United States Nuclear Regulatory Commission - Protecting People and the Environment

Bulletin 78-09: BWR Drywell Leakage Paths Associated with Inadequate Drywell Closures

                               UNITED STATES 
                       NUCLEAR REGULATORY COMMISSION 
                    OFFICE OF INSPECTION AND ENFORCEMENT 
                          WASHINGTON, D. C. 20555 
                                     
                               June 14, 1978  

                                                      IE Bulletin No. 78-09 

BWR DRYWELL LEAKAGE PATHS ASSOCIATED WITH INADEQUATE DRYWELL CLOSURES 

Description of Circumstances: 

Upon completion of the E. I. Hatch 1 plant refueling, the drywell head was 
reinstalled on April 1, 1978 and a local leak rate test (LLRT) was 
successfully passed, providing no indication of a potential problem at the 
time. Subsequently, during the containment integrated leak rate test (CILRT)
at the E. I. Hatch 1 plant on April 6, 1978, high leakage around the drywell
head was experienced. After the high leakage rate was detected, the 
containment was depressurized. Prior to detensioning the drywell head bolts,
a feeler gauge was used to determine that the clearance was greater where 
the leakage was occurring. 

Upon retorquing the drywell head for a second LLRT and CILRT, the tightening
sequence was started at the area of leakage and torque values of 1800 
foot-pounds were used. Feeler gauge readings between the head and drywell 
were recorded. The second LLRT was passed successfully and no leakage was 
indicated around the drywell head during the second and successful CILRT 
conducted at 59 psig. 

Another instance was identified during the CILRT at Millstone Unit 1 on 
November 22-23, 1976, when both the drywell head and the drywell head manway
cover "lifted" during a Type A test subsequent to successful Type B (LLRT) 
tests. 

Based on this experience, it appears that the LLRT following each 
reinstallation of the drywell head or other closures, such as after a 
routine refueling or other similar activity, cannot be the sole basis for 
assuring a suitable degree of drywell closure leak tightness. It appears 
that there must be controls to ensure that drywell closures are made in a 
reproducible manner. 

Action to be taken by all BWR power reactor facilities with an operating 
license or construction permit:  




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IE Bulletin No. 78-09                                        June 14, 1978 

1.   Determine if the procedural controls utilized at your facility are 
     adequate to assure that drywell head reinstallations achieve a degree 
     of leak tightness equivalent to that attained during the installation 
     immediately preceding the last successful CILRT. This determination 
     should include, but not be limited to, consideration of the following: 

     a.   Comparison of the applied bolt torque (or for turn-of-the-nut 
          technique, the number of flats on each nut/bolt after 
          metal-to-metal contact has been achieved) after any head 
          reinstallation to that used during the reinstallation verified by 
          CILRT, including any additional local retightening needed to reach
          LLRT acceptance criteria. 

     b.   Comparison of head-flange clearances after any head 
          reinstallation, to that used during the reinstallation verified by 
          CILRT. 

     c.   Determination of the suitability of the drywell head gaskets for 
          reuse. 

     d.   Determination of the maximum allowable bolt torques to avoid bolt 
          overstressing conditions. 

     e.   Determination of any special handling arrangements, tightening 
          sequence, gasket preparation, or other special considerations 
          caused by unique facility circumstances such as a warped drywell 
          head. 

2.   Should your determination called for in Item 1 above demonstrate a need
     for procedural revisions, your response to this Bulletin should include
     a description of the changes to be made and a timetable for their 
     implementation which must occur prior to the next drywell head closure.

3.   Identify other bolted containment closures that would tend to unseat on
     positive internal pressure and describe what actions are taken to 
     ensure that adequate leak tightness would exist at an internal pressure 
     of Pa. 

4.   Within 45 calendar days of the date of issue of this bulletin, report 
     in writing to the Director of the appropriate NRC Regional Office, the 
     results of your review and your plan of action with regard to Item 1 
     through 3. A copy of your report should be 

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IE Bulletin No. 78-09                                        June 14, 1978 

     sent to the United States Nuclear Regulatory Commission, Office of 
     Inspection and Enforcement, Division of Reactor Operations Inspection, 
     Washington, D. C. 20555. 

For all BWR power reactor facilities with a construction permit, this 
Bulletin is for information only and no written response is required. 

Approval by GAO, B180225 (R0072); clearance expires 7/31/80. Approval was 
given under a blanket clearance specifically for identified generic 
problems. 

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