ML19093A970

Letter to Discuss Overpressure Protection System & to Forward Copies of Mitigating Systems Transient Analysis Results of 07/1977 & Copies of Supplement of September 1977

ML19093A970
Person / Time
Site:	Surry
Issue date:	10/14/1977
From:	Stallings C Virginia Electric & Power Co (VEPCO)
To:	Case E Office of Nuclear Reactor Regulation
References
Download: ML19093A970 (7)

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V I R O I N I , i \ ~ C AND POWER COMPANY RICHMOND,VIRGINIA 23261 October 14, 1977 Mr. Edson G. Case, Acting Director Serial i'l'o. 446 Nuclear Reactor Regulation PO&M/TAP:das U.S. Nuclear Regulatory Commission Docket Nos. 50-280 Washington, D. C. 20555 50-281 License Nos. DPR-32 Attn: Mr. Robert W. Reid DPR-37 Operating Reactors Branch 4

Dear Mr. Case:

This letter is to discuss our overpressure protection system and to forward four copies of the "Mitigating Systems Transient Analysis Results of July 1977" and four copies of the supplement of September 1977. This completes the transient analysis and allows us to submit our final set-point study.

Information has been requested by your staff and is addressed below:

NRG Request

1. Final design must be capable of satisfying Appendix G limits over a 40 year plant life. If the plant can't meet Appendix G you may choose to propose meeting a lesser Appendix G fluence level, but with the understanding that these would be considered as interim design changes and final design must be proposed and changes implemented before the next refueling outage.

Response

All analyses for Surry have been done on the basis of satisfying Appendix G limits over a 40 year plant life. Without r_egard for the temperature, the Appendix G limit will never be less than 500 psig during the entire 40 year plant life. Therefore, 500 ps_ig has been used as an absolute pressure limit in determining the valve setpoints.

With the completed analyses now available, the analysis for our station has been completed and is shown in Attachment 1. The limiting pressure transient for Surry is the mass input case.

We have determined that the PORV setpoints should be as follows:

PORV 1 410 psig open 400 psig reset PORV 2 425 psig open 415 psig reset

e VIRQINIA ELECTRIC AND POWER COMPANY TO Hr. Edson G. Case

• P_age No. 2 This will provide assurance that the 500 psig Appendix G limit is not exceeded during the limiting pressure transient. Sufficient safety margin is provided by these setpoints since the transient analysis shows that only one PORV, set to open at 435 psig, is required to prevent exceeding the Appendix G limit. The PORV' s will be set to operate at the above values prior to and during the time that the plant is in a water solid condition.

NRC Request

2. Identify plant conditions, and components/systems to be controlled by Administrative Procedures - consider components/systems assumed to be unavailable and therefore not analyzed.

Response

The operational conditions which must be controlled are:

1) While water solid, only one charging pump is permitted to be operational.

2) The safety injection accumulators must be isolated so that they do not discharge into the RCS, while water solid.

3) The safety injection l_ogic must be blocked, while water solid.

0

4) The temperature of the RCS must not be greater than 50 F cooler than the bulk water in the steam generators before starting the first reactor coolant pump.

NRC Request

3. Previous plant submittals deferred addressing acceptance criteria until generic analysis was completed. Provide this information now.

Response

In our letter of February 25, 1977, we provided satisfactory re-sponse to your final acceptance criteria as evidenced by your letter of Hay 5, 1977, NRC Request

4. Include electrical schematics and logic diagrams.

Response

Attachment A of our letter of February 25, 1977, provided electrical

e VIR(?INIA ELECTRIC AND POWER COMPANY TO Mr. Edson G. Case

• P_age No. 3 schematics and logic diagrams.which were used for the final wiring drawings. The final drawings do not differ from the original con-cept and are therefore not provided.

• NRC Request

5. Dual setpoint enabling alarm must be included, a computer generated alarm is not acceptable; alarm must be hard wired to the PORV isola-tion to assure it is opened when required.

Response

The alarm as requested is part of our design as forwarded in our letter of February .25, 1977, NRC Request

6. Provide additional details on modeling of PORV's - consider effects of flashing on assumed relief capacity,

Response

The additional details are submitted as part of the analysis.described in attachments 3 and 4.

NRC Request

.7. Explain how the criteria will be satisfied regarding loss of air/loss of offsite power. Must be addressed in plant specific submittal.

Response

The back-up air supply to each PORV as discussed in our submittal of February .25, 1977-, and evaluated in the failure analysis in Table 1 of our April 1, 1977 letter is finally sized by the calculations in Attachment 2 of this letter.

The sizing of the redundant air supply considered both of the PORV's response time with the above.setpoints and that operator action is not expected for 10 minutes. The fastest system response is such that the PORV's may be caused to cycle at a rate of six seconds per cycle. This would require an air supply capable of 100 cycles.

We will provide four high pressure air bottles for each.valve with each bottle capable of .31 cycles.

The loss of offsite power was evaluated and satisfied in the above mentioned letters.

