Research reactor temperature effect

Pulsed research reactors, such as reactors of the Triga type, are especially designed for production and investigation of short-lived radionuclides. In these reactors the neutron flux is increased for about 10 ms to about 10 cm s by taking out the control rods (section 11.5). Due to the negative temperature coefficient of the zirconium hydride moderator, the outburst of power causes a sudden decrease of the moderator properties and shutting off of the reactor. After several minutes the effects have vanished and a new pulse can be started. The activities of radionuclides of various half-lives obtained with pulsed reactors are compared in Table 12.2 with those produced at constant neutron flux densities. The table shows that pulsed reactors are useful for production and investigation of radionuclides with half-lives < 10 s. 

Figure 12.3 Effect of reactor temperature on research octane number (RON) of alkylate produced in an HF alkylation unit [8].

A basin to store spent fuel assemblies is located near the reactor pool and is connected to the reactor pool via a sluice. The depth of this basin is 5.5 m.The basin liner is made of stainless steel. There are 120 cells in the basin to store fuel assemblies and spare blocks of the reactor s reflector. Each cell is made of the aluminium alloy AD-1, which has a minimum aluminium content of 99.3%. The maximum temperature of the storage basin water is 40°C. The IR-8 research reactor has operated for over 20 years. Its effective capacity is about 60%. 

Levels of radiation, temperature or pressure in normal operation conditions will affect the physical properties of a material. Radiation affects components in and outside the reactor core. Other components may be affected by radiation from radioactive materials circulating with the coolant. While the effects of temperature and pressure are more noticeable in power reactors, they are also present in research reactors in materials such as gaskets. Cycling temperature or pressure variations may accelerate deterioration. Table I provides summary information on specific ageing mechanisms. Additional information on these topics is given in Appendix IV which lists 12 case studies. Further information on material ageing mechanisms related to nuclear power plants but sometimes applicable to materials used in research reactors can be found in Ref. [2]. 

There has been considerable need for neutron irradiation units with high neutron fluxrfor use in research, industry, and education. Sources of various types have been used lor this purpose for maiiy years, but have lacked the intensity and volume, with level flux, for larger sample irradiation. While the research reactor can produce the desirable neutron flux, construction and operation is rather costly. A neutron multiplier has been described. .using a subcritical lattice of enriched uranium rods,with a central cylindrical flux trap. A Cf. source is used to provide the initial neutrons to drive the unit. This lattice unit was loaded at the Critical Mass Laboratory to study aspects of criticality including keff and effects of temperature, voids, and added material. 

Researchers have also demonstrated the in situ generation of diazomethane 20 and its use in the synthesis of methyl benzoate (Scheme 6.10). Using commercially available Diazald (Sigma-Aldrich, St. Louis, MO) 21, Struempel et al. screened the effect of reactor temperature (0°C to 85°C) with a fixed reaction time of 5 seconds, observing... 

Various researchers have studied thermal reactions during hydroprocessing of heavy oil fractions. Marafi et al. (2008) conducted a series of experiments at different space velocities and temperatures. They concluded that thermal reactions must be taken into account for an accurate hydroprocessing data analysis. Juraidan et al. (2006) showed that NHDS may change from 0.35% up to 21% in the range of 330°C-410°C of reactor temperature. This means that this thermal reaction is indeed important, and its effects must be taken into consideration when studying the catalytic hydrotreating of heavy oils. 

The results of research into the fluidised bed pyrolysis of plastic wastes are reported, with reference to determining the optimum process conditions for the process with respect to the reactor behaviour. The study investigates the effects of process variables such as bed temperature, polymer feed rate, bed hold-up, fluidising velocity, and size of inert material. Findings illustrate the importance of the knowledge of the hydrodynamics of the fluidised bed and of the interactions between bed and polymer particles in the design and operation of the reactor. 15 refs. 

