Part 21 Report - 1997-021
ACCESSION #: 9701230196
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ABB
January 17, 1997
LD-97-002
Document Control Desk
U.S. Nuclear Regulatory Commission
Washington, D.C. 20555
Subject: Report pursuant to 10 CFR 21 Regarding the Omission of Main
Steam Safety Valve Piping Pressure Loss in Safety Analyses
Dear Sir:
The purpose of this letter is to notify the Nuclear Regulatory Commission
of a defect pursuant to 10 CFR 21, "Reporting of Defects and
Noncompliance." The identified defect concerns the piping line loss
(i.e., [symbol omitted]P) between the Steam Generator (SG) and the Main
Steam Safety Valve (MSSV) inlet when the MSSVs are activated. Omission
of the subject line loss from analyses of occurrences during which MSSVs
actuate could adversely affect the results of corresponding LOCA and non-
LOCA safety analyses, MSSV performance, and piping system structural
analyses.
ABB-CE has discovered that the piping pressure losses between the SG and
MSSV inlets have not been fully evaluated with respect to MSSV
performance or not fully addressed within plant safety analyses which
involve MSSV actuation. These pressure losses reduce the effectiveness
of the MSSVs, which will affect the overpressure protection capability of
the MSSVs. Moreover, if the piping losses exceed the blowdown setting of
the MSSVs there is a potential for MSSV chattering, and there is a
concern whether the MSSVs limit main steam system pressure to less than
110% of design pressure under the design overpressure conditions.
Additionally, substantial pressure pulses (i.e., spiking) might occur as
a result of valve chattering. In general, such pressure pulses are not
specifically considered in the piping system stress analysis typically
performed by a plant's Architect Engineer (A/E). The piping stress
analysis was not part of the original ABB-CE scope of supply. As such,
ABB-CE can make no determination regarding acceptability of those
analyses with respect to this issue.
Based on ABB-CE's investigation comprising two utilities for which
relevant line loss data was available, it is known that the impact of
this issue is plant specific, since it is primarily dependent on the
geometry of the branch piping from the main steam header to the MSSV
inlet which
ABB Combustion Engineering Nuclear Power
Combustion Engineering, P.O. Box 500 Telephone (860) 285-9678
Inc. 2000 Day Hill Rd. Fax (860) 285-2337
Windsor, CT 06095-0500
Document Control Desk LD-97-002
January 17, 1997 Page 2
varies considerably between plants. The magnitude of the piping pressure
losses that we have examined ranges from approximately 10 psi to more
than 50 psi. ABB-CE considers that this issue may be applicable to
nuclear power plants other than those for which ABB-CE was the nuclear
steam supply system vendor.
We have recommended to the owners of plants for which ABB-CE supplied the
nuclear steam supply system that reviews are necessary to determine
whether or not the piping pressure loss between the SG and MSSV inlets
was considered in order to determine if a particular plant is adversely
affected by this issue. If such losses were not considered, a review of
the impact of the omission of the unrecoverable piping pressure losses
should be conducted to ensure that they are fully addressed in the
applicable LOCA and non-LOCA safety analyses.
We have also recommended that utilities confirm the proper adjustment of
the MSSV blowdown settings so as to preclude valve chatter and related
structural concerns.
Please feel free to contact me or Virgil Paggen at 860-285-4700 if you
have any questions.
Very truly yours,
COMBUSTION ENGINEERING, Inc.
Ian C. Rickard, Director
Operations Licensing
Attachment
Attachment to LD-97-002
Page 1 of 3
ABB Combustion Engineering Nuclear Operations
10 CFR 21 Report of a Defect or Failure Comply
The following information is provided pursuant to 10 CFR 21.21(c)(4):
(i) Name and address of the individuals informing the Commission:
Ian C. Rickard, Director
Operations Licensing
Combustion Engineering, Inc.
2000 Day Hill Road
Windsor, CT 06095-0500
(ii) Identification of the facility, the activity, or the basic
component supplied for such facility or such activity within
the United States which fails to comply or contains a defect:
The activity for which this report is being filed is the
omission of the effects of piping line loss (i.e., [symbol
omitted]P) between the Steam Generator (SG) and the Main Steam
Safety Valve (MSSV) inlet in those LOCA and non-LOCA thermal
hydraulic safety analyses of events in which the MSSVs are
activated. Further, ABB-CE found that this omission was
applicable to all safety analyses during which the MSSVs are
activated for nuclear power plants for which ABB-CE was the
nuclear steam supply system vendor.
(iii) Identification of the firm constructing the facility or
applying the basic component which fails to comply or contains
a defect:
Combustion Engineering, Inc.
