United States Nuclear Regulatory Commission - Protecting People and the Environment

Seismic Qualification of Auxiliary Feedwater Systems (Generic Letter No. 81-14)



                                UNITED STATES
                        NUCLEAR REGULATORY COMMISSION
                           WASHINGTON, D.C.  20555

                              February 10, 1981

TO ALL OPERATING PRESSURIZED WATER REACTOR LICENSEES 

SUBJECT:  SEISMIC QUALIFICATION OF AUXILIARY FEEDWATER SYSTEMS (Generic 
          Letter No. 81-14) 

Our letter to you dated October 21, 1980, identified concerns regarding the 
seismic qualification of Auxiliary Feedwater (AFW) systems.  That letter 
outlined the continuing evaluation program being conducted by the staff with
regard to this issue to assure conformance of each plant with General Design
Criteria 2 and 34, of Appendix A to Part 50.  As a result of the NRC's 
continuing review of this issue, including the completion of site visits 
described in our previous letter, we have determined that it is necessary to
request certain information from PWR licensees and to request that certain 
actions be performed by PWR licensees, as described below.  The purpose of 
our information request is to obtain sufficient information that identifies 
the extent to which AFW systems are seismically qualified.  We are also 
requesting that PWR licensees perform a walk-down of the non-seismically 
qualified portions of their AFW systems to identify apparent and practically
correctable deficiencies that may exist. 

For plants with AFW systems that are not seismically qualified either in 
hole or in part, our plan involves increasing the seismic resistance of the 
systems in a timely, systematic manner to ultimately provide reasonable 
assurance, where necessary, that they are able to function following the 
occurrence of earthquakes up to and including the design Safe Shutdown 
Earthquake (SSE) for the plant.  This plan is a result of a study of the 
seismic requirements which should be applied to AFW systems for those not 
presently seismically qualified, as discussed in NUREG-0667, "Transient 
Response of Babcock and Wilcox-Designed Reactors." 

Enclosure 1 to this letter contains a request for information from all 
operating PWRs concerning AFW system seismic design.  We have determined 
that docketed information from licensees is not sufficient to allow us to 
conduct a detailed review of this aspect of AFW systems.  In addition, for a 
number of older plants, this information is likely not to be current.  
Furthermore, since the safety significance of the system may not have been 
defined for all plants, the AFW system may not have been adequately 
maintained and considered to be included within the scope of IE Bulletins 
79-02, 79-04, 79-07, 79-14, and 80-11, and IE Information Notice 80-21.  
Therefore, the existing AFW systems, either in total or in part, may have 
as-built characteristics which result in uncertain seismic design 
characteristics. For plants with AFW systems, or portions thereof, which are 
not seismically qualified, Enclosure 1 also requests information concerning 
systems which provide an alternated decay heat removal path. 
.

                                    - 2 -

We are also requesting that you conduct a walk-down by personnel experienced
in the analysis, design and evaluation of such structures, systems and 
components, of the non-seismically qualified portions of the AFW system for 
the purpose of identifying more readily recognized deficiencies in seismic 
resistance. These walk-downs are requested for only those portions of the 
AFW system which have not been designed, constructed, and maintained as 
seismically qualified systems in accordance with the criteria for safety-
grade systems at the facility.  The scope of the walk-down should include 
the types of equipment, components, and piping described in Enclosure 2. 
Enclosure 1 describes what we consider to comprise the bounds of the AFW 
system, and any alternate decay heat removal paths. 

For plants with AFW systems that are not seismically qualified, we consider 
that actions should be taken soon to ensure a reasonable level of earthquake
resistance.  This applies to both the AFW system and the alternate system 
used for decay heat removal if portions of it are not seismically qualified. 
Based upon the consideration of the past performance of nuclear and fossil 
power plants, and other non-nuclear facilities subject to large earthquakes,
we note that well engineered structures, equipment, components and piping 
possess a substantial amount of inherent seismic resistance, even without 
the rigorous seismic qualification performed for safety-grade portions of 
nuclear facilities.  Of the failures of structures, piping, equipment and 
components noted in these past earthquakes, a large fraction have been due 
to brittle failure, lack of restraint, large displacements, or some other 
obvious caused by the seismic event.  Such identified deficiencies could 
have been corrected to significantly enhance reliability without detailed 
seismic analyses but by exercising careful engineering judgement.  These 
considerations were factored into the development of Enclosure 2.  In 
addition, certain of these deficiencies were noted as existing at the 
several facilities for which we conducted AFW system walk-downs (see 
Enclosure 3 for details of the visits). Accordingly, your walk-down of the 
non-seismically qualified portions of the AFW system and other alternate 
decay heat removal systems should identify any appropriate modifications in 
the context of the above discussion. 

Enclosure 2 identifies in more detail the actions we consider appropriate 
for plants with AFW systems,or portions thereof, that are not seismically 
qualified.  Although we are not at this time requesting that the AFW system 
be modified to be in conformance with the facility design seismic 
requirements, we have stated that our plan is to increase the seismic 
resistance, where necessary,k to ultimately provide reasonable assurance 
that the system will function after the occurrence of earthquakes up to and 
including the SSE. 
.

