ML050110079

Response to Request for Additional Information Re Reconciliation of Regulatory Requirements

ML050110079
Person / Time
Site:	Millstone
Issue date:	01/06/2005
From:	Hartz L Dominion Nuclear Connecticut
To:	Document Control Desk, Office of Nuclear Material Safety and Safeguards
References
04-771, M2-EV-04-0025, Rev 1
Download: ML050110079 (20)

Text

Dominion Nuclear Connecticut, Inc.

bliil~roticPower Station tbpc bcrrv I<oad W.ircrlord. .I:( 06385 January 6 , 2005 U.S.Nuclear Regulatory Commission Serial No.04-771 Attention: Document Control Desk MPS Lic/MAE R1 Washington, DC 20555 Docket No. 50-336 License No. DPR-65 DOMINION NUCLEAR CONNECTICUT, INC.

MILLSTONE POWER STATION UNIT 2 RESPONSE TO A REQUEST FOR ADDITIONAL INFORMATION RECONCILIATION OF REGULATORY REQUIREMENTS By a letter dated November 5, 2004, Dominion Nuclear Connecticut, Inc. (DNC) submitted a request for a limited exemption from the requirements of 10 CFR 50.68(b)(l) for loading fuel in a NUHOMS 32PT DSC in the Millstone Unit 2 Spent Fuel Pool.

On December 13, 2004, DNC received a request for additional information (RAI) from the Nuclear Regulatory Commission (NRC) staff that contained three questions. A second RAI was received on December 14, 2004 that contained four additional questions.

Attachment 1 contains DNC responses to the seven questions. Commitments made in this letter are listed in Attachment 2. Attachment 3 contains a copy of Technical Evaluation M2-EV-04-0025, Revision 1, Boron Dilution Analysis for the TN32PT Cask in the Millstone 2 Spent Fuel Pool. Attachment 4 contains two sketches of the Millstone Unit 2 Spent Fuel Pool and Cask Pit.

The exemption request was based on a bounding boron dilution analysis. DNC proposes that the applicability and continued validity of the proposed exemption request be tied to the continuing validity of the boron dilution analysis. This boron dilution analysis used bounding parameters, and as long as these bounding parameters remain valid, the exemption would continue to be applicable. This assures that as Technical Specifications (TS) amendments are issued to the NUHOMS CofC 1004, there is a defined basis for determining continued applicability of the proposed exemption.

Accordingly, DNC proposes that the following four conditions be applied to ensure continuing validity of the exemption:

1. Fuel shall not be loaded into the 32PT DSC that results in the need for a NUHOMS CofC 1004 TS required boron concentration greater than 2500 ppm.

2. For the fuel and 32PT DSC configuration that corresponds to the NUHOMS CofC 1004 TS required boron concentration of 2500 ppm, the critical boron concentration must be 1700 ppm or less.

Serial No.04-771 Response to RAI Page 2 of 3

3. If the NUHOMS CofC 1004 TS for the 32PT DSC is licensed to allow required boron concentrations less than 2500 ppm, then to use this reduced TS boron concentration, the critical boron concentration must be recalculated and it must be verified that the boron dilution times submitted in support of the exemption remain valid. Specifically, it must be verified that the time from the initial TS boron concentration until the critical boron concentration is reached is greater than or equal to 9.5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br />.

4. Modifications that may affect potential dilution sources to the Millstone Unit 2 spent fuel pool cannot adversely affect the design basis boron dilution time submitted in support of the exemption request. Specifically, if a modification is planned, it must be verified that the boron dilution time remains greater than or equal to 9.5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br /> from the initial TS boron concentration until the critical boron concentration is reached. Documentation of the acceptability of the change would be through the 10CFR50.59 and 10CFR72.48 processes either associated with the change itself, or as a pre-condition to fuel being inserted into a DSC in the SFP.

The additional information provided in this letter will not affect the conclusions of the Safety Summary and Significant Hazards Consideration discussion in the DNC November 5, 2004, letter.

