Dynamic scaling characteristics of single-phase natural circulation based on different strain transformations

To understand the dynamical system scaling(DSS)analysis theory,the applicability of DSSβ-andω-strain transformation methods for the scaling analysis of complex loops was explored.A simplified model consisting of two loops was established based on the primary and secondary sides of a nuclear reactor,andβ-andω-strain transformation methods were used to ana-lyze the single-phase natural circulation in the primary circuit.For comparison with the traditional method,simplified DSSβ-andω-strain methods were developed based on the standard scaling criterion.The strain parameters in these four methods were modified to form multiple groups of scaled-down cases.The transient process of the natural circulation was simulated using the Relap5 code,and the variation in the dynamic flow characteristics with the strain numbers was obtained using different scaling methods.The results show that both the simplified and standard DSS methods can simulate the dynamic characteristics of natural circulation in the primary circuit.The scaled-down cases in the simplified method exhibit the same geometric scaling and correspond to small core power ratios.By contrast,different scaled-down cases in the standard DSS method correspond to different geometric scaling criteria and require more power.The dynamic process of natural circula-tion can be simulated more accurately using the standard DSS method.

Startup scheme optimization and flow instability of natural circulation lead-cooled fast reactor SNCLFR-100

Owing to the inherent instability of the natural circulation system,flow instability can easily occur during the operation of a natural circulation lead-cooled fast reactor,especially during the startup phase.A comprehensive startup scheme for SNCLFR-100,including primary and secondary circuits,is proposed in this paper.It references existing more mature startup schemes in various reactor types.It additionally considers the restriction conditions on the power increase in other schemes and the characteristics of lead-based coolant.On this basis,the multi-scale coupling code ATHLET-OpenFOAM was used to study the flow instability in the startup phase under different power-step amplitudes and power duration times.The results showed that obvious flow instability phenomena were found in the different startup schemes,such as the short-term backflow phenomenon of the core at the initial time of the startup.Moreover,an obvious increase in the flow rate and temperature to the peak value at the later stage of a continuous power rise was observed,as well as continuous oscillations before reaching a steady state.It was determined that the scheme with smaller power-step amplitude and a longer power duration time requires more time to start the reactor.Nevertheless,it will be more conducive to the safe and stable startup of the reactor.

Two‑parameter dynamical scaling analysis of single‑phase natural circulation in a simple rectangular loop based on dilation transformation

Scaling analysis is widely used to design scaled-down experimental facilities through which the prototype phenomena can be effectively evaluated.As a new method,dynamic system scaling(DSS)must be verified as a rational and applicable method.A DSS method based on dilation transformation was evaluated using single-phase natural circulation in a simple rectangular loop.The scaled-down cases were constructed based on two parameters—length ratio and dilation number—and the corresponding transient processes were simulated using the Relap5 computational code.The results show that this DSS method can simulate the dynamic flow characteristics of scaled-down cases.The transient deviation of the temperature difference and mass flow rate of the scaled cases decrease with increases in the length ratio and dilation number.The distortion of the transient temperature difference is smaller than that of the mass flow;however,the overall deviation is within a reasonable range.

An Experimental Research of Natural Circulation Heat Transfer for PRHR Heat Exchanger in AP1000

The heat transfer characteristics of the PRHR （passive residual heat removal） HX （heat exchanger） are very important to reactor design and safety assessment of AP1000. The purpose of the present experiment was to obtain the natural circulation data in HX to research the heat transfer behavior. The PRHR HX was simulated by three C-type tubes with prototype sizes immerged in a cooling tank. Separate-effect tests of natural circulation in HX tubes have been performed within wide conditions which could cover the operation conditions in AP1000. The experiment provided lots of important data to indicate heat transfer phenomena of PRHR HX. The test conditions were calculated by RELAP5/MOD3.3. The calculation results agreed well with the experiment. RELAP5 could be applied with proper correlations to analyze the heat transfer in PRHR HX under the test conditions.

