Volume 9: Student Paper Competition
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Published By American Society Of Mechanical Engineers

9780791857878

Author(s):  
Zhixiong Tan ◽  
Jiejin Cai

After Fukushima Daiichi Nuclear Power Plant accident, alternative fuel-design to enhance tolerance for severe accident conditions becomes particularly important. Silicon carbide (SiC) cladding fuel assembly gain more safety margin as novel accident tolerant fuel. This paper focuses on the neutron properties of SiC cladding fuel assembly in pressurized water reactors. Annular fuel pellet was adopted in this paper. Two types of silicon carbide assemblies were evaluated via using lattice calculation code “dragon”. Type one was consisted of 0.057cm SiC cladding and conventional fuel. Type two was consisted of 0.089cm SiC cladding and BeO/UO2 fuel. Compared the results of SiC cladding fuel assembly neutronic parameters with conventional Zircaloy cladding fuel assembly, this paper analyzed the safety of neutronic parameters performance. Results demonstrate that assembly-level reactivity coefficient is kept negative, meanwhile, the numerical value got a relatively decrease. Other parameters are conformed to the design-limiting requirement. SiC kinds cladding show more flat power distribution. SiC cases also show the ability of reducing the enrichment of fuel pellets even though it has higher xenon concentration. These types of assembly have broadly agreement neutron performance with the conventional cladding fuel, which confirmed the acceptability of SiC cladding in the way of neutron physics analysis.


Author(s):  
Salima Kaissoun ◽  
Eric Climent ◽  
Corinne Prevost ◽  
Laurent Ricciardi

In order to understand airflow dynamics through small openings encountered in containment enclosures used for nuclear decommissioning operations, the results of experimental and numerical investigations are analyzed. The main purposes of this work are to identify the required conditions likely to generate flow inversions at the studied opening which lead to pollutant leakage outside depressurized enclosures, and also to verify the ability of CFD1 simulations to predict these flow inversions by using U-RANS2 and LES3 approaches. All along this work, we tried to reproduce the conditions of leakage occurring at the opening in terms of aerodynamics and openings geometries. Laser flow visualizations and CFD results show that an additional flow, such as a turbulent jet in competition with the directional flow and a disturbed level of pressure inside the enclosure are among the main causes leading to the leakage through the opening.


Author(s):  
Jian Song ◽  
Limin Liu ◽  
Simiao Tang ◽  
Yingwei Wu ◽  
Wenxi Tian ◽  
...  

Due to great deal of operation experience and technology accumulation, sodium cooled fast reactor (SFR) is the most promising among the six Generation IV reactors, which has advantages of breeding nuclear fuel, transmuting long-lived actinides and good safety characteristics. Thermal-hydraulic computer codes will have to be developed, verified, and validated to support the conceptual and final designs of new SFRs. However, work on developing thermal hydraulic analysis code for SFR is very limited in China, while the common software RELAP5 MOD3 is unable to analyze liquid metal systems. So the modified RELAP5 MOD3.2 is being considered as the thermal-hydraulic system code to support the development of the SFRs. The thermodynamic and transport properties of sodium liquid and vapor have been implemented into the RELAP5 MOD3.2 code, as well as the specific heat transfer correlations for liquid metal. The sodium liquid properties use polynomial equations based on data obtained from Argonne National Laboratory, and the vapor is assumed to be perfect gas. The property equations are acceptably accurate for analysis of SFR, especially for single-phase liquid. New files are added to the fluids directory to generate property tables for new working fluid, which are similar to the table interpolation subroutines for light and heavy water in the original file directory. The method of code modifications are universal for other working fluids and will not affect the code original performance. Some basic verification work for the modified code are carried out. The steam generator of CEFR is analyzed to verify the modified code. The calculated results show that all the water will boil off in the evaporator and the calculated results are in good agreement with the design values. By using modified RELAP5 to model the primary loop of EBR-II fast reactor, the SHRT-17 PLOF test was analyzed. The results show that the natural circulation can be established in the EBR-II primary system after main pumps off to remove the core decay residual heat effectively, and the peak temperature under the safety limits. Moreover, the results computed in this work compared well with the test experimental data for the steady state condition. During the transients, the changing trends of temperature and pressure are similar to experimental data. The discrepancies between calculation and experiment are considered acceptably which need to be improved in the future work. Our work could demonstrate the capability and reliability of the modified RELAP5 for the analysis of SFRs further.