If you have any questions or require additional information, please contact Mr. David W.

Dodson at (860) 447-1791, extension 2346.

Very truly yours, L. N. Hartz Vice President - Nuclear Engineering Attachments: (4)

Commitments made in this letter are listed in Attachment 2.

Serial No.04-771 Response to RAI Page 3 of 3 cc: U.S. Nuclear Regulatory Commission Region I 475 Allendale Road King of Prussia, PA 19406-141 5 Mr. V. Nerses Senior Project Manager U.S. Nuclear Regulatory Commission One White Flint North 1 1555 Rockville Pike Mail Stop 8C2 Rockville, MD 20852-2738 Mr. S. M. Schneider NRC Senior Resident Inspector Millstone Power Station

SN: 04-771 Docket No.: 50-336

Subject:

Response to RAI COMMONWEALTH OF VIRGINIA )

1 COUNTY OF HENRICO )

The foregoing document was acknowledged before me, in and for the County and Commonwealth aforesaid, today by Leslie N. Hartz, who is Vice President - Nuclear Engineering, of Dominion Nuclear Connecticut, Inc. She has affirmed before me that she is duly authorized to execute and file the foregoing document in behalf of that Company, and that the statements in the document are true to the best of her knowledge

- and belief.

Acknowledged before me ,2005.

My Commission Expires:

Notary Public (SEAL)

Serial No.04-771 Docket No. 50-336 Attachment 1 Reconciliation of Requlatorv Requirements Response to Request For Additional Information Millstone Power Station Unit 2 Dominion Nuclear Connecticut, Inc. (DNC)

Serial No.04-771 Attachment 1, Response to RAI Page 1 of 9 Response to the December 14. 2004 Request For Additional Information (four questions)

NRC Question 1:

DNC stated in its exemption request that the critical boron concentration calculations were petformed at optimum moderation conditions. The staff requests that DNC provide additional supportive information describing the optimum moderation conditions assumed in these calculations and basis for the values assumed. Additionally, the staff requests that DNC explain how these values correlate to the design basis allowed temperatures of the MPS2 spent fuel pool.

Response

The critical boron concentration values for 3.90 and 3.35 w/o U235 fresh fuel in the NUHOMS 32PT Dry Shielded Canister (DSC) were provided by Dominion Nuclear Connecticut, Inc. (DNC) in its submittal. These critical boron concentration values were performed at optimum moderation conditions. Optimum moderation conditions refer to those moderation conditions that result in the maximum value of K-effective.

Transnuclear (TN) performed these criticality calculations using KENO from the SCALE system. KENO calculations were performed using 20C (68F) as the reference (full density) moderator temperature. Additional KENO calculations were performed for the range of 60% to 100 o/o of full density. Maximum K-effective (optimum moderation) was determined to occur at 75% of full density. This implies that the moderator temperature coefficient (MTC) is positive in the range from full water density to 75% of full water density. This positive MTC is primarily a result of the high boron concentrations. This methodology is consistent with the approach used by TN in performing the calculations for determining the boron concentrations necessary to maintain K-effective 5 0.95 per the NUHOMS CofC 1004 Technical Specifications (TS) and FSAR.

While reaching 75% of full water density inside the DSC is possible during DSC drying operations, this water density condition is overly conservative for Spent Fuel Pool (SFP) conditions. Reaching 75% of full water density inside the DSC can only occur in the SFP by having the water temperature go to a boiling condition with significant voiding.

To put the value of 75% of full water density in perspective, at 150F, the water density is about 98% of full water density, and at 250F (under pressure at bottom of SFP), the water density is about 94% of full density. Thus, the only way to reach 75% of full water density in the SFP is with boiling and significant voiding. The Millstone 2 spent fuel pool normal operating temperature limit is approximately 9OF. Temperatures above 150F (98% of full density) would not be expected to occur and would be an accident condition. Therefore, only 98% of full water density need be considered for the determination of the critical boron concentrations while the DSC is in the spent fuel pool.

