ML103640203

Mhi'S Responses to US-APWR DCD RAI No. 668-5180 Revision 2 (SRP 19.0)

ML103640203
Person / Time
Site:	05200021
Issue date:	12/27/2010
From:	Ogata Y Mitsubishi Heavy Industries, Ltd
To:	Ciocco J Document Control Desk, Office of New Reactors
References
SRP 19.0, UAP-HF-10344
Download: ML103640203 (12)

Text

Ak MITSUBISHI HEAVY INDUSTRIES, LTD.

16-5, KONAN 2-CHOME, MINATO-KU TOKYO, JAPAN December 27 2010 Document Control Desk U.S. Nuclear Regulatory Commission Washington, DC 20555-0001 Attention: Mr. Jeffrey A. Ciocco, Docket No.52-021 MHI Ref: UAP-HF-10344

Subject:

MHI's Responses to US-APWR DCD RAI No.668-5180 Revision 2 (SRP 19.0)

References:

1) "Request for Additional Information No. 668-5180 Revision 2, SRP Section:

19.01 - determining the Technical Adequacy of Probabilistic Risk Assessment Results for Risk-Informed," dated November 29, 2010.

With this letter, Mitsubishi Heavy Industries, Ltd. ("MHI") transmits to the U.S. Nuclear Regulatory Commission ("NRC") a document entitled "Responses to Request for Additional Information No. 668-5180 Revision 2".

Enclosed are the responses to all of the RAIs that are contained within Reference 1.

Please contact Dr. C. Keith Paulson, Senior Technical Manager, Mitsubishi Nuclear Energy Systems, Inc. if the NRC has questions concerning any aspect of the submittals. His contact information is below.

Sincerely, Yoshiki Ogata, General Manager-APWR Promoting Department Mitsubishi Heavy Industries, LTD.

Enclosure:

1. Responses to Request forAdditional Information No. 668-5180 Revision 2

CC: J. A. Ciocco C. K. Paulson Contact Information C. Keith Paulson, Senior Technical Manager Mitsubishi Nuclear Energy Systems, Inc.

300 Oxford Drive, Suite 301 Monroeville, PA 15146 E-mail: ck-paulson@mnes-us.com Telephone: (412) 373-6466

Enclosure 1 UAP-HF-10344 Docket Number 52-021 Responses to Request for Additional Information No.668-5180 Revision 2 December, 2010

RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION 12/24/2010 US-APWR Design Certification Mitsubishi Heavy Industries Docket No.52-021 RAI NO.: NO. 668-5180 REVISION 2 SRP SECTION: 19.01 - Determining the Technical Adequacy of Probabilistic Risk Assessment Results for Risk-Informed APPLICATION SECTION: 19 DATE OF RAI ISSUE: 11/29/2010 QUESTION NO.: 19.01-9 On page 19.1-964 of the US-APWR DCD, Revision 2, Key Assumption 9, it states, "nitrogen will not be injected in the SG tubes to speed draining in the US-APWR design. The SG tubes will be filled with air during midloop operation". In response to RAI 19.01-3, MHI stated that the pressurizer vent valve, which is 3/4 inch in diameter, provides a sufficient vath path from preventing the RCS pressure to be negative compared to containment during RCS draining.

The staff requests MHI to provide an analysis to show that RCS draining from pressurizer full to midloop conditions (assuming draining by CVCS and a RCS vent of 3/4 inch in diameter) can be performed in the timeframe that MHI assumed.

ANSWER:

The results obtained from a simple calculation shows the pressurizer spray vent path is sufficient to support draindown in the timeframe modeled for RCS draining in the LPSD PRA.

