BL74004 UNITED STATES ATOMIC ENERGY COMMISSION WASHINGTON, D.C. 20545 MAR 22 1974 J. P. O'Reilly, Director of Region I N. C. Moseley, Director of Region II J. G. Keppler, Director of Region III E. M. Howard, Director of Region IV R. H. Engelken, Director of Region V RO BULLETIN #74-4 "MALFUNCTION OF TARGET ROCK SAFETY RELIEF VALVES" The enclosed Regulatory Operations Bulletin #74-4 is forwarded for dispatch to all BWR licensees with Operating Licenses for the requested action and to those licensees having a BWR Construction Permit for information only. The Region is to report to RO:HQ's when the licensee has responded to the Bulletin as well as when the licensee has informed the Region that the modifications have been completed. Harold D. Thornburg, Chief Field Support & Enforcement Branch Directorate of Regulatory Operations Enclosure: As stated cc: D. F. Knuth, RO J. G. Davis, RO B. H. Grier, RO A. Giambusso, RO J. Hendrie, L D. J. Skovholt, L Brodsky, Naval Reactors . To All BWR Facilities Date 3/22/74 With a Current Construction Permit DRO Bulletin #74-4 Gentlemen: The enclosed DRO Bulletin #74-4 "Malfunction of Target Rock Safety Relief Valves" has been sent for completion of the requested action to all utilities presently licensed to operate a BWR generating plant. This Bulletin is being sent to you as general information and requires no responsive action on your part. Sincerely, Director Enclosure: DRO Bulletin #74-4 . To All BWR Facilities with Current Date 3/22/74 Operating Licenses DRO Bulletin #74-4\ Gentlemen: The enclosed DRO Bulletin #74-4 "Malfunction of Target Rock Safety Relief Valves" is sent to provide you with information reported by Tennessee Valley Authority as an abnormal occurrence at the Brown's Ferry Unit 1 reactor facility. This information may have applicability at your facility(ies). Action requested on your part is identified in Section B of the enclosed Bulletin. Sincerely, Director Enclosure: DRO Bulletin #74-4 . MALFUNCTION OF TARGET ROCK SAFETY RELIEF VALVES We have reviewed information from the Tennessee Valley Authority describing the malfunction of a Target Rock (TR) safety relief valve at Browns Ferry Unit 1. As a result of this malfunction, the second stage piston of the valve was prevented from reseating after actuation, resulting in the primary system being blown down,to 20 psig before the spring on the assembly could reseat the piston. Description of Circumstances A. The reactor was in the shutdown condition following reactor isolation as a result of high temperature in the main steam tunnel. During blowdown of the reactor following main steam line isolation valve closure, one of the pressure relief valves on the main steam header failed to reseat until pressure had been reduced to about 20 psig. The valve was subsequently removed and disassembled for inspection. It was found that the keeper over the locking nut on the second stage piston had worked loose and up to the stem over the securing wire. The movement of the keeper prevented the second stage piston from reseating. As a corrective measure, all the TR valves on Unit 1 were replaced with valves from Unit 2 after the following modifications had been performed: 1. The tie wire and keeper were removed from the stem of the second stage piston. . -2- 2. A 1/16 inch diameter hole was drilled through the nut and the threaded portion of the stem. 3. A pin was inserted in the hole and the hole peaned over so that the pin could not come out. This modification has been recommended by the Nuclear Steam System Supplier to all BWR's using the Target Rock values. B. Action Requested 1. It is requested that during your next outage you complete the recommended modifications to the second stage piston stem locking nut. 2. It is requested that you ascertain what other modifications to the original design have been made or recommended for the Target Rock valves now installed in your facility and describe the action you have taken or will take to complete such modifications. 3. Please inform this office within 20 days of your receipt of this Bulletin: a. Of your plans to complete the modifications to second stage piston stem locking nut; and b. Of the action you have taken or will take to complete other modifications recommended for the Target Rock valves now installed in your facility.
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