Hydraulic testing of modified neutron source rod in type Q septifoil.

摘要

A Type Q septifoil, two modified partial length control rods, four full length control rods, a source rod containing a dummy neutron source and a guide tube assembly were installed in the Long Term Flow Facility (LTFF) of the HTL. The water level inside the guide tubes over the septifoil was measured by the use of sight tubes connected to pressure taps on the guide tubes or by pressure gages. Pressures were measured at tank bottom and inside the septifoil. The target tank bottom pressure for the experiments was 12.76 psig which gives the same no-flow freeboard in the LTFF as a blanket gas pressure of 5.00 psig in K Reactor. The first series of tests was performed with the existing source rods under a previous Task Plan, 92-057-1. The source rod was kept fully seated during testing to reduce the effect of the flow path through the source rod. Freeboards were adequate during the conditions of normal operation, but inadequate during scram conditions. The minimum freeboard measured during a scram for a septifoil flow of 106 gpm was 20 inches and 7 inches for 120 gpm, adjusted to the target tank bottom pressure. During a control rod scram the full length control rods are driven into the reactor core as a gauge. The reason that freeboards are small during a scram is that the rods pass through positions that tend to reduce freeboard, rather than the velocity of the rods having a negative effect. In fact, a lower freeboard occurs if the rod are held motionless at certain positions. The second series of tests was performed with a modified source rod in which the flow path through the source rod was eliminated. for these tests the source rod was lifted after the control rods had been positioned, the usual procedure in SRS Reactors. The source rod design change increased freeboards such that they were adequate under all conditions.