Active Heat Removal Research Articles

Application of REPAS to analyze the sump clogging issue following a LOCA and its impact on the reliability of the ECCS long-term core cooling function

Sump clogging has been identified as a relevant issue after an accident occurred in the Barsebäck-2 nuclear power plant in Sweden (1992). Following a steam line Loss of Coolant Accident (LOCA) due to the inadvertent opening of a safety relief valve, the jet stripped some insulation material from nearby pipes. The insulation debris were transported to the inlet of the strainers for the drywell spray system, thus clogging the intake. The accident was not serious but showed that the Emergency Core Cooling System (ECCS) could have failed. As a consequence, several actions have been undertaken by international organizations, regulatory bodies and nuclear power plant owners to characterize this issue, and propose solutions and improvements. In the present paper, the Reliability Evaluation of Passive Safety Systems (REPAS) methodology is applied to analyze the sump clogging issue and its effect on the long-term core cooling function. Originally developed to evaluate the reliability of passive systems, REPAS is here applied for the first time to an active system. The application is performed using the TRAC/RELAP Advanced Computational Engine (TRACE) code, developed by the USNRC, to simulate a generic three-loop PWR, with an active decay heat removal system.

MAAP 4.07 Analysis of Long Term Containment Heat Removal After Reactor Vessel Failure (DEC-B) for Nuclear Power Plant Krško (NEK)

The paper presents the MAAP 4.07 analysis of containment heat removal after reactor vessel failure resulting from the initial Station Blackout (SBO) accident. The accident is analysed considering mitigation measures for heat removal from the containment using alternative equipment (Alternative Residual Heat Removal (ARHR) pump and heat exchanger (ARHX) and, also, Alternative Safety Injection (ASI) pump). The mitigation actions are taken according to NEK Severe Accident Mitigation Guidelines (SAMG). There are several possibilities to remove the heat from the containment once the reactor vessel fails and, for all of them, the necessary condition is to have the sufficient source of water (Residual Water Storage Tank (RWST), Alternative Boron Water Tank (ABWT) or other) and the appropriate heat exchanger available. Two options are presented within this paper: 1. Injection to the Reactor Coolant System (RCS) using ASI pump and recirculation (sump to RCS) through ARHR system via ARHX, 2. Spraying the containment through Containment Spray (CI) system using ARHR pump and, then, recirculation (sump to spray) through CI and ARHR systems via ARHX. The results show that the containment heat removal can be done with either of analysed ways if the water is provided for recirculation (assumed containment level 3.9 m ~ 760 m3). However, with the fact that the reactor cavity is not flooded, the cooling using ASI will initially result in considerable containment pressure increase because the water is spilled through the RCS over the hot molten core debris. Therefore, it must be stated that the preferable way of containment pressure reduction, once the vessel has failed, is by using the containment spray. On the other hand, if RWST is not available, then the initial water delivery cannot be made from ABWT via CI system because this option does not exist. It shall also be pointed out that, if the active containment heat removal is started early enough, the Passive Containment Filtered Vent System (PCFVS) opening would be prevented and no fission products shall be released to environment.

Accident influence to the thermal conditions of the main buildings of the Kuosheng plant during the decommissioning process

The Kuosheng plant has two BWR/6 units and unit 1 has started the decommissioning process. The fuel assemblies are staying inside the reactor vessel due to insufficient space of the spent fuel pool. The reactor vessel remains open and the current configuration will last for years. Because there are assemblies in the reactor core, the safe-grade instruments located in the secondary containment are required to remain operable by the nuclear regulatory authority. However, the environmental condition of the secondary containment under a long-term-preservation configuration was not analyzed before. In this study, a model including the primary and secondary containments is established using the GOTHIC program to evaluate the thermal conditions, particularly the temperature behaviors during an accident. In addition, the time to actuate the active heat removal system with various fuel cooling times is also calculated. The results show that the secondary containment can be regarded as a mild environment for 5.23 days after an accident and the plant staff should initiate any possible mitigation in this period.

