ML24040A149

Response to NRC Request for Additional Information Regarding Final Response to Generic Letter 2004-02

ML24040A149
Person / Time
Site:	Calvert Cliffs
Issue date:	02/09/2024
From:	David Helker Constellation Energy Generation
To:	Office of Nuclear Reactor Regulation, Document Control Desk
References
GL 2004-02
Download: ML24040A149 (1)

Text

200 Exelon Way Kennett Square, PA 19348 www.constellation.com

10 CFR 50.54(f)

GL 2004-02

February 9, 2024

U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555- 0001

Calvert Cliffs Nuclear Power Plant, Units 1 and 2 Renewed Facility Operating License Nos. DPR-53 and DPR-69 NRC Docket Nos. 50-317 and 50-318

Subject:

Response to NRC Request for Additional Information Regarding Final Response to Generic Letter 2004- 02

References 1. Generic Letter (GL) 2004-02, Potential Impact of Debris Blockage on Emergency Recirculation During Design Basis Accidents at Pressurized-Water Reactors, dated September 13, 2004 (ADAMS Accession No. ML042360586)

2. Letter from D. P. Helker (Exelon Generation Company, LLC) to the U.S.

Nuclear Regulatory Commission, Calvert Cliffs Nuclear Power Plant, Units 1 and 2 - Final Response and Close-out to Generic Letter 2004- 02, dated November 12, 2020 (ADAMS Accession No. ML20317A112)

3. Electronic mail from M. Marshall (U.S. Nuclear Regulatory Commission) to W. Para (Constellation Energy Generation, LLC (CEG)), Request for Additional Information Regarding Final Response to Generic Letter 2004-02 (EPID L-2017-LRC- 0000), dated January 11, 2024 (ADAMS Accession No. ML24012A049)

GL 2004-02 (Reference 1) requested that licensees provide information confirming that their plants are in compliance with Section 50.46 of Title 10 of the Code of Federal Regulations (10 CFR) that requires plants to be able to maintain adequate long-term core cooling to ensure that the fuel in the core can be cooled and maintained in a safe and stable configuration following a postulated accident. In accordance with 10 CFR 50.54(f),

addressees for GL 2004-02 are required to submit written responses to the generic letter.

By letter dated November 12, 2020 (Reference 2) Constellation Energy Generation, LLC (CEG) (previously Exelon Generation Company, LLC), provided the CCNPP Final Response and Close-out to Generic Letter 2004- 02 for Calvert Cliffs Nuclear Power Plant, Units 1 and 2 (CCNPP).

Response to RAI Regarding Final Response to Generic Letter 2004- 02 February 9, 2024 Page 2

By electronic mail dated January 11, 2024 ( Reference 3 ), the U.S. Nuclear Regulatory Commission (NRC) identified that additional information is necessary to complete the review. The attachment to this letter contains the NRC's request for additional information immediately followed by CEGs response.

This letter and its attachment contain no regulatory commitments.

In accordance with 10 CFR 50.91, "Notice for public comment; State consultation," paragraph (b), CEG is transmitting a copy of this letter to the designated State Official.

Should you have any questions concerning this supplement, please contact Ms. Wendi E.

Para at Wendi.Para@Constellation.com or at (267) 533-5208.

Respectfully,

David P. Helker Sr. Manager - Licensing Constellation Energy Generation, LLC

Attachment:

Request for Additional Information and CEG Response

cc: USNRC Region I, Regional Administrator USNRC Senior Resident Inspector, Calvert Cliffs Nuclear Power Plant USNRC Project Manager, NRR - Calvert Cliffs Nuclear Power Plant S. Seaman, State of Maryland ATTACHMENT

Request for Additional Information and CEG Response

Calvert Cliffs Nuclear Power Plant, Units 1 and 2 Renewed Facility Operating License Nos. DPR-53 and DPR-69 NRC Docket Nos. 50- 317 and 50-318 RAI No. 1

On page 17 of 141 of Attachment 1 to the letter dated November 12, 2020, the licensee states that banded calcium silicate (cal-sil) insulation uses a zone of influence (ZOI) of 5.45D (D is equal to the diameter of the postulated break and determines the volume of the ZOI) and 100 percent fines is assumed for all cal-sil material within the ZOI. Table 2a o n page 18 of 141 states that a 6.4D ZOI is used for cal-sil and provides a three-category size distribution. The response states that there is no cal-sil within a 5.45D ZOI for any of the limiting Region I or II breaks.

