ML19276E275

Forwards Addl Info Requested at 790223 Meeting Re Proposed Steam Break Protection Sys

ML19276E275
Person / Time
Site:	Beaver Valley
Issue date:	03/07/1979
From:	Dunn C DUQUESNE LIGHT CO.
To:	Schwencer A Office of Nuclear Reactor Regulation
References
TAC-11010, NUDOCS 7903120252
Download: ML19276E275 (6)

Text

-

4 %s T@

Duquesne Udit e,n .,, _

435 Sixth Avenue Pittsburgh, Pennsylvania 15219 March 7,19 79 Director of Nuclear Reactor Regulation United States Nuclear Regulatory Commission Attention: A. Schwencer, Chief Operating Reactors Branch No. 1 Division of Operating Reactors Washington, D. C. 20555

Reference:

Beaver Valley Power Station, Unit No. 1 Docket No. 50-334 Additional Information on Technical Specification Change Request No. 35.

Gentlemen: .

Enclosed are three (3) signed originals and thirty-seven (37) copies of additional information relating to the proposed new Steam Break Protection System for Beaver Valley No. 1 Unit. This information is being provided as a result of questions asked at a meeting held in Bethesda, Maryland on February 23, 1979 between members of your staff and representatives of the Duquesne Light Company and the Westinghouse Electric Corporation.

Electrical Question 1 Indicate where the instrument channel descriptions are available to the NRC.

Answer 1 -

The description of instrument channels in terms of changes to the BVPS equipment of the as-licensed system are as follows, from a functional.

standpoint:

This engineered safety features activation systems (ESFAS) logic function is to be eliminated.

1. Safety injection on high dif ferential pressure between steam lines.

The following ESFAS logic function is to be revised:

FROM Safety Injection and main steam line isolation on high steam flow in 2/3 steam lines coincident with low Tavg or low steam line pressure.

79031207 7

~

s Beaver Valley Power Station, Unit No. 1 Docket No. 50-334 Additional Information on Technical Specification Change Request No. 35 Page Answer 1 (continued)

))! Safety Injection and main steca line isolation on 2/3 stean line low pressure in any steam line.

The following ESFAS logic function is to be added:

Main steam line isolation on high negative pressure rate.

TS The " derivative-lag" signal compensation (1 + TS) for this new activation requirement utilizes si'gnal compensation functionally the same as that used in'the Tavg term of the overpower AT reactor trip setpoint calculator, presently in operation at BVPS No. 1.

Electrical Question 2 What specific separation criteria were applied to the sensors, cabling, instruments, and logic for the existing steam line break protection system.

If, as we understand', the same criteria are to be applied for the proposed new system, explain why the criteria are still appropriate and acceptable.

Answer 2 The specific separation criteria applied to the sensors, cabling, instrumnts, and logic for the existing steam line break protection system were provided in the Beaver Valley Unit No. 1 FSAR Amendments in the responses to the following NRC staff questions and positions:

1. Question 7.4 - See BVPS FSAR Amendment 2, dated 5/7/73.

2. AEC Regulatory Staff Position 13 (7/19/73). See BVPS FSAR Amendment 4, dated 9/10/73.

3. AEC Regulatory-Staff _ Position 51 48/30/74) _See BVPS FSAR Amendment 19, dated January, 1976.

The additional equipment being added to the existing system so as to translate into hardware the added functions of the new system, described in question 1 above, will be housed in analog process racks that are the same as that found acceptable, without change, by the NRC staff, in their review of the following topical report:

WCAP-8892-A " Westinghouse 7300 Series Process Control System Noise Tests", by R. M. Siroky and F. W. Mavasco, June, 1977.

All changes are being made at the process racks which have been reviewed and approved from the standpoint of adequate separation. The cabling to the sensors is not being changed and, therefore, the presently existing approved spacing vill continue to be adequate.

Beaver Valley Power Station, Unit No. 1 Docket No. 50-334 Additional Information on Technical Specification Change Request No. 35 Page Systems Question 1 Please ensure that your Technical Specifications (proposed or existing) provide positive assurance that [ safety injection cannot be blocked on low steam line pressure] until the RCS is borated to a cold shutdown condition.

Answer 1 Technical Specification 3.1.1.1 requires that the SHUTD0b'N MARGIN shall be > 1.77% /di at all times when Tavg is greater than 200 F.

In K

order to assure compliance with this specification Station Operating Procedures for cooldown require that the reactor coolant system be borated to the Xenon free hot shutdowa boron concentration prior to beginning a station cooldown from the Hot Standby Mode.

