ML14199A384

Response to Request for Additional Information, License Amendment Request for Diesel Generator Initiation - Degraded Voltage Time Delay Setting Change

ML14199A384
Person / Time
Site:	Nine Mile Point
Issue date:	07/16/2014
From:	Costanzo C Exelon Generation Co
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
TAC MF1022
Download: ML14199A384 (10)

Text

AChris Costanzo Exelon Generation, Exeo GeatSite Vice President - Nine Mile Point P. Box 63 Lycoming, NY 13093 315-349-5200 Office www.exeloncorp.com Christopher.costanzo@exeloncorp.com July 16, 2014 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 Nine Mile Point Nuclear Station, Unit 1 Renewed Facility Operating License No. DPR-63 Docket No. 50-220

Subject:

Response to Request for Additional Information Nine Mile Point Nuclear Station License Amendment Request for Diesel Generator Initiation -

Degraded Voltage Time Delay Setting Change

References:

(1) Letter from C. Costanzo (NMPNS) to Document Control Desk (USNRC), License Amendment Request Pursuant to 10 CFR 50.90:

Diesel Generator Initiation - Degraded Voltage Time Delay Setting Change, dated March 8, 2013 (ADAMS Accession No. ML13073A103)

(2) E-Mail from B. Vaidya (USNRC) to E. Perkins (NMPNS), Request for Additional Information (RAI), Nine Mile Point Unit 1, MF1022, LAR Re: Revision to Diesel Generator Initiation - Degraded Voltage Time Delay Setting Change, dated May 27, 2014 Nine Mile Point Nuclear Station, LLC (NMPNS) hereby transmits supplemental information requested by the NRC Staff in support of a previously submitted request for amendment to the Nine Mile Point Unit 1 (NMP1) Renewed Facility Operating License DPR-63. The initial request, dated March 8, 2013 (Reference 1) included a revision to the NMP1 degraded voltage time delay setting change.

The supplemental information, provided in the Attachment to this letter, responds to the request for additional information that was provided in an e-mail from the NRC Staff to NMPNS on May 27, 2014 (Reference 2) and clarified during a conference call with the NRC Staff on June 11, 2014.

This supplemental letter does not change the initial determination of "no significant hazards consideration" justified in the original amendment request, Reference (1).

Pursuant to 10 CFR 50.91(b)(1), NMPNS has provided a copy of this supplemental information to the appropriate state representative.

This letter contains no new regulatory commitments.

U. S. Nuclear Regulatory Commission July 16, 2014 Page 2 Should you have any questions regarding the information in this submittal, please contact Everett (Chip) Perkins, Director Licensing, at (315) 349-5219.

I declare under penalty of perjury that the foregoing is true and correct. Executed on the 16th day of July, 2014.

Sincerely, Christopher R. Costanzo CRC/KJK

Attachment:

Response to NRC Request for Additional Information, SRXB - RAI 1, RAI 2 and RAI 3 cc: Regional Administrator, Region I, USNRC Project Manager, USNRC Resident Inspector, USNRC A. L. Peterson, NYSERDA

ATTACHMENT RESPONSE TO NRC REQUEST FOR ADDITIONAL INFORMATION, SRXB - RAI 1, RAI 2 AND RAI 3 Nine Mile Point Nuclear Station, LLC July 16, 2014

ATTACHMENT RESPONSE TO NRC REQUEST FOR ADDITIONAL INFORMATION, SRXB - RAI 1, RAI 2 AND RAI 3 By letter dated March 8, 2013, Nine Mile Point Nuclear Station, LLC (NMPNS) requested NRC approval to implement a degraded voltage time delay setting change at Nine Mile Point Unit 1 (NMP1) in accordance with 10 CFR 50.90. Specifically, the proposed amendment would modify Technical Specification (TS) Table 3.6.2i, "Diesel Generator Initiation," by revising the existing 4.16kV Power Board 102/103 Emergency Bus Undervoltage (Degraded Voltage) Operating Time value and updating the Set Point heading title. This attachment provides supplemental information in response to the request provided in an email from the NRC Staff to NMPNS on May 27, 2014; specifically, SRXB - RAI 1, SRXB - RAI 2, and SRXB - RAI 3. Each individual NRC question is repeated (in italics), followed by the NMPNS response.

The following terms are used in the request for additional information and responses provided below.

