ML17299B097
| ML17299B097 | |
| Person / Time | |
|---|---|
| Site: | Palo Verde  |
| Issue date: | 03/14/1986 |
| From: | Van Brunt E ARIZONA PUBLIC SERVICE CO. (FORMERLY ARIZONA NUCLEAR |
| To: | Knighton G Office of Nuclear Reactor Regulation |
| References | |
| ANPP-35545-EEVB, NUDOCS 8603180208 | |
| Download: ML17299B097 (8) | |
Text
DOCKET 0 05Q00528 0500Q529 osooa53o
SUBJECT:
Documents specific reasons for conclusions that addi testing of pressurizer vent sos unnecessary>
per Sb0225 telcon w/NRC.
Vent flow assumed in steam generator tube rupture analMsis conservative 5 based on acceptable analytic method.
DISTRIBUTION CODE:
8021D COPIES RECEIVED: LTR ENCL SIZE:
TITLE: OR/Licensing Submittal:
Combined General Distribution REGUL*TOR FORMATION DISTRIBUTION 8 EM (RIDS)
- 4) y ACCESSION NHR: 8603180208 DOC. D*TE: 86/03/14 NOTARIZED:
NO FACIL:STN-50-52S Palo Verde Nuclear Station>
Unit 1> Arizona Publi STN-50-529 Palo Verde Nuclear Station>
Unit 2> Arizona Publi STN-50-530 Palo Verde Nuclear Station>
Unit 3> Arizona Publi
- UTH. NAME AUTHOR AFFIL1ATION VAN BRUNT, E. E.
Arizona Nuclear Power ProJect (formerly Arizona Public Serv RECIP. NAME RECIPIENT AFFILlATION KNIGHTON> G. W.
PWR ProJect Directorate 7
NOTES: Standardized plant.
Standardi zed plant.
Standardi zed plant.
osoaos28 05000529 05000530 RECIPIENT ID CODE/NAME PNR-8
- DTS PNR-8 EH PNR-8 FOB LICITR*>E 01 PNR-8 RSB INTERNAL: ACRS 29 ELD/HDS3 NRR PWR-A ADTS NR 0 DIR EG IL 04 RM/DDAMI/MIB COP IES LTTR ENCL RECIPIENT ID CODE/NAME PWR-8 PD7 PD 05 PNR-8 PEICSB PNR-8 PD7 LA PNR-8 PEICSB
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1 EXTERN*L: 24X NRC PDR PNL GRUEL> R 02 LPDR NSIC 03 06 TOTAL NUMBER OF COPIES REQUIRED:
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Arizona Nuclear Power Project P.o. BOX 52034 4
PHOENIX, ARIZONA85072-2034 March 14, 1986 ANPP-35545 EEVB/BJA/98.05
~
Director of Nuclear Reactor Regulation Attention:
Mr. George W. Knighton, Project Director PWR Project Directorate.III7 Division of Pressurized Water Reactor Licensing B U. S. Nuclear Regulatory Commission Washington, D.C.
20555
Subject:
I Palo Verde Nuclear Generating Station (PVNGS)
Units 1, 2, and 3
Docket Nos.
STN 50-528 (License No. NPF-41)
STN 50-529 (License No. NPF&6)
STN 50-530 Information Concerning the Performance of the Pressurizer Vent System File:
86-056-026
Reference:
(1)
Letter from E.E.
Van Brunt, Jr.,
ANPP, to G.W. Knighton,
- NRC, dated October 15, 1985 (ANPP-33713).
Subject:
Auxiliary Pressurizer Spray Design.
(2)
Ietter from E.E.
Van Brunt, Jr.,
ANPP,.to G.W. Knighton,
- NRC, dated November 4,
1985 (ANPP-33905).
Subject:
Information Concerning the PVNGS Auxiliary Pressurizer Spray System.
Dear Mr. Knighton:
A telecon was held on February 25, 1986 between representatives of ANPP and the NRC Staff.
The subject of additional testing of the pressurizer vent system was discussed during this telecon.
ANPP concluded the telecon by stating that no additional testing of the pressurizer vent system is necessary.
