Environmental Engineering Reference
In-Depth Information
Programmes have been developed for ECT, cutting out and inspecting
pipes and similar mesures were proposed to verify the corrosion state of SG
and the water chemistry regime (WCR), as well as cleaning of SG piping
to remove sediments by chemical cleaning.
A number of leaking tubes (i.e., pipes with through-wall defects) were
identified: SG1 - 45, SG3 - 39, SG4 - 42.
Leaks were identified mainly in the tubes of the lower rows: the SG1
from the 106th to 31st, the SG3 from the 110-th to 99th, the SG4 from
110th to 89th.
Eddy current testing was performed using automatic equipment
manufactured by Interkontrol with a rotating probe. The technique allowed
to define only one size of damage - in the direction of wall thickness. In
addition, the coordinate of damage along the length of the tube (from the
collector) was also determined.
The scope of inspection was determined according to 'The working
program of inspection of HET metal and SG collectors lintels of unit 2 by
Interkontrol equipment'.
The rejection damage level was set at the level of 70% of the tube wall
thickness.
The results of monitoring showed:
1) the total number of defective tubes (with the depth of the defect
greater than 70%) for SG1 was 941 out of 10 947 inspected tubes, SG3 -
431 out of 10 380 inspected tubes, PG4 - 351 out of 10 942;
2) the percentage of damaged pipes (in relation to the inspected tubes):
PG1 - 8.6%, PG3 - 4.15% SG4 - 32%;
3) the density of defective tubes in the lower part of SG is significantly
higher than in the upper part, as evidenced by the results of the first stage
of inspection: SG1 - 23.2%; SG2 - 18.0%, SG3 - 22.9 %.
4) through-wall defects detected by the pneumatic-hydraulic method,
also located in the HETs of the lower rows;
5) defects are closer to the hot collector and most of them are located
in the second semicircle;
6) defects between spacer grids are located primarily in the lower rows;
7) defects in the spacer grids are located in both the lower and the upper
rows of HETs.
The distribution of defective HETs over the rows of tubes is shown in
Fig. 9.6. After SG drying visual inspection revealed that approximately 10
of the lower rows are immersed in the sludge.
On August 7, 1996 a tube 60-96 of the second semicircle in the region
of the hot collector was cut out from SG3 by the technology developed at
the Balakovo nuclear power plant (PR-026)
The surface at a distance of 70, 90 and 130 mm from the collector
was examined on the cut-out tube. At a distance of 70 mm there were
deposits,103.6 g/m
2
, black-brown, loose, easily removed by mechanical
means. Under the deposits there was a grey oxide slick, strongly bonded
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