ML20085D263

Ro:On 721105,power Operated Relief Valve RV-2 on Steam Line B Failed to Close.Caused by Relief Valve Sticking in Open Position.Inner Valve & Guide Bushing Polished

ML20085D263
Person / Time
Site:	Robinson
Issue date:	11/30/1972
From:	Utley E CAROLINA POWER & LIGHT CO.
To:	Oleary J US ATOMIC ENERGY COMMISSION (AEC)
Shared Package
ML20085D244	List: ML20085D263 ML20085D296
References
NUDOCS 8307210094
Download: ML20085D263 (3)

Text

,

..z . .

my

O DJ%M 0 -

go.ui Carolina Power & Light Company -

November,- ' 1) [ -

e,'$/*g ,, I\

4 N6,/, 1, \

vocs 2

q, VV' '. W

. Mr. John F. O' Leary 2 G Us;;tc

_g ' "'

f.

ff ' G' . - g

~]

Q"",

Directorate of Licensing

[;

0 4 19 3 c.,

U. S. Atomic Energy Commission 8' R ,

. ' O/

Phillips Building $ rygECDoy pl/ 8 s N . _ _ , '. <

7920 Norfolk Avenue b CW M' Bethesda, Maryland 20014 H. B. ROBINSON UNIT NO. 2

) LICENSE DPR-23 MALFUNCTION OF POWER OPERATED RELIEF VALVE

.gegulatory; JQk-

Dear Mr. 'O' Leary:

l l

In accordance with Section 6.6.1.c Technical Specifications, it is reported that at 0333, November 5, 1972, with the plant in a hot shutdown condition, power operated relief valve (RV-2) on the "B" steam line failed to close after being remotely opened by the control operator. This malfunc-tion initiated an unplanned plant cooldown. However, cooldown rates and plant conditions permitted an orderly plant cooldown to the cold shutdown

, condition.

Plant conditions immediately preceding and at the time of the incident were as follows: At 2330, November 4, 1972, reactor power had been reduced to 707. to perform a weekly turbine valve test. At about 0103, November 5, 1972, difficulties were encountered in the turbine valve testing and a rapid reduction in electrical load from 520 FM to 150 FM was experienced.

As a result of this transient, the operator elected to manually trip the reactor. The steam dump system operated satisfactorily to control steam generator temperature and pressure. However, when the no-load T average was reached, power operated relief valve RV-1 malfunctioned and remained open for five minutes, reducing plant primary temperature to 509 F. Emergency boration was initiated for two minutes during this transient and was secured once plant conditions had stabilized.

At 0326, all requirements for a reactor startup were met and control rod withdrawal begun. Reactor coolant temperature was being maintained at approximately 547 F using the main condenser dump valves and the power

! operated relief valves. At 0333, with the reactor still suberitical, power operated relief valve RV-2 opened and would not close, initiating a cooldown of the primary system. Efforts to fail RV-2 shut by isolation of the control air and pulling electrical fuses were unsuccessful. The control rods were i

8307210094 721213 PDR ADOCK 05000261

S PDR

w. ~. _ u.w. -n - - = --- - -n 33e e .. . ..po% , 1 .n4 3, N C r ' 2 6bN

[A

O '

() '

V '

. ', Mr. O' Leary November 30, 1972 inserted and emergency boration begun at 0348. At 0349 safety injection actuated as a result of coincident low level and pressure in the pressurizer.

At approximately 0430, and based on an analysis of the pressure and tempera-ture transients, it was decided to cool the plant to a cold shutdown condition.

Emergency boration was secured about 0440 and safety injection at 0506. At 0900, the residual heat removal system was placed in service and by 1500 the reactor coolant system was approximately 200 F.

No safety limits or cooldown rates were exceeded during the transients and cooldown. The engineered safety systems operated as expected with the exception of safety injection valve SI-867A which did not open on the safety injection signal. The redundant valve in this system, SI-867B, performed as designed establishing the required flow path. Immediately following the incident, the torque switch on valve SI-867A was adjusted and the operation of the valve tested.

The release of activity through RV-2 was small and well within authorized release limits. It is calculated that the gross beta gamma particulate activity released was 0.217 millicuries, and that the tritium released was 1.561 milli-curies.

The reactor incident resulted from power operated relief valve sticking in the open position. When the valve was disassembled for inspection, the inner valve and guide bushing were found to be badly scored. The inner valve and guide bushing were polished on RV-2 and, as a precautionary measure, RV-1 and RV-3 were also disassembled and polished. The valve vendor was consulted and concurred in the repairs effected. Discussion with the valve i vendor concerning the selection of valve internal materials have been held.

Modification of valve internals to prevent future scoring are being investigated and will be accomplished if engineering studies in progress indicate this to be a reasonable solution to the problem. In the interim, power operated relief valve operation will be minimized.

A meeting of the Plant Nuclear Safety Committee was held November 5, 1972, to discuss the incident. On November 7, 1972, a meeting of the Company Nuclear Safety Committee was held to review the incident and the plans for

, return to power. This Committee recommended that a careful leak check and inspection of all safety injection penetrations of the primary system be made prior to making the reactor critical. The Plant Nuclear Safety Co=mittee met again on November 8, 1972, to discuss the incident further. After reviewing all availabic data, it was concluded that no unresolved safety question existed and that after following the precautions recommended by the Company Nuclear Safety Committee, that the plant could return to power.

As recommended, and prior to reactor startup, the reactor coolant piping was inspected at the following conditions:

Date Primary Temperature F Primary Pressure Psig.

Nov. 7 255 400 Nov. 8 410 650 Nov. 8 500 1500 Nov. 8 500 2235 i

a o,

O ,

Mr'. O' Leary November 30, 1972 The areas where safety injection penetrations enter the primary system were given a thorough visual inspection. No abnormal conditions were observed. -At 1317, November 8, 1972, a primary leakage rate test was performed and a total leakage of 0.17 gpm determined.

Additionally, the three power operated relief valves were successfully tested at secondary pressure of 85 psig and 700 psig prior to critical operation.

Operation of the plant since this incident has been normal and no further problems have been experienced with the power operated relief valves.

Yours very truly, cf ,

m // p E. E. Utley h2 Vice President Bulk Power Supply NBB/za J ec: Mr. C. D. Barham Mr. N. B. Bessac Mr. B. J. Furr Mr. S. Grant F

s

..i W

d f

I

+

{

r _