ML17037C516

Letter Submitting Analyses Which Determine Effects of Fuel Densification and Appropriate Changes to Technical Specifications for Fuel to Be Inserted During Spring 1974 Refueling

ML17037C516
Person / Time
Site:	Nine Mile Point
Issue date:	01/22/1974
From:	Raymond P Niagara Mohawk Power Corp
To:	Ziemann D US Atomic Energy Commission (AEC)
References
Download: ML17037C516 (32)

Text

AEC DXS UTION FOR PART 50 DOCKET MATER (TEMPORARY FORM) CONTROL NO:

FILE: 8 FROAA1: DATE OF DOC DATE REC'D LTR MEMO RPT OTHER Niagara Mohawk Power Corp Syracuse, N; Y. 13202 1-22-74 1-23-74 P. D. Raymond TO: ORIG CC OTHER SENT AEC PDR x D. L. Ziemann 3 signedq SENT LOCAL PDR X CLASS UNCLASS PROP INFO INPUT NO C S REC'D DOCKET NO:

XXXX XXXX 40 50-220 DESCRIPTION: ENCLOSURES:

Ltr notarized 1-22-74, trans the following: Pro osed Chan e to Technical S ecifications:

Densification Analyses and Related Technical Specifications Changes for Type 5 and Type DO NOT REMOVE ACKNOWLEDGED PLANT NAME: Nine Mile Point Unit $P1 ( 3 Orig 6 37 cys rec'd )

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t, h'egUlatory Docket File NIAGARA MOHAWK POWER CORPORATION NIAGARA

~ MOHAWK 300 ERIE BOULEVARD, WEST SYRACUSE. N. Y. 13202 January 22, 1974 JAN23)974~

A)EIIpn ~ 'L'In It-iiVu~~

Mr. Dennis L. Ziemann, Chief Operating Reactors Branch 82 Directorate of Li cens ing United States Atomic Energy Commission Washington, D. C. 20545

Dear Mr. Ziemann:

Re: Nine Mile Point Unit 1 AEC Docket No. 50-220 ficationn Niagara Mohawk Power Corporation has committed in its letter of October 15, 1973 to supply analyses to determine the effects of fuel densi-and the appropriate changes to Technical Specifications for the fuel to be inserted during the Spring 1974 refueling. The analyses have been performed using the, guidance provided in the enclosure to your December 5, 1973 letter, "Modified GE Model f'r Fuel Densification".

These analyses and the proposed Techni:cal Specification changes are attached herewith. It is anti cipated that these changes will not limit plant power level below its full design rating of 1850 megawatts for power distributions expected during normal operation.

The Site Operations Review Commjttee and the Safety Review and. Audit Board concur with these proposed Telchnical Specification changes.

Very truly yours, Vi ce esi dent-Engineering

/sq Attachment r'~,

Subscribed and sworn to before me this ~~ay of January, 1974.

JANP3)ygI EENCE'Uqp lrQQ, ~fyICII VALERIE hl. KELLY )CEERX Notery Pobhc in the'tete of New York Qoeliiled In Onon. Eo.. No. 3C n50C729 My Corernlrrlon fnplret "Merch 30r l9

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~.,,,,<<,, Regulatory Docket File Specification Changes Type 5 and Type 6 Fuel For goaeraa~e. n naiad I. Anal ses of Fuel Densification Effects This section presents results of the effects of densification in the 8x8 reload fuel as determined from application of the models described in J

Re fer'ence 1.

A. Local Power Spikin A'n analysi's of potential local power. spikes due to axial gaps in a fuel pellet column for General Electric BMR's employinq an Rx8 fuel lattice design has been performed. This analysis employs the same method and basic assumotions that were reported in Reference l. Important asnects

.' f thi s analys is are noted as fo1 1 ows:

l. The, equation employed to calculate maximum qap size is that noted in Reference 1:

dL = ~965 - + 0.0025) L 2

where dL = maximum axial qao length L = fuel column length Pi = mean value of measured initial

- .5X) p llet density (immersion 0.0025 = allowance for irradiation induced cladding growth and axial strain caused by fuel-clad mechanical interacti on.

2. The magnitude of the power spike versus gap size for fuel rods of the 8x8 desiqn is shown in Figure 1 for normal operating condi ti ons and Fi gure 2 for col d zero voi d condi ti ons.

~ 4

3. The core power histogram employed v>>as for a 13.4 kl</ft C

maximum design linear heat generation rate:. see Figure 3.