Since cooldown caused by a steam break accident will be terminated at a temperature greater than 200*F, the boration necessary to achieve the required shutdown margin is sufficient to assure that the reactor will remain sub critical at any temperature above 200 F.

Systems Question 2 Provide justification that Safety Injection is not required for all steam line breaks when the low steam line pressure portion of the system is disabled (i.e., during heatup and cooldown).

Answer 2 Because boration to cold ahutdown (as required prior to blocking any SI signal per Beaver Valley 3perating Procedures) provides more shutdown reactivity comparable to the actuation and subsequent oleration of the safety injection systems. Any breaks occurring while the SI actuation logic is blocked will, from a core standpoint, be less severe than bi ss occurring from hot shutdown prior to blocking SI. The Beaver Valley N . 1 FSAR shows that the results from analyses of the breaks from hot shutdown are acceptable. In the absence of safety injection signals, the charging pumps and CVCS will maintain pressurizer level at the no load level.

System Question 3 Shows the minimum pressurizer level and RCS temperature during a steam line break during heatup/cooldowns (pick worst case initial condition). Compare this value to the valve with the existing system.

(Scoping calcolations are OK.)

e Beaver Valley Power Station, Unit No. 1 Docket No. 50-334 Additional Information on Technical Specification Change Request No. 35 Page Answer 3 During heatup and cooldown, the safety injection and steam line isolation signals which are available are summarized in the following table (note those functions such as containment pressure, where no changes are proposed, are not shown):

Function Existing System New System Safety Injection Steam line AP None Steam line Isolation High Steam line flow

• High negative (any 2 loops) pressure rate (any loop)

• actual logic is high steamline flow coincident with lo-lo Tavg, any ? loops.

Interlocks prevent blocking SI above lo-lo Tavg, hence, the coincidence, while SI is blocked is always satisfied.

For the existing system, the largest cooldown rates would result for the case where all steam generators discharge uniformly, initially having a flow incrementally less than the high flow setpoint at hot shutdown, i.e., 40% of loop nominal flow per the present BVPS Unit'No. 1 Technical Specifications. This case would result in neither safety injection on steam line AP nor steam line isolation on high steam flow. Breaks resulting in higher initial flows provide steam line isolation, terminating the blowdown.

Although automatic protective action is not necessary to meet safety

~

criteria for the case above, the new system (high negative pressure rate) would provide steam line isolation.

System Question 4 Is the existing system used in the mitigation for the feedwater break accident, or any of the plant transients?

Answer 4 The steam line break (condition lV) accidents are the only accidents in the BVPS No. 1 FSAR which take any credit for the safety injection or

' steam line isolation signals for which modifications have been proposed.

Beaver Valley Power Station, Unit No. 1 Docket No. 50-334 Additional Information on Technical Specification Change Request No. 35 Page Systems Question 5 Will the new [ steam line break protection] system be activated during a feedwater accident or a plant transient? Will credit have to be taken for its actuation?

Answer 5 The steam generator and steam line pressures for the broken steam generator will eventually actuate safety injection and steam line isolation on low steam line pressure in one loop following a postulated feedline break accident. Steam line isolation has no effect on the ssytem transient, since the FSAR analysis assumes that the steam line check valves (in the loop with the break) isolates the intact steam generators from the break. Because safety injection is a benefit for feedline break, no credit was taken in the FSAR for safety injection occurring on steam line AP; taking credit for safety injection on low steam line pressure with the new system will not be done. The FSAR, therefore, conservatively describes the system response to the limiting rupture of a main feedwater pipe, and the conclusions stated therein ,

remain valid.

If you have any further questions on this matter, please contact my office.

Very truly yours,

)L0W C. N. Dunn Vice-President, Operations O

6

3...,

(CORPORATE SEAL)

Attest:

t !) / h 4,g sd ,

H.W. Staas Secretary COMMONWEALTH OF PENNSYLVANIA)

) SS:

COUNTY OF ALLEGHENY )

On this 7-N day of , 1979, before me, HENRY G. STOECKER , a Notary Pdblic in and for said Common-wealth and County, personally appeared C. N. Dunn, who being duly sworn, deposed, and said that (1) he is Vice President of Duquesne Light, (2) he is duly authorized to execute and file the foregoing Submittal on behalf of said Company, and (3) the statements set forth in the Submittal are true and correct to the best of his knowledge, information and belief.

~

T HENRY G. STOEC4ER, Notary Fwie h*2 MIS. A.egteny Ccwy, Pa.

Mr Cemnes.cr. E,rires febiary 20,1962