ML20151G534
| ML20151G534 | |
| Person / Time | |
|---|---|
| Site: | Callaway  |
| Issue date: | 07/15/1988 |
| From: | Schnell D UNION ELECTRIC CO. |
| To: | NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM) |
| References | |
| ULNRC-1808, NUDOCS 8807280418 | |
| Download: ML20151G534 (6) | |
Text
7
" Umon Etscraic n
1901 Gratet Street. St. Louis Donald F. Schnell Vce President July 15, 1988 N U.S. Nuclear Regulatory Commission ATTH:
Document Control Desk Mail Station P1-137 Washington, D.C. 20555 Gentlemen:
ULNRC-1808 DOCKET NUMBER 50-483 CALLAWAY PLANT ACCID _ENT___ DOSE CALCULATIONS This letter is to inform you of an issue regarding a potential increase in calculated radioactive releases to the environment following postulated events involving stean, release from secondary side relief valves.
The increase is caused by the water level dropping below the tops of the steam generator tubes.
Westinghouse informed Union Electric (UE) of this issue in December, 1987, at which time UE initiated an extensive evaluation of our accident analysis dose calculations to determine the extent to which this issue applies to Callaway.
The results of our evaluation are presented in this letter.
Background
A fundamental assumption of the radiological analyses for accidents involving steam release from the secondary side has been that elemental iodine, transferred from the primary side via tube leaks, will partition between the steam generator water and steam, such that the iodine concentration in the steam is a small fraction of the water concentration.
However, if the tube bundle is uncovered in the area of the leak / rupture, a direct release path to the environment may result; i.e.,
there will be neither dilution, by the secondary side water, nor partitioning of the activity carried by the leakage flow.
This concern about steam generator water level was raised by Virginia Power following a tube leak at the North Anna Plant which is equipped with Westinghouse Model 51 steam generators.
The utility reported the finding to the NRC on 12/10/87.
Westinghouse did not find the condition earlier due to analysis assumptions which maximized the water in the generator to minimize the margin to overfill.
th-AT CK 83 P
'll Makg Address P O Box 149. St. Lours. MO 63166
n-Although Westinghouse believes that all of their plants are potentially affected, the Model F-generators used at Callaway are considered.less likely to uncover than earlier design models.
_ Evaluation An evaluation has been performed to determine the impact on Callaway accident dose calculations.. The effects on offsite dose frca changes in the primary to secondary partition coefficient due to potential of steam generator tubes to uncover were evaluated for accidents' involving steam release from the secondary side.
These accidents include:
- La.rge Break LOCA
- Steam Generator Tube Rupture
- Main Steam Line Break
- Feedline Break
- Small Break LOCA
- RCP Locked Rotor
- RCCA Ejection
- Loss of AC Power The Large Break LOCA will not be affected by tubes being uncovered since the primary system pressure will quickly drop below steam generator pressure.
As such, there will be no primary-to-secondary leakage and therefore no dose increase even if there were to be a steam release from the secondary side to the environment.
The above listed accidents were evaluated assuming tubes being uncovered for the duration of the accident.
The Steam Generator Tube Rupture and Main Steam Line Break accidents were not affected since no partition factor for flashing primary-to-secondary leakage was assumed in the original analysis.
The Main Steam Line Break continues to bound the Feedline Break accident.
An evaluation was conducted for a Small Break LOCA assuming uncovered tubes for the duration of the two-hour site boundary dose period.
Activity was assumed to be released to the environment directly from the steam generator with the activity source utilizing the maximum primary to secondary leakage allowed by the Callaway Technical Specifications.
The evaluation concluded that the radiological consequences of a Small Break LOCA with steam generator tubes being uncovered are bounded by those of the Large Break LOCA.
l The results of the evaluation for the remaining accidents are given in the following tabulation comparing the revised doses with those calculated for the VANTAGE-5 (V-5) submittal
[(Reference; ULNRC-1470 (3/31/87) and Callaway Operating License Amendment 28 (10/9/87)]:
?.
"l '
BCF LOCKED ROTOB-
)
V-5 Submittal Revised Values Exclusion Area Boundary Thyroid Dose = 0.861 Rem Thyroid Dose = 23.9 Rem
. Whole Body Dose = 0.144 Rem Whole Body Dose = 0.402 Rem Low Population Zone Thyroid Dose = 1.03 Rem Thyroid Dose = 9.39 Rem Whole Body Dose = 0.0396 Rem Whole Body Dose = 0.0912 Rem RCCA EJECTION V-5 Submittal Revised __ Values Exclusion Area __ Boundary Thyroid Dose = 13.0 Rem Thyroid Dose = 17.6 Rem Whole Body Dose = 0.088 Rem Whole Body Dose ' O.137 Rem Lowlopulation Zone Thyroid Dose = 15.4 Rem Thyroid Dose = 16.0 Rem Whole Body Dose = 0.033 Rem Whole Body Dose = 0.0352 Rem LOSS OF_AC POWER V-5 Submittal Revised Values Exclusion Area _ Boundary Thyroid Dose = 0.0226 Rem Thyroid Dose = 0.0673 Rem Whole Body Dose = 1.42 E-4 Rem Whole Body Dose = 1.94 E-4 Rem Low Population 7.one Thyroid Dose = 9.10 E-3 Rem Thyroid Dose = 0.0345 Rem Whole Body Dose = 5.12 E-5 Rem Whole Body Dose = 7,11 E-5 Rem These results are all within acceptable criteria specified in the Standard Review Plan (NUREG-0800) and within the limits of 10CFR100.
Union Electric will document this evaluation in a~ future annual update of the Callaway Plant Final Safety Analysis Report.
If you have any questions, please contact us.
Very truly yours, i
Donald F. Schnell DS/ dis I
I t
cc Gerald Charnoff, Esq.
Shaw, Pittman, Potts & Trowbridge 2300 N.
- Street, N.W.
Washington, D.C.
20037 Dr.
J. O. Cermak CFA, Inc.
4 Professional Drive (Suite 110)
"althersburg, MD 20879 R. C. Knop Chief, Reactor Project Branch 1 U.S.
Nuclear Regulatory Commission Region III 799 Roosevelt Road Glen Ellyn, Illinois 60137 Bruce Little callaway Resident Office U.S.
Nuclear Regulatory Commission RRil Steedman, Missouri 65077 Tbm Alexion (2)
Office of Nuclear Reactor Regulation U.S.
Nuclear Regulatory Commission Mail Stop 316 7920 Norfolk Avenue Bethesda, MD 20014 Manager, Electric Department Missouri Public Service Commission P.O.
Box 360 Jefferson City, MO 65102 U.S.
Nuclear Regulatory Commission ATTN:
Document Control Desk Washington, D.C.
20555
bcca D. Shafer/A160.761
/QA Record (CA-758)
Nuclear Date DFS/ Chrono D.
F.
Schnell J.
E. Birk A.
P. Neuhalfen M.
A.
Stiller G.
L.
Randolph R.
J.
Irwin II. Wuertenbaccher W.
R. Campbell A. C.
Passwater R.
P. Wendling D.
E.
Shafer D.
J. Walker O. Maynard (WCNOC)
N. P. Goel (Dechtel)
GS6.37 (CA-4 60)
T.
P. Sharkey NSRB (Sandra Auston)
Lt. G. BM N 6. O s. G...m (C A %C) i i
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