ML17266A044

LER 78-045/03L-1 on 790305:during Power Operation,Digital Data Processing Sys Malfunctioned.Caused by Error in Program Installed by Licensee in June 1978.Program Error Corrected

ML17266A044
Person / Time
Site:	Saint Lucie
Issue date:	03/05/1979
From:	Schoppman M FLORIDA POWER & LIGHT CO.
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
Shared Package
ML17206A704	List: ML17206A703 ML17266A044
References
LER-78-045-03L, LER-78-45-3L, NUDOCS 7903230155
Download: ML17266A044 (2)

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REPORTABLE OCCURRENCE 335-78-45 LICENSEE EVENT REPORT UPDATE REPORT-PAGE TWO PREVIOUS REPORT DATE 1/3/79 ADDITIONAL CAUSE DESCRIPTION AND CORRECTIVE ACTION At the request of NRC I&E, this update report is submitted to more fully explain this occurrence.

It has been determined that the DDPS halt (malfunction) was caused by a program attempting to use a subroutine prior to another program completing its use of this subroutine.

The DDPS uses a "clock interrupt" which periodically causes control of the Central Processing Unit to be returned to the "system executive". The executive program determines which programs are due to run, and if more than one program is due, it determines which program has priority.

At the time of the DDPS halt, the .Reactor Poison and Power Log Program (which runs once an hour) was utilizing the "double precision divide" subroutine (X DDI). Prior to completing use of this subroutine, the clock interrupt returned control to the executive which scheduled the Analog Scan Program (which runs every five seconds) to run prior to returning control to the Reactor Poison and Power Log Program. The Analog Scan Program also used the X DDI subroutine and changed certain parameters that the Reactor Poison and Power Log Program had established in this subroutine prior to being interrupted.

'.(hen control was passed back to the Reactor Poison and Power Log Program, the changed parameters caused the program to malfunction and subsequently halt the DDPS.

It is believed that this problem was also the cause of two previous DDPS failures (see LER 335-78-26 and 78-39) since the symptoms of the failures were identical, i.e., for all three events the computer printout log indicates that the halt occurred during performance of the Reactor Poison and Power Log Program.

To prevent recurrence of this problem, the Reactor Poison and Power Log Program has been modified so that all calculations are performed within the program without calling for subroutines. The Reactor Poison and Power Log Program was added to the OOPS system in June of 1978 by the Licensee. This is not a generic problem with the vendor's equipment.