
ISSN 10637788, Physics of Atomic Nuclei, 2011, Vol. 74, No. 14, pp. 1908–1911. © Pleiades Publishing, Ltd., 2011.
Original Russian Text © M.N. Zizin, S.N. Zizina, L.V. Kryakvin, V.A. Pitilimov, V.A. Tereshonok, 2010, published in Voprosy Atomnoi Nauki i Tekhniki. Seriya: Fizika Yadernykh
Reaktorov, 2010, No. 3, pp. 43–47.
1908
The choice of kinetic parameters and the method
for their estimation substantially influence the reactiv
ity in processing signals from ionization chambers
obtained during transient processes; this influence is
especially pronounced for the scram system effective
ness. Here, the kinetic parameters are the relative
yields
α
i
of delayed neutrons and the constants
λ
i
of
decay of delayed neutron precursors.
This study analyzes the influence of kinetic param
eters on the value of scram system effectiveness
obtained using the inverse solution of the kinetic equa
tion with the use of ionization chamber currents
recorded in the course of measurement of the scram
system effectiveness. The measurements were per
formed for the first fuel load of the third unit of the
Kalinin nuclear power plant in the case of operation at
a minimum controllable power level at the stage of
physical startup [1].
The reduction of the scram system effectiveness on
February 12, 2005, at 9 a.m. (
t
= 362.6 s) when the rod
13–36 (ninth group) was stuck and then sent in 20 s
later was considered. The corrections to the back
ground current were 0.190
×
10
–10
, 0.180
×
10
–10
, and
0.105
×
10
–10
for ionization chamber nos. 3, 14, and
25, respectively. The scram system effectiveness was
calculated using a program written in MathCad. This
program implements the integral form of the inverse
solution of the kinetic equation according to the algo
rithm described in [2]. The calculations were per
formed with and without the background current
taken into account.
The results of calculation were verified using a pro
gram written in Fortran; this program implements the
same integral algorithm. The results of calculations
performed by S.V. Tsyganov also completely agreed
with our results. The differential algorithm was also
implemented; the calculations using this algorithm for
smooth curves yield the same result under the condi
tion that a finer time step is used. The differential algo
rithm cannot be used for processing experimental
data. Thus, the correctness of implementation of
numerical methods in the programs was proved by the
complete agreement of the results obtained using sev
eral programs for the same initial data.
One of the aspects of the problem is taking into
account the isotopic composition in calculation of the
parameters of delayed neutrons. The sets of kinetic
parameters for fissionable isotopes differ for different
nuclides. This causes difficulties in formation of the
set of kinetic parameters for the real fuel, in which fis
sion takes place simultaneously in several nuclides.
For thermal reactors, a heterogeneous multigroup
cell calculation is usually performed; the homoge
neous fewgroup cross sections are prepared on the
basis of this calculation. At this stage, the kinetic
parameters should also be prepared; these parameters
are then used in space–time calculations. The same
parameters can be used in processing ionization
Calculation of Reactivities Using Ionization Chamber Currents
with Different Sets of Kinetic Parameters for Reduced Scram System
Efficiency in the VVER1000 of the Third Unit of the Kalinin Nuclear
Power Plant at the Stage of Physical StartUp
M. N. Zizin
a
, S. N. Zizina
b
, L. V. Kryakvin
b
, V. A. Pitilimov
b
, and V. A. Tereshonok
b
a
Russian Research Centre Kurchatov Institute, pl. Kurchatova 1, Moscow, 123182 Russia
b
JSC VNIIAES, ul. Ferganskaya 25, Moscow, 109507 Russia
Received February 18, 2010
Abstract
—The effectiveness of the VVER1000 reactor scram system is analyzed using ionization chamber
currents with different sets of kinetic parameters with allowance for the isotopic composition in the calcula
tion of these parameters. The most “correct, aesthetically acceptable” results are obtained using the eight
group constants of the ROSFOND (BNABRF) library. The difference between the maximum and minimum
values of the scram system effectiveness calculated with different sets of kinetic parameters slightly exceeds
2
β
. The problems of introducing corrections due to spatial effects are not considered in this study.
Keywords
: VVER1000, scram system effectiveness, BNAB78, BNAB90, ENDF/B6, ENDF/BVII.0,
TVSM, BNABRF.
DOI:
10.1134/S1063778811140110