Submitted te:

First International Symposium on Ultrasonic Doppler Methods for Fluid Mechanics and Fluid Engineering, 9.-11.

September 1996, Paul Scberrer Institute, Villigen, Switzerland.

An Overview of Experiments using the Ultrasonic Doppler Method at the Power Reactor and Nuclear Fuel Development Corporation (PNC).

A. Tokuhiro, J. Kobayashi, Y, Ohki, 12. I2ayashida and V. Kamide Oarai Engineering Center, Power Reactor and Nuclear Fuel Development Corporation (PN C),

4 002 Narita, Oarai-machi, Ibaraki, Japan, 311-13. T:+81-29-267-4141; F:+ 81-29-

266-3867;

e-mail: tokuhiro@oec.pnc.go.jp

KEY  WORD S: MAP, water, sodium, pip e fla w, mix:ed co nve ctive flo w per etratin g fIo w, verficoJ mix in g lay er, bJZOwant jet, stirred vortex flo w, flo w map pin g, two - dimensio nal veto c it y field, steady and transien t measurement, thermo-aco csbic calibration, high-temperature transdu cers.

Extended Absfract 

The Power Reactor and Nuclear Fuel Development Corporation is engaged in research and development of the Japanese Liquid Metal Fast Breeder Reactor. Within the scope of this program, the Reactor Engineering Section is undertaking various thermal-hydraulic experiments investigating the adequate cooling of the reactor core under nodal and transient conditions. One of the major measurement techniques used to study the various connective phenomena is ultrasound Doppler velocimetry. In this extended abstract, we present a brief overview of ltte experiments in which Metflow's UVP is used as a velocity measurement tool.

1. In vestigation of penetrating flow under mixed cos vection conditions.(COPIES)The penetration flow of cold coolant into the vertical sub-assembly channeJs under mixed connection conditions in the conventional design of the LMFBR has been investigated. A simplified schematic is shown in Figure 1. The phenomenom occurs under operating conditions when the natural convection- driven cold Flow is such that it penetrates a vertical channel in which there is upward forced-flow of warmer coolant. This situatlon is subsequently of significance to the natural convection head that determines ßow through the ieactor core. In the present experiment, we measured the penetration flow into a simulated vertikal channel and mmpared this with temperature measureinents taken at several locations. First, since the temperature nid velocity signals were qualitatively vely similar, temperature ineasurements were deemed sufficient in order to identify penetration ßow. An experimental correlation describing the penetration depth based dimensionless numbers characterizing the operating conditions was derived. Secondly, we are presently investigating the nature of the penetrating ßow itselt which appears to be detemüned by a local balance of inertiai and buoyant (turbu)ent) flows. Figure 1 shows the schematic and one typical result.
2. in vestigation of jetting flow of one cold Jet surrounded by two hotJets. (THERMAL STRIPING)Thermal striping refers to the phenomenom of thermal stresses induced on reactor components and structures as a result of contact with random streams of poorly mixed cold and hot coolant. One example is the above-core structure from flow of hot/cold streams coming out of the core in a LMFBR. Since the thermal fatigue of such components arid their locations are generally known, understanding the thermal mixing (or non-mixing) of buoyant and forced-fiow jets is importanl to the safe design of the reactor. As experiment in water consisting of UVP measurement of a cold planar jet surrounded by two hotter jets is being conducted. An analysis of preliminary data has been done with a traversing thermocoupJe array and the UVP. Additional 2D and 3D meanirements with an ultrasound probe away are underway. One sample result from preliminary measurements and a schematic of the experiment are shown in Figure E.
3. US-transduc er testing in pip e flow in sodium measurement oftransient.A high-temperature, ultrasound transducer development program for use in sodium is being undertaken at PNC. A simple vertical pipe flow within a sodium loop facility is used as the testbed for various transducer designs. Velocity measurementstaken with theand indiœte thata sufficient concentration of impurities ßowing with the sodium, velocity profiles can so far be measured at 300'C. Additional tests at higher temperatures will be performed. Furthermore, we have demonstrated that the UVP can adequately follow a pump-coastdown in our experimental loop. A schematic and one sample result is given in figure 3.
4. Study af vortex dynamics in water.

