Reactor Cavity Annulus Seal Ring (Generic Letter 78-03)


                               UNITED STATES 
                          WASHINGTON, D.C. 20555 
                              FEBRUARY 2 1978 

All PWR Licensees (except for Trojan) 


During the course of responding to the staff's review of an application for 
license amendment on the Trojan Nuclear Plant, the licensee informed the NRC
that the reactor cavity annulus seal ring (used as a water seal during 
refueling operations, and not removed during normal operations) and 
associated biological shielding over the reactor vessel cavity could become 
missiles in the event of a loss of coolant accident (LOCA) pipe break inside
the reactor vessel cavity. At the Trojan Nuclear Plant, these missiles could
affect the ability of the control rods to shut down the reactor. From our 
preliminary evaluation of the information provided to the NRC staff by the 
licensee, the Portland General Electric Company and by Westinghouse, 
Combustion Engineering, Babcock & Wilcox and Bechtel in telephone 
discussions on January 25 and 26, 1978, it appears that this problem could 
occur in other PWR facilities such as yours and could potentially pose a 
threat to the health and safety of the public in the event of a LOCA. 

Therefore, pursuant to 10 CFR 50.54(f) of the Commission's regulations, you 
are hereby requested to deliver to the Office of Nuclear Reactor Regulation,
Nuclear Regulatory Commission, Washington, DC 20555, within 20 days of the 
date of this letter, i.e., February 22, 1978, the following information: (a)
a statement as to whether the cavity annulus seal ring in your facility is 
left in place during normal operation or if biological shielding is 
installed in the reactor cavity annulus and, if the answer to (a) is yes; 
(b) when you will determine whether the cavity annulus seal ring or 
biological shielding could become a missile in your facility, and (c) a 
description of what you plan to do, and when, if the problem is found at 
your facility and (d) justification for continued operations until the 
problem has been resolved, such justification to support why continued 
operation will not create undue risk to the health and safety of the public. 

A copy of this letter is being provided to each licensee's current service 


                                        Victor Stello, Jr.,  Director 
                                        Division of Operating Reactors 
                                        Office of Nuclear Reactor Regulation


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