THE ESTIMATION OF THE CONTROL RODS ABSORBER BURN-UP DURING THE VVER-1000 OPERATION
22nd Symposium of AER on VVER Reactor Physics and Reactor Safety (2012, Průhonice, Czech Republic)
Advances in spectral and core calculation methods
The isotopic composition of the control rods absorber is changing under the neutron
flux influence, so the control rods efficiency can decrease. In the VVER-1000 control rods
boron carbide and dysprosium titanate are used as absorbing materials. In boric part of the
control rods the efficiency decreases due to the 10B isotope burn-up. In dysprosium part
dysprosium isotopes turn into other absorbing isotopes, so the absorbing properties of this part
decrease to a lesser degree.
For the estimation of the control rods absorber burn-up two models are developed:
VVER-1000 three-dimensional fuel assembly with control rods partially immersed (imitation
of the control rods? operation in the working group) and VVER-1000 three-dimensional fuel
assembly with control rods, located at the upper limit switch (imitation of the control rods?
operation in groups of the emergency shutdown system).