CR- Condition Report GE- General Electric GNF- GE Nuclear Fuels ECCS - Emergency Core Cooling System LAR- License Amendment Request LOCA - Loss of Coolant Accident LOOP - Loss of Offsite Power MAPLHGR - Maximum Average Planar Linear Heat Generation Rate MLO - Maximum Local Oxidation NCV- Non Cited Violation PCT - Peak Centerline Temperature SEC- Seconds UFSAR - Updated Final Safety Analysis Report SRXB-RAI I It was statedin page 2 and 3 of the submittal [Ref. 1],

"A 24 second time delay for diesel generatorinitiation under degraded voltage conditions results in a maximum time delay of 59 seconds from initiatingsignal to core spray pump at rated speed for the special scenario of degraded voltage conditions coincident with a LOCA. The GEH analysis determined that the ECCS will perform its safety function with a time delay of 60 seconds from event initiation to core spray pump at rated speed, resulting in insignificant differences in the PCT and MLO for both GEl1I and GNF2 fuel types in use at NMPI ."

Pleaseprovide the following additionalinformation:

1. Was the NMP1 core loaded with fuel designs other than GEl1 and GNF2 since the proposed amendment submitted in March 8, 2013 [Ref 1]? If so, discuss the impact of the proposed change on the PCT of those fuel types.

2. Provide the maximum time delay from initiatingsignal to core spraypump at rated speed assumed in the current analysis of record for the special scenario of degraded voltage 1 of 7

ATTACHMENT RESPONSE TO NRC REQUEST FOR ADDITIONAL INFORMATION, SRXB - RAI 1, RAI 2 AND RAI 3 conditions coincident with a LOCA, and the resulting PCT. Clarify, whether the maximum time delay assumed in this LOCA analysis changed as a result of the proposed amendment. If so, provide the new maximum time delay and the new PCT, as a result of this amendment.

3. Describe the most limiting LOCA analysis of record for the Current Licensing Basis (CLB) for NMP1, including the value of the PCT.

Response SRXB-RAI 1

1. No, NMP1 has only GEl 1 and GNF2 fuel. GNF2 fuel will continue to be the fuel type used in the upcoming NMP1 refueling outage.

2. A 60 second time delay from initiation to core spray pump at rated speed was used in the LOCA analysis coincident with a degraded voltage condition. The resulting PCT is 2113°F for GNF2 fuel and 2141 OF for GE11 fuel (See Table 1 on page 6). The analysis of record has been updated to incorporate the degraded voltage condition scenario (Reference 0000-0153-3787-RO, "Nine Mile Point Nuclear Station Unit 1 GNF2 ECCS-LOCA Evaluation with Sustained Under-Voltage Condition," January 2013.)

No additional changes are expected to be required as a result of this amendment. The degraded voltage LOCA scenario was analyzed in response to the NRC NCV in 2012 that is cited in the LAR. The degraded voltage LOCA scenario was not analyzed for GNF2 fuel prior to the NRC request.

3. The most limiting LOCA analysis of record for the Current Licensing Basis for NMP1 is the Large Recirculation Line Break with a Loss of Offsite Power (LOOP) using Appendix K assumptions and bottom-peaked Axial Power Shape at rated plant conditions. The PCT for this event is 2144°F for GNF2 fuel and 2142°F for GE11 fuel. Detailed discussion about the ECCS-LOCA analysis results can be found in Section 3.0 and Tables 3-1, 3-2 and 3-5 in the reference report (0000-0153-3787-RO, "Nine Mile Point Nuclear Station Unit 1 GNF2 ECCS-LOCA Evaluation with Sustained Under-Voltage Condition," January 2013).

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ATTACHMENT RESPONSE TO NRC REQUEST FOR ADDITIONAL INFORMATION, SRXB - RAI 1, RAI 2 AND RAI 3 SRXB-RAI 2

1. The staff noted that in the current Table XV-9 of NMP1 UFSAR, the maximum allowable delay time from initiatingsignal to pump at rated speed (sec)is listed as 35 sec for GEl I and 37 sec for GNF2 fuel; whereas, in the proposed Table XV-9, it is listed as 35 sec for both the fuel types. Explain why there was a two seconds difference in the delay time between the two fuel types in the current table.

2. The staff also noted that this two seconds difference in the delay time between the two fuel types was not discussed in the submittal [Ref 1], nor its impact on the NMP1 LOCA analysis (including PCT) was discussed. Pleaseprovide detail discussionto addressthe areasmentioned above.

Response SRXB-RAI 2

1. For the GNF2 LOCA analysis, a 2 second time delay was conservatively added to the time for the core spray pump to reach rated speed to account for low level indication to start Core Spray. During a LOCA event, NMP1 Core Spray system will likely start on high drywell pressure, making the additional 2 seconds for low level a conservative assumption. As NMP1 Diesel's start on a LOOP (not a LOCA signal), the 2 second delay is already covered within the 10 second diesel start time when the events happen concurrently. With respect to GEl 1, the analysis of record shows 35 seconds for the core spray time delay. Based on discussion with GEH, when the ECCS-LOCA analysis for GNF2 was initially performed in Cycle 20, the GEl 1 MAPLHGR limits were reconciled with the 37 second core spray delay. The PCT results between the GEl 1 35 second and 37 second cases are not significantly different.