It is well established that sulfur compounds even in low parts per million concentrations in fuel gas are detrimental to MCFCs. The principal sulfur compound that has an adverse effect on cell performance is H2S. A nickel anode at anodic potentials reacts with H2S to form nickel sulfide. Chemisorption on Ni surfaces occurs, which can block active electrochemical sites. The tolerance of MCFCs to sulfur compounds is strongly dependent on temperature, pressure, gas composition, cell components, and system operation (i.e., recycle, venting, and gas cleanup). Nickel anode at anodic potentials reacts with H2S to form nickel sulfide. Moreover, oxidation of H2S in a combustion reaction, when recycling system is used, causes subsequent reaction with carbonate ions in the electrolyte [1]. Some researchers have tried to overcome this problem with additional device such as sulfur removal reactor. If the anode itself has a high tolerance to sulfur, the additional device is not required, hence, cutting the capital cost for MCFC plant. To enhance the anode performance on sulfur tolerance, ceria coating on anode is proposed. The main reason is that ceria can react with H2S [2,3] to protect Ni anode. 

Consequently, in the early 1990s, interest in the direct processes decreased markedly, and the emphasis in research on CH4 conversion returned to the indirect processes giving synthesis gas (13). In 1990, Ashcroft et al. (13) reported some effective noble metal catalysts for the reaction about 90% conversion of methane and more than 90% selectivity to CO and H2 were achieved with a lanthanide ruthenium oxide catalyst (L2Ru207, where L = Pr, Eu, Gd, Dy, Yb or Lu) at a temperature of about 1048 K, atmospheric pressure, and a GHSV of 4 X 104 mL (mL catalyst)-1 h-1. This space velocity is much higher than that employed by Prettre et al. (3). Schmidt et al. (14-16) and Choudhary et al. (17) used even higher space velocities (with reactor residence times close to 10-3 s). 

With respect to the considerations above, research is split into three parts. The first is connected to the kinetic description of the release of ammonia from the biomass as function of temperature. This research employs infrared spectroscopy using a tunable diode laser. Here very small biomass particles are used that are heated up very rapidly in a small reactor, which ensures that transport effects are virtually excluded from the kinetic release effects. Since ammonia is released in very small quantities it is quite hard to detect. Therefore, we first measure CO release, which is easier. In the second part we investigate the propagation of a conversion front in biomass layers. Here we perform experiments and try to establish a modeling approach for the propagation by analytical and numerical approaches. In the third part the gas-phase conversion processes are described in terms of... 

Some controversy surrounds the usage of the term in situ. Some researchers even go so far as to suggest that unless a reactor and spectroscopic cell/probe are one and the same unit, the measurement cannot be in situ. The results of Section 4.3.1 suggest otherwise. If the fluid elements in the cell are compositionally similar to the fluid elements in the CSTR and are at similar temperature and pressure, then they are indistinguishable. The measurements are in situ. With proper care regarding transport effects, and reaction considerations, an experimental apparatus with a configuration like Figure 4.1 provides in situ spectroscopic capability for dark reactions. 

One of the major drawbacks to defining the influence of the feedstock on the process is that the research with respect to feedstocks has been fragmented. In every case, a conventional catalyst has been used, and the results obtained are only valid for the operating conditions, reactor system, and catalyst used. More rigorous correlation is required and there is a need to determine the optimum temperature for each type of sulfur compound. In order to obtain a useful model, the intrinsic kinetics of the reaction for a given catalyst should also be known. In addition, other factors that influence the desulfurization process such as (1) catalyst inhibition or deactivation by hydrogen sulfide, (2) effect of nitrogen... 

In the past ten years the number of chemistry-related research problems in the nuclear industry has increased dramatically. Many of these are related to surface or interfacial chemistry. Some applications are reviewed in the areas of waste management, activity transport in coolants, fuel fabrication, component development, reactor safety studies, and fuel reprocessing. Three recent studies in surface analysis are discussed in further detail in this paper. The first concerns the initial corrosion mechanisms of borosilicate glass used in high level waste encapsulation. The second deals with the effects of residual chloride contamination on nuclear reactor contaminants. Finally, some surface studies of the high temperature oxidation of Alloys 600 and 800 are outlined such characterizations are part of the effort to develop more protective surface films for nuclear reactor applications. ... 

The research subject in the given problem is the process of cementation based on squeezing out mercury from salt-acidic solution by means of a less useful metal, such as aluminum. A study of kinetics of the given chemical reaction shows that this process may be effectively conducted in a continuous chemical reactor. Process efficiency is measured by mercury concentration in the solution after refinement. This is simultaneously the system response as it may be measured quite accurately and quantitatively. These three factors influence the cementation process significantly Xi-temperature of solution, °C X2-solution flow rate in reactor, ml/1 and X3-quantity of aluminum g. The factor space is defined by these intervals 50[Pg.341]

---