ML18152A632

LER 87-038-00:on 871208,calculated Offsite Thyroid Dose from Steam Generator Tube Rupture Increased Due to Potential post-trip Steam Generator Tube Bundle Uncovery.Caused by Reanalysis Using Updated FSAR assumptions.W/880107 Ltr

ML18152A632
Person / Time
Site:	Surry
Issue date:	01/07/1988
From:	Benson D VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.)
To:	NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM)
References
87-044, 87-44, LER-87-038, LER-87-38, NUDOCS 8801120257
Download: ML18152A632 (5)

Text

POW 28-06-01 NRC Form 366 U.S. NUCLEAR REGULATORY COMMISSION (9-831 APPROVED OM a NO. 3150--0104 EXPIRES: 8/31/88 LICENSEE EVENT REPORT (LER)

DOCKET NUMBER (2l I PAGE 131 I

FACILITY NAME (1)

Surry Power Station, Unit 1 o I s I o* I o I o 12 I 8 I OI f \ OF O I 4 TITLE <41 Increased urr-::>1te 1 hyroid Dose Calculations from Steam Generator Tube Rupture Due To Post-Trip Steam Generator Tube Uncovery EVENT DATE (5l LER NUMBER (61 REPORT DATE (7) OTHER FACILITIES INVOLVED IB)

MONTH DAY YEAR YEAR tit SE~~~~1:f1. @t ~~~~~ MONTH DAY YEAR FACII.ITY NAMES DOCKET NUMBERIS) 11 2 oIs s 1 sI 1- oI 3 Is - o I o oI1 o 11 a Is o 1s1010101 I I THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR §: (Check one or more of the foiloV(ingJ 111)

OPERATING MODE (9) N I - 73.71(b) 20.402lbl 20.4051c)

- 50,73(1)(211ivl 20.40&1*ll1 llil S0.38lcH1l

- S0.7311)(2)(v)

- 73.71 lc)

POWER LEVEL. -

1101 11 0 I 0 20.405(1)(1 l(lll S0.38(c)(2)

- S0.73(1)(2)(vii)

- OTHER (Specify in Abstract ba/ow and_ in Text, NRC Form

• 11(8= -

20.40511>11 Hllil S0.73(11(21(il S0.73(1H2)(viiil1AI 366AJ 20.40S(11(1l(Jv) _x 50.73(11(2)(1i)

- S0.73(1112llviii)(B) 20.405(*>11 llvl 50.7311) 12l Uiil S0.7311)12>1x)

LICENSEE CONTACT FOR THIS LER 112)

NAME TELEPHONE NUMBER AREA CODE D. L. Benson, Stat ion Manager COMPLETE ONE LINE FOR EACH COMPONENT FAILURE DESCRIBED IN THIS REPORT 113)

MANUFAC- MANUFAC*

CAUSE SYSTEM COMPONENT CAUSE SYSTEM COMPONENT TURER R~o~;tgke l!lllll!lllllll!l!l!l!l!lll!l!l!l!l!l!l!lll!l!l!l!l!l TURER I I I I I I I I *, I I I I I I I I I I I I ll!l!lllll!l~!l!l!l!l!l!l!l!l!l!l!lilllll!l!l!l!l!l! I I I I I I I

. SUPPLEMENTAL REPORT EXPECTED (141 MONTH DAY YEAR EXPECTED n YES (If yes, comp/eta EXPECTED SUBMISSION DA TEI ~

ABSTRACT (Limit to 1400 sfJ(Jcas, i.e** epproximately fiftean sing/e-spaca typawrittsn Jines/ 118)

NO SUBMISSION DATE 115)

I I I On December 8., 1987, with Unit 1 at 100% power and Unit 2 in cold shutdown, it was determined that the upper portion of the steam generator tube bundle may uncover following a reactor trip. The previous analysis had assumed that the tube bundle would remain covered. This condition was discovered when a review of the expected Surry station steam generator post-trip response was performed as a follow-up item to the July 15, 1987 North Anna steam generator tube rupture event. Uncovering the break location has the effect of reduced iodine partitioning and results in increased calculated offsite thyroid dose for the postulated steam generator tube rupture event. A re-analysis of this event was made and indicates that while the calculated offsite thyroid doses are increased, they remain well below the 10CFRlOO limits.

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~801120257 880107

~DR ADOCK 05000280 \

S tiCD NRC Form 366

POW 28-06-01 NRC Form lseA e e U.S. NUCLEAR REGULATORY COMMISSION 19-831 LICENSEE EVENT REPORT (LEA) TEXT CONTINUATION APPROVED 0MB NO. 3150-0104 EXPIRES: 8/31 /BB FACILITY NAME 111 DOCKET NUMBER 12) LER NUMBER 16) PAGE 13) .

