Materials-related problems faced by light water reactor (LWR) operators and corresponding research needs - Materials' Ageing and Degradation in Light Water Reactors - page 322

Steam line

Containment
cooling system

3 Steam
generator

4

Control
rods

Reactor
vessel

Turbine
generator

Heater

Condenser

Condensate
pumps

2

Coolant loop

Core
1

Feed
pumps

Reactor
coolant
pumps

Demineralizer Pressurizer

Emergency water
supply systems

9.2 Graphic of the typical pressurized water reactor. (Published in
NUREG -1350, Volume 23, August 2011.)

￿ ￿ ￿ ￿ ￿ ￿

operation the cladding and other fuel assembly components operate under
very extreme conditions. These components are constantly bombarded by
neutrons (~10 12 neutrons/cm 2 /s), at moderate temperatures (~250-340°C),
pressures (~15.5 MPa), mechanical conditions (boiling surfaces, high veloc-
ity two-phase fl ow with large amounts of vibration), and chemical condi-
tions (up to ~2000 ppm of boron and up to 10 ppm Li for PWRs).

9.2.1 Understanding the fuel

A stable UO 2 fuel structure holds up most of the fi ssion products and even a
fair amount of the fi ssion gases (up to ~90%) in the pores of the UO 2 pellet.
Even though UO 2 pellets undergo a signifi cant amount of cracking due to