PBL2 Phase1 Assignment A2

The main causes of degradation of Steam Generators in the reference and the analysed plants are the following. Choose the wrong statement

• Denting was crucial in all events
• All designs include U-bend tubes
• All designs include anti-vibrations bars
• All SGs have problems of tube corrosion

The main causes of degradation of Steam Generators in the reference and the analysed plant are the following. Choose the wrong statement.

• The U-bend zone is the most sensitive area of tube bundle due to residual stress during manufacturing process
• Replacing anti-vibration bars during refuelling outage is not possible
• All tubes are made of Inconel-600
• All SGs had PWSCC (primary water stress corrosion cracking)

To preserve analysed plant SGs, the following actuations can be carried out. Choose the wrong statement

• Secondary side cupper elimination
• pH control between 9.3 and 9.6
• Continue with AVT (all volatile treatment ) using ammonia (NH3) for pH control
• Replacing anti-vibration bars to avoid high fretting

To preserve analysed plant SGs, the following actuations can be carried out. Choose the wrong statement

• Replace the material and condenser design
• Increase blow down capacity
• Use shoot-pinning in tubes with smaller radius
• Chemical cleaning in SG

After having plugged a 10% of tubes of the SGs in the analysed plant. Choose the wrong statement

• No adjustments in controls are strictly needed
• Vessel Delta-T has slightly increased
• Thermal power is no more fully extracted
• Secondary pressure has decreased

Increasing reference temperature (in the previous situation) about 1 K could lead the plant to a new stability with. Choose the wrong statement

• higher stable secondary pressure
• A slight closure of turbine valve
• The recovery of the capability of facing small load oscillations
• A reduction of main feed water pumps speed

Decreasing heat exchange surface in a plugged S. Choose the wrong statement

• Makes more crucial transients with primary side heating
• Results in higher pressure drops in primary system
• Makes less crucial transients with excessive cooling
• Has an impact on secondary heat extraction