Surrv Power Station Unit 1 o 1s 10101012 la Io al 7 - o 131 a -10 In nl? OF n In TEXT /ff,,,,,,. - ia twquitwl. u* MklitioMI NRC Form .11511A'1J (17) 1.0 Description of the Event On December 8, 1987, with Unit 1 operating at 100%

power and Unit 2 in cold shutdown for a maintenance outage, it was determined that the upper portion of the steam generator tube bundle may uncover following a reactor trip. This condition was determined to have the effect of increasing the calculated offsite thyroid dose during the postulated steam generator tube rupture (SGTR) event and is reported pursuant to the requirements of 10CFR50.73(a) (2)(ii). The duration of the uncovered tube bundle, using UFSAR assumptions of only one high head safety injection pump and 50%

auxiliary feedwater flow, is approximately fourteen (14)*minutes. During this time, the iodine partitioning factor (PF) used for offsite dose calculations was increased from the previously assumed value of 0.01 (no uncovered tube bunole) to 1.0 (assumes tube leakage occurs in uncovered portion of tube). This increase in PF was applied to the SGTR event safety analysis and revised offsite dose calculations were performed. The *results of this re-analysis are included in Table I. The re-analysis was performed using the existing UFSAR assumptions for operator response time and emergency equipment availability.

2.0 Safety Consequences and Implications Results of the SGTR re-analysis, taking into account the uncovered tube bundle, indicate that calculated offsite thyroid doses are increased.

However, revised offsite doses remain well below the limits set forth in 10CFRlOO.

3.0 Cause This condition was discovered when the expected post-trip response during a postulated steam generator tube rupture was examined for the Surry units. This was done following the North Anna tube rupture event to determine if post-trip tube uncovery was predicted for Surry. The evaluation predicted that the level dropped below the top of the tube bundle.

NAC FORM 366A

• U.S.GPO: 1986*0*824-538/455 19-831

POW 28-06-01 NRC Farm 386A 19-831 e e U.S. NUCLEAR REGULATORY COMMISSION LICENSEE EVENT REPORT (LEA) TEXT CONTINUATION APPROVED 0MB NO. 3150-0104 EXPIRES: 8/31 /88 FACILITY NAME (11 DOCKET NUMBER 121 LEA NUMBER (Bl PAGE 131 Surrv Power Station Unit 1 0 I5 I O I O I O I 2 I RI O RI i - OI OF n I r, TEXT /If - - ia -,und, u* MlditioMI NRC Form JISS4'*1 1171 The previous analysis had assumed that the tube bundle would remain covered following the reactor trip. As previously stated, uncovering the break location has the effect of reduced iodine partitioning and results in increased calculated offsite thyroid dose for the postulated SGTR event.

4.0 Immediate Corrective Action(s)

An initial estimate of the expected dose was made and calculated to be below the 10CFR100 limits.

5.0 Additional Corrective Action(s)

A re-analysis of the postulated SGTR event was made to calculate offsite dose and verify the expected dose was within applicable limits.

6.0 Action Taken to Prevent Recurrence None.

7.0 Similar Events Other plants with Westinghouse NSSS may be susceptible to this condition if post-trip tube uncovery is predicted for their steam generators.

8.0 Manufacturer/Model Number Westinghouse Model 51-F Vertical U-tube Steam Generator NRC FORM 366A 19-831

• U.S.GPO: 1986*0*824*538/455

POW 28-06-01 NRC Form 366A U.S. NUCLEAR REGULATORY COMMISSION (9-831 LICENSEE EVENT REPORT (LER) TEXT CONTINUATION APPROVED 0MB NO. 3150-0104 EXPIRES: 8/31/88 FACILITY NAME (11 DOCKET NUMBER (21 LER NUMBER (61 PAGE (31 Surry Power Station, Unit 1 o 1s Io 1*o Io 1 21 a I o s1 1 - 01 31 a - 01 o o 1 4 oF o 1 4 TABLE I Surry Steam Generator Tube Rupture Comparison of Calculated Doses to Limits

- Integrated Dose at Exclusion Area Boundary (REM)

SRP Section 15.6.3 10CFRlOO_

Calculated Acceptance Guideline Limit Thyroid/WB Thyroid/WB Thyroid/WB Existing UFSAR Case 0.25/0.27 Not Addressed 300/25 Case 1 11. 8/0. 082 300/25 300/25 Case 2 6.8/0.090 30/2.5 300/25 Case 1: Same assumptions as existing UFSAR case, except revised steam generator response, i.e., uncovered tube bundle is included, RCS and steam *generator secondary activity is equal to maximum allowable Technical Specification values and a pre-accident iodine spike has occurred.

Case 2: Same as Case 1, except. iodine spike is concurrent with the accident.

NRC FORM 366A 19-831

• U.S.GP0* 1986*0*6~4-53d,455

VIRGINIA ELECTRIC ANO POWER COMPANY Surry Power Station P. 0. Box 316 Surry, Virginia 23883 January 7, 1988 U.S .* Nuclear Regulat:ory Commission Serial No.: 87-044 Document Control Desk Docket No.: 50-280 016 Phillips Building Licensee No.: DPR-32 Washington, D.C. 20555 Gentlemen:

Pursuant to Surry Power Station Technical Specifications, Virginia Electric and Power Company hereby submits the following Licensee Event Report for Surry Unit: 1.

REPORT NUMBER 87-038-00 This report has been reviewed by the Stat:ion Nuclear Safety and Operating Committ:ee and will be reviewed by Safety Evaluation arid Cont:rol.

Very truly yours, David L. Benson Station Manager Enclosure cc: .Dr. J. Nelson Grace Regional Administrator Suite 2900 101 Mariet:ta Street, NW Atlanta, Georgia 30323