Primary circuit and reactor core T-H characteristics determination of WWER 440 reactors
The VVER-440 nuclear fuel vendor permanently improves the assortment of produced
nuclear fuel assemblies for achieving better fuel cycle economy and reactor operation safety.
During unit refuelling there also could be made some other changes in hydraulic parameters
of primary circuit (change of impeller wheels, hydraulic resistance coefficient changes of
internal parts of primary circuit, etc.). Therefore it is necessary to determine real coolant flow
rate through the reactor during units start-up after their refuelling, and also to have the skilled
methodology and computing code for analyzing factors, which affecting the inaccuracy of
coolant flow redistribution determination through reactor on flows through separate parts of
reactor core in any case of parallel operation of different assembly types. Computing code
TH-VCR and CORFLO are used for reactor core characteristics determination for one type of
fuel and control assemblies and also in case of parallel operation of different assembly types.
The code TH-VCR is able to calculate coolant flow rate for different combinations of three
different fuel assembly channel types and three different control assembly channel types. The
CORFLO code deals the area of the reactor core which consists of 312 fuel assemblies and 37
control assemblies. Regarding the rotational 60 o symmetry of reactor core only 1/6 of reactor
core with 59 fuel assemblies is taken into account. Computing code CORFLO is verified and
validated at this time. Paper presents some results from measurements of coolant flow rate
through reactors during start-up after unit refuelling and short description of computing code
TH-VCR and CORFLO with some calculated results.