ML19319C415

Forwards Evaluation of Proposed Tech Spec Change Prepared by Reactor Physics Section of Core Performance Branch.Physics Related Changes to Tech Specs Are Acceptable

ML19319C415
Person / Time
Site:	Davis Besse
Issue date:	05/31/1978
From:	Ross D Office of Nuclear Reactor Regulation
To:	Vassallo D Office of Nuclear Reactor Regulation
References
NUDOCS 8002140796
Download: ML19319C415 (6)

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1M MEMORA2DUM FOR:

D.H. Vasaallo, Assistant Director for Light ~

Water Reactors, DPM

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FROM:

D.F.

Ross, Jr.,

Assistant Director for Reactor Safety, DSS

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SU3 JECT:

EVALUATION OF PROPOSED TECHNICAL SPECIFICATION CHANCE, DAVIS BESSE-1 The Reqctor Physics Section of the Core Performance 3rsuch has prepared the enclosed evaluation of the request ~ by Toledo ~

Edison Conpany to change the Technical Specifications ~~ for the

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Davis-Besse Nuclear Power Station, Un'it 1.

Thi'chenge ~ is

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required to accommodate the removal of the harn'able poison' rod assemblics from the core'.

Vc find ~the phys'ics related

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changes to the Technical Specificition's to be ac~ cept'able.

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Ross, Jr., Assistant Director for Reactor Sa'fsty ~

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Division of Systems Safety,,] ]. ~

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Enclosure:

As stated cc:

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Hanauer R. Mattson/P. Schroeder J.

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ENCLOSURE EVALUATION OF TECHNICAL SPECIFICATION CHANGE REQUEST

.DB-1 I

The Toledo Edison Company has requested (letter, Ross to Stole, j

dated May 18, 1978) a change in the Technical Specifications for the Davis Besse Nuclear Generating Station, Unit 1 (DB1) reactor.

This request was occasioned by the decision of Toledo Edison to i

remove the burn'able poison rod assemblies (BPRAs) from the reactor in order to avoid the possible loss of burnable poison from the 4

i core as has occurred at another Babcock and Wilcox (B&W) supplied I

reactor.

Toledo Edison has supplied a document, BAW-1489, which i

describes the Technical Specification changes and provides analyses supporting the changes.

Our review of the request and supporting documentation follows.

BPRAs are used in the first c.ycle of B&W reactors to control part of the initial excess reactivity and to flatten the radial power distribution.

The reactivity controlled by burnable poison reduces the amount which must be controlled by soluble boron and prevents the occurrence of a positive moderator coefficient above i

95% of full power.

The DB1 reactor has achieved a first cycle l

l burnup of 87 effective full power days (EFPDs) and some of the i

burnable poison has been burned out.

However, sufficient l

burnable poison remains to require core changes in order to 4

l offset the effect of its removal.

These core changes were:

1.

Interchange of four intermediate (2.63 w/o) enrichment

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bundles near the center of the core with four low (1.98 w/ o )

I enrichment bundles near the core periphery.

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" 2.

Rearrangement of the control rod groupings and decoupling of group seven from the withdrawal sequence.

In the re-grouping control rod group-seven has been shifted toward the periphery and remains in the core until a burnup of i

145 EFPDs has been reached.

This arrangement serves to further flatten the radial power distribution and to re-i place some of the fixed poison in the core and thus prevent the moverator coefficient from becoming positive.

B&W has performed an analysis of the modified core, assuming that the modification occurr-4 at 80 EFPD and that the cycle length is increased from 433 to 485 EFPD.

The analysis was performed using the same calculational methods and techniques that have been employed in the design of other B&W reactors - including dbl.

2 The core physics parameters have been calculated for the modified i

i cycle - 80 to 145 EFPD with groups 5 and 6 essentially out of the core and group 7 completely inserted followed by 145 to 485 EFPD with groups 5 through 7 nearly out of the core.

The recalculated k

parameters included shutdown margins, rod bank worths, ej ected and j

dropped rod worths, stuck rod worth, Doppler coefficient, moderator coefficient, xenon worth, boron worth and critical boron concentratior During removal of the BPRAs it was discovered that sufficient wear was presented on the holddown devices for the orifice rod assemblies (ORAs) to warrant their removal.

The removal of the ORAs increases the flow through the guide tubes but does not alter significantly the physics parameters.

Thus the analyses presented in BAW-1489 J

remain in effect.

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7 We have reviewed the information presented in the submittal on the values of the physics parameters and their effect on the safety analyses for dbl.

For the rod withdrawal tran-sients at full and zero powers, the control rod misoperation transient, and the rod ejection accident, the significant parameters are shown to be bounded by those used in the FSAR analysis.

Thud the consequences of these transients and j

accident will not be greater than those described in the FSAR, 1

After completion of the core modification startup tests will be performed to assure that the various physics parameters are bounded by those in the FSAR.

Tests will be performed on rod drop times, critical boron concentration, temperature coefficients, control rod worths, power distribtuions and power coefficients.

Successful completion of tests at each power level will be re-quired before proceeding to the next higher power level.

On the basis of the use of approved calculation methods, and of the l

proposed startup tests we find the analysis of the physics parameters of the core modification to be acceptable.

We require, however, that the moderator temperature coefficient measurement be repeated at 1,45 EFPDs after removing group seven.

Because of the modification of core loading some changes have l

been made in power distributions in the core.

These changes necessitate changes in the technical specifications.

Further J"

changes are necessitated by the re-programming of the rod-groups i

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. The new Technical Specifications have been established using i

i procedures which have been previously employed.

New safety limits (Spec 2.1.2) and Trip Setpoints (Fig. 2.2-1) and Allowable Values (Fig. 2.2-2) have been specified.

New rod 4

insertion limits (Spec 3.1.2.6) have been specified along with new axial imbalance limits (Spec 3.2.1) to ensure that i

peaking factor, limits used as input to the LOCA-ECCS analysis j

are not exceeded.

The rod program description has been changed (Spec 3.1.7) to reflect the modification in group assignments.

i The procedures used to establish the Technical Specifications on power distribution limits have been previously reviewed and f

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approved.

Based on this review and approval we find the Technical Specifications changes described above to be accept-able.

A further Technical Specification change, unrelated to the core modificaction, is requested.

This requsst concerns the modifica-tion of alarm setpoints on quadrant tilt to accommodate a recently discovered increase in the measurement error associated with this quantity.

The original uncertainty evaluation was performed in 1974 based on data obtained from prototype detectors.

Observations of anomalies in operating reactors led to the re-evaluation of this error.

B&'4 has submitted (letter, Taylor j

j to Reid, dated May 11, 1978) a document describing the methods l

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- used to perform the statistical analysis of the uncertainties and giving revised quadrant tilt alarm setpoints f or dbl.

We have reviewed the document and conclude that the analysis method is acceptable.

We have not reviewed the data base used to obtain numerical results,but we know of no data that would make the application of the method to dbl non conservative.

We, therefore,' find the revised alarm setpoints on quadrant tilt to be acceptable.

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