Evaluation of Gap Heat Transfer between Boron Carbide Pellet and Cladding in Control Rod of FBR

1992 ◽  
Vol 29 (2) ◽  
pp. 121-130 ◽  
Author(s):  
Fumito KAMINAGA ◽  
Sennosuke SATO ◽  
Yoshizo OKAMOTO
Keyword(s):  
Heat Transfer ◽  
Boron Carbide ◽  
Control Rod

On Efficient Passive Cooling of Control Rod Drivers

2013 ◽  
Author(s):  
A. N. Gershuni ◽  
A. P. Nishchik ◽  
V. G. Razumovskiy ◽  
I. L. Pioro
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
High Performance ◽  
Cooling System ◽  
Vertical Channel ◽  
Passive Cooling ◽  
Primary Circuit ◽  
Two Phase ◽  
Primary Coolant ◽  
Control Rod

Experimental research of natural convection and the ways of its suppression in an annular vertical channel to simulate the conditions of cooling the control rod drivers of the reactor protection system (RPS) in its so-called wet design, where the drivers are cooled by primary circuit water supplied due to the system that includes branched pipelines, valves, pump, heat exchanger, etc., is reported. Reliability of the drivers depends upon their temperature ensured by operation of an active multi-element cooling system. Its replacement by an available passive cooling system is possible only under significant suppression of natural convection in control rod channel filled with primary coolant. The methods of suppression of natural convection proposed in the work have demonstrated the possibility both of minimization of axial heat transfer and of almost complete elimination of temperature non-uniformity and oscillation inside the channel under the conditions of free travel of moving element (control rod) in it. The obtained results widen the possibilities of substitution of the active systems of cooling the RPS drivers by reliable passive systems, such as high-performance heat-transfer systems of evaporation-condensation type with heat pipes or two-phase thermosyphons as heat-transferring elements.

Irradiation effects of boron carbide used as control rod elements in fast breeder reactors

1978 ◽  
Vol 74 (1) ◽  
pp. 114-122 ◽  
Author(s):  
Tadashi Inoue ◽  
Takeo Onchi ◽  
Hiroaki Kôyama ◽  
Hiroshige Suzuki
Keyword(s):  
Boron Carbide ◽  
Irradiation Effects ◽  
Control Rod ◽  
Fast Breeder Reactors ◽  
Breeder Reactors

Effect of CRGT Cooling on Modes of Global Vessel Failure of a BWR Lower Head

2012 ◽  
Author(s):  
Walter Villanueva ◽  
Chi-Thanh Tran ◽  
Pavel Kudinov
Keyword(s):  
Heat Transfer ◽  
Vessel Wall ◽  
Reactor Vessel ◽  
Creep Model ◽  
Guide Tube ◽  
Mechanical Loads ◽  
Control Rod ◽  
Melt Pool ◽  
Creep Analysis ◽  
Lower Head

An in-vessel stage of a severe core melt accident in a Nordic type Boiling Water Reactor (BWR) is considered wherein a decay-heated pool of corium melt inflicts thermal and mechanical loads on the lower-head vessel wall. This process induces creep leading to a mechanical failure of the reactor vessel wall. The focus of this study is to investigate the effect of Control Rod Guide Tube (CRGT) and top cooling on the modes of global vessel failure of the lower head. A coupled thermo-mechanical creep analysis of the lower head is performed and cases with and without CRGT and top cooling are compared. The debris bed heat-up, re-melting, melt pool formation, and heat transfer are calculated using the Phase-change Effective Convectivity Model and transient heat transfer characteristics are provided for thermo-mechanical strength calculations. The creep analysis is performed with the modified time hardening creep model and both thermal and integral mechanical loads on the reactor vessel wall are taken into account. Known material properties of the reactor vessel as a function of temperature, including the creep curves, are used as an input data for the creep analysis. It is found that a global vessel failure is imminent regardless of activation of CRGT and top cooling. However, if CRGT and top cooling is activated, the mode and timing of failure is different compared to the case with no CRGT and top cooling. More specifically, with CRGT and top cooling, there are two modes of global vessel failure depending on the size of the melt pool: (a) ‘ballooning’ of the vessel bottom for smaller pools, and (b) ‘localized creep’ concentrated within the vicinity of the top surface of the melt pool for larger pools. Without CRGT and top cooling, only a ballooning mode of global vessel failure is observed. Furthermore, a considerable delay (about 1.4 h) on the global vessel failure is observed for the roughly 30-ton debris case if CRGT and top cooling is implemented. For a much larger pool (roughly 200-ton debris), no significant delay on the global vessel failure is observed when CRGT and top cooling is implemented, however, the liquid melt fraction and melt superheat are considerably higher in non-cooling case.

