Nejdet Erkan

Nejdet Erkan
United Kingdom Atomic Energy Authority

PhD

About

89
Publications
5,982
Reads
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429
Citations
Introduction
Nejdet Erkan currently works at UKAEA. Nejdet does research in Fluid Dynamics, Nuclear Engineering and Mechanical Engineering. https://orcid.org/0000-0001-9868-4305
Additional affiliations
February 2022 - present
United Kingdom Atomic Energy Authority
Position
  • Thermal hydraulic test expert
December 2016 - February 2022
The University of Tokyo
Position
  • Professor (Associate)
July 2012 - December 2016
The University of Tokyo
Position
  • Professor (Assistant)

Publications

Publications (89)
Article
This work aims to introduce a new neutrons source technology for research and medical applications, by the conceptualization of the Micro Research Reactor cooled by Heat Pipes (MRR-HP). This is achieved by developing a 3D-detailed neutronics model using the Monte-Carlo Serpent-2.1.31 code, and investigating the neutronics behavior and define the de...
Conference Paper
Preventing the radioactive fission products from releasing into the atmosphere particles during the cutting of fuel debris is one of the main objectives during the Fukushima Daiichi Nuclear Power Plant decommissioning. Therefore, pool scrubbing is employed in nuclear power plants to avoid radioactive fission products being released into the atmosph...
Conference Paper
Preventing the radioactive fission products from releasing into the atmosphere particles during the cutting of fuel debris is one of the main objectives during the Fukushima Daiichi Nuclear Power Plant decommissioning. Therefore, pool scrubbing is employed in nuclear power plants to avoid radioactive fission products being released into the atmosph...
Article
For the Japan Sodium-cooled Fast Reactor (JSFR), should the hypothesized core disruptive accident (CDA) happened, the in-vessel retention (IVR) will be the main target to achieve. In the heat-removal phase of the CDA, the debris bed will be piled up on the debris catcher. The capability of stable cooling and avoiding recriticality on the debris bed...
Article
In the foreseen decommissioning plans of damaged Fukushima Daiichi reactors, submicron aerosol particles will be generated when retrieving fuel debris from reactor buildings by cutting it into small pieces. A multi-nozzle spray system will be used to scavenge these aerosol particles inside the primary containment vessel. To improve the aerosol remo...
Article
In this study, effects of a finned structure on downward-facing flow boiling were investigated. Compared to a bare surface, a heated surface with a finned structure has a higher CHF and heat transfer coefficient. Two high-speed cameras were utilized to observe boiling behaviors from the downward view and side view. Under low heat flux conditions, t...
Article
Research interest in eliminating airborne aerosol particles has been growing for decades. Aerosol particles with aerodynamic diameters between 0.2 and 1 μm are difficult to remove by traditional spray systems. To improve the aerosol scavenging efficiency, a new method is proposed that employs the addition of water mist. Water mist is supposed to ag...
Article
Surface wettability is an important parameter that affects nucleate boiling. Irradiation can alter the surface wettability on metal surfaces without altering the surface macrostructure. However, the wettability characteristics of indium tin oxide (ITO) and TiO2 film-coated sapphire substrates remain unknown. We experimentally investigated the gamma...
Article
In this study, experiments of downward-facing flow boiling were conducted to investigate material effects on CHF. Experiments were conducted using aluminum, copper, and carbon steel. It was found that different materials had different CHFs. Aluminum has the biggest CHF while copper has the lowest CHF for each mass flux. After experiment, surface we...
Article
Due to the important role critical heat flux (CHF) plays in the nucleate boiling field, it is of great significance to study CHF, especially the mechanism of boiling crisis occurrence. In this study, an extended numerical model to predict CHF for flow boiling was proposed based on the Monte Carlo method. This model considers of the bubble generatio...
Article
The resolidified fuel debris from the damaged Fukushima Daiichi reactors must be cut into small pieces prior to removing it from reactor buildings. Submicron radioactive aerosol particles are likely to be generated and dispersed into the primary containment vessel (PCV) atmosphere during this cutting process. However, traditional sprays cannot effe...
