■ Oarai Research and Development Center

Development of Experimental Techniques / Facilities at JAEA R&D Centers14-6 Measuring Displacement and Vibration of High Temperatureand High Radiation Components Using Optical Fiber–Development of Fast Reactor Integrity Monitoring Technology–
Calculation
Measurement

FBG

Reactor power (MWt)

Spectrum analyzer

Displacement (%)

SLD light source

Optical fiber

Reactor power

FBG
Primarypump

Measurement date

ReactorPrimary cooling system area
Fig.14-11 Experimental setup of measurement systemusing optical fiber in the “JOYO” primary cooling area
A few FBGs were combined into a single fiber, and mounted
on the piping supports. In the measurement, a wideband light
was injected into the optical fiber, and then the wavelengthof reflected light from FBGs was scanned with a spectrum
analyzer.

In the sodium-cooled fast reactor (SFR), circulating pumps
and several piping support systems were installed aroundthe primary cooling system piping. How to efficiently andaccurately measure the displacement and vibration in hightemperature and high radiation components is important,in order to monitor the SFR structural integrity. In theexperimental fast reactor “JOYO”, displacement and vibration
measurements of the primary cooling system were carried out
using Fiber Bragg Grating (FBG) to resolve this challenging
issue (Fig.14-11).
FBG is an optical fiber sensor, which reflects light at a
specific wavelength. Temperature variations or displacement
applied to the FBG causes the reflected wavelength to shift.
The FBG is a simple instrument, because several FBGs can becombined in a single fiber.
Displacement can be evaluated from a wavelength shift Δλ1of the FBG with both-ends fixed. However, Δλ1 includes
a wavelength shift Δλ2 due to temperature variation. This
becomes to be a source of displacement measurement error.
Therefore, Δλ2 of an FBG with one end fixed for detecting
only temperature variation was eliminated fromΔλ1. The

Fig.14-12 Measured displacement of the piping supportby FBG
Displacement following reactor power was successfullymeasured.

Signal voltage (mV)IHX

At the primary pump operation(flow rate:1538m3/h)
At the primary pump stopTime (ms)Fig.14-13 Measured vibration of the piping support byFBG
Vibration changes with the primary pump operation weresuccessfully measured.

measured displacement matched the calculation based on thethermal expansion. The measured result indicates that thermal
displacement of a piping support was accurately measured(Fig.14-12).
Vibration can be measured as a high frequency displacement.
A faster vibration, however, cannot be measured by aspectrum analyzer, because its sampling time is in the orderof seconds. In the measurement, the reflected wavelength shift
was converted into light magnitude using an optical filter,
and then the voltage signal corresponding to the displacement
was obtained using a photo diode. This enables a high speed
measurement of the vibration. Signal fluctuation at the primary
pump operation was larger than when the pump was stopped.
The measured result indicates that vibration due to the pump
operation was successfully measured (Fig.14-13).
The measurements were successfully conducted with nodegradation of the optical fiber up to an accumulated γ-ray
dose of 4×104Gy, corresponding to 120 effective full powerdays of operation. The measured results demonstrated thatthe FBG is suitable for the monitoring of the SFR structuralintegrity.

Reference
Matsuba, K., Ito, C. et al., Development of Fast Reactor Structural Integrity Monitoring Technology Using Optical Fiber Sensors, Journal of Power andEnergy Systems, vol.2, no.2, 2008, p.545-556.
JAEA R&D Review 2008107