New simple low-cost surgical approach to complex jejuno-ileal atresia

We report our experience of staged operations in the surgical treatment of complex jejuno-ileal atresia. Our study examined transgastric deflation of the proximal segment and feeding jejunostomy through the distal segment as a first stage followed by a definitive restoration of continuity secondarily at a tertiary centre over a period of three years. A cohort of 21 cases were studied. None suffered with intestinal perforation or volvulus. Tube plugging was seen in three patients who were relieved by flushing. Tube replacement was not required. One patient developed necrotising enterocolitis and died. Sepsis was seen in three. The age at the second operation was 56.2 ± 6.6 days. There was no complication after this second procedure. We therefore recommend this staged management for complex jejuno-ileal atresia, but suggest further studies.

Performance Analysis and Tube Inlet Orifice Length Evaluation of a Once–Through Steam Generator

A numerical study is conducted for performance analysis and secondary side screw-type tube inlet orifice design of a once–through steam generator (OTSG). Various tube plugging conditions and power levels are considered, and the secondary coolant flow rate is adjusted to maintain a constant thermal power. Comprehensive numerical solutions are acquired to evaluate the OTSG thermal–hydraulic performance and minimum orifice length under various operating conditions. The OTSG performance is analyzed according to the tube plugging condition in terms of the OTSG thermal power, steam outletsuperheat degree, and secondary coolant pressure drop. The results obtained show that a constant thermal power canbe maintained by properly adjusting the secondary coolant flow rate with a variation ofthe steam outlet superheat degree and secondary coolant pressure drop when the OTSG operates at high power level. The required minimum orifice length to suppress the flow oscillation below the allowablelevelis evaluated. The lowest power level results in the highest minimum orifice length, and non-plugging condition provides a limiting case for the orifice length criterion.

Hydraulic Characteristics Research on SG Under Tube Plugging Operations Using FLUENT

Steam Generator (SG) is a critical equipment in the nuclear power plant, it is the huge heat exchanger in reactor system which can achieve removing fission energy from the reactor system effectively to ensure safety of the whole nuclear system. It is located between the primary and the secondary loop in reactor system act as the intermediate hub of energy and the security barrier in nuclear power plant. Generally, there are numerous of U-shaped heat transfer tubes in SG it is one of the weakest structures throughout the primary loop system. So the integrity of the SG especially its heat transfer tubes is important to the safety of reactor operation. The degradation problem of heat transfer tubes together with ruptures accidents often occur under suffer environments in reactors, which include thermal stress, mechanical stress and so on, it is noteworthy that this kind of accidents is inevitable due to the limited properties of existing materials. The performance of the SG is seriously affected by the number of failure tubes. Plugging operations through various mechanical means is the most common method to solve the tubes ruptures problems which can reduce the economic losses to the utmost extent. However, plugging operations will make huge impact on the thermal hydraulic performances of both sides of SG. It’s meaningful to research the characteristics of the plugging affects under different operations. In this paper the hydraulic characteristics of primary side in AP1000 SG under a certain fraction of heat transfer tube plugging conditions is researched. Three dimensional hydraulic characteristics of primary side coolant in SG under different plugging conditions are obtained by using the thermal hydraulic software FLUENT. The typical plugging fraction in this simulation model is 10 percent, and the effect of plugging locations also be considered through changing the plugging positions using the zone marking method. The results shows that the pressure drop under the structure integrated SG is 358.01MPa which is accordance with the results from Westinghouse 343KPa. The pressure drop values varies when changing positions of the plugging tubes under the same plugging fraction condition. The flow fields in bottom head also change meanwhile and the maximum pressure drop can reach up to 388.05KPa when the plugging fraction is 10%. The growth rate become significant when tube plugging fraction larger than 5%, and differences between maximum and minimum values of total pressure drop under different plugging positions become larger gradually. Finally the local resistance coefficients and flow field distributions of primary side in SG under various plugging conditions are obtained which is meaningful for the reactor safety and it can be a good reference for the maintenance of SG.

Performance Corrections for Steam Turbines With Multi-Pressure Condensers

An accurate correction methodology is essential when analyzing test data and trending performance. One of the most critical parameters for steam turbines, which can result in large corrections, is condenser back-pressure or exhaust pressure. Many large fossil and all nuclear steam turbines are configured with either two or three low pressure condensing exhaust hoods. All exhaust hoods may not operate with the same condenser pressure. Factors affecting condenser pressures between hoods could include the cooling water arrangement, uneven fouling, tube plugging, air removal effectiveness, etc. The biggest impact is likely due to the cooling water arrangement. In a parallel arrangement, the condenser cooling water splits between the shells with each shell receiving an equal amount of flow at the same inlet temperature. In a series arrangement, all cooling water enters and exits the first shell before entering the next shell. In this arrangement the cooling water temperature entering the second shell is higher than the temperature entering the first shell resulting in the condensers operating at different exhaust pressures. One common practice is to apply a single exhaust pressure correction factor based on the average exhaust pressure of all condenser shells. In cases where the differences in condenser pressure are small, this practice can provide accurate corrected turbine performance. As the difference in condenser pressures increases, the potential for introducing error in the corrected performance results also increases. This paper will discuss the mechanism of why multi-pressure operation can result in correction errors if not modelled correctly and will also quantify the potential impact of these errors on the corrected performance results. In addition, guidance will be given on how exhaust pressure correction curves should be created and applied to most accurately model the performance of the turbine cycle when multi-pressure operation exists.

Aging Management of French PWR Nuclear Steam Generators Using Statistical Modeling

Electricité de France (EDF) has recently announced its intentions to extend the lifetime of some of its plants to 60 years which has lead to a large advance order of steam generators (SG) and therefore an intensive period of replacement. The detailed planning required during a shutdown and the industrial constraints for design and manufacturing necessitate the decision for a replacement to be taken a few years in advance. Predicting the end of life of a SG is principally governed by the level of degradation of the tube bundle which is largely dependent on the tube material and time in service. EDF carries out a risk assessment on the life of each SG based on the percentage of tubes plugged determined using statistical modeling that take into account factors such as the evolution and type of degradation. In addition, SG tube plugging rates have to be anticipated in advance to ensure the heat exchange capacity is within safety guidelines. This paper provides an overview of the status of active degradation growth rates and different calculation methods used at units with A600TT and A690TT tubing. Furthermore, their application on predicting the number of tubes to be plugged is illustrated. Finally, statistical models used to predict the evolution of different degradation types are also detailed.