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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