Article
Full-text available
In this study, the spreading velocities within the droplet impact on a sapphire glass surface is investigated with the aid of particle image velocimetry (PIV) method. Experiments are performed for unheated and heated surfaces and droplets with impact velocities ranging from 1.12 to 2.40 m/s which correspond to Weber numbers in the range 40–190. It...
Article
Multiple droplet impact on a heated sapphire glass is experimentally investigated to compare the hydrodynamic behavior of single and multiple droplet cases employing high-speed imaging techniques. Experiments are performed for a wide range of surface temperatures (23 • C-350 • C) and different Weber numbers. By using an image analysis software, the...
Article
Radioactive aerosols are strongly diffusive and migratory and thus have presented one of the greatest challenges during the decommissioning of the Fukushima Daiichi Nuclear Power Plant (NPP). Although cutting through debris underwater can suppress the generation of radioactive aerosols from pool scrubbing to some extent, the removal efficiency of b...
Article
In this study, irradiation effects of CHF on bare and porous honeycomb surfaces in downward-face saturated pool boiling with different downward inclination angles were investigated. After irradiation, the hydrophilicity of copper and porous honeycomb structure increased compared to that of the non-irradiated surface. For bare surface cases, CHF enh...
Conference Paper
In the foreseen decommissioning and debris removal plans of the damaged Fukushima Daiichi reactors, the fuel debris will be broken into small pieces using laser or mechanical cutting techniques prior to removing them from the reactor buildings. Regardless of the technique to be employed, submicron radioactive aerosol particles will be generated and...
Article
In the present study, experiments of downward-facing flow boiling were conducted to investigate oxidation effects of copper under atmospheric conditions. The copper surface was polished and then put into a drying oven for a period of 1 h, 3 h and 6 h under 300°C. Compared with a bare surface, a deterioration in the heat transfer coefficient and an...
Article
To increase the surface wettability is a feasible way to enhance critical heat flux (CHF) according to some CHF theories and many previous researches. It is found that surface wettability of metal can be increased after the surface being irradiated by Gamma-ray irradiation and CHF in pool boiling can thus be enhanced. In this study, whether CHF in...
Article
Full-text available
In the decommissioning of damaged Fukushima Daiichi reactors, the melted and re-solidified fuel debris in the bottom of the reactor pressure vessel and primary containment vessel need to be cut into small pieces before removing them from reactor buildings. During the cutting operations, submicron radioactive aerosol particles are expected to be gen...
Article
Surface wettability is one of the important metal surface characteristics which would affect boiling heat transfer performance of metal surfaces. In this study, different metal surfaces are irradiated by electron beam to investigate whether the surface wettability of metal surfaces can be increased by electron beam irradiation. The experimental res...
Article
There is a strong need to find a feasible approach to increase the Critical Heat Flux in downward-facing flow boiling effectively for the In-Vessel Retention strategy in advanced nuclear power plants. In this study, we designed metal porous honeycomb plates with different structures and used them in downward-facing flow boiling experiment to find a...
Article
Critical heat flux (CHF) plays an important role as the upper limit of heat dissipation process during the in-vessel reactor external reactor vessel cooling (IVR-ERVC). IVR-ERVC is regarded as a very effective way to release the decay heat after the core melt. This severe accident mitigation countermeasure has already been applied in some advanced...
Article
A calcium silicate insulator material was investigated for its interaction with non-radioactive cesium at room temperature by batch-type adsorption experiments. An industrial-grade calcium silicate was weighted and ground into powder with an average size of 15.4 ± 0.1 μm, which was then placed into polypropylene (PP) tube containing cesium chloride...
Article
This study aims to suggest a dimensionless number to determine the formation and disappearance of thermal stratification induced by direct contact condensation in a 1/20 scaled-down suppression pool of the Fukushima Daiichi nuclear power plant. The modified Richardson number, which represents the ratio of buoyancy force to inertia of steam, was emp...
