ML20112C049

Responds to NRC 841025 Request for Addl Info Re 840510 Application for Amend to License DPR-34,revising Tech Spec Re Helium Circulators Overspeed Trip Setpoint.Analysis Value Encl

ML20112C049
Person / Time
Site:	Fort Saint Vrain
Issue date:	12/27/1984
From:	Lee O PUBLIC SERVICE CO. OF COLORADO
To:	Johnson E NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV)
References
P-84537, TAC-55294, NUDOCS 8501110002
Download: ML20112C049 (11)

Text

'

PUBLIC SERVICE COMPANY OF COLORADO P. O. BOX 840 DENVER, COLORADO 80201 OSCAR R. LEE '

v,c c m. , o c,., Fort St. Vrain Unit No. 1 P-84537 Regional Administrator Region IV

, T.3

' g} Qi Nuclear Regulatory Commission )' i'#

611 Ryan Plaza Drive, Suite 1000 JAN- 41985 Arlington, Texas 76011 Attention: Mr. Eric H. Johnson DOCKET NO. 50-267 SL'BJECT: Circulator Overspeed Trip Setting:

Request for Additional Information

REFERENCES:

1.) PSC Letter, Lee to Collins dated May 10,1984(P-84137) 2.) NRC Letter, Johnson to Lee dated October 25, 1984 (G 84409)

Dear Mr. Johnson:

Attached for your review, as requested in Reference 2, is the additional information concerning PSC's application (Reference 1) to amend the Fort St. Vrain Technical Specification related to the helium circulators' overspeed trip setpoint. Your questions and the associated PSC responses are as follows:

Question 1 In the evaluation in Attachment 2 of the application it is stated that: "FSAR Section A.1.13.5 (new reference A.14.5) identifies the maximum credible overspeed condition as 135% of rated, resulting from a rupture of the reheat steam pipe downstream of the circulator, combined with failures of both the control system and the overspeed trip system." How is the speed limited to 135% of rated under these conditions?

8501110002 841227 F p DR ADOCK 05000267 NOC >

PDR ffji,y) O Rfff/l0 T b ro O V 8 I

i

PSC Response The maximum credible overspeed of a helium circulator is 12,890 RPM, which is 135% of rated speed. This condition results from a rupture of the reheat stea.r. pipe downstream of the drive turbine, combined with failures of both the control system and the overspeed trip system. Speed is then limited to 135% of rated due to the choked flow of- steam through the turbine nozzles, as was confirmed by proto type testing.

References:

FSAR Section A.14.5; GADR-85, page 67; GA-A12213, Part II, Page 22 (References are described in Attachment 1).

Question 2 The evaluation further states that the proposed increase in the trip setting "would still provide the automatic protective actions conservatively prior to the credible overspeed condition (135%) as designed." How has the response time of the protective system been tested to verify that the protective actions are completed conservatively prior to the credible overspeed condition?

PSC Response A response time delay of 50 milliseconds for solid state electronics and 1.5-2 seconds for hydraulically operated valves was utilized in the original 1969 accident analyses and WS 0004 (excerpt from GP-2335, and included as Attachment 2), both prepared by General Atomic Technologies, Inc. (GAT).

Calculations used in deriving the " Allowable Value" and " Trip Set Point", identified in Attachment 2, were in accordance with Reglatory Guide 1.105 (Instrument Set Points) and ISA-567.04-1982, " Set Points for Nuclear Safety Related Instrumentation used in Nuclear Power Plants." Actual response time testing is not performed since the maximum credible overspeed condition is not a safety limit and is less than the initial tested speed of 140% which was verified as non-damaging. Reference for response time testing: memorandum EL:1064:69:HAL.

Question 3 The evaluation also discussed the circulator disc and blade testing program at 140% of design speed and the testing that determined that blade shedding occurs at 170% of design speed (design speed is 9550 RPM). It is our understanding that these tests, described in FSAR Section A.14.5, " Disc Catcher," refer only to the helium compressor disc and blades and not the steam turbine. At what speed would disc failure or blade shedding of the steam turbine occur and how was this value determined? What other equipment could be damaged by the resulting missiles?

