Investigation of the saturated steam sampling method influence on the sample representativeness in chemical control systems at thermal power plants

The most important requirement for sampling is the sample representativeness, which is achieved by the design and location choice of sample nozzle, as well as the speed mode and the presence of sharp pressure drops in the saturated steam flow. The Ansys CFX software package simulates the sampling processes saturated steam in power units with low, medium and high pressure boilers which are used on operating thermal power plants. The saturated steam was sampled from low-pressure boiler by a single-strip probe with a Venturi nozzle, from the medium-pressure boiler was sampled by tapping a pipe at 90 to the main steam line, and the steam of the high – pressure boiler was sampled by a wellhead probe. In three sampling cases it is found that of saturated steam, the flow in the sample nozzle loses speed and decreases to values unacceptable for the selection of a representative sample-below tear rate of the moisture film from the surface. It is confirmed that in the industrial sampling conditions, the condition of speeds equality in the main steam line and in the sample nozzle is not met, which leads to a violation of the sample representativeness. The paper studies the change in the composition of the sampled saturated vapor sample after the film formation on the sample’s nozzle wall in relation to power units with ammonia dosing. It was found that the sample received by the chemical control analyzers is depleted due to the formation of a film and the ferrum and ammonia concentration in moisture droplets on the inner surface of the sampling line.

LOCA analysis of BWR-4/Mark-I nuclear power plant with TRACE

This study established an RCS-Containment coupled model that integrates the reactor coolant system (RCS) and the containment system by using the TRACE code. The coupled model was used in both short-term and long-term loss of coolant accident (LOCA) analyses. Besides, the RELAP5/CONTAN model that only contains the containment system was also developed for comparison. For short-term analysis, three kinds of LOCA scenarios were investigated: the recirculation line break (RCLB), the main steam line break (MSLB), and the feedwater line break (FWLB). For long-term analysis, the dry-well and suppression pool temperature responses of the RCLB were studied. The analysis results of RELAP5/CONTAN and TRACE models are benchmarked with those of FSAR and RELAP5/GOTHIC models, and it appears that the results of the above four models are consistent in general trends.

Thermal-hydraulic analysis of a VVER-1000 core in MSLB conditions

The objective of this paper is to analyze the ability of a VVER-1000 core and its control system to cope with a hypothetical main steam line break (MSLB) accident in case of multiple equipment failures. The study involves the use of advanced 3D core calculation models benchmarked and validated for reactivity accidents in preceding studies. A MSLB core boundary condition problem is solved on a coarse (nodal) mesh with the coupled COBAYA/CTF neutronic/thermal hydraulic codes. The core thermal-hydraulic boundary conditions are obtained from a preceding full-plant MSLB simulation. The assessment of the core safety parameters is supplemented by a fine-mesh (sub-channel) thermal-hydraulic analysis of the hottest assemblies with the CTF code using information from the 3D nodal COBAYA/CTF calculations. Thirteen variants of a pessimistic MSLB scenario are considered, each of them assuming a number of equipment failures aggravated by eight control rods stuck out of the core after scram at different locations in the overcooled sector. The results (within the limitations of the adopted modeling assumptions) show that the core safety parameters do not exceed the safety limits in the simulated aggravated reactivity accidents.

Analysis of reliability of design of stop valve of steam turbin

The stop valve is one of the «critical» elements of the steam turbine installation, the heating conditions of which determine the reliability of the power unit as a whole. The stop valve for cogeneration steam turbines of subcritical parameters of "UTZ" is unified for familiesT-110/120-130, T-185/210-130/15, ПT-140/165-30/15, P-100-130/15. The sequence of analysis of the valve design is presented for conditions, where only the static temperature and steam pressure at the inlet to the valve, the steam flow rate at the outlet of it, the restrictions for movement during heating are known. The results of the analysis of calculations of unsteady gas-thermodynamic and stress-strain state of the valve during the heating of the main steam line of the turbine T-110/120-130 from the cold state according to the standard instructions are shown. The calculations were carried out by the finite element method using a three-dimensional geometric model of the valve body with a slit filter. The height of the holes in the slit filter is 3.5 mm. The equations of the Nusselt criterion for the flange, the steam box, the lower half of the steam box and the fairing when using computers with limited computing resources are presented. It is shown that the peak of the maximum stresses occurs at the initial stage of the stop valve warming up on the inner (heated) surface of the stop valve body in the area of the flange and the cover. The maximum equivalent stresses are 300 MPa. The comparison of calculated temperatures and temperatures measured during the start-up at the CHP is presented; the temperature difference does not exceed 5–6%. It is proposed to analyze the stop valve reliability with a sequence given in this article in the design of new stop valves with significant differences from the existing prototypes.