Author(s):  
Dan Guo ◽  
Hong Xia

Steam generator (SG) water level system is a highly complex nonlinear time-varying system. It is complicated at low power levels due to shrink and swell phenomena which must be considered for plant safety and availability. To improve the transient performance of the SG level subject to power adjustments, an innovative set-point function method is put forward in this paper. The set-point functions based on the inverse-control theory and the swell and shrink effect which generate a desirable reference input to the widespread cascade Proportional Integral Derivative (PID) controller of the level control system respectively. The set-point function can apply appropriate control to the feed-water flow rate duly depended on the pivotal time between the power adjustment decision and the real start time of adjustment. Finally, comparative simulation is carried out under the same condition of power adjustment. The simulation results demonstrate that the water level control system added set-point functions can restrain the disturbance and improve the transient performance effectively. The method added the Inverse Control-Based Set-Point (ICSP) function can achieve better control performances than the swell-based set-point (SBSP) function.


Author(s):  
Yota Suzuki ◽  
Yusei Tanaka ◽  
Taku Sakka ◽  
Akinori Sato ◽  
Kazuyuki Takase ◽  
...  

Clarifying thermal-hydraulic characteristics in a nuclear reactor core is important in particular to enhance the thermo-fluid safety of nuclear reactors. Spacers installed in subchannels of fuel assemblies have the role of keeping the interval between adjacent fuel rods constantly. Similarly, in case of PWR the spacer has also the role as the turbulence promoter. When the transient event occurs, two-phase flow is generated by boiling of water due to heating of fuel rods. Therefore, it is important to confirm the two-phase flow behavior around the spacer. So, the effect of the spacer affecting the two-phase flow was investigated experimentally at forced convective flow condition. Furthermore, in order to improve the thermal safety of current light water reactors, it is necessary to clarify the two-phase flow behavior in the subchannels at the stagnant flow condition. So, the bubbly flow data around a simulated fuel rod were obtained experimentally at the stagnant flow condition. A wire-mesh sensor was used to obtain a detailed two-dimensional void fraction distribution around the simulated spacer and fuel rod. As a result of this research, the bubbly behavior around the simulated spacer and fuel rod was qualitatively revealed and also bubble dynamics in the sub-channels at the conditions of forced convective and stagnant flows were evaluated. The present experimental data are very useful for verifying the detailed three-dimensional two-phase flow analysis codes.


Author(s):  
N. Le Brun ◽  
A. Charogiannis ◽  
G. F. Hewitt ◽  
C. N. Markides

In this study we describe an experimental system designed to simulate the conditions of transient freezing which can occur in abnormal behaviour of molten salt reactors (MSRs). Freezing of coolant is indeed one of the main technical challenges preventing the deployment of MSR. First a novel experimental technique is presented by which it is possible to accurately track the growth of the solidified layer of fluid near a cold surface in an internal flow of liquid. This scenario simulates the possible solidification of a molten salt coolant over a cold wall inside the piping system of the MSR. Specifically, we conducted measurements using water as a simulant for the molten salt, and liquid nitrogen to achieve high heat removal rate at the wall. Particle image velocimetry and planar induced fluorescence were used as diagnostic techniques to track the growth of the solid layer. In addition this study describes a thermo-hydraulic model which has been used to characterise transient freezing in internal flow and compares the said model with the experiments. The numerical simulations were shown to be able to capture qualitatively and quantitatively all the essential processes involved in internal flow transient freezing. Accurate numerical predictive tools such the one presented in this work are essential in simulating the behaviour of MSR under accident conditions.


Author(s):  
Jun Chen ◽  
Liangzhi Cao ◽  
Zhouyu Liu ◽  
Hongchun Wu ◽  
Yijun Zhang

PWR core phenomena can be simulated and predicted more precisely and in more details with high-fidelity neutronics and thermal-hydraulics coupling calculations. An internal coupling between a newly developed high-fidelity neutronics code NECP-X and the sub-channel code SUBSC has been realized. In order to verify the NECP-X/SUBSC coupling system, another high-fidelity neutronics and thermal-hydraulics coupling system OpenMC/SUBSC was developed through external coupling method. Both coupling systems were applied to a simplified PWR 3×3 pin cluster case. The numerical result shows good agreement in both eigenvalue and normalized axial power distribution for a selected pin, demonstrating the success of the internal coupling of NECP-X and SUBSC.


