Operation Life Extension Research Articles

Ensuring Irradiation Conditions for Metal Specimens within a Materials Science Assembly to Validate the BN-600 Operational Life Extension

Ensuring Irradiation Conditions for Metal Specimens within a Materials Science Assembly to Validate the BN-600 Operational Life Extension

Thermodynamic and exergoeconomic analysis of a proton exchange membrane fuel cell/absorption chiller CCHP system based on biomass gasification

This work investigates an integrated system consisting of biomass gasification process, proton exchange membrane fuel cell (PEMFC) and absorption chiller. The proposed system is studied from the energetic and exergoeconomic point of view. In addition, parametric analysis and uncertainty analysis are carried out to investigate the effects of four key operational parameters and three uncertain parameters. System energy efficiency and exergy efficiency are obtained as 57.41% and 18.07%, respectively. 21.46% of the electricity production is consumed by auxiliary components of the PEMFC stack. Largest exergy destruction is in the gasifier and the stack, due to significant irreversibility of chemical/electrochemical reactions. Exergoeconomic results indicate that in the selective oxidation process, investment cost is much higher than the cost rate of exergy destruction. While gasifier, anode/cathode heat exchangers and humidifiers, condenser, solution heat exchangers and valves have poor exergetic performance. High current density, operation temperature and moisture content are unfavorable for exergy efficiency. Extension of operation life, lower interest rate and lower maintenance factor can guarantee a desired system exergoeconomic performance. This research provides pragmatic information about thermodynamic and exergoeconomic performance of this integrated system. Obtained results are important for system design and operational optimization on various PEMFC coupled polygeneration systems.

RISK-INFORMED METHOD FOR PREDICTING THE OPERATION LIFE EXTENSION PERIOD OF ACTIVE SAFETY SYSTEMS AT NUCLEAR POWER PLANTS

An original method has been developed for predicting the operation life extension period of thermal mechanical equipment of safety systems based on the assessment of the residual resource by the number of thermohydrodynamic and mechanical cyclic loads and the test frequency during design operation life. Based on the developed method, as well as the results of technical inspection of pump and armature bodies of emergency core cooling and steam generator emergency feedwater systems, it was found that the permissible operation life extension period is 4 years for the design test frequency, 8 years if the test frequency is reduced by 2 times, 16 years if the test frequency is reduced by 6 times, 20 years if the test frequency is reduced by 10 times. However, the possibility of reducing the test frequency requires additional substantiation for optimizing the test frequency, taking into account the effects of equipment wear and the accumulation of critical defects between tests. The need to optimize the test frequency de-termines the relevance of further research.

Evaluation of the aging management system for the Triga research nuclear reactor in Brazil / Avaliação do sistema de gerenciamento do envelhecimento do reator nuclear de pesquisa Triga no Brasil

As most research reactors have over 40 years of operational experience, maintenance, modernization and renovation are increasingly important for safety and operational life extension. This is due to the monitoring and development of techniques to control and mitigate the negative effects of operating conditions on structures, systems and components. Aging management is a strategy of engineering, operation, maintenance and other actions to control, within acceptable limits, the aging degradation of the facility. The first criticality of the IPR-R1 Triga research reactor (Training, Research, Isotopes, Atomics) occurred in 1960 with a maximum thermal power of 30 kW. Therefore, this reactor has been operating for more than 60 years. One of the issues that comes from the long time of the operation is the management of aging. This includes functions and issues related to operation, inspections, design changes, testing, and others. The IPR-R1 reactor is a North American project. So, the requirements of United State Nuclear Regulatory Commission (U.S.NRC) are applicable. This article discusses the International Atomic Energy Agency (IAEA), and U.S.NRC requirements to implement an aging management system for the CDTN IPR-R1 Triga Reactor.

The operational assessment of steam generator tubes based on a stochastic crack growth model

In pressurized water reactor plants, the degradation of steam generator tubes has been one of the main economic and safety problems. Steam generator tubes are subjected to the degradation mechanism of stress corrosion cracking, in which an unstable crack growth may lead to their structural failure. In general, deterministic criteria provide the least conservative assessment in order to plug or sleeve the cracked tubes. As the crack growth rate under stress corrosion cracking is of high random nature, the structural integrity assessment of steam generator tubes must be performed taking into account the failure probability at current and next inspections. In this paper, a stochastic model is applied for performing the operational assessment of steam generator tubes for any time interval. The results obtained with this model are compared with others, such as Monte-Carlo simulation and non-evolutionary statistical model. The proposed methodology is able to provide efficiently a less conservative failure probability. The plausibility of stochastic models in the structural integrity assessment of steam generator tubes is reached in favor of their operational life extension.

