Assessment of CTF boiling transition and critical heat flux modeling capabilities using the OECD/NRC BFBT and PSBT benchmark databases

The need to refine models for best-estimate calculations, based on good-quality experimental data, has been expressed in many recent meetings in the field of nuclear applications. The modeling needs arising in this respect should not be limited to the currently available macroscopic methods but should be extended to next-generation analysis techniques that focus on more microscopic processes. One of the most valuable databases identified for the thermalhydraulics modeling was developed by the Nuclear Power Engineering Corporation (NUPEC), Japan. From 1987 to 1995, NUPEC performed steady-state and transient critical power and departure from nucleate boiling (DNB) test series based on the equivalent full-size mock-ups. Considering the reliability not only of the measured data, but also other relevant parameters such as the system pressure, inlet sub-cooling and rod surface temperature, these test series supplied the first substantial database for the development of truly mechanistic and consistent models for boiling transition and critical heat flux. Over the last few years the Pennsylvania State University (PSU) under the sponsorship of the U.S. Nuclear Regulatory Commission (NRC) has prepared, organized, conducted and summarized the OECD/NRC Full-size Fine-mesh Bundle Tests (BFBT) Benchmark. The international benchmark activities have been conducted in cooperation with the Nuclear Energy Agency/Organization for Economic Co-operation and Development (NEA/OECD) and Japan Nuclear Energy Safety (JNES) organization, Japan. Consequently, the JNES has made available the Boiling Water Reactor (BWR) NUPEC database for the purposes of the benchmark. Based on the success of the OECD/NRC BFBT benchmark the JNES has decided to release also the data based on the NUPEC Pressurized Water Reactor (PWR) subchannel and bundle tests for another follow-up international benchmark entitled OECD/NRC PWR Subchannel and Bundle Tests (PSBT) benchmark. This paper presents an application of the joint Penn State University/Technical University of Madrid (UPM) version of the well-known subchannel code COBRA-TF, namely CTF, to the critical power and departure from nucleate boiling (DNB) exercises of the OECD/NRC BFBT and PSBT benchmark

Post-test simulation of a PLOFA transient test in the CIRCE-HERO facility

CIRCE is a lead–bismuth eutectic alloy (LBE) pool facility aimed to simulate the primary system of a heavy liquid metal (HLM) cooled pool-type fast reactor. The experimental facility was implemented with a new test section, called HERO (Heavy liquid mEtal pRessurized water cOoled tubes), which consists of a steam generator composed of seven double-wall bayonet tubes (DWBT) with an active length of six meters. The experimental campaign aims to investigate HERO behavior, which is representative of the tubes that will compose ALFRED SG. In the framework of the Horizon 2020 SESAME project, a transient test was selected for the realization of a validation benchmark. The test consists of a protected loss of flow accident (PLOFA) simulating the shutdown of primary pumps, the reactor scram and the activation of the DHR system. A RELAP5-3D© nodalization scheme was developed in the pre-test phase at DIAEE of “Sapienza” University of Rome, providing useful information to the experimentalists. The model consisted to a mono-dimensional scheme of the primary flow path and the SG secondary side, and a multi-dimensional component simulating the large LBE pool. The analysis of experimental data, provided by ENEA, has suggested to improve the thermal–hydraulic model with a more detailed nodalization scheme of the secondary loop, looking to reproduce the asymmetries observed on the DWBTs operation. The paper summarizes the post-test activity performed in the frame of the H2020 SESAME project as a contribution of the benchmark activity, highlighting a global agreement between simulations and experiment for all the primary circuit physical quantities monitored. Then, the attention is focused on the secondary system operation, where uncertainties related to the boundary conditions affect the computational results

Numerical simulation of electromagnetic coupling in explicitly meshed wiring looms and bundles

In this paper, the Unstructured Transmission Line Modelling (UTLM) method based on a tetrahedral mesh is applied to model the electromagnetic coupling into wire looms and bundles with multiple cores that are typical of an aircraft system, when they are exposed to plane wave illuminations. The impact on the electromagnetic coupling into wires of both bundle configuration and the positioning of the bundle relative to simple structures are investigated using the UTLM method with explicit meshing of the wires. The work not only confirms that UTLM method as a powerful tool for dealing with wire looms and bundles but provides invaluable information on the margins to be expected in key experimental waveform parameters such as peak amplitude and frequency response

Computational fluid dynamics modeling and comparison of advanced techniques for heat transfer augmentation for nuclear applications

