Environmental Engineering Reference
In-Depth Information
Operational experience is that ageing of neither the reinforced concrete
load bearing structure nor the liner would limit the LTO of the VVER-
440/213 plants.
Ageing of the containment structures of VVER-1000
At the VVER-1000 plants, ageing may affect the pre-stressing of the con-
tainment. Important ageing mechanisms of the pre-stressed containment
resulting in loss of pre-stress are the relaxation of tendons, shrinkage, creep
of steel. Requirements for the testing of the containment pre-stressing
system are defi ned both by the designer and regulation (Orgenergostroy,
1989a; 1989b). The scope of inspection should be extended if defects are
observed, and/or if average loss of tension force is more than 15%. If fur-
ther testing verifi es the results obtained, it is necessary to test 100% of the
tendons. Tendons with force losses of more than 15% should once again be
controlled after straining. If a force loss at 24 hours is more than 10%, the
tendon should be replaced.
In order to enable monitoring of the level of the containment pre-stress-
ing, measurement systems are installed permanently on the structure and
these systems measure structural deformations and pre-stressing force in
the cables. At VVER-1000 plants, detailed fi eld investigations and analyses
have been carried out for the assessment and evaluation of the condition
of pre-stressing tendons. There are design solutions for the replacement of
tendons. Thus, all existing defects leading to a loss of stressing force and
rupture of tendons have been avoided. At some plants, new pre-stressing
systems and an additional system for automatic control of stressing forces is
installed in the bundles.
8.3.4 Ageing of electrical systems and I&C
Electrical components and I&C are replaceable and the required perfor-
mance of these commodities can be ensured via maintenance and scheduled
replacement. The qualifi ed condition of the electrical and I&C equipment
has to be ensured.
Full scope ageing studies had been prepared for the Paks NPP for the fol-
lowing electrical and I&C items:
1
Equipment of electric power and transmission systems:
Bus cabinets
Overhead-line towers, medium- and high voltage insulators
LV and HV cables of power supply systems
Cables for containment electrical penetration
Cable joints and assemblies
Search WWH ::
Custom Search