ML20197C397

Task Action Plan A-38,Tornado Missiles.Problem:To Define Objects That Can Be Lifted & Thrown,Their Velocities & Effects Upon Impact

ML20197C397
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Issue date:	03/17/1978
From:	NRC OFFICE OF STANDARDS DEVELOPMENT
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ML20197C120	List: ML20197C117 ML20197C136 ML20197C150 ML20197C236 ML20197C256 ML20197C260 ML20197C289 ML20197C327 ML20197C348 ML20197C359 ML20197C380 ML20197C397
References
REF-GTECI-A-38, REF-GTECI-IT, TASK-A-38, TASK-OR NUDOCS 7811210078
Download: ML20197C397 (8)

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MARCH 17, 1978 TASK ACTION PLAN TASK NO. A-38

Title:

Tornado Missiles Lead Responsibility: Division of Site Safety and Environmental Analysis ,

Lead Assistant Director: Richard H. Vollmer, Assistant Director for Site Analysis Task Manager: James F. Costello, Engineering Methodology Standards Branch,

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1. Problem Description The requirement, of General Design Criterion 2, that structures, systems, and components important to safety be designed to withstand the effects of tornadoes without loss of capability to perform their safety functions has imposed new demands on the practice of structural engineering. For other i

than nuclear safety related structures, tornadoes have always been considered I too rare to be included in the design basis. Consequently, no body of practice I

existed and design criteria for tornado resistance had to be' developed. This was particularly difficult for the missile protection problem which required judgments on three questions:

1) What objects, available at plant sites or nearby, can be lifted and accelerated?

2) What velocities can they attain?

3) What will be their effects upon impact?

The first two questions had never been seriously studied prior to nuclear power plant design and information on the last was limited to ordnance-related test results.

The first staff requirements were published in SRP 3.5.1.4 in November 1975.

A set of missiles was postulated based on their existence at plant sites.

i Peak velocities for these missiles were chosen using conservative assumptions about their possible aerodynamic behavior. As a result of improved, but still crude, aerodynamic information developed in the interim, the SRP was revised in September 1976. The revision produced a list of peak velocities which are more consistent with aerodynamic properties of the missiles. However, the requirement of designing to acconnodate the effects of missile impact at these velocities is thought to be too conservative in the sense that the risk of having missile effects greater than designed for is much less than that of having a tornado exceeding the design basis tornado. If tornado missiles ,

APPROVED BY TASC MARCH 17, 1978

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occur, an impact on a critical plant area is not certain. Further, a missile's velocity is near the peak velocity for only a short portion of its trajectory. Finally, the current practice is to assume that the missile will impact in the most damaging orientation.

A definition is needed of a set of design basis missiles (whose effects envelop those expected at plant sites) that do not impose unnecessary design requirements on plant construction and for which a sound technical basis exists.

2. Plan for Problem Resolution The subtasks listed below concentrate on defining design basis tornado missiles. The objective is specificatior, of a set of design missiles whose effects will envelop those to be expected at plant sites. The set will probably consist of a relatively rigid missile with potential for causing local damage and a relatively soft but massive missile with potential for overall structural damage. Such missiles tend to control, respectively, slab thicknesses and amount of reinforcement. Ideally, the missile charac-teristics should be specified t more than one level of estimated annual exceedance, say 10-5/ year,10 / year, and 10-7/ year. Subtask schedules and manpower requirements are shown in Attachments 1 and 2.

Task No. A-32, Missile Effects, includes Subtasks on evaluation of both local and overall structural response to tornado missile impacts. Subtask 2 of TAP A-38 will provide definition of design basis missiles which can be used as input to Subtssks 1 and 2 of TAP A-32. This missile spectrum will be based on deterministic considerations and may be moJified as a result of the probabilistic study of Subtask 3. However, any changes are not likely to be disruptive of progress on TAP A-32 since they would probably involve adjustments in missile mass and velocity, but not geometry. Any contem-plated changes will be coordinated with TAP A-32.

s 2.1 Subtask 1 - Force-Time Histories for Vehicle Impact Observations of objects displaced large distances by tornadoes and likely to exist in tne vicinity of plant sites combine to make a motor vehicle the most likely candidate for a bounding, deformable missile with the poten-tial of causing overall structural damage. Specification of a mass and impact velocity will not suffice for input to . structural damage analyses.

A force-time history which accounts for the energy ab: orbed as a vehicle defonns on impact is required. In particular, a series of histories characterizing impacts at different velocities will be required to account for different tornado regions and to include the differences to be expected due to vehicle orientation upon impact. A proposal to develop force-time histories applicable to the tornado problem from test data generated in vehicular safety studies is currently under consideration by the Site Safety Research Branch, RES. Some NRC staff effort will be required to review the work and evaluate its conclusions.

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2.2 Subtask 2 - Detenninistic Assessment An asses. ment of the most recent work relating to the tornado missile problem and a comparison with earlier studies will be undertaken. The major sources will be reports expected to be available during Cr 1978:

(1) " Aerodynamic Considerations on the Injection of Tornado Generated Missiles from Ground Level into Tornado Flow Fields," Naval Surf ace Weapons Center Report, available March 1978.

(2) "Windfield and Trajectory Models for Tornado Propelled Objects,"

EPRI Report, available April 1978.

The end product of this task will be the specification of both rigid and defonnable missiles for enveloping purposes in each of the tornado regions.

