ML19220B873
| ML19220B873 | |
| Person / Time | |
|---|---|
| Site: | Crane  |
| Issue date: | 10/15/1976 |
| From: | Bunch D Office of Nuclear Reactor Regulation |
| To: | Silver H Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 7904270556 | |
| Download: ML19220B873 (4) | |
Text
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OCT 15 'c7E
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l.
AA8/APCSB: Have we examined possible interactions between Unit Nos. I and 2 in the event of an airplane c-ash?
The airspace around Three Mile Island is pre-empted by operations at Harrisburg International Airport. The plant safety related structures for each unit are designed to withstand the impact of a 200,000 pound airplanee impacting at a speed of 200 knots. The most likely accident would be that caused by a large aircraft experiencing a malfunction while taking off. Such an accident would generally result in an impact on one unit only, although it might produce a glancing impact on the upper elevations of Unit No.1 followed by a descent upon Unit No. 2.
In such a case the forward momentum would cause the wreckage pattern to be thrown in the forward direction, away from Unit No.1, for distances of the order of hundreds of feet. This type of crash would thus not be likely to cause damage to safety related structures of Unit No. 1.
Aircraft crashes into any of tha four cooling towers on the site, followed by a collapse of the wer, would not result in damage to any safety relatec structures due to the adequate separation distance between them. Both units share the same electrical switchyard, though this is situated between two cooling towers and is non-safety related. Therefore, damage to the switchyard would not lead to un-acceptable consecuences. The staff believes therefore that possible interacticns between Unit Nos. I and 2 that would lead to unac-ceptable consequences in tne event of an aircraft crash, are remote.
2.
AAB: With regard to Figure 2.4 of the SER, against what criteria was population distribution evaluated?
Standard Review Plan 2.1.3 gives population density criteria that the staff uses for review purposes. These are:
- 2 If, at the CP stage, the population density, including weighted transient population, projected at the time of initil plant operation exceeds 500 persons per square mile averaged over any radial distance divided by the area at that distance), or the projected population density over the lifetime of the facility exceeds 1,000 persons per square mile averaged over any radial distance out to 30 miles, special attention should be given by the staff to the consideration of alternative sites in the environmental review.
Such an evaluation is not made for plants at the OL stage.
If, at the CL stage, a plant meets Part 100 then a consideration of alternative sites for population reasons is not necessary. Figure 2.4 was there-fore presented for information purposes only.
In fact, the 1970 popu-lation density and the projected 2010 density are less than 500 and 100' persons per square mile, respectively, out to 30 miles from the site.
3.
AAB: Discuss turbine missiles and the probabilities of a missile strike from the Unit No. 2 turbine and interactions resulting from turbine missiles from Unit No.1.
Because both units of Three Mile Island have been designed for a design basis aircraft impact, the wall thicknesses are such that the plant is considered to be adequately protect 3d against the risks of turbine missiles. None of the safety related structures of Unit No. 2 are within the low trajectory turbine missile strike zones of the Unit No.1 turbine. Although Unit No. 2 is arranged so that the reactor building and a portion of the control room building are within the low trajectory strike zones of its own turbine, penetration of these s-tructures is unlikely since the effective thicknesses of the exposed control room and reactor building walls are 10 feet and 5 feet of concrete, respectively.
In addition, protection against high trajectory turbine missiles is adecuate since all safety related structures are covered by high strength concrete
^
roofs of at least three feet thickness.
03 % 3
3 4
AAS:
Status of revised containment spray chemical additive system, if any update after September 13.
The applicant has proposed a sodium-thiosulfate spray additive system to reduce post-accident thyroid doses. The system, as presently proposed, falls short of our guidelines for sodium-thiosulfate systers (as outlined in the Standard Review Plan, Section 6.5.3).
In addition, the method of spray additive injection chosen by the applicant has been shown to be unsuitable for this system in previcus tests. At present the applicant is re-designing the thiosulfate spray additive system.
We will require the applicant to demonstrate that the system will be able to achieve the design requirements and can overcome the difficulties experienced in previous systens of this type. This demonstration must be verified by appropriate pre-operational testing of the spray additive function of the system. Alternatively, we will require installation of a spray additive system of proven performance.