Conference Paper
Radioactive aerosols which show strong diffusion and migration have become one of the most difficult problem during the decommissioning of Fukushima Daiichi Nuclear Power Plant. Although cutting the debris underwater can suppress the generation of radioactive aerosols due to pool scrubbing to some extent, the removal efficiency of bubble columns ca...
Article
Tokyo Electric Power Company Holdings, Inc. (TEPCO) reported a unique dose rate distribution during investigation in the primary containment vessel (PCV) of Fukushima Daiichi Nuclear Power Plant unit 2 pedestal area in JanuaryFebruary 2017. The pedestal area, in regard to the accident progression, should exhibit a higher dose rate than those of any...
Article
CHF plays an important role in the heat transfer process during the external reactor vessel cooling (IVR-ERVC) which is deemed as a very effective way to release the decay heat after the core melted. In this paper, the experiment of the macro-fin structure experiment positioned on slope that is declined at angles of 5° and 10° was done. The results...
Article
Full-text available
Due to the important role critical heat flux (CHF) plays in the boiling field, it is of great significance to study CHF, especially the mechanism of CHF in the nucleate boiling. In this study, a new model to predict CHF both in pool boiling and flow boiling of downward-face was proposed and the relationship between CHF and nucleation site density (...
Article
Full-text available
This study investigates the radial velocity distributions during the early phase of spreading inside the water droplets impinging onto a heated sapphire glass surface as the second part of the author’s previous paper about the droplet impacts onto an unheated surface (Erkan and Okamoto in Exp Fluids 55:1–9, 2014). The surface was heated to the temp...
Article
The containment spray system is an accident mitigation system used in nuclear reactors that reduces the high temperature and pressure generated inside the containment vessel during reactor accidents by condensing the steam and cooling the gas atmosphere. However, the heat and mass transfer mechanisms of flying spray droplets in a surrounding gas mi...
Conference Paper
Full-text available
When considering the safety of the reactor after the core melted, the external reactor vessel cooling (IVR-ERVC) is regarded as one of the most prominent method and is now widely being studied. And in order to apply this method more efficiently, CHF is the utmost part because it limits the upper threshold of the cooling effect. There has already be...
Article
Full-text available
This study conducts a critical heat flux (CHF) experiment on a carbon steel block, and the block is positioned on slope that is declined at angles of 5° and 10°. The results of the carbon steel block experiment were then analyzed and compared with the results obtained from a copper block experiment that had been conducted previously at the same tes...
Article
In previous research on nuclear reactors, the effect of irradiation on heat transfer has rarely been studied. We investigated the electron beam irradiation effect on downward-facing flow boiling heat transfer and critical heat flux. All the critical heat flux values in flow boiling decreased after irradiation, particularly at low doses, whereas hea...
Article
For the Fukushima decommissioning, the distribution of boron species in the fuel debris must be determined to assess the risk of recriticality, the debris hardness and thus complicate its successful retrieval. As a result, the relocation behavior of boron carbide (B4C) control rod materials has attracted significant attention. In this work, the inf...
Article
The effectiveness of ex-vessel cooling systems in response to severe nuclear reactor accidents is attributable, in part, to the critical heat flux (CHF). As such, CHF enhancement has been the focus of significant research. Prior studies have demonstrated that porous and specifically, honeycomb surfaces can increase the CHF. In this study, we compar...
Article
During a severe accident, ex-vessel cooling may pose a risk for larger-powered reactors. The current in-vessel retention (IVR) (through ex-vessel cooling) capability may not be sufficient for the larger-powered reactors, and critical heat flux (CHF) conditions may eventually lead to vessel failure. A manner in which the CHF can be increased is by a...
Article
Ex-vessel cooling is an important concept for ensuring safety in a nuclear power plant. Many researchers have focused on critical heat flux (CHF) enhancement using reactor pressure vessels. Previous studies mainly focused on other types of enhancement methods, and few investigated the use of radiation to improve boiling heat transfer. In this study...
Article
Enhancing the Critical Heat Flux (CHF) is extremely needed in some engineering applications. Many methods involving nanofluids and surface modifications have been investigated to enhance the CHF. Most of the previous works focus on pool boiling and upward-facing surface conditions. An experimental research on enhancing the CHF in downward-facing sa...
