ML19249F159
| ML19249F159 | |
| Person / Time | |
|---|---|
| Site: | Crane  |
| Issue date: | 10/26/1973 |
| From: | Bernero R US ATOMIC ENERGY COMMISSION (AEC) |
| To: | |
| Shared Package | |
| ML19249F153 | List: |
| References | |
| NUDOCS 7910100556 | |
| Download: ML19249F159 (12) | |
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October 26, 1973 THREE MILE ISLAND NUCLEAR STATI0fl - DOCKET NO. 50-289 SUPPLEMENTAL TESTIMONY ON AIRCRAFT HAZARD BY ROBERT M. BERNERO Contention #2 The facility should be so constructed, pri_or to operation, so as to withstand a direct impact from a 707 Jet airplane crash or from the crash of a super jet.
It is contended that the probability of a 707 or super jet crashing into the facility is significantly high enough to warrant such protection.
It is further contended that if the facility is not designed to withstand the impact from the aforesaid aircraft, cdequate monitoring systems nust be provic'ed and adequate arrangements with nearby airports must be made in order to avoid flight patterns of said aircraft near or over the facility.
INTRODUCTI0ft The evaluation of the potential interaction between the Three Mile Island fluelear Station and aircraft using the Harrisburg International Airport was performed by the Regulatory staff as part of the construction permit consideration. As a consequence of that evaluation Three Mile Island Unit 1, was constructed with special design features to protect vital areas of the plant from impact and fire effects of the crash of most of the aircraft using the aircor', that is, aircraft weighing no more t
7910100 4~ zpi i85
. than -200,000 lbs. Consequently, the risk analysis discussed later in this testimony is concerned only with heavy aircraft, those weighing more than 200,000 lbs. During the Regulatory staff review of Three Mile Island Unit 1, for the operating license, the aircraft hazard evaluation was reviewed to ensure its adequacy.
I participated in that review of the aircraft hazard evaluation. A summary of the evaluation was presented in Section 3.6 of the staff Safety Evaluation Report on Three Mile Island Unit 1, dated July 11, 1973. This testimony is intended to define that evaluation in greater detail with particular address of the concerns identified in the intervenors' Contention 2.
HARRISBURG INTERNATIONAL AIRPORT The Harrisburg International Airport is located alongside the Susquehanna River on the East bank with the long, single runway parallel to the river. The river takes a bend to the right before reaching Three Mile Island. Consequently, the Three Mile Island nuclear piants lie about 2.5 miles along and about 1.5 miles to the right side of the extended centerline of the runway.
Harrisburg International Airport heidles scheduled and nonscheduled passenger and cargo fiights, general aviation, and sone military cargo traffic. Originally designed as an Air Force base, Harrisburg International Airport is capable of handling flights by the largest aircraft in use today. The October 15, 1973 1411 186
. edition of the Official Airline Guide (published by Reuben H.
Donnelly) shows scheduled passenger flights mostly by twin-engined aircraft, including the propellor-driven Beechcraft and Convair models and the jet-engined McDonnell Douglas DC-9 and Boeing 737.
A number of the three-engined Boeing 727 jet aircraft also make scheduled flights to Harrisburg International Airport as well as one four-engined aircraft, TWA Flight 16 (a Boeing 707), which uses the airport daily. Table I shows the weights of some of the aircraft which use the Harrisburg International airport now.
I also consulted with the Facility Manager at Harrisburg International Airport to determine how much other traffic, of large aircraft, currently uses the airport. The number of cargo and charter flights of size comparable to or greater than the Boeing 707 averages about three or four movements (takeoff or landing) per day. The aircraft involved are Boeing 707's, McDonnell Doublas DC-8's, and a few Convair 880's; these are all approximately 300,000 lb aircraft.
In addition, one charter operator is expected to bring a Boeing 747 into the airport occasionally, and the U.S. Air Force sometimes lands a Lockheed C-5A.
Considering all of these large aircraft movements, it was estimated that there are now about 2000 movements per year (5-6 movements per day) at Harrisburg International Airport of aircraft weighing more than 200,000 lbs. These constitute about 2 or 3 percent of the total traffic.
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TABLE I TYPICAL AIRCRAFT WEIGHTS Aircraft Type No. and Type of Engines Weight (1bs)*
Beechcraft King Air 2 Prop.
10,000 Gates Learjet 2 Jet 12,000 Lockheed Jetstar 2 Jet 40,000 Convair 600 2 Prop.
