The VVER plants developed different types and systems of ageing management programmes:
• Overall plant AMP
• AMPs addressing a degradation mechanism
• Structure — or component-oriented AMP.
Overall plant AMP
An AMP for an overall plant can be developed and implemented for: definition of goals of the operating company, distribution of responsibilities in
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Table8.5 Identification of the ageing mechanisms for civil structures and structural components.
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Component Degradation Degradation process/ageing effect
location
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Reinforced Reinforced concrete
concrete in the hermetic compartments
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Corrosion/boric acid corrosion/ material loss
Change of material properties due to heat/decrease of strength, modulus of elasticity
Change of material properties due to irradiation
Fatigue/crack initiation and propagation
Settlement/increasing stress levels breaking, cracking
Corrosion/boric acid corrosion/ material loss
Fatigue/crack initiation and propagation
Local corrosion/material loss/crack initiation and propagation
Change of material properties due to heat/decrease of strength, modulus of elasticity
Change of material properties due to irradiation
Fatigue/crack initiation and propagation
Corrosion/material loss
Settlement/increasing stress levels, breaking, cracking
Change of material properties due to heat and/or irradiation
Corrosion/boric acid corrosion/ material loss
Change of material properties due to heat/decrease of strength, modulus of elasticity
Change of material properties due to irradiation
Fatigue/crack initiation and propagation
Corrosion/boric acid corrosion/ chemical corrosion/material loss
(Continued)
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Decontaminable
coatings
Other reinforced Reinforced concrete concrete structures
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Table 8.5 (continued)
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Component
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Degradation
location
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Degradation process/ageing effect
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Liner
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Fatigue/crack initiation and propagation
Local corrosion/material loss/crack initiation and propagation
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Coatings
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Change of material properties due to heat and/or irradiation
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Service shafts
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Carbon steel
cladding of spent fuel and refuelling pool and shaft number 1
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Local corrosion/material loss/crack initiation and propagation
Boric acid corrosion/material loss
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Syphon of refuelling pool
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Local corrosion/material loss/crack initiation and propagation
Boric acid corrosion/material loss
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Stainless steel cladding of shafts
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Local corrosion/material loss Wear, cracking/material loss
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Welds and heat affected zone of stainless steel claddings
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Local corrosion/material loss/crack initiation and propagation
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Supports and insertion elements
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Local corrosion/material loss/crack initiation and propagation
Wear, cracking/material loss
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Welds between the shaft cladding and connecting pipelines
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Local corrosion/material loss/crack initiation and propagation
Wear, cracking/material loss
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Notes: Examples are based on Hungarian regulatory guide No. 1.26.
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the organization and policy level activities, and definition of the programme system structure for ensuring the required plant condition, that is the implementation of the concept described in the introduction of section 8.4.
Several operating VVERs have utility — or even industry-level or umbrella type ageing management programmes. For example, in Ukraine the plant level programme has to be deduced from the overall one and the unit level programme from the plant level one. The overall plant AMP also includes the categorization of the SCs in accordance with safety relevance, importance and complexity. In considering the structuring and organization of AMPs, a graded approach should be applied according to the safety relevance of the
Table 8.6 Degradation mechanisms which an AMP may address
Low-cycle fatigue Irradiation damage Boric acid corrosion Local corrosion
Irradiation-assisted stress corrosion Swelling
Thermal stratification fatigue Erosion-corrosion Water hammer Deposition [16] [17]
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Table 8.7Attributes for the definition of commodity groups
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Safety classification
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Type of SSC
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Medium
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Material
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Safety Class 1
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Valve body
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Borated water
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Stainless steel
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Safety Class 2
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Pump body
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Prepared water
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Cast stainless steel
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Safety Class 3
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Pipe and pipe elements
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River/sea water
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Carbon steel
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Non-safety class,
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Heat exchanger
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Steam, gas-steam
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failure of which may inhibit intended safety function
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Tank
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mixture Acid or alkali Oil, other
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The pipelines, pipe elements (elbows, T-pieces), valves and heat exchangers can be grouped into commodity groups according to type, material and working environment. The SCs within a group have the same degradation mechanism and approximately the same operational and maintenance history. It is very reasonable to develop specific ageing management programmes addressing the ageing of commodity groups. The definition of the commodity groups is decided by applying the attributes given in Table 8.7 in all reasonable combinations.
