ML20033B506
| ML20033B506 | |
| Person / Time | |
|---|---|
| Site: | Atlantic Nuclear Power Plant  |
| Issue date: | 11/27/1981 |
| From: | Campe K, Obrien J, Rothberg O NRC |
| To: | |
| Shared Package | |
| ML20033B480 | List: |
| References | |
| NUDOCS 8112010478 | |
| Download: ML20033B506 (8) | |
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f8d 11 UflITED STATES OF A!! ERICA fl0 CLEAR REGULATORY COMitISSION
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BEFORE THE AT0111C SAFETY AND LICEllSIllG BOARD l
In the flatter of
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0FFSHORE POWER SYSTEMS Docket No. STri 50-437 (Floating liuclear Power Plants) f1RC STAFF'S UPDATE OF ITS TESTIM 0!iY REGARDIllG TURBINE 111SSILES by John A. O'Brien Owen 0. Rothberg Kazimieras it. Campe On May 10, 1977, following Tr. 5660 in the captioned proceeding, the Staff presented its testimony in response to the liniited appearance statement of Ernst Effenberger. The Staff's testimony consisted of a turbine missile risk assessment for the FNP in which we evaluated the probability for unacceptable damage to safety-related plant structures due to destructive overspeed missiles. The turbine missile analyzed was characterized as a 90 segment of disc 5 of the low pressure turbine rotor, with an exit speed of 790 feet /second when ejected without impacting the 4.5 inch steel missile shield which covers the lower half of the turbine rotor (pp. 3-4).
When impacting the shield, the missile was estimated to have the potential for penetrating it and continuing with a residual speed of 540 feet /second (pp. 39-40).
Dr. O'Brien, the Staff's structural expert, indicated that the same missile at design
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overspeed could not penetrate the missile shield.
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t' Subsequent to the Staff's testimony, a series of turbine missile impact tests were conducted by the Electric Power Research Institute at the Sandia Laboratories in New flexico. The results indicated that the BRC formula used in the Staff's risk assessment for estimating missile penetration through steel barriers did not adequately predict missile penetration. This Board was so informed on December 22, 1978.
The EPRI test results indicate' to the Staff that our estimated turbine exit speed for the missiles evaluated in the testimony were too l ow. We have determined that, for conservatism, we should use values of 790 and 923 feet /second, corresponding to missiles ejected with or without impacting the steel missile shield, respectively. These values are considered conservative because the downward moving missile velocity (790) was estimated assuming rpl credit for the 4.5 inch missile shield, and the velocity of the upward moving missile (923) corresponds to that of the missile as it leaves the turbine shaft without taking credit for 4
interaction with the turbine internals and casing.
The above revised values do not change our conclusions regarding the turbine missile risks for the floating nuclear plant design. The basis for this finding is the conservatism that was used in our estimates of the strike and damage probabilities for safety-related targets.
For example, in estimating the strike and damage probability for the primary system boundary, we assumed in our analysis that the missile penetrated the concrete wall of the containment shield building, and then dropped l
down under g.ravity with a uniform strike probability distribution over the plan area of the containment. Because containment penetration was I
already assumed, the revised higher value of the missile speed does not
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. affect the probability of a missile entering the containment and damaging the primary system boundary. For a downward moving missile, even without taking credit for the missile shield, there would be no penetration of the containment because of the massive concrete turbine pedestal which would stop the missile.
With respect to the spent fuel racks, our original evaluation was based on estimatn3 that a 675 feet /second missile was necessary such that intervening barriers would slow it down to near zero speed.
This would allow the missile to " drop" towards the spent fuel racks from above. The revised penetration calculations would indicate that lower speed missiles would be capable of reaching the pool area with near zero speeds. This means that in terms of percent overspeed, a lower overspeed turbine coul<l introduce missiles over the pool area.
For example, let us assume that the necessary overspeed at failure is revised from 162% to 130%. Using the linear distribution model described in our previous testimony, the probability for missile ejection at 130% overspeed is 3.3 x 10-6, as compared to 1.37 x 10-5 previously estimated for the 162%
overspeed failure.
The corresponding overall probability of a destructive overspeed low trajectory turbine missile dropping into the 6
spent fuel pool is (0.016) (3.3 x 10 ) or 5.3 x 10-8 per turbine year.
Our previous estimate was 2.2 x 10-7 per turbine year.
In general, since the ejection probabilities decrease with decreasing overspeeds, the revised missile exit speeds lead to somewhat lower strike and damage probability estimates for the spent fuel pool area. Consideration of missiles which can impact the spent fuel pool walls lead to conclusions which are essentially the same as in our previous testimony, namely,
. that the increased missile speeds are still insufficient to cause penetration of the massive concrete turbine pedestal, the two and one foot concrete walls, and finally the five foot spent fuel pool walls.
