Environmental Engineering Reference
In-Depth Information
1. causes for beynd-design states of tube bundles arising during operation
were defined;
2. the target function of the system for ensuring of integrity of the heat
exchanger tubes during operation was defined, taking into account the
capabilities of modern technical means and technologies;
3. analysis of existing nuclear power technologies and practices ensuring
integrity of heat exchanger tubes envisaged primarily in SG operating
manuals was performed; effectiveness of these measures was evaluated
and based on the results of the work performed were used to design the
structure of the system ensuring integrity of the heat exchanger tubes in
operation was not affected;
4. the individual elements of the system were upgraded to ensure the
integrity of the heat exchanger tubes up to the state in which the system
can fulfil its function (purpose).
Causes of damage in the heat exchanger tubes of SG1, SG3, SG44 of
unit No. 2 of the Balakovo NPP were analyzed by retrospective network
modeling 5,149,etc . Figure 9.26 shows the course of analysis in the systematised
form, using the data described above, as well as the results of additional
calculations.
In the first stage the main characteristics of damage to the heat exchanger
tubes of SG1, SG3, and SG4 in unit No. 2 of the Balakovo NPP, as well as
the information from other blocks (if it was important), were processed. One
of the main criteria for correct analysis is the condition that these (this)
cause (causes) explain all the features of damage and the damage process.
Hypotheses about the causes (mechanisms) of damage were defined in
the second stage. All hypotheses formulated at meetings of working groups
and other meetings to discuss the steam generator of unit No. 2 of the
Balakovo NPP (8 hypotheses) were considered.
The third stage included analysis of the facts, the survey data,
calculations, the results of experimental analysis, and other circumstances
that could prove or disprove a particular hypothesis.
As a result of tests carried out in stages 3 and 4, it was found that the
root cause of damage such as pits and pits with cracks is the transfer of
corrosion products from the condensate feed circuit and their accumulation
in the form of deposits and sludge.
Accumulation of corrosion products from the condensate feed circuit in
combination with products which arrived as a result of suction, as well as
short-term violations of water chemistry were the cause of damage such
as cracks (Fig. 9.26).
The development of damage over time is described schematically in
Fig. 9.27. The time when the first of damage to the heat exchanger tubes of
SG1, SG3 and SG4 (1992) was caused is approximate and may be specified
by additional studies.
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