ML072680835
| ML072680835 | |
| Person / Time | |
|---|---|
| Site: | Indian Point  |
| Issue date: | 09/17/2007 |
| From: | Dacimo F Entergy Nuclear Northeast |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| GL-04-002, NL-07-074 | |
| Download: ML072680835 (11) | |
Text
Entergy Nuclear Northeast Indian Point Energy Center 450 Broadway, GSB
"====
P.O. Box 249 Buchanan, NY 10511-0249 Tel 914 734 6700 Fred Dacimo Site Vice President Administration September 17, 2007 Re:
Indian Point Nuclear Generating Unit No. 2 Docket No. 50-247 NL-07-074 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001
SUBJECT:
Request for Extension of Completion Date for Indian Point Unit 2 Corrective Actions and Modifications Required by Generic Letter 2004-02, "Potential Impact of Debris Blockage on Emergency Recirculation During Design Basis Accidents at Pressurized-Water Reactors"
REFERENCES:
- 1) Entergy letter NL-05-094, 9/01/05, "Response to NRC Generic Letter 2004-02, Potential Impact of Debris Blockage on Emergency Recirculation During Design Basis Accidents at Pressurized-Water Reactors"
- 2) Entergy letter NL-05-0133, 12/15/05, "Supplemental Response to NRC Generic Letter 2004-02, Potential Impact of Debris Blockage on Emergency Recirculation During Design Basis Accidents at Pressurized-Water Reactors"
Dear Sir or Madam:
By letters dated September 1, 2005 (Reference 1) and December 15, 2005 (Reference 2), Entergy provided a response to Generic Letter (GL) 2004-02, "Potential Impact of Debris Blockage on Emergency Recirculation During Design Basis Accidents at Pressurized-Water Reactors", for Indian Points Units 2 and 3. In the September 1, 2005 correspondence, Entergy described plans for plant modifications that included the installation of new sump strainers during the Unit 2 spring 2006 refueling outage. Entergy also described plans for evaluating the adequacy of the strainer design and to address chemical effects once test results to quantify the effect on head-loss had been completed. In the December 15, 2005 correspondence, Entergy provided the results of the downstream effects evaluation and stated that further evaluations were being performed to resolve the issue.
During the spring 2006 refueling outage the original internal recirculation and containment sump screens were replaced by strainers. Other significant attendant modifications were also made including flow channeling. These modifications represent a significant improvement over the original design by providing greatly increased strainer surface areas, reduced debris transport and reduced downstream effects.
4 1(I~
NL-07-074 Docket No. 50-247 Page 2 of 2 This letter requests an extension until restart following the Unit 2 spring 2008 (2R1 8) refueling outage, currently scheduled to start March 25, 2008, to complete modification and licensing activities determined to be needed to achieve full compliance with the regulatory requirements of GL 2004-02. The basis for the proposed extension is provided in Attachment 1. Entergy respectfully requests approval of this extension request by October 19, 2007.
There are no new commitments being made in this submittal.
Should you have any questions or require additional information, please contact Mr. R. Walpole, Manager, Licensing at (914) 734-6710.
I declare under the penalty of perjury that the foregoing is true and correct. Executed on September 17
, 2007.
1
- ely, Fred R. Dacimo Site Vice President Indian Point Energy Center Attachments:
- 1.
Request for Extension of Completion Date for Indian Point Unit 2 Corrective Actions and Modifications Required by Generic Letter 2004-02, "Potential Impact of Debris Blockage on Emergency Recirculation During Design Basis Accidents at Pressurized-Water Reactors" cc:
Mr. John P. Boska, Senior Project Manager, NRC NRR DORL Mr. Samuel J. Collins, Regional Administrator, NRC Region 1 NRC Resident Inspector, IP2 Mr. Paul D. Tonko, President, NYSERDA Mr. Paul Eddy, New York State Dept. of Public Service
ATTACHMENT 1 TO NL-07-074 Request for Extension of Completion Date for Indian Point Unit 2 Corrective Actions and Modifications Required by Generic Letter 2004-02, "Potential Impact of Debris Blockage on Emergency Recirculation During Design Basis Accidents at Pressurized-Water Reactors" ENTERGY NUCLEAR OPERATIONS, INC.
