ML19345F345

Forwards marked-up Responses to NRC 801217 Questions Re Combined Seismic & LOCA Loads on Fuel Assembly,Channel Box Wear & Fuel Element Ballooning.Requests Use of MAPLHGR Correction Factors as Alternative to Accident Reanalysis

ML19345F345
Person / Time
Site:	LaSalle
Issue date:	02/12/1981
From:	Delgeorge L COMMONWEALTH EDISON CO.
To:	Youngblood B Office of Nuclear Reactor Regulation
References
NUDOCS 8102170307
Download: ML19345F345 (11)

Text

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Commonwealth Edison One First National Plaza, Chicago.11hnois Address Reply to: Post Office Box 767 Chicago. !!hnois 60690 February 12, 1981 Mr. B. J. Youngblood, Chief Licensing Branch 1 Division of Licensing U.S. Nuclear Regulatory Commission Washington, D. C. 20555

Subject:

LaSalle County Station Units 1 and 2 Response to Informal NRC Questions Concerning Fuel Element Design Adequacy NRC Docket Nos. 50-373/374

Reference:

(a) L. O. DelGeorge letter to B. J.

Youngblood; dated February 9, 1981 (LOD 81 11 ) .

Dear Mr. Youngblood:

The purpose of this letter is to provide information in response to informal questions raised by the NRC Staff with respect to General Electric fuel design. These questions were reviewed by the BWR Licensing Review Group, which presented positions responding to the Staff questions at a meeting of December 17, 1980. The issues to be addressed are: (1 )

Combined Seismic and LOCA Loads on the Fuel Assembly, (2)

Channel Box Wear, and (3) Fuel Element Ballooning. These issues will be discussed in enclosures to this letter. A fourt" issue, " Water-Side Corrosion" has been addressed prev'ously in Reference (a).

It is also requested that in its consideration of fission gas modelling in the LaSalle County design, that the NRC Staff allow the use of accepted MAPLHGR correction factors as an alternative to accident reanalysis if, at the time the LaSalle i

County fuel exposure approaches 20,000 Mwd / ton, agreement between GE and the NRC Staff has not been reached but sufficient time is not available to perform the required analysis with the approved model without jeapordizing unit availability.

Al though it is likely that agreement will soon be reached on the GESTR model, some recognition should be given to the potential engineering delays which are likely to result if reanalysis of all operating BWR's using the new model is mandated without adequate time allowed to complete the reanalyses.

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Mr. B. J. Youngblood i Page Two February 12, 1981 (

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f In the event you have any questions in this regard, ,

please direct them to this office.  !

L Very truly youps, )

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L. O. De1 George  !

4 Nuclear Licensing  ;

Administrator  :

Enclosures 1-3

! cc: NRC Resident Inspector-LSCS t

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ENCLOSURE 1 COMBINED SEISMIC AND LOCA LOADS ON THE FUEL ASSEMBLY The NRC Staff requested that the applicant perform analyses with GE approved analytical models as reported in GE Report NEDE - 21175 - P to show compliance with the Regulatory Position defined in Standard Review Plan 4.2 Appendix A. This reanalysis has been completed and the results are reported in a draft revision to LaSalle County FS AR Ta bl e 3. 9-4. These results, which will be formally documented in a future FSAR amendment, are provided as an attachment to this enclosure along with a proposed textual revision to Section 4.2.3.17 of the FSAR.

'LSCS-FSAR 4.2.3.17 Puel Assembiv During shipment the fuel bundle is in a horizontal position with flexible packing separators installed between the fuel rods no that the weight of the fuel rods is supported by the shipping container rather than the spacer grids. Fuel bundle shipping procedures are qualified by a test performed on each new design, and each individual bundle is inspected relative to important dimensional characteristics follcwing shipment to verify that no dimensional deviations have occurred.

The two major handling loads of concern are (1) the loads due to maximum upward acceleration of the fuel assembly while grappled, and (2) the loads due to impact of the fuel assembly into the fuel support while grappled. Analyses of these loading conditions have been performed and the resulting fuel assembly component stresses are within design limits. Additional information of fuel handling and shipping loads is presented in

% __section 5 of Reference 1.