PSC Response Tests described in the FSAR, Section A.14.5, refer only to the belium compressor disc and blades, not the steam turbine disc and blading. However, an analysis was performed by computer code D0VTAL on the steam. turbine blade footing (root) which is expected to be the initial part to fail at 26,044 RPM or 273 percent of design speed. This is considerably higher than any anticipated operating speed of the circulator.

.The steam turbine is situated within a protective ring in the

. turbine casing. The protective ring and steam casing will absorb the energy of any disc fragments without damage to the primary closure or penetration liner.

References:

GADR-85, pages 57 through 60, Figures 33 and 34; FSAR Sections 5.10.2.2, 4.1.2, 4.2.2.1 and Figures 4.2-2 and 4.2-4.

Question 4-The Reference Design Manual, Document DC-21-1, Issue C, was reviewed for backgound information. In Section 2.6, " General Design Limits," Item d), the Allowable Continuous Speed-is stated to be 10,800 RPM-maximum,

a. What is the basis for this limit?

b. How is compliance with this limit ensured?

PSC Reponse

a. The " General Design Limit" for helium circulator allowable continuousspeed(steam drive) is 10,800 RPM, 113% of rated. From 10 to 13 percent above rated speed is a generally accepted industry standard for an electronic overspeed trip.

References:

GA Operation and Maintenance Manual, GA-A10349, page 32; FSAR Section 4.4.4.2.

b. During power operation there is a " low selected" signal which limits circulator speed to 105-110 percent of rated.

100% feedwater flow and normal two-loop operation correspond to helium circulator rated speed of 9550 RPM.

Refer to Piping and Instrumentation Diagrams 22-3 and 22-8, FSAR Section 7.1.2.6 and Figure 7.1-11.

Question 5 Our review of the Technical Specification Surveillance Requirements indicates that only the instrumentation components of the circulator trip system are required to be tested. In order to provide assurance of a timely trip, it appears that integrated system testing should be conducted which would verify completion of the trip function within the required response time. Provide a surveillance requirement to incorporate this type of testing.

PSC Response The individual instrumentation components of the circulator trip system are checked, tested,and calibrated on daily, monthly and refueling intervals, respectively. The trip circuitry, steam turbine supply, exhaust, and bypass valves, circulator auxiliaries and associated loop feedwater salves are tested in accordance with Fort St. Vrain Technical Specification Surveillance Requirements SR-5.4.1.3.7.a-R, 5.4.1.2.3.b-R, 5.4.1.2.4.b-R. The helium circulator overspeed trip set point is not an Engineered Safety Feature nor an input to the basic Reactor Protection System, but, is provided for the purpose of equipment protection only. Based on the above, PSC maintains that a requirement to incorporate response time testing is not needed.

References:

FSV Technical Specifications, Basis for LCO 4.4.1, page 4.4-13, " Circulator Shutdown Inputs"; FSV FSAR Section 7.1.3.

Question 6 Describe the safety classification of the components of the circulator trip system, including their power supplies.

PSC Response All components of the circulator trip system, including their power supplies, are Class I, Safety Related. All components of the circulator trip system, including their power supplies, are Safe Shutdown with the exception of the " Speed Switches - High" (steam turbine), which are not required for Safe Shutdown Cooling. It is noted that the " Speed Switches -

High" (water turbine) are Safe Shutdown.

References:

SR-6-2, " Safety Related Component Lists"; FSAR Sections 7.1.1, 7.1.3, 8.2.2.3, 8.2.2.4, and Appendix C-Criterion 19 through 26; Control Logic Diagram, 18-93-8; Piping and Instrumentation Diagram 21-1.

Question 7 Describe the status of the equipment qualification program required by 10 CFR 50.49 (e) and (f) for the comoonents of the circulator trip system.

PSC Response The equipment qualification program, required by 10 CFR 50.49 (e) and (f) for the components of the circulator trip system, is complete.

References:

P-83178; P-83280; P-84012.

If you have any questions, please contact Mr. M. H. Holmes at (303) 571-8409.

