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 305

Maximum defect size, %

9.25 Probabilities of large-scale failure of heat exchanger tubes
in relation to the maximum defect size for steam generator No. 4:
1) realistic appoach; 2) conservative estimate; 3) permissible level.

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Table 9.10 Justification of serviceability of steam generator heat exchanger
tubes of VVER-440 reactors

Minimum permissible defect depth, %
Novovoronezh NPP

Steam generator
No.

Kola NPP

Unit No. 3 Unit No. 4 Unit No. 1 Unit No. 2

1 60 79 67 67

2 58 71 68 67

3 61 67 69 66

4 55 70 65 68

5 60 74 76 65

6 63 58 75 65