Information Notice No. 84-32: Auxiliary Feedwater Sparger and Pipe Hanger Damage

                                                       SSINS No.:  6835 
                                                       IN 84-32 

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

                               April 18, 1984 

Information Notice No. 84-32:   AUXILIARY FEEDWATER SPARGER AND PIPE 
                                   HANGER DAMAGE 

Addressees: 

All holders of nuclear power reactor operating licenses (OLs) or 
construction permits (CPs) for pressurized water reactors (PWRs). 

Purpose: 

This information notice is provided to advise licensees and applicants of an 
event involving sparger and pipe hanger damage, which apparently was caused 
by water hammer in the auxiliary feedwater system despite specific design 
considerations intended to preclude such an event. We expect recipients of 
this notice will review the information for applicability to their 
facilities and consider actions, if appropriate, to preclude a similar 
problem occurring at their facilities. However, suggestions contained in 
this information notice do not constitute NRC requirements and, therefore, 
no specific action or response is required. 

Description of Circumstances: 

During a recent inspection following shutdown for refueling at the Palisades 
Nuclear Power Plant, damage to the auxiliary feedwater system was found. As 
shown on the attached figure, the damage included: 

     Steam Generator "A"                          Steam Generator "B" 

     Thermal sleeve cracked                  Weld at elbow broken 
     (see 3 on attached figure)              (see 1 on attached  figure) 

     One (of three) hold down clamp          Clamp broken on riser pipe to 
     for sparger missing                     sparger 
     (see Detail "C" on attached figure)     (see 2 on attached figure) 

An inspection conducted just prior to the discovery of the internal steam 
generator damage revealed that eight hangers were loose or damaged on the 
auxiliary feedwater piping external to the steam generators. These hangers 
were inspected before the beginning of the fuel cycle and were known to have 
been in good repair at that time. The damage described above is consistent 
with the occurrence of water hammer during the cycle. 




8404130404 
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                                                            IN 84-32 
                                                            April 18, 1984 
                                                            Page 2 of 3 

Palisades Nuclear Power Plant began feedwater testing in May 1980, following 
water hammer events at other nuclear power plants. At that time, the 
auxiliary feedwater system discharged through two independently controlled 
branches and through check valves to the main feedwater lines immediately 
outside containment. From this point, the flow of the auxiliary feedwater 
was through the main feedwater lines, through containment penetrations to 
the steam generators, and through the main feedwater spargers internal to 
the steam generators. During the testing, water hammer was induced at low 
pressure and high flow rates; so, testing was stopped, and operational 
limits were established for auxiliary feedwater flow rates. 

In the fall of 1981, Palisades began modifications that consisted of 
disconnecting the auxiliary feedwater lines from the main feedwater lines; 
routing the lines through existing spare containment penetrations to the 
existing, but previously unused, auxiliary feedwater nozzles on the steam 
generators; and providing a separate,auxiliary feedwater sparger inside each 
steam generator. The existing auxiliary feedwater nozzle forgings were 
equipped with thermal liners to allow cold feed injections, and the 
acceptable number of such cycles was analytically determined. The piping 
reaction at the nozzles also was evaluated for acceptability. The new 
spargers for auxiliary feedwater were designed in accordance with the 
current design practice for Combustion Engineering (CE) steam generators. A 
number of design features were incorporated specifically to reduce the 
susceptibility to water hammer. The piping in the vicinity of the steam 
generators was sloped down away from the generators. The sparger was 
arranged with top discharge "L" tubes and provided with a water trap to 
prevent the sparger from draining when the steam generator water level drops 
below the sparger. A vent was provided at the highest point of the, sparger 
water trap. 

In December 1981, Palisades Nuclear Power Plant completed a series of 
apparently successful water hammer tests on the newly installed auxiliary 
feedwater system. These tests included use of auxiliary feedwater with the 
steam generators at 200 psi and 900 psi. 

From December 1981 until August 1983, auxiliary feedwater was used and 
tested routinely without apparent incident. Testing included monthly 
surveillances at 150 gpm to each steam generator with the plant at near full 
power. 

Discussion: 

The auxiliary feedwater system damage both internal and external to the 
steam generators is thought to be the result of water hammer in the 
auxiliary feedwater system. This event is one of approximately 30 water 
hammers that have occurred in top feed ring design steam generators. Two of 
the steam generator water hammers have resulted in rupture of the secondary 
side pressure boundary. The first instance was at Indian Point 2 in November 
1973, when the feedwater piping cracked and steam was released to the 
containment building. The second was at Maine Yankee in January 1983, when 
the #2 main feedline ruptured. 

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                                                            IN 84-32 
                                                            April 18, 1984 
                                                            Page 3 of 3 

Unlike these two earlier events, the Palisades event did not result in pipe 
rupture external to the steam generators. 

One aspect of the auxiliary feedwater system design suggesting the 
possibility of water hammer is the placement of the new spargers. These 
spargers are located at the normal steam generator water level of 65%. With 
the expected variation of water level (+-2%), it would be expected that the 
sparger and its top mounted discharge "L" tubes are alternately and 
frequently covered and uncovered. 

Whether or not the damage to the auxiliary feedwater system at the Palisades 
Nuclear Power Plant is ultimately attributed to water hammer, this event 
demonstrates the need for continued vigilance on the part of operations and 
engineering staff. Plant operations staff should be alert to the possibility 
of water hammer phenomenon even though the plant is designed to reduce 
susceptibility to it. Plant engineering staff should investigate loose or 
damaged hangers and operational parameters for the possibility of the water 
hammer phenomenon. 



                              Edward L. Jordan, Director
                              Division of Emergency Preparedness
                                   and Engineering Response 
                              Office of Inspection and Enforcement 

Technical Contact:  E. Weiss, IE 
                    (301) 492-4973 

Attachments: 
1.   Palisades Nuclear Power Plant Auxiliary Feedwater 
2.   List of Recently Issued IE Information Notices