A Very Efficient New Source for Restart of Frm Ii

Abstract

The German multi-purpose neutron source FRM II features two sources for reactor restart. The sources feed the fuel element and wide range detectors for power signalling. Clear minimum rate expectations exist for all three signals before allowing any movement of the low lying control rod at restart.Detailed calculations have shown that the secondary source alone would have the necessary n-source strength only for about two to three times the 60d-half-value period of Sb-124.The author presents his idea of inserting a very small ring of Sb in the central hole of the existing control rod. This possibly simple measure would ensue huge benefits; the new secondary Sb(Be)-source would be recharged automatically during operation and with more than an order of magnitude more efficiency for power detection with respect to the secondary source.