INDIAN POINT NUCLEAR GENERATING UNIT NO. 2 DOCKET NO. 50-247
NL-07-074 Page 1 of 8 Request for Extension of Completion Date for Indian Point Unit 2 Corrective Actions and Modifications Required by Generic Letter 2004-02
1.0 Background
In Generic Letter (GL) 2004-02 (Reference 1), the NRC requested licensees to perform a mechanistic evaluation of the potential for the adverse effects of post-accident debris blockage and operation with debris-laden fluids to impede or prevent the recirculation functions of the Emergency Core Cooling System (ECCS) and Containment Spray System (CSS) following all postulated accidents for which these systems are required. By letters dated September 1, 2005 (Reference 2) and December 15, 2005 (Reference 3), Entergy provided a response to GL 2004-02 for Indian Point Units 2 and 3. In the September 1, 2005 correspondence, Entergy described plans for plant modifications that included the installation of new sump strainers during the Unit 2 spring 2006 refueling outage. Entergy also discussed plans for evaluating the adequacy of the strainer design and to address chemical effects once test results to quantify chemical debris effect on head-loss have been completed. In the December 15, 2005 correspondence Entergy provided the results of the downstream effects evaluation and stated that further evaluations were being performed to resolve the issue.
Information Notice (IN) 2005-26 (Reference 4) informed licensees that recent research results indicate that a simulated sump pool environment containing phosphate and dissolved calcium can rapidly produce a calcium phosphate precipitate that, if transported to a fiber bed covered screen, produces significant head loss. This information is relevant to plants containing phosphate (e.g.,
plants using trisodium phosphate (TSP) as a sump pool buffering agent) and calcium sources (e.g.,
insulation, concrete) that may dissolve within the post-LOCA containment pool with sufficient concentrations to form calcium phosphate precipitate. These test results indicate that substantial head loss can occur if sufficient calcium phosphate is produced in a sump pool and transported to a preexisting fiber bed on the sump screen. IN 2005-26 is applicable to Indian Point Unit 2 because TSP is used as the buffering agent and calcium silicate insulation is used within Containment. In response to IN 2005-26, Entergy concluded that no additional compensatory actions were warranted at that time (Reference 5). The major factors considered in the review included the small amount of calcium silicate at Indian Point Unit 2 when compared to the tested configuration, the compensatory actions that address sump blockage already implemented as a result of Bulletin 2003-01 (Reference 6), and plant specific mitigating features. Since that time additional information indicates that changing the buffer would provide considerable benefits in addressing chemical effects as discussed below.
Entergy installed replacement strainers and other significant attendant modifications, including flow channeling, during the spring 2006 refueling outage. These modifications are more fully described below under 3.2 Mitigative Measures. The evaluations of the adequacy of the strainer design to handle the predicted post LOCA debris and chemical loads have continued in accordance with Reference 7 with justifiable refinements. These evaluations show that in order to ensure compliance with the regulatory requirements of GL 2004-02 additional modifications and License Amendments are required as described in 2.1 Additional Modifications and 2.2 License Amendments.
NL-07-074 Page 2 of 8 2.0 Reason for the Request for Extension There are two independent sumps in containment that provide for the recirculation function. The Recirculation Sump serves the two 100% capacity Internal Recirculation (IR) Pumps, which are the preferred source of cooling in the recirculation phase of an accident. The Containment Sump serves as a backup to the Recirculation Sump, and feeds two 100% capacity Residual Heat Removal Pumps that are located outside Containment. The Containment Sump is not placed in service unless the Internal Recirculation Pumps (or associated equipment) are unavailable.
The current design and licensing basis for the Recirculation and Containment Sumps is that they are functionally redundant at the initiation of recirculation. This redundancy is provided to assure that the ECCS design functions are met in the event of a loss of the recirculation flow path. Recent GL 2004-02 vendor evaluations have shown that, if the additional hardware modifications identified below are made, that both the Recirculation and Containment Sumps are capable of handling the debris loads associated with LBLOCA (Large Break), ABLOCA (Alternate Break) and SBLOCA (Small Break) events. These evaluations exclude chemical effects.
Entergy's strategy for the resolution of GL 2004-02 is to utilize the Alternate Break Methodology to provide margin to accommodate chemical effects. This strategy involves demonstrating that:
(1) For a LBLOCA (a break greater than the ABLOCA) the Recirculation and Containment Sumps, taken together, are capable of accommodating the debris and chemical loads.
