United States Nuclear Regulatory Commission - Protecting People and the Environment

ACCESSION #:  9612030134       

SIEMENS

November 22, 1996
HDC:96:064

Document Control Desk
ATTN: Chief, Planning, Program and Management Support Branch 
U.S.  Nuclear Regulatory Commission
Washington, D.C.  20555

10 CFR 21 Evaluation and Notification for EXEM PWR LOCA Model

This letter is written notification of a reportable defect per 10 CFR
Part 21 reported to the NRC Operations Center by facsimile on November
21, 1996.

In a telephone conversation on October 10, 1996, Siemens Power
Corporation (SPC) and its current PWR utility customers were informed the
NRC had rejected SPC's proposed 1991 changes made to the FCTF reflood
heat transfer correlations in the TOODEE2 code in the approved 1986 EXEM
PWR large break loss of coolant accident (LBLOCA) evaluation model. 
These changes were submitted to eliminate a non-physical trend in heat
transfer coefficients as a function of reflood rate in the 1986 EXEM PWR
LBLOCA evaluation model.

The NRC also determined, based on the information available to the staff,
the non-physical trend in the 1986 EXEM PWR LBLOCA evaluation model
constituted an unacceptable error.  These NRC determinations were
documented in a letter from R. C. Jones (USNRC) to H. D. Curet (SPC)
dated October 11, 1996.  As a result of these determinations, SPC
performed a 10 CFR 21 evaluation in accordance with the SPC procedures. 
This letter documents the results of this Part 21 evaluation.

The SPC Part 21 evaluation concluded the defect in the FCTF heat transfer
correlations in the 1986 EXEM PWR evaluation model to be a substantial
safety defect.  The basis for this conclusion rests on the fact that
certain plants analyzed with interim corrections to the FCTF heat
transfer correlations exceeded 10 CFR 50.46 limits.

Siemens Power Corporation

Nuclear Division         2101 Horn Rapids Road    Tel: (509) 375-8100
Engineering & 
  Manufacturing          P.O.  Box 130            Fax: (509) 375-8402
                         Richland, WA 99352-0130


Document Control Desk                                  HDC:96:064
November 22, 1996                                          Page 2

The affected PWR utilities have been kept informed of this issue by the
above-mentioned telephone conversation, a meeting conducted by the NRC
held on Wednesday, October 16, 1 996 in Rockville, Maryland regarding the
impact of the defect on calculated 10 CFR 50.46 criteria, and direct
communications between the utilities and SPC.  Actions taken and to be
taken to address the issue are provided in the Attachment.

Very truly yours,

H. Donald Curet, Manager
Product Licensing

/smg

Attachment

cc:  L.  J.  Callan (NRC)
     T.  E.  Collins (NRC)
     E.  Y.  Wang (NRC)
     L.  J.  Federico
     B.  N.  Femreite
     L.  E.  Hansen
     L.  J.  Maas
     J.  H.  Nordahl
     C.  M.  Powers
     R.  S.  Reynolds


                               Attachment
                                                                 Page A-1

                            REPORTABLE DEFECT

(i.)      Name and address of the individual informing the Commission

          H.  D.  Curet, Manager, Product Licensing, Siemens Power
          Corporation, 2101 Horn Rapids Road, Richland, WA 99352

(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.

          Each SPC fueled PWR that was analyzed with the SPC 1986 EXEM
          PWR LBLOCA model which contained a non-physical reflood heat
          transfer trend in the TOODEE2 code may have operated based on a
          non-conservative LOCA analysis prediction.

(iii.)    Identification of the firm constructing the facility or
          supplying the basic component which fails to comply or contains
          a defect.

          Siemens Power Corporation, Richland, WA.

(iv.)     Nature of the defect or failure to comply and the safety hazard
          which is created or could be created by such a defect or
          failure to comply.


          SPC observed a non-physical trend in the approved 1986 EXEM PWR
          LBLOCA evaluation model heat transfer coefficients computed by
          the FCTF correlations in the reflood rate range of
          approximately 1 in/sec to 1.77 in/sec.  In this range, as the
          reflood rate decreases, the calculated heat transfer
          coefficient can under certain conditions increase.  Though non-
          physical, the trend was considered by SPC to be conservative
          compared to FCTF experimental data.

          In 1991 SPC made changes to the FCTF reflood heat transfer
          correlations in the TOODEE2 code in the approved 1986 EXEM PWR
          LBLOCA evaluation model.  These changes were made to eliminate
          a non-physical trend in heat transfer coefficients as a
          function of reflood rate in the 1986 EXEM PWR LBLOCA evaluation
          model.  The NRC rejected those changes and also concluded,
          based on the information available to the staff, that the FCTF
          correlation model includes an unacceptable error not only
          because of the non-physical @eat transfer trend but also
          because of non-conservative heat transfer model predictions.