Multiple concurrent and independent accidents, such as a loss of SFP cooling that allowed the SFP temperature to exceed 150F and a simultaneous boron dilution event,

Serial No.04-771 Attachment 1, Response to RAI Page 2 of 9 would not need to be considered. Thus, conservatively high K-effective values were calculated by using the optimum moderation condition (75% of full density) as opposed to the moderator density possible (98% of full density) that is allowed by the design limits of the SFP operating temperature range (150F). The end result of this conservatism is higher calculated (conservative) critical boron concentration values.

Thus, there is additional conservatism in the time to reach criticality during a postulated boron dilution event due to the use of optimum moderation conditions.

NRC Question 2:

DNC stated in its exemption request that the loading of higher enrichment assemblies (i.e. greater than 3.8 weight percent) in the Transnuclear (TN) HUHOMS-32PT Dry Shielded Canister (32PT DSC) was acceptable provided poison rod assemblies (PRAs) were also loaded into the cask for criticality control. The staff requests that DNC provide additional information describing the controls and procedures currently in place to direct the loading of fuel assemblies and PRAs into the cask. Specifically, the staff requests that DNC provide information demonstrating that interim loading and unloading storage configurations are bounded by the analyzed technical specification storage patterns.

Please provide a detailed description of the sequential loading of fuel assemblies and PRAs into the 32PT DSC.

Response

DNC does not plan to use and load PRAs for a considerable period of time. Therefore, we are willing to except as a limitation that the proposed 10 CFR 50.68(b)(l) exemption not allow the use of PRAs.

NRC Question 3:

In response to Criterion 5a. DNC stated that: The use of PRAs to allow higher enrichments does not alter these [critical] boron concentrations. However, DNC did not provide supporting information to demonstrate that a 32PT DSC loaded with higher enrichment fuel assemblies and PRAs is bounded by a 32PT DSC loaded with 3.8 weight percent fuel assemblies and no PRAs. The staff requests that DNC provide additional information which demonstrates that a 32PT DSC loaded with 3.8 weight percent enriched fuel assemblies and no PRAs represents the most limiting storage configuration.

Response

DNC does not plan to use and load PRAs for a considerable period of time. Therefore, we are willing to except as a limitation that the proposed 10 CFR 50.68(b)(l) exemption not allow the use of PRAs.

Serial No.04-771 Attachment 1, Response to RAI Page 3 of 9 NRC Question 4:

As part of its exemption request, DNC provided a list of commitments to ensure subcritical conditions can be maintained in the 32PT DSC. In Commitment #2 DNC stated that: DSC procedures will be modified to include a requirement that the spent fuel pool will be sampled for boron concentration after each interval of 500 gallons of unborated water has been added to the pool. The staff requests that DNC provide additional information describing how it will monitor and determine when 500 gallons of unborated water have been added to the spent fuel pool.

Response

The connection that will be used to supply unborated Primary Makeup Water (PMW) for cask handling operations has a flow integrator installed. This flow integrator will be used to determine when 500 gallons of PMW has been added to the spent fuel pool.

Once this value of 500 gallons is reached, boron sampling of the pool will be required.

This is a current plant operating practice (Procedure OP2209A) and is being incorporated into ISFSI operations.

Response to the December 13, 2004 Request For Additional Information (three questions)

NRC Question 1:

Criterion 5b, Boron Dilution Analysis, specifies that the analysis provided is a summary of the Boron Dilution Analysis for TN32PT C a s k performed in the MP2 Spent Fuel Pool (Reference 8 of DNC letter). The staff recognizes the similarity of Reference 3 of DNCs letter to the current dilution analysis. However, because the current analysis prescribes critical boron concentrations higher than the former and includes possible direct dilution sources to the dry storage cask (DSC) we are requesting a copy of that analysis (Reference 8 of DNCs letter).

