United States Nuclear Regulatory Commission - Protecting People and the Environment

Bulletin 74-014: BWR Relief Valve Discharge to Suppression Pool



BL74014 

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

                               NOV 13 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 74-14 - BWR RELIEF VALVE DISCHARGE TO SUPPRESSION POOL 

The subject Bulletin has been revised and should be dispatched for action to
all BWR facilities with operating licenses, and for information to holders 
of construction permits for BWR's by close of business on November 15, 1974.
The text of the Bulletin together with draft letters to licensees is 
enclosed for this purpose. 


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

Enclosure: 
As stated 

cc:  D. F. Knuth, RO:HQ 
     H. D. Thornburg, RO:HQ 
     J. L. Crews, RO:HQ 
     H. H. Brown, OGL 
     D. Thompson, OOE 
     Regional Coordinators 
     B. H. Grier, RO:HQ 
     K. R. Goller, L:HQ 
     L. I. Cobb, A/D, RO (3) 
.

(Draft letter to holders of construction permits only for BWR's) 
 
                                                         RO Bulletin 74-14 

Gentlemen: 

     The enclosed RO Bulletin is forwarded to you for information, regarding
your boiling water reactor under construction. No written reply is required 
of you in response to the Bulletin. 

                                   Sincerely, 


                                   Director 

Enclosure: 
RO Bulletin 74-14 
.

(Draft letter to BWR's with operating licenses). 

                                                         RO Bulletin 74-14 

Gentlemen: 

The enclosed RO Bulletin requests actions by you with regard to your boiling
water reactor (BWR) facility(ies) with operating license. 

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

                                   Sincerely, 


                                   Director 

Enclosure: 
RO Bulletin 74-14 

          This request for generic information was approved by GAO under a 
          blanket clearance number B-180225 (R0072); this clearance expires 
          July 31, 1977. 
.

RO Bulletin 74-14                                          Date: 11/14/74 

BWR RELIEF VALVE DISCHARGE TO SUPPRESSION POOL 

Description of Circumstances: 

Various BWR licensees have in the recent past, experienced unplanned 
actuation of reactor coolant system steam relief valves. These valves 
typically discharge to the suppression pool, where the discharge steam is 
quenched. With the suppression pool water at its normal temperature, the 
steam quenching proceeds in the expected manner. Extended discharge of a 
single relief valve, however, may raise the local temperature of the 
receiving water to a level at which the steam quenching becomes erratic and 
local pressure pulses of significant magnitude may be generated. 

Past occurrences at several AEC licensed reactors have resulted in varying 
degrees of damage, such as baffle displacement and piping support damage. 
This damage has previously been attributed to a variety of causes; however, 
based upon more recent evaluations by the nuclear steam system supplier, 
General Electric Company, damage may have resulted from local pressure 
pulses as described above. Since only a limited number of temperature 
sensors are provided within the suppression pool, local temperature 
increases and resulting pressure pulses have not been specifically 
identified in past occurrences. 

It appears that, during events in which relief valves cannot be closed 
promptly, primary attention by the operator may be directed under current 
procedures toward minimizing temperature and pressure transients in the 
reactor coolant system, without sufficient attention to the effects of 
extended steam discharge on the pressure suppression pool structure. This 
situation is currently under review by the Regulatory staff including 
consideration of whether revision to technical specifications may be 
required. 

Action Requested of Licensees: 

1.   Review your current operating procedures which are applicable to the 
     situation discussed above, to determine whether they are adequate or 
     should be modified in any of the following areas: 
.

RO Bulletin 74-14                 -2- 

     a.   Limiting bulk suppression pool temperatures during normal 
          operation and during controllable transients. 

     b.   Requiring reactor trip if the bulk suppression pool temperature 
          exceeds that established as a limit for controllable transients or
          if relief valve(s) fails to reseat properly. 

     c.   Taking prompt steps in case of inadvertent relief valve actuation 
          or failure to reseat, to minimize the duration of steam discharge 
          to the suppression pool. 

     d.   In cases of relief valve discharge, promptly initiating 
          suppression pool circulation to dissipate local peaking of water 
          temperatures. 

     e.   Conduct of visual internal and external inspection of suppression 
          pool structure for evidence of damage in instances where one or 
          more relief valve(s) fails to reseat properly or discharges to the
          suppression pool for an extended period of time. 

     During this review, the various aspects of plant operations should be 
     considered so that procedural changes designed to minimize the effect 
     of steam discharge to the suppression pool do not have an adverse 
     effect in other areas. 

2.   Report to this office in writing within 20 days of receipt of this 
     Bulletin the results of your procedural review and any changes you have
     made or plan to make in your operating procedures, including the date 
     when such changes were or will be completed. 
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