LIC-06-0032, Response to Request for Additional Information Related to the Use of M5 Fuel Cladding

Response to Request for Additional Information Related to the Use of M5 Fuel Cladding

ML061040257
Person / Time
Site:	Fort Calhoun
Issue date:	04/12/2006
From:	Faulhaber H Omaha Public Power District
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
LIC-06-0032, TAC MC8096
Download: ML061040257 (7)

Text

Omaha Public Power Di;tnct 444 South 16th street Mall Omaha NE 68102-2247 April 1.2, 2006 LIC-06-0032 U. S. Nuclear Regulatory Commission Attn: I)ocument Control Desk Washington, DC 20555-0001

Reference:

1. Docket No. 50-285

2. Letter from Ross Ridenoure (OPPD) to Document Control Desk (NRC) dated August 11, 2005, Fort Calhoun Station Unit No. 1 - License Amendment Request to Support Use of M5 Fuel Cladding, and 10 CFR 50.46 and 10 CFR Appendix K Exemption Request (LIC-05-0089)

(ML052240083)

3. Letter from Ross Ridenoure (OPPD) to Document Control Desk (NRC) dated November 8, 2005, Fort Calhoun Station Unit No. I - Revised License Amendment Request to Support Use of M5TM Fuel Cladding (LIC-05-0127) (ML053120421)

4. Letter from Alan Wang (NRC) to Ross Ridenoure (OPPD) dated March 2, 2006, "Fort Calhoun Station, Unit 1 - Request for Additional Information Related to the Use of M5 Fuel Cladding (TAC No. MC8096)" (NRC 0032) (ML060550294)

5. EMF-2103(P)(A), "Realistic Large Break LOCA Methodology,"

Framatome ANP, Inc.

SUBJECT:

Response to Request for Additional Information Related to the Use of M5 Fuel Cladding References 2 and 3 provided the Omaha Public Power District's request for a license amendment to permit the use of AREVA (Framatome ANP) M5Tm advanced alloy for fuel rod cladding and structural components such as guide tubes, intermediate spacer grids, end plugs and guide thimble tubes, beginning with Cycle 24. In Reference 4, the NRC requested additional information regarding Reference 3. Attachment 1 provides the response to the request of Reference 4.

In the answer to NRC Request #2 of Attachment 1, proprietary information has been withheld as indicated by empty brackets. This information is available in Reference 5.

I declare under penalty of perjury that the foregoing is true and correct. (Executed on April 12, 2006.)

5RO I Employment wvith Equal Opportunity 4171

U.S. Nuclear Regulatory Commission LIC-06-0032 Page 2 If you have additional questions, or require further information, please contact Thomas R. Byrne at (402) 533-7368.

Sincerely, Harry J. haber Division Manager Nuclear Engineering HJF/TRB/trb Attachment 1 - Response to Request for Additional Information Related to the Use of M5 Fuel Cladding

LIC-06-.0032 Page 1 ATTACHMENT 1 Response to Request for Additional Information Related to the Use of M5 Fuel Cladding

LIC-06-0032 Page 2 Response to Request for Additional Information Related to the Use of M5 Fuel Cladding NRC Request #1 To demonstrate compliance with 10 CFR 50.46 criteria, complete the tables below by providing the comparison results obtained using the base evaluation model methods with Zircaloy-4 cladding and the results obtained for an identical case using the M5 swelling and rupture mcdel.

Specifically, provide the LBLOCA and SBLOCA analysis results for calculated peak clad temperature (PCT), maximum local oxidation, and whole core hydrogen generation for both the M5 cladding (Mark-B-HTP fuel design) and the co-resident Zircaloy cladding. Also, state whether coolable geometry and long term cooling are demonstrated.

OPPD Response:

This question was discussed with the NRC in a telephone call on March 29, 2006. It was agreed that a summary of the large break LOCA (LBLOCA) results as presented below would be a sufficient response.

The results of the analysis of a large break loss of coolant accident for the Fort Calhoun Station Unit No. 1 (FCS) Cycle 24 reload using fuel assemblies with M5 cladding is presented in the report BAW-2502, "Fort Calhoun Station Realistic Large Break LOCA Summary Report." This report was provided to the NRC in Reference 1.

A summary of the results of the LBLOCA evaluation is presented below for each of the five criteria in 10 CFR 50.46:

Peak Cladding Temperature, 'F 1675 Maximum Local Oxidation, % 0.82 Total Oxidation (whole core hydrogen) % 0.02 Coolable geometry Confirmed Long Term Cooling Confirmed The LBLOCA results are for the fresh fuel in the core and are conservative relative to the once-burned and beyond fuel. The LBLOCA results are more limiting (higher PCT) than the small break LOCA (SBLOCA) results.

A comparison of the results for Zircaloy-4 and M5 cladding is provided in the table below. This data is obtained from topical report EMF-2103PA for LBLOCA and from BAW-10240PA for SBLOC'A. Similar results would be expected for FCS on a relative basis.

LIC-06 0032 Attachraent 1 Page 3 Differences LBLOCA SBLOCA Peak Cladding Temperature <10T <10T Maximum Local Oxidation <0.1% <0.3%

Total Oxidation (whole core hydrogen) <0.1% <0.1%

NRC Request #2 Does the LOCA Evaluation Model used consider both the pre-LOCA and LOCA oxidation in demonstrating compliance with 10 CFR 50.46 requirements? If not, provide justification why it does not.

