Passive Coolant Research Articles

Neutronic characteristic analysis of the GAMA microreactor

The GAMA Microreactor is a low-power nuclear power plant dedicated for remote area with a power output of 300 kWe. The primary characteristics of the GAMA Microreactor are its system compactness, design simplicity, and safe operation without moving parts. The fuel is uranium hydride powder, which works simultaneously as a moderator, contained within a stainless-steel vessel and surrounded by a graphite reflector. Liquid sodium-filled heat pipes are embedded in the fuel powder to extract fission-generated heat via passive coolant flow due to capillary action. As a part of the design process, neutronic parameters of the GAMA Microreactor have been determined using SCALE6.2 and OpenMC codes. Among the analyzed parameters are the excess reactivity as a function of burn-up, shutdown margin, control rod worth, temperature coefficient of reactivity (TCR), fuel density coefficient of reactivity (DCR), and reactivity coefficient due to hydrogen dissociation. From the calculation results, the GAMA Microreactor has a maximum excess reactivity of 0.049 at the operational temperature (700 °C) and 0.0788 at ambient temperature. The TCR value is negative (−2.267 pcm/°C) at the beginning of the cycle (BOL) and −4.9618 pcm/°C at the end of the cycle (EOC). Hydrogen dissociation imposes negative reactivity on the reactor both at the BOL (−0.2631 Δk/k-%dissociation) and EOC (−0.3524 Δk/k-%dissociation). Therefore, the GAMA Microreactor maintains its inherent safety characteristics over a considerably long operation time.

Experimental Study of Air-Water Heat Exchanger as a Passive Coolant in Air Vents

Indonesia, a tropical climate country, has experienced a notable increase in temperatures during the dry season due to global warming, leading to decreased thermal comfort. This experimental study aims to investigate and analyze the performance of an air-water heat exchanger serving as a passive cooler in tropical ventilation systems. Before being introduced into the room, the hot outdoor air is passively cooled by colder water. Air, propelled by an inline duct fan at a constant speed of 9.6 meters per second, passes through a PVC hose integrated into a tube filled with water measuring 100 cm in diameter and 110 cm in height, which serves as the main heat exchanger. Measurement results indicate that the designed air-water heat exchanger provides a significant passive cooling effect, reducing air temperature by up to 6.83°C. By harnessing passive cooling, the cooling capacity achieved during the measurement period in the ventilation system ranges from 3.08 kJ to 7.67 kJ.
 Indonesia, yang memiliki iklim tropis, mengalami kenaikan suhu yang cukup besar selama musim kemarau akibat pemanasan global, sehingga mengurangi kenyamanan termal. Penelitian eksperimental ini bertujuan untuk menguji dan menganalisis kinerja alat penukar panas udara-air yang berfungsi sebagai pendingin pasif dalam sistem ventilasi di daerah tropis. Sebelum masuk ke dalam ruangan, udara panas dari luar didinginkan secara pasif oleh air yang lebih dingin. Udara yang didorong oleh kipas saluran udara dengan kecepatan tetap sebesar 9,6 meter per detik melewati selang PVC yang terhubung dengan tabung berisi air berdiameter 100 cm dan tinggi 110 cm, yang berperan sebagai penukar panas utama. Hasil pengukuran menunjukkan bahwa penukar panas udara-air yang dirancang memberikan efek pendinginan pasif yang signifikan, mengurangi suhu udara hingga 6,83 °C. Dengan memanfaatkan pendinginan pasif, kapasitas pendinginan yang dicapai selama periode pengukuran dalam sistem ventilasi berkisar antara 3,08 kJ hingga 7,67 kJ.

