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#REDIRECT [[05000298/LER-1993-015, :on 930420,design Discrepancy in HPCI Sys Identified.Caused by Design Deficiency in Original Design. Mods Will Be Made to Startup from Current Refueling Outage to Correct Design Discrepancy]]
| number = ML20044E630
| issue date = 05/20/1993
| title = LER 93-015-00:on 930420,design Discrepancy in HPCI Sys Identified.Caused by Design Deficiency in Original Design. Mods Will Be Made to Startup from Current Refueling Outage to Correct Design discrepancy.W/930520 Ltr
| author name = Gardner R, Myers J
| author affiliation = NEBRASKA PUBLIC POWER DISTRICT
| addressee name =
| addressee affiliation = NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
| docket = 05000298
| license number =
| contact person =
| document report number = CNSS933117, LER-93-015, LER-93-15, NUDOCS 9305250256
| document type = LICENSEE EVENT REPORT (SEE ALSO AO,RO), TEXT-SAFETY REPORT
| page count = 4
}}
 
=Text=
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COOPER NUCLEAR ST ATION Nebraska Public Power District            "" " iA"N;"??s L""."Y" "'"
CNSS933117 May 20, 1993 U.S. Nuclear Regulatory Commission Document Control Desk Washington, D.C. 20555
 
==Dear Sir:==
 
Cooper Nuclear Station Licensee Event Report 93-015, Revision 0, is forwarded as an attachment to this letter.
Sincerely, R. L. Gardner Plant Manager RLG/j u Attachment cc:    J. L. Milhoan G. R. Horn J. M. Meacham R. E. Wilbur V. L. Wolstenholm D. A. Whitman INPO Records Center NRC Resident Inspector R. J. Singer CNS Training CNS Quality Assurance I
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On April 20, 1993, during efforts associated with the Design Basis Reconstitution Program for Cooper Nuclear Station, a design discrepancy in the High Pressure Coolant Injection (HPCI) System us identified. Due to an inconsistency in the                                                                                              ;
specifications for the flow orifice and the flow transmitter in the flow control                                                                                          !
system, the design flow of 4250 gpm for the HPCI system would not have been                                                                                              ,
automatically attained under transient or accident conditions.                                                                                                            [,
The flow orifice for the HPCI system was specified with a differential pressure range of 0 to 350 inches of watcr corresponding to a flow range of 0 to 5000 gpm.                                                                                        !
However, the associated flow transmitter was specified with a differential pressure                                                                                        i range of 0 to 300 inches of water corresponding to a flow range of 0 to 5000 gpm.
Tha effect of this difference is that the flow transmitter will indicate a higher                                                                                          ,
HPCI flow thsn the actual flow sensed by the flow orifice. The HPCI flow controller, which receives input from the flow transmitter, will adjust the HPCI turbine speed to produce a pump flow of 4250 gpm as indicated by the flow transmitter. Due to this inconsistency, it is estimated that the actual HPCI flow                                                                                        l rate would be 3934 gpm, rather than the design flow of 4250 gpm.
This design discrepancy was part of the original design of the Cooper Nuclear                                                                                              ;
Station. The Nuclear Steam System supplier has been notified of this concern to                                                                                            ;
i            further industry knowledge of any additional applications. Modifications will be                                                                                          j made prior to startup from the current refueling outage to correct this design discrepancy.
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  *        .                            LICENSEE EVENT REPORT (LER) TEXT CONTINUATION                                                ArmovEo oua uo siso oio.
EXPIRES: t/3itas FACatfYY NAME (1)                                                  ' DOCKET NUMBER (a                LER NUMBER 46)                                  PACE (3) vfAR    9 SENEM*'                  is$'8$''
Cooper Nuclear Station                                              o l5 jo l0 l0 l2 l9 l8    9l 3 ~~
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Ol0 0 l2        OF n l3 TEXT (# ancre spec, e sec*est, see eaWennef NAC Form J66AW IIM A.            Event Descriotion During the ongoing Design Basis Reconstitution Program for Cooper Nuclear Station, a design discrepancy was identified in the HPCI System.
This design discrepancy would result in a lower HPCI flow during transient and accident conditions than that used in the accident analysis. On April 20, 1993, at approximately 3:00 pm, this condition was determined to be reportable.                Since the plant was in a shutdown and defueled condition, the HPCI System was not required to be operable in accordance with Technical Specification 3.5.C.
