ML043570209

E-mail Ennis, NRR, to Daflucas, Entergy, New RAI Questions, on Vermont Yankee EPU

ML043570209
Person / Time
Site:	Vermont Yankee
Issue date:	06/30/2004
From:	Richard Ennis Office of Nuclear Reactor Regulation
To:	Daflucas R Entergy Nuclear Northeast
References
Download: ML043570209 (15)

Text

Rick Ennis - New RAI questions Page Paie 1ill11 Rick Ennis New RAI auestions From: Rick Ennis To: Ronda Daflucas Date: Wed, Jun 30, 2004 5:26 PM

Subject:

New RAI questions Ronda, The attached file adds 2 new RAI questions (questions 32 and 33, starting on page 5) from Rich Lobel. I realize that your 7/30 response time for this set of RAls was not based on these additional questions. If you think this will affect the response time, please let Allen Howe know ASAP since he has the RAI letter for signature.

Thanks, Rick CC: Allen Howe; Donna Skay;Richard Lobel

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Mail Envelope Properties (40E33019.BDB:115: 20516)

Subject:

New RAI questions Creation Date: Wed, Jun 30, 2004 5:26 PM From: Rick Ennis Created By: RXE@nrc.gov Recipients Action Date & Time owf2-po.OWFNDO DMS6 CC (Donna Skay) Opened 07/14 8:17 AM RML CC (Richard Lobel) owf4_po.OWFNDO Delivered 06/30 5:26 PM AGH1 CC (Allen Howe) Opened 07/01 7:19 AM entergy.com rdafluc (Ronda Daflucas)

Post Office Delivered Route owf2.po.OWFNDO Pending owf4_po.OWFNDO 06/30 5:26 PM Pending entergy.com Files Size Date & Time MESSAGE 986 Wednesday, June 30, 2004 5:26 PM raiO3 mc0761.wpd 50280 Wednesday, June 30, 2004 5:21 PM Options Auto Delete: No Expiration Date: None Notify Recipients: Yes Priority: Standard Reply Requested: No Return Notifilcation: None Concealed

Subject:

No Security: Standard To Be Delivered: Immediate Status Tracking: Delivered & Opened

Rick Ennis - raiO3 mcO761.wod Paged1 Pacie 1Ii Rick Ennis rai03 mc0761 .wDd Mr. Michael Kansler President Entergy Nuclear Operations, Inc.

440 Hamilton Avenue White Plains, NY 10601

SUBJECT:

REQUEST FOR ADDITIONAL INFORMATION - EXTENDED POWER UPRATE, VERMONT YANKEE NUCLEAR POWER STATION (TAC NO. MC0761)

Dear Mr. Kansler:

By letter dated September 10, 2003, as supplemented on October 1, 2003, October 28, 2003 (2 letters), January 31, 2004 (2 letters), March 4, 2004, and May 19, 2004, Entergy Nuclear Vermont Yankee, LLC and Entergy Nuclear Operations, Inc., submitted a proposed license amendment to the U.S. Nuclear Regulatory Commission (NRC) for the Vermont Yankee Nuclear Power Station (VYNPS). The proposed amendment, "Technical Specification Proposed Change No. 263, Extended Power Uprate" would allow an increase in the maximum authorized power level for VYNPS from 1593 megawatts thermal (MWT) to 1912 MWT.

The NRC staff is reviewing your submittal and has determined that additional information is required to complete the review. The specific information requested is addressed in the enclosure.

We request that the additional information be provided by July 30, 2004. The response timeframe was discussed with Ms. Ronda Daflucas of your staff on June 30, 2004. If circumstances result in the need to revise your response date, or if you have any questions, please contact me at (301) 415-1420.

Sincerely, Richard B. Ennis, Senior Project Manager, Section VY Project Directorate I Division of Licensing Project Management Office of Nuclear Reactor Regulation Docket No. 50-271

Enclosure:

As stated cc w/encl: See next page

I Rick Ennis - raiO3 mc0761.wpd Pae2 Rick Ennis rai03 mc0761 .wDd Pane 2 Mr. Michael Kansler President Entergy Nuclear Operations, Inc.