Article
Phosphorescence-based temperature measurements usually employ in situ calibration in macro-scale flow domains. However, the application of conventional in situ calibration in millimetre scales such as in 2 mm droplets is difficult because temperature probing using an intrusive technique such as thermocouple-based measurement can deform a droplet in...
Article
Since the 1980s, numerous experiments have been performed to explore the mechanisms of molten core–concrete interaction (MCCI) phenomena. However, previous experimental results show uncertainties pertaining to several aspects such as the dependence of concrete type on the ablation profile (isotropic for limestone-rich concrete and anisotropic for s...
Article
The purpose of this work is to validate the debris coolability analysis (DCA) module in the severe accident analysis code SAMPSON by simulating the first steady stage of the LIVE-L4 test. The DCA module is used for debris cooling in the lower plenum and for predicting the safety margin of present reactor vessels during a severe accident. In the DCA...
Article
The distribution of boron in the fuel debris is one of the massive concern for the Fukushima Daiichi NPS decommissioning mainly because its distribution affects the hardness of the debris and possibility of the re-criticality. The distribution might be partially determined by the relocation behavior of the B4C control blade. Thus, it is important t...
Conference Paper
In this study, the behavior of the eutectic melts consisting with boron carbide (B4C) control rod materials has been investigated in a time-resolved manner at over 1200 °C using the techniques of high temperature visualization. A pole comprising type-304 stainless steel (SS) filled with B4C powder (approximately 20~30µm in particle size) was used a...
Article
It is important to clarify the molten material jet breakup process to estimate corium behavior in the lower plenum of a boiling water reactor (BWR). To identify the effect of control rod guide tubes (CRGTs) on the jet breakup behavior, a molten material (U-alloy) breakup experiment considering CRGTs in a BWR lower plenum was conducted under isother...
Article
Thermal stratification in the suppression pool of the Fukushima Daiichi nuclear power plants was experimentally investigated in sub-atmospheric pressure conditions using a 1/20 scale torus shaped setup. The thermal stratification was reproduced in the scaled-down suppression pool and the effect of the steam flow rate on different thermal stratifica...
Article
To investigate the eutectic reaction process of control-rod materials in a boiling water reactor (BWR), fundamental tests using boron carbide (B4C) powder inserted between stainless steel (SS) plates were performed and dynamically visualized. The eutectic reaction process near the contact area of the two materials and the behavior of molten materia...
Article
Full-text available
This study aimed to verify the characteristics of thermal stratification induced by direct contact condensation using a 1/20-scale suppression pool of the Fukushima Daiichi nuclear power plants. A blow-down nozzle was used to inject steam into the toroidal suppression pool. Vertical temperature profiles were measured by vertically aligned thermocou...
Article
Numerous experiments have been performed to explore the mechanisms of molten core-concrete interaction (MCCI) phenomena since the 1980s. However, previous experimental results show that uncertainties pertaining to several aspects such as the mixing process and crust behavior remain. To explore the mechanism governing such aspects, as well as to pre...
Article
The reactor core isolation cooling (RCIC) system is an auxiliary system of a boiling water reactor (BWR) that provides makeup water in the case of a severe accident. During the Fukushima accident, the extended operation of the RCIC had a large influence on the accident progression and delayed the core meltdown by almost 70 h. During the Fukushima a...
Article
This work analyzes the effect of the non-condensable gas on the direct contact condensation in suppression pool with thermal stratification. Both the Particle Image Velocimetry (PIV) system and high speed camera are used for the experiments. The influences of the non-condensable gas on the thermal stratification, the condensation behavior, and the...
Article
Full-text available
The liquefaction and relocation of control rods at temperatures over 1200°C due to the eutectic reaction between boron carbide and stainless steel are important phenomena for the clarification of the Fukushima Daiichi Nuclear Power Plant accident. However, the mechanism and behavior of these phenomena have not yet been understood completely. The ti...