Развитие систем пассивного отвода тепла

Passive heat removal system (SPOT) designed for long-term heat removal of the core to the final absorber through the second circuit in case of out-of-design accidents. The system duplicates the corresponding active heat removal system to the final absorber if it is not possible to perform its design functions. In the development of security systems, there is a tendency to move from active to passive security systems.

Additive manufacturing techniques for smart prosthetic liners

Elastomeric liners are commonly worn between the prosthetic socket and the limb. A number of improvements to the state of the art of liner technology are required to address outstanding problems. A liner that conforms to the residuum more accurately, may improve the skin health at the stump-socket interface. Previous work has shown that for effective thermal management of the socket environment, an active heat removal system is required, yet this is not available. Volume tracking of the stump could be used as a diagnostic tool for looking at the changes that occur across the day for all users, which depend on activity level, position, and the interaction forces of the prosthetic socket with the limb. We believe that it would be advantageous to embed these devices into a smart liner, which could be replaced and repaired more easily than the highly costly and labour-intensive custom-made socket. This paper presents the work to develop these capabilities in soft material technology, with: the development of a printable nanocomposite stretch sensor system; a low-cost digital method for casting bespoke prosthetic liners; a liner with an embedded stretch sensor for growth / volume tracking; a model liner with an embedded active cooling system.

Performance evaluation of a PCM-embedded wall integrated with a nocturnal sky radiator

In recent years, building energy saving technologies are attracting more and more attention worldwide. A PCM-embedded wall coupled with a nocturnal sky radiator is proposed for active heat defense with the outer dynamic thermal environment. This new system can improve the building energy performance and utilization efficiency of PCM with diurnal building insulation through co-work of the PCM, nocturnal sky radiator, and active heat removal mechanism of circulating water. This paper investigates the thermal and energy performance of a typical room with the new wall system in cooling season. The system energy efficiency is analyzed by comparing with a common PCM wall and a common wall without PCM. Main influential factors on system energy efficiency are analyzed and results show that, comparing with a common wall, the average temperature of internal surface of the new system is reduced by 1.6 °C. The reduction of the cooling demand and energy-saving ratio are respectively 37.8%–57.8% and 15.7%–24.1% comparing with the reference system. Besides, the impacts of pump operation hours, area of the nocturnal sky radiator, the wall orientations and phase change temperature are discussed in depth, which can provide a useful guide for its further developments and applications.

Heat transfer intensification in emergency cooling heat exchanger and dry cooling towers on nuclear power plant using air-water mist flow

Advanced nuclear power plants are equipped with passive emergency heat removal systems (PEHRS) for removing the decay heat from reactor equipment in accidents accompanied by primary circuit leakage to the final heat absorber (ambient air). Herein, the intensity of heat dissipation to air from the outer surface of the heat exchanger achieved by buoyancy induced natural convection is extremely low, which need to a large heat exchanger surface area, apply different types of heat transfer intensification including (grooves, ribs and extended surfaces, positioning at higher altitudes, etc.). The intensity of heat removal is also strongly dependent on the ambient air temperature (disposable temperature head). Construction of nuclear power plants in countries with high ambient temperatures (Iran, Bangladesh, Egypt, Saudi Arabia, and others) which are characterized by a high level of ambient temperature imposes additional requirements on the increase of the heat exchange surfaces. The experimental investigation results of heat transfer intensification by a low energy ultrasonic which supply a fine liquid droplet (size ~3 µm) in the cooling air are presented in the present paper. In such case, the heat transfer between the surface and cooling flow involves the following three physical effects: convection, conductive heat transfer, and evaporation of water droplets. The last two effects weakly depend on the ambient air temperature and provide an active heat removal in any situation. The investigation was performed using a high-precision calorimeter with a controlled rate of heat supply (between 7800 and 12831 W/m2) imitating heated surface within the range of Reynolds numbers from 2500 to 55000 and liquid (water) flow rates from 23.39 to 111.68 kg·m-2·h-1. The studies demonstrated that the presence of finely dispersed water results in a significant increase in heat transfer compared with the case of using purely air-cooling. With a fixed heat flux, the energy efficiency increases with increasing water concentration, reaching the values over 600 W·m-2·C-1 at 111.68 kg·m-2·h-1, which is 2.8 times higher than for air cooling. With further development of research in order to clarify the optimal areas of intensification, it is possible to use this technology to intensify heat transfer to the air in dry cooling towers of nuclear power plants and thermal power plants used in hot and extreme continental climates.

