ML20093C990

Forwards Proposed Final Draft of Tech Spec Section 3/4.3.4 Re Turbine Overspeed Protection & Revised FSAR Figure 10.1-1 to Support Proposed Tech Spec Requirement for Inservice Testing of Steam Valves

ML20093C990
Person / Time
Site:	Byron
Issue date:	10/04/1984
From:	Tramm T COMMONWEALTH EDISON CO.
To:	Harold Denton Office of Nuclear Reactor Regulation
References
9272N, NUDOCS 8410110031
Download: ML20093C990 (12)

Text

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_p f'T Commonwealth Edison

' - [ ) one First National Plazt, Chic'go, llhnois j C '~J Addr;ss R; ply to: Post Offica Box 767 N /. Chicago. Illinois 60690 October 4, 1984 Mr. Harold R. Denton, Director

.0ffice of. Nuclear Reactor Regulation U.S.: Nuclear Regulatory Commission

Washington,:DC 20555 Sub ject: Byron Generating Station Units 1 and 2 Technical Specifications NRC Docket Nos. 50-454 and 50-455

. References (a):' August- 27,'1984 letter from B. J.

Youngblood to D. L. Farrar.

(b): September 19, 1984 letter from T. R.

Tramm to H. R. Denton.

Dear Mr. Denton:

This letter provides additional information to support proposed technical specification requirements for inservice testing of steam valves associated .with protection against turbine overspeed. NRC review is needed to finalize the Byron technical

. specifications.

Attachment 2 to reference (b) transmitted proposed technical specification section 3/4.3.4 regarding turbine overspeed protection. These changes were discussed in detail with the NRC Staff -shortly af ter the Proof and ' Review version of the Byron

. Technical Specifications was issued in December, 1983. The Technical Specification' changes proposed in-reference (b) are included in. Attachment A to this letter.

The bases for the proposed valve testing requirements are provided in Attachment B to this letter. Attachment C is the

. Westinghouse Steam Turbine Division's " Operation and Maintenance

, Memo 041" which contains the manufacturer's recommendation on the testing of the steam admission valvea for the Byron /Braidwccd turbines.

Attachment D 10 a revised FSAR Figure 10.1-1 which depicts the correct number and arrangement of the extraction steam non-return

check valves. A completely revised: figure will be incorporated into the~FSAR at the next amendment.

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October 4, 1984

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+ - We will be happy to make' cognizant design and operating h ' personnel-.available to discuss these specifications further. Please direct questions to this office.

O'ne:: signed original-and fifteen copies of this letter the

- attachments-are provided for NRC review.

Very truly yours, f/? fW T. R. Tramm Nuclear Licensing Administrator.

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cc: . Byron Resident Inspector nf t

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ATTACHMENT A Proposed Changes to Final Draft 4

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INSTRUMENTATION i 3/4.3.4 TURBINE OVERSFEED PROTECTION LIMITING CONDITION FOR OPERATION MOO 2 O 1904 l 3.3.4 At least one Turbine Overspeed Protection System shall be OPERAEL:.

APPLICABILITY: MODES 1, 2, and 3.

ACTION:

a.

With one throttle valve or one governor valve per high pressure turbine stea,m line inoperable and/or with one reheat stop valve or one reheat intercept valve per low pressure turbine steam line inoperable, restore the inoperable valve (s) to OPERABLE status within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />, or close at least one valve in the affected steam line(s) or isolate the turbine from the steam supply within the next 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />.

b.

With the above required Turbine Overspeed Protection System otherwise inoperable, within 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> isolate the turbine from the steam supply.

1 SURVEILLANCE REQUIREMENTS 4.3.4.1 The provisions of Specification 4.0.4 are not applicable.

1 4.3.4.2 The above required Turbine Overspeed Protection System shall be

k. demonstrated OPERABLE:

p torioW4. operaHen .31 dir ect- observuHow of %e movemht- of M

a. A aKt least once per Pdays by,4yci'n ;e;n ef tL. f.,11 ;q valves beim through at 1:est one complete cycle from the running position:

1) Four high pressure turbine throttle valves,

2) Four high pressure turbine governor valves,

3) Six turbine reheat.stop valves,

4) Six turbine reheat intercept valves, and

,b. by cycling Within 7 days prier to entering MODE 3 from-MODE 4,4each of the l

12 extractic.. steam nonreturn check valves :n !' M cymd from the closed position.

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c #: Aakt least once per 31 days by direct observation, v+4F 44y freedom of movement of^the 12 extraction steam nonreturn check valve weight arms.

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At. least once per 18 months by performance of, CHANNEL CALIBRATION on the Turbine Overspeed Protection Systems,1nd

e. f: At least once per-40 months by disassembling at least one of each of the va ves given in Specifications 4.3.4.2a. and b. above, and per-forming a' visual and' surface inspection of valve seats, disks and stems and verifying no unacceptable. flaws or corrosion.

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-ATTACHMENT B BASIS 4

3/4.3.4 TURBINELOVERSPEED PROTECTION This specification is provided.to ensure that the turbine overspeed protection instrumentation and the turbine speed control valves;are OPERABLE and will protect the turbine from excessive Loverspeed. ' Protection'from turbine excessive overspeed is required i since excessive overspeed of-the turbine could generate potentially damaging missiles which could impact and damage safety-related components,-equipment, or structures.

bORVEIL'LANCEREQUIREMENT4.3.2a (High Pressure Turbine and Reheat Valves)

These valves isolate large quantities of steam with high

, ipotential for_ delivering' energy to the rotor system. The turbine design. recognizes this potential in providing rapid action, dual

' shut,off capability in each path, remote testing capability, and a Iflow path that reduces the-effects of changes in flow distribution,

. load reducticns and thermal transients during testing. The testing

, intervals are'in accordance with the latest manufacturer's recommer.-

dations: " Operation and Maintenance Memo 041," Steam Turbine JDivision, Westinghouse.