440 Hamilton Avenue White Plains, NY 10601

SUBJECT:

REQUEST FOR ADDITIONAL INFORMATION - EXTENDED POWER UPRATE, VERMONT YANKEE NUCLEAR POWER STATION (TAC NO. MC0761)

Dear Mr. Kansler:

By letter dated September 10, 2003, as supplemented on October 1, 2003, October 28, 2003 (2 letters), January 31, 2004 (2 letters), March 4, 2004, and May 19, 2004, Entergy Nuclear Vermont Yankee, LLC and Entergy Nuclear Operations, Inc., submitted a proposed license amendment to the U.S. Nuclear Regulatory Commission (NRC) for the Vermont Yankee Nuclear Power Station (VYNPS). The proposed amendment, *Technical Specification Proposed Change No. 263, Extended Power Uprate' would allow an increase in the maximum authorized power level for VYNPS from 1593 megawatts thermal (MWT) to 1912 MWT.

The NRC staff is reviewing your submittal and has determined that additional information is required to complete the review. The specific information requested is addressed in the enclosure.

We request that the additional information be provided by July 30, 2004. The response timeframe was discussed with Ms. Ronda Daflucas of your staff on June 30, 2004. If circumstances result in the need to revise your response date, or if you have any questions, please contact me at (301) 415-1420.

Sincerely, Richard B. Ennis, Senior Project Manager, Section VY Project Directorate I Division of Licensing Project Management Office of Nuclear Reactor Regulation Docket No. 50-271

Enclosure:

As stated cc w/encl: See next page DISTRIBUTION:

PUBLIC TChan, EMCB-B JCai, IROB-B HWalker, SPSB-C PDI-2 Reading RDavis, EMCB-B JBongarra, IROB-B MHart, SPSB-C AHowe LLund, EMCB-C JTappert, RLEP-C FAkstulewicz, SRXB-A REnnis KParczewski, EMCB-C Simboden, RLEP-C EKendrick, SRXB-A AMcMurtray KManoly, EMEB-B JYerokun, SPLB-A CAnderson, RGN I CWu, EMEB-B DReddy, SPLB-A EMarinos, EEIB-A TScarbrough, EMEB-B SWeerakkody, SPLB-B HGarg, EEIB-A DThatcher, IPSB-A RGallucci, SPLB-B RJenkins, EEIB-B RPettis, IPSB-A MRubin, SPSB-A NTrehan, EEIB-B SKlementowicz, IPSB-B M~tutzke, SPSB-A MMitchell, EMCB-A RPedersen, IPSB-B RDennig, SPSB-C BElliot, EMCB-A DTrimble, IROB-B RLobel, SPSB-C ACCESSION NO.: ML041740039 OFFICE PDI-VY/PM PDI-VY/SC NAME REnnis AHowe DATE R OFFICIAL RECORD COPY

IRick Ennis - raiO3 mc0761.wpd Page 31j I Rick Ennis rai03 mc0761 .wpd Page 311 Vermont Yankee Nuclear Power Station cc:

Regional Administrator, Region I Ms. Carla A. White, RRPT, CHP U. S. Nuclear Regulatory Commission Radiological Health 475 Allendale Road Vermont Department of Health King of Prussia, PA 19406-1415 P.O. Box 70, Drawer #43 108 Cherry Street Mr. David R. Lewis Burlington, VT 05402-0070 Shaw, Pittman, Potts & Trowbridge 2300 N Street, N.W. Mr. James M. DeVincentis Washington, DC 20037-1128 Manager, Licensing Vermont Yankee Nuclear Power Station Ms. Christine S. Salembier, Commissioner P.O. Box 0500 Vermont Department of Public Service 185 Old Ferry Road 112 State Street Brattleboro, VT 05302-0500 Montpelier, VT 05620-2601 Resident Inspector Mr. Michael H. Dworkin, Chairman Vermont Yankee Nuclear Power Station Public Service Board U. S. Nuclear Regulatory Commission State of Vermont P.O. Box 176 112 State Street Vernon, VT 05354 Montpelier, VT 05620-2701 Director, Massachusetts Emergency Chairman, Board of Selectmen Management Agency Town of Vernon ATTN: James Muckerheide P.O. Box 116 400 Worcester Rd.

Vernon, VT 05354-0116 Framingham, MA 01702-5399 Operating Experience Coordinator Jonathan M. Block, Esq.