VII~GINIA ELECTRIC AND POWER COMPANY TO Mr. Edson.G. Case

• P.age No. 4 The progress to date on our commitment to have the overpressure protection system installed by December 31, 1977 is as follows:

1. Final installation design has been completed. This design is identical to that previously submitted. The installation drawings and procedures required for installation, including seismic mounting of the back-up air system, are included.

2. All parts have been ordered.

3. Electrical cable has been installed inside of the contain-ment for Unit No. 2 with Unit No. 1 to be installed in.

November, 1977. The installation of the electrical cable and components in the instrument racks is progressing and scheduled to be finished prior to December 31, 1977, in both units.

4. Mechanical installation within Unit No. 2 containment was not accomplished during the refueling out.age due to design and procurement problems which have since been resolved.

5. The system installation will be completed in Unit No. 2 prior to placing the plant in a water solid condition in any future scheduled outage. Materials will be on site and installed in Unit No. 1 during the scheduled November, 1977 steam generator inspection outage.

M. Stallings Vice J esident-Power Supply and Production Operations Attachments:

1. PORV valve setpoint calculations

2. Back-up air supply calculations

3. Four(4) copies - Pressure Mitigating Systems Transient Analysis Results (July 1977)

4. Four(4) copies - Supplement to July 1977 Report

-(September 1977) cc: Mr. James P. O'Reilly (Attachment 1 & 2)

e *tachment 1

..,age 1 of 2 PORV VALVE SETPOINT CALCULATIONS Calculations for Mass Input per Section 4.2.1 of Attachment 4 Relief Valve Setpoint 435 psig Relief Valve Opening Time 1. 7 seconds Mass Input (1 chg. pp.) 600 gpm - 83.0 lb/sec.*@ l00°F RCS Volume 10,000 cu. ft.

Step 1. Setpoint 435 psig

• Step 2. L'-PRef 114 psi Step 3. Fv 0.71 Step 4. Fz 0.65 Step 5. Fs 1.21

/

Step 6. Product of (2,3,4,5) = 63.66 -+ 64 psi t.P Step 7. Max. Pressure = (1) + (6) = 435 + 64 = 499 psig I

NO,TE: All of the numbers used above are very conservative so tl:.2.t !:.O"!'."!!l2l i!l-St:r*-11.!lent rlri fr i R c0nR:i ..-i.Pred i_ncluded.

However, peak for selected setpoints is:

425 psig - 486 psig 410 psig - 472 psig

Attachment 1 e Page 2 Heat Input using Example 1 and 2 of Attachment 4 Initial RCS Pressure 300 psig SG Heat Transfer Area 58,000 ft 2 RCS volume area -10, 000 cu. ft.

Initial RCS Temp. 250°F RCS/SG /:::,T 50°F Relief Valve Opening Time 1. 7 sec.

Relief Valve Setpoint 435 psig.

pg. 35 - Step 1 and 2 l'iP400 (Figure 3) 64 psi 6,000 cu. ft. t::,p500 (Figure 5) 90 psi tiP400 + s - 400 (tiPsoo - tiP400) 500-400 64 + 435 - 400 (90-64) =

100 64 + ( ,35 X 26) = ]3,1 psi pg. 35 - Step 1 and 2 /:::,P400 (Figure 4) = 48 psi 13,00Dcu. ft. /:::,P500 (Figure 6) 78 psi An,,..,,....

LH4UU + s - f A("\

'tVV (t.Psoo hr L,(10) 500-400 l18 + 435 - 400 (78--48) = 58.5 ESi = l1P13K 100 Step 2 for RCS volume 10,000 cu. ft.

pg. 39 t:,plOK = l'iP6K - VRCS - 6,000 13,000-6,000 l'iP10K = 73.1 - 10,000 - 6,000 (73.1 - 58.5) 7,000 t::,plOK = 64.76 psi Peak Pressure= Psetpoint + l'iP

= 435 + 64.76

= 499.76 psig As the steam generator size used is larger than ours (58,000 - 51,560) this number is not the limiting condition.

Attachment 2 j

1: '

~ack-up Air Supply Calculations for Surry a) initial pressure - 2200 psig b). low pressure alarm - 2100 psig c) calculation start - 2000 psig - CJ1L d) the valve operator size is 180 cubic inches = 0 .104 cu. ft.

e) 0.2 cu. ft. loss per cycle used f) 1.74 cu. ft. air bottles used g) 1. 7 cu. ft. used in calculation (V1) h) 61 psig is minimum to fully stroke the valve P,,. V,,. P2 Vz where Vz = Vl + 0.2 cu. ft. l. 9 cu. ft.

Pz = PJ V1 2000 psig (J.7 cu. ft.) 1789.47 psig after 1st Vz 1.9_ cu. ft. actuation

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PJ2 = P31 . J.'. L After 31th Actuation 63.6 psig remains in one bottle therefore, each bottle will cycle one valve 31 times. Four(4) bottles per valve will be used.