United States Nuclear Regulatory Commission - Protecting People and the Environment


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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