Vermont Yankee Nuclear Power Station Main Street 320 Governor Hunt Road P.O. Box 566 Vernon, VT 05354 Putney, VT 05346-0566 G. Dana Bisbee, Esq. Mr. John F. McCann Deputy Attorney General Director, Nuclear Safety Assurance 33 Capitol Street Entergy Nuclear Operations, Inc.

Concord, NH 03301-6937 440 Hamilton Avenue White Plains, NY 10601 Chief, Safety Unit Office of the Attorney General Mr. Gary J. Taylor One Ashburton Place, 19th Floor Chief Executive Officer Boston, MA 02108 Entergy Operations 1340 Echelon Parkway Ms. Deborah B. Katz Jackson, MS 39213 Box 83 Shelburne Falls, MA 01370

Rick Ennis - raiO3 mcO761.wpd Page Page 4 4 Rick Ennis raio3 mc0761 .wpd Vermont Yankee Nuclear Power Station cc:

Mr. John T. Herron Sr. VP and Chief Operating Officer Mr. Kenneth L. Graesser Entergy Nuclear Operations, Inc. 38832 N. Ashley Drive 440 Hamilton Avenue Lake Villa, IL 60046 White Plains, NY 10601 Mr. James Sniezek Mr. Danny L. Pace 5486 Nithsdale Drive Vice President, Engineering Salisbury, MD 21801 Entergy Nuclear Operations, Inc.

440 Hamilton Avenue Mr. Ronald Toole White Plains, NY 10601 1282 Valley of Lakes Box R-10 Mr. Brian O'Grady Hazelton, PA 18202 Vice President, Operations Support Entergy Nuclear Operations, Inc. Ms. Stacey M. Lousteau 440 Hamilton Avenue Treasury Department White Plains, NY 10601 Entergy Services, Inc.

639 Loyola Avenue Mr. Michael J. Colomb New Orleans, LA 70113 Director of Oversight Entergy Nuclear Operations, Inc. Mr. Raymond Shadis 440 Hamilton Avenue New England Coalition White Plains, NY 10601 Post Office Box 98 Edgecomb, ME 04556 Mr. John M. Fulton Assistant General Counsel Mr. James P. Matteau Entergy Nuclear Operations, Inc. Executive Director 440 Hamilton Avenue Windham Regional Commission White Plains, NY 10601 139 Main Street, Suite 505 Brattleboro, VT 05301 Mr. Jay K. Thayer Site Vice President Mr. William K. Sherman Entergy Nuclear Operations, Inc. Vermont Department of Public Service Vermont Yankee Nuclear Power Station 112 State Street P.O. Box 0500 Drawer 20 185 Old Ferry Road Montpelier, VT 05620-2601 Brattleboro, VT 05302-0500

l Rick Ennis - raiO3 mcO761 .wpd Page Rick Ennis rai03 mc0761 .wpd Page 51 5I 5

REQUEST FOR ADDITIONAL INFORMATION REGARDING PROPOSED LICENSE AMENDMENT EXTENDED POWER UPRATE VERMONT YANKEE NUCLEAR POWER STATION DOCKET NO. 50-271 By letter dated September 10, 2003, as supplemented on October 1, 2003, October 28, 2003 (2 letters), January 31, 2004 (2 letters), March 4, 2004, and May 19, 2004 (References 1 through 8), Entergy Nuclear Vermont Yankee, LLC and Entergy Nuclear Operations, Inc.

(Entergy or the licensee), submitted a proposed license amendment to the U.S. Nuclear Regulatory Commission (NRC) for the Vermont Yankee Nuclear Power Station (VYNPS). The proposed amendment, "Technical Specification Proposed Change No. 263, Extended Power Uprate" would allow an increase in the maximum authorized power level for VYNPS from 1593 megawatts thermal (MWT) to 1912 MWT.

The NRC staff is reviewing your Extended Power Uprate (EPU) amendment request and has determined that additional information is required to complete the review. The specific information requested is addressed in the following request for additional information (RAI).

Note, the question numbers are a continuation of the numbering used in the RAI issued by the NRC on May 28, 2004.

