglects the existence of a crust layer and its thermal effects. With the inclusion of the crust behavior in the model, the experimental results were predicted fairly well. From the present experiments, a Nusselt number of the turbulent heat transfer, which takes into account simultaneous melting and freezing in the impingement region of a molten jet, is correlated by a Reynolds number and a Prandtl number as follows: Nu_m = 0.0033 Re---Pr.In conclusion, the existence of a crust layer plays an important role in the erosion process of a solid plate by the molten fuel jet with high melting point as in a reactor situation.     

The generation of shallow dopant layers by low-angle implantation

A simple arrangement for the generation of shallow dopant profiled by low-angle ion implantation is described. High resolution Rutherford backscattering has been employed to measure profiles of arsenic and antimony which have been obtained by implantation into (100) silicon at angles of incidence as low as 4° with respect to the wafer surface. These profiles have been compared with Monte Carlo calculations using the TRIM II code and found to be in good agreement. Electrical activity > 5 × 10¹⁹ cm^?3 has been achieved for dopant profiles with peak concentrations within 30 Å of the surface. The technique is amenable to the generation of tailored (e.g. uniform) implantation profiles at constant energy by variation of implant angle.     

Neutron yield of the reactions Li6(t,n) and Li7(t,n)

The differential cross section is determined for the formation of neutrons at an angle of 0 ° in the reactions Li⁶(t,n) and Li⁷(t, n) in the 0.175–2.4 Mev triton energy range. In the reaction Li⁶(t,n) resonance in the neutron yield is observed at E_t = 1.875 Mev, corresponding to a Be⁹ excitation level of 18.936 Mev.Two resonances are detected in the neutron yield of the reaction Li⁷(t, n): at E_t = 0.765 Mev and E_t = 1.735 Mev, which indicates the presence of Be¹⁰ nucleus excitation levels of 17.78 and 18.46 Mev, respectively. The cross section of the reaction Li⁶(t, n) in resonance is d/d(0 °)_res = 37.2 mb/sr; for the reaction Li⁷ (t, n) the cross section at the first resonance is d/d(0 °)_res = 95 mb/sr; at the second resonance d/d(0 °)_res = 159 mb/sr.The angular distributions of neutrons are given for the interval of angles 0–135 ° (every 15 °) for triton energies of 0.358, 0.559, 1.006, 1.218, 1.370, 1.572, 2.123 Mev.The total cross section for the formation of neutrons at E_t = 2.123 Mev in the reaction Li⁶ (t,n) is equal to 324±32.3 mb in the reaction Li⁷ (t, n) to 1332±83.3 mb.     

Finite element analyses of a BWR vessel and penetration under severe accident conditions

This study assesses the two-dimensional thermal response of a BWR vessel and drain line penetration to three types of debris bed; primarily metallic, primarily ceramic and metallic and ceramic layered, with sensitivity studies for the most severe case. Structural finite element analysis evaluates vessel elastic, plastic and creep response for two cases which bound the thermal challenge to the vessel.Thermal analysis results indicate that drain line failure does not occur for the case when metallic debris relocates to the lower head; structural analysis predicts that the vessel also remains intact for this case. In cases where ceramic debris relocates to the lower head, drain line temperatures peak near values where failure may occur within several minutes; whereas vessel failure is not predicted for 3.5 to 4.0 hours. Sensitivity studies indicate that large porosity debris or high heat removal rates from the vessel and drain line outer surfaces can preclude failure temperatures from occurring.     

Time dependence of interface trap formation in MOSFETs followingpulsed irradiation

The time dependence of interference trap (N_it) formation in MOSFETs was studied as a function of gate oxide thickness, oxide growth type, substrate orientation, temperature, and gate bias. Two different N_it formation mechanisms are observed. Most (typically 90%) of the formation, called the late process, occurs slowly at long times (1-10000 s) after the radiation pulse. From a variety of experimental data, it is concluded that the rate of the late process is limited by drift of a radiation-induced positive ion, probably H⁺ , through the gate oxide to the Si-SiO₂ interface where the N_it are formed. A relatively fast, or early, process is responsible for a small percentage of the total N_it formation. The time constant for this process appears to be consistent with hole drift through the oxide     

3-D-micro-ERDA microscopy of trace hydrogen distributions in diamond using a 2-D-PSD with event reconstruction

A fast-imaging technique for the total elemental hydrogen concentration distribution is described, which is helpful in the study of its chemistry and dynamics in the diamond system. The micro-scanned Heavy-Ion Elastic Recoil Detection Analysis (HI-ERDA) technique can deliver information on hydrogen distributions in three dimensions. In our system, the count rate is enhanced by use of a 2-D position and energy sensitive detector for the hydrogen recoils. Software geometry collimation and recoil energy rebinning ensure that the increased rate is in fact accompanied by an improvement in effective energy resolution. The system has been used to study the mobility and trapping behaviour of a collimated implant of hydrogen into a pre-damaged natural type IIa diamond sample as well as the mobility and trapping behaviour of collimated implants of hydrogen into diamond, which has not been pre-damaged.     

Structural evaluation of thermal stratification for PWR surge line

Recent observations at operating plants and subsequent US NRC requirements have identified flow stratification in surge lines as a phenomenon that must be considered in the design basis of surge lines. To address these concerns, the stratified loading conditions were included in the design of YGN 3 and 4 surge line as a design basis transient and pipe temperature and displacement measurement were taken during YGN 3 pre-core hot functional testing to determine the degree of surge line flow stratification. The measured displacements and temperatures were extensively reviewed and evaluated in detail: (1) to verify the validity of the thermal hydraulic model used to predict the pipe top-to-bottom temperature differentials; (2) to analytically correlate measured surge line temperatures and displacements; and (3) to confirm the validity of the stratified flow analysis procedure. This paper shows that the stratified flow phenomenon is generic and therefore generic loadings can be developed and evaluated for the surge line analyses.     

Cyclic mode of neptunium, americium and curium transmutation in heavy-water reactor

Characteristics of process of transmutation of neptunium, americium and curium from spent nuclear fuel in heavy-water reactor during first 10 lifetimes and at transition to equilibrium mode are calculated. During transmutation, dangerous nuclides, first of all, ²⁴⁴Cm and ²³⁸Pu are accumulated. They cause an increase of radiotoxicity. At first 10 cycles of transmutation, the radiotoxicity is increased by 8.7 times in comparison with radiotoxicity of initial load of transmuted actinides. Heavy-water reactor with thermal power of 1000 MW can transmute neptunium, americium and curium extracted from 3.7 VVER-1000 type reactors. It means, that the required power of transmutation reactor makes about 8% of thermal power of VVER-1000 type reactors.