Study on Eutectic Melting Behavior of Control Rod Materials in Core Disruptive Accidents of Sodium-Cooled Fast Reactors: Thermophysical Properties of Eutectic Mixture Containing of High Concentration Boron in a Solid State

2020 ◽  
Author(s):  
Toshihide Takai ◽  
Tomohiro Furukawa ◽  
Hidemasa Yamano
Keyword(s):  
Stainless Steel ◽  
Solid State ◽  
Boron Carbide ◽  
Specific Heat ◽  
Thermophysical Properties ◽  
Crystalline Phase ◽  
Eutectic Mixture ◽  
Severe Accident ◽  
Eutectic Melting ◽  
Control Rod

Abstract In a core disruptive accident scenario, boron carbide, which is used as control rod material, may melt below the melting temperature of stainless steel due to the eutectic reaction with it. Produced eutectic mixture is assumed to relocate widely in the degraded core, and this behavior plays an important role to reduce the neutronic reactivity of the degraded core materials significantly. However, these behaviors have never been simulated in the severe accident computer codes, and reducing the uncertainty is important for reasonable assessment. To contribute improvement of the core disruptive accident analysis code to handle these eutectic melting and relocation behavior, authors had been carried out the evaluation of the thermophysical properties of stainless steel containing boron carbide, which needed as a basic data for cord improvement. Since the solubility range of boron against iron is expected to be wide, the crystalline phase of eutectic mixture may change according to boron concentration in the eutectic mixture. And this may affect the thermophysical properties themselves. In this work, the density and specific heat of stainless steel containing 17 mass% boron carbide in a solid state are obtained and compared with these of stainless steel containing 0 and 5 mass% boron carbide. By adding 17 mass boron carbide to stainless steel type 316L, the density decreased approximately 24% and the specific heat increased approximately 25% at 293 K. The density of stainless steel containing boron carbide tended to decrease almost linearly depending on the amount of boron carbide added, none the less for difference of crystalline phase. On the other hand, increasing trend of the specific heat of stainless steel containing 17 mass% boron carbide accompanying elevating temperature showed different behavior from that of stainless steel containing 0 and 5 mass% boron carbide. This difference in the trend of the specific heat was considered to be caused the difference in the crystalline phase.

Control Rod Blades Size Reduction Using Underwater Plasma Cutting and its Effects on Boron Carbide Powder Scattering

2020 ◽  
Author(s):  
Yassine Serbouti ◽  
Keisuke Kurihara ◽  
Yutaka Kometani ◽  
Masatoshi Itagaki ◽  
Makoto Tatemura
Keyword(s):  
Boron Carbide ◽  
Cross Sections ◽  
Hydrogen Plasma ◽  
Argon Plasma ◽  
Size Reduction ◽  
Carbide Powder ◽  
Neutron Absorber ◽  
Control Rod ◽  
Last Stage ◽  
Actual Control

Abstract Control rod blades are comprised of a stainless steel sheath, which contains neutron absorber tubes (filled with boron carbide powder). During decommissioning, the first stage of size reduction consists of cutting the connector (bottom portion) of the control rod, while the second stage consists of separating the blades of the control rod by cutting through the tie rod. The last stage consists of segmenting the control rod blades by cutting through absorber tubes. In this study, the control rod blades segmentation (last stage of size reduction) is investigated using an actual control rod (unused). During the experiments, we used a forming press on the cut locations followed by a plasma arc cutting underwater. The purpose of this cutting technique is to minimize the scattering of boron carbides into water by using the stainless sheath melt to seal the absorber tubes. After the segmentation, we confirmed the sealing of the absorber tubes by visually examining the cut cross-sections. The water analysis showed that the boron carbide scattering was relatively low (only 0.07% of the total boron carbides was scattered). Finally, we confirmed that the off-gas emission is considerably reduced by using Argon plasma instead of Argon-Hydrogen plasma.

Control Rod Blades Size Reduction Using Underwater Plasma Cutting and its Effects on Boron Carbide Powder Scattering

2021 ◽  
Author(s):  
Yassine Serbouti ◽  
Makoto Tatemura ◽  
Keisuke Kurihara ◽  
Yutaka Kometani ◽  
Masatoshi Itagaki
Keyword(s):  
Boron Carbide ◽  
Size Reduction ◽  
Carbide Powder ◽  
Plasma Cutting ◽  
Control Rod

Comparison of Experimental and Numerical Analysis Data for BMI Mock-Up With Dissimilar Metal Welds

2008 ◽  
Author(s):  
Seung-Cheon Yu ◽  
Yoon-Suk Chang ◽  
Young-Jin Kim ◽  
Sung-Woo Kim ◽  
Seong-Sik Hwang ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Residual Stress ◽  
Welding Process ◽  
Analysis Data ◽  
Test Method ◽  
Heat Transfer Analysis ◽  
Numerical Analyses ◽  
Primary Coolant ◽  
Control Rod ◽  
Dissimilar Metal

During the last decade, several defects due to primary water stress corrosion cracking (PWSCC) have been reported at bottom-mounted instrumentation (BMI) and control rod drive mechanism nozzles. The exact locations were dissimilar metal weld parts which are greatly important because the cracking could lead to leakage of primary coolant. The PWSCC of BMI mock-up’s penetration with dissimilar metal welds was examined by using doped steam test method by Korea Atomic Energy Research Institute. In this work, numerical analyses are performed for the same environment condition with the doped steam test. With respect to the numerical analyses, heat transfer analyses are carried out based on thermal conduction. The welding paths are simulated by using lumped path method for conservative evaluation and model change (remove/rebirth) method. Then residual stress analyses are conducted using the heat transfer analysis results, in which annealing effect of welding process simulation is considered for resetting the plastic deformation. However, the plastic behaviour of steels during phase transformations is not considered with experimental data. In addition, the consequence of weld residual stress that is known as the cause of PWSCC is being investigated.