2. In summary, for the NMP1 GNF2 and GEl 1 Current Licensing Basis LOCA analysis coincident with a LOOP, the core spray delay time used in in the analyses for both fuel types is 37 seconds (35 seconds + 2 seconds for low-low level indication). As the 2 seconds is a conservative assumption, not part of the actual timing of the event, the NMP1 UFSAR will show 35 seconds in Table XV-9. In order to further clarify the additional conservatism applied to the LOOP/LOCA a note will be added to the table stating the following: "(2) 2 seconds are added to the maximum time delay for Core Spray start on Reactor Low-Low Level for LOCA coincident with LOOP."

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ATTACHMENT RESPONSE TO NRC REQUEST FOR ADDITIONAL INFORMATION, SRXB - RAI 1, RAI 2 AND RAI 3 SRXB-RAI 3 The current Table XV-9 of NMP1 UFSAR, titled: "Significant Input Parameters to the LOCA Analysis" does not include the Note (1). However, the Note (1) has now been proposed to be included in the new table. Does this mean that the current LOCA analysis for the special scenario of degraded voltage conditions coincident with a LOCA was performed assuming maximum allowable delay time to be 35 seconds for GEl1I and 37 seconds for GNF2, as opposed to (24 + 35=) 59 seconds (60 seconds to be conservative), as it should be? If so, then this difference in the delay time should have made a significant impact on the LOCA results, including the PCT. Please provide the discussion on the impact of this difference on the LOCA Analysis.

Response SRXB-RAI 3 The NMP1 ECCS-LOCA Licensing Basis is the LOOP event coincident with a LOCA. Based on NRC review of the NMP1 Degraded Voltage Technical Specification and the resultant NCR NCV in January 2012, CR-2012-001018 was written requiring that the LOCA coincident with a Degraded-Voltage event be analyzed. In response to the CR, the NMP1 LOCA analysis was performed for the Degraded-Voltage scenario for both GEl 1 and GNF2 fuel types. This scenario assumed a 60 second time delay for core spray injection based on the existing 35 seconds discussed above plus 24 seconds from TS Table 3.6.2i for the degraded voltage time delay. There is also an additional 1 second added for conservatism. As discussed above, the additional 2 seconds in the original LOOP-LOCA analysis is assumed for the reactor low level indication starting core spray. As the LOCA and the Degraded Voltage events are occurring coincidently, the 2 seconds for LOCA initiation is absorbed under the 24 second degraded voltage time delay. Table 1 summarizes these scenarios and the resultant PCT (

Reference:

0000-0153-3787-RO, "Nine Mile Point Nuclear Station Unit 1 GNF2 ECCS-LOCA Evaluation with Sustained Under-Voltage Condition," January 2013). As shown in the summary Table 1, the LOOP-LOCA design basis analysis remains the Current Licensing Basis, setting the PCT for both GNF2 and GEl 1 fuel. The degraded-voltage- LOCA results, as shown, satisfy the 10 CFR 50.46 acceptance criteria and are bounded by the CLB scenario.

The LOCA analysis for the special scenario of degraded voltage conditions was performed using the SAFER/CORCL methodology with Appendix K conditions by applying the maximum allowable delay time of 60 sec for both GEl 1 and GNF2 fuel. The analysis is described in 0000-0153-3787-RO, "Nine Mile Point Nuclear Station Unit 1 GNF2 ECCS-LOCA Evaluation with Sustained Under-Voltage Condition," January 2013. Table 1 gives a comparison of the results for representative GNF2 and GEl1 bundles considering delays times of 37 sec and 60 sec.

Results are given for two different exposures in order to characterize the relative PCT and oxidation responses since cladding oxidation limits the fuel performance at higher burnup.

Notably, increasing the core spray delay time from 37 sec to 60 sec decreases the GNF2 PCT by 31 °F for 15 GWd/STU (an exposure within the PCT-limiting range). Similarly the maximum local oxidation decreases by 0.7% for the same increase in core spray delay time when analyzed for the same bundle at 35 GWd/STU (an exposure within the oxidation-limiting range).

Response for the GEl1 fuel is much less pronounced for similar analysis conditions on core spray delay time and exposures. These results contribute to the general conclusion of the core spray delay time increase to 60 sec in NMP1 as having insignificant impact on the LOCA response.

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ATTACHMENT RESPONSE TO NRC REQUEST FOR ADDITIONAL INFORMATION, SRXB - RAI 1, RAI 2 AND RAI 3 This somewhat counterintuitive response was thoroughly investigated by GE Hitachi over the range of core spray delay times from 30 sec to greater than 120 sec for both GNF2 and GEl 1.