- - - . - - - - - - - - - - - __ __ .. , - -- - - - . - __- - - - - - - - - - -,. - - I--- - _- . . - -_ - - 11 -I e Rick Ennis - raiO3 mcO761.wpd Pagie Rick Ennis rai03 mc0761 .wpd Paae 6I 61 6

Plant Systems Branch (SPLB)

Balance of Plant Section (SPLB-A)

Reviewer: Devender Reddy

7. Spent Fuel Pool Cooling and Cleanup System:

(Reference 1, Attachment 6, Section 6.3) a) Spent Fuel Pool (SFP) Cooling Capacity:

Please describe the analyses that were performed and assumptions and input parameters that were used for the proposed EPU to address the following review criteria in NRC Review Standard, RS-001, Attachment 2 to Matrix 5, "Supplemental Spent Fuel Pool Cooling Review Criteria," Section 3.1.1.1:

i) heat removal capability is based on bounding estimates of ultimate heat sink temperature, cooling system flow rates, and heat exchanger performance (e.g., fouling and tube plugging).

ii) alternate heat removal paths (e.g., evaporative cooling) should be appropriately validated and based on bounding input parameter values (e.g., air temperature, relative humidity, and ventilation flow rate).

b) Heat Removal Capability and Limiting Case for Core Offload:

Table 6-3 in Attachment 6 to Reference 1 provides five SFP cooling/core offload configurations. Please update this table to include the following configurations discussed in the VYNPS Updated Safety Analysis Report (UFSAR),

Section 10.5.5, page 10.5-9, third paragraph:

i) Limiting Normal Batch (one-third core) Off load: One train (one heat exchanger and one pump) of Standby Fuel Pool Cooling Subsystem (SFPCS) in service, and ii) Limiting Full Core Offload: Both trains (two heat exchangers and two pumps) of SFPCS in service.

Also, discuss the assumptions and input parameters that were used in the analyses for the two additional configurations discussed above and confirm that they are consistent with the existing plant licensing basis and that the worst-case ultimate heat sink temperatures were used.

I IRick Ennis - raiO3 mcO761.wpd Page 7 7

8. Service Water Systems (SWS):

(Reference 1, Attachment 6, Section 6.4) a) In Section 6.4.1.1 of Attachment 6 to Reference 1, it is stated that:

"The performance of the safety-related portion of the SW system during and following the most demanding design basis event, the LOCA, was demonstrated.

Adequate SW system heat transfer capabilities exist at CPPU [constant pressure power uprate] to support the above components. In addition, the SW flow rates do not change."

i) With regard to performance, heat-loads, heat transfer capabilities, flow rates, and flow velocities in the SWS for post CPPU conditions, please explain how the above conclusions were reached.

ii) Also, describe the analyses that have been performed, assumptions, and input parameters that were used; and explain the impact of the proposed EPU on UFSAR Section 10.6.4, Safety Design Bases, Items 1, 2, and 3.

b) Regarding the Residual Heat Removal Service Water (RHRSW) system, in Section 6.4.1.3 of Attachment 6 to Reference 1, it is stated that:

"The post-LOCA containment and suppression pool responses have been calculated based on an energy balance between the post-LOCA heat loads and the existing heat removal capacity of the RHR and RHRSW systems. As discussed in 3.5.2 and 4.1.1, the existing suppression pool structure and associated equipment have been reviewed for acceptability based on this increased post-LOCA suppression pool temperature....Thus, the RHRSW system has sufficient capacity to serve as the coolant supply for long-term core and containment cooling as required for CPPU conditions. The RHRSW system flow rate is not changed."

i) With regard to performance, heat-loads, heat transfer capabilities, flow rates, and flow velocities in the RHRSW system for post CPPU conditions, please explain how the above conclusions were reached.

ii) Also, describe the analyses that have been performed, assumptions, and input parameters that were used; and explain the impact of the proposed EPU on the UFSAR Section 10.7.4, Safety Design Bases, Item 1.

c) Confirm that the analyses performed for the proposed EPU are consistent with the existing plant licensing basis and that the worst-case ultimate heat sink temperature was used in calculating flow requirements of the safety-related SWS and the RHRSW systems for the proposed CPPU conditions.

!Rick Ennis - rai03 mcO761.wpd Page 8 l 8

d) Please describe any impacts that the proposed EPU will have on the issues discussed in Generic Letters 89-13 and 96-06 including the basis for your determination. Also, confirm that water hammer and two-phase flow will not occur in the SWS, RHRSW, and other safety-related cooling water systems due to the EPU.

