ML19317D621

Program for Insertion of Zirconium Oxide Spacers in Batch 4.

ML19317D621
Person / Time
Site:	Oconee
Issue date:	10/23/1974
From:	DUKE POWER CO.
To:
Shared Package
ML19317D620	List: ML19317D619 ML19317D621
References
NUDOCS 7912060859
Download: ML19317D621 (10)

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PROGRAM FOR INSERTION OF ZIRCONIUM OXIDE SPACERS IN OCONCE 1, BATCH 4 I w m.x.asu id _23-7V I. INTRODUCTION The following is a descriptf on of a program for loading Zr02 spacers between UO2 pellets in one fuel rod of an Oconec 1, Batch 4B fuel assembly.

Displacement of fuel pellets with Zr02 spacers will create gaps of known size which can be used to further calibrate the movable incore detectors (MIDS). Such in-reactor data vill confirm the ability of the MIDS to detect densification gaps and would thus be of significant benefit in the effort to rcouce densification penalties. Inclusion of known gaps in a batch 4B assembly will not adversely affect full power operation during the core residence time of the asse: ably (cycles 2,2, and 4) . Zr02 spacers have been irradiated previously in a similar test at Point Beach #1 (Ref. 1).

II. A!U. LYSIS A. Spacer Loading Threc Zr02 spacers having lengths of 0.40, 0.70, and 1.00 inches will be loaded into a fuel rod adjacent to the instrument tube (see Figure

1) in a batch 4B (3.20 wt % 235 U) assembly. The axial locations of the spacers are indicated in Table 1 and Figure 2. The axial locations were chosen to place the larger gaps in the low power regions indicated by 3D PDQ calculations consistent with the fuel densification power spike factors currently accepted by the USAEC (Reference 2).

The assembly containing the spacers will be loaded into core position D-14 (see Figure 3) . This position has a relatively low power during cycle 2 and is a position in which a MIDS drive can be mounted. The spacer assembly is scheduled to be moved to core position F-13 (or a position symmetric with F-13) at the end of cycle 2 and should remain in that. position during cycles 3 and 4. The assembly will be discharged at the end of cycle 4. Both core locations D-14 and F-13 contain fixed incore deteccors which will provide monitoring of the spacer assembly.

B. Power Peaking Power peaking caused by the simulated gaps only (coplanar densifi-cation gaps not included) has been determined using data from Reference 2. Table 2 shows that the power increase in rods adjacent to the simulated g ye will be much less than the power increase isnposed by the current power spike model (Ref. 2) for hypothetical gaps due to fuel densification. Table 2 also shows that the power increase in adjacent rods is less than is calculated with B6W's revised power spike model, which is currently being reviewed by the USAEC.

The effect on power peaking of additional gaps coplanar with the simulated gaps has been calculated using both the current and revised power spike raadclo. Calculations were made for the spacer assembly by including gaps represented by the Zr02 and for a normal assembly in s

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which only gaps due to postulated densification were considered. The and gaps spacer assembly calculations include the effects of both the Zr02 Caps due to hypothetical densification. Batch 4B fuel parameters (3.20 wt% 235 U, initial density of 95% and final density of 96.5%) were used in th; calculations. Results indicate a manimum power spike ine; case due to the spacers of 2.1% with the current power spike model and ,value of spike, based on the revised model (Table 3) .

The spacer assenbly will be placed in low power positions to insure that even with a[value of spike increase in local peaking the spacer assembly power will be significantly les's than the power in the hottest as-sembly. Calculations for fuel cycles 2 and 3 indicate that the maximum power in the assembly containing the Zr02 spacers will be no greater than 1.26 times the core average assembly power and no greater than 0.85 times the maximum assc=bly power in the core. Relativ'e-power values for the spacer assembly for cycles 2 and 3 are given in Table 4. The power in the twice-burned spacer assembly during cycle 4 is expected to be no greater than the cycle 3 power. Application of the maximum increase in the power spike factor for the spacer assembly

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({alue of spik h-Table 3) vields a spacer assembly power that is no greaterthan[valueofspik{}timesthemaximumassemblypower.