Flow Mixing Inside a Control-Rod Guide Tube: Part II—Experimental Tests and CFD-Simulations

2010 ◽  
Author(s):  
Kristian Angele ◽  
Mathias Cehlin ◽  
Carl-Maikel Ho¨gstro¨m ◽  
Ylva Odemark ◽  
Mats Henriksson ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Temperature Fluctuations ◽  
Thermal Fluctuations ◽  
Experimental Results ◽  
Flow Structures ◽  
Scaling Analysis ◽  
Guide Tube ◽  
Cfd Simulations ◽  
Control Rod ◽  
Control Rods

A large number of control rod cracks were detected during the refuelling outage of the twin reactors Oskarshamn 3 and Forsmark 3 in the fall of 2008. The extensive damage investigation finally lead to the restart of both reactors at the end of 2008 under the condition that further studies would be conducted in order to clarify all remaining matters. Also, all control rods were inserted 14% in order to locate the welding region of the control rod stem away from the thermal mixing region of the flow. Unfortunately, this measure led to new cracks a few months later due to a combination of surface finish of the new stems and the changed flow conditions after the partial insertion of the control rods. The experimental evidence reported here shows an increase in the extension of the mixing region and in the intensity of the thermal fluctuations. As a part of the complementary work associated with the restart of the reactors, and to verify the CFD simulations, experimental work of the flow in the annular region formed by the guide tube and control rod stem was carried out. Two full-scale setups were developed, one in a Plexiglass model at atmospheric conditions (in order to be able to visualize the mixing process) and one in a steel model to allow for a higher temperature difference and heating of the control rod guide tube. The experimental results corroborate the general information obtained through CFD simulations, namely that the mixing region between the cold crud-removal flow and warm by-pass flow is perturbed by flow structures coming from above. The process is characterized by low frequent, high amplitude temperature fluctuations. The process is basically hydrodynamic, caused by the downward transport of flow structures originated at the upper bypass inlets. The damping thermal effects through buoyancy is of secondary importance, as also the scaling analysis shows, however a slight damping of the temperature fluctuations can be seen due to natural convection due to a pre-heating of the cold crud-removal flow. The comparison between numerical and experimental results shows a rather good agreement, indicating that experiments with plant conditions are not necessary since, through the existing scaling laws and CFD-calculations, the obtained results may be extrapolated to plant conditions. The problem of conjugate heat transfer has not yet been addressed experimentally since complex and difficult measurements of the heat transfer have to be carried out. This type of measurements constitutes one of the main challenges to be dealt with in the future work.

Study on Eutectic Melting Behavior of Control Rod Materials in Core Disruptive Accidents of Sodium-Cooled Fast Reactors: Kinetic Study of Boron Carbide-Stainless Steel Eutectic Melting by Differential Thermal Analysis

2020 ◽  
Author(s):  
Shin Kikuchi ◽  
Hidemasa Yamano ◽  
Kinya Nakamura
Keyword(s):  
Thermal Analysis ◽  
Stainless Steel ◽  
Differential Thermal Analysis ◽  
Boron Carbide ◽  
Early Stage ◽  
Kinetic Feature ◽  
Eutectic Melting ◽  
Validation Data ◽  
Exponential Factor ◽  
Control Rod

Abstract In a postulated severe accidental condition of sodium-cooled fast reactor (SFR), eutectic melting between boron carbide (B4C) as control rod element and stainless steel (SS) as control rod cladding or related structure may take place. Thus, kinetic behavior of B4C-SS eutectic melting is one of the important phenomena to be considered when evaluating the core disruptive accidents in SFR. In this study, for the first step to obtain the fundamental information on kinetic feature of B4C-SS eutectic melting and compare the pervious findings, the thermal analysis using the pellet type samples of B4C and Type 316L SS as different experimental technique was performed up to 1773 K at different heating rates of 2.5–10 K/min. The differential thermal analysis (DTA) endothermic peaks for the B4C-SS eutectic melting appeared from 1483K to 1534K and systematically shifted to higher temperatures when increasing heating rate. Based on this kinetic feature, apparent activation energy and pre-exponential factor for the B4C-SS eutectic melting were determined by Kissinger method. It was found that the kinetic parameters obtained by thermal analysis were comparable to the literature values of thinning experiment at high temperatures. In addition, the microstructure and element distribution formed in the interdiffusion layer composed of the B4C / SS system were analyzed by the electron probe microanalyzer (EPMA), which can provide key validation data on elemental interdiffusion behavior in the early stage of the eutectic melting.

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