Dynamic simplified PCM models for the pipe-encapsulated PCM wall system for self-activated heat removal

The energy efficiency of traditional PCM wall is low in summer since the PCM storing heat in the daytime will become a secondary heat-source and release the heat into the room again at night. In this paper, a novel pipe-encapsulated PCM wall system for self-activated heat removal is proposed. It integrates PCM, nocturnal radiation cooling and gravity heat-pipe technology, and can realize automatic heat insulation and self-activated removal for buildings. Three simplified models for pipe-encapsulated PCM are developed to predict its thermal characteristics. Model Parameters are determined and identified by using genetic algorithm. The pipe-encapsulated PCM is prepared by RT28 and expanded graphite. An experiment setup is established for model validation. Results shows that the 4R2C PCM model are preferable since the identified parameters are relatively less and the accuracy is also acceptable. Furthermore, a simple application about pipe-encapsulated PCM wall is proposed based on the coupled wall model with 4R2C PCM model. Compared with conventional wall, the internal surface accumulated heat transfer of the pipe-encapsulated PCM wall with night active heat removal in 7 days can be reduced by 74.5% in hot climate. It shows great application potential for energy-saving in buildings.

CLIMA 2019-Modelling study on pipe-encapsulated PCM wall system for building insulation and active heat removal

Phase change material (PCM) can be used in building envelope for heat insulation and energy-saving. However, the energy-saving effect of the PCM wall system is limited in summer since the PCM storing heat in the daytime will become a secondary heat source and release heat into the room again at night. This paper proposed a novel pipe-encapsulated PCM wall system. It integrates phase change technology and nocturnal radiation cooling technology together to realize building insulation and active heat removal. A simulation platform is established for the thermal performance simulation of this wall system. It mainly includes the simplified pipe-encapsulated PCM wall model and nocturnal radiation model. The simplified wall model includes the 5R2C wall model, 4R2C PCM model and 2R1C pipe model. The model parameters are identified and the model is also validated with good accuracy. Based on this platform, the thermal performance of a light weight room with pipe-encapsulated PCM wall system in Wuhan is simulated. About 50%-60% of heat from the outdoor environment can be conserved by the pipe-encapsulated PCM wall, and 50% of that can be removed by the radiant cooler at night. Results show the pipe-encapsulated PCM wall system has good thermal performance for light weight building.

Mathematical approach for optimization of magnetohydrodynamic circulation system

The geometrical and electromagnetic variables of a rectangular-type magnetohydrodynamic (MHD) circulation system are optimized to solve MHD equations for the active decay heat removal system of a prototype Gen-IV sodium fast reactor. Decay heat must be actively removed from the reactor coolant to prevent the reactor system from exceeding its temperature limit. A rectangular-type MHD circulation system is adopted to remove this heat via an active system that produces developed pressure through the Lorentz force of the circulating sodium. Thus, the rectangular-type MHD circulation system for a circulating loop is modeled with the following specifications: a developed pressure of 2 kPa and flow rate of 0.02 m3/s at a temperature of 499 K. The MHD equations, which consist of momentum and Maxwell's equations, are solved to find the minimum input current satisfying the nominal developed pressure and flow rate according to the change of variables including the magnetic flux density and geometrical variables. The optimization shows that the rectangular-type MHD circulation system requires a current of 3976 A and a magnetic flux density of 0.037 T under the conditions of the active decay heat removal system.

