ML17289B155

Requests for Temporary Relief from Tornado Missile Design Criteria as It Relates to Protective Soil Cover Requirements Above Underground safety-related Diesel Oil Storage Tanks

ML17289B155
Person / Time
Site:	Columbia
Issue date:	02/09/1993
From:	Sorensen G WASHINGTON PUBLIC POWER SUPPLY SYSTEM
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
GO2-93-028, GO2-93-28, NUDOCS 9302170331
Download: ML17289B155 (7)

Text

-

seem,m REGUL O VOCurvrmm Ors RY INFORMATION mmrow sesame DISTRIBUTI~ SYSTEM (RIDS)

ACCESSION NBR'.9302170331 DOC.DATE: 93/02/09 NOTARIZED: NO DOCKET FACIL:50'-'397 WPPSS Nuclear Project, Unit 2, Washington Public Powe 05000397 AUTH. NAME AUTHOR AFFILIATION SORENSEN,G.C. Washington Public Power Supply System RECIP.NAME RECIPIENT AFFILIATION Document Control Branch (Document Control Desk)

SUBJECT:

Requests for temporary relief from tornado missile design criteria above as it relates to protective soil cover requirements underground safety related diesel oil storage tanks.

DISTRIBUTION CODE: A001D COPIES RECEIVED:LTR ENCL SIZE:

TITLE: OR Submittal: General Distribution NOTES:

RECIPIENT COPIES RECIPIENT COPIES ID CODE/NAME LTTR ENCL ID CODE/NAME LTTR ENCL PD5 LA 1 I' PD5 PD CLIFFORDFJ INTERNAL: ACRS NRR/DET/ESGB NRR/DOEA/OTSBll NRR/DST/SELB 7E NRR/DST/SICB8H7 NRR/DST/SRXB 8E NUDOCS-ABSTRACT OC/J B OGC/HDS1 EG PTL Ol EXTERNAL: NRC PDR NSIC NOTE TO ALL"RIDS" RECIPIENTS:

PLEASE HELP US TO REDUCE WASTEI CONTACT THE DOCUMENT CONTROL DESK, ROOM Pl-37 (EXT. 504-2065) TO ELIMINATEYOUR NAME FROM DISTRIBUTION LISTS FOR DOCUMENTS YOU DON'T NEEDI TOTAL NUMBER OF COPIES REQUIRED: LTTR 21 ENCL

~ ~

~ '

Pt j>,

A WASHINGTON PUBLIC POWER SUPPLY SYSTEM P.O. Bm 96'8 ~ 3000 George Wasbtngton Way ~ Richland, Wasbtngton 99352<968 ~ (509) 372-5000 February 9, 1993 G02-93-028 Docket No. 50-397 U.S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, D.C. 20555 Gentlemen:

Subject:

WNP-2, OPERATING LICENSE NPF-21 REQUEST FOR TEMPORARY'RELIEF FROM TORNADO MISSILE DESIGN CRITERIA

Reference:

Letter G02-91-116, dated June 7, 1991, GC Sorensen (SS) to NRC "Request for Approval to Revise Tornado Design Criteria" The Supply System hereby requests temporary relief from the WNP-2 tornado missile design criteria as it relates to protective soil cover requirements above the underground safety related diesel oil storage tanks. This relief is requested to facilitate installation activities of a new diesel fuel oil polishing system to be installed during the spring 1993 refueling outage.

Current design requirements for protection of under ground safety related components from tornado missile hazards are defined in FSAR Section 3,5.3.3. Based on the requirements of this section, five feet of soil cover is provided above underground safety related components to insure that safety related functions are maintained following a design basis tornado. This requirement is based on providing protection for the following design basis tornado missiles as specified in FSAR 3.5.1.4:

Weight Horizontal Impact Missile (lbs) Dimensions Velocity (ft/sec)

Utility Pole 1600 14" dia. x 35 ft long 241 1" Steel Rod 8 1" diax 3 ftlong 259 9302170331 930209 PDR ADOCK 05000397 P PDR

L s

"'F00<'z

~o 5'age Two REQUK$ T FOR TEMPORARY RELIEF FROM TORNADO MISSILE DESIGN CRITERIA The velocities were developed for a postulated maximum tornado wind speed of 360 mph.