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. SURVEILLANCE REQUIREMENTS 4 3.4.2b and c.(Extraction Steam Non-Return Check Valves)

_ These_ valves are provided to protect the turbine from reflux:ofisteam remaining in the feedwater heater shells and piping -

(following the pressure reduction caused by the actuation of valves 11n specification 4.3.4.2a. -The quantities of stored steam

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controlled by these valves are smaller and are divided up into

' separate, heater shells. .The feedwater heating system design, including these valves, did not intend routine full stroke. testing.

The extraction steam check valves are self closing swing

~ disk non-return valves which shut under the combined effect of

. gravity ' and reverse flow of . steam. The weight of the disk is partly cbalanced by a counterweight-and lever on the pivot shaft. A spring-cylinder acting.on (the -lever assists the start of the automatic closirg, butEis not! intended to close the valve fully against normal 1 steam flow and-pressure. In normal operation the spring assist is heldJclear by' air pressure acting on a piston under the spring. The

turbineltrip system releases the air pressure to assist the closing.

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l IManually stroking of the extraction steam non-return valves is possible under shutdown conditions by latching the turbine and applying the air pressure to the spring cylinder.

It is possible to hear and feel the disk contact the the seat solidly. This manual stroking--was not provjded for in the-design-but will be done within 7 days prior to entering Mode 3 from Mode 4.

_ The? engineering specifications provided for testing the extraction steam non-return check vaves during cperation by equali-zing 1the air pressure across the piston in the spring cylinder, permitting the spring-to partially close the disk against the steam flow. The ' rotation of the shaft accompanying the disk closure can be observed by movement of_the weight lever. The amount of movement observed'in other stations has depended on the extraction steam conditions and valve size, but has been ample to indicate freedom of movement, and-this will be verified during startup testing.

1Partia1' stroking demonstrates that the disk system is free at the beginning of the closing stroke where the steam closing Lforces are' smallest. As the disk enters a reverse steam flow the closing forces build up rapidly with progressive closure.

The design of the feedwater heating system is such that full stroke testing of the extraction steam non-return valves during turbine operation involves several penalties without~significant additional advantages over partial stroke testing. The motor-operated isolating valve must-be closed on on individual heater. Heater stages 1, 2, 3 and 4 are arranged in three parallel strings with cascaded-drains in each. string and heater stages 5, 6 and 7 are similarly arranged-in two parallel strings. An entire string is taken out of service, isolated and bypassed for maintenance. Isolating the extraction steam to a single intermediate heater involves several complications.

The motor operated valves are too large for routine manual operation,'do not have bypasses to allow controlled warmup conditions, stroke quickly (about 15 seconds), and are intended for

, _ turbine. protection against heater flooding. A comparison'of the thermal capacity of aiheater and the rate of heat transfer to the flowing condensate or_feedwater shows that cycling an extraction steam isolating valve' would cause rapid cooling and heating transients.

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Isolating the steam to a top heater drops the feedwater temperature to the steam generators. Isolating the steam to an intermediate heater causes the next heater to assume the heating load, approximately ~ doubling the steam demand and drain flow, and nearly quadrupling the potential for erosion and vibration in the affected heater and piping. The shell pressure collapses in the isolated w-

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+-  : heater? causing' insufficient: head-to discharge the cascading-drains to the,next--lower. heater. ' Rapid action of_the emergency drain control is required.to prevent 1 flooding, with the-potential.for. flashing in the' drain cooler ~section':from pressue decay.

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Isolating a heater degrades the cycle thermal performance, requiring a corresponding drop.in electrical output-for the same

= reactor. thermal = power.

Partial: closing of the extraction steam non-return check ,

';valvesLwith,the installed-test provisions demonstrates freedom of

- movement lwhile avoiding transient states. A 31. day interval will be-

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adequate:since it is likely that sticking conditions would develop during shutdown conditions'rather than in operation.

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4 ATTACHMENT C WESTINGHOUSE STEAM TURBINE DIVISION RECOMMENDATIONS 9272N

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' OPERATION & MAINTENANCE MEMO '

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i RECOMMENDED TESTING FREQUENCY FOR STEAM ADMISSION VALVES ON

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BB 296 NUCLEAR TURBINES WITH STEAM CHESTS NOVEMBER 14,1983 t lo ,

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I OW9d: - Approved:

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TxhrWcot Development Commercut OpereHone Powe Generation Serwce DMolon Steam Turt#*-Generator DMeion

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' ' OPERATION & MAINTENANCE MEMO 041

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Based on a review of testing frequency and performance data from Westinghouse turb incidents records and a 1982 survey of utilities operatine Westinghouse nuclear turbin concluded that for nuclear units with steam chests there 16 no significant difference in the v between testing fr valves tested weekly and those tested monthly. it was further noted that mont uency may be beneficial because it reduces the time a plant is operating in a " transient state."

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i 2 OPERATION AND MAINTENANCE INFORMATION N Westinghouse recommends that the throttle, governor. interceptor and reheat stop valves generator units with steam chests be tested monthly.

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ATTACHMENT D REVISED FSAR FIGURE 10.1-1 t

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