Onset of Nucleate Boiling in Natural Circulation Systems Predicted Using the Second Stir Theory

Experimental data and calculated results for the onset of nucleate boiling （ONB） in natural circula- tion systems show that for the same operating conditions, the equilibrium vapor quality for ONB in natural circulation is lower than for forced convections. The differences can be explained using second stir theory. The weak vortices and small stir energy in natural circulation systems result in nucleate boiling occurring earlier than in forced convection systems. In natural circulation systems high mass flow rates are accompa- nied by large kinetic energies and large stir energies, which enables changes in the directions of flow eddies and energy transport. The equilibrium vapor qualities at ONB are then higher at higher mass flow rates. The influence of other flow parameters on ONB can be evaluated by the relationships between these flow pa- rameters and the mass flow rate. The same values can lead to different results due to different eddy direc- tions. This indicates that the quantitative comparability in mathematics cannot be considered as only scien- tific standard. The second stir theory offers a new visual angle for researches on natural circulation.

Experimental Study of a Stoppage Natural Circulation during a Nuclear Heating Reactor LOCA

The 5MW nuclear heating reactor is an integral natural circulation reactor. The rupture of the coolant penetrating tube is a typical accident causing coolant loss. When the water level drops down to the upper edge of the inlet of the heat exchanger, the natural circulation stops. This influences the core cooling and the stability of the main loop. A series of tests showed that there is a stable drop of pressure, and the heated element temperature is not too high to cause burnout. But the backward flow or flow oscillation in the primary coolant circuit occurs when the flow breaks completely in the end. The whole flow process is described and the mechanism is discussed.

Calculation of natural circulation under heaving motion

Wide validation of self-developed program of natural circulation under oceanic conditions has been conducted compared with experimental data of inclination,zero-power condition and hot-state condition.Experiments were performed on a full-scale,whole parameterization natural circulation loop designed with reference to 5 MW experimental low temperature nuclear heating reactor(NHR)of Tsinghua University.Investigation of natural circulation and parameter effect under heaving motion was carried out using the program and comparison of heaving,inclination and rolling on natural circulation respectively to reveal the influence mechanism.Results indicate that:(1)significant influence of heaving motion on natural circulation was observed,and heaving motion with high level of strength and long cycle would lead to severe flow fluctuation;(2)slight effect was caused by short cycle heaving motion which was completely different from long cycle heaving motion;(3)comprehensive action of alternating force and flow density distribution would result in natural circulation under heaving motion;(4)most severe accidents maybe result from the long cycle heaving motion rather than inclination and rolling motion.Investigation of influence of heaving motion on natural circulation could have important reference significance in the optimization design of nuclear reactors.

Thermo-hydraulic experimental validation of an integrated modular small reactor operating in full power natural circulation

Small reactors have become a new hotspot of international nuclear energy research.The nuclear heating reactor(NHR)technology developed by Tsinghua University is an important multipurpose small reactor solution with features such as high integration,modular design and full power natural circulation.A new small reactor based on the existing NHR-200 reactor was developed by the Institute of Nuclear and New Energy Technology of Tsinghua University.A full-scale natural circulation test loop with the same operating parameters as the actual reactor was built in order to experimentally validate the natural circulation ability of the reactor primary loop and heat-transfer ability of fuel assemblies and heat exchangers.Corresponding results are given in detail,including parameter validation of the reactor primary loop,flow rules of the natural circulation and heat-transfer coefficients of heaters and heat exchangers,which can be directly used in the actual reactor as a reference for optimization design.Finally,a characteristic parameter k is proposed to represent the natural circulation ability of a system.By using the new data arrangement method in the form of parameter k,comprehensive experimental results of the natural circulation can be represented by a simple integrated expression.The work in this paper is of importance in broadening application fields and pushing forward commercialization of the NHR type reactors.