A similar expectation existed as that noted in RAI #3 - namely, the PCT should increase with increasing core spray delay times. The investigation indeed demonstrates relative insensitivity of calculated PCT and oxidation results for NMP1 until a threshold core spray delay time at which the responses become very sensitive, much like a figurative "hockey stick" trend. Figure 1 shows a pictorial representation of the trend with maximum PCT as a function of core spray delay times. Bundle design influences the trend to some degree, in that the GNF2 trend shows a relatively small decrease in PCT over the core spray delay time range comprising the "handle" of the hockey stick, including the 37 sec to 60 sec range of interest for the NMP1 Degraded Voltage LAR. The representative GEl 1 bundle did not demonstrate a slight decrease, but generally maintained PCT variation within 10 *F over the investigated range of core spray delay times up to the threshold delay time. Similar threshold trends are followed by the oxidation results at higher bundle exposure. The threshold delay times are similar for each bundle type, however, indicating system-wide factors govern the threshold.

Underlying the observed behavior in these LOCA simulations is the interplay of core spray inventory in the upper plenum, counter current flow limitation effects across the top of fuel bundles, and the impact on the steaming rate in the lower plenum of spray coolant draining through the core bypass. Core spray injection timing clearly affects the trajectory of cladding temperatures during core heatup. Shortly after the time core spray is introduced into the upper plenum following nearly complete vessel depressurization (occurring quickly for the BWRJ2 large recirculation suction line break LOCA event), the PCT trajectory inflects with a decreased slope caused by the additional cooling provided by spray injection. Figure 2 shows a pictorial representation of PCT traces during the simulated LOCA event for progressively longer core spray delay times. The first inflection relates to the initial effects of core spray injection. A portion of the spray drains from the upper plenum through the bypass and into the lower plenum, introducing cooler fluid in the lower plenum steam environment, and effectively decreasing the steaming rate through the core until a new equilibrium is established. An increasing core spray delay time postpones the change in core steaming rate, and the relative magnitude of the change is affected by bundle design. Cladding temperature at the outset of core spray injection, however, increases with longer delay times, such that the magnitude of cladding temperature at which inflection occurs does increase with a longer core spray delay time. This aspect of the event progression reflects the expected PCT increase, but the effect of the increased cladding temperature is masked in the fact that the reported PCT value is a maximum value for the entire event. Figure 2 shows how the maximum PCT is a single characteristic of the PCT trajectory, which may have other transient occurrences affected by changing cooling mechanisms. In other words, delayed core spray injection certainly affects the PCT trajectory in the timeframe of injection, but if the delay occurs soon enough, the trajectory will generally recover and provide the maximum PCT at a later time being driven predominately by decay heat balanced with bulk cooling from core spray. The transition from longer-term maximum PCT to the maximum PCT determined solely by core spray delay timing manifests as a threshold sensitivity, i.e. the "hockey stick" trend. The relative insensitivity - the hockey stick handle - reflects the core spray timing for which the maximum PCT is determined by the longer-term response. Since the local cladding oxidation response is driven by the core thermal response, this phenomenological reasoning and threshold trend extends to oxidation results.

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ATTACHMENT RESPONSE TO NRC REQUEST FOR ADDITIONAL INFORMATION, SRXB - RAI 1, RAI 2 AND RAI 3 The LOCA analysis performed for the NMP1 Degraded Voltage condition is explained by the mechanistic behavior found in the investigation. Core spray delay times up to 60 sec in NMP1 fits well within the time period demonstrating insensitive response for PCT and oxidation, and the general behavior applies to both GNF2 and GEl 1 fuel types.

15.00 37 2144 10.2 GNF2 35.00 37 1985 15.7 15.00 60 2113 9.3 GNF2 35.00 60 1970 15.0 15.00 37 2142 9.4 GEl1 35.00 37 2006 15.6 15.00 60 2141 9.4 GEl1 35.00 60 2000 15.6 Table 1 LOCA Analysis Results Comparing 37 and 60 seconds Core Spray Delay Times 6 of 7

ATTACHMENT RESPONSE TO NRC REQUEST FOR ADDITIONAL INFORMATION, SRXB - RAI 1, RAI 2 AND RAI 3 I'

E E

Core Spray Initiation Time (sec)

Figure 1 Demonstration of Maximum PCT Trend with Core Spray Delay Time LV E ~Relative Core Spray Delay Time I--

"3 -

• t2l t-2 t_3

- t4

- t5

- t6 Time Following LOCA Initiation (sec)

Figure 2 Representative PCT Response for Progressively Longer Core Spray Delay Times 7 of 7