View source for RBG-26890, Forwards Review Results Re Issue on Security Computer & Mux Loop Communications.Addl Investigation Required to Adequately Determine Permanent Solution to Computer Power Circuitry

{{Adams
| number = ML20236K400
| issue date = 10/30/1987
| title = Forwards Review Results Re Issue on Security Computer & Mux Loop Communications.Addl Investigation Required to Adequately Determine Permanent Solution to Computer Power Circuitry
| author name = Booker J
| author affiliation = GULF STATES UTILITIES CO.
| addressee name = 
| addressee affiliation = NRC OFFICE OF ADMINISTRATION &amp; RESOURCES MANAGEMENT (ARM)
| docket = 05000458
| license number = 
| contact person = 
| document report number = RBG-26890, NUDOCS 8711090212
| document type = CORRESPONDENCE-LETTERS, INCOMING CORRESPONDENCE, UTILITY TO NRC
| page count = 2
}}

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a o<                               October 30, 1987 RBG-26890 File Nos. G9.5, G9.42-U.S. Nuclear Regulatory Commission                                                                     l Document Control Desk                                                                                !
Washington, D.C.. 20555 Gentlemen:
u River Bend Station - Unit 1                                             )
Docket No. 50-458
                                      ~
In Gulf- States Utilities Company's        (GSU)   {{letter dated|date=January 19, 1987|text=letter dated January 19, 1987}}-(RBG-25240), a report was provided pursuant to 10CFR73.71 regarding an issue l'                on security computer and MUX loop communications.. GSU has performed its initial review and.provides the results in the attached information.
If further information is required, please contact Mr. Rick J. King at -(504) 381-4146.
Sincerely.
                                                                      -b                                                   i J. E. Booker Manager-River Bend Oversight River Bend Nuclear Group JEB/E      JK/ch Attachment cc:   U.S. Nuclear Regulatory Commission Region IV 611 Ryan Plaza Drive, Suite 1000 Arlington, TX 76011                                                                          :
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NRC Resident Inspector Post Office Box 1051 St. Francisv111e, LA 70775                                                                   l V
8711090212 871030                                                                              [g2/
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i ATTACHMENT The short term corrective action has been implemented for 1) providing spare fuses for I6C technicians to replace blown fuses quickly if the CAS or SAS DC power 'should fail and 2) a solid metal panel door has been replaced with a clear plexiglass door for visual observation to detect wnether       a. DC power source is either on or off.
The long term review, documented on EEAR 87-0E174 includes 1) consideration of a design change to separate power circuits for MUX Loops 1 and 2 in both the CAS and SAS, 2) redesigning of the modem to computer interface, 3) redesign the modems to pass the loop through, back to the other computer, on loss of power and 4) provide multiple sources of power to the modems in both the CAS and SAS.
As a result of GSU's initial review, items 2 and 4 were determined to not be viable solutions to the problem. Additional investigation, which will include the vendor, is required for items 1 and 3 to adequately determine a permanent,                                       l feasible solution to the computer power circuitry. This review will include identification of similar potential problems on similar systems with reference to other utility experiences.
To date, there have been no occurrences of blown fuses which would place the system in the configuration of concern.        Further,  the subject safeguards system is very complex and diverse requiring extensive engineering evaluation, discussion and scheduling with several disciplines and the vendor. Therefore, CSU currently expects its final evaluation to be completed by July 1988.                                             1 l
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