Very truly yours,_

0. R. Lee Vice President Electric Production ORL/DLF/sem Attachments

UNITED STATES OF AMERICA NUCLEAR REGULATORY COMMISSION In the Matter )

)

Public Service Company of Colorado ) Docket No. 50-267 Fort St. Vrain Unit No.1 )

AFFIDAVIT

0. R. Lee, being duly sworn, hereby deposes and says that he is Vice President of Electric Production of Public Service Company of Colorado; the Licensee herein; that he has read the foregoing responses regarding circulator overspeed conditions and knows the contents thereof, and that the statements and matters set forth therein are true and correct to the best of his knowledge, information and belief.

kW

0. R. Lee Vice President STATE OF h_.Iz> )

COUNTY OF rnie)

Subscribed y d sworn to before me, a Notary Public on this J/ap day of f()ft,,,t/ap/ , 1984.

, 64$,u, Notary Public h NJ My commission expires h- h ,198[.

Attachment 1 to P-84537 REFERENCES

1. Fort St. Vrain updated Final Safety Analysis Report.

2. GADR-85, April, 1971 (General Atomic), "PSC Helium Circulator Design Report."

3. GA-A12213, Part I and II, September, 19f2 (General Atomic),

" Steam Turbine Driven Circulators For HTGR."

4. GA-A10349, February, 1972 (General Atomic), " Operation and Maintenance Manual For The FSV 330 MW(e) HTGR Helium Circulators."

5. GA Technologies Inc. Letter dated September 4, 1984 (GP-2335), Kowal to Brey;

Subject:

Helium Circulator Trip Setpoint - Analysis Value Package.

6. Regulatory Guide 1.105, Revision 2, " Instrument Set Points."

7. ISA Standard 567.04-1982, " Set Points fct Nuclear Safety Related Instrumentation U,.ed in Nuclear Power Plants."

8. GGA Memorandum dated March 11,1969(EL:1064:69:(:HAL),

H. A. Long to E. V. Haake

Subject:

Helium Circulator Turbine Subsystem Transient Analyses.

9. PSC Piping and Instrumentation Diagrams; 21-1 Issue P, 22-3 Issue BQ, and 22-8 Issue Bk.

10. FSV Technical Specification Surveillance Requlrements SR-5.4.1.3.7.a-R, 5.4.1.2.3.b-R, 5.4.1.2.4.b-R.

11. SR-6-2, Issue AL (10/15/84), "FSV Safety Related Component Lists."

12. PSC Control Logic Diagram, IB-93-8 Issue AC.

13. PSC letters dated May 17,1983 (P-83178), August 15, 1983 (P-83280), and January 9,1984 (P-84012), Lee to Collins, Brey to Collins, Brey to Collins respectively;

Subject:

10 CFR 50.49 Environmental Qualification of Safety Related Electrical Equipment.

14. Fort St. Vrain Technical Specifications, as revised through Amendment No. 45.

m

__ _ _ = . . - - - - - . _ . . - _ . - . .-

o , l

\

Attachment 2 l

. to P-84537 l l

l l AllALYSIS VALUE ,

Page 1 of 4 Prepared by A.J. Kennedy j Date 12/06/84 j iERK SPEC NO. W5-93-004 REV. NONE FUNCTION: Circulator Trip

) RINCTIONAL UNIT: Circulator Speed High-Steam ,

ANALYSIS VALUE:

4 11,700 rpa (P-84137 dated 5/10/84).

PRESENT TECH SPEC TRIP SETTING: I 11,000 rpn LICENSING BASIS:

The speed sensing systen response and trip setting are chosen so that tmder

! the maxistat overspeed situation possible (loss of restraining torque) the circulator will remain within design capabilities (FSAR Section 7.1.2.6).

i SAFETY LIMIT:

None in tenns of fuel fhilure or breach of primary coolant pressure boundary. The design overspeed of the circulator is 13,500 rpm (FSAR Table 4.2-2).

