Research and Development of Advanced Nuclear System

2-2

Measurement of Temporospatially Fluctuating Flow
－ Development of Ultrasonic Flowmeter for Fast Reactor －Table 2-1 Comparison of main specifications of prototype
and commercial fast reactors in Japan

Piping B

In commercial reactor design, high-chrome steel with low thermal
expansion is used for piping, and the pipe drawing is shortened. Further,
the flow velocity is increased because the loop number is reduced.

Heat Exchanger

Specification
Electricity output
Piping material
Number of loops
Flow velocity

Piping A(InstallationPosition)

Reference Flowmeter0.175Flow Velocity

Example Installed
1 Flowmeter Pair

Average flow rate (m3/s)

SensorAs one of the fundamental engineering tasks towards
commercialization of a fast reactor cycle technology, aflow rate measurement technique for the sodium coolant isdeveloped. The development requirements and investigation
results are presented below.
As shown in Table 2-1, because the piping material is anonmagnetic stainless steel, an electromagnetic flowmeter has
been used as the flowmeter in fast reactors that use a liquidmetal, such as the prototype reactor “MONJU”. However,
because the piping material in a commercial reactor is a highchrome magnetic steel, which can shorten the required piping
length, the electromagnetic flowmeter cannot be applied. Inaddition, the flow velocity is increased to reduce the loop
number and simplify the heat transport systems. Because of theshort straight pipes and high velocity, the flowmeter needs tomeasure a flow that exhibits greater temporospatial fluctuation
than before. Because an examination of the flowmeter underfluctuating flow conditions and with high-chrome steel pipes
revealed that an ultrasonic flowmeter was most suitable, its
applicability was investigated experimentally.
A schematic of the test loop is shown in Fig.2-5. Because
the test loop can circulate water at a flow velocity comparable
to that in a commercial reactor, the flow condition of a

：1 pair：2 pairs

Commercial
1500 MWe
High-chrome steel
29 m/s：4 pairs：Reference

0.170
0.165
0.160
0.155
0.150
0.48

Fig.2-5 Test loop of ultrasonic flowmeter
Several pairs of ultrasonic flowmeters were set in a water
test loop to examine their applicability to a temporospatiallyfluctuating flow. The parameters are the position and number offlowmeters used to measure the instantaneous velocity profilein the fluctuating flow.

Prototype
280 MWeSUS
36 m/s

0.52

0.56

0.60

0.64

Installation position (m)Fig.2-6 Measurement characteristics depending
on installation position and number of ultrasonicflowmeters
Increase in number of flowmeter pairs resulted inconstant flow rate even near the nozzle (highlyfluctuating flow).

temporospatially fluctuating flow can be simulated. Although
the flowmeters are installed in piping A and B at the outlets
of a heat exchanger, the measured flow rate should preferably
be independent of the installation position to increase thelayout design flexibility. Then, the installation position andthe number of ultrasonic flowmeters (which corresponds tothe measured instantaneous velocity profile in the pipe crosssection) were changed, and the flow rate measurement wastested.
A test result is shown in Fig.2-6. For one or two pairs offlowmeters, the measured flow rate varied with the installation
positions relative to the heat exchanger outlet. On the other
hand, for four pairs of flowmeters installed at intervals of 90 °in the circumference angle, the position dependency of themeasured flow rate was reduced, and the flow rates were thesame as that measured by the reference flowmeter. This result
indicates that the ultrasonic flowmeter can be applied to thetemporospatially fluctuating flow.
The present study was performed under a contract with
Mitsubishi Fast Breeder Reactor (MFBR) Systems, Inc., aspart of a study that was entrusted to MFBR Systems, Inc.,by the Ministry of Education, Culture, Sports, Science andTechnology of Japan (MEXT).

Reference
Hirabayashi, M. et al., Development of Ultrasonic Flowmeter for Sodium-Cooled Fast Breeder Reactor −Applicability Verification of Multi-Path UltrasonicFlowmeter−, Jikken Rikigaku, vol.12, no.4, 2012, p.391-397 (in Japanese).
JAEA R&D Review 201335