OPPD Response:

The manner in which the Realistic Large Break LOCA evaluation model considers the initial cladding oxidation is described in the response to Question 28d in the NRC approved topical report EMF-2103(P)(A), "Realistic Large Break LOCA Methodology," Framatome ANP, Inc.

The question and response in the NRC approved topical report are repeated below:

Question 28d: In the time-in-life study, what inside and outside initial oxidation thickness were used for the BOL analysis. What oxide thickness is used for once and twice burned fuel?

Response 28d: The NRC reviewed and approved RODEX3A code is used to calculate an exposure dependent oxidation thickness that is transferred to S-RELAP5. S-RELAP5 uses this informationfor calculating cladding thermal conductivity which affects the initialstored energy results. However, a zero oxidation thickness is assumed to initialize the metal-water reaction rate calculation. Framatome ANP experience with regard to oxidation calculations has been that the oxidation calculatedfor a zero initial oxide thickness provides the largest oxidation thickness increase during the transient simulation. The results shown for maximum local and core-wide oxidation are those computedfor the high temperature mnetal-water reaction. This is the same approachtaken for FramnatomeANP Appendix K methodologies.

The response to this question was initiallyprovided in response to an RAI on the topical report EMF-2328PA, PWR Small Break LOCA Evaluation Model, S-RELAP5 Based. The response provided and accepted by the NRC is shown below followed by some additionalcomments.

"The Framatome ANP methodology described in EMF-2328(P), PWR Small Break LOCA Evaluation Model, S-RELAP5 Based, results in a conservative calculation of peak local oxidation for comparison to the 17% oxidation criteria of 10 CFR 50.46. The methodology assume.; that the pre-accident cladding oxidation is zero in order to maximize the rate and extent

LIC-06 0032 Attachrient 1 Page 4 of oxidation during a LOCA. This assumption results in higherpeak cladding temperatures and higherpeak local oxidation than assuming a non-zero pre-accidentoxidation value.

Cladding oxidationfrom two sources is considered: (1) pre-accident or pre-transientoxidation due to corrosion at operating conditions, and (2) transient oxidation which occurs at high temperature during the LOCA. Pre-transient oxidation is determined by a fuel performance calculaiion and is afunction of burnup. Over the burnup range that the fuel rod is at high power and can approach technical specification peaking limits, the pre-transientoxidation is small, however at high burnups,pre-transientoxidation can become significant.

Transient oxidation is calculated as part of the LOCA analyses. By nrle, this oxidation must be computed using the Baker-Just reaction rate equation. Using this equation, the calculated reaction rate decreases in directproportionto the increasein thickness of the layer oxidized and increases exponentially with absolute temperature. Therefore, the transient oxidation is maximized by minimizing the initial oxidation layer which yields the highest reaction rate. The increasedreaction rate produces higher temperatures which fiurther increases the reaction rate, thus compounding the effect.

The reason that the assumption of zero pre-accident oxidation value results in a conservative calculation of peak cladding temperature and total peak local oxidation is that Framatome's calculations show that a non-zero pre-accident oxidation assumption reduces the transient oxidation by an amount greater than the pre-accident oxidation. Therefore, the maximum oxidation; i.e., the sum of both pre-transient and transient oxidation is greatest when zero pre-transient oxidation is assumed. These results apply for conditions where the transient oxidation is the dominant contributor to the total oxidation, which is the case for calculated PCTs ik excess of 20007F and for burnups at which peaking can approach the technical specification limits. These are the most limiting casesfor both LBLOCA and SBLOCA.

Framatome also recognizes that conditions exist where the total oxidation is dominated by the pre-transient oxidation. This situation occurs when lower PCTs are calculated and at High burnups. For cases with low PCTs, the pre-accident oxidation becomes dominant because the transient oxidation is substantially reduced or effectively eliminated due to the low absolute temperature. For high burnups, the transientoxidation is reduced or effectively eliminated due to the inherent low power and associated low transient temperatures,and is further reduced by the presence of a significant initial oxide layer. For these cases, the maximum total oxidation is essentially equal to the initialpre-accident oxidation value. This oxidation value can exceed the value calculated using a zero initialpre-accident oxidation for these conditions; however, the total oxidation is precludedfrom approachingor exceeding the 17% value by the design limit on pre-acc.'dent oxidation. Framatomehas a design limit on pre-transientoxidation of I J microns defined on a 95/95 basis that cannot be exceeded. This limit corresponds to [ J of the thin.test cladding currently used by Framatome.

The above response is also applicable to the Realistic Large Break LOCA evaluation model. The key concept is that the metal water reaction rate models, Baker-Just and Cathcart-Pawel, are highly oxidation level dependent. If the transient starts with an oxidation level, the subsequent

LIC-06-0032 Page 5 oxidation formation is significantly reduced; the larger the initial level, the more the formation of additional oxidation during the transient is reduced. The reduction of the oxidation formation during the transient then leads to a reduction in the cladding temperature since a heat source, oxidation formation, is reduced.

Reference

1. Letter from Ross Ridenoure (OPPD) to Document Control Desk (NRC) dated September 30, 2005, Fort Calhoun Station Unit No. 1 - License Amendment Request to Support Use Df AREVA Realistic Large Break Loss of Coolant Accident Methodology (LIC-05-0].06)

(ML052770174 and ML052770176)