Magnetohydrodynamics approach for active decay heat removal system in future generation IV reactor

In this work, a helical-type magnetohydrodynamics transportation system for active decay-heat-removal system in a prototype fourth-generation sodium fast reactor was numerically analysed considering operational conditions of atmospheric pressure, for liquid sodium transportation in a loop. The prototype fourth-generation sodium fast reactor is a reactor with high uranium utilisation and an electric power output of 150 MWe, subjected to a developed pressure of 10 kPa and flowrate of 0.005 m3/s under a temperature condition of 468.75 K for the active decay-heat-removal system. A helical-type magnetohydrodynamics transportation system was used to develop pressure in such a loop to reduce the current compared with that in a rectangular-type one; this could overcome the principal limitation of the requirement of a high current in a magnetohydrodynamics transportation system. The main parameters of the considered helical-type magnetohydrodynamics transportation system were the inner diameter, silver brazing, number of turns, and radius of pump, which affect the current, magnetic-flux density, and its velocity. The parameters were analysed in relation to the minimisation of the pump current while maximising the pressure. The specifications of the optimised helical-type magnetohydrodynamics transportation system—current of 352 A and magnetic-flux density of 0.466 T—were derived to satisfy the conditions of the active decay-heat-removal system.

Experimental investigation of the thermal hydraulics of a spent fuel pool under loss of active heat removal conditions

In case of a temporal undefined failure of the active cooling system of a spent fuel pool (SFP), the water inside the pool heats up depending on the decay heat of the stored spent fuel. In the worst case, this leads to a boil-off scenario with a water level decrease and, after appropriate time, to a progressive uncovery of the fuel assemblies (FA). The cooling of the uncovered structures is limited by the steam production in the lower still wetted part of the FA, radiative heat transfer, radial heat conduction and convection inside the FA and interaction with ambient air depending on the storage conditions. As a result, the removal of decay heat can be endangered and, by reaching certain cladding temperatures, the integrity of the cladding tubes can be compromised. The detailed heat and mass transfer mechanisms of the boil-off scenario are not yet sufficiently investigated – especially experimentally. Therefore, reliable conclusions about the development of the cladding temperatures cannot be made.Against this background, the SINABEL project was launched in 2013 at TU Dresden for an improved understanding of the heat transport processes inside a SFP under accident conditions. Studies are performed both experimentally on the test facility ALADIN and theoretically by using computational fluid dynamics (CFD) calculations and integral codes for severe accidents. The test facility simulates a generic boiling water reactor (BWR) FA on almost original scale with regard to the boundary and ambient conditions within a SFP. Through an appropriate unique net of instrumentation, the distribution and development of radial and axial cladding temperatures and the development of the water level can be investigated in detail.Experiments were carried out for various decay heats respectively rod powers and changing storage distances. The thermal hydraulics of the heat-up and the boil-off phase with the occurrence of subcooled boiling in the beginning followed by geysering-like instabilities are described in the present paper. The higher the heat load, the faster the heat-up and, as boiling temperature is reached, the lowering of the water level. The maximum limit of the water level and the influence by the radial heat conduction, convection and radiative heat transfer is shown and explained.The experimental data and thermohydraulic findings provide the basis for the phenomenological understanding of this accident scenario and are used for the validation and improvement of numerical simulations.

Analytical and numerical study on the fast refill of compressed natural gas with active heat removal