A production circulator was tested up to 13,070 rpn at 180 psig helita -

pressure and subsequent teardown indicated no change to the hardware. Each production brake and disc assembly was spin tested (a 16,000 rpn at room temperature) which is an overspeed representative of 13,500 rpa at reactor operating conditions. Further, from tests and analyses, the disc catcher has been shown to provide complete containment of discs and blades for a failure at 190% (18,145 rpn) of rated speed (9550 rpn). (FSAR Section 1

A.14.3.3 and A14.5.

LIMITING INITIATING EVENT:

Loss of restraining torque (no compressor blades) and reheat steam pipe I ruptures. ,

1 i

._..,_..,-,..w-.,_,._.______. --, .,.,__.-m_,,__m.-~. . . _ _ , . . . . , . _ _ - . - - , _ , _ _ _ . _ , . , _ _ _ _

• Attachment 2 to P-84537 ANALYSIS VALUE Page 2 of 4 Prepared by A. J. Kennedy Date 12/06/84 FUNCTIONAL UNIT: Circulator Speed-High, Steam TRANSIENT OVERSHOOT:

See " Discussion" for details.

TRANSIENT TIME RESPONSE:

50 milliseconds for solid state electronics (utilized in 1%9 accident analyses performed by GA).

PROCESS MEASUREMENT ACCURACY:

Not applicable.

1

4

. Attachment 2 to P-84537 AMar.vMTM YALUE h se 3 of 4 Prepared by A. J. Kennedy i Date 12/06/P4  !

j FUNCTIONAL UNIT: Circulator Speed-High, Steam i DISCUSSION:

The two limiting accidents leading to circulator overspeed are loss of restraining torque (blade diedding) and reheat stean line ruptures. For loss of restraining torque, two trip settings were analyzed with both assuning a delay of 50 milliseconds due to solid state electrical circuitry with the following results:

I

Overspeed Trip Setting Peak Speed Beyond Trip 4

PM RPM Setting RPM 11,000 13,050 2,050 11,500 13,267 1,767 While an analysis value trip setting cf 11,700 rpa ( P-84137) was not investigated by GA at the time the above analyses were perforT:ed in 1969, an extrapolation of past analysis results indicate that a trip setting of 11,700 would also give acceptable results. Note that a change in trip setting of 500 rpn from 11,000 to 11,500 rpn results in only a 217 rpn in increased overspeed. This is due to limited driving power for the

circulator. An incranental increase of 200 rpn in the analysis value trip

, setting to 11,700 rpn then at most should result in about one half that increment in circulator overspeed. The resulting peak overspeed then would be 13,360 - 13,370 rpn which is less than the design overspeed of 13,500 rpm and thus acceptable.

1 Steen line ruptures downstrean of the circulator turbines were

! investigated. For these analyses the overspeed trip setting was 11,000 rpn and a 50 millisecond delay was utilized with the following results:

l l

i

'* Attachment 2 )

to P-84537 ANALYSIS VALUE l

Page 4 of 4 l Prepared by A. J. Kennedy  :

Date 12/06/84 FUNCTIONAL UNIT: Circulator Speed High-Steam DISCUSSION: (Continued)

Time Peak Speed Reached Peak Speed (Seconds)

Failed Other Failed Other 1422 1&Q2 1&Q2 1&Q.2 Cold Reheat Line Rupture:

No Control Action or Trip 13,26 4 1 2,587 4 .6 8.0 Nonnal Control 10,399 9,922 0 .4 1.1 Trip Active but No Control 11,517 11,345 0.6 1.4 Both loops Hot Reheat Line Rupture:

No Control Action or Trip 13,036 4.5 Nonnal Control 10,371 0.4 Trip Active but No Control 11,450 0.6 Fran the above it can be seen that with no control action or trip the design overspeed of 13,500 rpn is not reached. Further, with normal control, the trip setting is not reached. With the trip active but no normal control the transient overshoots are not large. The above data support an analysis value trip setting of 11,700 rpn since the design overspeed of 13,500 rpn is not reached for reheat stean pipe nJptures assuming no control or PPS trip.

.- _- - - , - - - _ - - _ - _ - - - _ _ - - _ _ _ - . - _ _ .