ML17290A890

Forwards Request for Approval to Revise WNP-2 Tornado Design Criteria Per Rg 1.76 Section C.1.2

ML17290A890
Person / Time
Site:	Columbia
Issue date:	01/06/1994
From:	Parrish J WASHINGTON PUBLIC POWER SUPPLY SYSTEM
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
Shared Package
ML17290A891	List: ML17290A890 ML17290A918
References
RTR-REGGD-01.076, RTR-REGGD-1.076 GO2-94-001, GO2-94-1, NUDOCS 9401240247
Download: ML17290A890 (6)

Text

ACCELERATED DI BUTION DEMONST ATION SYSTEM REGULATORY INFORMATION DISTRIBUTION SYSTEM (RIDS)

ACCESSION NBR:9401240247 DOC.DATE: 94/01/06 NOTARIZED: NO DOCKET FACIL:50-397 WPPSS Nuclear Project, Unit 2, Washington Public Powe 05000397 AUTH. NAME AUTHOR AFFILIATION PARRISH,J.V. Washington Public Power Supply System LAFRAMBOISE,W. Washington Public Power Supply System NOBLE,L.D. Washington Public Power Supply System R RECIP.NAME RECIPIENT AFFILIATION Document Control Branch (Document Control Desk) I Forwards request for approval to revise WNP-2 tornado design j

SUBJECT:

criteria per RG 1.76 section C.1.2.

DISTRIBUTION CODE: AOOID COPIES RECEIVED:LTR ENCL i SIZE:

TITLE: OR Submittal: General Distribution NOTES' RECIPIENT COPIES RECIPIENT COPIES ID CODE/NAME LTTR ENCL ID CODE/NAME LTTR ENCL D PDV LA 1 1 PDV PD 1 1 CLIFFORD,J 2 2 D

INTERNAL: ACRS 6 6 NRR/DE/EELB 1 1 NRR/DORS/OTSB 1 1 NRR/DRCH/HICB 1 1 NRR/DRPW 1 1 NRR/DSSA/SPLB 1 1 NRR/DSSA/SRXB 1 1 NUDOCS-ABSTRACT 1 1 CjZQD.C3 1 0 OGC/HDS1 1 0 REG FILE Ol 1 1 EXTERNAL: NRC PDR 1 1 NSIC 1 1 R

I D

A D

D NOTE TO ALL "RIDS" RECIPIENTS:

PLEASE HELP US TO REDUCE WASTE! CONTACT THE DOCUMENT CONTROL DESK, ROOM Pl-37 (EXT. 20079) TO ELIMINATEYOUR NAME FROM DISTRIBUTION LISTS FOR DOCUMENTS YOU DON'T NEED!

TOTAL NUMBER OF COPIES REQUIRED: LTTR 22 ENCL 20

WASHINGTON PUBLIC POWER SUPPLY SYSTEM P.O. Bm 96'8 ~ 3000 George Wasbtngton Way ~ Rtcbland, 1Pasbtngton 993524968 ~ (509) 372-5000 January 6, 1994 G02-94-001 Docket No. 50-397 V.S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, D.C. 20555 Gentlemen:

Subject:

NUCLEAR PLANT NO. 2, OPERATING LICENSE NPF-21 REQUEST FOR APPROVAL TO REVISE TORNADO DESIGN CRITERIA

Reference:

Letter, GO2-91-116, dated June'7, 1991, GC Sorensen (SS) to NRC, same subject II By the reference, in accordance with the guidance of Regulatory Guide 1.76, Section C.1.2 the Supply System requested approval to revise the WNP-2 tornado design criteria. Based upon discussions with the Staff, the Supply System has decided to revise this request with regard to the assumed wind speeds, pressure drops and the missiles to be considered. This revised request follows. This request is a complete replacement for the reference.

WNP-2 current tornado design criteria, as stated in FSAR 2,3.1.2.1.3 and 3.3.2.1, are for wind speeds of 300 and 60 mph rotational and translational respectively with a pressure drop of 3 psi occurring at 1.0 psi/sec. These criteria were found acceptable by the Staff as documented in the WNP-2 SER for the Operating License Safety Evaluation Report (NVREG-0892); Section 3.3.2.

The Supply System proposes to change the design criteria to 157 and 35 mph rotational and translational velocities with a pressure drop of 0.70 psi occurring at 0.24 psi/sec.

Relative to the requirements of Regulatory Guide 1.76 the current design requirements represent an over-commitment in that WNP-2 is a Region III site for which the criteria are 190 and 50 mph and a 1.5 psi pressure drop at 0.6 psi/sec. FSAR 3.3.2.4 and Appendix C.3 discuss the WNP-2 design relative to Regulatory Guide 1.76. It is also apparent that the proposed criteria are less than those proposed by the Regulatory Guide for a Region IIIplant.