PREDICTION OF OPERATION LIFE EXTENSION OF HEAT POWER EQUIPMENT

Based on the analysis of known researches, it is revealed that the quantity and accumulation rate of cyclic thermal and dynamic loads in the transient modes of normal operation conditions, when violating normal operation conditions and in accident conditions (except for the nuclear reactor vessel) are the key factors of prediction of operation life extension for a heat power equipment (heat exchangers, pumps, armature). The method for predictive estimation of terms of operation life extension of a heat power equipment depending on stress amplitudes in transient and accident conditions, quantity and accumulation rate of cyclic loads, strength metal parameters of a heat power equipment vessels (except for a reactor vessel) is provided. The method is implemented on the example of steam generators of WWERs and using operational data of South-Ukraine-1 (by 2010). Admissible accumulation rate of cyclic loads during operation life extension by 30, 40 and 50 years is a result. The results define insufficient substantiation of nuclear power plant operation in the “maneuverable” modes with a variable reactor power. In this case, the quantity of cyclic equipment loads increases dramatically, and terms of safe operation are limited. The developed method and the obtained results of prediction of operation life extension of heat power equipment can be used for industry programs to extend the operation of Ukrainian nuclear power plants, as well as to improve the regulatory documents governing the conditions and requirements for acceptable safe extension of the operation life of heat power equipment of nuclear and thermal power enterprises. Further improvement of the method proposed in the work for predicting operation life extension of heat power equipment can be based on the development of methods for analyzing the reliability of heat power equipment and databases on operation disturbances.The materials of the presented work are used in the educational process for the training, retraining and advanced training of specialists in the energy industry.

Modeling mining company activities under conditions of resource base depletion: Ecological-and-economic aspect

Depletion of the resource base is typical of many mining companies in the major sector in the recent decades, which dictates that some scientific and applied problems are to be solved in order to develop business strategy to function further, considering ecological consequences of such solutions. This article addresses waste management as a new resource base for mines. The substitute resources are characterized and evaluated with regard to accumulated volumes of overburden rocks, content of useful component (copper) and potential reserves of copper in stock piles. It is substantiate that each substitute resource in mine waste should be provided with model and method of processing. In terms of Erdenet Mining Corporation in Mongolia, the methods of economical-and-mathematical modeling of a mining company’s activities by the criterion of cost minimization in ore processing and waste disposal are discussed. Furthermore, the forecasting up to 2040 is carried out based on the data extrapolation. This allows estimating the operational life of the mining company and the reduction in the environmental impact owing to use of the substitute resources. The waste management efficiency model is based on the substitution of primary natural resources by waste materials from tailings and dumps. Evaluation of the waste use efficiency dynamics determines relative economy and profit gained by a user in manufacturing of marketable products from waste in comparison with traditional production, i.e. using primary resources. The calculations are performed with regard to the ecology factor—reduction in contaminated land as a result of treatment of substitute resources. The formulation and implementation of the model completes a number of strategic missions, namely, extension of operational life of mining company owing to utilization of waste, transfer of waste, mitigation of ecological stress, release of lands withdrawn earlier for placement of waste, as well as cost saving in prospecting and exploration of new mineral deposits.

Spacecraft Drift Counteraction Optimal Control: Open-Loop and Receding Horizon Solutions

The objective of drift counteraction optimal control is to maximize the time that a given system satisfies prescribed constraints. This paper describes novel open-loop and receding horizon/model predictive control-based approaches to solve this problem. To illustrate the potential for drift counteraction optimal control applications to spacecraft operational life extension, two examples of geostationary satellite station keeping near the end of satellite operational life and spacecraft attitude control considering the effects of reaction wheel failures and reaction wheel speed saturation are presented. For the satellite station-keeping problem, the objective is to counteract drift imposed by orbital perturbations and maximize the time before prescribed position constraints are violated, given fuel limitations. For the attitude control problem, the spacecraft is subject to disturbances from solar radiation pressure; and tight pointing constraints need to be satisfied for as long as possible using reaction wheels. The cases of underactuated spacecraft (one or two reaction wheels) and fully actuated spacecraft are treated.

