The influence of the water ingression and melt eruption model on the MELCOR code prediction of molten corium-concrete interaction in the APR-1400 reactor cavity

Muritala A. Amidu,Yacine Addad 한국원자력학회 2022 Nuclear Engineering and Technology Vol.54 No.4

In the present study, the cavity module of the MELCOR code is used for the simulation of molten coriumconcrete interaction (MCCI) during the late phase of postulated large break loss of coolant (LB-LOCA)accident in the APR1400 reactor design. Using the molten corium composition data from previousMELCOR Simulation of APR1400 under LB-LOCA accident, the ex-vessel phases of the accident sequenceswith long-term MCCI are recalculated with stand-alone cavity package of the MELCOR code to investigatethe impact of water ingression and melt eruption models which were hitherto absent in MELCOR code. Significant changes in the MCCI behaviors in terms of the heat transfer rates, amount of gases released,and maximum cavity ablation depths are observed and reported in this study. Most especially, theincorporation of these models in the new release of MELCOR code has led to the reduction of themaximum ablation depth in radial and axial directions by ~38% and ~32%, respectively. These impacts aresubstantial enough to change the conclusions earlier reached by researchers who had used the olderversions of the MELCOR code for their studies. and it could also impact the estimated cost of the severeaccident mitigation system in the APR1400 reactor.

Design of air-cooled waste heat removal system with string type direct contact heat exchanger and investigation of oil film instability

Moon, Jangsik,Jeong, Yong Hoon,Addad, Yacine Korean Nuclear Society 2020 Nuclear Engineering and Technology Vol.52 No.4

A new air-cooled waste heat removal system with a direct contact heat exchanger was designed for SMRs requiring 200 MW of waste heat removal. Conventional air-cooled systems use fin structure causing high thermal resistance; therefore, a large cooling tower is required. The new design replaces the fin structure with a vertical string type direct contact heat exchanger which has the most effective performance among tested heat exchangers in a previous study. The design results showed that the new system requires a cooling tower 50% smaller than that of the conventional system. However, droplet formation on a falling film along a string caused by Rayleigh-Plateau instability decreases heat removal performance of the new system. Analysis of Rayleigh-Plateau instability considering drag force on the falling film surface was developed. The analysis results showed that the instability can be prevented by providing thick string. The instability is prevented when the string radius exceeds the capillary length of liquid by a factor of 0.257 under stagnant air and 0.260 under 5 m/s air velocity.

Controlled Fabrication of Nanoporous Oxide Layers on Zircaloy by Anodization

Park, Yang Jeong,Ha, Jun Mok,Ali, Ghafar,Kim, Hyun Jin,Addad, Yacine,Cho, Sung Oh Springer US 2015 NANOSCALE RESEARCH LETTERS Vol.10 No.1

<P>We have presented a mechanism to explain why the resulting oxide morphology becomes a porous or a tubular nanostructure when a zircaloy is electrochemically anodized. A porous zirconium oxide nanostructure is always formed at an initial anodization stage, but the degree of interpore dissolution determines whether the final morphology is nanoporous or nanotubular. The interpore dissolution rate can be tuned by changing the anodization parameters such as anodization time and water content in an electrolyte. Consequently, porous or tubular oxide nanostructures can be selectively fabricated on a zircaloy surface by controlling the parameters. Based on this mechanism, zirconium oxide layers with completely nanoporous, completely nanotubular, and intermediate morphologies between a nanoporous and a nanotubular structure were controllably fabricated.</P>

Studies of various single phase natural circulation systems for small and medium sized reactor design

Wibisono, A.F.,Ahn, Y.,Williams, W.C.,Addad, Y.,Lee, J.I. North-Holland Pub. Co 2013 Nuclear engineering and design Vol.262 No.-

Passive safety is a primary motive behind the development of small and medium sized reactors of various coolants. After the Fukushima accident, there is an increased interest in a nuclear reactor's reliance on passive safety systems. Most of the existing passive systems, regardless of the reactor type, utilize buoyancy force to drive the cooling flow. Hence, it is essential to evaluate if the naturally developed cooling flow is sufficient to maintain the heated surface temperature of the fuel elements below the design limit. Evaluating passively driven flows can be quite a challenging task in both two phase natural circulation systems and also in single phase natural circulation systems. Previous research works have found that single phase heat transfer can be deteriorated and becomes uncertain when the driving force of a system is shifted from external force (forced convection) to self generated buoyancy force or a combination of both (natural or mixed convection). In this paper, single phase gas, water, and liquid metal reactors with passive systems are reviewed briefly. A simple theoretical analysis of each reactor type is performed to find the tendency of the shift in the operating heat transfer regime into the deteriorated region. The analysis results show that single phase water system can maintain operation within the forced convection regime but the operating regime gets closer to the deteriorating heat transfer regime as the system's physical size reduces from a large nuclear power plant to the small and medium reactor scale. The gas cooled system has a high tendency to operate in the deteriorated heat transfer regime when the driving force changes from forced to natural. Meanwhile the liquid metal system demonstrates more margins to operate outside from the deteriorated heat transfer region compared to the two other fluid systems. However further studies are needed to clearly identify the boundaries of the deteriorated heat transfer regime for each coolant since the deterioration greatly depends on the thermophysical properties variation of the coolant and the near-wall flow behavior of the coolant with respect to temperature change.

