Quality assurance of reactor operation by computer methods

The necessity and value of computer auditing has been proven at N Reactor. During a recent audit, discrepancies were noted when temperature calculations did not agree within +- 10F upon comparison of Quality Assurance and Reactor Operations calculations. Input data was checked and no discrepancies noted. Quality Assurance and Reactor Operations programs were executed again, using new data, and all calculations agreed within the required accuracy. A subsequent diagnostics test was performed on the Quality Assurance computer system, revealing hard (gross) computer memory failures, although further routine computer operation did not reveal this. The incident demonstrates that errors in operating limits could occur, undetected, if reliability were based solely on limits calculated by the Reactor Operations computer, without verification by means of the Quality Assurance computer. This type of incident is similarly possible at Commercial nuclear facilities which rely on one computer system only, without verification (auditing) of input parameters, subsequent calculation of operating parameters (limits), and computer operation