United States Nuclear Regulatory Commission - Protecting People and the Environment

Bulletin 74-011: Improper Wiring of Safety Injection Logic at Zion 1 & 2



BL74011 

                              UNITED STATES 
                         ATOMIC ENERGY COMMISSION 
                          WASHINGTON, D.C. 20545 

                                OCT 16 1974 

J. P. O'Reilly, Director, Region I 
N. C. Moseley, Director, Region II 
J. G. Keppler, Director, Region III 
E. M. Howard, Director, Region IV 
R. H. Engelken, Director, Region V  

RO BULLETIN 74-11 - IMPROPER WIRING OF SAFETY INJECTION LOGIC AT ZION 1 & 2 

The subject Bulletin should be dispatched to Westinghouse - supplied PWR 
facilities with operating licenses and construction permits by close of 
business on October 17, 1974. The text of the Bulletin together with draft 
letters to licensees is enclosed for this purpose. 


                              J. G. Davis, Deputy Director 
                                   for Field Operations 
                              Directorate of Regulatory Operations 

Enclosure: 
As stated 

cc:  H. D. Thornburg, RO:HQ 
     J. L. Crews, RO:HQ 
     H. H. Brown, OGL 
     D. Thompson, OOE 
     Regional Coordinators 
     A. Giambusso, L 
.

(Letter to all licensees of Westinghouse PWR's with operating licenses.) 
Gentlemen: 

The enclosed RO Bulletin requests actions by you with regard to your 
Westinghouse - supplied pressurized water reactor (PWR) facility(ies) with 
an operating license. 

Should you have questions regarding this Bulletin or actions required of 
you, please contact this office. 

                                   Sincerely, 


                                   Regional Director 

Enclosure: 
RO Bulletin 74-11 
.

(Letter to all licensees of Westinghouse PWR's with construction permits.) 

Gentlemen: 

The enclosed RO Bulletin is sent to you for information and action as 
applicable to your Westinghouse - supplied PWR facility(ies) under 
construction. A written response to this Bulletin is not required of you, 
however, prior to operation you should examine the safeguard logic and 
safeguard logic testing procedures at your Westinghouse - supplied PWR 
facility(ies) presently under construction to determine if conditions or the
potential for conditions similar to those described in this Bulletin exist 
at your facility(ies). We will examine your actions in t response to this 
Bulletin during subsequent inspections of your facility(ies). 

Should you have questions regarding this Bulletin, please contact this 
office. 

                                   Sincerely, 


                                   Director 

Enclosure: 
RO Bulletin 74-11 
.

RO Bulletin 74-11                                           Date 10/16/74 

IMPROPER WIRING OF SAFETY INJECTION LOGIC AT ZION 1 & 2. 

A recent abnormal occurrence report by the Commonwealth Edison Company 
described a design error in the wiring of the safety injection logic 
circuitry at the Zion Generating Station. The licensee's evaluation revealed
serious inadequacies in the implementation of the quality assurance programs
for both construction and preoperational testing. 

A.   Description of Circumstances: 

     During a hot shutdown of Zion Unit 1, reactor Coolant Loop B was 
     isolated, reactor coolant pump 1B was secured and the B main steam 
     isolation valve (MSIV) was subsequently closed due to inoperability of 
     the MSIV closure circuit. The complete isolation of the steam generator
     allowed the steam pressure to drop as the isolated loop cooled. 

     As the pressure in the isolated loop (B) dropped the differential 
     pressure between this loop and the three other Loops (A, C, & D) 
     reached a value causing bistables in the safety injection (SI) logic to
     trip. The logic trips, however, resulted in "half trips" in the 2/3 
     logic on Loops A, C, & D rather than an SI trip on Loop B which should 
     have occurred. 

     Investigation by Commonwealth Edison personnel revealed that the input 
     signals to the dual comparators (514A/B, 534A/B, 515A/B, 525A/B, 516C/D
     and 526C/D) were reversed, thus rendering this portion of the SI 
     initiation circuity inoperable. The wiring error had existed from the 
     time of plant construction, and had gone undetected during functional 
     testing by the supplier, Westinghouse, and preoperational testing by 
     the licensee. The Zion Unit 2 was found to have a similar wiring 
     discrepancy. 

     The licensee found that the preoperational testing procedures were 
     inadequate to detect the miswiring because the logic testing was done 
     in parts similar to the component test done at the factory. A test that
     includes the entire logic train from process sensor inputs to final 
     logic output was not performed. Westinghouse agreed to provide 
     guidelines from which the licensee could establish a more meaningful 
     and comprehensive functional test to check systems following 
     installation. 

     Corrective actions by the licensee included revising the applicable 
     circuit drawings, modifying the circuit wiring, and functionally 
     testing the modified circuits at both Units 1 & 2. The functional 
     testing included bistable actuation, status light verification and 
     simulated differential pressure conditions for safety injection. Other 
     similar circuits at the Zion station were examined and no other 
     deficiencies were identified. 
.

B.  Action Requested of Licensees: 

     It is requested that you examine the safeguard logic and the methods 
     employed to verify that the as-built safeguard circuitry is in 
     agreement with the safeguard logic design at your Westinghouse - 
     supplied PWR facility(ies) with operating license to determine if 
     similar circumstances or the potential for circumstances similar to 
     those described above exist at your facility(ies), and provide to this 
     office in writing within 30 days the following: 
     
     1.   If your findings indicate that circumstances or the potential for 
          circumstances similar to those described above exist at your 
          facility(ies), describe the corrective actions which you have 
          taken or plan to take, together with the date these actions were 
          or will be completed. 
          
     2.   If your findings indicate that circumstances or the potential for 
          circumstances similar to those described above do not exist at 
          your facility(ies), a report stating this finding is requested. 
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