A new designed linear Fresnel lens solar concentrator based on spectral splitting for passive cooling of solar cells

The use of solar concentrators can be an alternative for initial cost reduction in the PV systems. However, they suffer from high cell temperature that can be overcome by different active or passive cooling approaches. Spectral splitting and the elimination of high-energy solar photons are effective solutions for cell temperature reduction. In this study, we developed a Polymethyl methacrylate Spectral Splitting Fresnel Lens (SSFL) for linear concentration using a new design, which directs the desired portion of the spectrum towards the cell and diffracts the rest to eliminate the use of beam splitters or nanofluids in the spectral splitting system. Different SSFLs were considered for directing the spectral ranges from 400 to 1150 nm to 800–1150 nm onto the silicon solar cell under a 10x concentration ratio. For this purpose, optical and heat transfer models were developed through simulation in the Comsol Multiphysics software and validated using available experimental dada in literature. Regarding the assumed parameters, the SSFL with 600–1150 nm spectral range with an optical efficiency of 81% was selected as the optimal lens that not only increases the weighted energy output by 14% but also reduces the cell temperature by 48 °C compared to the lens with 400–1150 nm spectral range. Indeed, no active or passive coolant is used in this system and no cost is imposed on the system. The cost-free property of this method in the FL-based CPV systems makes it an economical option for industrial production.

Passive/active photovoltaic-thermal (PVT) system implementing infiltrated phase change material (PCM) in PS-CNT foam

Power efficiency of Photovoltaic (PV) cell reduce due to the warm up under solar irradiation. Several passive and active cooling experimental investigations are implemented on a PV cell in this study to find out their impacts on the electrical and thermal performance of a PVT system. All experiments are performed in a solar simulator under a wide range (regular-concentrated) of solar radiation power (800–1700 W m−2). PCM is used as passive coolant system, whereas to overcome the malfunction of PCM, due its low thermal conductivity, PCM is infiltered in a special heat conductive foam (PS-CNT foam). Results revealed that PCM-composite can diminish the PV-cell temperature up to 6.8% and increase electrical effciciency up to 14.%. Separately, active cooling are examined by passing water with the range of 0.3–1 lit.min−1 through a cooling block mounted undre the PVT system. In the active cooling system, due to the efficient electrical power generation as well as harvesting thermal energy, the system performance is much higher than passive PVT systems. The best PVT system examined in this study is the PV-PCM-composite system which its energy efficiencies in the active cooling is 66.8–82.6%.

Numerical investigation on PCM encapsulation shape used in the passive-active battery thermal management

This paper investigates three different configurations of a hybrid battery thermal management system (BTMS) using phase change material (PCM) as passive and air coolant as active cooling system. The PCM surrounded the battery cell is encapsulated in three different vessel cross-sections as circular, rectangular, and hexagonal with equal volumes. Each of these BTMS consists of 12 Sony 18650 batteries with the same pack holder. The thermal management of the battery pack is examined in the course of different charging and discharging rates. Results reveal that the thermal performance of both hexagonal and circular PCM vessels show generally the same behavior. Utilization the latent heat as the passive coolant in the battery thermal management is the strong point, which results show that the circular PCM configuration is the best one. However, in the high rate of charging or discharging condition, the uniform air channel around the rectangular shape makes a more efficient cooling compared to the other arrangements.

A comparative study on the modeling of a latent heat energy storage system and evaluating its thermal performance in a greenhouse

Thermal Energy Storage (TES) systems can be compared with batteries. As batteries can be charged when electricity is available for using during the power failure, TES systems can do the same for the thermal energy, i.e., they can absorb the available heat in one cycle, called charge cycle, and release it in a consecutive cycle, called discharge cycle. Among different kinds of TES systems, Phase Change Materials (PCM) have drawn considerable attention, since by changing from one phase to another, they can exchange a significant amount of energy in a small temperature difference. In this quest, a one dimensional mathematical model is solved using two different techniques and the results are compared together; one method is based on the enthalpy and the other is based on the effective heat capacity as well. Secondly, through eight experiments designed by using factorial approach, effects of inlet air velocity and temperature on the outlet stream has been investigated. The results proved that having a determined temperature difference between the inlet air and the PCM in both hot and cold cycles can enhance the efficiency. Finally, the feasible applications of a LHTES system for reducing the temperature swing in a greenhouse is studied numerically and the results are compared with experimental values. As a result, by using this passive coolant system diurnal internal temperature can be reduced for 10 °C.