The time for RCS draining from the pressurizer-full water level to the mid-loop water level (the center of the main coolant piping[MCP] NOTEl) was estimated from the RCS water volume drained when evolving from POS 3 to POS 4-1 (the center of the MCP) and the RCS drain rate anticipated in the US-APWR operation. The water volume drained when evolving from RCS full to mid-loop water level is 8040 ft3. With a draindown flow rate of 88 gpm (706 ft3/h) NOTE2, the duration of RCS drain is estimated to be approximately 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />, which is within the timeframe considered in the LPSD PRANOTE 3 The possibility of negative RCS pressure caused by the limited size of RCS vent path during draindown does not restrict draindown flow rate because draindown via the low pressure letdown line is achieved by the CS/RHR pump. Even if the pressure in the pressurizer becomes negative compared to containment pressure, drandown ability will not significantly degrade. It 19.01-9-1

should also be noted that the US-APWR design allows vacuum venting, and the equipment in the RCS is designed to allow negative RCS pressure during the RCS draining process.

Based on the above discussion, it is anticipated that RCS draining to mid-loop (the center of the MCP) can be performed within the timeframe considered in LPSD PRA.

NOTE 1:

While it is assumed in the LPSD PRA that the RCS water level is at the center of MCP, the RCS water level is actually maintained above the center of MCP during POS 4-1...

NOTE 2:

The drain rate of 88 gpm was chosen as a reasonable value based on experience of chemical and volume control system (CVCS) letdown in US operating plants and the capability of the CVCS letdown in the US-APWR design. As stated in the response, negative pressure in the pressurizer compared to the containment that can potentially occur due to the relatively small RCS vent path size, does not restrict the ability of CVCS letdown.

NOTE 3:

The duration of each POS considered in the LPSD PRA is summarized in Table 19.01.09-1, which also shows a comparison of the duration for each POS between experiences of US and US-APWR shutdown schedules assumed in DCD Rev. 2 LPSD risk assessment. The duration is changed from DCD Rev. 2 (of 14 hours1.62037e-4 days <br />0.00389 hours <br />2.314815e-5 weeks <br />5.327e-6 months <br />) to reflect the response to Question No.19.493 of RAI

1. 669-5219 (of 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br />), and the new duration will be used in the LPSD PRA model reported in DCD Rev. 3. The boxed value in Table 19.01.09-1 shows the duration of 14 hours1.62037e-4 days <br />0.00389 hours <br />2.314815e-5 weeks <br />5.327e-6 months <br /> for RCS draining considered in the current LPSD PRA.

Reference

1. Low Power and Shutdown Risk Assessment Benchmarkinq Study, EPRI 1003465, Washington, DC, December 2002.

Impact on DCD There is no impact on DCD.

Impact on R-COLA and S-COLA There is no impact on R-COLA and S-COLA..

Impact on PRA There is no impact on PRA.

19.01-9-2

Table 19.01.09-1 Comparison of Duration for Each POS (Sheet I of 2)

Description EPRI TR 1003465 Duration used in PRA [HI]

POS Group of plant operating Dutrtionio Operational PWR US-nAPWRShutdown Remarks Plant State From To Interpretatin of EPRI Expenence Schdule states [Nr] lBase Case) (Used in DCDren.2)

Low power operation Power operation Insertion of control rods The "normal pressurizerlevel, eady" is 3 2 Not modeled in LPSD PRA Normal Pressurizer Level, assumed to cover the transition from normal power operation to RHR 12 of ct RHR connection Early 2 sdb I0 2S oG stng y withoio of control (RCS temperature reaches connection. 9 8 Not modeled in LPSD PRA (St coolingwithout RHRcooling) rods 350F) The "prssurizr solid is asumed t RHR connection The "pressurizer solid" is assumed to RHR operation Pressurizer Solid, Early cover the state from RHR connection 24 24 2 (RCS is filled with coolant) (RCS temperature Initiation of RCS draining reaches 350F) to initiation of RCS draining.

