Properties of zirconium alloys and their applications in light water reactors (LWRs) - Materials' Ageing and Degradation in Light Water Reactors - page 89

4.5 Draft of the RBMK-1500 fuel assembly. (Cox et al. , 2006).

4.2.2 RBMKs

RBMKs are basically vertical channel-type boiling water reactors (Cox
et al ., 2004). They use E110 alloy (Zr-1%Nb) fuel cladding in the fully
recrystallized conditions. The fuel assembly consists of two fuel bundles of
18 rods supported on a central stainless steel rod, see Fig. 4.5, with 11 stain-
less steel grids on each bundle. The overall length of the assembly is 10.01 m
(Kupalov-Yaropolk et al ., 1998 ).

4.2.3 VVERs

E110 alloy (Zr-1%Nb) has been the universal fuel cladding in the Voda
Voda Energo Reactor (VVER) design, which is a pressurized water reactor
(Cox et al ., 2004). In the early VVER-440 (MWe) reactors the fuel assem-
blies were hexagonal arrays of 126 E110 clad fuel rods, with 10 or 11 stainless
steel grid spacers, enclosed in an E125 hexagonal wrapper (which performs
the same function as a BWR channel) (Smirnov et al ., 1994 ) see Fig. 4.6a .
In the VVER-1000 type reactors each assembly contains 312 fuel rods, a
central E125 alloy support tube and 18 stainless steel guide tubes for control
and shut-down rods. Except for the fi rst VVER-1000 (Novo-Voronezh-5)
such VVER-1000 fuel assemblies do not have 'wrappers'.

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4.2.4 Material used in fuel assemblies

The materials used for the FA components are Zr alloys, Inconel (precip-
itation hardened Inconel X-750, Inconel 718 and solution treated Inconel
625) and stainless steel (SS 304L) (Cox et al ., 2006). A low cobalt content is
desired in the stainless steel and nickel base alloys to keep the activity trans-
port by the coolant and the radiological exposure of the workers (man-rem)
low. Since these alloys have high thermal neutron capture cross sections