Environmental Engineering Reference
In-Depth Information
successive settlement of the raft foundation measured during past years.
The settlement at Unit 4 is somewhat larger than at Units 1-3, which is due
to the slight in homogeneity of the subsoil and the highest alteration of the
level of the water-table, occurring in the vicinity of Unit 4.
Detailed analyses have been performed for the subsidence and differen-
tial settlements of the main reactor buildings for the end-of-life situation
taking into account the static loading (immediate settlement), groundwa-
ter fl uctuation, seismic settlement, dynamic settlement due to machinery
and tectonic subsidence. The calculation model and procedure has been
calibrated to the measured time-history of subsidence. An appropriate con-
stitutive model has to be defi ned for the soil, which includes the develop-
ment of a non-linear hardening model and proper defi nition of the decay
curve for cyclic loading due to groundwater fl uctuation based on soil tests
results.
In regard to LTO, the analyses show that a value of differential settlement
that may cause non-allowed tilting of the RPV axis due to the inclination of
the building should not be expected. The structural integrity of the founda-
tion and the containment part of the main building structures is not affected
by the settlement and is not expected as a result of further subsidence.
Basic fi ndings of the revalidation/reconstitution of the TLAAs
Dedicated ageing management programmes already control some of the
processes addressed by the time-limited ageing analyses presented above,
for example the process of settlement of the main building and erosion-
corrosion of piping wall. The results of the above analyses show that only a
few non-compliances or lifetime-limiting cases have been found and all of
them can be managed by the extension/amendment of the existing ageing
management programmes and/or other plant programmes. For example, in
relation to RPV and internals the stud joints fi xing the polygon mantle to
the core basket are the critical structures from the point of view of irradia-
tion-assisted stress corrosion cracking and void swelling. In order to man-
age these mechanisms, review and extension of the present programmes are
ongoing. Regarding operational limits and conditions for injection into the
pressurizer, the margin to allowable stresses is minimal and the number of
allowable cycles is rather small; consequently, the number of cycles should
be monitored. It was also found that during certain heat-up and cool-down
processes the averaging intervals of the temperature measurements have
to be modifi ed at certain components. With respect to the containment civil
structures the existing ageing management programme should be extended
for managing the change of material properties of heavy concrete structures
and for the corrosion of the steel liner on a heavy concrete surface.
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