The results from this analysis are shown in Fiaure 4 with initial fuel density as a parameter. The line shown for an initial fuel density of 95%

T.D. is considered to be most representative considering curr nt General Electric data on manufactured fuel pellet densities. The power snike penalty shown in Figure 4 for several mean pellet densities as a function of axial position, is the required margin which must be maintained durinq normal ooeration between the actual peak operating condition and the oeak design LHGR; i.e., 13.4 kM/ft, Maintaining this margin will assure, with better than 95% confidence, that no more than one rod will exceed the desi qn neak LHGR due to the random occurrence of power spikes- resulting from axial fuel column gans. Consistent with General Electric's position on densification previously discussed in Reference 2 and its supplements, the results of this analysis are considered to he a very conservative representation of the power oeakinq penalty requi red4 to accommodate potential axial fuel column gaps during normal operating conditions in General Electric BHR's.

Since the results of the power spikinq analysis for normal oneration will be utilized to limit bundle power to assure that the random occurrence of power spikes will not result in exceeding the design peak LHGR, it is not believed necessary to separately consider power snikes in the analysis of transients or accidents which have as an initial condition some form of normal oneration. The control rod drop acci dent is unique in the respect that it begins at the cold condi tion, and is not affected by normal operating power level. Further, the existence of fuel column gaps can result in oower spiking in the cold condition

during a control rod drop which should thus be considered in the evaluation of this accident. For this purpose, a separate power spikinq analysis has been performed using the same assumptions as indicated above, but employina a power spi ke versus gap si ze calculated to occur in the cold condi tion with zero voWs

( Fi gure 2). This analysis was performed for a conservative maximum gap si ze calculated employing a pellet average immersion density of 94.5Ã T.D., and a position near the top of the core in order to maximize the oower sniking effect.

This analysis yielded a 99K probabil'ity th'at any qiven fuel rod would have a power spike of 45K.

B. Cladding Creep Collapse Using the same conservative bases presented in References 1 and 2, the critical pressure ratio; i.e., ratio of collapse pressure to actual coolant pressure, was calculated. Figure 5 presents the clad mid-wall temperature versus time for the 8x8 reload fuel.. No credit is taken for internal qas pressure due to released fissi on gas or volati les. The internal pressure due to helium backfill at 1 atmosphere during fabrication is considered. The fuel characteristics for creep collapse 'calculations are as follows:

Clad O.D., in. 0.493 Clad Thickness, in. 0.034 + 0:003 Peak LHGR, kw/ft 13. 4 Fast Flux vl Nev. n/cm2-sec 4.37 x 1013 Figure 6 gives the calculated critical pressure ratio. As evidenced by the curve, the calculated critical oressure ratio is always o1.0.

C. Increased Linear Heat Generation Rate The following expression was employed to calculate the decrease in fuel column length due to densification in calculation of a penalty in linear heat generation rate:

~0. 965 5L = 2 L

0 ~ I Where hL = decrease in fuel column. length L = fuel column length p; = mean value of measured initial pellet density (immersion - .5/}

The length reduction due to densification as calculated by the above equation requires knowledge of the mean immersion density (p;} obtained from the gC data. A correction of 0-.5A T.D. is applied to convert the immersion densi ty to a geometric density. The mean pellet immersion density for Nine Mile Point 1 8xS reload fuel is 95.29/. T.D. This results in:

AL = 0.965 - 0.9529 - 0.005 = 0.01709 = 0.009 L 2 2 or AL = 0.9X L

Due =-to thermal expansion, an SxS pellet normally exnands in goinq from the cold to hot condition, an amount equal to 1.25 for a pellet at 13.4 kW/ft.

This increase in length from the cold to hot condition is not taken credit for in either design calculations or in the process of core nerformance analysis during reactor operations. The cold pellet length is assumed for these condi ti ons.

Therefore, the decrease in pellet length due to densification is more than offset by pellet axial thermal expansion.

D. Decreased Pellet-Cl ad Thermal Conducti vi t Figure 7 provides plots of Maximum Average Planar Linear Heat Generation Rate (MAPLHGR) versus exposure, for Nine Mile Point Sx8 reload fuel. Them (omega}

curve is suitable for incorporation into the plant technical specifications.

The LOCA analyses were performed using the approved Interim Acceotance Criteria Model with gap conductance values as calculated per the new GEGAP III model with AEC modifications.(1 }

REFERENCES

l. Hinds, J.A., (General Electric) letter to Y.A. Hoore (USAEC),

"Plant Evaluations with GEGAP III," December 12, 1973.

2. "Generic Design Information for General Electric Reload Fuel",

NEDO-20103; September 1973.

