Cold-water injection reanalysis for N Reactor

A re-analysis of the cold water injection transient, with a space- dependent, two-dimensional reactor kinetics code TWIGL has been completed. The analyses considered the impact of flux flattening on the consequences of this accident. Separate categories of cold water source were evaluated. Introduction of a sixth steam generator cell, postulated as a significant cold water transient in previous studies, was re-analyzed in greater depth. Activation of the emergency core cooling system (ECCS) and the main steam line break on the secondary side were also evaluated for worst-case condition. In all instances, the results of the analyses confirmed that N Reactor is well protected against the consequences of cold water reactivity transients by appropriate trip settings and by fast acting control systems. Accidents were analyzed for the possibilities that the control rods failed to insert, and safe shutdown was accomplished with the ball backup safety system. All calculations were performed for the flattened core. The flux flattened core did not alter the timing or the severity of the transient. The results of the re-analyses compare favorably with the analysis discussed in N Reactor Updated Safety Analysis Report (NUSAR) (UNI 1978). Total control aspects of cold water injection, a steady-state analysis, aremore » unaffected by the conclusions of this report. The document contains detailed discussion of the computer analyses including the preparation of input, underlying assumptions, code validation discussion, and comparisons to past work. 10 refs., 27 figs.« less