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9 .~ 2. 3.1 8 Scacer Grid and channel Boxes Refer to subsection 4.2.3.14.

4.2.3.19 Burnable Poison Rods The gadolinia-urania fuel rod experience is included in Table 1 4.2-6.

The failure rate of these rods has been trivial over the past 10 years.

4.2.3.20 control Rods 4.2.3.20.1 Materials Adequacy Throughout Desien Lifetime The adequacy of the materials throughcut the design life was evaluated in the mechanical design of the control rods. The primary materials, B 4C powder and Type 304 austenitic stainless steel, have been found suitable in meering the demands of the BWR environm ent.

l 4.2.3.20.2 Dimensional and Tolerance Analysis Layout studies are done to ensure that, given the worst combination of extreme detail part tolerances at assembly, no interference exists which will restrict the movement of control l rods. In addition, preoperational verification is made on each control blade assembly to show that the acceptable levels of operational performance are met.

4.2.3.20.3 Thermal Analysis of the Tendency to Waro All parts of the control rod assembly remain at approximately the j same temperature during reactor operation, negating the problem of distortion or warpage. Differential thermal growth is allowed -

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1 4.2.3.17.1 Loads Assessment Of Fuel Assembly Components The analysis methods and acceptance criteria applied in determining the fuel assembly response to externally applied forces are both deemed to be in accordance with the requirements of Appendix A to SRP4.2 LaSalle County fuel assembly capability has been evaluated accordingly with acceptable results. Information on load assessment of fuel assembly components is provided in Table 3.9-4.

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• TADLE 3.9-4 FUEL ASSEMBLY (INCLUDING CIIANNEL)

DESIGN BASIS

• COMBINED

• LOADING PRIMARY LCAD TYPE ALLOWADLE ACCELERATIONS ACCELERATIONS Normal and upset con- Acceleration profile dition loads:

2.60 3 1.14g

1. Operating basis earthquake

2. Normal pressure load

3. Safety relief valve Paulted condition Acceleration profile g load:

3. b g

1. Safe shutdown w l.5$}

earthquake

2. Normal pressure load ta

3. LOCA

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• The Design Assessment Evaluation shows that the appropriately combined accelerations are lower than design basis accelerations.

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ENCLOSURE 2 CHANNEL BOX WEAR The NRC Staff requested that the applicability of GE Report NE00-21354 to the LaSalle County channel box be addressed in the FSAR and that previously proposed tests be considered. It should be pointed out that the subject report has been incorporated by reference into the LaSalle County FSAR in Section 4.2.1.2.16.4 (see Reference 17, Amendment 31, April 1978). To clarify the applicability of this report to the LaSalle County design, a proposed addendum to Section 4.2.1. 2.16.4. f i s a ttached to thi s encl osure. This revision will be formally documented in a future amendment to the FSAR.

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LSCS-FSAR

, 4. Stress outputs (ccmbined by the theory of t

s' constant clastic strain energy of distortion) are compared to the data of Reference 12. Damage accumulation is determined using Miner's rule.

5. Stress outputs (combined by the theory of constant elastic strain energy of distortion) are compared to creep rupture data correlated against the Larson-Miller parameter and a damage accumulation determined.

6. Combined damage accumulation in items 4 and 5

• above is determined using the relation shewn in J Subsection 4.2.1.2.15.1.1.

JS E RT> 9. AirAcTie uesPlates

4. 7.1.2.16.5 The upper and lower tie platet serve the functions of supporting the weight of the fuel and positioning the rod ends during all phases of operation and handling. The loading on the lower tie plate during operation and transients comprise the fuel weight, the weight of the channel, and the forces from the expansion springs at the top of the fuel roda. The loading of the upper tie plate is the expansion springs' force. The expansion springs permit differential expansion between the fuel rods without introducing high axial forces into the rods.