Development of a feed-and-bleed operation strategy with hybrid-SIT under low pressure condition of PWR

While safety functions in current nuclear power plants are mainly provided by active safety systems, recently passive safety systems are being combined with the active systems to strengthen accident mitigation capability and therefore enhance overall plant safety. To this end, securing long-term cooling of the core is of particular importance. This study considers the hybrid safety injection tank (H-SIT), a passive injection system, as a target component to develop a long-term cooling strategy using active and passive systems concurrently.In the feed-and-bleed (F&B) operation, one of the important long-term cooling strategies to maintain core safety in pressurized water reactors, low pressure safety injection (LPSI) pumps are typically considered inoperable as depressurization is first required, which leads to core dry-out before reaching LPSI operable pressure. This study investigates whether H-SITs, with the important design feature of passive coolant injection under any pressure condition of the primary coolant system, can make up the core during depressurization thereby allowing LPSI pumps to be used in F&B operation as an additional means of long-term cooling. The effectiveness of the H-SITs is verified using thermal-hydraulic simulations, and based on the results a novel F&B operation strategy with H-SITs and LPSI pumps is developed. A probabilistic safety assessment (PSA) model is then developed in order to assess the risk effect of the suggested strategy. PSA results demonstrate that the proposed strategy lowers core damage frequency in the target plant by 5.0 percent in the case of a small break loss of coolant accident. Total core damage frequency of the plant decreases by 4.8 percent compared to the reference model, and also lowers the number of cutsets by around 13 percent from the original value.

Investigation of the thermal-hydraulic characteristics of supersonic steam injector

Steam injector (SI) is known as passive jet pump and heat exchanging device which operates without external power source or mechanical machineries. It utilizes direct contact condensation heat transfer between steam and water-jet as a driving mechanism of the operation and is capable of discharging subcooled water at higher pressure than the inlet fluids pressure. In addition, it has an excellent heat transfer capability, more than 1000 times that of shell and tube heat exchanger. In the present study, thermal-hydraulics characteristics of the water-jet-centered supersonic SI system were investigated from both experimental and analytical approaches. The SI body was manufactured with stainless steel equipped with overflow port. The water injection nozzle was designed with shaft-driving mechanism to freely adjust the axial location of the water nozzle and steam inlet cross sectional area. High pressure steam was supplied to the SI from once-through boiler, which is capable of supplying saturated steam at the maximum pressure of 0.63MPa for the current test facility. Water jet was injected at mass flow rate of 0.4–0.8kg/s. Pressure and temperature measurements were conducted at inlet and outlet of the steam injector system as well as at the overflow port to investigate the operation characteristics of the SI. Results showed the water-jet centered SI’s promising functionality as a passive coolant injection in view of its quick-start up, operable condition limits, discharge pressure and heat transfer capabilities at current inlet conditions. In addition, obtained experimental results were compared with analytical model to assess the predictive capability of discharge pressure value and reasonable agreement was obtained.

Analysis of Turbulence Modelling Approaches to Simulate Single-phase Buoyancy Driven Counter-current Flow in a Tilted Tube

