ML19312C676

Forwards List of Addl Info Required for Review Re Core Physics

ML19312C676
Person / Time
Site:	Oconee
Issue date:	12/04/1969
From:	Rosen M US ATOMIC ENERGY COMMISSION (AEC)
To:	Boyd R US ATOMIC ENERGY COMMISSION (AEC)
References
NUDOCS 7912190882
Download: ML19312C676 (6)

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.c DCJJE2 a"JCLZLt STATION U;i1TS 1, 2, AND 3 Responses to the enclosed list of information requests are needed to conclude review of core physics for the Oconee units.

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RT-901A Morria Rosen, Chief DRL:NT3:MD/32 iuclear Technology 3 ranch Division of Reactor Licensing

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DEC t 1959 ADDITIONAL INFORMATION REQUIRED FOR REVIEW 0F OCONEE REACTORS 1.

Reactivity Calculations 1.1 There is insufficient material in Section 3.2.2.2.1, Analytical Models, to permit evaluation of adequacy of the physics calculations.

For example, greater detail should be provided as to the specific

' application of the referenced codes.

l.2 On p. 3-19 of the FSAR it is stated:

"Recent check calculations on critical experiments have a standard deviation of less than 0.5%ak/k."

Furnish details of such comparison calculations including calculational method used and description of the experiments.

1.3 Describe the methods and experimental verification for the ability to calculate reactivity of the fuel as a function of lifetime (uranium-plutonium lattices) and to calculate boron worth.

1.4 Are calculations which verify experimental data available to illustrate the ability to determine power distributions in nonuniformly loaded reactor cores?

If so, provide examples.

1.5 Provice positions, enrichments and BOL and EOL average and maximum burnups for each zone of the first, second, and equilibrium cycles for Oconee I, II, III.

1.6 Provide x-y power distributions at 30L for the possible combinations of part length, xenon transient, and other control rod banks which may be in the core at full power, and for no rod insertion.

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Reactivit doefficients 2.1 Discuss in detail the calculational and experimental bases for predicted Doppler coefficients, indicating maximum uncertainty.

2.2 Provide information on the temperature dependence of the average BOL l

I moderator temperature coefficient for an unrodded core. Provide such information at EOL, for the fuel cycle in which the coefficient will be most negative, with the rods in the core (This pertains to possible reactivity insertion in the steam line break accident.).

2.3 What is the spatial variation in the BOL moderator temperature coeffi-4 cient for the fuel loading arrangement and enrichments which will be I

used? We are concerned that such variation might lead to larger j

l maximum reactivity insertion in a depressurization accident than if l

l the, isothermal (density) coefficient is considered.

What is the largest l

reactivity insertion possible considering the spatial variation of the i

coefficient and the worst possible configuration of voiding?

2.4 Provide details of the calculations predicting reduction in the BOL moderator temperature coefficient as xenon builds in as indicated in lines 5 and 7 of Table 3-7.

Is there experimental verification of this reduction? This question is related to the potential for azimuthal xenon stability.

2.5 In connection with your desire to operate with a positive BOL moderator,

-4 temperature coefficient of 0.5 x 10 ak/k/*F, discuss startup measure-I ments which will ensure that the coefficient is not actually larger.

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, DEC

1959 Include uncertainties in the measurements, and how the effects of the coefficients from fuel Doppler, axial expansion,'and other sources will be treated in predicting the full power moderator coef ficient.

(Although credit for axial expansion and second order coefficients is not claimed in UO fueled reactor transient analyses, such effects might be present 3

at BOL and at least would be nonconservative to neglect.)

3.

Shutdown Margin 3.1 Additional information is required regarcing reactivity control require-ments and maintenance of a minimum shutdown margin during the lifetime of the reactor. This relates to use of some control rods for the purpose of overriding transient xenon in restarts.

Possible reassign-ment of rods for this purpose and their worth should be included in the response.

It would seem that the minimum shutdown margin, when

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there are transient xenon control rods, might not occur at the BOL or EOL conditions discussed in the FSAR, but rather when the boron concentration re, aches zero, and the remaining core life is achieved through gradual withdrawal of these rods.

3.2 We believe that continued operation with a control rod stuck out of the core constitutes an operating condition, and that another rod mignt then fail to insert in a shutdown.

In view of this, show how an adequate shutdown margin would be maintained.

4.

Xenon Stability 4.1 What is the value of the positive moderator coefficient for the thres-hold of aximuthal xenon instability? What are the experimental and

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calculational bases for the ability to predict such thresholds and

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the possible error in the prediction? What is the sensitivity of the l

j predicted threshold to variations in the Doppler coefficient? What are the least favorabia predicted values and bases for establishment of the values of the Doppler coefficient and magnitude of the reduction of the positive moderator coefficient as xenon builds in the reactor?

5.

Detection and Control of Power Maldistributions 5.1 Furnish details of proposed use of part length control rods, including criteria for their placement in terms of detector responses. What is the effect of an inoperative out-of-core detector string? Will the part length rods be used only as a bank?

5.2 What'are the peaking factors and margins to thermal limits for worst conditions of a control rod left in the core, a misaligned part length rod, and one control rod left out of the core when.the remainder of a permitted group is fully inserted?

5.3 What are the means available to ensure over the long term that design peaking factors are not exceeded? The response should include ability to detect radial power tilts, as from out of place control rods, azimu-thal xenon oscillaticas, or fuel loading errors. How would gross errors in, fuel loading, such as improper enrichment in a substantial fraction of the fuel, be detected?

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5.4 What calibrations are made on the out-of-core instrument readings both for axial and diametral related signals? What are the conditions for a

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5-DEC t legg and/or frequency of recalibrations? Addres's in particular the problem of identifying real axial or diametral power tilts so they are not calibrated out.

5.5 Our calculations' indicate out-of-core detector readings would not read correctly if a rod bank were inserted in the core, or if a reassignment of the rods in xenon transient bank were made, or if the reactor were returned to full power at the time of maximum xenon buildup. These conditions do not' produce tilts, but change'the radial power shape, and therefore the out-of-core detector readings.

Further changes also occur until a new point of equilibrium is reached.

What is your evalua-tion of the magnitude and effect of such tilts? How would such changes in the instrument readings be prevented from changing the true reactor.

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