ML20008D771

App 5B to Midland 1 & 2 PSAR, Reactor Bldg Pressure Tests. Includes Revisions 1-36

ML20008D771
Person / Time
Site:	Midland
Issue date:	01/13/1969
From:	CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.)
To:
References
NUDOCS 8007300659
Download: ML20008D771 (3)

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APPENDIX 5B REACTOR BUILDI".G PRESSURE TESTS The basic purpose of a structural prese re test ic to substantiate that tne reactor building vill safely carry tne leads as predicted by the design analysis. By testing the reactor building to an overpressure, a pressure sreater than the design level by sc=e =argin, it can be de=cnstrated that failure vould not be incipient under dead lead plus design pressure. In addition, a correlation of predicted shell strai , versus =easured strains can show that the original prestress level has wt been reached or exceeded.

The overall structural integrity of the reactor building depends primarily upon the integrity of the prestressing tendons. Therefore, it is appropriate that the test pressure at least creates a stress in the tendons equivalent to the= stress due to dead load and design accident pressure. Most previous steel and reinforced concrete reactor buildings and a nu=ber of the European prestressed concrete reactor buildings have been tested to 115 percent of design pressure. Therefore, in order to confor= to past practices, it has been decided to test the reactor building at 115 percent of design pressure.

At the test pressure, there is still compressive stress in the reactor build-ing liner and there is no concern that it will develop a crack during the test.

The safety =argin of the prestressed structure at test, co= pared to ultimate, v ) can be compared to a steel vessel by reviewing safety =argins on various

- types of stresses and the significance of the stresses in the failure = ode of the respective' structures.

The prestressed structure relies upon the tensile strength of the tendens for its ulti= ate strength. The secondary stresses of the structure are

' isclated fro = the tendons. At ultimate capacity of the vessel, the secon-dary stresses and the ther=al stresses have been relieved by local' cracking of the concrete and the tendons are subjected to internal pressure and dead Icad culy. Dead load stresses are insignificant and tend to rt. duce the tendon stresses.

i The engineered =argin of safety for ul'ti= ate structural integrity of a

- steel vessel is based on the ulti= ate stress as related to stress at test pressure for various combinations of stresses. The margin of safety for

. a steel vessel is as follows

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FACTOR OF -SAFETY TO ULTIMATE FOR A bmL VESSEL

-(Based on ASME Boiler and Pressure vessel Code,Section III)

Stress at Test Type of -Stress (1.25 x Allevable, S ) Margin of Safety 4

Me=brane 21,900 32 Me=brane Plus Bending 32,800 2.13 SE-1 #7 4

d Stress at Test Type of Stress (1.25 x A11cvable, S) Margin of Safety Membrane Plus Bending Plus Secondary 65,600 0 92 The prestressed reactor building has varicus material ele =ents centributing to the structural integrity of the structure. The margin of safety at test pre.-

sure of the tendons, which are the =0st critical ele =ents of the structure, is 1 90. This =argin of safety for the prestressed reacter builiing is 1cwer than chat of a steel rea^'-- k""ng when it is based cn a :c=parisen cf membrane stresses. Ecwever, the cargin cf safety of 3 2 shewn for re=brane stress in a steel vessel neglects the effect of secondary and therral stresses and their ability to propagate failure. Since the memb-ane integrity at ultimate strength is controlled by the secondary stress cencentrations, the margin of safety for this case for=s a more reasonable basis for ce=parison with the reactor building. Certainly the =argin of safety at ultimate failure is larger than 0 92 and =ust lie between o.92 and 2.13, depending en the significance of the secondary stresses. An exact value for the margin of safety for a steel vessel would be virtually i=possible to evaluate. On this basis, the margin of safety of a steel vessel and the prestressed reactor building are rcughly ec= parable.

The prestressed reactor building is a liga =ent type vessel where the fai: 2re of a single ligament would result in a load redistributien to adjacent liga-

=ents. This type of gradual progressive failure of isolated lign=ents gives a=ple warning of distress during tests rather than a possible sudden cata-strophic failure of a biaxially stressed steel =e=brane.

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U The selected test pressure cannot be considered as proof of individual tenden strength, but rather the safe desi on of the integrated ec=penents of the struc-ture, =ainly the collective tendon syste= and the concrete and, to sc=e limited extent, the reactor building liner. The design accident pressure is not con-sidered to act before ther=al stresses have been developed in the shell. There are sete regions of the reactor building where the test pressure produces higher stresses than the cc=bined the:=al and accident pressure stresses, there-by requiring design specifically for the test pressure. It is for this reason that a test pressure above 115 percent of the design accident level is not advisable. ,

The pressure test does not duplicate the stress distribution which wculd be. caused by accident pressure and te=perature. The =e=brane stresses caused by the pressure test with prestress acting are approxi=ately uni-for=1y distributed across the concrete section. These concrete stresses are generally the =axi=u=. However, the strains of the reactor building liner and interior one-third of the concrete thickness due to accident temp-erature would reduce the prestress in the outer two-thirds of concrete thick-ness.

~ Indirectly, verification of structural integrity is also possible with observations during post-tensiening since, if defor=ations are similar to those predicted by analysis, inferences can be drawn that the analysis also provides- reasonable predictions of structural integrity for other lead cen-ditions.

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