Response

A copy of the current revision of Reference 8 of DNCs letter dated November 5, 2004 is attached. That document is Technical Evaluation M2-EV-04-0025, Revision 1, Boron Dilution Analysis For TN32PT Cask in The Millstone 2 Spent Fuel Pool.

NRC Question 2:

In page 11 of DNCs letter, DNC stated that dilution times are based on a feed and bleed operation with instantaneous complete mixing. DNC also indicated that the Cask Loading Pit volume was conservatively neglected when calculating the volume of the Spent Fuel Pool (SFP), and mentions that the DSC is located at the bottom of the cask

Serial No.04-771 Attachment 1, Response to RAI Page 4 of 9 handling pit that is connected to the SFP through a gate opening. DNCs analysis does not include the possibility of localized boron dilution and stratification in the cask handling area as described in Reference 10 of DNCs letter. Please, provide a description (and pertinent drawings) of the SFf configuration (including the cask handling area) that adequately represent a justification for DNCs assumptions.

Response: contains 2 sketches of the Millstone 2 Spent Fuel Pool and Cask Pit to assist in understanding the physical layout. The sketch labeled Millstone 2 Spent Fuel Pool provides a view looking down onto the SFP to orient the main portion of the SFP with respect to the transfer canal on the west side of the pool, and the cask pit in the northeast corner of the pool. The gate openings to the cask pit and transfer canal are also shown. A Transfer CasWDSC is shown in the cask pit. The second sketch labeled Millstone 2 Cask Pit provides key dimensions related to the cask pit and the top elevation of the Transfer CasWDSC.

To provide a comprehensive answer to this question, first the results of spent fuel pool dilution will be discussed with an instantaneous mixing model. Next a discussion will be presented where the spent fuel pool dilution is modeled with no mixing and stratification assumed. A discussion of direct dilution to the cask handling pit is provided in response to Question 3 of the December 13, 2004, RAI response.

Spent Fuel Pool Dilution with Instantaneous Mixing The boron dilution results provided by DNC represented a dilution directly to the Spent Fuel Pool (or Transfer Canal). This source of dilution can enter the SFP through either of two general pathways (1) the two SFP cooling discharge pipes at the bottom of the north central section of the SFP, or (2) a spill into the SFP (or transfer canal) from the top at the operating deck. As described in the DNC submittal, the limiting events are through the SFP cooling discharge pipes. Possible sources of unborated water into the SFP cooling discharge piping are 200 gpm from an inadvertently open PMW valve, 142 gpm of Reactor Building Closed Cooling Water (RBCCW) flow from a tube rupture in a SFP Cooling Heat Exchanger, or 100 gpm from an inadvertently open auxiliary feed valve. The SFP would eventually overflow and a feed and bleed dilution would be established.

The concern is the boron concentration inside the DSC at the bottom of the cask pit.

The fuel in the DSC requires 1700 ppm of boron to maintain subcriticality. The 1700 ppm requirement assumes the DSC contains highly enriched fresh fuel. In fact, the DSC will contain fuel with significant burnup and the likely boron concentration needed to maintain subcriticality will be 0 ppm. However, the analysis does not credit fuel burnup, but rather demonstrates that 1700 ppm can be maintained in the DSC. Nonetheless, it is important to understand the significant level of conservatism in ignoring the actual substantial fuel burnup of the fuel in the DSC.

Serial No.04-771 Attachment 1, Response to RAI Page 5 of 9 The boron concentration requirements for the fuel in the fuel storage racks of the SFP are not being addressed by this submittal. The fuel storage racks in the spent fuel pool were previously licensed by the NRC and a boron dilution analysis was submitted and approved by the NRC. As part of the licensing basis for the fuel storage racks, even if the boron concentration went to 0 ppm, subcriticality would be maintained. This request for exemption to 10CFR50.68(b)(l) for loading fuel in the 32PT DSC and any of the supporting analysis provided to support the exemption request is not intended to affect or apply to the existing analysis and licensing basis of the fuel storage racks.

