Current status and future plan for thermaI striping investigations at JNC

; kasahara, Naoto; ; ; Kamide, Hideki

JNC TN9400 2000-010, 168 Pages, 2000/02

JNC-TN9400-2000-010.pdf:8.78MB

Thermal striping is significant issue of the structural integrity, where the hot and cold fluids give high cycle fatigue to the structure through the thermal stress resulted from the time change of temperatur distibution in the structure. In the sodium cooled fast reactor, temperature change in fluid easily transfers to the structure because of the high thermal conductivity of the sodium. It means that we have to take care of thermal striping, The thermal striping is complex phenomena between the fluid and structure engineering fields. The investigations of thermal striping are not enough to evaluate the integrity directly. That is the fluctuation intensity at the structure surface is assumed to be temperature difference between source fluids (upstream to the mixing region) as the maximum value in the design. 0therwise, the design conditions are defined by using a mockup experiment and large margin of temperature fluctuation intensity. Furthermore, such evaluation manners have not yet been considered as a design rule. Transfer mechanism of temperature fluctuation from fluid to structure has been investigated by the authors on the view points of the fluid and structure. Attenuation of temperature fluctuation was recognized as a dominant factor of thermal fatigue. We have devdoped a numerical analysis system which can evaluate thermal fatigue and crack growth with consideration of the attenuation of temperature fluctuation in fluid, heat transfer, and structure. This system was applied to a real reactor and the applicability was confirmed. Further verification is planned to generalize the system. For the higher cost performance of the fast reactor, an evaluation rule is needed, which can estimate thermal loading with attenuation and can be applied to the design. An idea of the rule is proposed here. Two methods should be prepared; one is a precise evaluation method where mechanism of attenuation is modeled, and the other is simple evaluation method where ...

Thermal striping; an experimental investigation on mixing of jets; Part III Remaining hydrodynamic results from initial experiments

Tokuhiro, Akira; Kimura, Nobuyuki;

JNC TN9400 2000-014, 86 Pages, 1999/06

JNC-TN9400-2000-014.pdf:11.72MB

Experiments were performed using the WAJECO facility to investigate the thermohydraulic mixing of multiple jets flowing out of a LMFBR core. Mixing is the root of the thermal striping problem. The multiple jets are typically at different velocities and temperatures and may induce thermal stresses upon components they impinge. In our study we modeled the mixing of three vertical jets, the central at a lower temperature than the two adjacent jets at equal temperatures. The jets are quasi-planar. The parameters were the average exit jet velocities (Uo,av) and the temperature difference between the "cold" and "hot" jets (Thc=Thot-Tcold). Measurements of the liquid velocity, initially using laser Doppler velocimetry (LDV) and later ultrasound Doppler velocimetry (UDV), for both our reference single-jet and the triple-jet configuration, comprised Phase I of the experiments (up to 1994). Two reports (TN9410 96-181 and TN9410 96-296; in Japanese) reported on the hydraulic and heat tra

Numerical investigation on thermal striping conditions for a tee junction of LMFBR coolant pipes (I); Investigation on velocity ratio between the coolant pipes

PNC TN9410 98-007, 93 Pages, 1998/02

PNC-TN9410-98-007.pdf:7.52MB

This report presents numeical results on thermal striping charactelistics at a tee junction of LMFBR coolant pipe, carried out using a direct numerical simulation code DINUS-3. In the numerical investigations, it was considered a tee junction system consisted of a main pipe (1.33 cm) with a 90 elbow and a branch pipe having same inner diameter to the main pipe, and five velocity ratio conditions between both the pipes, i,e., (V / V) = 0.25; 0.5; 1.0; 2.0 and 4.0. From the numerical investigations, the following characteristics were obtained: (1)Temperature fluctuations in the downstream region of the tee junction were formulated by lower frequency components (< 7.0Hz) due to the iteractions between main pipe flows and jet flows from the branch pipe, and higher frequency components (> 10.0 Hz) generated by the vortex released frequency from the outer edge of the branch pipe jet flows. (2)On the top plane of the main pipe, peak values of the temperature fluctuation amplitude was decreased with increasing flow velocity in the main pipe, and its position was shifted to downstream direction of the main pipe by the increase of the main pipe flow velocity. (3)On the bottom plane of the main pipe, contrary to (2), peak values of the temperature fluctuation amplitude was increased with increasing flow velocity in the main pipe.

Development of analytical model for evaluating temperature fluctuation in coolant (X); Investigation of thermally response characteristics of in-vessel structures using the BEMSET code

PNC TN9410 96-136, 92 Pages, 1996/05

PNC-TN9410-96-136.pdf:2.53MB

Thermal striping phenomena characterized by stationary random temperature fluctuations are observed in the region immediately above the core exit of liquid-metal-cooled fast breeder reactors (LMFBRs) due to the interactions of cold sodium flowing out of a control rod (C/R) assembly and hot sodium flowing out of adjacent fuel assemblies (F/As). Therefore the in-vessel components located in the core outlet region, such as upper core structure (UCS), flow guide tube, C/R upper guide tube, etc, must be protected against the stationary random thermal process which might induce high-cycle fatigue. In this study, thermally response characteristics of the flow guide tube made by SUS 316 stainless steels were investigated using a boundary element method code BEMSET under the temperature transient conditions of Sine wave, quasi-random wave, and Sine wave with quasi-random components. From the numerical investigations, it was concluded that the detailed handling on turbulence phenomena in coolant is very important in the evaluation of actual LMFBRs, because of the thermally response of the structures are influenced significantly on random fluctuating components.

Development of analytical model for temperature fluctuationin in coolant (VII); Invesligation for reduction measures to coolant temperature fluctuations using numerical method

PNC TN9410 94-205, 114 Pages, 1994/07

PNC-TN9410-94-205.pdf:3.34MB

Thermal striping phenomena are characterized by random temperature fluctuations and observed in the region immediately above the core exit of Liquid Metal Fast Breeder Reactors (LMFBRs) due to the interactions of cold sodium flowing out of a control rod (C/R) assembly and hot sodium flowing out of adjacent fuel assemblies (F/As). Therefore the in-vessel components located in the core outlet region, such as upper core structure (UCS), flow guide tube, C/R guide tube, etc., must be protected against the random thermal processes which might induce high-cycle fatigue. In this regard the MONJU reactor adopted ALLOY 718 as a coating material to protect these components against the fatigue. In this study, reduction measures of coolant temperature fluctuations have been investigated using a multi-dimensional thermohydraulic analysis code AQUA with the Algebraic Stress turbulence Model (ASM). From the analysis, it was confirmed that the area to be protect in-vessel components against the thermal fatigue can be decreased to 1/10 of the total area of ALLOY 718 adopted in the MONJU reactor by the tuning of the support plate height and the flow rate ratio between F/A and C/R assemblies.