50,000 Grunnan Gulfstream 2 Jet 55,000 McDonnell Douglas DC-9 2 Jet 100,000 Boeing 737 2 Jet 100,000 Lockheed Electra 4 Prop.
120,000 Boeing 727 3 Jet 150,000 Boeing 720 4 Jet 200,000 Boeing 707 4 Jet 300,000 McDonnell Douglas DC-8 4 Jet 300,000 Boeing 747**
4 Jet 700,000 Lockheed C-5A**
4 Jet 700,000
" Approximate mean of loaded takeoff and landing weights.
- 0ccasional use expected (see text) 1411 188
_4 AIRCRAFT HAZARD ANALYSIS The aircraft hazard analysis of a nuclear power plant such as Three Mile Island Unit 1, is concerned with the possibility that an aircraft might strike the plant and, either by direct impact effects or. by attendant fire, cause a release of radioactivity to the environment in excess of the design basis. Therefore, the vulnerable areas of the plant which merit concern are the reactor coolant pressure boundary, the spent fuel in storage, and those plant systems which are needed for safe shutdown of the plant. These vital portions of the plant are ordinarily enclosed by some protecting structure such as the reactor containment building which surrounds the reactor coolant system.
It is possible that a crashing aircraft might breach one of these enclosures without causing the significant release of radioactivity with which we are concerned.
However, because of the difficulties in properly analyzing the course and consequences of such an event, it is customary to make the conservative assumption that any breach of the enclosing structure is potentially damaging.
The aircraft hazard or risk analysis therefore requires establishment of the protective capabilities of the structures which enclose the vital areas of the plant and then an assessment of the likelihood of a crash on these structures by an aircraft which exceeds those capabilities. The Regulatory staff agreed in the construction permit review that it was acceptable to design the plant so that vital areas are protected by structures capable of withstanding impact at the worst angle of incidence on the weakest point by an aircraft weighing 200,000 lbs. and cravelling at 200 knots.
It is 1411 189
. probable that the structures can withstand the impact of much larger aircraft without penetration if they strike at an angle to the surface of the structure or at some point other than the weakest. Special fire protection systems were also required to cope with the large quantities of fuel which might be spilled and ignited. The 200-knot impact velocity was selected as a reasonable upper limit for aircraft involved in takeoff or landing accidents. The 200,000 lbs. weight is characteristic of a Boeing 720, a four-engined jet, and this size limit was expected to include most of the aircraft which use the Harrisburg International Airport. The details of the structural analysis and the fire protection systems are presented in the Final Safety Analysis Report by the applicant and the Safety Evaluation Report by the Regulatory staff; they will not be addressed here.
Accepting the 200,000 lb. capability of the key structures, the risk or probability of impact by a larger aircraft was calculated by using the equation:
P=DxAxM where:
P is the probability D is the distribution function A is the target area M is the number of movements Cr, in words, the probability is the product of the likelihood of an aircraft crashing in an area near an airport runway, the size of the vulnerable area, and the number of movements by aircraft of significant i411 190
. size.
The distribution function was claculated on the basis of ten years' accident statistics drawn from data provided by the National Transportation Safety Board of the U.S. Department of Transportation. The data for air carrier crashes during the period 1956 to 1965 were used and a distribution of crash probability as a function of distance from the end of the runway was calculated. The crash distribution is listed in Table II and, as indicated, is based on fatal crashes which occurred on takeoff or landing 0
within a 60 arc of the projected path of the runway. Attention was confined to those crashes which caused fatalities because it was believed that these included all the crashes where the lack of aircraft control or ignorance of position and heading were sufficient to make collision with a large power plant a possibility. As previously noted, the Three Mile Island Nuclear Station is about 2.5 miles beyond the end of the runway and about 1.5 miles to one side, putting it just at the side of a 60 arc. Going to Table II we therefore idertified 0.96 x 10-8 per square mile per aircraft movement as the crash distribution function appropriate to the Three Mile Island calculation.
It should be pointed out that the use of 1956-1965 data is also somewhat conservative since, with improvements in equipment and control procedures, successive years have shown lower accident rates.