Article
Ex-vessel cooling is an important subject in the field of nuclear safety so that many researchers focus on CHF (critical heat flux) enhancement study of pressure vessel reactor. In this study, pool boiling experiment is carried out to test CHF value. Meanwhile, a new structure design, honeycomb plate, is introduced for enhancement study of CHF. Dur...
Article
This study aims to examine the relationship between thermal stratification and flow patterns in a steam-quenching suppression pool using particle image velocimetry. Thermal stratification was experimentally evaluated in a depressurized water pool under different steam mass flux conditions. The time evolution of the temperature profile of the suppre...
Article
New BWR containment designs are considering cavity flooding as an accident management strategy. Unlike the PWR, the BWR has many Control Rod Guide Tube (CRGT) penetrations in the lower head. During a severe accident scenario with core melt in the lower plenum along with cavity flooding, the penetrations may affect the heat transfer on the ex-vessel...
Article
After the Fukushima accident, several investigation reports, including experiments and simulations have been done for each of the affected units to completely understand the accident progression and use their results to improve the knowledge of severe accident management and the severe codes performance. In Unit 2, the major uncertainties are relat...
Article
Full-text available
Plenty of numerical simulations were performed to analyze the Molten Core-Concrete Interaction (MCCI) phenomena since 1980s. However, uncertainties remain among thermal hydraulic codes. Thus, in order to avoid the effect of uncertainties due to the different empirical formulas and interfacial models, a new CFD code based on Moving Particle Semi-imp...
Article
Reactor vessel depressurization is an important measure before an accident sequence progresses to the point of vessel bottom head penetration failure under high-pressure condition. The passive depressurization systems can depressurize the reactor coolant system to prevent or to mitigate the effects of direct containment heating instead of the safet...
Article
According to the current severe accident management guidance, operators are required to depressurize the reactor coolant system to prevent or mitigate the effects of direct containment heating using the safety/relief valves. During the course of a severe accident, the pressure boundary might fail prematurely, resulting in a rapid depressurization o...
Article
A fundamental principle of accident management in a nuclear power plant is the injection of water to cool the core. In this framework, a series of QUENCH tests have been conducted at Karlsruhe Institute of Technology (formerly Forschungszentrum Karlsruhe). The test results constitute a significant experimental database not only for further understa...
Conference Paper
Full-text available
Four tests related to post-accident LWR containment behaviour have been carried out at the large-scale thermal-hydraulic facility, PANDA, and are presented here. The tests aim to check the predictability of the accumulation of hydrogen (helium) in certain regions of a multi-compartment system during steam injection. The correct simulation of the ac...
Article
Liquid droplets impinging onto heated and dry unheated surfaces have been the subject of experimental and numerical investigations in various fields. Experimental studies have not provided sufficient quantitative data for the proper validation of numerical studies. Moreover, experimental efforts have focused on droplets impinging onto unheated surf...
Article
Due to complexity of direct contact condensation (DCC), it is difficult to predict thermal hydraulic phenomenon in a suppression pool (SP) of LWRs. Especially, the momentum, induced at condensation interfaces, depends on several interrelated parameters such as the steam mass flux, subcooling, and the diameter of the injection nozzle. Complicated in...
Article
Liquid droplet impacts onto solid surfaces have attracted enormous amount of attention from wide range of research fields including experimental and numerical investigations. Unlike experimental efforts, numerical and analytical studies generated various sets of data. In this study, we investigated the spreading velocities inside the water droplets...
Article
Droplet entrainment and deposition are a couple of significant mechanisms for the heat transfer in annular two-phase flows existing in some heat exchange systems. The basic physics include the peeling of droplets from the liquid film due to high friction with the gas phase and the collision of droplets with the liquid film or deposition into the li...
Article
Experimental and numerical studies into thermal stratification by direct steam condensation in a torus type suppression pool were carried out to investigate the reactor core isolation cooling in the accidents of Fukushima Daiichi nuclear power plants. The suppression pool was manufactured to be a 1/22 scaled model of a Fukushima Daiichi nuclear pow...