ML19098B408

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Letter Response to Request, Forward Overpressure Long-Term Improvement Design for NRC Review & Approval
ML19098B408
Person / Time
Site: Surry  Dominion icon.png
Issue date: 02/25/1977
From: Stallings C
Virginia Electric & Power Co (VEPCO)
To: Reid R, Rusche B
Office of Nuclear Reactor Regulation
References
Download: ML19098B408 (12)
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VIRGINIA ELECTRIC.A.ND POWER COMPANY RICHMOND, VIRGINIA 23261 WfB 2 5 1977 Mr. Benard C. Rusche Director of Nuclear Reactor Regulation U. s. Nuclear Regulatory Commission Washington, D. C.

20555 Docket Nos. 50-280 50-281 DPR-32 DPR-37 Attn:

Mr. Robert W~ Reid, Chief Operating Reactors Branch 4 License Nos.

Dear Mr. Rusche:

IR\\egu,atorv Docket A\\e.

As requested in your letter of January 10, 1977, we are forwarding our overpressure long-term improvement design for your review and approval.

We will have this system installed prior to December 31, 1977. Attachment "A" includes logic and system diagrams of our existing system and of the proposed modifications. This system meets your requirements for schedule and design as set forth in your letter of January 15, 1977.

Specifically, as requested, any exceptions to your final criteria are hereby addressed. This design meets all of the final criteria except the following tw_o requirements, from IEEE 279, for electrical components:

1) The requirement of automatic removal of a bypass (Section 4.12)

The bypass function will be served by two key lock switches, one for each power operated relief valve, under administrative control. The switch will be enabled at the proper point (temperature vs. pressure) on the cooldown curve and disabled at the proper point on the heatup curve. The position of the switch versus system requirements will be annunciated to indicate improper system aligrnnent.

2) The requirement of identifying components as to protection grade (Section 4.22)

The existing components are mounted and wired in control cabinets and wireways. However, channel independence conditions of section 4.6 are met, as the channels are totally separate and the new system will also be installed separately. To disrupt the existing system to move the components and wires into protection marked areas does not provide a sufficient *advantage to be worth the risk involved to the rest of the station.

These exceptions to the final design criteria represent good engineering practice and do not adversely affect plant safety or introduce potential common mode failures that could both cause the overpressure event and disable

e VIRGINIA ELECTRIC AND POWER COMPANY TO Mr. Benard C. Rusche Page 2 the protection system. It must be noted that the boundary analysis is not yet completed; hence, the size requirements and set points for the overpressure system have not been finalized. However, the submitted design allows sufficient flexibility to accommodate any expected developments.

Attachment "B" includes our response to the staff positions and requests for additional information identified in the attachment of your January 10, 1977 letter.

Attachments Vice and Very truly yours,

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-w>j C. M. Stallings

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President-Power Supply Production Operations

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I I !. e ATTACHMENT B . ANSWERS TO STAFF POSITIONS AND ADDITIONAL INFORMATION REQUESTS 1 a&b) The fonnal discussions with operation's personnel will be held during formal retraining sessions by June 1, 1977. 1 c) Due to equipment.differences the following overpressure event is not credible: a) Conditions leading to overpressure e*vents when the RHR system automatically isolates - the RHR isolation valves have no automatic closure feature. 1 d) The likelihood of otherwise credible events is minimized by:

1) eliminating isolation of RHR by inadvertant closure of a suction valve - lock open isolation valves and HCV-1142 implemented by change to OP-1.1,14 and 3.4(4.14)
2) Minimizing the time of water solid conditions impl~mented by Standing Order
3) Minimizing charging pump use at low pressure -* lock 2/3,*

pump breakers out of service implemented by change to OP-lcl

4)

Insuring letdown - open nonnal and orifice.letdownvalve imple-mented by change to OP-lel

5)

Insuring instrument air to containment by use of turbine building instrument air tie-in implemented by change t.o OP-L l

6)

Lowering operating pressure for RCP operation implemented by Westinghouse Technical Bulletin 76-11 and change to OP-1.1

7)

Using computer trend for pressure and temperature monitoring implemented by change to OP-1.1

8) Starting RCP while solid will be limited as follows:
1)

When RCS temper.ature is less than 150 degrees F, pressure must be between 320 and 350 psig.

2)

When RCS temperature is greater than seal water temperature; the Operating Supervisor's permission is required to start a RCP..

3)

One RCP shall be running at RCS temperature greater than 160 degrees Fe

2 a) e

9)

A setpoint change to give an alarm in the control room when the RHR pressure is greater than 480 psig. All water solid conditions have been eliminated other than the fill and vent procedure, with the Operating Supervisor's permission required for that procedure; implemented by change to OP-1,:

  • 2,
  • 3, 14 2 b)Reasons not to use the following procedures:
1) Nitrogen gas is not desired for a pressurizer bubble as nitric acid formation occurs in the pressurizer with resulting clad cracking.
2)

An air bubble is not desired since it contains 80% nitrogen and nitric acid formation can also occur. The high oxygen concentrations are also not desirable.