In a FBR, the entrainment of cover gas situated above the free surface, into the circulation loop is of concern, since the ingested gas may cause operational transients inside the reactor core’s flow channels. One recognized entrainment mechanism is by vortices generated in the vicinnity of protruding structual components (oCt of the free surface); that is, sufficiently energetic vortices may ingest cover gas and transport this into the circulating flow loop. In an basic experiment investigating the liquid velocity Ee1d associated with a vortex generated by stirring or

a given volume of ßuid, the

is used as the measurement tool. Fife 4 shows the experimental apparatus and a sample preliminary result.

S. Con vectiv e heat transfer in 4 sub-channel and 37-pin bundle

geometries

In connective heat transfer of coolant dow through tube bundles, the existence of flow blockages poses safety questions. Additionally, if the blockage is porous and participates in the heat transfer process, the safety criteria may be different than when the blockage is impermeable. Figure 5 shows representative scEematics of two ongoing convective heat transfer experiments in which there is a flow blockage in the flow path. The 4 sub-channel experiment focuses on the 4 sub-charinels deáneô by a triangular flow chamiel (cross-section) with four (partial) pins and a blockage in the central region. The objective here is to meæure the local œnvective heat transfer within these 4 sub-channels. lõ tire second experimenl, the global for characteristic of a 37-pin bundle, enclosed in a hexagonal vertical chamiel (the full-scale geometry of the 4 sub-channel counterpart), is being investigate with the blockage along one

of the hexagon (see shaded

Each of the 37-pins addiiiona1ly has a wire-spacer wound along its length in order to promote swirling how. This flow and that around the blockage are being investigated by both a laser Doppler anemometer (LDA) and a UVP vclocimetry.

Gne example UVP velocity profile of flow above the blockage is prmenled.

6. Inter-wraxk*• flow(IWF) and łieat transfer

In the present design of the FBR, the fuel pins of the reactor are placed òiside a hexagonal enclosure

conveniently called a wrapper . A large number wrapper cans in tuni comprise the reactor

When thermal energy is transported out of the core by the coolant, it exits into an upper volume mlled an upper- plenum. Here the hot Duid can be moled by heat exchangers (DI-Œ, liquid-tœliquid) and may flow back to a lower plenum beneath the core. It has been shown that, under certain thermal-hydraulic conditions, the inter-wrapper connective heat transfer contributes a significant amount to the heat removal capability of the reactor’s cooling system. This has been attibuled to the inter-wrapper flow (IWF); that is, convective heat transfer amongst the wrapper mns. In order to quantify convective cooling by IWF, a sector model of the relevant geometry is being constructed. A top view and a representative side-view is shown in Figure 6. It is our objective in this experiment to use the

for: 1) loml measurements, 2) cross correlational measurements and 3) regional, 2D and 3D, UVP measurements.

Fip•ure la) Schematic of COPIES test section with TCs and UDP-TDX. Cord liquid now’s irom colling box io veriical channel which has upward, heated ßoiv. ß) E:iample ve!ociiy profile of penetratinp• ßow.

Figure 4a) Schematic of vortex apparatus with multi-probe arranp•ement. b) E.xample v•1ociix profile.

Side New

O O

Figure 5a) Isometric view of both the 4-subchanne1 and a segment of lhe pin-bundle with wire-spacers, as well as a cross-sectional view of the 37-pins with a blockage. b) Example velocity profile of the wake rep•ion above the blockage.

Figure 6 Top-down view of the sector and a schematic view of the iWF iesl apparatus for natural circulation tests. There is another arrangement for forced circulation. One UY'P will be used in various regions

' TEST FAC I LITY

NATURAL C IRCULATION TEST