NUCLEAR FUEL FOR VVER-440 REACTORS

Water-water energy reactor VVER-440 is a pressurised water reactor where water acts both as coolant and moderator of neutrons.

VVER-440 fuel is manufactured and supplied in fuel assemblies (FAs) designed to generate thermal energy and pass it over to the coolant flow (i.e. water) in VVER‑440 core. VVER-440 core is comprised of FAs ans rod cluster control assemblies (RCCAs) that include meat and absorber extension. During reactor operation FAs are held in fixed position. FA consists of fuel rods (FRs), spacer grids, shroud tube, headpiece and tailpiece. RCCA meat by design is similar to FA design, the difference lies in head- and tailpiece structure.

VVER-440 reactor operation provides considerable flexibility of fuel cycles:

I — ADVANCED 3-YEAR FUEL CYCLE

When using this cycle, reactor may operate at weekly power maneuvering (within 70-105 % range of rated capacity);

II — 4-YEAR FUEL CYCLE allows to obtain a more substantial gain, both in uranium consumption as well as in the quantity of manufactured, transported and stored FAs. In this case it is also possible to operate the reactor with weekly power maneuvering;

III — 4-YEAR FUEL CYCLE AT 105% REACTOR POWER should be considered as evidence of the possibility to organise the core operation with the increased capacity factor, which may substantially improve economic indicators of unit operation;

IV — 5-YEAR FUEL CYCLE at 108% power, as compared to 4-year fuel cycle, allows to additionally reduce effective comsumption of naturally enriched uranium and quantity of manufactured, transported and stored FAs. This cycle allows to use U-Gd fuel;

V — FUEL CYCLE WITH 18-MONTH RELOADS

Unit 4 of Paks NPP is currently in the process of implementing the fuel cycle with 18-month reloads.

In 2002 JSC MSZ started to manufacture 2^nd-generation FAs for stage 2 VVER‑440 reactors (V-213). In addition to reliability margin these FAs allow to increase VVER-440 reactor power by 5-8%, which is currently realised at NPPs in the Czech Republic, the Slovak Republic, Hungary, and Russia (Kola NPP). In 2005 JSC MSZ started to manufacture the so called “shockproof” 1^st‑generation FAs for stage 1 VVER‑440 reactors (V-230). These FAs are characterised by increased reliability. In 2010 twelve (12) 3^rd-generation FAs – shroudless skeleton-type design with increased loading within 6-year fuel cycle during seven years ‑ were manufactured for and put to pilot operation at unit 4 of Kola NPP.

Specifications

Indicators	Fuel cycle type
	Full core			Core with shield assemblies
	Advanced 3-year	4-year	5-year without U-Gd fuel /5-year with U‑Gd fuel	Advanced 3-year	4-year
Thermal reactor power, MWt	1375	1375	1485	1375	1375
Coolant pressure at reactor outlet, MPa	12.26
Average coolant temperature at core outlet, 0С	265…270
Maximum coolant temperature at FA outlet,0С	317
Number of FAs in core, pieces	349	349	349	313	313
Total U mass in core, tonnes	41.8	41.8	41.8	37.4	37.4
Time interval between fuel reloads, months	12	12	18	12	12
Number of annually replaced FAs, pieces	117.5	90.5	78.5/66	102.5	81.5
Average enrichment of makeup fuel, %	3.28	3.62	4.01/4.87	3.59	4.01
Average discharge burnup, MWt·day/kgU	29.37	38.29	42.66/57.5	33.08	41.95
	1st generation / 2nd generation/ 3rd generation
Rated U mass per FA, kg per RCCA, kg	120,2 / 126,3 / 132,3 115,2 / 120,3 / -

FRs
Type	smooth-rod cylindrical
Dimensions, mm:	1st generation / 2nd generation/ 3rd generation
- length	2536 / 2601.5 / 2601.5
- outer diameter	9.10
- inner cladding diameter	7.73 / 7.73 / 7.93
Centre hole in fuel pellet	with / with or without/ without
Cladding material	Zr + I% Nb alloy
Fuel	sintered uranium dioxide pellets
U-235 enrichment, design-wise, %	1.6; 2.4; 3.3; 3.6; 3.7; 4.0; 4.2; 4.4; 4.6; 4.95
Pellet dimensions, mm:
diameter	7.54.. .7.57 / 7.57…7.60 / 7.8 or 7.77…7.8/7.77…7.8
height	9... 12
rated diameter of central hole	1.4 / 1.2 / -