Techniques for fuel element testing at variable power rates in the SM-2 and MIR reactors

Techniques and designs of the irradiation devices of the SM-2 and MIR reactors for investigating WWER type reactor fuel elements at variable power are described. The techniques assume power variation in the 30-100% range with 1-6% min. rate at cycling of 1-2 cycle/day and power jumps of 1-2 cycle/month. In the SM-2 reactor a device for testing fuel elements under thermocycling conditions which is capable to withdraw fuel elements quickly from the irradiation zone and insert them in it is applied as well as a device for in-reactor investigations of fission products yield and studying axial deformations of fuel meat and cladding at variable thermal loads. In the MIR reactor the tested fuel elements turn in relation to the neutron-absorbing screen which leads to energy release redistribution between fuel elements. The irradiation devices equipped with the self-contained furel element power control systems do not exert visible effect on the reactors operation in which they are mounted and experiments simultaneously conducted in these reactors. All irradiation devices have been subjected to long-term testing under reactor conditions and have shown reliable performance