In consideration of the previous discussion, the boron dilution problem for the DSC in the cask pit can essentially be considered a two volume problem. The two volumes are the Spent Fuel Pool (and transfer canal) volume and the Cask Pit volume. Any dilution will initiate in the SFP volume with forced flow for mixing. The adjacent Cask Pit volume is connected to the SFP volume through the gate opening.

There is no forced flow in the Cask Pit or between the Cask Pit and the SFP.

Initially prior to the dilution, both the SFP and Cask Pit volumes are at 2500 ppm. In fact, higher boron concentrations will initially be present to provide margin to the TS limit. However, this will not be credited. As stated previously, the dilution to the SFP volume is assumed to be through one of two entry pathways, either through the SFP cooling discharge pipes at the bottom of the SFP, or water spilling into the top of the SFP (or transfer canal).

Water spilling into the top of the SFP is assumed to be unborated water.

A dilution through the SFP cooling discharge pipes can occur by adding unborated water to the normal recirculation cooling flow. If we take the limiting case of 200 gpm of unborated water mixing with 850 gpm of SFP recirculation cooling flow, for a total flow of 1050 gpm, then the lowest boron concentration from SFP cooling discharge would be 2023 ppm.

That is: 2500 ppm (850 gpdlO50 gpm) = 2023 ppm At the start of the dilution event to the SFP, through either of the two pathways to the SFP, water will be added to the SFP and the entire interconnected SFP/transfer canal and Cask Pit water levels will rise to overflow. During this initial time interval the boron concentration of 2500 ppm in the Cask Pit will not be adversely affected.

This is because the dilution into the SFP through either entry pathway should have the initial effect of pushing 2500 ppm SFP water into the Cask Pit through the gate opening between the SFP and Cask Pit.

When the pool begins to overflow, a feed and bleed dilution is established with up to 200 gpm of unborated water being added to the SFP, through either of the two entry

Serial No.04-771 Attachment 1 , Response to RAI Page 6 of 9 pathways, with overflow of the pool as the water exit path. Crediting only the SFP and transfer canal volumes and assuming instantaneous mixing (since there is forced flow in the SFP), it will take 9.5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br /> for the boron concentration to drop from 2500 ppm to 1700 ppm in the SFPhransfer canal volume.

During this time interval when the SFP boron concentration is dropping from 2500 ppm to 1700 ppm, the Cask Pit boron concentration is also dropping due to the interconnection between the SFP and the Cask Pit through the gate opening.

Considering that there is no relative forced flow between the Cask Pit and the SFP, and the gate opening is of limited size, the Cask Pit boron concentration will not drop as fast as the boron concentration in the SFP. As a result, there will be more than 9.5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br /> before the Cask Pit reaches 1700 ppm.

As discussed in the DNC submittal, 9.5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br /> is more than sufficient time to identify and mitigate the consequences of this boron dilution event.

Spent Fuel Pool Dilution With No Mixinq and Stratification As previously discussed, a minimum SFP boron concentration of 1700 ppm must be maintained inside the DSC at the bottom of the Cask Pit during a postulated boron dilution event.

Localized Dilution throuqh SFP Coolinq Discharqe Pipes with No Mixinq As described in the DNC submittal, dated November 5, 2004, the limiting events are through the SFP cooling discharge pipes. The SFP cooling discharge pipes are near the bottom of the SFP, and the SFP suction pipe is near the top of the SFP.

As described previously, a dilution flow of 200 gpm of unborated water through the SFP cooling discharge pipes would result in 1050 gpm of total water flow at 2023 ppm boron concentration. Rather than using an instantaneous mixing model of this boron dilution of the SFP, alternatively this situation can be analyzed with a slug flow model, in which no mixing occurs. With this slug flow model, the initial 2500 ppm water in the SFP, transfer canal and Cask Pit will be displaced by water of 2023 ppm at a rate of 1050 gpm. If no mixing were to occur, it would take 5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br /> for the water in the SFP, transfer canal and Cask Pit to drop to 2023 ppm boron concentration.