Clarify which of the two debris generation models is used for the estimation of cal-sil debris generation at Calvert Cliffs.

CEG RESPONSE:

The ZOI for generated debris was determined using approved methodologies presented in NEI 04-07 and the associated NRC safety evaluation. The ZOI for banded cal-sil insulation uses the approved methodology default value of 5.45D. Any cal-sil within this ZOI was assumed to become 100% fines.

Reference 1, Table 2a documents the refined size distributions for cal-sil insulation based on Air Jet Impact Test (AJIT) data for future evaluations should it become pertinent. The intent of including this data is captured in the Reference 1 statement on page 17 of 141, While [Table 2a] is not needed to address any break that could challenge strainer performance it is available for future evaluations. The refined model based on AJIT data was provided for information only and was not used in the analysis of record for the estimation of cal-sil debris generation at Calvert Cliffs Nuclear Power Plant (CCNPP).

RAI No. 2

Even if there is no deaeration at the mid-point of the strainer it may occur at higher strainer elevations due to lower submergence. Therefore, using the midpoint of the strainer may underestimate the amount of deaeration that occurs and the potential effects of this phenomenon. The strainer midpoint is identified as the reference location on page 41 of and the phenomenon is discussed on page 71 of Attachment 1 with respect to the maximum allowable head loss values provided in Table 11a. On page 71 it is stated that deaeration is the limiting failure mode for some anticipated operational conditions for the strainer. Therefore, a realistic or conservative deaeration value is required for the analysis.

Provide justification for using the mid-point of the strainer as a reference point for the deaeration evaluation.

Attachment:

Request for Additional Information and CEG Response Page 2 of 5

CEG RESPONSE:

A review of Reference 1 shows that acceptable results can be obtained when strainer submergence is referenced from the top of the strainer.

The strainer submergence to the top of the strainer was provided in Reference 1, Table 8.

These submergence values can be used to replace the last four values in the Maximum Allowable Head Loss values given in Reference 1, Table 11a. In Reference 1 on page 72 of 141 in the section entitled Demonstration that Strainer Head Losses will be Below Maximum Allowable Limits, the various cases are re-evaluated using these revised submergence values. The results are summarized in the following table.

Section Title Previous New Head Max. Comparison Head Loss Loss Actual Allowable Allowable Head (mid-point) (top) Note 1 Loss A All Breaks, TSump > 2.07 ft 1.3583 ft 0.444 ft 1.3583 >

140F 0.444 B Breaks 0.08 ft2 2.812 ft 1.4808 ft 0.322 ft 1.4808 >

TSump 140F 0.322 C Region I Breaks > 3.227 ft 1.8958 ft 0.322 ft - 1.8958 >

0.08 ft2 1.271 ft 1.271 TSump 140F D1 Region II 11A Cold 3.227 ft 1.8958 ft 0.906 ft 1.8958 >

Leg Break, TSUMP Note 2 0.906 140F D2 Region II 12B Cold 3.227 ft 1.8958 ft 0.717 ft - 1.8958 >

Leg Break, TSUMP 1.271 ft 1.271 140F D3 Region II 12 Hot Leg 3.227 ft 1.8958 ft 0.906 ft 1.8958 !

Break, TSUMP 140F Note 2 0.906 D4 Region II 11 Hot /eg 3.168 ft 1.8958 ft 1.856 ft 1.8958 !

Break, TS80P 140F Note 3 1.856

Note 1 The design calculation for the evaluation of NPSH margin, deaeration, and flow during containment sump recirculation was revised and the current calculated values show additional significant digits. The calculated values, including the additional significant digit s, are provided for completeness, where applicable.

Note 2 For the Region II 11A Cold /eg and Region II 12 Hot /eg break cases the same methodology previously submitted for only the Region II 11 Hot /eg Break in Section D4 (Reference 1, page 79 of 141) is now employed.

Test No. 3 from the Summer 2010 Tests was used to qualify the Region II 11A Cold /eg and Region II 12 Hot /eg Break Cases (Sections D1 and D3). If the measured strainer head loss from the Summer 2010 Test No. 3 of 3.155 feet is linearly scaled to 675 gpm and the clean strainer head loss is scaled down by the square of the flows (Affinity /aws) the resulting head loss is 0.906 feet. The available submergence of 1.8958 feet exceeds the head loss of 0.906 feet therefore, deaeration will not occur.