“Eternal Motion” as a “Form of Movement of a Special Nature” and the Main Condition for the Creation of the Universe

The article hypothesizes that DE and DM (UCM) are a “Form of Motion of a Special Nature”, where “Form of Motion” means “Eternal Motion” as the power of dynamics of different levels and varying degrees of self-sufficiency, and by “Special Nature”, gravitational and two other properties of matter, “tied” to the “Eternal Movement” and completely dependent on it. Carriers of key properties of a “Special Nature” have been established: “0”-DE particles and “3”-DM particles (UDM). The unity of their inherent “motionally-gravitational” properties and the peculiarity of the relationship between “motion” and “gravity” are revealed: the higher the intensity of “Eternal Motion”, the stronger the gravitational properties of matter are manifested (and vice versa). The relationship of “time” with the “vibration frequency” and the “mass” of photons with the “degree of bonding and deformation properties of the field” is shown. The maximum level of gravity has been determined, which allows Nature to successfully create the Universe: such a landmark is the proximity to the property of the Primary Source—the “pure graviton” of the OSP space, the most powerful “motionally-gravitational” particle of the Universe. The reasons for the emergence of such an identity of the gravitational properties of particles with the indicators of a “pure graviton” are established: for “0”-DE particles, this is the acquisition of the function of “freedom of movement”;for “3”-DM particles (UDM), the creation of a special structure—a “double field” (“Main” and “Small”). The presence in the “double field” of specific “tools” for the creation of the worlds of the Universe—gravitational “waves” gives rise to impulses (shocks) of varying intensity and shape. A list of functions performed by “waves” in the “Main” and “Small” fields has been compiled. The specific conditions for the formation of “UDM Streams”, their transformation into a “Vortex” and, under the influence of a powerful Initial Impulse (push), sending them to the “place” of the creation of galaxies, are shown. It is suggested that there is a “Cycle of Matter in Nature” in the closed structure of our Universe due to the “work” of “waves” and the functioning of special “factories” in the form of exotic space objects—Black holes.

Plant Dynamics Evaluation of a MONJU Ex-vessel Fuel Storage System during a Station Blackout

The prototype fast breeder reactor ＂MONJU＂ has an EVSS （ex-vessel fuel storage system） which consists mainly of an EVST （ex-vessel fuel storage tank） and an EVST sodium cooling system. EVST sodium cooling system consists of three independent loops. During the normal operation, the primary sodium in the EVST is circulated by natural convection and the secondary circulation in the EVST sodium cooling system is powered by electromagnetic pumps. When an SBO （station blackout） occurs, all the pumps and blowers are tripped. Therefore, it was necessary to evaluate the cooling ability by the natural circulation of sodium in the EVST sodium cooling system and air through the air cooler during the SBO. In this study, an analysis and evaluation of the plant dynamics for the spent fuel and the EVSS structural integrity during an SBO were performed. When the number of cooling loops was not changed and natural circulation occurred in only two loops, the sodium temperature in the EVST increased to approximately 450 ~C. However, the structural integrity of the EVSS was maintained. The analytical results, therefore, help clarify the number of necessary cooling loops for efficient decay heat removal and sodium temperature behavior in an SBO.

Research and Development of Nuclear Heating Reactors in China

The research and development (R & D) of nuclear heating reactors (NHRs) have been conducted as one of the national key projects in science and technology in China since the 1980s. This paper presents the development status. main design featur and safety concepts of the NHR.

Design and application of a novel coal-fired drum boiler using saline water in heavy oil recovery

In this paper,the design and operation of a novel coal-fired circulating fluidized bed(CFB)drum boiler that can generate superheated steam using saline water were introduced.The natural circulation water dynamics with a drum was adopted instead of the traditional once-through steam generator(OTSG)design,so that superheated steam can be generated for the better performance of the steam assisted gravity drainage(SAGD)technology in heavy oil recovery.The optimized staged evaporation method was proposed to further decrease the salinity of water in the clean water section of the boiler.The evaporating pipes of the salted water section were rearranged in the back pass of the boiler,where the heat load is low,to further improve the heat transfer safety.A CFB combustion technology was used for coal firing to achieve a uniform heat transfer condition with low heat flux.Pollutant control technologies were adopted to reduce pollutant emissions.Based on the field test,the recommended water standard for the coal-fired CFB drum boilers was determined.With the present technology,the treated recovery wastewater can be reused in steam-injection boilers to generate superheated steam.The engineering applications show that the boiler efficiency is higher than 90%,the blowdown rate is limited within 5.5%,and the superheat of steam can reach up to 30 K.Besides,the heavy oil recovery efficiency is significantly improved.Moreover,the pollutant emissions of SO2,NOV and dust are controlled within the ranges of 20-90 mg/(N·m^(3)),30-90 mg/(N·m^(3))and 2-10 mg/(N·m^(3))respectively.

