ML20056B558

Records Understanding of Several Items of Concern Discussed at 700107 Meeting That Should Be Communicated to ACRS

ML20056B558
Person / Time
Site:	Monticello
Issue date:	01/07/1970
From:	Mcelroy D NORTHERN STATES POWER CO.
To:	Morris P US ATOMIC ENERGY COMMISSION (AEC)
References
NUDOCS 9102070464
Download: ML20056B558 (3)

Text

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S NORTHERN STATES POWER COMPANY

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h M lN N E A PO LI S M I N N E G OTA 554Q1 Y

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January 7, 19

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,e Dr. Peter A. Morris, Director h

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l Division of Reactor Licensing 5

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l United StatesAtomic Energy Commission washington, D.

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Dear Dr. Morris:

MONTICELLO NUCLEAR GENERATING PLANT E-5979 l

Docket Number 50-263 Regulatory Fila C;.]

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In a meeting with your staff yesterday, we reached an understanding on several concern items.

This letter is to record these understandings so that they can be communicated to the ACRS.

Protection against a leak in the HPCI line in the steam tunnel has been a staff concern item.

Presently this leak is l

limited to a maximum flow of approximately 200,000 lbs/hr or 200%

of the HPCI system flow.

The HPCI line was to be isolated on a I

total flow of 300% with 100% flow to the HPCI Turbine.

Presently we assume that the operator does not isolate the unprotected leak (less than 300% flow) for a ten minute period.

During this time some 33,000 lbs. of steam is released and the resulting radiological consequences (off-site) are much less 1/3000) than for a main steam line break.

To further reduce the release from a HPCI line leak, we will modify the instrumentation to isolate the line for a flow l

of 120-150% of system flow.

This means a leak of 20-50% flow will be automatically isolated.

A timed delay will temporarily over-ride the isolation signal to allow for flow transients caused by the HPCI turbine start.

Assurance of detecting leaks of this magnitude will be obtained by calibrating the elbow flow element located in the HPCI steam line.

The resulting radiological con-sequences will be reduced by at least an additional factor of four (assuming 150% flow isolation).

62 !

9102070464 700107 CF ADOCK 05000263 a CF u

NOR. NERN, CTATED POWER C PANY The fourth paragraph of Page 3-6.9 should be revised to l

read:

"The largest peak strain intensity range was found to occur at point B.

An ' Upper bound' strain range was determined to be 8.64%.

l This value of strain range is the largest value to occur in the j

reactor internals.

This value is based on the following:

A finite element model of the support plate-to-shroud junction in which in-elastic strains are considered, the actual temperature distribution 2

j in the geometry and conservatively defined deformation boundary conditions."

i The effect of HPCI transcient operation on the reactor

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pressure vessel has been analyzed in response to the AEC staff j

questions for the following affected components:

I Shroud Support Geometry t

P + Q (Max.) = 79,756 psi i

(3 Sm = 69,900)

Sa (Max.) = 121,000 1

l Usage factor for 15 cycles - 0.02 - allowable cycles - 732 (by elastic-plastic analysis).

The usage factor for other transients is j

negligible.

CRD Geometry A

Stainless P + Q (Max.) = 38,700 psi.

(3Sm = 48,000)

B Inconel j

P + Q (Max.) = 52,300 psi

( 3 Sm = 60,000) i Usage factor for 385 specified cycles (includes l

15 HPCI + 370 others) = 0.15.

Total allowable cycles are 2500.

i The effect of each HPCI operation on the feed water nozzle is a less severe transient than that for which the nozzles were 4

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1 NOR. 4ERN CTATED POWER CC PANY a.

i i analyzed.

Reference PSAR Vol. VII, Exhibit 4.

The vessel nozzle I

was specified for 1500 such cycles, however only 1350 cycles have been assigned.

The difference of 150 cycles is more than adequate to accommodate the 15 cycles of HPCI operation.

I The following statement should be made in connection with the seismic stress discussion on Page 12-2.11:

"The maximum primary plus secondary bending stress intensity for the suction header nozzle in the suppression chamber vessel is l

32,470 psi for the design basis earthquake.

This maximum stress

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intensity is below the yield strength of the material which is 38,000 psi."

All of the above information will be formally confirmed by later submission of an appropriate amendment to our application.

Sincerely, NORTHERN STATES POWER COMPANY i

Y By: / A A' D. F. McElroy Vice President-Engineering CC:

D. E. Nelson J. Barnard J. B. Violette

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