The value of 5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br /> is calculated as:

[297000 gal. (SFP & transfer canal) + 18000 gal. (Cask Pit)] /lo50 gpm =

300 minutes = 5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br /> Since a boron concentration of 2023 ppm is greater than the 1700 ppm boron concentration required for criticality of the fuel in the DSC, there is no threat of criticality during this 5 hour5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br /> time interval if there is no mixing. If any mixing occurs, this time will be extended. Therefore, the instantaneous mixing model is

Serial No.04-771 Attachment 1, Response to RAI Page 7 of 9 conservative for estimating the time to reach 1700 ppm in the Cask Pit during a boron dilution event.

Localized Dilution from Water Spillinq into the SFP As will be described in the response to Question 3 below, DNC will commit to having an individual continuously present on the SFP operating floor, whenever a DSC is in the SFP, and fuel is in the DSC. This means that any spill of water into the SFP (or transfer canal) will be immediately identified with minimal unborated water entering the SFP or transfer canal before the event is terminated. As such, the amount of unborated water that could be added to the SFP would negligibly affect the SFP boron concentration given the large volume of water in the SFP. Since the SFP boron concentration would be negligibly affected, the Cask Pit boron concentration also would be negligibly affected. If no mixing was to be assumed, any small amount of cold unborated water that did enter the SFP or transfer canal before the event was terminated, would sink to the bottom of the SFP or transfer canal. This volume of cold unborated water that sinks to the bottom is small in relation to the volume of free water below the elevation of the top of the transfer casklDSC. Thus the small volume of cold unborated unmixed water would not reach the fuel inside the DSC.

NRC Question 3:

One of the proposed commitments associated with this request is to establish appropriate controls or measures to minimize the possibility of direct dilution of the cask handling area of S F f prior to DSC loading. Please, explain with more details the controls and measures to be used during fuel handling activities. Also, describe any sources of direct dilution that DNC has considered during the analysis (e.g. addition of cold water directly to the cask pit through a fire hose) that could allow localized boron dilution.

Response

A copy of the current revision of Reference 8 (Technical Evaluation M2-EV-04-0025 Revision 1) of DNCs letter dated November 5, 2004, is provided in Attachment 3. That document specifies what additional controls are necessary to assure that direct dilution to the Cask Pit is minimized.

These additional controls, as required by the Technical Evaluation are summarized as:

When a 32PT DSC is in the Millstone 2 SFP with fuel inside the DSC: then (1) Valve 2-RW-350 must remain closed, and (2) Valves 2-PMW-295, 2-PMW-408 and 2-PMW-409 must be placed in the closed position if all personnel leave the SFP operating deck.

Serial No.04-771 Attachment 1, Response to RAI Page 8 of 9 The purpose of shutting 2-RW-350, which is the SFP cooling discharge isolation valve to the Cask Pit, is to prevent a direct dilution pathway to the Cask Pit.

The purpose of shutting valves 2-PMW-295, 2-PMW-408 and 2-PMW-409 is to ensure that an inadvertent dilution from the nearby PMW hose station does not occur, if all personnel leave the SFP operating deck. However, as will be discussed later in the response to this question, DNC is now committing to continuous coverage on the SFP floor whenever a DSC is in the SFP with fuel in the DSC. Continuous personnel coverage on the SFP floor is more conservative and precludes the need for shutting these three valves.

Also as documented in Technical Evaluation M2-EV-04-0025 Revision 1, DNC identified the only credible inadvertent addition of unborated water directly to the Cask Pit could be through the Primary Makeup Water (PMW) hose station located near the Cask Pit.

