Study of definition: Investigation of different variants for the third core of KNK II

The present report describes the results of investigations, which were performed at INTERATOM at the request of the KfK Karlsruhe on different versions for the third core of KNK II. These variants were: Variant 1 like the first core, variant 2 like the second core, variant 3 as mixed oxide core with 7.6 mm fuel pins, variant 4 as Uranium oxide core and variant 5 as mixed oxide core with 8.5 mm fuel pins. Furthermore statements about a possible reduction of the number of absorber positions had to be done. The investigations concerning the core design, fuel assembly and fuel pin design, operational and accidental behavior, radiology and shielding revealed the following main results: 1. All investigated variants are technically feasible, guarantee the normal operation and give the test operation similar flexibility. 2. No major licensing problems are to be expected, whereby detailed problems will require special proofs. 3. The number of absorbers could be reduced by one, but a more favourable absorber pin design (pressureless, thicker pins) should be chosen. 4. In view of a gain in experience for future breeder reactors, a core with 8.5 mm fuel pins is recommended