ML19257D498

Forwards Response to NRC 791217 Request for Addl Info Re Containment Purge & Venting Sys.Discusses Primary Containment Atmosphere Control Piping Penetrations & Leak Rate Testing of Containment Purge & Vent Valves

ML19257D498
Person / Time
Site:	Vermont Yankee File:NorthStar Vermont Yankee icon.png
Issue date:	02/01/1980
From:	Moody D VERMONT YANKEE NUCLEAR POWER CORP.
To:	Ippolito T Office of Nuclear Reactor Regulation
References
WVY-80-24, NUDOCS 8002040489
Download: ML19257D498 (6)

Text

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rCn I VERMONT Y AN K EE NUCLEAR POWER CORPOR ATION C'V43 SEvErJTY SEVEN GROVE STREET B.3.2.1 RUTI.AND, VEID10NT 05701 kVY 80-24 REPLY TO ENGINEERING OFFICE TURFt TE Ro AD W EST DO RO. M ASS AC HU SE T T S C 15 L 1 9 TELEPHONE 617-366 9019 United States Nuclear Regulatory Commission Washington, D.C. 20555 Attention: Thomas A. Ippolito, Chief Operating Reactors Branch #3 Division of Operating Reactors

References:

(a) License No. DPR-28 (Docket No. 50-271)

(b) NRC Letter to YAEC dated December 17, 1979 (c) VYNPC Letter to USNRC dated December 27, 1979 (d) VYNPC Letter to USNRC dated December 10, 1976

Subject:

NRC Request for Additional Information on the Containment Purge and Venting System at Vermont Yankec.

The enclosed information is in response to your letter, Reference (b),

regarding the Containment Purge and Venting System at Vermont Yankee.

The modes of operation discussed in this response were previously described in References (c) and (d).

We trust this information adequately addresses your concerns; however, if you should desire additional information, please contact us.

Very truly yours, -

VERMONT YANKEE NUCLEAR POWER CORPORATION M

' Donald E. Moody Manager of Operat. ions see Enclosures 1866.170 p no,on er9

NRC Question la With regard to the containment purge and venting system, provide the following information:

Discuss the provisions to ensure that isolation valve closure will not be prevented by debris which could potentially become entrained in escaping air and steam.

Answar:

The Primary Containment Atmosphere Control Piping penetrations are designed with a tail piece that projects into the containment. The drywell connection is high up, far from any inside equipment. The torus connection is on top of the torus. No additional provisions were made in the original design to prevent entrance of debris. In addition, in the small BWR containments, there is not much that could generate debric; therefore, it is not likely that dabris would be carried into the piping. The redundant back-up valves are located far from the containment, further reducing the probability of debris preventing containment isolation.

NRC Question 1b Discuss the provisions made for testing the availability of the isolation function and the leakage rate of the isolation valves, individually, during reactor operation.

Answer:

Dae to the system arrangement of the containment purge and vent valves, there is no existing method of leak rate testing these valves on an individual basis.

Vermont Yankee is required to test all containment isolation valves in accordance with 10CFR50, Appendix J which specifies the necessary leak rate test requirements and acceptance criteria. These requirements are reflected in station Technical Spe,cifications and operating and surveillance procedures.

The subject containment purge and vent valves require " Type C" leak rate testing each refueling shutdown, stroking once per quarter, and testing for &utomatic initiation and closure times once per operating cycle. A formal test report for Appendix J testing is submitted to NRC for review.

NRC Question ic Quar.tify the amount of containment atmosphere released through the purge and vent isolation valves for a spectrum of break sizes during the maximum closure time allowed in your Technical Specifications.

186,6 171

Answer In order to determine the maximum amount of gas released, a number of break locations and single failure assumptions have been considered.

The results of our investigation are summarized on Table I.

NRC Question 1d Provide an analysis to demonstrate the acceptability of the provisions made to protect structures and safety related equipment; e.g., fans, filters, and duct work located beyond the purge system isolation valves against loss of function from the environment created by escaping air and steam.

Answer

1. The piping system downstream of the containment isolation valves leading to the Standby Gas Treatment System (SBGT) is constructed of pipe, fittings, and valves designed to 150 psi.

This exceeds the containment design pressure of 56 PSI.

2. The SBGT units themselves consist of charcoal and HEPA filters contained within a sheet metal enclosure which is designed to withstand 2 PSI.

