Investigation of the effects of some safety system modifications on the safety of the HFIR

A need for noise reduction in the HFIR has led to proposals to modify Modes 2 and 3 by adding smoothing capacitors to signal amplifiers and by removing the rate trip to lessen the effects of noise. Since both proposals can slow the safety system response, it must be demonstrated that the modified system still gives satisfactory protection against design basis accidents. Analog simulation was used to determine the effect of the proposed changes on the overall safety system response. In addition, many previously run transient simulations were repeated using up-to-date values for system parameters. Safety system response with the proposed changes was found to give adequate protection against the most challenging combination of mishaps which are even marginally possible