10 CFR 50.71(e) - Maritime Administration - U.S. Department of ...

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Updated Final Safety Analysis Report - (STS-004-002)In its present (2009) condition, the NSS will most often be stationary; either moored at a layberth or in aship repair facility. In most such cases there will be an allision threat if the mooring location is adjacentto a regularly-travelled transit or channel. Marine allisions are striking incidents between a moving vesseland a stationary object. The stationary object can be any marine structure (quay, dock, bridge, etc.) ormoored/anchored vessel. Allisions are generally of much lower total energy than collisions;consequently, the design provisions that protect against collision effects will also adequately protectagainst the effects of allisions.During the ship’s design and construction phase, a thorough study of contemporary collision records wasundertaken to determine the mechanisms of collision and to define the magnitude of damage to beexpected. In the course of the investigation, the available data on some 60 major collisions werereviewed. Data were collected from USCG reports on collision circumstances, the ABS and UnitedStates Salvage Association damage surveys, testimony of passengers and crew members who hadexperienced collisions and U.S. Navy damage reports. Additionally, statistical data on ship collisionswere obtained from U. S. Salvage, Lloyds and underwriting organizations.Very few collisions are recorded involving passenger ships in harbors, and none are included in thestatistical sample used to develop the probability data. In the rare event of a harbor collision, the very lowspeeds used would preclude penetration of the reactor compartment.The findings of the contemporary collision studies are summarized as follows:Collision offers no danger of shock damage to the reactor components.Containment rupture resulting from collision in a harbor is practically impossible.Collisions involving containment rupture are limited to areas outside of harbors. The probability ofsuch an event over the life of the ship is very low, in the order of 1.0E-5. This figure comparesfavorably with values given by the AEC for an uncontained release from shore-based reactor plants.Additionally, since the area of greatest danger extends to 100 miles at sea, the degree of probableisolation is greater than that for any shore-based power reactor.Given that the few remaining ship movements for the NSS will take place under tow and that the ship’spassive collision protection systems remain functional even in an era of much larger ships thancontemplated by the designers of the NSS, the vessel remains adequately protected against collision and/or allision effects. Because the primary, auxiliary and secondary systems have been drained to themaximum practical, the reactor has been permanently defueled, the tanks containing radioactive wasteshave been drained and the demineralizers and their resins have been removed, the consequence of anycollision or allision is greatly reduced from that during the period of NSS operation.12.4 GroundingWhether underway or under tow, the effects of grounding are similar to those of collision, becausecrushing of the ship’s structure and shock may be expected. In all severe cases of grounding, extensivecrushing of structures held accelerations to very low levels, indicating that shock in grounding is of littleconcern from the standpoint of reactor safety.The damage sustained in grounding is strongly dependent upon the state of the sea and the type of bottomon which the grounding takes place. In harbors or sheltered waters, structural damage is generally limitedto that incurred in initial contact since there is little tendency for working of the ship by the action of thewater. The majority of these groundings would be bow-on or stern-on and would not normally involvethe reactor compartment. Damage to the inner bottom near the reactor compartment could result fromcertain infrequent harbor groundings. Even if low-level, liquid wastes were again stored in the innerRev. VI 130
Updated Final Safety Analysis Report - (STS-004-002)bottom tanks, releases from these tanks and the low level of activity of the wastes limits the hazard to thegeneral public. The probability of even a very limited release of low-level waste is considered negligible.On very rare occasions ships have been known to lie over on one side following grounding or sinking inshallow water. This heeling action occurs over a relatively large period of time. Few, if any, activitieswould be in progress during any ship movement and those could be secured or completed prior to severeheeling. The reactor primary system and other vital auxiliaries are sufficiently braced to preventdislocation of components should this occur. No failure of primary system or containment can resultfrom the ship resting on its side.Grounding in unprotected waters results in more extensive damage because of the working of the ship bythe action of the sea. In the worst case, the ship may pivot about the point of contact and eventually breakup. Such breaks will not occur in way of the NSS’s reactor containment, because of the deliberatelydesigned discontinuities in the hull girder forward and aft of the reactor compartment. This has beenmodified to some degree in the case of the hull girder forward of the reactor compartment by thereinforcement of the port and starboard sides of A-deck in the way of hold hatches 3 and 4 withcontinuous longitudinal and transverse intercostal girders.However, calculations for the ship’s strength in the way of the reactor compartment as compared withhold 4 indicate that the structure in the way of the reactor compartment is still considerably strongeragainst bending in a vertical plane than the structure forward of the reactor compartment. It is particularlystronger in the bottom section modulus, which indicates that the ship could sustain substantially highersecondary stresses from hydrostatic loads or grounding concentrations in the way of the reactor space.Calculations for bending in a horizontal plane indicate that the section through the reactor compartment isabout 22% stronger than the section through hold 4 after reinforcement.After the reactor compartment section has broken free of the water-borne sections or after the water-bornesections have sunk, the relatively short containment vessel, with its great strength and weight, will havelittle tendency to move under wave action, and structural damage will be greatly diminished. Under theseconditions, release of any residual low-level wastes and other equipment outside of the containment mustbe assumed. The small radioactive inventory in this equipment is not considered a source of danger to theenvironment because areas in which such groundings can occur are fairly remote. Since the primary,auxiliary and secondary systems have been drained to the maximum practical, the reactor has beenpermanently defueled, the tanks containing radioactive wastes have been drained and the demineralizersand their resins have been removed, the consequence of any grounding is greatly reduced from that duringthe period of NSS operation.Ship grounding occurs much less frequently than collision. The ports where the NSS will be layberthedand eventually, decommissioned are well-charted ports. The tugboat operators and pilots are generallywell aware of the local hazards. As such, the NSS, which had operated as a cargo ship in liner-berth typeservice, continues to be less likely to be grounded than other types of vessels.12.5 Heavy WeatherWhile under tow in heavy weather conditions, the NSS is exposed to the most severe loadings onequipment foundations and structures. Since accelerations in collision and grounding are much less thanthose imposed by roll, pitch and heave, the design of the NSS was dictated by the heavy weatherconsiderations.Although considerable data have been compiled on roll, pitch and heave in moderate-to-very rough seas,only spot reports are available for extreme conditions. Since extreme conditions occur at rather rareintervals, long periods of careful measurement at sea are required to obtain an adequate statistical sample.Therefore, maximum accelerations under extreme conditions cannot be defined at present (i.e., 1968).Rev. VI 131
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10 CFR 50.71(e) - Maritime Administration - U.S. Department of ...

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