ML20247N154

Forwards Answers to NRC 890403 Questions Re Seismic Qualification of Plant Deep Wells.Municipal Water Wells in Vicinity of Plant Found Functional After Earthquakes

ML20247N154
Person / Time
Site:	Byron
Issue date:	04/11/1989
From:	Chrzanowski R COMMONWEALTH EDISON CO.
To:	Olshan L Office of Nuclear Reactor Regulation
References
NUDOCS 8908020298
Download: ML20247N154 (5)

Text

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.Mr. Leonard N. Olshan Nuclear' Reactor Regulation U.S. Nuclear Regulatory Commission Washington DC 20555~

Subject:

Byron Station Units 1 and 2 Seismic Qualification of Deep Wells NRC Docket Nos. 50-454 and 50-455 Eference (a): -November 30, 1988, letter;from R.A.

Chrzanowski to T.E. Murley Q s'an:

h Dear

.. Reference (a) submitted the " Seismic Qualification of the Byron Deep' Wells".

The enclosure to this letter contains the answers to the.four NRC questions that were telecopied to Commonwealth Ediso'n on April 3, 1989, regarding the deep well qualification.

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=Please~ direct any further questions concern'tng this matter to this office.

Very truly yours, Y

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G R.A. Chrzanowski Nuclear Licensing Administrator I

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i-Seismic Qualification of Deep Wells Responses to NRC Request. for Additional Information l

Question 1:

Explain and clarify the meaning of '6elsmic qualification".

State the acceptance criteria of analytical and testing results for determining the seismic qualification of the deep well system.

Answer:

The " seismic qualification" is the process of evaluation of the Byron Deep Well System which shows that the system will withstand the effects of the postulated safe shutdown earthquake (SSE) and will c.till be capable of performing its function.

The evaluation is summarized in the report, Seismic Qualification of the Byron Deep Wells," SL-4492, Nov.

1988 Revision 1.

The following reviews and analyses were performed for the seismic qualification:

1.

Sev'eral worldwide earthquakes with magnitudes greater than the Byron SSE were reviewed.

Wells of construction similar to or less than the Byron wells were found to I

remain functional following the earthquakes which had larger magnitudes, higher accelerations, and longer duration motion created during multiple events.

(See Section 4 of the report).

i 2.

The earthquake performance of several municipal water wells in the vicinity of Byron was reviewed.

These wells were found to be functional after the earthquakes. (See Section 5 of the report).

3.

A comparison was performed of the construction recommendations given in various standards used for construction of wells in areas of high seismicity to the construction of the Byron wells.

The Byron wells exceed the recommendations of these standards. (See Section 2 of the Report).

4.

Seismic analysis and stress checks were performed for the well system.

The major components and acceptance I

criteria used for each are:

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(i)-

Uncased Well Cavity Seismic induced tensile stress in the cavity rock is less than'the allowable tensile strength of' the rock.

This criteria ensures that in the uncased portion of the well the rock does-not break loose and fall in the well.

(ii) 16" Di4 meter Steel Pipe Casino and 8 inch Diame'.er Steel Discharge Pipe The SSE induced stresses in combination with stresses under operating or non operating condition are within ASME Code allowables-(Section III ASME Subsection NC, 1986) 1.e.,

Service Level Stress C Loads Type Allowable Dead load, pressure, Membrane 1.5S temperature and SSE Membrane + Bending 1.8S where S = 15 ksi for the pipe material (iii)

Buried Reinforced Concrete Duct The. stress in longitudinal reinforcement during SSE, including other normal loads, is smaller than 0.95 Fy, where FY is the yield stress of reinforcing steel.

(iv)

Pump Shelter Structure Seismically induced loads '(SSE) on the walls and the roof of the structure are smaller than the tornado pressure loads for which the pump shelter structure is already designed.

(v)

Motor and Pump The experience data discussed in Section 4 of the report shows that there is no failure of pumps and motors, even during much stronger er.rthquake events than the Byron SSE.

See Section 7 of the report for further information.

Question 2:-

Provide a topographical map of the plant site showing the location of the deep well and the ultimate heat sink facilities.

Please also show, on Exhibit ES-1 of the report SL-4492, the elevations of the ground surface and depth O' at i

the pump shelter structures.

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' Answer:

1.

l-Thefdeepwell locations with respect to the ultimate heat sink i

are shown on Exhibit 1.

The elevation of the ground surf ace-with respect to the elevation O' (top of the'well casing) is shown in Exhibit 2.

Question'3:

Explain how is the gap element modeled-in the seismic l

structural analysis.

Is it assumed to be nonlinearly elastic, viscoelastic, spring-dashpot combination or else?

Answer:

The' gap element is modeled by a' nonlinear gap spring element.

The characteristics of the gap element is as shown in the following figure p

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displacement

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g gap

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radial stiffness of pipe k

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when it hits casing (a large stiffness)

Question 4:

In the seismic analysis provide the natural frequencies of the discharge pipe with the pump attached under operating and non-operating conditions.

Show that precaution has been taken to avoid resonance while the pump is operating.

Answer:

For the seismic analysis a nonlinear time-history analysis (direct integration technique) has been used, hence the natural frequencies of the discharge pipe are not calculated.

However, it should be noted that the discharge pipe is comparatively very long, (over 400 feet) hence the predominant natural frequencies of the system are very small as compared to the operating speed of the pump.

This avoids i

resonance while the pump is operating.

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