In the present paper, both Large Eddy Simulation (LES) and unsteady-RANS (uRANS) CFD studies of single-phase buoyancy-driven counter-current flow in a pipe are presented for an Atwood number of 1.15×10−2 and an inclination angle of 15 degrees from the vertical. The basic flow phenomena involved are fundamentally the same as those encountered in various industrial applications including passive coolant flow in the loops of a nuclear reactor. Earlier work on this type of flow was focused on its physical aspects using both experimental measurements and Direct Numerical Simulation (DNS). The present work investigates the performance of several commonly used LES eddy viscosity subgrid-scale models. The results show that LES is able to reproduce accurately the experimental results and that the dynamic Smagorinsky subgrid-scale model gives the best predictions. The results of those calculations were then used to obtain more information on the physics of such flow. As regards uRANS simulations, a range of classic two-equation linear eddy viscosity models, based on low-y + formulation at the wall and the single gradient diffusion hypothesis for the turbulent density fluxes were compared against experimental data available in the literature. An elliptic blending Reynolds stresses model (EBRSM) with generalised gradient diffusion hypothesis (GGDH) for the scalar fluxes was then implemented and compared with experiments. The latter showed very good agreement for the first order moment with the experimental data whereas all the two-equation eddy viscosity based models showed rather high levels of discrepancy. The main cause of discrepancy was found to be the underprediction of the axial turbulent buoyancy production effect, which has a more detrimental impact on the eddy viscosity models than the second moment closure one.

Detailed evaluation of safety injection tank effects on in-vessel severe accident progression in a small break LOCA without safety injection

The effects of coolant injection into a reactor vessel by the passive actuation of SITs (Safety Injection Tanks) on the in-vessel core melt progression under a severe accident have been evaluated in an APR (Advanced Power Reactor) 1400. A best estimate simulation from initiating events of 2-in. and 3-in. break SBLOCAs (Small Break Loss Coolant Accidents) without SI (Safety Injection) to a reactor vessel failure has been carried out using the SCDAP/RELAP5 computer code in conditions with and without the passive actuation of the SITs. The SCDAP/RELAP5 results have shown that the passive coolant injection into the reactor vessel by the actuation of the SITs leads to postpone the reactor vessel failure time by 4–5h in the SBLOCA without SI. At the time of the reactor vessel failure, 44.5% and 42.8% of the fuel rod cladding were oxidized in the 2-in. and 3-in. SBLOCAs with the actuation of the SITs, respectively. However, 37.5% and 34.6% of the fuel rod cladding were oxidized in the 2-in. and the 3-in. SBLOCAs without the actuation of the SITs, respectively. Even though the SITs are designed for a large break LOCA, their actuation is very effective on the delay of a reactor vessel failure in spite of more hydrogen generation in the SBLOCA without SI.

A Concept of Passive Safety, Pressurized Water Reactor System with Inherent Matching Nature of Core Heat Generation and Heat Removal

The reduction of manpower in operation and maintenance by simplification of the system are essential to improve the safety and the economy of future light water reactors. At the Japan Atomic Energy Research Institute (JAERI), a concept of a simplified passive safety reactor system JPSR was developed for this purpose and in the concept minimization of developing work and conservation of scale-up capability in design were considered. The inherent matching nature of core heat generation and heat removal rate is introduced by the core with high reactivity coefficient for moderator density and low reactivity coefficient for fuel temperature (Doppler effect) and once-through steam generators (SGs). This nature makes the nuclear steam supply system physically-slave for the steam and energy conversion system by controlling feed water mass flow rate. The nature can be obtained by eliminating chemical shim and adopting in-vessel control rod drive mechanism (CRDM) units and a low power density core. In order to simplify the system, a large pressurizer, canned pumps, passive residual heat removal systems with air coolers as a final heat sink and passive coolant injection system are adopted and the functions of volume and boron concentration control and seal water supply are eliminated from the chemical and volume control system (CVCS). The emergency diesel generators and auxiliary component cooling system of “safety class” for transferring heat to sea water as a final heat sink in emergency are also eliminated. All of systems are built in the containment except for the air coolers of the passive residual heat removal system. The analysis of the system revealed that the primary coolant expansion in 100% load reduction in 60 s can be mitigated in the pressurizer without actuating the pressure relief valves and the pressure in 50% load change in 30 s does not exceed the maximum allowable pressure in accidental conditions in regardless of pressure regulation.

A Concept of Passive Safety Pressurized Water Reactor System with Inherent Matching Nature of Core Heat Generation and Heat Removal.