          To correct the unacceptable error, SPC implemented two
          specific, interim modifications to the FCTF reflood heat
          transfer correlations in the TOODEE2 code in the 1986 EXEM PWR
          LBLOCA evaluation model to eliminate the non-physical trend in
          the two following ways:

          Interim Option 1.  The reflood heat transfer coefficients were
          restricted to increase linearly between the values calculated
          by the FCTF reflood heat transfer correlations for reflood
          rates of 1 in/sec and 1.77 in/sec.

          Interim Option 2.  The reflood heat transfer coefficients
          calculated over the entire reflood range were not allowed to
          exceed the heat transfer coefficient value at the reflood rate
          of 1.77 in/sec.

          LBLOCA analyses with Interim Options 1. and 2.  were or are
          being performed for SPC fueled plants.


                               Attachment

                                                                 Page A-2

(v.)      The date on which the information of such defect or failure to
          comply was obtained, October 10, 1996 was when the NRC informed
          SPC of the determination of an unacceptable error in the 1986
          EXEM LBLOCA evaluation model (i.e., TOODEE2 code).  LBLOCA
          analyses on October 12-13, 1 996, with the interim options
          implemented in TOODEE2 determined that 10 CFR 50.46 criteria
          could have been exceeded for certain plants.

(vi.)     In the case of a basic component which fails to comply, the
          number and the location of a# such components in use at,
          supplied for, or being supplied for one or more facilities or
          activities subject to the regulations in this part.

          Each SPC fueled PWR, which can have reflood rates of less than
          1.77 in/sec before the occurrence of PCT and are analyzed with
          the SPC 1986 EXEM PWR LBLOCA model, as modified with Interim
          Options 1. and 2. to eliminate the non-physical reflood heat
          transfer trend, may be predicted to exceed 10 CFR 50.46
          criteria.  (See Table 1).

(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.

          SPC has evaluated six SPC fueled PWRs (See Table 1): four with
          Interim Option 1.  and two with Interim Option 2.  With the
          exception of Kewaunee, all have provided the NRC with 50.46
          notifications of the impact of the evaluations.  If required,
          plants took compensatory action to remain within 50.46
          criteria.

          TU Electric evaluated Comanche Peak Units 1 and 2 and has
          provided or will provide the NRC with 50.46 notifications.

          SPC is currently developing a modification to the TOODEE2 code
          which eliminates the previously observed non-physical reflood
          heat transfer trend.  A topical report to the NRC describing
          and justifying this modification is scheduled for submittal to
          the NRC by December 16, 1996.

          Once NRC approval of the topical report is received, LBLOCA
          analyses with the new model will have to be performed for SPC
          fueled PWRs to establish analysis of record PCTs for each
          impacted plant.

(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.

          All current SPC fueled licensees have been and are maintained
          fully informed of the defect and actions being taken to correct
          the defect.  All such licensees will be advised that once the
          NRC approves a modification to TOODEE2 to correct the defect,
          they should assess if notification of the NRC under 10 CFR
          50.73 requirements is necessary.

          SPC supplied a final reload to AEP's D. C. Cook Unit 2 in 1988. 
          This reload was analyzed with the 1986 EXEM PWR LBLOCA
          evaluation model containing the nonphysical trend.  AEP will be
          made aware of this defect and advised that once the NRC
          approves a modification to TOODEE2 to correct the defect, AEP
          should assess if notification of the NRC under 10 CFR 50.73
          requirements is necessary.


                               Attachment
                                                                 Page A-3

Table 1

Summary of SPC Interim Evaluations

     Plant                         Disposition

Harris         Analyzed with Interim Option 2. and determined to meet
               50.46 criteria without compensatory action.

Palisades      Analyzed with Interim Option 2. and determined to meet
               50.46 criteria without compensatory action.

St.  Lucie 1   Analyzed with Interim Option 1. and determined to meet
               50.46 criteria without compensatory action.

Millstone 2    Analyzed with Interim Option 1. and determined to meet
               50.46 criteria without compensatory action.

Robinson       Analyzed with Interim Option 1. and determined to require
               compensatory action to meet 50.46 criteria.

Kewaunee       Analyzed with Interim Option 1. and determined to require
               compensatory action to meet 50.46 criteria.

     Note:

     Interim Option 1.  The reflood heat transfer coefficients were
     restricted to increase linearly between the values calculated by the
     FCTF reflood heat transfer correlations for reflood rates of         
     1 in/sec and 1.77 in/sec.  With the 1986 model reflood rates greater
     than 1.77 in/sec, heat transfer coefficients are not to exceed the
     heat transfer coefficient value at the reflood rate of 1.77 in/sec.

     Interim Option 2.  The reflood heat transfer coefficients calculated
     over the entire reflood range were not allowed to exceed the heat
     transfer coefficient value at the reflood rate of 1.77 in/sec.


*** END OF DOCUMENT ***

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