Heavy-duty vehicles powered by compressed natural gas (CNG) store the fuel in large onboard cylinders. Fast fill of depleted CNG cylinders is a common refueling method because it achieves refueling time comparable to liquid fuels. However, under-filling of CNG cylinders occurs during fast fill due to the recompression work of CNG in the cylinder that heats the fuel during the fill. The heated fuel has a lower density at the rated pressure, and thus less mass of CNG can be stored than if it was at ambient temperature. To increase the mass of dispensed CNG during fast fill, an active heat removal method is proposed. In this study, analytical and numerical models of the filling process of CNG into a Type-III cylinder with and without active heat removal are developed. In the analytical study, mass and energy conservation equations are coupled with an ideal-gas equation of state and orifice flow equations to predict the heat generation rates during fast fill. The influence of heat removal via a cooling coil inserted into the cylinder during fill on the dispensed mass and fill time is quantified. The analytical study is compared to numerical simulations employing a two-dimensional axisymmetric computational fluid dynamics (CFD) model for unsteady, compressible turbulent flow in a Type-III cylinder with and without active heat removal. Dynamic average temperature, pressure and mass curves as well as the local temperature distribution in the cylinder are obtained at different time instances during the fill. The effect of the location of the heat removal coils is also investigated. The results of the analytical/numerical study illustrate the benefit of heat removal from the cylinder as a means of improving fast-fill efficiency in natural gas fueled heavy-duty vehicles.

Comprehensive energy analysis of a photovoltaic thermal water electrolyzer

The use of photovoltaic thermal (PVT) technologies enables improvement in the electrical efficiency of a photovoltaic (PV) module by reducing the temperature of the PV module via active waste heat removal. In current PVT systems, the removed heat is mainly used for specific applications, such as water and/or room heating, but their need is intermittent and seasonal. For a more efficient and versatile use of the removed waste heat, we propose a new architecture where the PV module is integrated with a dual-functional electrolyzer that removes the waste heat by active cooling and produces hydrogen via electrolysis. The excess heat from the PV cell is utilized to enhance the reaction kinetics of the electrolysis process (due to an increase in temperature) inside an electrolyzer, which is located below the PV module. In this paper, we used finite-element analysis (FEA) simulations to optimize the geometry and operating conditions of an electrolyzer to maximize overall energetic efficiency and hydrogen production. To evaluate the practical feasibility of the approach, we performed a comprehensive energy analysis of the PVTE system using data from Phoenix, AZ. The energetic efficiency of the proposed PVTE system was calculated to be 56–59%, which is comparable to those of current PVT systems. Additionally, the integration of the electrolyzer with the PV module led to an almost 2.5-fold increase in hydrogen production compared to a stand-alone electrolyzer operated at ambient temperature. The analyzed hybrid approach potentially represents a viable and useful alternative for utilization of waste heat energy from PV cells. This approach may further increase the use of photovoltaic technologies as a renewable energy source.

Procedure of Active Residual Heat Removal after Emergency Shutdown of High-Temperature-Gas-Cooled Reactor

After emergency shutdown of high-temperature-gas-cooled reactor, the residual heat of the reactor core should be removed. As the natural circulation process spends too long period of time to be utilized, an active residual heat removal procedure is needed, which makes use of steam generator and start-up loop. During this procedure, the structure of steam generator may suffer cold/heat shock because of the sudden load of coolant or hot helium at the first few minutes. Transient analysis was carried out based on a one-dimensional mathematical model for steam generator and steam pipe of start-up loop to achieve safety and reliability. The results show that steam generator should be discharged and precooled; otherwise, boiling will arise and introduce a cold shock to the boiling tubes and tube sheet when coolant began to circulate prior to the helium. Additionally, in avoiding heat shock caused by the sudden load of helium, the helium circulation should be restricted to start with an extreme low flow rate; meanwhile, the coolant of steam generator (water) should have flow rate as large as possible. Finally, a four-step procedure with precooling process of steam generator was recommended; sensitive study for the main parameters was conducted.

Analysis of core heat removal capability under DLOFC accidents for HTGRs

Design envelope of prismatic high temperature gas-cooled reactors (HTGRs) in terms of core heat removal capability under depressurized loss-of-forced-circulation (DLOFC) accidents without operating active or passive decay heat removal systems are investigated. Lumped element models consist of core, reactor pressure vessel (RPV) and cavity wall are presented in order to evaluate transient response of core temperature. The analysis considers internal decay heat generation, transient conduction from core to RPV, cooling of vessel outer surface by radiation and natural convection, and radiation from outer surface of cavity wall to the ultimate heat sink. Parametric calculations changing the core height, initial core temperature, thickness of side reflector, cavity size and peaking factor are performed. A series of calculation provides relationships of core radius to average power density and reactor thermal power which can remove the heat in core without reliance on specific design features. The results clarified the design envelope for the naturally safe HTGR in terms of core decay heat removal.

