Information Notice No. 79-07, Rupture of Radwaste


                              March 23, 1979 

MEMORANDUM FOR:     B. H. Grier, Director, Region I 
                    J. P. O'Reilly, Director, Region II 
                    J. G. Keppler, Director, Region III 
                    K. V. Seyfrit, Director, Region IV 
                    R. H. Engelken, Director, Region V 

FROM:               J. H. Sniezek, Director, Division of Fuel Facilities 
                      and Materials Safety Inspection, IE 

SUBJECT:            Information Notice No. 79-07, RUPTURE OF RADWASTE 

The subject Information Notice No. is transmitted for issuance on March 26, 
1979. The Information Notice should be issued to all power reactor 
facilities with an operating license or a construction permit. 

Enclosed is a draft copy of the transmittal letter.  No inspection followup 
is necessary since no action by the licensee is requested. 

                                        J. H. Sniezek, Director  
                                        Division of Fuel Facilities and 
                                          Materials Safety Inspection 
                                        Office of Inspection and Enforcement 

1.   IE Information Notice
       No. 79-07
2.   Draft Transmittal Letter 

CONTACT:  L. J. Cunningham, IE 

(Draft transmittal letter for Information Notice No. 79-07 to all power 
reactor facilities with an operating license or a construction permit.) 

                                           Information Notice No. 79-07 


The enclosed Information Notice No. 79-07 is forwarded to you for 
information. No specific action is requested and no written response is 
required. If you desire additional information regarding this matter, please
contact this office. 


                                        (Regional Director) 

Information Notice No. 
  No. 79-07 

                             UNITED STATES 
                          WASHINGTON, D.C. 20555 
                              March 26, 1979 

                                           Information Notice No. 79-07 


Description of Circumstances: 

In November, 1977 a radwaste tank ruptured at the Millstone Nuclear Power 
Station. Two problems led to the tank failure. First, the tank vent, which 
was intended to relieve excessive pressure in the radwaste tank, had been 
plugged by accumulated solidified concentrates. Second, corrosion had 
weakened the capability of the radwaste tank to withstand pressure. 
Individually, or in combination, these problems were causative factors in 
the rupture of the radwaste tank due to overpressurization. 

The Licensee Event Report states that an aerated waste concentrates tank was
overpressurized and ruptured. The tank contained radwaste evaporator 
concentrates with a 10-12 percent boric acid concentration. These 
concentrates, when cooled to ambient temperatures, formed a solid 
crystalline structure. Apparently, concentrate had entered the vent line by 
previous tank overflows or purging of air through the tank so that a solid 
buildup occurred in the vent line. This buildup eventually led to a flow 
blockage in the vent line. The licensee, in an attempt to blow out or clear 
a radwaste pipe, applied 100 PSI air pressure to the tank. The tank was 
designed for 15 PSI and the plugged vent could not relieve pressure. 
Therefore, the tank overpressurized and ruptured. 

This tank had a history of corrosion problems such that the corrosion 
probably caused some weakness which contributed to the rupture. The tank was
constructed of type 304 stainless steel. The plant was a seacoast site such 
that significant amounts of chlorides were present in the aerated waste 
system and, consequently, in the waste concentrate tank. The presence of 
significant amounts of chlorides, coupled with residual welding stresses in 
the type 304 stainless steel, resulted in chloride stress corrosion. 

Information Notice No. 79-07                             March 26, 1979 
                                                             Page 2 of 2   

Since radwaste tanks of this type are used at most power reactors, the 
potential may exist for similar events at other power reactors. Also, such 
events can be avoided by proper procedures and periodic examination if 
personnel are aware of the problem. In addition, proper consideration of 
design features (e.g., materials selection and vent designs) can minimize 
the probability of such an event. Prevention of such events will minimize 
the possibility of personal injury, in-plant contamination, releases of 
radioactivity, and occupational radiation exposure resulting from the repair
and clean-up operations. 

No specific action or written response to this Information Notice is 
required. If you require additional information regarding this subject, 
contact the Director of the appropriate NRC Regional Office. 

List of IE Information 
  Notices Issued in 1979


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