ML19317F244

Submits Addl Info Re AO-287/75-07 Submitted 750627 Re Excessive Cooldown Rate.Corrective Action:Shutdown Procedures Revised for All Units & Pressurizer Relief Valves to Be Examined

ML19317F244
Person / Time
Site:	Oconee
Issue date:	08/08/1975
From:	Parker W DUKE POWER CO.
To:	Moseley N NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
References
NUDOCS 8001080955
Download: ML19317F244 (4)

Text

.

• * . s. NR, ~ $1STRIBUTION FOR PART 50 DOC T MATERIAL

. (TEMPORARY FORM)

A'CA CONTROL NO:

FILE: INCIDE!T REPORT rn.

FROM:hke Pcwer Co. DATE OF DOC DATE REC'D LTR TWX RPT OTHER Charlotte, North Carolina William O. Darker 8-8-75 8-18-75 :C{

ORIG CC OTHER SENT AEC PDR m TO:

' :CCC NEC 1 St.~ned SENT LOCAL PDR CLASS UNCLASS PROPINFO INPUT NO CYS REC'D DOCKET NO:

CCC 1 50-287 DESCRIPTION: ENCLOSURES:

Re their let ur of 6-27-75. . . . . . . Trans th'e Abnormal Occursnee f 75-7,C: aing miner fol1cving................. system transit............

(1 Copy Enclosura Feceived)

PLANT NAME: Cconee 1-212 s FOR ACTION /INFORMATION m: ?-go 7c BUTLER (L) SCHWENCER (L) ZIEMANN (L) REG AN (E)

W/ Copies W/ Copies W/ Copies W/ Copics CLARK (L) STOLZ (L) DICKER (E) LEAR (L) DONOT REMO3TE W/ Cocies W/ Cocies W/ Cocies W/ Copies PARR (L) VASSALLO (L) KNIGHTON (E) SPELS W/ Copies W/ Copies W/ Copics W/ Copies KNIEL (L) YOUNGBLOOD (E)

CKhy0WLEDGED

/ PURPLE (L)

W/ Copies V/lfCopies W/ Copics W/ Copies INTERNAL DISTRIBUTION 6 REG FILD TECH REVIEW DENTON LIC ASST A/T IN D .

yGRIMES BRAITHAN f NhG FOR SCHROEDER R. DIGGS (L )

SALTZMAN OGC ROO*4 P.50GA #MACCARY GAMMILL H. GE ARIN (L)

GOSSICK/ST AF F KNIGHT KASTNER E. GOULBOURNE (L) MELTZ f CASE PAWLICKl BALLARD P. KREUTZER (E)

GIAMBUSSO SHAO SPANG LE R J. LEE'L) PLAMS BOYD **s STE LLO M. RUSHER 00K (L) MCDONALD MOORE (L) **fHOUSTON ENVIRO S. REED (E) CHAPMAN DEYOUNG (L) NOVAK MULLER M. SERVICE (L) DUBE (L:r) f SKOVHOLT (L) ROSS DICKER jS. SHEPP ARD (L) E. COUPE KNIGHTON M. SLATER (E) PETERSON GOLLER (L) (Ltr) f lPPOLITO P. CO LLINS /TEDESCO YOUNGBLOOD H. SMITH (L) HARTFIELD (2)

DENISE J. COLLINS REGAN S. TEETS (L) KLECKER REG OPR LAIN AS PROJECT LDR G. WILLI AMS (E) EISENHUT

/Fil E &TEGION (2) BENAROYA V. WILSON (L) *WIGGINTON p.?dIPC/PS (3) ,VOLLMER HAR LESS R. INGRAM (L) F. WILLI /c!S STEELE x, puncan (g3 , nAxy.p, EXTERNAL DISTRIBUTION p1 - LOCAL PDR Walhalla, South Carolina pl - TIC (ABERNATHY) (1)(2)(10) - N ATION AL LABS 1 - PD R. SAN /LA/NY 1 - W. PENNINGTON, Rm E 201 GT 1 - BROOKHAVEN NAT LAB f l - NSIC (BUCHANAN) 1 - G. ULRIKSON. ORNL 1 - ASLB 1 - CONSU LTANTS 1 - Newton Anderson NEWM ARK /BLUME/AG B ABI AN 1 - AGMED (RUTH GUSSMAN)

Rm B 127 GT 4- ACRS . SE:7 To LIC t.ssT 1 - J. D. RUNKLE'S, Rm E-201

• • SEND ONLY TEN DAY REPORTS GT

[ [ 80010 8 0 7[ J

p *

. . N 3 g , m!s,.g DUKE POWER COMPANY ,.

'7  %

Powra Btntonwo f A b 422 Socin Cut:ncu Srazer CnAntoriz. N. C. asa.aaN O ISIE  !!- '

N E.Z,p*

ds

,N wiwu o. manaca.sa,

1. cc pacs,ec , _

cy ,s f'

.yy tmap 7a.