P,g 9tqt-7g 9401240247 940106

,PDR ADOCK 05000397 PDR

Page Two REQUEST FOR APPROVAL TO REVISE TORNADO DESIGN CRITERIA In addition, FSAR 3.5.1.4 establishes the following design basis tornado generated missiles:

Weight Impact

~Mi iie Qbbs limen 14" diax3'orizontal i n ~VI i f UtilityPole 1600 dia x 35'"

241 Steel Rod 8 259 The NRC found these missiles acceptable in SER 3,5.1.4.

Based upon the guidance of the above mentioned Regulatory Guide section, NRC approval of the use of revised tornado design criteria is requested. The criteria are; Wind Speeds 192 mph total 157 mph rotational 35 mph translational Pressure Drop 0.70 psi at 0.24 psi/sec Missiles Weight Horizontal Impact Velocity Missile Qbbs Dimensions ft/ ec Wood Plank 115 3.6 "x 0.94'x 12'long 6" Sch 40 Pipe 287 6.6" dia x 15'ong 29.2 1" Steel Rod Utility Pole 8.8 1124 1" diax 3'ong 4.3'50.7 13.5" dia x 35'ong 27 33.1 12" Sch 40 Pipe 750 12.75" dia x 15'ong 23.8 Automobile 3990 16.4' 6.6' 95.9 The selection of these criteria is based on extensive studies which define site specific tornado hazards for the Hanford area. These include Department of Energy (DOE) sponsored studies

- of various DOE nuclear related sites including the Hanford Site and NRC sponsored studies of tornado climatology in the United States. These and other studies are discussed in detail in the attached report titled "Justification for Revised Tornado Design Criteria."

Page Three REQUEST FOR APPROVAL TO REVISE TORNADO DESIGN CRITERIA As listed above, this request is based upon a total wind speed of 192 mph. The request of the referenced letter was for 180 mph. As is discussed in the attached report, the proposed 192 mph design basis is consistent with the results contained in NUREG/CR-4461, which is the most conservative of the three recent tornado hazards studies applicable to the WNP-2 site.

In addition, the Supply System is proposing that the missiles to be considered consist of the full spectrum of missiles contained in Standard Review Plan (SRP) Section 3.5.1.4. For these missiles, the proposed velocities will be based on a wind speed of 192 mph. These missile velocities were developed by the Supply System using a methodology we believe is consistent with that used to develop the SRP missile velocities for each of the tornado intensity regions.

The previous request did not include an automobile and utility pole as potential missiles. There were concerns expressed by the Staff that there was insufficient evidence that the automobile and utility pole missiles would not become airborne at the postulated wind speeds. In addition, the methodology used to predict missile speeds was not previously reviewed and approved by the NRC (i.e., EPRI Report NP-748). The current request addresses these concerns.

For comparison purposes, the following table summarizes the horizontal missiles speeds for the original design basis, NRC Tornado Intensity Region III, the referenced request, and the current request.

Original WNP-2 NRC Tornado WNP-2 Current Design Intensity Proposed WNP-2 Basis Region III 6/7/91 Proposed Missile Qffs~ ~fs~ec ~fs~ec ~ft/.~ec Wood Plank 190 167 150.7 6" Pipe 33 17 29.2 Automobile 134 95.9 1" Rod 259 26 20 27.0 UtilityPole 241 85 33.1 12" Pipe 23 13 23.8 By implementing the proposed revisions, the tornado design criteria will realistically reflect the tornado hazards at WNP-2 while maintaining the objective of providing an annual probability of exceedance of design loads of less than or equal to 1 x 10 . These revisions will result in more realistic wind velocities, differential pressure loads, missile velocities, and load combinations. The proposed revisions will benefit the design of exterior structures and components that must consider postulated tornado effects. Significant benefit is expected during the implementation of future plant modifications where relief of tornado design criteria will facilitate construction.

Page Four REQUEST FOR APPROVAL TO REVISE TORNADO DESIGN CRITERIA The Supply System believes the proposed tornado design criteria will continue to provide adequate protection to safety related structures, systems and components such that, for the most severe tornadoes that would be reasonable to postulate to occur near the site, the safety functions of these structures, systems and components will not be impacted.

Sincerely,

. V. Parrish (Mail Drop 1023)

Assistant Managing Director, Operations WLF/AGH/bk Attachments CC: KE Perkins - NRC RV NS Reynolds - Winston & Strawn JW Clifford - NRC DL Williams - BPA/399 NRC Site Inspector - 927N