Using probabilistic methods for solving the problem of ensuring leak tightness of heat exchanger tubes of nuclear power plant steam generators - Probabilistic Safety Assessment for Optimum Nuclear Power Plant Life Management (PLiM) - page 274

Table 9.1 Replacement of vertical steam generators because of
problems with heat exchanger tubes made of 600 MA alloy

Parameter USA France Japan Others

Total number of steam generators (SG) 209 198 68 175

Of these:
with HET made of 600MA 176 63 29 59

with HET made of 600TT 33 111 20 —

with HET made of 690TT 0 24 19 —

Total number of replacements 121 45 29 53

Of these:
with SG with HET made of 600TT 25 0 0 —

with SG with HET made of 690TT 93 45 29 26

with SG with HET made of 600MA 3 0 0 —

with SG with HET made of 800NG 0 0 0 10

Mean life, years 18.1 17.9 20.4 —

Maximum life, years 31 25 26 —

Minimum life, years 8 10 11 —

Basic data on changes of VSGs are shown in Table 9.1.
In Russian nuclear power plants only three SGs were replaced at nuclear
power plants with VVER-1000 reactors (Unit 2 of the Balakovo nuclear
power plant, 1999).
Of 176 (57 units) VSGs with HET of the 600MA alloy 127 SGs on 43
units were replaced in 2005 (the state at 01.01.06). By 2009, according to
published plans 122 , there would be only 5 SGs in units. Since plans often
change, the data given here refer to 55 VSGs in 20 units (4 of them were
marked for replacement in 2005 but they passed technical inspection of
the HET).
As can be seen from Table 9.2, the era of replacements of SGs with HET
made of the 600MA alloy is close to completion. Apparently, by 2010 there
will be no such SGs anywhere in the world (only a few in the U.S.). There
were nearly 350 of them. Replacement of one SG costs about $100 million.
The analysis shows that there are in fact two defect formation
mechanisms in HSG and VSG: stress corrosion cracking (SCC) and crevice
corrosion (CC). Their action is quite specific because of different HET
materials as well as their location due to vital differences in the structure.
All the mechanisms for 600MA alloy and 08Cr18Ni10Ti steel are
considered separately below.
Figure 9.1 show a localisation scheme for the mechanisms of defect
formation in the HET of the VSG in the U.SA 124 . The black box indicates
the area of occurrence of SCC in the VSG in the primary circuit. In the
USA this type of corrosion was detected for the first time at the beginning

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