RRFM 2009 Transactions - European Nuclear Society

Fig. 3:
Surface temperature over the width
of the typical fuel plate of FRM II
averaged over a whole cycle of
60 days of full power operation.
Next is shown the evolution with time of the temperature profile of the hot fluid element at a width in the
channel of 5.0 cm (compare Fig. 3):
• NBK calculated the absolute maximum values to lie at the bottom borders over an extent of the
plates of only some mm (height =-35cm in Fig. 4). But this is not fairly true when respecting also
the axial heat transfer in the plates, which cannot be neglected at the plate ends.
The description of NBK shows the typical effect of heat transfer in the plates at the meat
edge, where a clear local maximum in the power distribution occurs over a few mm only. The
peak is fairly drawn down and in the actual case it will be not higher than the broad maximum
value inside at the plate surface. This can also be confirmed by plausibility considerations.
• At reactor start the power in the inner core region is shoved down by the CR being present above
-7 cm (relative to the core mid plane CMP). The hottest point at the plates is located down at
about -20 cm and reaches slightly more than 90°C.
• With operation time during a cycle the hottest point at plates surface moves up towards the CMP
and becomes clearly cooler, about 80°C till the operation cycle end at 60 FPDs. The CR is then
nearly totally removed and the power density is rather symmetrically around the CMP, although
the temperatures remain higher at the bottom side, since the coolant water comes from the top.
228 of 455