Scaling Analysis of Thermal-Hydraulics for Steam Generator Passive Heat Removal System

Steam generator passive heat removal system(SG-PHRS) is used as a passively safe mode to provide decay heat removal in some advanced pressurized water reactors. Due to the structure characteristics of steam generator(SG), there are two natural circulation loops coupling in SG-PHRS in case of a safety-related event. The existing natural circulation scaling criteria could be used to simulate the natural circulation inside SG. Two-phase natural circulation loop is studied carefully, and the dominant effects of SG on behaviors of natural circulation in passive heat removal system are presented. Based on the understanding of SG-PHRS operation, system pressure transient scaling and two-phase natural circulation scaling are analyzed by establishing the relevant continuity,integral momentum and energy equations in one-dimensional area-averaged forms. With modified equations,similarity criteria for SG-PHRS are obtained for engineering application. In addition, equal height simulation and reduced height simulation are studied.

Simulating Experimental Investigation on the Safety of Nuclear Heating Reactor in Loss－of－Coolant Accidents

The 5MW low temperature nuclear heating reactor (NHR-5) is a new and advanced type of nuclear reactor developed by Institute of Nuclear Energy Technology (INET) of Tsinghua University of China in 1989. Its main loop is a thermal-hydraulic system with natural circulation. This paper studies the safety of NHR under the condition of loss-of-coolant accidents (LOCAs) by means of simulant experiments. First, the background and necessity of the experiments are presented, then the experimental system, including the thermal-hydraulic system and the data collection system, and similarity criteria are introduced. UP to now, the discharge experiments with the residual heating power (20% rated heating power) have been carried out on the experimental system. The system parameters including circulation flow rate, system pressure, system temperature, void fraction, discharge mass and so on have been recorded and analyzed. Based on the results of the experiments, the conclusions are shown as folios: on the whole, the reactor is safe under the condition of LOCAs, but the thermal vacillations resulting from the vibration of the circulation flow rate are disadvantageous to the internal parts of the reactor core.

Establishment and solution of the RNC flow network model

Refrigerant natural circulation(RNC)system is a closed loop recycling system which is composed of evaporator,condenser,gas pipe and the liquid pipe.The difference in indoor and outdoor temperatures will lead to the refrigerant phase-change,and the gravity difference caused by different heights of condenser and evaporator will make the low boiling point refrigerants carry on natural circulation to realize the indoor heating or cooling.In order to analyze the effect of changes in the RNC system upon the working conditions of the indoor and outdoor units as well as the function of the indoor unit,this paper describes the incidence relations among the various components of the RNC system,and establishes gas–liquid two-phase fluid network mathematical model by using the method of fluid network;besides utilizing the model,it also conducts simulator investigation of coupling characteristics of the RNC system’s refrigeration condition,and makes an analysis of indoor temperature,indoor unit’s air volume,the number of indoor units and the indoor unit capacity and other factors’changes on the coupling characteristics of the RNC system.The results show that under refrigeration conditions,the increase in the air volume of a single indoor unit or room temperature will result in an increase in the cooling capacity of its own indoor units,a decrease in the cooling capacity of other indoor units and a reduction in the total cooling capacity of indoor units of the RNC system;however,the decrease in the outdoor units’inlet temperature will lead to a drop in the evaporation temperature of the system and increase in the cooling capacity.