ML19206A718
| ML19206A718 | |
| Person / Time | |
|---|---|
| Site: | Crane  |
| Issue date: | 04/26/1977 |
| From: | Trowbridge G SHAW, PITTMAN, POTTS & TROWBRIDGE |
| To: | |
| References | |
| NUDOCS 7904200376 | |
| Download: ML19206A718 (13) | |
Text
April 26, 1977 8
B#
UNITED STATES OF AMERICA NUCLEAR REGULATORY COMMISSIO'..
BEFORE THE ATCMIC SAFETY AND LICENSI::G SOARD In the Matter of
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METROPOLITAN EDISON COMPANY,
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Docket No. 50-320 et al.
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(Three Mile Island Nuclear
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Generating Station, Unit 2)
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APPLICANTS' RESPONSE TO INTERVENORS' MOTION DATED APRIL 15, 1977 Intervenors have filed with the Board a motion dated April 15, 1977, to compel Applicants to provide a witness (or witnesses) to discuss tue consequences, if any, to the nuclear safety related structures from the impact of a large, fully loaded aircraft, such as a Lockheed C-5A
\\
or a Boeing 747, at TMI #2.
As explained by Intervenors' motion, such testimony would have to address a wide range of necessary parameters, including but not limited to the angle of impact, the point of impact, the kind of load car-ried, and the fuel inventory.
Intervenors' motion also makes it clear that if the nuclear safety related structures are not capable of withstanding the i.apact frca such large air-craft, the next line of inquiry which Intervenors wish to pursue is the full consequences of the impact upon the plant internals and any possible consequences to the public.
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a-Applicants oppose Intervenors' motion on the grounds, more fully discussed below, that the crash of a large aircraft, such as the Lockheed C-5A or Boeing 747, upon the vital TMI #2 structures is of such low probability that the consecuences of such crash need not be considered in this proceeding.
Factual Setting The Three Mile Island, Unit 2, design criteria for protection against aircraft accidents were established at the time of issuance of the TMI #2 construction permit and are the same as the design criteria previously approved for TMI #1.
The vital structures of TMI #2 are designed to withstand, without loss of structural ~ integrity, the impact of a 200,000 pound airplane with a velocity of 200 knots.
Most of the aircraft operating ar Harrisburg International Airport are smaller than this design basis aircraft.
The probability of a strike en the Unit from larger a#rcraft operating at the Harrisburg International Airport was de-termined during the construction permit proceeding to be less than one chance in a million per year, even assuming that the number of large aircraf t operations were to increase to as many as 2400 per year.
Both the Applicants and the NRC Staff have testi-fied in this proceeding that, applying statistical models60-260
.w-o currently in use, the probability that a large aircraft, i.e. an aircraft in excess of 200,000 pounds, operating at the Harrisburg airport would strike TMI #2 is less than 10~
per year even if large aircraft operations at the airport reach 2400 per year.
Operations of large aircraft currently number about 600 per year, and Appli-cants' best estimate of current probability of a large
-9 aircraft strike on TMI #2 is 3x10 The Staff has tes-tified that it will include in the technical specifica-tions to the TMI #2 operating license a requirement that Applicants continue periodic monitoring and reporting to NRC of airport usage, and the Staff will reevaluate the adequacy of plant protection if large aircraft operations are projected to exceed 2400 per year.
It should be emphasized that the pr<aabilities calculated both by Applicants and the Staff are for a large aircraft hitting TMI #2 and not for damaging strikes to vital structures.
Many aircraft strikes would not hit vital structures or, if they did, would not hit parts of the vital structures which would either result in signif-icant release of radioactivity or in disabling more than one of the redundant and spatially separated systems needed for safe shutdown.
Further, some strikes would be at a shallow angle to the surface struck and would not cause-serious damage.
Additionally, no account is taken of the 60-261 w
fact that critical structures would be shielded by the cooling towers or other noncritical structures from some fraction of the aircraft.
Applicants have not attempted to make a quanti-tative estimate of the probabi'.ity that a large aircraft striking the TMI 02 facility would in fact be a damaging
- strike, i.e. hit a vital structure and cause a signifi-cant release of radioactivity or inhibit safe shutdown of the plant.
It is obvious, however, that the probability of such a damaging stTike would be much lower than the probability of hitting any of the TMI # 2 s tructure s.
Regulatory Precedents Since the issuance of the TMI #2 construction permit, the NRC Staff has issued its Standard Review Plan codifying the Staff's position and past practice with re-spect *-
' ant protection against low-probability hazards.
Sectic 2.3 of the Plan deals generally with design cri-teria for potential accidents due to the presence of haz-ardous materials or activities in the vicinity of the plant.
Section 3.5.1.6 deals specifically with aircraft hazards and incorporates by reference the provisions of Section 2.2.3.
The applicable portions of Sections 2.2~.3 and 3.5.1:6 read as follows:
G0-262
-Q Standard Review Plan Section 2.2.3, Part II:
Acceptance Criteria The identification of design basis events resulting from tha presence of hazardous materials or activities in the vicinity of the plant is acceptable if the design basis events i.nclude each postulated type of accident for which a realistic estimate of the probability of occurrence of potential e:cposures in excess of the 10 CFR Part 100 culdelines exceecs the :iRC_staf f cblectiva or ao-proximately 10~'
per year.