                                    - 3 -

According, the following actions are requested by this letter: 

1.   In accordance with 10 CFR 50.54(f) of the Commission's regulations, all
     PWR licensees are requested to provide the information contained in 
     Enclosure 1 within 120 days of receipt of this letter; and 

2.   The results of any walk-downs are requested within 120 days of receipt 
     of this letter.  These results should include all identified 
     deficiencies and all corrective actions taken, or planned along with 
     the schedules for such.  Such modifications, if any, shall be handled 
     in the customary manner consistent with the provisions of your license 
     and the Commission's regulations. 

Responses should be submitted to enable us to determine whether or not your 
license should be modified, suspended, or revoked. 



                              Darrell G. Eisenhut, Director 
                              Division of Licensing 

Enclosures:
As stated





"This request for information was approved by GAO under a blanket clearance 
number R0072 which expires November 30, 1983.  Comments on burden and 
duplication may be directed to the U.S. General Accounting Office, 
Regulatory Reports Review, Room 5106, 441 G Street, N.W., Washington, D. C. 
20548." 
.

                                                               Enclosure 1 

                          REQUEST FOR INFORMATION 

                    AUXILIARY FEEDWATER SEISMIC DESIGN 

In responding to this letter, the AFW system boundary from suction to 
discharge (including the water source and heat sink) shall include those 
portions of the system required to accomplish the AFW system function and 
connected branch piping up to and including the second valve which is 
normally closed or capable of automatic closure when the safety function is 
required.  The AFW system boundary shall also include any portion of branch 
piping that is structurally coupled to the AFW system boundary such that the
seismic response of the branch piping transmits loads to the AFW system.  As
a minimum, this includes the branch lines outside the AFW system boundary to
a point of three orthogonal restraints.  All mechanical and electrical 
equipment, piping (e.g., instrument air), conduits and cable trays, which 
are necessary or contain items which are necessary, for the operation of the 
AFW system shall also be considered.  In addition, the structures housing 
these systems and components shall be included.  Similar considerations 
shall be applied when considering means of decay heat removal. 

A.   Specify whether your AFW system is (a) designed, constructed, and 
     maintained (and included within the scope of seismic related Bulletins 
     79-02, 79-04, 79-07, 79-14, and 80-11, and IE Information Notice 80-
     21), in accordance with Seismic Category I requirements (e.g., 
     conformance to Regulatory Guides 1.29 and the applicable portions of 
     the Standard Review Pan or comparable criteria) or (b) designed, 
     constructed and maintained (and included within the scope of seismic 
     related Bulletins 79-02, 79-04, 79-07, 79-14, and 80-11, and IE 
     Information Notice 80-21) to withstand a Safe Shutdown Earthquake (SSE) 
     utilizing the analytical, testing, evaluation methods and acceptable 
     criteria consistent with other safety-grade systems in your plant.  To 
     assist the staff in an expedious assessment of your plant, if your AFW 
     system, or portions thereof, is not qualified to withstand an SSE 
     utilizing the analytical, testing and evaluation criteria consistent 
     with other safety-grade systems in your plant, we request that you 
     identify those components and structures not seismically qualified in 
     the appropriate row of the attached Table 1. 

B.   Where seismic qualification is indicated by leaving Table 1 blank, 
     provide a description of the methodologies and acceptance criteria used
     to support your conclusion of seismic qualification,including: Seismic 
     analyses methods employed, seismic input, load combinations which 
     include the SSE, allowable stresses, qualification testing and 
     engineering evaluations performed. 

     In addition, where seismic qualification of a secondary water supply or
     path is relied upon, provided a summary of the procedures which would 
     be followed to enable you to switch from the primary to secondary 
     source. 
.

                                    - 2 -

C.   If a lack of seismic qualification is indicated for items 1, 2, 3, 4, 
     5 and 6, 7, or 8 in Table 1, provide additional information which 
     specifies the level of seismic qualification afforded in the original 
     design for each of these areas. 

D.   If substantial lack of seismic qualification is indicated for items 1, 
     2, 3, 4, 5 and 6, 7, or 8 in Table 1, provide the same information 
     requested in A through C for any alternate decay heat removal system. 
     The bounds of these systems shall be considered to a similar extent as 
     that described for the AFW system.  Provide a summary of the procedures
     by which operation of these alternate heat removal systems will be 
     accomplished. 
.

                                 TABLE 1 

                 AUXILIARY FEEDWATER SEISMIC QUALIFICATION 

(1)  Pumps/Motors

(2)  Piping

(3)  Valves/Actuators

(4)  Power Supplies

(5)  Primary Water and Supply Path

(6)  Secondary Water and Supply Path*

(7)  Initiation and Control System

(8)  Structures Supporting or Housing these AFW System Items

*Applicable only to those plants where the primary water supply or path is
 not provided, however, a seismically qualified alternate path exists. 
.

