Mohamed Elsafi, Aljawhara Almuqrin, Mohammad Sayyed
This work focuses on the preparation of borotellurite glasses doped with BaO, Bi2O3, and Er2O3, and the investigation of their radiation attenuation parameters. A narrow beam experiment was conducted to assess the attenuation factors of the glasses. A positive relationship was observed between the linear attenuation coefficient and the concentration of Er2O3. The linear attenuation coefficient for the Er2O3-free glass at 0.059 MeV is 19.729 cm-?, while for the sample with 3 mol % Er2O3, it is 26.113 cm-?. At 0.662 MeV, the linear attenuation coefficient for the Er2O3-free glass and the glass with 3 mol % Er2O3 are 0.426 cm-? and 0.461 cm-?, respectively. The mean free path of the glasses exhibited an inverse relationship with increasing Er2O3 content. For the glass containing 1 mol % Er2O3, the mean free path values are 0.046 cm, 2.285 cm, and 3.556 cm at 0.059 MeV, 0.662 MeV, and 1.173 MeV, respectively. The half-value layer was calculated, and the results indicated that the addition of Er2O3 causes a decrease in the half-value layer, suggesting an enhancement in the radiation attenuation performance of the prepared glasses as more Er2O3 is added.
A system with a passive mechanism has been considered to have better trustworthiness because it does not require an external driving force to function. Several nuclear reactor designs have implemented this feature either fully or partially in their safety systems. Some of them combine boiling and condensation phenomena to deal with decay heat when an accident occurs. This paper reviews studies on condensation heat transfer in passive residual heat removal systems and passive containment cooling systems of light water-cooled reactors. The emphasis is on the applicability of acknowledged correlations for accident conditions and its development for a better model. In the explanation, the passive mechanism and type of condenser implemented in the system are first identified. Afterward, comparative formula assessment using test data, parametric studies using computer simulation, and new correlation development are discussed. The evaluation showed that the use of existing correlation needs tuning in the case of light water reactor passive safety system design. Besides, it was also suggested to take into account the geometric form of the condensation surface. Further research on helical shape is needed to assess the possibility of an integral reactor's steam generator changing role as a condenser during the loss of coolant accident that is followed by safety system failure.
The use of a new Monte Carlo Serpent code for the calculation of water-cooled reactors is presented and a calculation scheme of the fuel assembly for VVER-1000 reactors developed. The calculation of neutron-physical characteristics for the fuel assembly of VVER-1000 is carried out for different states and the results obtained by the Serpent model compared with the results of other reactor codes. The analyses of these results are presented in the paper submitted here. Based on this article, the Monte Carlo Serpent code could be used for neutron-physical calculations of VVER-1000 reactors.
One second shutdown system is proposed for the Tehran Research Reactor to achieve the goal of higher safety in compliance with current operational requirements and regulations and improve the overall reliability of the reactor shutdown system. The proposed second shutdown system is a diverse, independent shutdown system compared to the existing rod based one that intends to achieve and maintain sub-criticality condition with an enough shutdown margin in many of abnormal situations. It is designed as much as practical based on neutron absorber solution injection into the existing core while the changes and interferences with the existing core structure are kept to a minimum. Core neutronic calculations were performed using MCNPX 2.6.0 and MTR_PC package for the current operational core equipped with the second shutdown system, and one experiment was conducted in the Tehran Research Reactor to test the neutronic calculations. A good agreement was seen between theoretical results and experimental ones. In addition, capability of the second shutdown system in the case of occurrence of design basis accident in the Tehran Research Reactor is demonstrated using PARET program.
In this study kinetic parameters, effective delayed neutron fraction and prompt neutron generation time have been investigated at different burn-up stages for research reactor's equilibrium core utilizing low enriched uranium high density fuel (U3Si2-Al fuel with 4.8 g/cm3 of uranium). Results have been compared with reference operating core of Pakistan research Reactor-1. It was observed that by increasing fuel burn-up, effective delayed neutron fraction is decreased while prompt neutron generation time is increased. However, over all ratio beff/L is decreased with increasing burn-up. Prompt neutron generation time L in the understudy core is lower than reference operating core of reactor at all burn-up steps due to hard spectrum. It is observed that beff is larger in the understudy core than reference operating core of due to smaller size. Calculations were performed with the help of computer codes WIMSD/4 and CITATION.
Abstract Since prices are constrained to discrete tick multiples while dividends are essentially continuous, ex day price changes will not equal dividends. We argue that the expected price drop is strictly less than the dividend but within one tick of the dividend. The price-drop-to-dividend ratio will (i) be less than one, (ii) increase with dividends generally, and (iii) decline between tick multiples, giving a sawtooth pattern in the data. Since dividends and dividend yields are highly correlated, discreteness will give the impression of tax-induced dividend clienteles even if there are none. Taxable cash dividends and nontaxable stock dividends exhibit similar ex day behavior.