t"is 29 A

dranin thdleRCSe to intato Mid-loop operation wfth RHR cooling Initiation of RCS Initatio RCS T "midloop, eady 4-1 (from initiatinn of draining the RCS tole) assumed to cover the state from RCS mid-loop level e Opening the SG manhole Midloop. Eady, No Vent initiation of RCS draining to installation 31 11 C.o op n tof the 1SG nozzle lid because the RCS level is kept below the top of the main 4-2 (from opening the SG manhole to Opening the SG Installation of SO nozzle lid coolant pipe.' ' 2 12 Co installation ofthe SG nozzlelid) mahl122 Installation of SG Initiation of RCS suppling The "6 below RCS flange early no vent" is assumed to cover the state from the installation of the SG nozzle Initiation of RCS R" below RCS lange, Early, lid to RCS fange level because (1) the RCSflangelevwl NoVent RCS level is kept below flange level 36 supplying and (2) there is no vent in this configuration. (The RV head is Mid-loop operation with RHR cooling 4-3 C (from installation of the SG nozzle lid to RCS flange level RCS flange level removed after P08 4-3 D.) 36 39 cavity full) 122 D RCS flange level RCS lange level The "before fuel movement ends" is assumed to cover the state from the RCS flange level to the time that the Befor FuelgeMoemn Cafuel movement ends because this 72 SROBflange level Casity full Ends configuration should not be included in the prevous POS due to the venting with the RV head off.

5 Fuel offload Initiation of fuel offload Fuel movement ends 72 83 Not modeled in LPSD PRA 6 No fuel or partial offload Fuel movement ends Initiation of fuel load 5168 f108 Not modeled in LPS° PRA Not mentioned in EPRI report. 168 240 - 184 7 Fuel load nitiation of fuel load Fuel movement ends 72 76 Not modeled in LPSD PRA

Table 19.01.09-1 Comparison of Duration for Each POS (Sheet 2 of 2)

Description EPRI TR 1003465 Duration used in PRA [Hr]

Plant State From To Group of plant operating Duration UOperiona U Shuto Remarks Interpretation of EPRI Experience Schdule states [rj IBar Casel (Usedin DCDre,2l The "after fuel movement ends" is A Cavityfull RCAflangelevel AfterFuelMovement fEndsassumedIn coverthe slatefromthe 72 cavity full to the RCS flange level.

B RCa flange level RCS flange level The "6 below RCS flange late vented" is assumed to cover the state from the Mid-loop operation with RHR cooling a-1 c (from cavity fullto removal ofithe SG RCS flange level RCS flange level RCS flange level to the removal of the 60 56 nozzle lid) SG nozzle lid because (1) the RCS level is kept below the flange level and RRbelowRCA flange. Late, (2) the RV head is offor the 72 ReVented pressurizer safety calves are removed during the instatlation of the RV head.

RCS mid-loop level Removal of the SG nozzle lid In additian, aoter the removal ofthe 52 48 Hr AG anozze lid,the AGmanhole is Co Mid-loop operation with RHR coaning open.

8-2 (from removal of the SG nozzle lid to Removal of the AG Installation ofthe AG manhole 12 12 nozzle lid dosing the SG manhole)

The "midloop, late, not vented" is JL Mid-loop operation with RHR cooling (fromdlosing the SG manhole to RCS Installation of the SG RCS full assumed to cover the state from the Midloop, Late, Not Vented installation of SG monhole to the RCS hl e R fu(frmosig manhole full because them is no vent in this It t configuration. (The SG manhole is closed at the end of POS 8-2.)

