Environmental Engineering Reference
In-Depth Information
Operating life, years
9.33
Curves of integral probability of finding tubes with leaks:
1) prior to SPM 96; 2) after plugging defective tubes during SPM
96, without washing the tube bundle; 3) after plugging defective
tubes, washing the tube bundle and operation in boiler water with
nominal parameters.
Safe operation of tube bundles 2SG1, 2SG3 and 2SG4 was evaluated
taking into account the limited detectability of defects by ECT. Safe
operation means that the integrity of the HETs with sudden fracture of one
or several tubes with leakage from the primary to secondary circuit greater
than 5 l/h cannot take place. The analysis results described above show
that sudden appearance of such a leak can be the result of a combination
of the following events:
Normal operation at nominal conditions + propagation of a large crack
in one or more HETs with the leak of less than 5 l/h due to bl21ckage of
the tube by its corrosion products and (or) because of the special form of
the crack + sudden break of the steam line with the steam pressure drop in
the second circuit to 0 at a pressure in the primary circuit
p
HT1
= 17.64 MPa.
As shown by the calculations of critical crack dimensions, the regime
of hydraulic testing with the pressure
p
HT1
= 24 MPa,
p
HT2
= 0 is a more
stringent regime for the identification of tubes with large cracks compared
with the above scenario.
Due to HT, detection of pipes with leaks revealed by HT, and plugging
of one or several pipes, sudden rupture of one or several tubes becomes
impossible. At the same time, the growth of critical cracks in the HT mode
to critical cracks in the NSC mode + steam line fracture is nine heating-
cooling cycles. The influence of hydraulic pressure on the time period of
absolutely safe operation is shown in Fig. 9.34.
This shows that the control of leakage with reactor shutdown at a leak
of 5 l/h also allows timely crack detection before cracks reach the critical
Search WWH ::
Custom Search