Low cycle thermomechanical fatigue of VVER-440 reactor pressure vessel steels: Investigation the fatigue kinetics and development of a life assessment model

The fatigue life of the structural materials 15Ch2MFA (CrMoV-alloyed ferritic steel) and 08Ch18N10T (CrNi-alloyed, Ti-stabilized austenitic steel) of the VVER-440 reactor pressure vessels was investigated under fully reversed total strain controlled low cycle fatigue tests. The measurements were carried out in isothermal conditions at 260 °C and with thermal-mechanical conditions in temperature range of 150 to 270 °C using the GLEEBLE 3800 servo-hydraulic thermal-mechanical simulator.Owing the nominal fatigue lifetime for different testing conditions interrupted fatigue tests were carried out to investigate the kinetics of the fatigue evolution. Microstructural evaluation of the samples was performed using transmission electron microscopy as well as X-ray diffraction, and measurement of the dislocations was completed. The course of dislocation density in relation to cumulative usage factor was similar for both materials. However, the nature and distribution of dislocations were different in the individual steels and this resulted in different mechanical behaviours.Using scanning electron microscopy the crack shapes and fracture surfaces were observed and analysed. Crack propagation was assessed in relation to the actual crack size and the loading level.A new low cycle fatigue criterion is presented based on the stored energy, which accumulates in the material during fatigue loading. The new damage parameters are based on the assumption that only the stored part of the introduced energy causes the changes in the microstructure. The proposed model is physically consistent and its prediction accuracy is higher than by the classical strain amplitude and strain energy based approaches.The low cycle fatigue behaviour investigated with the developed engineering model can provide a reference for the remaining life assessment and possible operation life extension of nuclear power plant components.

Computational and experimental studies of the causes of crack network formation in the area of the heat exchanger tube sheet in the BN'600 reactor

In order to examine the condition of intermediate sodiumtosodium heat exchangers (IHX) and to substantiate their operation life extension to 45 years at the BN600 reactor plant at Beloyarsk NPP Unit 3, one of the six heat exchangers was removed from the reactor in April 2006. Inspection revealed cracks with 7 maximum depth of mm on the outer surface of the upper tubesheet (UTS) and adjacent shell.To predict durability of substantially fatigued metal, verification of the existing relationship for the threshold stress intensity factor range for the 10Cr18Ni9 steel was needed. To this end, specimens of two structural elements in the IHX – upper tube sheet and protection block were tested.To identify failure mechanisms, fractographic studies were performed on the surface of cracks detected in the tube sheet and produced in the specimens. The studies led to the conclusion that the failure mechanism for cracks detected on the tube sheet was identical to the mechanism generated in the test specimens. In both cases the intergranular failure prevailed that is typical for the material stress level indicative of crack growth termination. This result makes it possible to speak about crack initiation and propagation in the IHX tube sheet in the high-cycle fatigue region at low-level strain ranges and stress intensity factor ranges.An analysis of causes of crack formation showed that the cracks could have formed as a result of the temperature pulsation effect produced by mixing of sodium flows having different temperatures – sodium entering the IHX inlet and sodium coming from the reactor vessel cooling system.Computational analysis results showed that for all thermal pulsation conditions and crack propagation cross-sections under consideration, the leak-tightness condition is met for the upper tube-sheet and IHX outlet chamber shell that divide the primary and secondary coolant circuits.The computational and experimental studies have proved that presence of these cracks does not limit the potential service life extension to 45 years for the IHX in the BN600 reactor plant.

Demand Response for Operational Life Extension and Efficient Capacity Utilization of Power Transformers During Contingencies

Severe overloads, caused by the outage of units in multi-transformer substations, may affect transformer life adversely. This paper presents a novel demand response (DR) based optimization model to limit load on healthy transformers during contingencies. The model selects combination of the best remedial actions among DR, load curtailment (LC) and transferring load to a neighboring substation. IEEE standard thermal and aging models are used for transformer loss-of-life (LOL) calculation. For a realistic study, the proposed model is applied to a Finnish residential two-transformer primary substation for case studies of load with and without DR. The load profile and flexibility of the demand are estimated by hourly metered consumption and survey data. Simulations are performed for two situations depending upon availability of connection with a neighboring substation. The results show that the LOL of transformers can be reduced by employing DR following contingency events and the capacity utilization can be increased correspondingly.