9. Ultimate Heat Sink (UHS) / Alternate Cooling System (ACS):

(Reference 1, Attachment 6, Section 6.4.5) a) In Section 6.4.5 of Attachment 6 to Reference 1, it is stated that:

"The ACS was evaluated for CPPU in a manner that is similar to the UHS evaluation for newer plants (e.g., inventory requirements and heat removal capability with increased decay heat)....The heat removal requirements of the following affected components during the ACS operating mode have been evaluated and found to be acceptable at CPPU...."

I) With regard to performance, heat-loads, heat transfer capabilities, flow rates, and flow velocities in the ACS for post CPPU conditions, please explain how the above conclusions were reached.

ii) Also, describe the analyses that have been performed, assumptions, and input parameters that were used; and explain the impact of the proposed EPU on UFSAR Section 10.8.2, Safety Design Bases, Items 1, 2, and 3.

b) In Reference 5, Attachment 6, MATRIX 5, Page 8, SE 2.5.3.4, it is stated that no SW flow or SW supply temperature changes are required to support the CPPU normal, LOCA or shutdown operations. Please explain.

c) Confirm that the analyses performed for the proposed EPU are consistent with the existing plant licensing basis and that the worst-case ultimate heat sink temperature was used in calculating flow requirements of the ACS for the proposed CPPU conditions.

d) In Reference 1, Attachment 6, Section 6.4.5, as well as in Reference 5, Attachment 6, MATRIX 5, Page 8, SE 2.5.3.4, it is stated that a modification to re-circulate ACS (RHRSW) pump motor cooler water back to the cooling tower, instead of discharging it to the river, is planned to ensure adequate inventory to meet the 7-day requirement associated with the ACS design-basis functional scenario. Please provide a description of the modification, including a flow diagram. In addition, discuss the regulatory requirements applicable to the modification.

Rick Ennis - raiO3 mcO761.wpdq, Page_9 l 9

Probabilistic Safety Assessment Branch (SPSB)

Containment and Accident Dose Assessment Section (SPSB-C)

Reviewers: Richard Lobel (Containment), Harold Walker (HVAC), Michelle Hart (Dose) 28.* Provide additional information regarding the potential impact of the CPPU on those HVAC systems discussed in the Standard Review Plan sections 6.4, 6.5.1, 9.4.1, 9.4.2, 9.4.3, 9.4.4 and 9.4.5. This should include a discussion of the impact, if any, during both normal and post-accident operations resulting from increases in heat loads due to CPPU and the bases for your determination of system acceptability post-CPPU.

• Note, this question was previously transmitted to the licensee via e-mail on June 3, 2004.

29. Please provide the design basis and realistic values of inputs used in the determination of emergency core cooling system (ECCS) pump available net positive suction head (NPSH) (i.e., the values used in the MAAP probabilistic risk assessment (PRA) calculations and the SHEX calculations). Please include:

a) service water temperature b) initial containment temperature c) initial containment pressure d) initial drywell and wetwell humidity e) initial suppression pool temperature f) drywell and wetwell airspace volume g) suppression pool water volume

30. Please describe how containment leakage is modeled in the design basis NPSH calculations. Is MSIV leakage included? If not, why not?

31. The VYNPS Individual Plant Examination (IPE) report dated December 21, 1993 (Reference letter BW 93-139), Section 3.1.2.1, Large LOCA Event Tree," Event Al (Alternate Injection), models the failure of long-term core cooling due, in part, to "loss of LP/CS NPSH at high suppression pool temperature if the containment vent opens and the operator fails to control pressure by reclosing the vent." Concerning the accident sequence modeling for large LOCAs, describe all differences between the IPE and the PRA performed to support the EPU application.

32. Please provide input to the computer calculation (data in ASCII format) of the containment accident pressure used for ECCS pump NPSH calculations. Please verify that the input is consistent with the VYNPS emergency operating procedures. In addition, provide a schematic of containment with dimensions and ECCS schematic for this analysis . The input parameters needed are included in Attachment 1.

