International Symposium (NDT-CE 2003)Non-Destructive Testing in Civil Engineering 2003
|Start > Contributions >Posters > Case Study:|
INTEGRATED LEAKAGE RATE TEST
Csaba Nyárádi, Paks, Hungary
|Fig 1: Confinement building with the Bubble Conde.|
The confinement's wall is the third border between the nuclear radiation's source and environment.
Shape of confinement is extremely complicated, it has a lot of small compartments having corner joint welded on liner.
Thickness of concrete is 800÷1500 [mm]. Thickness carbon steel liner 6÷8 [mm], welded with hermetic joints.
Around steam generator box the carbon steel liner is on the outer side of concrete- include rector compartment -, elsewhere on the inner side.
External dimensions of confinemet building:
|lower stage:||- 06,50 [m]|
|higher stage:||+ 50,40 [m]|
|net volume:||50 000 ÷ 52 000 [m3]|
Containment characteristics during the normal operation:
|Pressure:||- 2 [mbar]|
|Relative humidity:||20÷30 [%]|
Containment characteristics during the Designed Base Accident case:
|Max temperature:||127 [°C]|
|Max pressure:||0,25 [MPa]|
|Max. relative humidity:||100 [%]|
|Overpressure's time:||12 [min]|
There are about 400 hermetical penetrations for different technological pipes - steam, feedwater, cooling materials, sample, measuring purpose -, wiring to control and checking processes, cables for power supply through the liner, four compartment with airlock doors for personal traffic, 32 sealed equipment hatches, one reactor dome, and some different hermetic closures.
The leakage of confinement is strictly limited, which is one of the fundamental conditions of plant operation. Hungarian Nuclear Authority determines the maximal leakage rate and the error of measure.
The base of this limitation is the inhalation of radioactive methyl-iodine by a subject on the border of a ring has a radius3 [km] near power plant at the Designed Base Accident.
To assess the integrity of the confinement, the utility has to determine the leak rate of the confinement, even there has been a locally uncontrolled hole opened on the barrier of hermetic volume.
Outage for maintenance and refueling is a typical occurrence.
We had carried out a leakage test in full designed pressure - 250 [kPa] - at first start-up phase, and we had measured deformation of walls most loaded by pressure. We had measured the leakage of confinement at three level gauge:
120, 170, 250 [kPa]
We generated the leakage rate curve by pressure and leaka rate from database of first measure. We calculated coefficients for the extrapolation from low pressure to maximal gage by leakage curve. Repeated ILRT are achieved on pressure 120 [kPa].
We had managed a leakage test at 170 [kPa] on each unit in 1994÷1997.
We use two point method , while pressure drops. The first ILRT was term 24 hours at each pressure level, repeated ILRT requires measuring time 6 hours.
We can characterize the volume of hermetic compartment by
We monitories the mean physical parameters of air closed in hermetic volume.
We generate this quantity as average of measured data counted average by volume proportion.
The two point method calculates with the mass of closed air at the first and last measuring point.
The instruments used for test:
|temperature||PT-100 resistant thermometer|
range: 0 ÷ 100 [°C]
accuracy : 0,1 [%] for full scale
|relative humidity:||Ahlborn FH9716-51B capacity method|
range: 20 ÷ 100 [% RH]
accuracy: 0,1 [%] for full scale
|pressure:||RUSKA 6220-1 absolute pressure gauge meter|
range: 0 ÷ 260 000 [Pascal]
accuracy 10-4 [%] for full scale
|data compiler||Ahlborn THERM 5500-3. V4.5|
Company management has decide shortening the outage time. It has assigned a duty to staff of ILRT.
We measured the mass of filling air while pressurized confinement due ILRT to determine net volume of hermetic compartment at each unit.
We decided developing this method based on experiences gained due measuring processes.
FASO method suppose that,-if the pressure of compartment is stabile, while we charge pressure air to space - the quantity of feed air end leakage are equal. Scheme of principle you can see on picture 3.
We has have produce a measuring system according to assumption of accuracy and responsibility. Requires range to realise task is 20 ÷ 900[kg/hour].
We selected the measuring edge and measuring flange. It has have made three measuring pipeline overlapping range between them. You can see the arrange of pipelines and measuring part on picture 4. The measuring process assemblages three part.
First of all we pressurize hermetic volume to 120 000 [kPa]. After a stabilization period starts the measuring process.
First step is a short measure with method loss of mass to determine leakage rate approximately. We can get possibility to count the quantity of feed air required.
The next action is to adjust the airflow, while overpressure keeps at 120 000 [Pa].
The last measure intervention is measuring airflow.
At the end we calculate leakage rate of actual process.