소듐냉각고속로 붕괴열교환기의 고온 설계 및 건전성 평가

In this study, high temperature design and creep-fatigue damage evaluation of a decay heat exchanger (DHX) in the decay heat removal systems of a sodium-cooled fast reactor (SFR) have been performed. Detail design and 3D finite element analysis have been conducted for the DHXs to be installed in active and passive decay heat removal systems in Korean Generation IV SFR, and the DHX installed in the STELLA-1(Sodium integral effect test loop for safety simulation and assessment) at KAERI (Korea Atomic Energy Research Institute). Evaluations of creep-fatigue damage based on full 3D finite element analyses were conducted for the two Mod.9Cr-1Mo steel heat exchangers according to the elevated temperature design codes of ASME Section III Subsection NH and RCC-MR code. Code comparisons were made based on the creep-fatigue damage evaluation and issues on conservatisms of the design codes were discussed.

A Silicon-Tungsten Electromagnetic Calorimeter with Integrated Electronics for the International Linear Collider

We present an update of the development of an electromagnetic calorimeter for the Silicon Detector concept for a future linear electron-positron collider. After reviewing the design criteria and related simulation studies, we discuss progress in the research and development of the detector. This concept has from the outset made the case for highly integrated electronic readout with small (1 mm) readout gaps in order to maintain a small Moliere radius for electromagnetic showers and to avoid active heat removal. We now have fully functioning 1024-channel readout chips which have been successfully bonded to 15 cm silicon sensors. We present initial results from these assemblies.

CFD modeling and thermal-hydraulic analysis for the passive decay heat removal of a sodium-cooled fast reactor

In this study, a pool-typed design similar to sodium-cooled fast reactor (SFR) of the fourth generation reactors has been modeled using CFD simulations to investigate the characteristics of a passive mechanism of Shutdown Heat Removal System (SHRS). The main aim is to refine the reactor pool design in terms of temperature safety margin of the sodium pool. Thus, an appropriate protection mechanism is maintained in order to ensure the safety and integrity of the reactor system during a shutdown mode without using any active heat removal system. The impacts on the pool temperature are evaluated based on the following considerations: (1) the aspect ratio of pool diameter to depth, (2) the values of thermal emissivity of the surface materials of reactor and guard vessels, and (3) innerpool liner and core periphery structures. The computational results show that an optimal pool design in geometry can reduce the maximum pool temperature down to ∼551 °C which is substantially lower than ∼627 °C as calculated for the reference case. It is also concluded that the passive Reactor Air Cooling System (RACS) is effective in removing decay heat after shutdown. Furthermore, thermal radiation from the surface of the reactor vessel is found to be important; and thus, the selection of the vessel surface materials with a high emissivity would be a crucial factor for consideration in safety design. This study provides future researchers with a guideline on designing safety measures for the fourth generation of the fast reactors with no particular reference to any specific manufacturer.

Preliminary transient thermal analysis for safety of the dual-cooled waste transmutation blanket for the FDS-I

The dual-cooled waste transmutation (DWT) blanket is one of the key components of the fusion-driven subcritical system (FDS-I). Because of the large energy gain, the heat removal in accidents remains a major safety concern. In this contribution, several representative transients such as unprotected loss of flow accident in helium gas and LiPb (ULOFA), protected loss of flow accident in helium gas and LiPb (LOFA) and loss of power accident (LOPA) are calculated and analyzed. The blanket will not melt until several hours if the plasma core is shut down in time when the accidents occur. It has enough time to start additional action to keep the system safety. The results show that passive solution to shut down the plasma shall be given due to the little scale of responding time. Also, the results show an effective active heat removal solution such as liquid metal (LM) drain system and emergency blanket cooling system is needed.