IGCAR : Annual Report - Indira Gandhi Centre for Atomic Research

IGC
Annual Report 2007
IV.C.6. Temperature Evolution in Spent Fuel Subassembly
during Handling in Fuel Transfer Cell
Spent fuel subassembly (FSA)
is removed from the sodium
filled transfer pot at the
location of Ex-Vessel Transfer
Post (EVTP) for handling in Fuel
Transfer Cell (FTC) and
subsequent storage in water
pool storage bay. To prevent
possible release of radioactivity
due to failure of FSA clad, the
temperature of clad should not
exceed its permissible limit of
923 K. To achieve this, the FSA
is force cooled from the top of
the FSA by supplying nitrogen
at 323 K filled in FTC itself in
re-circulation mode (Fig. 1). In
the event of loss of forced
cooling, the temperatures of
clad and hexcan increase, till
the heat loss under natural
convection and radiation
equals the decay power. It is
essential to determine the final
steady state values of these
temperatures, to assess whether
natural cooling adequate. Also,
knowledge of transient
temperature evolution in the
FSA is essential to determine
the time available for the
operator to take safety action.
These have been evaluated by
detailed
conjugate
computational fluid dynamics
studies.
In the absence of forced
cooling, the mode of heat
transfer within the bundle (i.e)
between the pins is only
conduction and radiation as
natural convection of nitrogen
through the compact fuel
bundle is negligible. Heat
transfer from hexcan to FTC
ambient (nitrogen) is by natural
convection and radiation. A 30
degree sector of FSA with the
active fuel pin region of 1 m
height has been considered in
the analysis. For a single pin,
the temperature difference
Fig.1 Spent fuel subassembly force cooled by nitrogen from top
112 FUEL CYCLE