The target area of the Three Mile Island fluclear Station for this calculation was taken as 0.01 square miles per nuclear unit or 0.02 square miles for the station. This value for the target area was established 1411 191
3 TABLE II CRASH DISTRIBUTION 8
DISTANCE FROM END PROBABILITY (x 10 ) 0F A FATAL CRASH OF RUtiWAY PER SOUARE MILE PER AIRCRAFT MOVEMENT U.S. AIR CARRIER 0-1 Mile 16.7 1-2 Mile 4.0 2-3 Mile 0.96 3-4 Mile 0.68 4-5 Mile 0.27 5-6 Mile 0.00 6-7 Mile 0.0 7-8 Mile 0.0 8-9 Mile 0.14 9-10 Mile 0.12 0
1/No crashes occurred at these distances within a 60 flight path.
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by a conservative evaluation of the area exposed to impact when considering conservative angles of incidence on a typical nuclear power plant.
It includes allowance for aircraft which might strike the. ground adjacent to a vital structure and skid into it. A sense of the conservatism of this target area may be obtained by comparing it, 0.01 square miles or 280,000 square feet, to a simple projected area for the largest sihgle vital structure of the Three Mile Island plant, the reactor building, which stands about 160 feet above grade with a 140 foot diameter and presents a side view area of about 22,000 square feet.
It should also be noted that using this large target area is additionally conservative because the impact rating of the structure was based on the 200,000 lb. aircraft striking the structure at the weakest point as well as at the worst angle. Taking into account impacts at stronger points on the structures or at different angles would give either a higher structural rating or a smaller target area for use in the calculation.
The number of aircraft movements used in the calculation was 2400 per year.
This was originally established by estimating a total of 80,000 movements per year by all aircraft and postulating that 3% of that traffic would be aircraft weighing more than 200,000 lbs. Compared to the current icvel of heavy aircraft traffic, about 2000 movements per year, the value used in the calculation is about 20% conservative. There is further conservatism of a factor of about two since, depending on the wind direction, only about half of the takeoffs and landings en the runway would have a route in the direction of the facility. An additional conservatism is involved in that the calculation assumes that all these movements pass over the power 1411 193
plant, no dis' count of either the number of movements or the crash distri-bution is made to reflect the fact that the plant is far to one side of the runway path, over which aircraft would not tie likely to travel.
Combining all the preceding terms, the probability of a potentially damaging crash was calculated:
P=DxAxM 2
2
= 0.96 x 10-8/ movement /mi /yr x 0.02 mi x 2400 movements
= 5 x 10-7 per year (considering both plants)
CONCLUSIONS Probabilities calculated in this manner are not intended to be precise values of probability with high confidence levels. Rather, they are intended to be upper bound estimates of the probability of an event which can be used to assess how seriously that event may affect the health and safety of the public. A probability less than 10-6 per year calculated by this conservative model, is considered acceptably low for a potentially damaging aircraft crash. Therefore, I consider the probability of 5 x 10~7 per year for a potentially damaging aircraft strike calculated for the Three Mile Island Nuclear Station acceptably low. I must emphasis that such a probability is not the probability of a major radiological accident but is rather only the probability of a potentially damacina aircraft strike. Having concluded that the
-7 calculated probability of 5 x 10 per year is acceptably low, I have further concluded that no arrangements were necessary to avoid flight 14)\\
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_g.
patterns of heavy aircraft near or over the Three Mile Island plants.
No traffic growth prediction..:.idies were performed because, in my judgement, the repeatedly conservative bases and the result calculated indicate that even a tenfold increase would not be critical. Moreover, I don't believe that the Harrisburg area, with a population in the range of a hundred thousand rather than millions, is likely to generate so great an increase for large size aircraf t traffic in the future.
The aircraft hazard analysis was based on a heavy aircraft traffic of 2400 movements per year, about 20% greater than the current traffic, as well as the other conservative bases indicated. The applicant ha; agreed to monitor the airport traffic and report on it to the AEC at least annually. This is sufficient to detect changes important to the safety of the plant in time to permit appropriate consideration.
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_g.
patterns of heavy aircraft near or over the Three Mile Island plants.
No traffic growth prediction studies were performed because, in my judgement, the repeatedly conservative bases and the result calculated indicate that even a tenfold increase would not be critical. Moreover, I don't believe that the Harrisburg area, with a population in the range of a hundred thousand rather than millions, is likely to generate so great an increase for large size aircraft traffic in the future.
The aircraft hazard analysis was based on a heavy aircraft traffic of 2400 movements per year, about 20". greater than the current traffic, as well as the other conservative bases indicated. The applicant has agreed to monitor the airport traffic and report on it to the AEC at least annually. This is sufficient to detect changes important to the safety of the plant in time to permit appropriate censideration.
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