Attachment:

Request for Additional Information and CEG Response Page 3 of 5

Also, as described in Reference 1 on page 76 of 141, a refilled refueling water tank (RWT) will be available. If necessary, the plant can return to injection mode when ECCS pump distress is detected. Once a second RWT inventory has been injected there would be 6.398 feet of submergence which is greater than the strainer head loss of 3.219 feet at a flow of 2365 gpm. Thus, there is sufficient water height to prevent pump distress even if a Containment Spray pump were left operating.

Note 3: As discussed in Reference 1 on page 79 of 141, Test No. 3 from the Late 2008 Head Loss Tests is used to qualify the Region II 11 Hot Leg Break Case (Section D4). That same discussion still applies except that now the head loss is scaled down to a flow of 675 gpm and is 1.8561 feet. The available submergence of 1.8958 feet exceeds the head loss of 1.8561 feet; therefore, deaeration will not occur. The discussion on Operator action continues to apply both to secure unnecessary pumps in the event pump distress is detected, and to refill the RWT. It is noted that if a second RWT inventory has been injected the submergence would be 6.398 feet and though slightly less than the strainer head loss of 6.549 feet at a flow of 2365 gpm there is still assurance of successful operation. As mentioned in Reference 1, linear scaling of head loss with flow was found to be quite conservative. A review of test results showed it to be between 13% and 87% conservative with the average value being 41% conservative. Reducing the head loss by just 3% after linearly scaling results in a strainer head loss of 6.360 feet which is less than the available submergence of 6.398 feet. A 3% reduction in head loss is well within the conservatism described above. Furthermore, as mentioned in Reference 1 on page 76, the fiber load used in Test 3 from the Late 2008 testing is 20% greater than the fiber load predicted for the 11 Hot Leg Break case. Fiber load is the foremost factor affecting debris bed head loss, and head loss varies linearly at a minimum with fiber load. Reducing the debris bed head loss by 20% results in a total strainer head loss which is less than the submergence of 6.398 feet. Therefore, there is sufficient defense-in-depth for mitigating this Region II break.

RAI No. 3

On pages 75 and 76 of 141 of Attachment 1 to the letter dated November 12, 2020, the licensee states that the excessive particulate included in the Summer 2010 tests can be credited to make up for a lack of chemical precipitate added to those tests for the 12B cold-leg break and 12 hot-leg break at the steam generator. Theoretically this may be true, but the effect of chemicals on head loss is generally much greater than that of typical particulate coatings surrogates. In the Calvert Cliffs tests, precipitates had a much larger effect than coatings. The effect of precipitates and coatings on head loss depends on other factors in the test.

Provide additional information to justify that the tests bound the plant conditions for the Region II tests or provide justification that the testing justifies that the strainer will perform its function under realistic conditions as allowed by a Region II analysis.

CEG RESPONSE:

Head loss test results do show that chemical precipitates have a larger impact on strainer head loss than particulate. The discussion on the excess particulate used in the test was provided to show defense-in-depth. Head loss testing also showed that as chemical precipitant was added strainer head loss increased up until the point that a debris bed breakthrough occurred. A debris bed breakthrough occurs when the underlying fiber bed can no longer withstand the differential pressure. Once the strainer head loss reaches the

Attachment:

Request for Additional Information and CEG Response Page 4 of 5

maximum strength of the fiber bed, a debris bed breakthrough occurs, and additional chemical precipitate will not cause further increases in strainer head loss. The strength of the fiber bed correlates strongly if not entirely with the amount of fiber used.

For the 12B Cold Leg Break Case both Tests 5 and 7 had debris bed breakthroughs and peak strainer head loss occurring before the chemical precipitant addition was complete.

Additionally, Test 5 used 4.8% less chemical precipitate than Test 7 yet the head loss from Test 5 was nearly double the Test 7 head loss. The increased head loss for Test 5 as compared to Test 7 is directly attributable to the 12.6% increase in fiber load used in Test 5.