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Most of this loading arises from the ueight of the fuel rods and the channel, which are not cyclic loadings. During accidents the tie plates are subjected to the normal operational loads plus the blowdown and seismic loadings. During handling, the tie plates are subjected to acceleration and impact loading. The stress design limit for the tie plates for all phases of operational and normal handling is the 0.2% offset yield strength, or equivalent strain evaluated at the temperature of interest.

4.2.1.2.17 Reactivity Control Assembly and Burnable Poison Rods 4.2.1.2.17.1 Safety Design Bases for Reactivity Control The limiting criteria for shutdown reactivity margins are given in Subsection 4.3.1.1 as items a and f. The cold-clean shutdown margin is shown in Figure 4.3-27. The presence of the burnable poison Gd20 3 is apparent in the curve shape as kefg rises concurrent with poison depletion. The negative reactivity worth of the gadolinia-containing fuel reds decreases in a nearly linear manner so that it closely matches the depletion of fissile material.

The reactivity control mechanical design includes control rods and gadolinia burnable poison in selected fuel rods within fuel assemblies and meets the following safety design bases.

4.2-1.

4.2.1.2.16.4 f.

Reference 17 provides a description and evaluaticn of the fuel channel mechanical design and deflection utilized at LaSalle. Operating experience with this channel design has demonstrated that excessive deflection and subsequent channel wear is not likely to occur. Consequently, the periodic control rod driveline friction test suggested in Section 4.4.2 of reference 17 is no longer deemed necessary. The periodic technical specification requirements for scram time testing and rod notch testing would provide an indication of a pending driveline friction concern. Should either of these tests suggest a drive friction problem, the pressure test described in Section 4.4.2 of reference 17 is recommended as an aid in isolating the cause of the drive malfunction.

ENCLOSURE 3 FUEL ELEMENT BALLOONING The NRC Staff requested the applicant to perform supplemental ECCS analyses using the materials models of NUREG-0630. The present FSAR analyses in Section 6.3.3 conservatively bounds the clad swelling and rupture model concerns of NUREG 0630. GE's position is that additional analyses are of little or no value for an ECCS Performance Evaluation review based on the reasons discussed in the following GE generic references:

1. GE letter MF-268-79 of November 2,1979 from R. H.

Buchholz to Darrell G. Eisenhut, "0RNL Cladding, Swell and Rupture Date - BWR Evaluation."

2. GE letter MFN-278-79 of November 16,1979 from R. H. Buchholz to Darrell G. Eisenhut "GE Cladding Hoop Stress at Perforation."

3. GE letter MFN-066-80 of December 7,1979 from R. H.

Bu c hhol z to Richard P. Denise, Comments on the Draft Report, " Cladding, Swelling and Rupture Models for LOCA Analyses, NUREG-0630" dated November 8,1979.

4. GE letter MFN-066-80 of March 24, 1980 from G. G.

Sherwood to Richard P. Denise.

Additionally, by letter of September 9,1980 the ACRS's Milton S. Plesset wrote to NRC's William I. Dircks under the subject, " Cladding, Swelling and Rupture Models for LOCA Analysis - NUREG - 0630" as follows:

"The ACRS recommends that implementation of the NUREG -

0630 models and other significant changes in the evaluation models be held in abeyance until a thorough revision of the Appendix K requirements can be undertaken by the NRC Staff."

As the result of recent generic discussions between General Electric and the NRC Staff regarding the potential need to modify the existing BWR fuel models, Genera'. Electric has undertaken to perform a more thorough reassessment of the additional test data currently under revied by the NRC ~ Staff .and I

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its Oak Ridge consultants. This reassessment is scheduled to be completed within two weeks. Therefore, by March 1, 1981 Commonwealth Edison will provide the results of the generic reassessment applicable to LaSalle County Station and define 4 if deemed necessary at that time, any short term supplemental 4

analysis to be performed. In the event this GE reassessment reaches the same conclusion as was previously documented in the materia'.s referenced above, this applicant will continue to rely on the weight of the ACRS recommendation to defer model changes until a later time.

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