The methods of calculating the radiological expo-sures resulting from these events are acceptable if they are consistent with methods used for calculation of other accident radiological exposures (e. g.,
SRP 15.6.5).
Because of-the difficulty of assigning precise numerical values to the probability of occurrence of the types of potential hazards generally considered in this review plan, judgment must be used as to the acceptability of the orerall risk presented by an event.
In view of the low probability events under consideration, the proba-bility of occurrence of the initiating events leading to potential consequences in excess of 10 CFR Part 100 exposure guidelines should be estimated using assumptions that are as realistic as is practicable.
In addition, because of the low orchability events uncer consid-eration, valic statistical data are often not avallacle to normit accurate quantitative calculation of crocacilities.
Accorcincly, a conservative calculation showing tnat ene crobacility of occur-ence of cotential exrosurcs in excess of the 10 CFR Part 100 culcclines is accrox-imatelv 10 0 ter year is acceotaole if, when comoinac vita reasoracio cualita-tive arcuments, the realistic prooabliity can ce snown to be lower.60-263
-s-
o The effects of design basis events have been appropriately considered if analyses of the effects of those acci-dents on the safety-related features of the plant have been performed and appro-priate measures (e.g.,
hardening, fire protection) to mitigate the consequences of such events have been taken.
(Empha-sis added.)
Section 3.5.1.6, part II:
Acceptance Criteria 1.
The plant is considered adequately desicned acainst aircraft nazaras if the probability of aircraft accicents re-sultinc in radiolccical consecuences greater tnan 10 CFR Part 100 exposure guidelines is less than about 10 e per year (see Stancard Review Plan 2.2.3).
2.
The probability is generally consid-ered acceptable by inspection if the level of aircraft activity near the site falls below the criteria given in Sec-tion 2.2.3 of Regulatory Guide 1.70 (Ref. 2) for analysis of hazards due to commercial, experimental, and general aviation aircraft.
For military air-space, a minimum distance of five miles fran the reactor is adequate for low level training routes except those asso-ciated with usage greater than 1000 flights per year or activities (such as practice bombing) where an unusual stress situation exists.
3.
Aircraft accidents which could lead to radiological consequences in excess of the exposure guidelines of 10 CFR Part 100 with a probability of occurrence greater than about 10-7 per year should be considered in the design of the plant.
4.
The evaluation of fire hazards will be done on an individual case basis.60-264
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Concrete structures are generally as-sumed to withstand fire, but protection must be provided to prevent fire, smoke, or flammable mixtures frcm entering safety-related ventilation intakes, such as those for the control rcom, areas housing shutdown equipment, and the diesel generators.
(Emphasis added.)
Two aspects of Sections 2.2.3 and 3.5.1.6 need to be emphasized.
First, the probability of 10-7 per year to which both sections refer is the probability that a hazardous activity in the vicinity.of the plant would result in radiological consequences greater than 10 CFR Part 100 exposure guidelines.
Obviously if the probability of a large aircraft impacting on any TMI #2 structure is less than 10-7 per year, the probability that the impact would be such as to result in 10 CFR Part 100 guidelines be'~.g exceeded is very much less.
Second, Section 2.2.3 expressly recognizes that because of the low probability events under consideration, valid statistical data are often not available to permiu accurate quantitative calculation of probabilities.
Ac-cordingly, a conservative statistical calculation showing probability of occurrences to be approximately 10-6 per year is acceptable if, when combined with reasonabl'c qual-itative arguments, the realistic probability can be shown GO-265
.A to be lower.
In the case of TMI #2 Applicants have already shown by a conservative statistical calculation that the probability of a large aircraft strike is less than 10-7 per year, and qualitative arguments are not necessary to show compliance with the 10-7 criterion of Section 2.2.3.
The Board should nevertheless recognize that strong quali-tative arguments do exist that the probability of causing radiological consequences greater than 10 CFR Part 100 ex-posure guidelines is far less than the probability of a strike on any of the TMI #2 structures.
The Staff's probability guidelines have not been incorporated in Commission regulations.
The Staff's prob-ability approach has, however, been accepted in decisions by Licensing and Appeal Boards.
To begin with, of coarse, the circrash protection criteria for both TMI il and TMI #2 were accepted by separate Licensing Boards at the construc-tion permit stage.
The Staff approach to design criteria for low probability aircraft accidents has also been ex-pressly approved in at least two other proceedings.
Com-monwealth Edison Company (Zion Station, Units 1 and 2)
LPB-73-35, 5 AEC 861, 887-91 (October 5, 1973); Lone Island Lichting Company (Shoreham Nuclear Power Station), ALAB-156, 6 AEC 831, 845-46 (October 26, 1973).
The " ion decision' in particular cpells out the Staff's probability approach and techniques in establishing aircraft protection criteria.60-266 In neither case was the applicant required to take special precautions against low probability aircraft impacts on the facility or to evaluate the consequences of such an impact.