For the 12 Hot Leg Break Case the qualifying Test 3 also had debris bed breakthroughs demonstrating that the fiber bed strength had been exceeded, and additional chemical precipitate would have been inconsequential. Again, for defense-in-depth purposes only, it is noted that the 12.3% underage in chemical precipitant used is offset, at least in part, by the 13.3% surplus of particulate that was used.

Reviews of other test results show that even with an increase in particulate load of 24.8%,

an increase in chemical precipitant load of 19.1%, and an increase in fiber load of 5.6% the strainer head loss increased by only 10%. Based on reviews of other tests this would be the head loss increase expected based on the increased fiber load alone. Therefore, the surplus of particulate and chemical precipitate had an inconsequential effect. For the CCNPP design, running strainer head loss tests with sufficient amounts of chemical precipitate to cause debris bed breakthroughs is sufficient to demonstrate how the strainer would perform under realistic conditions.

RAI No. 4

On page 76 of 141 of Attachment 1 to the letter dated November 12, 2020, the licensee states that the head loss from Test No. 3 is scaled down to 1150 gallons per minute (gpm) and that is below all applicable head loss limits in Table 11A.

Provide the head loss value calculated at 1150 gpm that was used in the evaluation.

CEG RESPONSE:

In Reference 1, strainer performance was evaluated at 1150 gpm. This flow is conservatively high compared to the actual strainer flow rate of 603.2 gpm which is in effect when both Containment Spray pumps are secured. The reference point for deaeration evaluation has been revised from the strainer mid-point to the top of the strainer.

Consequently, strainer performance is now revaluated at 675 gpm which is still conservative as compared to the actual strainer flow of 603.2 gpm.

At a strainer flow of 675 gpm the strainer head loss as scaled from Test 3 would be 1.8561 feet.

Note that the head loss data above has been scaled down from the late 2008 Test No. 3, not the similarly labeled Summer 2010 Test No. 3.

Attachment:

Request for Additional Information and CEG Response Page 5 of 5

RAI No. 5

On page 92 of 141 of Attachment 1 to the letter dated November 12, 2020, the limiting net positive suction head (NPSH) margin value for the containment spray system pump is listed as 1.63 feet for maximum sump pool temperature cases. On page 71 the minimum NPSH margin value is listed as 2.07 feet for cases greater than 140 degree Fahrenheit.

Provide an explanation for the difference between these values.

CEG RESPONSE:

Reference 1 on page 71 of 141 identifies 2.07 feet as the maximum allowable strainer head loss and not the minimum NPSH margin. The NPSH margin is the difference between the NPSH available and the NPSH required.

For the Containment Spray pump the limiting NPSH margin is 1.63 feet and occurs at sump temperatures greater than 140F. This value was obtained assuming the maximum strainer head loss at temperatures greater than 140F which is 0.444 feet. If this strainer head loss of 0.444 feet is added back on to the NPSH margin a maximum allowable strainer head loss value of 2.07 feet is obtained.

RAI No. 6

If the flow rates are not controlled per the procedural changes that are stated to be in progress by the submittal, the NPSH margins in the submittal will be non-conservative. The commitment to revise the EOP is listed in Attachment 2 of and discussed on Page 4 of 141 of Attachment 1 of the letter dated November 12, 2020.

Confirm that the emergency operating procedures (EOPs) have been revised to ensure the maximum flow rate through the strainer is limited to 2365 gpm during recirculation and that the procedures are in place to ensure that post-recirculation actuation signal flow is limited to 600 gpm.

CEG RESPONSE:

As stated in Reference 1 on page 83 of 141, the strainer design flow rate is 5000 gpm. This flow bounds the maximum flows which occur at the start of containment sump recirculation operation. As of February 8, 2021 the final changes to the CCNPP Emergency Operating Procedure EOP-01-1/2, Loss of Coolant Accident, have been made (for CCNPP, Units 1 and 2, respectively). These changes ensure that the maximum flow rate through the strainer is limited to 2365 gpm prior to the onset of chemical precipitation. Once containment temperature drops below 120 F all Containment Spray flow may be secured, and the total strainer flow will be 603.2 gpm.

REFERENCE

1. Letter from D. P. Helker ( Exelon Generation Company, LLC) to the U.S. Nuclear Regulatory Commission, Calvert Cliffs Nuclear Power Plant, Units 1 and 2 - Final Response and Close-out to Generic Letter 2004-02, dated November 12, 2020 (ADAMS Accession No. ML20317A112)