C. Materials Compatibility .

Zirconia spacers can be used in zircaloy clad UO2 fuel rods with no adverse effects due to materials incompatibility. The spacers proposed for use in Oconce 1 are stabilized zirconia containing 3 wt% Ca0 in solid solution. The spaccrs are to be used to create axial gaps in the fuel column by inserting a set of annular zirconia spacers with a zirconia disk at the top (see Figure 2). The spacers will be in contact with the zircaloy cladding and the fuel pellets. The com-patibility of the zirconia with the cladding has been demonstrated by a test conducted at the Lynchburg Research Center in which zirconia and zircaloy were kept in intimate contact for 2, 3, and 4 months at 700 F.

There will be no compatibility prob 1cm with the zirconia disk and the UO2 pellet. The maximum fuel temperature expected is 22600C (41000F).

At that temperature there will be a solid state reaction of the zirconia with the UO2 In the reaction zone, the melting point will be lowered to 2550 C (4622 F). The presence of Ca0 will also lower the melting point. The melting point of the calcia-zirconia-urania system in the reaction zone has been found to be greater than 2450 C. No Cross structural changes are expected except for a slight increase in volume (6% maximum) at a UO2 concentration of 12 wt.%.

The increase in volume will be more than offset by high temperature sintering. The length change of the gap fabricated by the addition of zirconia spacers will be confined to a UO2-Zr02 reaction in the spacer disk and will be limited to an observable length change of approxi-mately 0.1 inch during the three cycles of irradiation.

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s Babcock & Wilcox has irradiation experience with UO2 fuel and stabilized zirconia spaccrs. B6W conducted a high and low burnup irradiation program in which experimental fuel rods containing foamed circonia spacers were run at high linear heat ratings (up to 26 kv/f t) in the Babcock and Wilcox test reactor. These fuel rods were irradiated to burnups of up to 60,000 MWD /MTM. The post irradiation examination showed no evidence of incompatibility of the zirconia with the 2ircaloy 4 cladding. A solid-state reaction occurred between.the UO2 fuel pellets anc circonta 2s expected, but no adverse effects were noted.

D. REFERENCES

1. llellman, J. M. , " Fuel Densification Experimental Results and Model for Reactor Application," WCAP-S219, October, 1973 (p. 2. 6-1).

2. Fuc1 Densification Report, BAW-10054, Rev. 2, May 1973.

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Spacer Lenoth. Inches .

• 0.40 l Tolerance Depween3rdand4thSpacerGrids-on spacer 73 utolerance on locationifrom ~ lower end of length active fuel .

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Between 4th and 5th Spajcr Grids -

95(tolerance on location!from ~ lower end of active fuel 1.00 ,, Betvicen 5th and 6th Spacgr Grid, -

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TABLE 2 POWER PEAKING DUE TO GAPS Zr02 Simulated Gaps (Effect gaps of hypothetical not included coplanar)

Power Spike Factor for 95'3TD Power ~ Spike Factor for 9C+TD Spacer Length, Distance from Lower Power Spike Factor Fuel Based on Current Power Fuel Based on Revised Pv_Je inches End of Fuel, inches in Adjacent Rod

• Spike tiodel** _

Spike Model*** ,

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.40 tolerance 73 tolerance .l.015 1.053 Power spacer on

.70 95 1.023 1.070 . spike length location Eactor 1.00 __. 117 1.0.31 1.090 -

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• From figure 2.4-2, reference 2 _

• • Calculated for 3.2 wt.% 235 U, TDI = 95.0, TDF = 96.5 as per reference 2

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• • • Calculated for 3.2 wt.% 235 U, TDI - 95.0, TDF = 96.5 as per reference 3

TABLE 3 POWER PEAKillG EITH C0 PLANAR GAPS Power Spike Fac' tor -

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Spacer Lower End of Active florraa l Spacer

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Fuel, in. Assembly Assembly  % increase As.;embly Asserbly  % increase

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1.053 1.066 1.2 .

Power Spike tolerance *

}  % Increase 70 95 . 1.070 1.088 1.7 7,ct,y on 1.00 117 1.090 1.113 2.1 location . , .

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Power in Assy. with Zr02 Power in Assy. with Zr02 Spaccr/ltox Assy. Power Spacer / Ave Assy. Po.ie r EFPD Cycle 2 Cycle 3 Cycle.2 Cycle 3 0 53 74 .83 1.15 4 .52

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. . .85 1.14 265/267 36 .83 59 1.26 290/292 .43 .85 .65 1.23

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