ML20214N720

Safety Evaluation Conditionally Supporting Rod Swap Technique & Util Nuclear Analysis Methods for Control Rod Worth Measurements

ML20214N720
Person / Time
Site:	Byron, Braidwood, 05000000
Issue date:	09/09/1986
From:	Office of Nuclear Reactor Regulation
To:
Shared Package
ML20214N712	List: ML20214N710 ML20214N720
References
NUDOCS 8609160445
Download: ML20214N720 (3)

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,D SAFETY EVAI.UATION BY THE OFFICE OF NUCLEAR PEACTOR REGUI.ATION REl.ATED TO OPERATION OF BYRON STATION, UNITS 1 AND 2 BRAIDWOOD STATION, UNITS 1 AND 2 COMPONWEAI.TH EDISON COMPANY DOCKET N05. STN 50-454, STN 50-455, STN 50-456 AND STN 50-457 INTRODUCTION In a letter dated October 24, 1983, Commonwealth Edison Company (Edison) submitted information describing the nuclear analysis methods used by Edison in support of control rod worth measurements using the rod swap technique for their Zion, Byron and Braidwood reactors.

BACKGROUND In March 1981 (Ref.1), we approved use of the rod swap technique for control rod worth measurements for Zicn Station Units 1 and 2, provided the predictions were done by Westinghouse. The rod swap technique has been used for four reload cycles on the Zion Units. Edison is now requesting approval of their use of their nuclear analysis methods to do the predictions for rod swap starting with the Zion 1 Cycle 8 reload.

To support its request, Edison has performed a rod swap benchmark study in

.. which rod swap analyses were performed for the four cycles of Zion data. The computer codes are as described in the Edison Topical Report on Benchmark of PWR Nuclear Design Methods NFSR-0016 (Ref. 2) which has recently been approved by the NRC. The calculational methodology used to generate the rod swap parameters is identical to that used by Westinghouse as described in Section 3.2 of WCAP-9863-A Rod Bank Worth Measurements Utilizing Bank Exchange (Ref. 3).

REVIEW The sumary of the Edison rod swap benchmark study, in the form of the percent l

differences between measured or inferred rod worth and the Edison predictions.

I has been reviewed. We have compared these results with the results obtained using Westinghouse predictions. In general the differences between measured or l

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inferred and predicted rod worths were smaller for the Edison data than for the Westinghouse data. The Edison differences (measurement-prediction x 100) prediction tended to be both positive and negative while the Westinghouse differences are almost totally negative. Of the 64 cases (4 cycles x 8 banks x 2 predictors) there were no differences greater than the design criteria of 215%. Only two differences were larger than 10%. Our review showed that over the four cycles analyzed, the average difference between the measured and predicted total rod worth values was -2.3% for Edison and -5.38% for Westinghouse. The average difference for individual control rod banks was

-1.0% for Edison and -5.09% for Westinghou.ie.

CONCI.USION Due to the intricacies of the rod swap calculations and measurement technique, previous NRC approval for rod swap use has required a baron dilution versus rod swap comparison. Edison has not performed a boron dilution versus rod swap comparison to validate their calculational ability. However, the benchmark study that they did perform is quite extensive and the results show their ability to perfonn the rod swap analysis with results comparable or better than those previously approved. On this basis we approve Commonwealth Edison Company's use of their nuclear analysis methods in support of control rod worth measurements using the rod swap technique. Use of the rod swap technique is still sub.fect to the other conditions of the March 12, 1981 approval, namely:

l (1) All banks (control and shutdown) will be measured, (2) Procedures as outlines in WCAP-9863-A will be followed.

(3) Design Criteria, Safety Criteria and Remedial Action as stated in Refs.

1, 4 & 5 will be followed, and (4) A report comparing measured and predicted rod worths will be sLbmitted to the NRC within 45 days of completion of the rod worth tests for the first use of rod swap on a reload at each unit.

Date of Issuance:

i l

t REFERENCES

1. Letter from S. A. Varga (NRC) to J. S. Abel (Edison) March 12, 1981.

2. Letter from F. C. Lentine (Edison) to H. R. Denton (NRC) "Comonwealth Edison Company Topical Report on Benchmark of PWR Nuclear Design Methods,"

July 27, 1983.

3. T. M. Camden, et al. " Rod Bank Worth Measurements Utilizing Bank Exchange,"WestinghouseElectricCorporationWCAP-9863-A(Proprietary)

May 1982.

4. Letter from T. R. Tram (Edison) to H. R. Denton (NRC) March 5,1981.

5. Letter from J. S. Abel (Edison) to H. R. Denton (NRC) February 4, 1981.

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eise as

{ inferred and predicted rod worths were smaller for the Edison data than for i the Westinghouse data. The Edison differences (measurement-prediction x 100) prediction

! tended to be both positive and negative while the Westinghouse differences j are almost totally negative. Of the 64 cases (4 cycles x 8 banks x 2

{ predictors) there were no differences greater than the design criteria of ,

! 115%. Only two differences were larger than 10%. Our review showed that over i

the four cycles analyzed, the average difference between the measured and ,

j predicted total rod worth values was -2.3% for Edison and -5.38% for- '

) Westinghouse. The average difference for individual control rod banks was t

j -1.0% for Edison and -5.09% for Westinghouse.

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! CONCLUSION i

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Due to the intricacies of the rod swap calculations and measurement technique,

) previous NRC approval for rod swap use has reouired a boron dilution versus j rod swap comparison. Edison has not performed a boron dilution versus rod 4

swap comparison to validate their calculational ability. However, the l benchmark study that they did perform is quite extensive and t'ie results show l

l their ability to perfom the rod swap analysis with results comparable or better than those previously approved. On this basis we approve Commonwealth

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Edison Company's use of their nuclear analysis methods in support of control rod worth measurements using the rod swap technique. Use of the rod swap technique is still subject to the other conditions of the March 12, 1981 l approval, namely

) (1) All banks (control and shutdown) will be measured.

l (2) Procedures as outlines in WCAP-9863-A will be followed.

(3) Design Criteria Safety Criteria and Remedial Action as stated in Refs, l

i 1, 4 & 5 will be followed, and

! (4) A report comparing measured and predicted rod worths will be submitted to the NRC within 45 days of completion of the rod worth tests for the first use of rod swap on a reload at each unit.

I Date of Issuance:

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