R-RHR operation Initiation of the RCS leakage RC ultest 81 (RCAis filiedwith coolant) 10 (R RCA leakagetestRCS)

S leasolatedsfrom Initiation ofthe RCA End of the RCS leakage test leakagehtest 16 21 Not modeled in LPSD PRA (RHRA isolated from RCA) leakage test The "normal pressurizer level, late" is 11RHR operation And ofthe RCA (SIsolation of RHR Normal Pressurizer Level, assumed to cover the state from the 9 98 32 129 4 (RCS is filled with coolant) leakage test t 3( approaches Late RCS full and the RCS lakage test to start-up, 12 Hot standby Isolation of RHR Critial state of the reactor 38 51 Not modeled in LPSD PRA C3at stt at tnthe Powersparatipn Not modeled 1NomdedinLSPR [PAD PRA 14 13 LoIoe prto reactor (flatstart-up)3

RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION 12/24/2010 US-APWR Design Certification Mitsubishi Heavy Industries Docket No.52-021 RAI NO.: NO. 668-5180 REVISION 2 SRP SECTION: 19.01 - Determining the Technical Adequacy of Probabilistic Risk Assessment Results for Risk-Informed APPLICATION SECTION: 19 DATE OF RAI ISSUE: 11/29/2010 QUESTION NO. : 19.01-10 On page 19.1-963 of the DCD, Revision 2, Table 19.1-119, Key Insights and Assumptions, and in Section 5.4.7.2.3.6, of the DCD, it states, "Hydrogen peroxide addition is adopted instead of aeration because it decreases the duration of the mid-loop operation. As a result, the mid-loop operation is needed only to drain the SG primary side water while being able to maintain a high RCS water level for most of the oxidation operation". In US operating plants, often the duration of midloop is based on the time to install and remove SG nozzle dams to isolate the SGs to perform maintenance and testing. As the staff understands, MHI plans to use SG nozzle dams to isolate the SGs to perform maintenance and testing. The staff is requesting MHI to document in Section 5.4.7.2.3.6 and Table 19.1-119 of the DCD why hydrogen peroxide decreases the duration of midloop.

ANSWER:

The following design features of the US-APWR help to reduce the duration of mid-loop operations:

(a) Adoption of hydrogen peroxide (b) Installation and removal of SG nozzle dams at the water level above the top of the main coolant piping (MCP)

Item (b) has been described in DCD Subsection 5.4.7.2.3.6 Item B "High RCS water level." MHI will document a description of Item (a) in Section 5.4.7.2.3.6 Item A "Chemical addition (hydrogen peroxide)." In addition, the above features will be incorporated in Table 19.1-119 as key assumptions during LPSD PRA. Detailed discussion of these items is provided below.

The elevation of the SG nozzles for the US-APWR is higher than the elevation for a typical 19.01-10-1

4-loop PWR plant. This design feature enables SG nozzle dams to be installed and removed when the MCP is filled with water. (Refer to DCD Subsection 5.4.7.2.3.6 Item B). Therefore, installation and removal of SG nozzle dams does not dominate the duration of mid-loop operation in the US-APWR design as it does for a typical 4-loop PWR.

Hydrogen peroxide addition is adopted instead of aeration because it decreases the duration of mid-loop operation; hydrogen peroxide addition operation does not require mid-loop duration.

As a result of adopting hydrogen peroxide addition, which is done at a high RCS water level for most of the oxidation operation and a higher SG nozzle level, mid-loop operation is needed only to drain the SG primary side water, thus reducing overall duration of mid-loop operation.

Impact on DCD The above discussion will be inserted in Section 5.4.7.2.3.6 and Table 19.1-119 as follows:

5.4.7.2.3.6 Mid-loop and Drain Down Operations A. Chemical addition (hydrogen peroxide)

Hydrogen peroxide addition is adopted instead of aeration because it decreases the duration of mid-loop operation: hydrogen peroxide addition operation does not require mid-loop duration.

As a result of adopting hydrogen peroxide addition which is done at a high RCS water level for most of the oxidation operation, and a higher SG nozzle level (Refer to Item B), the-mid-loop operation is needed only to drain the SG primary side water, thus reducing overall duration of mid-loop operation whole being able to mintain a high RGS w.ater level for mo.st of the oxidation opeFatie.

