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.
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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.
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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."
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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.
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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.
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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.
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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.
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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.
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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
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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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