The reduction of manpower in operation and maintenance by simplification of the system are essential to improve the safety and the economy of future light water reactors. At the Japan Atomic Energy Research Institute (JAERI), a concept of a simplified passive safety reactor system JPSR was developed for this purpose and in the concept minimization of developing work and conservation of scale-up capability in design were considered. The inherent matching nature of core heat generation and heat removal rate is introduced by the core with high reactivity coefficient for moderator density and low reactivity coefficient for fuel temperature (Doppler effect) and once-through steam generators (SGs). This nature makes the nuclear steam supply system physically-slave for the steam and energy conversion system by controlling feed water mass flow rate. The nature can be obtained by eliminating chemical shim and adopting in-vessel control rod drive mechanism (CRDM) units and a low power density core. In order to simplify the system, a large pressurizer, canned pumps, passive residual heat removal systems with air coolers as a final heat sink and passive coolant injection system are adopted and the functions of volume and boron concentration control and seal water supply are eliminated from the chemical and volume control system (CVCS). The emergency diesel generators and auxiliary component cooling system of “safety class” for transferring heat to sea water as a final heat sink in emergency are also eliminated. All of systems are built in the containment except for the air coolers of the passive residual heat removal system. The analysis of the system revealed that the primary coolant expansion in 100% load reduction in 60 s can be mitigated in the pressurizer without actuating the pressure relief valves and the pressure in 50% load change in 30 s does not exceed the maximum allowable pressure in accidental conditions in regardless of pressure regulation.

Photomask array placement on slices in LSI processing : A. F. Tasch, Jr. and V. R. Porter. Microelectron & Reliab.12, 539 (1973)

The effects of coolant injection into a reactor vessel by the passive actuation of SITs (Safety Injection Tanks) on the in-vessel core melt progression under a severe accident have been evaluated in an APR (Advanced Power Reactor) 1400. A best estimate simulation from initiating events of 2-in. and 3-in. break SBLOCAs (Small Break Loss Coolant Accidents) without SI (Safety Injection) to a reactor vessel failure has been carried out using the SCDAP/RELAP5 computer code in conditions with and without the passive actuation of the SITs. The SCDAP/RELAP5 results have shown that the passive coolant injection into the reactor vessel by the actuation of the SITs leads to postpone the reactor vessel failure time by 4–5 h in the SBLOCA without SI. At the time of the reactor vessel failure, 44.5% and 42.8% of the fuel rod cladding were oxidized in the 2-in. and 3-in. SBLOCAs with the actuation of the SITs, respectively. However, 37.5% and 34.6% of the fuel rod cladding were oxidized in the 2-in. and the 3-in. SBLOCAs without the actuation of the SITs, respectively. Even though the SITs are designed for a large break LOCA, their actuation is very effective on the delay of a reactor vessel failure in spite of more hydrogen generation in the SBLOCA without SI.

Sealing action of packing rings

The effects of coolant injection into a reactor vessel by the passive actuation of SITs (Safety Injection Tanks) on the in-vessel core melt progression under a severe accident have been evaluated in an APR (Advanced Power Reactor) 1400. A best estimate simulation from initiating events of 2-in. and 3-in. break SBLOCAs (Small Break Loss Coolant Accidents) without SI (Safety Injection) to a reactor vessel failure has been carried out using the SCDAP/RELAP5 computer code in conditions with and without the passive actuation of the SITs. The SCDAP/RELAP5 results have shown that the passive coolant injection into the reactor vessel by the actuation of the SITs leads to postpone the reactor vessel failure time by 4–5 h in the SBLOCA without SI. At the time of the reactor vessel failure, 44.5% and 42.8% of the fuel rod cladding were oxidized in the 2-in. and 3-in. SBLOCAs with the actuation of the SITs, respectively. However, 37.5% and 34.6% of the fuel rod cladding were oxidized in the 2-in. and the 3-in. SBLOCAs without the actuation of the SITs, respectively. Even though the SITs are designed for a large break LOCA, their actuation is very effective on the delay of a reactor vessel failure in spite of more hydrogen generation in the SBLOCA without SI.