In accordance with the ABLOCA methodology a single failure need not be assumed when demonstrating ECCS performance for LBLOCA evaluations. However, use of this approach requires an exemption from 50.46(d) as related to single failure assumptions.
(2) For an ABLOCA (a break with an area equal to the largest line connected to the Reactor Coolant System (RCS) piping per Chapter 6 of Reference 7), the Recirculation and Containment Sumps individually are capable of accommodating the debris and chemical loads. In accordance with the ABLOCA methodology, a single failure must be assumed when demonstrating ECCS performance for ABLOCA evaluations.
Implementation of this strategy requires additional modifications and License Amendments as discussed below.
2.1 Additional Modifications The following modifications are considered necessary to bring the installation into full compliance with GL 2004-02:
(1) Containment Sump Buffering Agent Replacement A measure expected to reduce the magnitude of chemical effects is the replacement of the TSP buffer with Sodium Tetraborate. This replacement will require a modification and a License Amendment. Additional chemical effects options currently under review by Entergy include the reduction of debris amounts by zone of influence (ZOI) refinements, failed coatings characterization, reduction in precipitate formation by utilizing the PWROG WCAP model refinement, reduction in aluminum quantity exposed to containment spray, and chemical testing.
(2) Installation of screens on certain crane wall penetrations
NL-07-074 Page 3 of 8 (3) Installation of grating on the containment sump trench (4) Screen modification to sump level instrument LT-938 housing (5) Installation of containment sump extension strainers in the annulus outside the crane wall 2.2 License Amendments (1) Buffer replacement See 2.1 (1) above. Technical Specification SR 3.6.7.1 specifies the type and quantity of the buffering agent. A License Amendment is required to implement the change from Trisodium Phosphate to Sodium Tetraborate.
(2) Exemption to the Single Failure Requirements of 10CFR 50.46(d)
The Entergy strategy for resolving GL 2004-02 utilizes the Alternate Break Methodology as endorsed by the NRC in Reference 7 In order to fully realize the benefits associated with the Alternate Break Methodology, Entergy proposes not to assume a single failure for the LBLOCA evaluation of sump strainer performance. Therefore, a License Amendment is required to exempt LBLOCA analysis from the single failure requirement of 10CFR 50.46(d).
3.0 Technical Basis for Proposed Extension Entergy considers that the conditions at Indian Point Unit 2 meet the criteria identified in SECY 0078 (Reference 8) for extension beyond the completion date of December 31, 2007 specified in GL 2004-02. The SECY criteria are, Proposed extensions to permit changes at the next outage of opportunity after December 2007 may be acceptable if, based on the licensee's request, the staff determines that:
The licensee has a plant-specific technical/experimental plan with milestones and schedule to address outstanding technical issues with enough margin to account for uncertainties.
The licensee identifies mitigative measures to be put in place prior to December 31, 2007, and adequately describes how these mitigative measures will minimize the risk of degraded ECCS [emergency core cooling system] and CSS [containment spray system] functions during the extension period.
For proposed extensions beyond several months, a licensee's request will more likely be accepted if the proposed Mitigative measures include temporary physical improvements to the ECCS sump or materials inside containment to better ensure a high level of ECCS sump performance.
Indian Point Unit 2 meets these criteria as described below.
NL-07-074 Page 4 of 8 3.1 Plant Specific Technical/Experimental Plan In Reference 2, Entergy submitted a description of the actions it is taking to address GL 2004-02, and updated that response in Reference 3. The key actions of the plan are summarized below.
(1) Completed Actions (a) Installation of recirculation sump, containment (excluding extension) sump strainers and flow channeling modifications. The vast majority of the Unit 2 plant modifications to address GL 2004-02 were installed during the spring 2006 refueling outage.
(b) Strainer debris head loss testing.
(c) Strainer bypass testing.
(d) Dissolution/erosion measurements of plant specific calcium silicate.
(e) Debris generation, debris transport, and downstream effects calculations and evaluations.
(2) Actions in Progress (a) Development of chemical effects test protocol.
(3) Planned Actions (a) Installation of modifications as described in 2.1 above during 2R18 which is scheduled to begin on March 25, 2008.
(b) License Amendments as described in 2.2 above required for implementation prior to restart following 2R1 8.
(c) Chemical effects testing scheduled for November 2007.
(d) Reevaluate downstream effects to incorporate WCAP-1 6406P Revision 1 scheduled for completion November 2007.