Thus, we do not find that the strike and damage probabilities for the spent fuel racks increase significantly due to the estimated increases in the turbine missile exit speeds.
The strike and damage probabilities with respect to the main steam lines were determined primarily on the basis of geometric considerations involving the angles subtended by the steam lines with respect to the tu rbine. Once a pipe was perceived to be struck, unacceptable damage was assumed. The only missile interaction considered in our analysis prior to striking the steam lines was the potential for ricochets from the surrounding concrete walls.
Intervening barriers were neglected in the analysis. As pointed out in our previous testimony, consideration of higher missile speeds leads to a lower strike probability, since there would be a greater tendency for " forward scattering" of the missiles.
Hence, the revised missile speeds are not perceived to affect the estimated strike and damage probabilities for the main steam lines.
In summary, the revised missile speeds do not affect significantly the strike and damage probabilities and hence the turbine missile risk assessment described in our previous testimony. The basis for this finding is that most of the missile strike and damage estimates involved the assumption of eitner complete penetration with certainty where barriers were, judged to be marginal (e.g., containment shield building wall) or the perception of total missile stoppage where barriers were extremely massive (ed., turbine pedestal, spent fuel pool wall).
In the m
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fomer case, the missiles are assumed to penetrate with full certainty, as before.
In the latter case, they are judged to be still insufficiently energetic to penetrate the barriers.
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1 CLIFFORD DAVID SELLERS.
SENIOR MATERIALS ENGINEER MATERIALS ENGINEERING BRANCH DIVISION OF SYSTEMS SAFETY _
PROFESSIONAL QUALIFICATIONS us In my present position as Senior Materials Engineer in the Materials Integrity Section of the Materials Engineering Branch I am involved in safety review and evaluation of materials used in the construction of nuclear power plants.
The The Materials Engineering Branch consists of two sections.
Metallurgy Section is responsible for materials application, metallurgical investigative studies, fabrication problems, and inservice degradation The Materials processes such as corrosion and radiation effects.
Integrity Section is responsible for materials integrity, fracture toughness criteria, inservice inspection requirements, and potential inservice degradation processes such as crack growth, material creep and fracture for the wide range of materials used in the construction of In actual practice this division of nuclear power plant components.
responsibility is not rigorously followed and I have been involved in problems from both sections.
I have a BS degree in Metallurgy (Penn State 1951) and have done graduate work at the University of Delaware and University of Idaho.
From 1968 to 1973 I was a Senior Engineer with Westinghouse Nuclear Energy Systems-PWR Systems Division in Monroeville, Pennsylvania.
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1 2-In this position my duties involved design assistance and trouble-
. hooting on reactor internals, control rods and instrumentation, and reactor pressure vessels.
These duties and other field problem investigatory activities led to preparation and use of a field metal-lography lab.
In this and other connections I have been involved in vaFious activities at Beaver Valley, Cook, Zion, Turkey Point, San Onefre, Ginna, Yankee Rowe, Haddam Neck, Indian Point, Salem, and SENA.
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During the years 1964 to 1968, I was employed as a Quality Engineer at
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the Naval Reactors Facility located near Idaho Falls, Idaho and served as site materials engineer.
In my capacity of quality assurance engineer I prepared procedures, reviewed procurement documents and performed audits.
My major accomplishments were the establishment of materials receiving inspection and a verification program.
From 1961 through 1963 I was a senior metallurgical engineer at the Bettis Atomic Power Laboratory.
In this position I was a " cognizant engineer" for various. high strength structural alloys such as 17-4 PH; 12% chromium steels;; low alloy (bolting) steels; Inconel X; Haynes 25, etc., with responsibility for specification preparation and troubleshooting.
Additionally, I was involved in failure analysis of components fabricated from these alloys.
I performed field and in-plant inspection of 17-4 PH control rod drive mechanism components.
Involved in testing of specimens prepared from irradiated components and preparation of irradiation program of high strength bolting materials.
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F' rom graduation in 1951 I was employed in various degrees of increasing responsibility at the Westinghouse Electric Corporation Avaiation Gas Turbine Division until that Division's dissolution at the end of 1960.
I initially was responsible for the radiographic inspection of and shop
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contact on aluminum and magnesium base castings and investment cast refractory alloys and fabrications.
Subsequently I wa; involved in shop contact and troubleshooting of casting and forging shop.
Later I was t
responsible for development of and applications for improved lignt-alloy and refractory alloys, including preparation of design data and testing of engine hardware. Near the end of my service with this division I
/P performed extensive failure analysis work on both engine and test rig r,
failure, both in-house and in the field. During this period I received 13 patent disclosure awards and was involved in personnel training.
In my last year of college and the preceeding summer I worked at Penn State as an undergraduate lab technician with responsibilities for fabrication, testing, and photography of aquipment and specimens and for the metallurgy of test specimens. The project was a joint Metallurgy /
Ceramics Department project on the vitreous enameling of steel.
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