United States Nuclear Regulatory Commission - Protecting People and the Environment

ACCESSION #: 9805190359


May 11, 1998


Document Control Desk

ATTN: Chief, Planning, Program and Management Support Branch

U.S. Nuclear Regulatory Commission

Washington, D.C. 20555-0001

Interim Report of Evaluation of a Deviation Pursuant to 10 CFR


The following information is provided pursuant to the requirements of 10

CFR 21 to submit an interim report on issues that will not be completed

within 60 days of discovery.

An interim report for an issue under evaluation by Siemens Power

Corporation is enclosed:

Interim Report No. 98-002 "TOODEE2 Axial Nodalization"

Those SPC customers potentially impacted by this issue will be provided a

copy of this interim report.

If you have any questions or if I can be of further assistance, please

call me at (509)375-8757.

Very truly yours,

James F. Mallay, Director

Regulatory Affairs



cc:  Mr. E. Y. Wang (USNRC)

     Project No. 702

Siemens Power Corporation

Nuclear Division             2101 Horn Rapids Road  Tel: (509) 375-8100

Engineering & Manufacturing  P.O. Box 130           Fax: (509) 375-8402

                             Richland, WA 99352-0130

                         Interim Report (98-002)


Interim report of evaluation of a deviation pursuant,to 10 CFR



TOODEE2 Axial Nodalization

Identification of Basic Activity:

PWR Large Break LOCA Analysis

Basic Activity Supplied by:

Siemens Power Corporation - Nuclear Division

Nature of Deviation:

The axial nodalization in TOODEE2 (part of the NRC-approved EXEM/PWR

LBLOCA evaluation model) consists of 3 inch nodes near the peak power

node, where rupture and peak cladding temperature are expected to occur,

and larger nodes in other regions.  The methodology requires that rupture

be calculated to occur in a 3 inch node, and standard practice at SPC has

been that PCT should also be calculated on a 3 inch node.  Larger axial

node "illegible print" of between 6 inches and one foot are commonly used

at the top of the core where the power is lower than the axial peak

value.  With this nodalization, the peak cladding temperature for an

axial power shape skewed toward the top of the core generally occurs at

or slightly above the peak power node which is between 9 and 10.5 feet

for a 12 foot core.  If the larger nodes at the top of the core are

replaced by 3 inch nodes.  the EXEM/PWR model may calculate an even

higher peak cladding temperature near the top of the fuel (above 10.5

feet) even though power is somewhat lower at this elevation.

The prediction of the peak cladding temperature at reduced power nodes

near the top of the core is considered unrealistic.  Reflood cooling is

by steam and entrained liquid flowing from the quench front in the core. 

Once this mechanism is established and calculated to be sufficient to

cool the maximum power nodes and the high power nodes immediately

downstream, higher elevations at reduced power should also be cooled.

An evaluation of whether this behavior represents a reportable defect

under 10 CFR 21 has been initiated.  A schedule for completing the

evaluation is provided below.

Discovery Date:

March 12, 1998

Corrective Actions to Date:

Condition Report (CR) 6580 was issued in March 1998.  The cause of the

unrealistic calculations is being investigated.

There is no indication at this time that the TOODEE2 axial nodalization

problem, after correction, will result in peak cladding temperatures

which violate 10 CFR 50.46 limits.

Evaluation Completion Schedule Date:

September 30, 1998




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