Based on information contained in the referenced letter, NUREG/CR-4461, and previous discussions with the NRC Staff, a design wind speed of 192 mph appears to be a more realistic design basis and is currently being considered by the staff as the revised design basis for WNP-2. A wind speed of 192 mph will result in a significantly reduced tornado missile hazard.

In the referenced letter, the following revised design basis missiles were proposed:

Impact Weight Velocity (ft/sec)

Missile (lbs) Dimensions (see discussion below)

Wood Plank 115 3.6" x 0.94' 12'ong4.3'orizontal167 6" Sch 40 Pipe 287 6.6" dia x 15'ong 17 1" Steel Rod 8.8 1" dia x 3'ong 20 Utility Pole 1124 13.5" dia. x 35'ong 12" Sch 40 Pipe 750 12.75" x 15'ong 13 Automobile 3990 16.4' 6.6' The utility pole and the automobile are not considered to be credible missiles for wind velocities less than 200 mph. The remaining missiles are considered to strike surfaces in any direction.

Vertical velocities are taken to be 70 percent of the horizontal velocities except the 1" steel rod which is assumed to have the same velocity for any direction. The impact velocities of credible missiles are based on studies documented in EPRI Report NP-748 and are conservatively based on a maximum wind speed of 240 mph. The technical justification for adopting these missiles as the WNP-2 design basis is provided in the referenced letter.

The Supply System has performed preliminary evaluations of these missiles for postulated impacts above the safety related diesel storage tanks and concluded that 2 feet of soil cover provides adequate protection for the tanks. The evaluations will be formalized and verified before soil cover is removed.

The justifications for adopting the above tornado protection criteria for the installation of the diesel fuel oil polishing system are as follows:

The probability of tornado hazards exceeding the proposed temporary design criteria during the installation of the diesel fuel oil polishing system is extremely small. NURE-G/CR-4461 estimates the annual probability of a tornado strike to be 4.88 x 10~.

Tornado wind speeds within the vicinity of WNP-2 have never been observed to be as

<~

-> ~ 'Page Three REQUEST FOR TEMPORARY RELIEF FROM TORNADO MISSILE DESIGN CRITERIA high as 192 mph. Therefore, even if a tornado was to strike the facility, the median (

expected value of the wind speed will be less than 192 mph. See the referenced letter and NUREG/CR-4461 for additional discussions of tornado hazards in the vicinity of WNP-2.

The two foot soil cover requirement is conservative. The largest penetration depth of any of the above missiles is substantially less than 2 feet. Therefore, there is a significant margin for potentially more damaging missiles.

Although the Supply System's tornado missile protection evaluations have not directly evaluated an automobile missile at velocities comparable to those specified in the applicable NRC Standard Review Plan, two feet of soil cover will provide adequate protection for a hazard consisting of an automobile tumbling along the ground surface.

The activity of exposing the tanks is expected to begin March 1, 1993 and be complete by May 31 1993. The temporary relief is requested for the time period of March 1, 1993 to August 1, 1993. The additional duration is requested to provide contingency in accomplishing the modification.

After the installation activities are complete, the soil cover will be returned to the design basis of 5 feet. At no time during the installation will the soil cover be less than 2 feet above a tank,,;

required to support diesel generator operability.

To provide for adequate planning for the installation of the diesel fuel oil polishing system, a response is requested from the NRC staff by February 15, 1993.

Sincerely, G. C. orensen, Manager Regulatory Programs (Mail Drop 280) cc: JB Martin - NRC RV DL Williams - BPA/399 NS Reynolds - Winston & Strawn NRC Site Inspector - 901A JW Clifford - NRC R Copeland - Siemens