The bases for choice of the missiles will be availability at plant sites and aerodynamic properties. This effort can be accomplished solely by NRC staff. ,

2.3 Subtask 3 - Probabilistic Assessment The first attempt at a systematic study relating availability of objects at a plant and estimates of their aerodynamic properties to probabilities of impact on plant structures was undertaken in an EPRI project entitled,

'" Tornado Missile Risk Analysis." (A final report is expected to be available in May 1978.) That study involved survtys at a number of plants and treated objects postulated as , atential missiles by the NRC staff as well as others actually found at the <ites. After the final report becomes available,'its results and methodology will be reviewed by the NRC staff. Some of the results, such as the information derived from site surveys, will be directly useful. Others may be biased, particularly by the model selected fcr the tornado windfield or the assumed aerodynamic properties of the missiles. A _

technical assistance contract to recast the basic data into results directly useful for regulatory purposes is anth.fpated. The end result will be definition gf missile spectra consistent with annual exceedance levels from 10-3 to 10-/. NRC staff effort will be needel for evaluation of the EPRI results, definition of scope for the technical assistance contract, and synthesis of its results.

2.4 End Products Staff positions, defining characteristics of both rigid and deformable missiles, will be developed based on the results of Subtasks 2.1, 2.2, and 2.3. RRRC approval of the positions will be sought to modify SRP 3.5.1.4. The Office of Standards Development will be requested to develop a Regulatory Guide setting forth the approved positions.

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3. NRR Technical Organizations Involveu 3.1 Accident Analysis Branch, DSE Prime responsibility for definition of tornado missile characteristics rests with AAB. Involvement will be required in all subtasks with lead responsibility for Subtasks 2, 3, and 4.

3.2 Hydrology-Meteorology Branch, DSE' HMB has responsibility for definition of the design basis tornado. HMB in-volvement in subtasks 2 and 3 is required to. assure compatability of the tornado windfield models used in assessment of the missile problem with those used for more encompassing purposes, as well as with meteorological sensibility.

Participation can be limited to e. view and comment.

3.3 Structural Engineering Branch, DSS SEB is responsible for assessment of missile effects on structures. Their involvement is required to assure that the parameters used to characterize missiles are, or are directly translatable to, those used in analyses of their effects. Participation is needed on Subtasks 2 at:d 3 to assure com-patability with TAP A-32.

3.4 Environmental Evaluation Branch and Engineering Branch, D0R EEB and EB are responsible for, respectively, tornado missile definition and design adequacy for operating plants. Participation can be limited to Subtask 4.

4. Technical Assistance Requirements A techn'ical assistance contract, to develop impact velocities to be used in Subtask 3, is anticipated. Monte Carlo simulation, based on a missile tra-jectory computer program, will be required to estimate velocities at given exceedance levels. The work should cost ir, the neighborhood of $60,000 and take about 6 months. These funds will be required in FY 1978. The National Bureau of Standards, having previously developed a computer program for missile calculations, is a likely caididate.

5. Interactions with Outside Organizations

! Two programs, currently sponsored by the Electric Power Research Institute (EPRI) will be reliad upon in Subtasks 2 and 3. Interaction with EPRI will be required to assure NRC staff access to the data bases for the studies as well as the final reports.

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6. Assistance Requirements from Other NRC Offices 6.1 Office of Nuclear Regulatory Research Funding and management will be required for a research contract to develop the technical basis for Subtask 1. The anticipated funding level is $50,000 to be committed in FY 1978.

6.2 Applied Statistics Branch, EDO Statistical consultation will be required on the Monte Carlo simulations t' involved in Subtask 3. ,

6.3 Office of Standards Development Management of Task A-38 will be provided by the Office of Standards Development.

Additional effort will be required to develop a Regulatory Guide outlining staff positions.

7. Schedule for Problem Resolution The major milestones are summarized below. A more detailed schedule is provided in Af 'achment 1.

7.1 Subtask 1 Initiation of Research Contract - April 1978.

Completion of Research Contract - January 1979.

Development of Force-Time Histories - April 1979.

7.2 Subtask 2 Publication of EPRI report - April 1978.

Development of Deterministic Missile Spectrum - August 1978.

7.3 Subtask 3 Publication of EPRI report - May 1978. S Initiation of Technical Assistance Contracc - June 1978.

Completion of Technical Assistance Contract - January 1979.

Development of Probabilistically Based Nissile Spectrum - June 1979.

7.4 Subtask 4 e

Begin Analysis of Results of Subtasks 2, 3, 4 - April 1979.

Develop Staff Position - September 1979.

Revise SRP 3.5.1.4 and transmit to OSD - dovember 1979.

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8. Potential Problems The dates used for availability of EPRI reports are current best estimates.

Minor slippages of these dates are possible and beyond the control of the NRC staff.

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n i Attachment 2 - Resource Requirements Manpower Estimates (Man-Years)

Oraanization FY 78 FY 79 FY 80 . -

NRR/DSE/AAB .4 .6 NRR/DSE/HMB .1 .1 NRR/ DSS /SEB .1 .1 OSD/ DES /EMSB .2 .3 RES/RSR/SSRB .1 .1 NRR/00R/EB and EEB .1 .1 ,

E00/ASB .1 .0 TOTAL 1.1 1.3 i

Technical Assistance Requirements ,

FY 78: $60,000 A

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