3 The SBGT filter trains are located after 104 feet of 8 inch pipe beyond the outermost isolation valve which itself is located 188 feet from the innermost valve.

4. SBGT system operation is initiated by a single switch which opens both inlet and discharge valves to that unit.

5. The outlets from the SBGT trains are led approximately 1300 feet to the plant stack where the effluent gas is released at the top of the 300 foot stack.

6. Present operating procedures do not permit the drywell vent valves (SB 16-19-6A, 7A) to be opened with the reactor coolant system above 2120F.

7. Peak torus pressure following a DBA is 23.8 psig.

8. Only the 3 inch valve from the torus is open.

As a result of the above, it is the opinion of VYNPC that no safety class equipment downstream of the isolated valves will lose is function and the pressure available at the SBGT piping is insufficient to cause failure.

The pressure on the sheet metal filter housing should be insufficient to cause failure of the filter housing due to the restricted supply. and the open discharge. These same facts minimize the possibility of damage to the filters themselves.

1866 ~172

NRC Question le For the containment purge isolation valves, specify the differential pressure across the valve for which the maximum leak rate occurs.

Further, provide test results (e.g., from vendor tests of leakage rate versus valve differential pressure) which support the above in formati on.

Answer:

The valve manufacturer has stated that he does not have data showing leakage rate versus valve differential pressure. However, based on information from the manufacturer, leak testing of these valves at maximum differential pressure would be considered conservative. The leak tightness of these valves was originally verified by the manufacturer, and subsequently reverified during the performance of on-site testing as required by 10CFR50 Appendix J.

1866 173

TABLE 1 l

7 BREAR **

CASE SINGLE ASSUMPTIONS RELEASES FAILURE *

~

LOCATION AIR STEAM 1 Between flow Valve SB16-19-8 1. Valve 16-19-6B closes in 10.5 sec. 18.1# 268.4#

element and 2. Air flow restricted at lb orifice Valve 16-19-23 3. Valve 16-19-23 closes in 10.5 sec.

4. Steam flow restricted by 6" line ,

2 Between flow Valve SB16-19-8 1. Valve 16-19-6B closes in 10.5 sec. 50.2# 16.8#

element and 2. Air flow restricted at 2b" valve 1-156-10 Valve 1-156-10 3. Valve 16-19-23' closes in 10.5 sec.

4. Steam flow restricted by 14' orifice 3 RRU-18 suction Valve SB16-19-8 1. Valve 16-9-6B closes in 10.5 sec. . 72.3# 16.8#

piping (3") 2. Air flow restricted by 3" line

3. Valve 16-19-23 closes in 10.5 sec.

4. Steam flow restricted by 1 " orifice 4 Valve SB16-19-6B 1. Valve SB-6 closes in 10.5 sec. 72.3#

1

2. Air flow restricted by 3" line 1

5 1. Valves 16-19-6A & 6B close in 10.5 sec. 72.3# 67.1#

• Single failures in valves other than those noted above will not change the results of the calculations.

• • The releases described in Cases 1, 2.& 3 require a passive failure in the " closed loop" pump back system.

Cases 1, 2 and 3 - Breaks in various locations in torus-dry well pumpback system Case 4 - Release thru SBGTS when instrument air is used for drywell pressurization (alternate to pumpback system)

Case 5 __, - Release thru SBGTS as valves 6A & 6B close CO Ch Ch b.

VERMONT YANKEE

, PURGE & VENT SYSTDI TO STACK

^'C4 E SBGTS"B"' @ ~C

1. • ]'

2B w 16-19-100 1-156-10 1B FROM RB EXHAUST INSTRUMENT W,'1A g 'g ' *

• AIR SUPPLY -

2AT "'

SBGTS"A"

^ 16-20-20 M N

3"-HPf_I-13 \__

4A

'TO RTF-5 ,

16-20-22B PURGE FAN 1 __

k 6 7A Y

18"-AC-5  :

s/y 3"-AC-8 16-20-22D L , f 3"-AC-7 18"-AC-14A 18"-AC-15 ] [

-h -4 _

14 m

~ .I 20"-AC-13 AIR PURGE Co SUPPLY O j/i l Ch r^

__, 3"AC-4 7-l/F f"3-AC-3 VACUUM RELIEF r-FROM SECONDARY b CON,TAIN'1ENT FIGURE 1

.