                                                               ENCLOSURE 2 

                     ACTIONS REQUESTED OF PRESSURIZED 

                      WATER REACTOR LICENSEES WITHOUT 

                          A SEISMICALLY QUALIFIED 

                        AUXILIARY FEEDWATER SYSTEM 


1.   For all mechanical and electrical equipment and components including 
     battery racks, controls, instruments, motors, compressors, tanks 
     electrical supplies and the cabinets containing such items, note all 
     items which are not securely attached to their supporting structures 
     such that there is substantial resistance to movement caused by 
     seismically induced forces. 

2.   For piping, note cases where relatively large deflections cannot be 
     accommodated without impairing system function.  Where such 
     displacements will lead to loss of system function, note where 
     sufficient amounts of restraint could be afforded, thus significantly 
     reducing stresses that would be imparted to such items as pump nozzles 
     and branch connections, as appropriate.  Further, note eccentric valve 
     operators that are not sufficiently supported and act to severely 
     overload the pipe.  Where such support is lacking, you should note 
     where substantial restraints could be added to the extent practical.  
     Also, where pipes are resting on existing supports, note where 
     substantial resistance to the pipe moving off these supports could be 
     added where it does not already exist. 

3.   For cable trays and conduits, assure that relatively large 
     displacements can be accommodated without impairing system function 
     where seismic restraint to substantially less than required for these 
     which are seismically qualified.  Focus particularly attention on 
     preventing the breakage of the electrical and control cables they 
     contain at such places as points of attachment of the cables to 
     equipment or other relatively fixed points.  Note where any 
     deficiencies exist. 

Given the time frame we are recommending for the completion of these 
actions, no explicit analyses are requested to demonstrate system 
qualification unless deemed necessary by you.  However, sound engineering 
judgement should be applied considering the level of seismicity specified 
for your site and the design requirements for other seismically qualified 
systems in the facility when judging the necessity for and adequacy of any 
modifications (e.g., piping, cable trays, conduit, equipment and component 
restraints, and estimations of displacement levels).  Further, these actions 
shall be accomplished using personnel who are experienced in the analysis, 
design and evaluation of such structures, systems and components. 
.

                                    - 2 -

Where you have determined that it is prudent to institute modifications, no 
modifications should be instituted which will detrimentally affect the 
function of the piping, equipment and components of the system, considering 
all other loads in addition to seismic.  For example, when providing 
additional restraints to piping systems, assure that they do not have a 
detrimental impact on the system considering all loads, in addition to 
seismic, including thermal loads and support displacement induced loads. 

Similar considerations as described above should be given to other non-
seismically qualified piping, equipment and components in the vicinity of 
the non-seismically qualified portions of the AFW and the alternate decay 
heat removal systems to provide for a substantial decrease in their 
susceptibility to failure if such failure could impact the function of the 
AFW and alternate decay heat removal systems. 
.

                                                               ENCLOSURE 3 

                           RESULTS OF NRC STAFF 

                         WALK-DOWNS OF AFW SYSTEMS 

Plant 1 - Seismically Qualified AFW System (Operating License issued in 
1975) 

Several locations were found in which the supports for the control-air for 
the auxiliary feedwater umps or for the auxiliary feedwater control valve 
were disconnected from their intended mounting locations.  These were 
examples of important, but non-essential systems (i.e., local manual control
of the pumps and valves could be used if the air-system were damaged) which 
could be easily upgraded to increase the plants ability to remove decay heat
following an SSE. 

Plant 2 - Non-Seismically Qualified AFW System (Operating License issued in 
          1963) 

At least two supports to the auxiliary feedwater piping were either not 
connected to piping or not connected at the mounting location.  The bolts 
securing the auxiliary feedwater water supply tank (demineralized water 
tank) to its pad were rusted and not tightened down (i.e., 3/4 inch space 
between the support and nut intended to hold it down).  Also, a long span of 
2-inch piping was found having vertical support only to which lateral 
support could easily be provided. 

Plant 3 - Non-Seismically Qualified AFW System (Operating LIcense issued in 
          1967) 

Three areas were identified for which remedial actions could be implemented 
in a reasonably short time.  The first of these was one of the station's 
battery racks.  While the existing racks provided for some degree of lateral
seismic and resistance, the configuration did not appear to have a level of 
integrity commensurate with the important of the batteries to plant safety. 
Thee racks appeared flimsy in comparison to those which were installed to 
current seismic design criteria prescribed by the licensee for safety 
related systems. 

The second area was the suction side of the Auxiliary Feedwater pumps which 
consists of a single header from the condensate storage tank.  The header 
has some lateral support, however, the condensate storage tank was not 
qualified. The tank is not anchored at its base and the permanent alternate 
supply is through the tank.  There is a capability to install a hose from a 
qualified water source to the pump suction and bypass the condensate storage 
tank. Keeping such a hose in place would enhance system reliability. 

The third area was the main instrumentation and control panels in the 
control room.  These are supported at the bottom by a concrete channel and 
at the top by steel knee braces anchored to the concrete ceiling with 
expansion anchors. The requirements of IE Bulletin 79-02 had not 
.

                                    - 2 -

been applied to these anchor bolts and base plates.  Conformance with the IE
Bulletin requirements for the factors of safety and considering base plate 
flexibility for the original seismic loads would increase reliability.  
Also, some loose and missing screws were noted in these panels which could 
be easily tightened and replaced. 
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