More recently, in an analogous proceeding, a Li-censing Board was called upon to consider the prob 2bilit/
that a flammable cloud released by an accident involving an LNG tanker in the Delaware River 'till reach the site of the Hope Creek facility and whether in the light of this possibility the facility met the Commission's safety design criteria reflected in 10 CFR 50, Appcndix A.
Public Service Electric and Gas Company, et al (Hope Creek Gener-ating Station, Units 1 and 2), LP3, NRCI-77/3 (March 28, 1977).
The Board tock cognizance of the Staff's position reflected in Section 2.2.3 of the Standard Review Plan and concurred in the Staff's conservative estimate that the probability of such an event was less than 10-7 per year.
On this basis the Board decided that no provision need be made in the design of the Hope Creek facility to prevent or mitigate the possible consequences of such an event.
In addition, the Board expressly found that "the probability of that event is so low that no analyses of the consequences thereof need be undertaken."1/
-1/ Id.,
slip opinion at 33.
The Eoard in the Hope Creek proceeding was also called upon by intervenors to con-sider, as a separate issue, whether the consequences of such an accident needed to be considered in the NEPA review of tha project.
The Board also decided this question in the negative.
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J In a broader context it is an inherent premise of the Commission'~s scheme of regulation that applicants not be required either to guard against or pursue the con-sequences of extremely improbable, accident events.
The premise has only occasionally been articulated, as in the Appeal Board and Commission decisions on the need to pro-tect against the failure of a pressure vessel.
Consoli-dated Edison Co=0any of New York (Indian Point Unit No. 2)
CLI-72-29, 5 AEC 20 (October 26, 1972); ALAB-71, 5 AEC 290 (September 27, 1972).
It is reflected, however, in NRC licensing practice in many areas.
A single example will suffice to illustrate the point.
Nuclear power plants are designed to seismic criteria which acconnodate a highly improbable earthquake for the area in question.
Applicants are expected to perform and do perform extensive engineer-ing analyses and establish detailed design criteria to dem-onstrate that the seismic criteria have been met.
They are not, however, expected to perform the far more diffi-cult engineering feat of conducting a failure analysis of the plant in the remote contingency that an earthquake might exceed the design basis earthquake.
Thus, Applicants' opposition to conducting a failure analysis of TMI #2 in the event of the impact on the plant of an aircraft _ larger than the design basis aircraft is wholly consistent with 60-268
.a s
NRC requirements with respect to other potential accident events.
Respectfull / tabmitted, SHAW, PITTrd, ?OTTS & TROWBRIDGE
) %h nu nwA/ a
"$'rge/F. Trowbricge
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60-269
.a o
UNITED STATES OF A'1 ERICA NUCLEAR REGULATORY CC:CIISSION BEFORE THE ATOMIC SAFETY AND LICENSI:IG BOARD In the Matter of
)
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METROPOLIT!.N EDISCN CC:1PANY,
)
et al.
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Docket No. 50-320
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(Three Mile Island Nuclear
)
Generating Station, Unit 2)
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CERTIFICATE OF SERVICE I hereby certify that copies of " Applicants' Re-sponse to Intervenors' Motion Dated April 15, 1977," daced April 26, 1977, have been served upon each of the persons listed on the attached service list, by mail postage prepaid, this 26th day of April, 1977.
/ #A/
- /WA ' //
g"Gprge F.
Trowcric'ge Dated: April 26, 1977 60-270
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UNITED STATES OF A ERICA NUCLEAR REGULATORY CC:01ISSION BEFORE THE ATOMIC SAFETY AND LICENSING BOARD In the Matter of
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METROPOLITAN EDISON CO:.iPANY,
)
Docket No. 50-320 et al.
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(Three Mile Islar ' Nuclear
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Generating Station, Unit 2)
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SERVICE LIST Edward Luton, Esq., Chairman Henry J. McGurren, Esq.
Atomic Safety and Licensing Board Office of the Executive Legal U.S.
Nuclear Regulatory Commission Director Washington, D.C.
20555 U.S.
Nuclear Regulatory Commission Washington, D.C.
20555 Mr. Gustave A.
Linenberger Atomic Safety and Licensing Board Karin W.
Carter, Esq., Assistant U.S. Nuclear Regulatory Ccmmission Atrorney General Washington, D.C.
20555 Office of Enforcecent Department of Environmental Resources Dr. Ernest O.
Salo 709 H 'lth and Welfare Building Professor, Fisheries Research Harrisburg, PA 17120 Institute, WH-10 University of Washington Atomic Safety and Licencing Board Seattle, NA 98195 Panel U.S.
Nuclear Regulatory Commission Mr. Chauncey R.
Kepford Washington, D.C.
20555 433 Orlando Avenue State College, PA 16801 Atomic Safety and Licensing Appeal and Board 2586 Broad Street U.S.
Nuclear Regulatory Commission York, PA 17404 Washington, D.C.
20555 Docketing and Service Section Office of the Secretary U.S.
Nuclear Regulatory Commission Washington, D.C.
20555 60"271