The most PMW that could be inadvertently added, and go undetected for a period of time, would be a leak in an un-isolable section of PMW pipe at the nearby PMW hose station. The potential identified leak rate is c 7 gpm through this pipe. As identified in the Technical Evaluation, an un-isolable PMW pipe leak could be quickly terminated by securing the PMW pumps. A leak rate this small (c 7 gpm) would not challenge the 1700 ppm boron limit given termination within the 3 hour3.472222e-5 days <br />8.333333e-4 hours <br />4.960317e-6 weeks <br />1.1415e-6 months <br /> surveillance interval of the SFP area that was previously committed to. With a continuous presence on the SFP floor, identification and termination of leakage pathways will occur very quickly and the potential for inadvertent water additions entering the cask pit will be minimized.

It should also be noted that it is expected during normal DSC handling operations that up to 500 gallons of unborated water may be added to the SFP or Cask Pit. As previously committed to, after each addition of 500 gallons of unborated water to the SFP (or Cask Pit) sampling will be performed to assure that the NUHOMS CofC 1004 TS limit for boron concentration is maintained.

During a conference call with the NRC on December 14, 2004, concerning this question, the possibility was raised of a single personnel error resulting in the inadvertent addition of unborated water into the Spent Fuel Pool or Cask Pit, during the time period when the DSC was loaded with fuel with no one stationed in the area to detect and prevent the error.

To provide assurance against a single personnel error, DNC will commit to keeping an individual present on the SFP floor whenever a DSC is in the SFP with fuel in the DSC.

This is an enhancement to the previous commitment to perform a check every 3 hours3.472222e-5 days <br />8.333333e-4 hours <br />4.960317e-6 weeks <br />1.1415e-6 months <br /> that the pool was not overflowing. As a result of this commitment, detection of an inadvertent dilution of the SFP with a fueled DSC in the SFP will be prompt. The prompt detection of any dilution into the Cask Pit will result in prompt termination of the source of flow into the Cask Pit.

Serial No.04-771 Attachment 1, Response to RAI Page 9 of 9 Given the continuous presence of an individual on the SFP floor, there will not be a significant amount of unborated water that could inadvertently enter and potentially stratify in the Cask Pit.

Serial No.04-771 Docket No. 50-336 Attachment 2 ReconciIiation of Requlatory Requirements List of Requlatow Commitments Millstone Power Station Unit 2 Dominion Nuclear Connecticut, Inc. (DNC)

Serial No.04-771 Attachment 2 Page 1 of 1 The following commitments have been identified in this submittal and are being incorporated into our commitment management program:

1. DNC will revise ISFSI procedures and calculations to state that poison rod assembly (PRA) use is not authorized by the 10CFR50.68(b)(l) exemption.

2. DNC will revise ISFSI procedures to require that when a 32PT DSC is in the MPS2 SFP with fuel inside the DSC, Valve 2-RW-350 must remain closed.

3. DNC will revise ISFSI procedures to require that when a 32PT DSC is in the MPS2 SFP with fuel inside the DSC, Spent Fuel Pool cooling flow must be at least 850 gpm.

4. DNC will revise ISFSI procedures to require that when a 32PT DSC is in the MPS2 SFP with fuel inside the DSC, an individual will remain on the SFP floor at all times, to ensure that no water is unintentionally spilling into the SFP and the SFP is not overflowing.

Serial No.04-771 Docket No. 50-336 Attachment 3 Reconciliation of Requlatorv Requirements Technical Evaluation M2-EV-04-0025 Millstone Power Station Unit 2 Dominion Nuclear Connecticut, Inc. (DNC)

DB or LB document change required? yes r]no TECHNICALEVALUATION for Boron Dilution Analysis for TN32PT Cask in the Millstone 2 Spent Fuel Pool Millstone Unit 2 M2-EV-040025 Revision 1 December 13,2004 Date Cary LaRoe Engineering Appro6 sg2z/

i I-i

Technical Evaluation M2-EV-04-0025Revision 1 Page 2 of 30 12/ 1312004 1 .O PURPOSE This Technical Evaluation analyzes all the potential boron dilution sources to the Millstone 2 Spent Fuel Pool (SFP), and verifies that sufficient time is available to detect and terminate the boron dilution event, to ensure that criticality is not reached in the &el within the NUHOMS 32PT Dry Storage Canister.