Potential advantages of coupling supercritical CO₂ Brayton cycle to water cooled small and medium size reactor

Yoon, H.J.,Ahn, Y.,Lee, J.I.,Addad, Y. North-Holland Pub. Co 2012 Nuclear engineering and design Vol.245 No.-

The supercritical carbon dioxide (S-CO<SUB>2</SUB>) Brayton cycle is being considered as a favorable candidate for the next generation nuclear reactors power conversion systems. Major benefits of the S-CO<SUB>2</SUB> Brayton cycle compared to other Brayton cycles are: (1) high thermal efficiency in relatively low turbine inlet temperature, (2) compactness of the turbomachineries and heat exchangers and (3) simpler cycle layout at an equivalent or superior thermal efficiency. However, these benefits can be still utilized even in the water-cooled reactor technologies under special circumstances. A small and medium size water-cooled nuclear reactor (SMR) has been gaining interest due to its wide range of application such as electricity generation, seawater desalination, district heating and propulsion. Another key advantage of a SMR is that it can be transported from one place to another mostly by maritime transport due to its small size, and sometimes even through a railway system. Therefore, the combination of a S-CO<SUB>2</SUB> Brayton cycle with a SMR can reinforce any advantages coming from its small size if the S-CO<SUB>2</SUB> Brayton cycle has much smaller size components, and simpler cycle layout compared to the currently considered steam Rankine cycle. In this paper, SMART (System-integrated Modular Advanced ReacTor), a 330MW<SUB>th</SUB> integral reactor developed by KAERI (Korea Atomic Energy Institute) for multipurpose utilization, is considered as a potential candidate for applying the S-CO<SUB>2</SUB> Brayton cycle and advantages and disadvantages of the proposed system will be discussed in detail. In consideration of SMART condition, the turbine inlet pressure and size of heat exchangers are analyzed by using in-house code developed by KAIST-Khalifa University joint research team. According to the cycle evaluation, the maximum cycle efficiency under 310<SUP>o</SUP>C is 30.05% at 22MPa of the compressor outlet pressure and 36% of flow split ratio (FSR) with 82m<SUP>3</SUP> of total heat exchanger volume while the upper bound of the total cycle efficiency is 37% with ideal components within 310<SUP>o</SUP>C. The total volume of turbomachinery which can afford 330MW<SUB>th</SUB> of SMR is less than 1.4m<SUP>3</SUP> without casing. All the obtained results are compared to the existing SMART system along with its implication to other existing or conceptual SMRs in terms of overall performance in detail.

Prismatic-core advanced high temperature reactor and thermal energy storage coupled system - A preliminary design

Alameri, Saeed A.,King, Jeffrey C.,Alkaabi, Ahmed K.,Addad, Yacine Korean Nuclear Society 2020 Nuclear Engineering and Technology Vol.52 No.2

This study presents an initial design for a novel system consisting in a coupled nuclear reactor and a phase change material-based thermal energy storage (TES) component, which acts as a buffer and regulator of heat transfer between the primary and secondary loops. The goal of this concept is to enhance the capacity factor of nuclear power plants (NPPs) in the case of high integration of renewable energy sources into the electric grid. Hence, this system could support in elevating the economics of NPPs in current competitive markets, especially with subsidized solar and wind energy sources, and relatively low oil and gas prices. Furthermore, utilizing a prismatic-core advanced high temperature reactor (PAHTR) cooled by a molten salt with a high melting point, have the potential in increasing the system efficiency due to its high operating temperature, and providing the baseline requirements for coupling other process heat applications. The present research studies the neutronics and thermal hydraulics (TH) of the PAHTR as well as TH calculations for the TES which consists of 300 blocks with a total heat storage capacity of 150 MWd. SERPENT Monte Carlo and MCNP5 codes carried out the neutronics analysis of the PAHTR which is sized to have a 5-year refueling cycle and rated power of 300 MW_th. The PAHTR has 10 metric tons of heavy metal with 19.75 wt% enriched UO₂ TRISO fuel, a hot clean excess reactivity and shutdown margin of $33.70 and -$115.68; respectively, negative temperature feedback coefficients, and an axial flux peaking factor of 1.68. Star-CCM + code predicted the correct convective heat transfer coefficient variations for both the reactor and the storage. TH analysis results show that the flow in the primary loop (in the reactor and TES) remains in the developing mixed convection regime while it reaches a fully developed flow in the secondary loop.

Fabrication of Uniform Nanoporous Oxide Layers on Long Cylindrical Zircaloy Tubes by Anodization Using Multi-Counter Electrodes

Park, Yang Jeong,Kim, Jung Woo,Ali, Ghafar,Kim, Hyun Jin,Addad, Yacine,Cho, Sung Oh Springer US 2017 NANOSCALE RESEARCH LETTERS Vol.12 No.1

<P>We have presented a method to prepare a uniform anodic nanoporous oxide film on the surface of a cylindrical zircaloy (Zr) tube. The distribution of the electric field around the Zr tube determines the distribution of the thickness of the anodic nanoporous oxide film. The electric field generated when a cylindrical Zr tube is electrochemically anodized was simulated by using commercial code COMSOL. When four Pt wires were used as counter electrodes, a uniform electric field was achieved with minimal use of Pt. Based on the simulation results, a cylindrical Zr tube was anodized and the distribution of the thickness of the anodic nanoporous oxide layer was measured by FESEM. Also, mass production of uniform nanoporous anodic oxide films was possible by symmetrically arranging the zircaloy tubes and Pt wires.</P><P><B>Electronic supplementary material</B></P><P>The online version of this article (doi:10.1186/s11671-016-1774-1) contains supplementary material, which is available to authorized users.</P>