Table 19.1-119 Key Insights and Assumptions (Sheet 8 of 23)

Key Insights and Assumptions Dispositions

'20. Instrumentation piping is installed up side of the RV. No 5.3.3.1 penetrations through the RV are located below the top of the reactor core. This minimizes the potential for a loss of coolant accident by leakage from the reactor vessel, allowing the reactor core to be uncovered.

21. Hydrogen peroxide addition is adopted instead of aeration 5.4.7.2.3.6 to reduce the duration of mid-loop operation.

22. The SG nozzle dam installation level for the US-APWR is 5.4.7.2.3.6 higher than in most conventional operating plants.

Impact on R-COLA and S-COLA There is no impact on R-COLA and S-COLA..

Impact on PRA There is no impact on PRA.

19.01-10-2

RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION 12/24/2010 US-APWR Design Certification Mitsubishi Heavy Industries Docket No.52-021 RAI NO.: NO. 668-5180 REVISION 2 SRP SECTION: 19.01 - Determining the Technical Adequacy of Probabilistic Risk Assessment Results for Risk-Informed APPLICATION SECTION: 19 DATE OF RAI ISSUE: 11/29/2010 QUESTION NO. : 19.01-11 In Table 19.1-119, Key Insights and Assumptions, of the DCD, Revision 2, in assumption 4 on page 19.1-950, assumptions 6 and 7 on page 19.1-960, and assumption 7 on page 19.1-963, please update the disposition of these assumptions to include the new Technical Specification for automatic low pressure letdown line isolation, TS 3.4.8.

ANSWER:

MHI will update the dispositions of the assumptions regarding automatic isolation of the low pressure letdown line. In addition to TS 3.4.8, the response to RAI 19.01-8 (RAI #628-4866) describing the automatic isolation function of the low pressure line will be incorporated in TS 3.9.6. Reference to these new TSs will be added to Table 19.1-119.

Impact on DCD TS 3.4.8 and TS 3.9.6 will be inserted in Sheet 3 (page 19.1-950) and Sheet 16 (page 19.1-963) of Table 19.1-119, as shown on the marked-up page.

Impact on R-COLA There is no impact on R-COLA.

Impact on PRA There is no impact on PRA.

19.01-11-1

Table 19.1-119 Key Insights and Assumptions (Sheet 3 of 23)

Key Insights and Assumptions Dispositions The RHR system is used to provide core cooling when 5.4.7.2.3.6 the RCS must be partially drained to allow maintenance or inspection of the reactor head, SGs, or reactor coolant pump seals.

During mid-loop operation, if the water level of the RCS 5.4.7.2.3.6 drops below the mid-loop level, low pressure letdown TS 3.4.8 lines are isolated automatically. This interlock is useful TS 3.9.6 to prevent loss of reactor coolant inventory.

5. Refueling Water Storage Pit The RWSP is located on the lowest floor inside the 6.3.2.2.5 containment. The coolant and associated debris from a pipe or component rupture (LOCA) and the containment spray drain into the RWSP through transfer pipes.

Four independent sets of ECC/CS strainers located in 6.3.2.2.6 the RWSP. The strainer design includes redundancy, a large surface area to account for potential debris blockage and maintain safety performance, corrosion resistance, and a strainer hole size to minimize downstream effects.

19.01-11-2

Table 19.1-119 Key Insights and Assumptions (Sheet 16 of 23)

Key Insights and Assumptions Dispositions

7. For the US-APWR, low-pressure letdown line isolation 19.2.5 valves are installed. One normally closed air-operated COL 19.3(6) valve is installed in each of two low-pressure letdown lines TS 3.4.8 that are connected to two of four RHR trains. During normal TS 3.9.6 plant cooldown operation, these valves are opened to divert part of the normal RCS flow to the CVCS for purification and the RCS inventory control. These valves are automatically closed and the CVCS is isolated from the RHRS by the RCS loop low-level signal to prevent loss of RCS inventory at mid-loop operation during plant shutdown. There are no features that automate the response to loss of RHR.

19.01-11-3