2.0 BACKGROUND

Current Situation Millstone 2 (MP2) currentiy credits 600 ppm of soluble boron in the MP2 SFP to maintain km of the fuel in the storage racks of the SFP to less than or equal to 0.95 on a 95/95 basis. The MP2 Operating License Technical Specifications (TS) currently require a minimum of 1720 ppm of soluble boron when fuel is stored in the SFP. This value of 1720 ppm soluble boron concentration ensures that should a boron dilution event occur, sufficient time is available to detect and terminate the boron dilution event prior to reaching 600 ppm of boron, thus ensuring that the fuel in the storage racks of the SFP would have a ker of less than or equal to 0.95. This analysis was previously reviewed and approved by the NRC (Ref 7.15). The boron dilution analysis presented in this evaluation does not alter this existing boron dilution analysis for the firel in the storage racks.

Proposed Situation Millstone 2 is proposing to load fuel in a NUHOMS 32PT Dry Storage Canister (DSC) because the MP2 SFP is nearly full. The DSC would be located in the Cask Laydown Pit of the SFP.The Technical Specifications associated with the NUHOMS 32PT Dry Storage Canister (DSC) require a certain solubte boron concentration or loading and unloading of fuel within the DSC to ensure that of the fuel in the DSC is maintained below 0.95. This DSC TS boron concentration is extremely conservative since it does not credit fuel burnup. This Technical Evaluation demonstrates that if a boron dilution event were to occur in the Millstone 2 SFP, that the boron dilution event could be detected and terminated before criticality is reached by the fuel in the NUHOMS 32PT DSC. The boron dilution analysis presented here for thefiel in the DSC,does not alter the previous boron dilution analysis that was for thefiel in the storage rack.

3.0DISCUSSION Attachment 1 analyzes the potential sources that could dilute the boron concentration in the MP2 SFP.

This analysis demonstrates sufficient time is available to detect and terminate the boron dilution event prior to reaching criticality in the NUHOMS 32PT DSC located in the MP2 SFP.

-~..-. - .-... -

Technical Evaluation M2-EV-04-0025Revision I Page 3 of 30 12/13/2004 4.0 SAFETY SIGNIFICANCE No RAC12 screening or evaluation is required for this Technical Evaluation, since it will support LBDCR LBC-MP2-04-006 that will be submitted to the NRC.

5.0 CONCLUSION

Based on the evaluation of Attachment 1, an unplanned or inadvertent dilution event would be detected and stopped before the boron concentration was reduced to a level that would cause criticality in the fuel contained within the 32PT DSC. The large volume of water required to dilute the SFP, the TS controls on SFP boron concentration, control room alarms, and regular observation of SFP water level would ensure that detection of the dilution event allowed sufficient time to terminate the dilution.

The acceptability of this conclusion is based on the addition of 5 procedural requirements for the ISFSI procedures when a 32PT DSC is in the MP2 SFP with fuel inside the DSC: (1) The requirement to verifi that the transfer canal bulkhead gate is not in place to block the opening to the spent he1 pool.

(2) Visual verification every 3 hours3.472222e-5 days <br />8.333333e-4 hours <br />4.960317e-6 weeks <br />1.1415e-6 months <br /> that the spent fuel pool is not overflowing. (3) Valve 2-RW-350 must remain closed. (4) Valves 2-PMW-295,2-PMW-408 and 2-PMW-409 must be placed in the closed position if all personnel leave the SFP operating deck. ( 5 ) Spent Fuel Pool Cooling Flow must be at least 850 gpm.

6.0 ATTACHMENTS Attachment 1 Millstone Unit 2 Spent Fuel Pool Boron Dilution Analysis for the NUHOMS 32PT DSC Attachment 2 Independent Reviewers Comment Sheet