Author(s):  
Wei Zhou ◽  
Rong Liu ◽  
Wenzhong Zhou

In this paper, we first propose a novel composite nuclear fuel of UO2-GaN, which has never been reported before, and then its fully coupled multiphysics fuel performance is investigated using the CAMPUS code developed by ourselves. We propose two different fabrication methods to obtain the UO2-GaN fuel, which are Green Granule/Slug Bisque and Spark Plasma Sintering, respectively, resulting in different fuel thermal conductivities. By comparing two kinds of UO2-GaN fuel which are fabricated by two methods, we found that fuel fabricated by Green Granule/Slug Bisque possesses high thermal conductivity and performs well during the reactor operation. The gap width, gap conductance, fission gas release, plenum pressure, deviation of oxygen to metal ratio and displacement are all studied in this work. The performance of this novel fuel is also compared with the traditional UO2 fuel. The UO2-GaN enhanced thermal conductivity composite fuel shows the potential of decreasing the fuel temperature, and improving fuel performance and reactor safety. This makes GaN a good candidate to fabricate composite fuel with UO2 from the thermal standpoint. However, this work is to conduct an exploratory approach to the effect for the GaN addition to UO2 fuel with very limited data. So, further studies are still needed on GaN’s compatibility with UO2, neutronic behavior, fission product retention capabilities and irradiation performance, both on experimental measurements and numerical simulations.


Author(s):  
N. Boyle ◽  
B. Archambault ◽  
A. Hagen ◽  
C. Meert ◽  
R. P. Taleyarkhan

Alpha radiation emitting radon (Rn) gas seepage into homes in the USA leads to over 21,000 annual lung cancer deaths (according to the US-Environmental Protection Agency, EPA) leading to mandatory monitoring for Rn throughout the USA. In the nuclear industry alpha emitting radionuclides in air (e.g., in spent fuel reprocessing) also constitute a major safety and security-safeguards related issues. Purdue University, along with Sagamore Adams Laboratories LLC, is developing the tensioned metastable fluid detector (TMFD) technology for general-purpose alpha-neutron-fission spectroscopy. This paper focuses on rapid, high-efficiency detection of Rn and progeny in air using the novel TMFD technology; Rn and progeny isotopes in air are sparged through the TMFD detection fluid (to entrap the radioactive gas), which is then placed under a metastable state. Through tailoring the metastable fluid state, an audible and visible cavitation detection event is created and readily detected from transient bubble formation. Changing the tensioned state allows for the spectroscopic differentiability of Rn and its daughters which can be used to actively measure the equilibrium between the parent and daughter products. Such a technique can also be used to monitor the atmosphere in critical nuclear facilities for contamination from other alpha emitting isotopes (e.g., Pu, Cm, U...). TMFDs offer the unique ability for high intrinsic efficiency (>95%) alpha-neutron-fission fragment detection, while remaining blind to background beta and gamma radiation (qualified to >3.8×108 Bq m−3 using a dissolved 32P beta source, and also via gammas from a 53 R/hr 137Cs gamma source). Immunity to beta and gamma is beneficial for the discrimination of buildup of beta-emitting Thoron and Rn progeny in the detection fluid allowing for reusability. This paper will discuss the research results pertaining to detection of Radon and progeny in air, for concentrations between 74 Bq m−3 (2 pCi/L) and 740 Bq m−3 (20 pCi/L). The system measures a radon concentration between these levels to within ±15% intrinsic relative error (IRE) within 24 hours meeting the standards outlined by the American Association of Radon Scientists and Technicians-National Radon Proficiency Program (AARST-NRPP) Device Evaluation Program. Precision evaluation was also performed and the relative standard deviation defined by the AARST-NRPP was <5% exceeded the requirement of 25%. Ambient temperature effects were assessed at 10 °C and at 27 °C, which revealed a large increase in collection efficiency with decreasing sampling temperature and slight increase with increasing sampling temperature. Temperature effects on sensitivity thresholds and volumetric expansion were measured and used to compensate for variability in temperature over time. Blind testing with the help of Bowser-Morner Radon Reference Laboratory was performed and succeeded in accurately determining the Rn in air concentration to within 20% within only 6h of sampling. Finally, a 48-hour based collection time has also been developed for use in dwellings where Rn in air concentrations may vary in a day. Overall, the reproducibility and precision of TMFD technology is found to allow for an efficient, cost-effective, reliable, and environmentally friendly means of Rn and progeny detection, and by extension for use for general actinide in air monitoring for the nuclear industry.


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