Incorporating Environmental Impacts in Strategic Redesign of an Engineered System

Large engineered systems do not often live out their life cycles as originally planned. Traditional design methods do not address redesign issues that arise during long term operation of these systems. The problem of how to consider the environmental impacts of stranded assets is especially problematic, particularly during system operational changes. This paper presents a method for analysis of a dynamically changing system that includes consideration of both economic and environmental impacts. A case study of an electrical power system illustrates the approach. Using a 100yr time period and using several decision rules (e.g., keep all plants operating until planned retirement age or retire all plants 10% early), the aggregated results were derived. The best sequence of decision or decision rule can now be determined by the highest multiattribute utility score. The best decision sequence is one that immediately retires and decommissions all fossil fueled electrical power plants, although early retirement without immediate decommissioning produces inferior utility values. There is little gained in utility when extending operational life of the plants, and as the 100yr period moves forward, all solutions collapse on the final system configuration. The results provide several insights that were gained through the ability to forecast the environmental impact caused by changes within the life cycle phases of a system, such as early retirement or operational life extension of facilities.

Selection of large-scale functional film-coating systems

In order to examine the condition of intermediate sodiumtosodium heat exchangers (IHX) and to substantiate their operation life extension to 45 years at the BN600 reactor plant at Beloyarsk NPP Unit 3, one of the six heat exchangers was removed from the reactor in April 2006. Inspection revealed cracks with 7 maximum depth of mm on the outer surface of the upper tubesheet (UTS) and adjacent shell.To predict durability of substantially fatigued metal, verification of the existing relationship for the threshold stress intensity factor range for the 10Cr18Ni9 steel was needed. To this end, specimens of two structural elements in the IHX – upper tube sheet and protection block were tested.To identify failure mechanisms, fractographic studies were performed on the surface of cracks detected in the tube sheet and produced in the specimens. The studies led to the conclusion that the failure mechanism for cracks detected on the tube sheet was identical to the mechanism generated in the test specimens. In both cases the intergranular failure prevailed that is typical for the material stress level indicative of crack growth termination. This result makes it possible to speak about crack initiation and propagation in the IHX tube sheet in the high-cycle fatigue region at low-level strain ranges and stress intensity factor ranges.An analysis of causes of crack formation showed that the cracks could have formed as a result of the temperature pulsation effect produced by mixing of sodium flows having different temperatures – sodium entering the IHX inlet and sodium coming from the reactor vessel cooling system.Computational analysis results showed that for all thermal pulsation conditions and crack propagation cross-sections under consideration, the leak-tightness condition is met for the upper tube-sheet and IHX outlet chamber shell that divide the primary and secondary coolant circuits.The computational and experimental studies have proved that presence of these cracks does not limit the potential service life extension to 45 years for the IHX in the BN600 reactor plant.

Origin of magnetization-induced uniaxial anisotropy in evaporated Fe-Co and Ni-Co films

In order to examine the condition of intermediate sodiumtosodium heat exchangers (IHX) and to substantiate their operation life extension to 45 years at the BN600 reactor plant at Beloyarsk NPP Unit 3, one of the six heat exchangers was removed from the reactor in April 2006. Inspection revealed cracks with 7 maximum depth of mm on the outer surface of the upper tubesheet (UTS) and adjacent shell.To predict durability of substantially fatigued metal, verification of the existing relationship for the threshold stress intensity factor range for the 10Cr18Ni9 steel was needed. To this end, specimens of two structural elements in the IHX – upper tube sheet and protection block were tested.To identify failure mechanisms, fractographic studies were performed on the surface of cracks detected in the tube sheet and produced in the specimens. The studies led to the conclusion that the failure mechanism for cracks detected on the tube sheet was identical to the mechanism generated in the test specimens. In both cases the intergranular failure prevailed that is typical for the material stress level indicative of crack growth termination. This result makes it possible to speak about crack initiation and propagation in the IHX tube sheet in the high-cycle fatigue region at low-level strain ranges and stress intensity factor ranges.An analysis of causes of crack formation showed that the cracks could have formed as a result of the temperature pulsation effect produced by mixing of sodium flows having different temperatures – sodium entering the IHX inlet and sodium coming from the reactor vessel cooling system.Computational analysis results showed that for all thermal pulsation conditions and crack propagation cross-sections under consideration, the leak-tightness condition is met for the upper tube-sheet and IHX outlet chamber shell that divide the primary and secondary coolant circuits.The computational and experimental studies have proved that presence of these cracks does not limit the potential service life extension to 45 years for the IHX in the BN600 reactor plant.