2000 Day Hill Road
Windsor, CT 06095-0500
(iv) Nature of the defect or failure to comply and the safety hazard
which is created or could be created by such defect or failure
to comply:
The identified defect involves the omission of the piping line
loss (i.e., [symbol omitted]P) between the SG and the MSSV
inlet. The effect of this is to potentially cause steam
generator pressure and temperature to be somewhat higher during
transients which involve MSSV actuation than was reported in
the safety analyses of those transients. The amount of this
difference is a function of the geometry of the MSSV inlet
piping and the MSSV blowdown setting. ABB-CE is concerned that
this pressure loss has not been fully evaluated with respect to
MSSV performance or fully addressed within plant safety
analyses that involve MSSV actuation. The unrecoverable
pressure loss reduces the effectiveness of the MSSVs, which
will affect the overpressure protection capability of the
MSSVs.
Attachment to LD-97-002
Page 2 of 3
Moreover, depending on the magnitude of the line loss, there is
a potential for MSSV chattering if the loss exceeds the
blowdown setting of the MSSVs, and concern whether the MSSVs
will limit maximum main steam system pressure to less than 110%
of design pressure under design overpressure conditions.
Additionally, substantial pressure pulses (i.e. spiking) might
occur as a result of valve chattering.
(v) The date on which the information of such defect or failure to
comply was obtained:
The absence of the line loss was first noted in early 1996
while ABB-CE, under contract to Baltimore Gas & Electric, was
revising the overpressure protection report for Calvert Cliffs
Units 1 & 2. The overpressure protection report brings
together the Chapter 14 safety analysis and the ASME code
requirements. The ASME code requires that:
"...in determining the setting pressures and discharge
capacities required to comply with these rules, full
account shall be taken of the pressure drop in both inlet
and discharge sides of the pressure relief devices at full
discharge conditions. In addition, back pressure arising
from discharge of other devices through common discharge
piping shall be considered..."
Later, this observation set off a series of checks to determine
whether the existing safety analyses which support the
overpressure protection reports for other units accounted for
the line losses; it was found that the analyses omitted these
losses.
ABB-CE determined on December 6, 1996 that the omission of the
piping line loss constituted a deviation to be evaluated for
reportability pursuant to 10 CFR 21.
(vi) In the case of a basic component which contains a defect or
fails to comply, the number and location of all such components
in use at, supplied for, or being supplied for one or more
facilities or activities subject to the regulations in this
part:
The identified defect, omission of the pressure loss between
the SG and the MSSV inlet from safety analyses, applies to all
ABB-CE safety analyses involving MSSV actuation for nuclear
power plants for which ABB-CE was the nuclear steam supply
system vendor. Additionally, ABB-CE considers that this issue
may be applicable to other nuclear power plants regardless of
the nuclear steam supply system vendor.
ABB-CE has evaluated the non-LOCA thermal hydraulic safety
analysis consequence of omitting the pressure loss for Calvert
Cliffs Units 1 & 2, and San Onofre Units 2 & 3 because the
relevant line loss information was available. Information for
these facilities is summarized in the following table.
Table omitted
Attachment to LD-97-002
Page 3 of 3
These results indicate that the blowdown setting for Calvert
Cliffs Units 1 & 2 should be increased to preclude the
potential for MSSV chattering; a recommendation for such has
been made to BG&E. The San Onofre 2 & 3 results indicate that
no MSSV blowdown setting adjustment is necessary to preclude
potential chattering. For both the Calvert Cliffs and the San
Onofre facilities, a review of the affected thermal hydraulic
safety analyses determined that omission of the pressure loss
did not result in unacceptable analysis results with respect to
peak SG pressure.
A small break LOCA analysis was performed for Calvert Cliffs 1
& 2. This evaluation, based on information currently available
to ABB-CE, confirmed that the existing SBLOCA results for
Calvert Cliffs remain valid. SBLOCA analyses have not been
performed for other plants for which ABB-CE was the nuclear
steam supply system vendor.
(vii) The corrective action which has been, is being, or will be
taken; the name of the individual or organization responsible
for the action; and the length of time that has been or will be
taken to complete the action:
For plants for which ABB-CE was the nuclear steam supply system
vendor, ABB-CE has recommended that licensees conduct a review
to ensure that the unrecoverable piping pressure losses between
the SG and MSSV inlets have been fully addressed in the
applicable LOCA and non-LOCA thermal hydraulic safety analyses.
Utilities were also advised to review and adjust MSSV blowdown
settings if necessary to assure stable valve operation.
(viii) Any advice related to the defect or failure to comply about the
facility, activity, or basic component that has been, is being,
or will be given to purchasers or licensees:
ABB-CE notified each licensee for which it was the nuclear
steam supply system vendor of this issue on January 16, 1997.
The notification described the issue and indicated that ABB-CE
does not have sufficient information to perform all relevant
analyses. The notice also indicated that ABB-CE could not
assess the safety significance of potential structural aspects
of the issue which typically fall within the A/E's scope.
By way of supplemental information, the ABB-CE notification
also forwarded the Abstract from Licensee Event Report No 96-
031, dated November 4, 1996, submitted for the Millstone Unit 2
nuclear power plant on a related subject.
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