5.1.1. Pressure loss test
The pressure loss coefficient is needed to design the evaluation and compatibility analysis. The pressure loss test measures the pressure loss across various components in the test section as a function of the Reynolds number. The differential pressure is measured for the 8 spans as shown in Fig. 4. The superposed differential pressure loss for each span is cross checked by the differential pressure for the fuel assembly. The pressure loss coefficient for the inlet and outlet region, the spacer grid span, and the bare bundle friction was reduced by using equitation (1).
1 2
/2
i i
K = ∆P ρU (1)
where
K is the pressure loss coefficient,
△P is the measured differential pressure loss (Pa), ρ is the the coolant density (kg/m3),
U is the bundle average coolant velocity (m/s), and subscript i means each span.
The test is to be performed by varying the flow rate at two different temperature, 40°C and 120°C as shown in Table I. The pressure loss coefficient for the core condition can be calculated by extrapolating the measured results for the core condition as a function of the Reynolds number [7].
We assure the function of the loop, sensor, and DAS system by comparing the measured pressure loss for the reference condition at the beginning of the test.
Table I. Test condition
Test Flow rate
Fuel assembly vibration 0, 3~8.2
0.3 △V temperature room
Lift-off flow rate is needed to assure the hold down spring force. The lift-off test measures the flow rate at which the test bundle is lifted from the simulated core support plate. The Lift-off flow rate is determined by detecting a sudden variation of the bottom end piece region due to a flow path change as a lift-off for the fuel assembly and also checked by detecting the acoustics by detaching the bottom end piece from the lower core simulator [8]. The lift-off test is performed at the 40°C as shown in Table I.
5.2. Vibration Test
5.2.1. Fuel assembly vibration
The frequency and amplitude of the fuel assembly is measured by the DVRT mounted on the housing at the middle spacer grid level on the 180 and 270 degrees face with a flow rate change. We judge the resonance flow rate from the measurement. Prior to installing the housing with a fuel assembly to the pressure vessel, the initial position is measured. In the loop condition, the distance between the housing wall and spacer grid is measured at a stagnation flow condition and a flow rate from 3 m3/min to the 8.2 m3/min at 120° C [9]. The fuel assembly vibration phenomenon is not highly sensitive to the temperature and flow density [10]. The test flow covers a range of possible reactor flows. The difference of the measured results between the outside of the vessel and a 0 flow rate shows the thermal expansion effect on the gap between the grid strip and housing wall. The test was performed by two methods. One is the continuous measurement and the other one is the discrete method. The continuous method means continuously increasing the flow rate from 3 m3/min to 8.2 m3/min within 2 minutes. The discrete method means a step by step increasing of the flow rate with a increment of
3
5.2.2. Rod vibration
Fuel rod excitations by the axial coolant flow and an interaction of the fuel and spacer grid support system occurs. Amplitude of the fuel rod under the condition of the flow induced vibration is an important parameter to assure the design of the spacer grid support system [11]. Amplitude and frequency of the rod under the various flow rate conditions is measured by the accelerometers inserted into the rod. The accelerometer is located at the middle spacer grid span. The test is performed under the flow rate condition from 3 m3/min to 8.2 m3/min with 0.3 m3/min increments as shown in Table I.
5.2.3. Housing & vessel vibration
Minimization of the vibration effect from the recirculation pump source is needed to measure an independent flow induced vibration. At the position expected to have the high amplitude, the amplitude is measured at the flow condition from 3 m3/min to 8.2 m3/min with 0.3 m3/min increments.
6. SCHEDULE
Figure 8 shows the schedule for reconstruction of the PWR hydraulic test facility. The loop control system has already been accomplished in June 2004. The functional check and repair of the components including the recirculation pump and injection pump will been accomplished by December 2004. The DAS for the hydraulic test were accomplished by June 2004 and for the vibration will be established by June 2005. The test section has already been designed and will be manufactured by the end of next year. The test fuel assembly will be fabricated by the end of 2005.
The start up test of the loop will be start in January 2005. The main test will be accomplished by June of 2006.
FIG. 8. Schedule on PWR hydraulic test.
7. SUMMARY
KAERI is performing a project on out-pile test technology development for full scale PWR fuel assembly. We have introduced the hydraulic test facility, a test assembly, test parameters, test methods, and a data acquisition system. The start up test will begin in January 2005 and the main test will be accomplished by the end of 2006. The established test facility and measuring technique will be contributed to the satisfaction of domestic needs for the design verification to improve reliability of PWR plant operation.
ACKNOWLEDGEMENTS
This work has been carried out under the Nuclear R&D Program supported by Ministry of Science and Technology in Korea.
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