(e) Preparation of a program to inspect and control containment coatings scheduled for completion November 2007.
(f) Preparation of a program to inspect and control containment cleanliness scheduled for completion November 2007.
(g) Issue strainer certification/qualification report to include chemical effects scheduled for February 2008.
The extent of the modifications and analyses already performed and those in progress and planned demonstrate that Entergy has developed a plant-specific technical/experimental plan, with
NL-07-074 Page 5 of 8 milestones and schedule to address outstanding technical issues including sufficient margin to account for uncertainties.
3.2 Mitigative Measures Entergy has put in place the following mitigative measures that minimize the risk of degraded ECCS and CSS functions during the extension period.
(1) Installation of replacement sump strainers During the spring 2006 refueling outage the original IR (approx. 50 ft2) and Containment Sump screens (approx. 30 ft2) were replaced. The replacement strainers are of a modular design and have respective surface areas of approximately 3200 ft2 and 412 ft2. Each strainer is a matrix of multi-tube (Top-Hat) modules fabricated from perforated plate and mounted in a horizontal orientation. The perforated plate has circular holes sized to 3/32" diameter. The strainer tube modules have four concentric, parallel perforated surfaces for straining debris from the water and the design maximizes the interstitial volume to strainer surface area ratio to better accommodate the predicted fiber to particulate debris loading.
The Top-Hats feature an internal vortex suppressor which helps prevent air ingestion into the piping system. In addition, the Top-Hats also possess a bypass elimination feature that minimizes fiber debris bypass. The bypass elimination feature dramatically reduces the magnitude of fiber debris bypassing the screens. These strainers were designed to minimize fiber debris bypass to reduce downstream effects, and to provide a substantial increase in available strainer surface area. The new strainers provide increased margin against blockage and excessive wear of downstream components due to debris in the water.
(2) Installation of flow channeling modifications The original containment layout was not conducive to debris settlement. Flow channeling, which involves diverting or distributing flows to reduce average velocities and turbulence levels offer a relatively efficient method for reduction of debris that is transported to the sumps. The installed flow channeling modifications divert break and containment spray flows inside the crane wall down through the reactor cavity then up and out through the in-core instrumentation tunnel and then towards the sumps. The reactor cavity/in-core instrumentation tunnel offers an expansive area that produces velocities low enough to allow settlement of small and large debris pieces, free from the turbulence inducing break flow and containment spray effect. Consequently, only fines and particulate matter may remain transportable. The flow channeling modifications provide increased margin against strainer blockage independent of the benefit of larger strainer area.
(3) Implementation of mitigative measures in response to NRC Bulletin 2003-01 In addition to the plant modifications described above, current mitigative measures in response to NRC Bulletin 2003-01, "Potential Impact of Debris Blockage on Emergency Sump Recirculation at Pressurized-Water Reactors" (Reference 6), are in place and continue to be in effect. Entergy's response to Bulletin 2003-01 is documented in References 9 and 10. By letter dated August 22, 2005 (Reference 11), the NRC staff concluded that Entergy's compensatory measures that have been implemented to reduce the risk which may be associated with potentially degraded or nonconforming emergency
NL-07-074 Page 6 of 8 core cooling system and containment spray system recirculation functions were responsive to and met the intent of Bulletin 2003-01.
These measures include:
(a) Provision of training to the licensed operators to present the mechanisms and potential consequences of sump clogging.
(b) Provision of procedural guidance within the Emergency Operating Procedures (EOPs) on symptoms and identification of sump blockage.
(c) Development of a new EOP (ECA-1.3, "Loss of Emergency Coolant Recirculation Caused by Sump Blockage").
(d) Provision of procedural guidance not to start a second recirculation pump if cavitation is expected.
(e) Provision of procedural guidance to consider refilling the Refueling Water Storage Tank should sump blockage be a concern.
(4) Implementation of mitigative measures that assure containment cleanliness, foreign material exclusion, and sump and flow channel/barrier operability:
(a) Containment cleanliness is assured by procedural controls (OAP-007 "Containment Entry and Egress") that apply after each containment entry and prior to exiting mode 5 during plant startup.
(b) Foreign material exclusion is assured by procedural controls (IP-SMM-MA-118 "Foreign Materials Exclusion") that apply to inspection, operation, maintenance and outage activities.
(c) Operability of the sumps and flow channel/barrier operability is satisfied by Engineering visual inspection and procedure step signoff (OAP-007 "Containment Entry and Egress").