The specific reasons for this conclusion are documented, at the request of the NRC Staff, in the following discussion.
The Steam Generator Tube Rupture (SGTR) event is the design basis accident in which the pressurizer vent system is used for mitigation of the event.
The function of the pressurizer vent system during a SGTR is to remove steam from the pressurizer steam space in order to recover pressurizer level.
Once pressurizer level has been recovered, the operators can throttle the High Pressure Safety Injection (HPSI) flow.
The throttling of HPSI flow results in the depressurization of the Reactor Coolant System (RCS).
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1
Mr. Knighton Information Concerning the Performance of the Pressurizer Vent System ANPP-35545 Page 2
References (1) and (2) provided SGTR analyses in which the RCS depressurization was delayed for two hours after event initiation in order to maximize the offsite dose consequences.
The Reference (1) analysis utilized the Auxiliary Pressurizer Spray System (APSS) to depressurize.
The Reference (2) analysis achieved RCS depressurization through combined use of the pressurizer vent system and throttled HPSI flow.
The results of both of these analyses met the NRC acceptance criteria.
A conservative model was used to predict the flow through the pressurizer vent system for the Reference (2) analysis.
The pressurizer vent system was modeled as a 7/32-inch orifice in the wall of the pressurizer.
Choked flow was calculated by using the same critical flow correlation as that used for the primary safety valves.
Additionally, a comparison of predicted flow with data from Semiscale tests shows that the flow correlation under-predicts flow and is therefore conservative.
A sensitivity analysis was conducted on the Reference (2) analysis to determine the sensitivity of the offsite dose results to a reduction in the pressurizer vent'low rate.
The Reference (2) analysis was repeated assuming a
20K reduction in the vent flow.
The results of this sensitivity analysis were acceptable as the offsite dose actually decreased by less than one REM due to the additional cooling of the RCS by the increased HPSI flow.
The cooler RCS fluid results in less steam release to the enviroment due to the smaller amount of leaked fluid flashing to steam in the steam generator.
It should be noted that most of the dose in these analyses is the result of releases during the initial two hours of the event before the depressurization is initiated.
- Thus, the analyses are relatively insensitive to small changes in the depressurization rate after two hours.
The possible effects of the downstream piping on pressurizer vent flow were also investigated using a
RELAP model of the pressurizer vent system.
This investigation was conducted under conditions which are representative of the SGTR.
The RELAP model predicted flows in excess of the assumptions made in the Reference (2) analysis.
- Thus, this work verified that the pressurizer vent flow used in the analysis was conservatively low.
Operationally, the pressurizer vent system will behave in the same manner as the reactor vessel head vent system.
Both of these vent paths contain 7/32 inch orifices and all piping is similar.
The reactor vessel head vent path was tested during the recent natural circulation test at PVNGS Unit 1.
ANPP is evaluating the data obtained from this test to determine if the data can be used to predict the pressurizer vent flow rate.
~ < g aI'l
Mr. Knighton Information Concerning the Performance of the Pressurizer Vent System ANPP-35545 Page 3
A functional test was performed on the pressurizer vent system during the preoperational testing phase.
Additionally, the operability of the pressurizer vent system is verified periodically by surveillance testing in accordance with the requirements of the PVNGS Technical Specifications.
Additional testing of the pressurizer vent system to verify system capability would be difficult and prone to multiple sources of error since the vent flow cannot be directly measured.
The vent flow would have to be determined by analysis based on the measured pressurizer level changes from the test.
- Also, due to the low pressurizer vent flows involved, long periods of testing would be required to obtain meaningful results.
In conclusion, ANPP does not believe that additional testing is needed for the pressurizer vent system.
The vent flow assumed in the SGTR analysis is conservative and is based on an acceptable analytic method.
Additionally, testing has been conducted on a system that is similar to the pressurizer vent system.
If you have any additional questions on this matter, please contact Mr. W. F.
Quinn of my staff.
Very truly yours, 4 g~C E. E. Van Brunt, Jr.
Executive Vice President Project Director EEVB/JRW/BJA/dk cc:
E. A. Licitra C. Y. Liang R. P.
Zimmerman A. C. Gehr