3. NEDtl-10735, Supplement 6, "Fuel Densification Effects on General Electric Boiling Mater Reactor Fuel," August 1973.

FIGURE 1 8x8 POWER SPIKE VERSUS GAP SIZE - NORMAL OPERATION

, 7.0 ~

6.0 ROD RELATIONSHIP (g O2 Oe 5.0 O2 O3 O5 hP p 4.0 O~ 05 (I) adjacent P ellet 3.0 -n pod g on 59 ~op g

~o ~ on 2.0 go<

on Rod 8

~

9@9 in Ro d yp of a 9 ap grecc Ef fec d g4 on Rod N

1.0 Effect of a 9ap in Ro d g5 on Rod 81 Effect of a gap 0

0 1.0 2,0 3.0 4.0 5.0 6.0 GAP SIZE (CM)

FIGURE 2 8x8 POWER SPIKE VERSUS GAP SIZE - COLD ZERO VOID CONDITION ROD RELATIONSHIPS Ol O2 O4 02 03 05 o~

O4 O~

0 1

on Rod Ro d >

~~0 o~ in

~"

og gaP o

<~g.ect in Rod R 4 on Rod 1 Effect of qap Effect of gap vari Rod 5 on Rod ]

GAP SIZE (Cg)

FIGURE 3 4.0 A'.0 1.2 1.0

.8 C)

.6

.2 0 0 12 13 14 LHGR (KH/FT = X)

FIGURE 4 8x8 POMER SPIKE PENALTY YS AXIAL POSITION - NORMAL OPERATION 1.0 2.0 96,0 95.0 3.0 4.0 4.0 3.0 94.0 2.0 95.0 96.0 5 6 7 8 10 12 DISTANCE FROM BOTTOM OF CORE (FEET)

FIGURE 5 CLADDING AVERAGE TEMPERATURE AT A FUEL COLUMN AXIAL GAP 690 680 670 660 650 0

640 UJ 630 620 8 6'j0 a- 600 590 580 570 560 550 0

IRRADIATION TIME, YEARS

FIGURE 6 CLAD CRITICAL COLLAPSE PRESSURE RATIO VERSUS TIME 8x8 RELOAD FUEL 4.0 3.0 1.0 2 3 IRRADIATION TIME, YEARS

0 FIGURE 7 MAPLHGR VERSUS EXPOS I7 MAXIMUM ALLOWABLE TO STAY BELOW CURRENT TECHNICAL SPECIFICATION LIMIT FOR LHGR 0 MAXIMUM ALLOWABLE WITH GEGAP III AND AEC lODI FICATIONS 16 15

~ 14 13

~ 12 OC 10 0 5,000 10,000 15,000 20,000 25,000 30,000 AVERAGE PLANAR EXPOSURE (mWd/t)

II. Proposed Chan es to Techni cal Speci fi cations Change pages 37a, 37b, 37c, etc. as follows:

~Chan e A Add the attached Figure 3.1.7e to the Technical Specification. Under the Limiting Condition for Operation 3.1.7, add Figure 3.1.7e to the list of figures at the end of the last sentence in paragraph a.

~Chan e B Rep'lace the notes; to the equation in Limiting Conditions for Ooeration 3.1.7b wi th the following:

" kw/ft for fuel or 13.4 kw/ft for LHGRd = Design LHGR = 17.5 7x7 8x8 fuel Qp/p)~AX = Maximum power spiking penalty' 0.040 for 7x7 fuel or 0.027 for Bx8 fuel.

LT = Total Core lenath = 12 ft.

L = Axial posi tion above botton of core "

~Chan e C Add Figure 3.1.7e to the list of fiqures in the third oaraaranh of the Bases 3.1.7a.

Reasons for Chan es A, B R C The results of analyses performed for 8x8 reload fuel has indi cated that limits on flAPLHGR and power soiking oenalties due to densification are required. These limits as they apply to Type 5 and Type 6 fuel are presented for incorporation into Nine Nile Point Unit 1 Technical Specifications.

Similar limits for previously loaded 7x7 fuel are already nart of -the

'echni cal Speci fi cati ons.

J IE

17 NINE hflLE POINT-PilIT 1

~4 16

~ 14

~ 13

~ 12 OC 10 0 5,000 10,000 15,000 20,000 25,000 30,000 AVERAGE PLANAR EXPOSURE (ml<d/t)

FIGURE '.1.7. e ftAXIfGAUM ALLOWABLE AVERAGE PLANAR LHGR APPLICABLE TO FUEL TYPE 5 and 6

0 0 A 'l