FUEL CYCLES OF VVER-440
22nd Symposium of AER on VVER Reactor Physics and Reactor Safety (2012, Průhonice, Czech Republic)
CORE DESIGN, OPERATION AND FUEL MANAGEMENT
Abstract
This paper presents the current status of the development and VVER-440 fuel
assemblies (FA) modernization as well as VVER-440 nuclear fuel cycles update are
performed lately. The studied and the embedded innovations of the improved neutronics and
operational characteristics are coincided. Discussions were held in relation to the operation of
the reactor at 100% power in a steady state refueling. As an example of using the new
development we demonstrates a program of operation experience with RK-3 and some
numerical results are compared with measurements.
In spite of the fact that the VVER-440 has been present on the market for 40 years ago
it is still subjected to upgrading in order to improve the economic parameters of the fuel cycle
and increase the fuel reliability during its operation. In the process of VVER-440 gaining
operation experience 1, numerous advancements of fuel assembly (FA) design
characteristics have been realized 2. Achievement of these advancements required the
constant upgrading of existing FA designs to increase their service life, improve their
operational reliability and reactor safety and economics of fuel cycle (Table 1). A big effort
has been made in the reactor community to reach these goals. Below we show the effect of
these advancements and modifications on the neutronics and operational characteristics for
the initial and end of the modernization stages (Table 2 and Figure 1-6).
Now it is clear that improvement strategies refueling and development of the neutronic
codes helped to optimize the core load. This allowed to increase the fuel cycle economy and
to substantiate the overload (in-in-out) type scheme which provides to lower neutron leakage
from the core and to decrease the radiation load on the reactor vessel.
Advancement of the FA base design allowed to significantly improve fuel efficiency
by:
- using of zirconium spacer grids and reducing of FA shroud tube thickness resulting to the
increasing FA multiplication factor;
- grading of fuel enrichment in the cross-sectional plane of FA thus reducing a peaking
factor of linear fuel pin powers and ensuring by this a lightened realization of core loads
with reduced neutron leakage;
- increasing of initial enrichment of fuel feed and reducing of fresh fuel replaced during fuel
reloading;
- using of burnable gadolinium (Gd2O3) poison integrated with fuel ensuring desirable fuel
load arrangement and leading to improvement of load safety;
- raising the average fuel enrichment up to 4.87% and the application TVEGs;
- increasing the amount of fuel in the fuel elements by increasing the diameter of the fuel
pellets to 0,78 cm, excluding the central hole in tablets and replacing the cover on the nonshrouded design, increasing the spacing between fuel rods to 1,26 cm
- fuel assembly of the Third generation;