“Passive safety is the most important feature of NuScale’s reactor designs. Twist tape is one passive heat enhance heat technique. The present research investigated thermo-hydraulic characteristics of natural and forced convection of water under different configurations of twisted tape inserted in tube as well as NuScale rod bundles for uniform wall heat flux using computational fluid dynamics (CFD) using ANSYS Fluent 18.1. Results for twist tape inserted in tube under natural circulation showed that heat transfer enhanced and pressure drop increased to 28% and 102.8% over the plain tube respectively. Regularly spaced tapes, and different widths of the twisted tapes also played a significant role in both heat transfer and pressure drop. Moreover, the results revealed a strong effect of twist ratios on the inner wall temperature. The impact of twisted tapes along sub-channel for the water flow through NuScale SMR’s 2X2 RB at the normal operating conditions showed that the Nusselt number (Nu) and secondary flow were enhanced by 101% and 0.16 as compared to the case of plain sub-channel, respectively. On the other hand, the pressure drop for a sub-channel with twisted tape is always higher than the plain sub-channel. The flow in rod bundle sub-channels under natural convection with twist along the sub-channel showed that heat transfer and pressure drop are increased by 39.5% and 112.5% as compared to the case of plain sub-channel respectively. In addition, all results showed that Nu and pressure drop are influenced by changing the twist ratio, and tape geometry. Finally, twisted tapes were effective in enhancing the Nu in sub-channels under both natural and forced convection conditions. The smallest twist ratio in all cases resulted in the high pressure drop and Nu”--Abstract, page iii

Membrane evaporator/sublimator investigation

Data are presented on a new evaporator/sublimator concept using a hollow fiber membrane unit with a high permeability to liquid water. The aim of the program was to obtain a more reliable, lightweight and simpler Extra Vehicular Life Support System (EVLSS) cooling concept than is currently being used

Indicating Asynchronous Array Multipliers

Multiplication is an important arithmetic operation that is frequently encountered in microprocessing and digital signal processing applications, and multiplication is physically realized using a multiplier. This paper discusses the physical implementation of many indicating asynchronous array multipliers, which are inherently elastic and modular and are robust to timing, process and parametric variations. We consider the physical realization of many indicating asynchronous array multipliers using a 32/28nm CMOS technology. The weak-indication array multipliers comprise strong-indication or weak-indication full adders, and strong-indication 2-input AND functions to realize the partial products. The multipliers were synthesized in a semi-custom ASIC design style using standard library cells including a custom-designed 2-input C-element. 4x4 and 8x8 multiplication operations were considered for the physical implementations. The 4-phase return-to-zero (RTZ) and the 4-phase return-to-one (RTO) handshake protocols were utilized for data communication, and the delay-insensitive dual-rail code was used for data encoding. Among several weak-indication array multipliers, a weak-indication array multiplier utilizing a biased weak-indication full adder and the strong-indication 2-input AND function is found to have reduced cycle time and power-cycle time product with respect to RTZ and RTO handshaking for 4x4 and 8x8 multiplications. Further, the 4-phase RTO handshaking is found to be preferable to the 4-phase RTZ handshaking for achieving enhanced optimizations of the design metrics.Comment: arXiv admin note: text overlap with arXiv:1903.0943

Multimegawatt thermionic reactor systems for space applications

Design features and performance characteristics of thermionic reactor systems for space application

Study on Swirl and Cross Flow of 3D-Printed Rotational Mixing Vane in 2??3 Subchannel

Department of Nuclear Engineeringn pressurized water reactor (PWR), spacer grid is installed to support the fuel rod bundles, located between the fuel rod bundles. The mixing vane is installed on top of the spacer grid to generate swirl and cross flow. The swirl and cross flow enhance heat transfer and can promote critical heat flux of PWR. The safety margin of PWR could be estimated with heat transfer performance and CHF. So, the swirl and cross flow generation could bring about the safety margin and power uprate enhancement. 3D-printing technology enables to produce exquisite mixing vane blade component. The part of mixing vane was built by 3D printing. The general material is gypsum, the other is metal, stainless steel. The mixing vane is attached on top of the spacer grid, which also made by 3D printing. Rotational mixing vane is a swirl generator between the fuel rod, improve the cross flow and heat transfer characteristics. Centrifugal force provides bubble detachment from the fuel rod surface. Various types of rotational mixing vanes (RV) are studied. They are : the fan vane (FV), impeller vane (IV), the wind turbine vane (WT). Each RV shows different mixing performance and pressure drop. The FV shows the average mixing performance and pressure drop increase. The IV shows the most mixing performance, and the WT shows the least pressure drop. Experimental approach, the Particle Image Velocimetry (PIV) experiment technique visualizes flow field and evaluates mixing performance. Flow pattern visualization is accomplished inside the 2??3 subchannel, 2.5 times scale-up test section. Tests shows the flow pattern tracking and measures pressure drop. The test assures durability and maintainability of 3D printed mixing vane parts equipped in the subchannel. Numerical analysis is conducted using the commercial using computational fluid dynamics (CFD) code FLOW-3D. General Moving Object (GMO) method is used to simulate flow-driven coupled rotational motion. The Fluid-structure interaction (FSI) problem is too complex to solve analytically, so the computational technique to validate the rotational motion is also researched. The mixing performance of rotational mixing vane is evaluated by swirl and cross flow of coolant. The cross flow and swirl are qualified the mixing performance as mixing parameters. The lateral velocity, vorticity, and bubble tracking method shows the mixing of coolant, as the mixing parameters. The pressure drop is also measured and friction factor evaluation is done to assure the system safety of the reactor. For recommendation, further optimization of 3D printed mixing vane will be keep researched. Heat transfer characteristics and thermal performance enhancement for experimental and numerical analysis would be validated in extended subchannel. Adopting the rotational mixing vane in the PWR could results enhancement of the heat transfer performance, safety margin and power uprate.clos