Ri~ck_ Enni.-_rai03 mc0761.ywpd___ Page 10 I 10

33. Please provide the results of the containment accident pressure calculation used for ECCS pump NPSH calculations. Include:

a) drywell pressure vs. time b) drywell temperature vs. time c) wetwell pressure vs. time d) wetwell air temperature vs. time e) suppression pool temperature vs. time f) suppression pool level vs. time

Rik nsraiO3 mcO76ljwpd, _Page_ Page 1i1 1 REFERENCES

1) Entergy letter (BVY 03-80) to NRC dated September 10, 2003, "Vermont Yankee Nuclear Power Station, Technical Specification Proposed Change No. 263, Extended Power Uprate"

2) Entergy letter (BVY 03-90) to NRC dated October 1, 2003, "Vermont Yankee Nuclear Power Station, Technical Specification Proposed Change No. 263, Supplement No. 1, Extended Power Uprate -Technical Review Guidance"m

3) Entergy letter (BVY 03-95) to NRIC dated October 28, 2003, "Vermont Yankee Nuclear Power Station, Technical Specification Proposed Change No. 263, Supplement No. 2, Extended Power Uprate - Grid Impact Study"

4) Entergy fetter (BVY 03-98) to NRC dated October 28, 2003, "Vermont Yankee Nuclear Power Station, Technical Specification Proposed Change No. 263, Supplement No. 3, Extended Power Uprate - Updated Information"

5) Entergy letter (BVY 04-009) to NRC dated January 31, 2004, "Vermont Yankee Nuclear Power Station, Technical Specification Proposed Change No. 263, Supplement No. 4, Extended Power Uprate - NRC Acceptance Review"

6) Entergy letter (BVY 04-008) to NRC dated January 31, 2004, "Vermont Yankee Nuclear Power Station, Technical Specification Proposed Change No. 263, Supplement No. 5, Extended Power Uprate - Response to Request for Additional Information"

7) Entergy letter (BVY 04-025) to NRC dated March 4, 2004, "Vermont Yankee Nuclear Power Station, Technical Specification Proposed Change No. 263, Supplement No. 6, Extended Power Uprate - Withholding Proprietary Information"

8) Entergy letter (BVY 04-050) to NRC dated May 19, 2004, "Vermont Yankee Nuclear Power Station, Technical Specification Proposed Change No. 263, Supplement No. 7, Extended Power Uprate - Confirmatory Results"

Rick Ennis - raiO3 mc0761.wpd Page 12 12 Attachment 1 Parameters Needed for Question 32 Containment Volume (upper uncertainty range) drywell (including free volume of vents at low suppression pool water level) drywell hold-up volume - i.e., the pool volume prior to falling into the vents wetwell atmosphere (at low suppression pool water level) wetwell suppression pool (including vent water volume at min. level) initial suppression pool depth (minimum) initial suppression pool surface area (at min. depth) vent lengths and diameters from drywell to wetwell (include number of downcomers)

Initial Pressure (minimum) drywell wetwell Initial Temperature (maximum) drywell wetwell Initial Humidity (maximum) drywell wetwell List all structures (heat sinks) by providing the upperuncertainty range for surface area, thickness, material composition, and identify the exposed volume boundary. Include:

- Heat transfer properties (upper range) (including description of coatings, if applicable)

- Consider heat transfer characteristics, e.g., two-sided exposed structures will have half-thickness, the outside boundary of the drywell and torus structures, etc.

Wetwell to Drywell Vacuum Breakers Number Diameter ,

Differential pressure setpoint Opening Time Loss Coefficient Rx Building to Wetwell Vacuum Breakers Number Diameter Differential pressure setpoint Opening Time Loss Coefficient Containment Leakage (upper range)

Drywell to Reactor Building; Area & Loss Coefficient Wetwell to Reactor Building; Area & Loss Coefficient

RickEnns -raiO mc761wpdPage 13}

13 Drywell Spray performance mass flow vs. time temperature vs. time Initial spray droplet size (smallest)

Wetwell Spray performance mass flow vs. time temperature vs. time Initial spray droplet size (smallest)

Initial RPV water Level (with expected range)

Recirc Line Diameter and Break Area SRV Performance (if applicable)

SRV Discharge flow mass and energy vs. time Number Diameter Differential pressure setpoint Opening time Loss Coefficient Recirc Break flow mass and energy vs. time Decay Heat vs. Time Pump Heat vs. Time ECCS injection flowrates/enthalpy versus time from suppression pool to RPV and/or drywell/wetwell sprays RHR Heat Exchanger Heat Removal Performance (assumed single failure) upper range for heat transfer with lowest service water temperature