B.            Plant Status Shutdown for the 1993 Refueling Outage, with the reactor defueled.
C.            Basis for Renort A condition that could have prevented the fulfillment of a safety function of a system needed to mitigate the consequences of an accident, reportable in accordance with 10CFR50.73(a)(2)(v).
D.            Cause This condition was a design deficiency in the original Cooper Nuclear Station design. Revision 2 of the vendor design specification changed the flow orifice differential pressure range from 0 to 300 inches of water to O to 350 inches of water corresponding to a HPCI flow of 0 to 5000 gpm.          This change was made because of a change in the pipe size from schedule 80 to schedule 100. However, the flow transmitter specification was not revised accordingly and remained at the original 0 to 300 inches of water corresponding to a flow of 0 to 5000 gpm.                                                Due to this inconsistency in the specifications, the design flow of 4250 gpm for the HPCI system would not have been attained automatically under transient or accident conditions.
E.            Safety Sirnificance The HPCI system is designed to provide core cooling and vessel depressurization for transient and accident conditions, particularly for small and intermediate sized LOCAs. For a large LOCA the vessel is depressurized rapidly and the HPCI system does not provide a significant contribution. For small breaks the HPCI system can provide sufficient flow to maintain vessel level and to'depressurize the vessel to the
                                      -point where the low pressure ECCS systems can provide long term core cooling. As the break size becomes larger, there is a point where the HPCI system cannot maintain vessel vater level, but the vessel pressure remains above the point where the low pressure ECCS . systems can inject into the vessel to provide core cooling.                  In this situation, the' Automatic Depressurization System (ADS) functions to depressurize the vessel below the pressure threshold of the low pressure ECCS systems.
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EXPIRES. 8/31/C9 F ActuTY NAME til  .                                        DOCKET NOABER U)            LER NUtd8f R f6)                        PACE (3) n~        "w                +ars,7:
l Cooper Nuclear Station                                      0l5l0l0l0l2lglg      9l3  --
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i E.      Safety Sinnificance - (continued)                                                                                          ;
The effect of the design discrepancy, which would result in a lower HPCI                                                    !
flow, is to slightly reduce the break size where the HPC1 would be                                                          I unable to maintain the vessel level. With this smaller break size the ADS would still be able to accomplish its safety function so that there would be no net effect on the accident consequences. The small break                                                      .l LOCA analysis applicable to the Cooper Nuclear Station assumes a total                                                      i i
loss of HPCI as a limiting single failure.              In addition, manual operation of HPC1 at actual flows of 4250 gpm or greater would not have                                                    =
been prevented, and an operator could reasonably be expected to manually                                                    j increase flow if level were not being maintained.                    Thus there is minimal significance associated with the lower HPCI flow.                                                                          j F.      S a fe ty Implications The safety implications associated with this design discrepancy are fully addressed above.
G.      Corrective Action At the time that this condition was discovered, the plant was in a refueling outage with the reactor defueled. The HPCI system is required to be operable when the reactor pressure is greater than 113 psig and thus is not required to be operable under these current refueling outage                                                    '
conditions.            Prior to reactor startup, this design discrepancy will be corrected by recalibrating the HPCI flow transmitter and ensuring that all applicable calibration procedures are revised.                        The only other                                  ,
system presently in service using the same general vendor design specification is the RCIC system and it has already been determined to be correctly calibrated. There was an RHR head spray orifice plate _                                                        ,
purchased under the same general vendor design specification, but this system has since been removed by a design change. To determine if this same problem exists with other systems, an investigation of other safety related flow instrumentation will be made before startup to provide assura. e that the HPCI flow design discrepancy is an isolated                                                              ;
occurrence.
The Nuclear Steam System supplier has been advised of this design discrepancy.                                                                                                                i H.      Similar Events None.
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