ML17289B259

Safety Evaluation Supporting Licensee Request for Temporary Relief from Tornado Missile Design Criteria

ML17289B259
Person / Time
Site:	Columbia
Issue date:	03/23/1993
From:	Office of Nuclear Reactor Regulation
To:
Shared Package
ML17289B258	List: ML17289B256 ML17289B259
References
RTR-NUREG-CR-4461 NUDOCS 9303260258
Download: ML17289B259 (3)

Text

~P,S RECIr~

0~s

+>>*++

UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO TEMPORARY RELIEF FROM TORNADO MISSILE DESIGN CRITERIA FOR WASHINGTON PUBLIC POWER SUPPLY SYSTEM NUCLEAR PROJECT NO.

2 DOCKET NO. 50-397

1.0 INTRODUCTION

The licensee has indicated the need for a temporary change to the tornado design basis in a submittal dated February 9, 1993.

The licensee has provided justification for the proposed modification to the diesel fuel oil system on the basis of the low likelihood of tornado missile damage during a limited period of time.

To meet the present criteria, the soil overburden would have to be approximately five feet in order to account for the current missile spectrum.

The licensee proposes to retain two feet of soil overburden as a

compensatory measure while the modification is being made.

2. 0 EVALUATION The licensee plans to install diesel fuel oil polishers which would require diesel generator fuel oil tanks to be uncovered during the next refueling outage.

Loss of both fuel tanks with concurrent loss of offsite power could incapacitate the plant due to a tornado with missiles of sufficent velocity.

However, the likelihood of such an event occurring during the time of the

shutdown, in the specific location of both diesel fuel oil tanks is very low as noted below.

Additionally, the licensee intends to provide at least two feet of soil cover during the modification as a compensatory measure.

WNP-2 current tornado design criteria specify wind speeds of 300 mph rotational and 60 mph translational.

Additionally, the current design basis tornado generated missiles are a utility pole and a steel rod.

Based on Section 3.5.3.3. of the Final Safety Analysis Report, five feet of soil is required above underground safety-related components to ensure that their functions are maintained following a design basis tornado.

Previously, by letter dated June 7,

1991, the licensee requested to revise the WNP-2 tornado design criteria wind speeds.

The licensee requested the change

because, relative to the requirements of Regulatory Guide 1.76, WNP-2 should be a Region III site.

The current tornado design criteria for WNP-2 are for a Region I site, which is very conservative.

In addition, the licensee proposed revised design basis missiles which include four missiles.

The licensee

. 'r'I303260258 930323 "PDR AXIOCK 05000397 P'

PORE

4 II

proposed not to consider utility poles and automobiles as normally specified in the regulatory guide as creditable missiles for wind speeds below 200 mph.

The staff has not completed the review of these tornado design criteria yet.

However, the licensee has referenced the analysis in the June 7, 1991, letter in support of the February 9, 1993, temporary relief request.

The licensee provided the following justification for adopting the revised tornado protection criteria during the diesel fuel polishing system installation:

The probability of tornado strike is estimated to be 4.88 x 10 according to NUREG/CR-4461 Tornado wind speeds within the vicinity of WNP-2 have never been observed to be as high as 192 mph.

The two feet of soil cover will provide adequate protection against missiles during the proposed design basis tornado wind speeds.

Additionally, the licensee has committed to provide at least two feet of soil above the tank at all times during the installation of fuel oil polishing system and, after the installation is completed, the soil cover will be returned to the current design basis of five feet.

3.0 CONCLUSION

Based on the information provided above, the staff concludes that the licensee's evaluation supports the conclusion that there is a low likelihood of tornado damage during the time frame required to complete the modification to the diesel fuel oil tanks, extending from March 1, 1993 until August 1,

1993.

4.0 REFERENCES

1.0 Letter G02-93-028, dated February 9,

1993, G.

C. Sorensen (SS) to USNRC, "Request for Temporary Relief from Tornado Missile Design Criteria."

2.0 Letter G02-91-116, dated June 7,

1991, G.

C. Sorensen (SS) to USNRC "Request for Approval to Revise Tornado Design Criteria."

Principal Contributors:

R. Assa J. Clifford N. Wagner Date:

March 23, 1993