3)

A steam bubble is not desired as oxygen content must be less than 0.15 ppm when the RCS temperature is greater than 250 degrees F (T.S. 3.1 F) Therefore~a steam bubble must be formed after the system is filled and vented and chemistry control established. 3 a&c) A schematic of the SIS is attachment 11C1' 3 b) The head-flow characteristics of the low-head SI pumps are attach-ment "D" The head-flow characteristics of the high-head SI pumps are attach-ment "E" 3 d&e) The procedural changes have been accomplished. One charging pump is required to be operating when the RCP seal flow is required 3 f) 3 g) 3 h) 3 i) or i£ RCS Chemistry must be maintained. A low-head SI pump is needed for filling the system (shutoff head is less than 200 psig-reference head curve) Safety Injection is prevented by utilizing the SI BLOCK at less than 543 degrees F and less than 2000 psig The breakers to be opened are in the Emergency Switchgear Room and are tagged. They cari be controlled from the control room or at the breaker, Valve position is lost when a breaker is opened. OP-1.1, 1.2, 1.3, 3.1, 3.2, 3.3, 3.4, 5.1, 8.1, 14 and MOP-5-6 The supervisory personnel responsible for maintaining control are the Shift Supervisor and the Operating Supervisor At (360 degrees - 510 degrees/1000 psig) (OP-3.2) Accumulator isolation valves are shut dur.ing the Shutdown operation. The breaker

3 j) 4 a) 4 b) is in the Emergency Switchgear Room and is controlled from control room or at the breaker. Reducing nitrogen pressure is expensive and.time consuming during re-pressurization. This would delay plant recovery. Isolation of the accumulators serves the same purpose. The SI system is tested during the refueling outage and is a potential cause of an overpressure transient, The PT will be changed that no charging pumps are running and all charging pump breakers are racked in the test position during testing. 5ac&d) The setpoint to an alarm in the-control room indicating high RHR pressure has been lowered from 650 psig to 480 psig with reset at 460 psig. This pressure switch is at the RHR pumps1 discharge., 5 b) 6 a) 6 b) 6 c) The RHR isolation valves are locked 9pen (reference - ans~er, ld-

1) during cold. shutdown conditions, thus. assuring continuity with the RCS.

The attached final design includes a change to annunciate the existing RCS pressure indications. RHR design pressure is 600 psig. There are two. series MOV's at the suction of the RHR pumps and two parallel MOV's at the return to the loops. The interlock is such that at greater than 460 psig the inlet isolation valves can not be opened (reference sheet 1 of attach-ment 11A11 ) 6 d&e) Attachment "A" should clarify that no interlock or alarm will* be defeated. 6 f) The nominal stroke time of the isolation valves is;discharge valves

  • close in 10 sec. and the inlet in 2 min. 40 sec.

6 g) The setpoint of the RHR relief valve is 600 psig. The capacity is 750 gpm (water) at a back pressure of 5 psig 6 h) The setpoint for the RHR pressure alarm was resetc It was set at 550 psig and was reset to 480 psig to give an earlier warning of high pressure conditionso 7 a) On a pressurizer cooldown, at least one RCP is kept operating 7 b) at temperatures greater than 1'60 degrees F. The spray valve from the charging header is left open to circulate coolant through the pressurizer. During solid plant operat{~*ns, the primary is filled with the use. of the low head SI pumps. The high points are vented and chemistry is begun to be b~ought into specifications. The RCP's are jogged artd the system vented. This is continued until the plant is solid. The same reasoning as answer 2a exists for a nitrogen or air bubble

7 c) 7 d) 7 e) 7 f) e A steam bubble is required prior to starting a RGP unless the RCP is being started or jogged for the fill and vent procedure. If the RCS temperature is less than 150 degrees F, the RCS pressure. should be between 320-350 psig If the RCS temperature is greater than the seal water injection temperature,.,special Operations Supervisor permission is required. The computer trends the hot leg temperature during shutdoi,m conditions per Standing Order. Th*e wide range temperature recorder. is available for further determination of the temperature profile. On the RHR system, a suction header temperature indicator and heat exchanger discharge temperature indicator is available. Indication and computer trend are available for RCS pressure. All preparations for solid plant operation are in effect per OP-1.1. The RHR system is in operation taking suction from Loop A hot leg and discharging to Loop B & G cold legs. The RGP jogs during the fill and vent procedure and, if a loop isolation valve is closed, the.temperature interlocks, which must be satisfied prior to the outlet valves being opened, assure the equalization of temperatures in the loops. The following precautions are also in effect during RCP starts. OP-1.1 (Preparations for "Solid Plant Operations") requires* the RHR system to be in service with the inlet isolation valves open and their breakers open; the low pressure letdown control valve full open; the normal letdown isolation valves and all three orifice isolation valves open; the RCS pressure at the lowest allowable pressure for RCP operations (325-350 psig); the charging flow controller at the reduced rate; and close operator monitoring of RCS pressure during venting operat~ons.

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