Sn. pacewerto= TRegulatory ' file Cy2 6 >4ces August 8, 1975 fs Me m - .

^

Mr. Norman C. Moseley, Direct.or J U. S. Nuclear Regulatory Commission Suite 818 230 Peachtree Street, Northwest Atlanta, Georgia 30303 Re: Oconee Nuclear Station Docket No. 50-287

Dear Mr. Moseley:

My letter of June 27, 1975, transmitted to you Abnormal Occurrence Report A0-287/75-7, Excessive Reactor Coolant System Cooldown Rate.

The following'information provides additional information relating to this occurrence and associated corrective action.

As stated in A0-287/75-7, when reactor power level had decreased in the course of a routine maintenance shutdown,. a minor system transient

, occurred, which resulted in the opening of the power-operated. relief valve 3RC-66. Prior to the system transient, reactor power was being reduced from 100% FP to 15% FP in an orderly manner by the Integrated

, Control System. When 15%.FP was reached, unit load demand was 65 MWe, and power generation was 115 MWe. This difference between unit load demand and power generation existed because the reactor was operating at its low limit of 15% FP while in automatic ICS control and could not further follow unit load demand. Meanwhile the control operator placed the turbine control station in manual, leaving the ICS in the " load tracking" mode. This led to a rapid increase in unit load demand to match the generated megawatt output. In the meantime, the main steam bypass valves opened; and when the main steam pressure decreased, the valves closed. The ICS control of feedwater flow could not follow the rapid change in unit load demand and steam pressure; consequently, feedwater flow and steam generator level oscillated, resulting in the Reactor Coolant -System temperature and pressure transient.

The power operated relief valve, 3RC-66, opened w'ra RCS pressure reached 2255 psi but failed to close when the pr_asure dropped below 2220 psi, although the open/ closed lights in the control room did not

-indicate that the valve was open. Consequently, RCS pressure dropped, the reactor tripped on low pressure, and the HPI system actuated.

v D'9p 4

~

Mr. Norman C. Moseley Page 2 August 8,1975 Although the operator closed the isolation valve, 3RC-4, immediately af ter the reactor trip to terminate the depressurization, the valve was reopened because of the rapidly rising pressurizer level. Valve 3RC-4 was finally closed when RC pressure reached 800 psi, terminating the pressure transient. The subsequent controlled cooldown of the Reactor Coolant System, when combined with the temperature drop during the transient, resulted in a cooldown of 101 F during the first hour when temperature was below 530 F, contrary to the provisions of Technical Specification 3.1.2.3. The transient and associated events also caused the quench tank rupture disc to blow open, Mirror insulation to be separated from the bottom nozzle of the pressurizer, and the release of approximately 1500 gallons of reactor coolant to the Reactor Building sump.

The release of reactor coolant did not cause any significant increase of radiation level in the Reactor Building, and no radioactivity was released into the environment.

As addressed in A0-287/75-7, the excessive cooldown rate associated with the transient has been evaluated and it was determined that the health and safety of the public was not affected. No other system limits were exceeded.

The failure of 3RC-66 to close and the malfunctioning of the valve position indication in the Control Room have been investigated. It has been found that the valve was stuck in the open position because of heat expansion, boric acid crystal buildup on the valve lever, rubbing of the level against the solenoid brackets, and bending of the solenoid spring bracket. The valve was repaired and reinstalled.

The malfunctioning of the valve position indication was not observed when the repaired valve was reisstalled. This malfunctioning was apparently caused by the sticking of the solenoid plunger at slightly less than the full open position or by the crud buildup around the plunger operated microswitch to the open/ closed lights.

Additionally, to prevent recurrence of this incident, the following corrective actions have been or will be implemented.

1. The unit shutdown procedures for all Oconee units have been revised to include a change that will prevent decreasing unit load demand belcw 120 MWe before placing the ICS in the tracking mode. This would minimize the error between the unit load demand and generated power and thus would reduce the possibility of feedwater flow and RCS transients.

2. The Units 1 and 2 power-actuated pressurizer relief valves will be examined as soon as possible for any indication of boric acid crystal buildup.

f 1 O e

- t'

,.o. ,--

~.

Mr. Norman C. :foseley Page 3 August 8, 1975

3. To verify the proper functioning of RC-66, a test to cycle RC-66 prior to startup with a test signal corresponding to 2285 psi will be incorporated into the station operating procedures.

4. The quench tank rupture disc has been replaced, and the bottom nozzles on the pressurizer were dye penetrant tested and the Mirror insulation replaced.

5. Operating personnel have been advised of this incident with specific instructions that immediate closure of 3RC-4 is the proper corrective action for such an occurrence.

Ve truly yours, 7-q..

, Willi a.

am O. Parker, Jr.

PMA:vr cc: Mr. Angelo Giambusso