(5) Implementation of mitigative measures to assure that potential sources of debris in containment are minimized:
(a) Procedure changes to ensure that as part of the engineering change process, materials (including insulation) that are introduced to containment are identified and evaluated to determine if they could affect sump performance or lead to downstream equipment degradation (EN-DC-115 "Engineering Change Development").
(b) Procedure changes to ensure that configuration control of insulation inside containment is maintained in compliance with GL 2004-02 (0-SYS-404-GEN).
These mitigative measures are already in place and minimize the risk of degraded ECCS and CSS functions during the extension period.
NL-07-074 Page 7 of 8 3.3 Generic Letter 2004-02 Basis for Continued Operation In addition to the mitigative measures identified above the basis for continued operation provided by GL 2004-02 include a number of factors that remain applicable to Indian Point Unit 2 during the period of the proposed extension.
The NRC staff provided a justification for continued operation (JCO) (as discussed in Reference 1), that justifies continued operation of pressurized water reactors through December 31, 2007.
Elements of the JCO applicable to Unit 2 include:
(1) The containment is compartmentalized making transport of debris to the sump difficult.
(2) Switchover to recirculation from the sump during a LBLOCA would not occur until 20 to 30 minutes after accident initiation, allowing time for much of the debris to settle in other places within containment.
(3) The probability of the initiating event (i.e., large and intermediate-break LOCAs) is extremely low.
(4) Leak-before-break (LBB) has been approved by the NRC in relation to breaks in the reactor coolant loop primary piping. Qualified piping is of sufficient toughness that it will most likely leak rather than rupture.
(5) The NPSH analysis for the IR and the RHR pumps do not credit containment overpressure.
4.0 References
- 1. NRC Generic Letter 2004-02, "Potential Impact of Debris Blockage on Emergency Recirculation During Design Basis Accidents at Pressurized-Water Reactors," dated September 13, 2004.
- 2.
Entergy Letter NL-05-094, "Response to NRC Generic Letter 2004-02, 'Potential Impact of Debris Blockage on Emergency Recirculation During Design Basis Accidents at Pressurized-Water Reactors,"' dated September 1, 2005.
- 3. Entergy Letter NL-05-133, "Supplemental Response to NRC Generic Letter 2004-02, 'Potential Impact of Debris Blockage on Emergency Recirculation During Design Basis Accidents at Pressurized-Water Reactors,"' dated December 15, 2005.
- 4. Information Notice 2005-26, "Results of Chemical Effects Head Loss Tests in a Simulated PWR Sump Pool Environment," dated September 16, 2005.
- 5.
Entergy Letter NL-05-126, "Industry Actions Resulting from Information Notice 2005-26," dated November 28, 2005.
- 6. NRC Bulletin 2003-01, "Potential Impact of Debris Blockage on Emergency Sump Recirculation at Pressurized-Water Reactors", June 9, 2003.
- 7. Nuclear Energy Institute (NEI) 04-07, Volume 1, "Pressurized Water Reactor Sump Performance Methodology," and NEI 04-07, Volume 2, "Safety Evaluation by the Office of
NL-07-074 Page 8 of 8 Nuclear Reactor Regulation Related to NRC Generic Letter 2004-02," Revision 0, dated December 2004.
- 8. SECY-06-0078, from L. A. Reyes, NRC Executive Director for Operations, to NRC Commissioners, "Status of Resolution of GSI-1 91, 'Assessment of [Effect of] Debris Accumulation on PWR [Pressurized Water Reactor] Sump Performance,"' dated March 31, 2006.
- 9. Entergy Letter NL-03-128, "60 Day Response to NRC Bulletin 2003-01 Regarding Potential Impact of Debris Blockage of Emergency Sumps" dated August 7, 2003.
- 10. Entergy Letter NL-04-151, "Reply to RAI Regarding Bulletin 2003-01, 'Potential Impact of Debris Blockage on Emergency Sump Recirculation at Pressurized-Water Reactors,"' dated December 8, 2004.
- 11. NRC Letter, "Indian Point Nuclear Generating Unit Nos. 2 and 3 - Response to NRC Bulletin 2003-01, "Potential Impact of Debris Blockage on Emergency Sump Recirculation at Pressurized-Water Reactors."" (TAC Nos. MB9582 and MB9583) dated August 22, 2005.