United States Nuclear Regulatory Commission - Protecting People and the Environment

Actions Required from OL Applicants of NSSS Designed By Westinghouse and CE Resulting From NRC B&O Task Force Review of TMI2 Accident (Generic Letter 80-21)



GL80021                                                  SSINS No. 6820 
                                                         Accession No.: 
                                                         7912190687 
                                 UNITED STATES 
                         NUCLEAR REGULATORY COMMISSION 
                     OFFICE OF INSPECTION AND ENFORCEMENT 
                            WASHINGTON, D.C.  20555 

                                                 IE Bulletin No. 80-05 
                                                 Date:  March 10, 1980 
                                                 Page 1 of 2 

VACUUM CONDITION RESULTING IN DAMAGE TO CHEMICAL VOLUME CONTROL SYSTEM 
(CVCS) HOLDUP TANKS (SOMETIMES CALLED "CLEAN WASTE RECEIVER TANKS") 

In July 1977, IE Circular No. 77-10 identified two instances which resulted 
in radioactive gaseous releases when tanks at Trojan and Rancho Seco buckled 
due to partial vacuum conditions.  The Circular "recommended that you 
examine the systems of your reactor facility(ies) that contain low pressure 
process or holdup tanks and assure that adequate measures have been taken to 
protect against vacuum conditions that could result in tank inward buckling 
and failure with subsequent release of radioactive material or cause other 
detrimental effects with regard to overall safety of plant operations." 
Despite issuance of the Circular, similar events have subsequently occurred 
at Turkey Point 3 (LER's 78-17, 79-8, and 79-25) and Salem (LER's 79-67 and 
79-76). 

The accident at TMI has re-emphasized the importance of protecting against 
unexpected radioactive release paths during abnormal conditions.  The CVCS 
Holdup Tanks (HUT) represent such a path since normal letdown flow is 
directed into the CVCS which could add radioactive water to the HUT during 
abnormal conditions if fuel failures are present.  It is also possible for 
the same "abnormal conditions" to cause HUT damage, since there is a greater
probability of operational errors resulting from the combination of manual 
and automatic maneuvers made to respond to the abnormal condition.  These 
errors could cause a partial vacuum to be drawn in the HUT, causing tank 
rupture and a release path that bypasses the normally present reactor vessel 
and containment barriers to such releases. 

We note that both Turkey Point and Salem have elected to install vacuum 
breakers in their CVCS-HUTS.  As specified by the required Actions below, 
you should consider installing vacuum protection in your plants, 
appropriately designed to preclude collapse of the tanks.  Any proposed or 
already installed vacuum protection system must consider the necessity for 
precluding adverse effects due to operation or misoperation of the system 
(for example, creation of an explosive gas mixture if hydrogen gas is 
present in the HUT).  Any proposed or already installed system must also 
include consideration of the following:  (a) tanks with a cover gas must be 
able to admit the cover gas fast enough to keep up with the maximum rate of 
liquid removal from the tank; (b) vacuum relief valves must be covered by an 
acceptable surveillance program; (c) tanks that are located outside must 
have adequate freeze protection from the tank and for the vacuum relief 
system. 
.

                                                 IE Bulletin No. 80-05 
                                                 Date:  March 10, 1980 
                                                 Page 2 of 2 

Action to be taken by all PWR licensees and permit holders: 

1.    Review the design of all systems that contain low pressure or holdup 
      tanks that can be valved to contain primary system water.  Assure that
      adequate measures have been taken to protect against vacuum conditions
      that could result in tank damage with the potential for release of 
      radioactive material or detrimental effects with regard to overall 
      safety of plant operations. 

2.    Provide a listing of those systems reviewed in Item 1.  Describe any 
      measures that already exist for those systems to protect against 
      vacuum conditions, and either:  (1) explain why those measures are 
      adequate in light of the events referenced above, or (2) identify 
      corrective actions taken or planned to provide acceptable protection, 
      and provide a schedule for any planned corrective actions. 

Licensees of all operating power reactor facilities shall submit the 
information requested within 90 days of the date of this letter.  Include in
your response to this Bulletin, (a) your schedule for correcting these 
items, (b) if reactor operation is to continue prior to correcting 
identified deficiencies, include your justification for continued operation.  
Licensees with a construction permit shall also submit the design 
information requested within 90 days of the date of this letter. 

Reports shall be submitted to the Director of the appropriate NRC Regional 
Office and a copy forwarded to the Director, NRC Office of Inspection and 
Enforcement, Washington, D.C. 20555. 

Approved by GAO, B180225 (R000072): clearance expires 7-31-80.  Approval was
given under a blanket clearance specifically for identified generic 
problems. 

Page Last Reviewed/Updated Monday, June 17, 2013