ML20215B727

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Feedwater Nozzle Insp Rept for Refueling Outage RF86A, Spring 1986
ML20215B727
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Site: Columbia Energy Northwest icon.png
Issue date: 11/25/1986
From:
WASHINGTON PUBLIC POWER SUPPLY SYSTEM
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ML20215B717 List:
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NUDOCS 8612120296
Download: ML20215B727 (7)
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O WASHINGTON PUBLIC POWER SUPPLY SYSTEM NUCLEAR PLANT NO. 2 FEEDWATER N0ZZLE INSPECTION REPORT FOR REFUELING OUTAGE RF86A l SPRING 1986 l

'O PREPARED BY: N% 11 / 2 s / 8 6 ISI ENGINEE10 DATE g REVIEWED BY: 4 6N U'-' _//[?v/%'

MANAGER, ENGINEERING SYSTEMS SUPPORT DATE 8MANAGER,

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DATE APPROVED BY: b/YI wu>> ///2r/94 iO PLANT MANAGER DATE

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EEDWATER N0ZRE INSPECTION REPORT PAGE 1 of 7 O

'O SUMARY

g This report addresses feedwater nozzle thermal cycling and inspection for WNP-2 for the period of initial start-up ( April 1984) through the first refueling outage (April 1986).

During the spring 1986 refueling outage (RF86A) ultrasonic examination of one

!O reactor feedwater nozzle was perfomed at WNP-2. No recordable indications were found. The plant had experienced 45 startup/ shutdown cycles during this initial inspection period.

'O On/off operation of the feedwater startup level control valve during low flow /startup conditions resulted in themal cycling of the feedwater nozzles.

To minimize this themal cycling, changes were made in the low flow /startup sequence. The reactor feedwater drive turbine low speed stops were reduced to allow the turbine speed level control to operate at lower flow rates. This reduced the time the startup level control valve was required to operate.

Because the thermal cycling of the feedwater nozzles could not be completely prevented, the Supply System perfomed an analysis to determine the effects of O this mode of operation during the initial inspection period. The analysis concluded that no detrimental effects were caused by this cycling.

The Supply System plans to continue its augmented feedwater nozzle inspection 0 at the next refueling outage as committed in the WNP-2 ISI Program Plan. That is one feedwater now . bure, inner radius and safe end will be ultrasonically examined from the reactor outside diameter (00) at the next refueling outage -

currently scheduled for April 1987.

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'O 10 FEEDWATER N0ZZLE INSPECTION REPORT PAGE 2 of 7 O

.O NDE INSPECTION O During tne first refueling outage, RF86A, at WNP-2, the Supply System per-fonned ultrasonic examination of one reactor feedwater nozzle safe end, bore and inner radius from the vessel 00. This examination is part of WNP-2's com-mitznent described in FSAR section 5.2.4.10 and Inservice Inspection Program Plan Section 5.3.2 to ultrasonically examine one feedwater nozzle from the OD O

each refueling outage for the first six refueling outages.

The Supply System has developed an angle beam shear wave technique that is unique to the WNP-2 feedwater nozzle design. The procedure was qualified on O

the WNP-2 feedwater nozzle mock-up which is a feedwater nozzle from the scrapped Douglas Point Unit 1 reactor vessel. The inner radius, zone 1, of the nozzle is scanned using a 72 degree angle transducer. The inner radius, zone 2, and bore region, zone 3, are scanned using a 25 degree angle trans-O ducer. The procedures used, QCI 6-4 rev. 3 and QCI 6-13, rev. 3, are con-tained in Appendix I to this report.

Calibration data for reactor feedwater nozzle inner radius exams have been O

predetermined using the WNP-2 feedwater nozzle mock-up. This allows the examiner to use the reactor vessel calibration block representing the shell course containing the feedwater nozzle for calibration. The transfer data is contained in Table I of procedure QCI 6-4. Indications that exceed 25% full O screen height (FSH) are recorded and indications that exceed 50% FSH are evaluated.

The examinations were performed by two teams of Supply System examiners certi-O fled to either Level II or Level III UT per the Supply System Q. A. program.

During the examination they were under the direct supervision of the Supply System Level III responsible for the technique and procedure development.

lO Na recordable indications were found.

Total examiner radiation dose was less than 0.5 Man Rem.

O FEE 0 WATER N0ZZLE INSPECTION REPORT PAGE 3 of 7 O

10 SYSTEM AND PROCEDURE CHANGES THAT AFFECT FEEDWATER FLOW Reactor vessel water inventory is maintained by a control system which O

receives input signals from main steam mass flow rate, feedwater mass flow rate and either of two vessel level transmitters. A switch allows selection of either a single-element mode, utilizing only the vessel level signal, or a three-element mode, in which steam and feedwater flow rates are compared and

O the resultant error signal modifying the level signal to provide an antict-patory feature. During nonnal power operation the feedwater control signal is used to control the speed of steam turbine-driven feefwater pumps. During startup, shutdown and low plant load conditions the steam turbine-driven feedwater pumps are run at a constant speed and the feedwater control signal is used to modulate an air operated, startup feedwater control valve (startup valve) to maintain proper reactor water level and avoid feedwater nozzle thennal cycling. However, the valve design does not allow effective control

",O of feed flow at these low flow conditions. Therefore cyclic operation of the valve is the only alternative. It has been detennined that the installed valve is not suited for its current application and plans for its replacement are underway.

To reduce the thermal cycling to the feedwater nozzles induced by the cyclic operation of the startup level control valve, changes to the system and its operating procedures have been completed. The low speed stop of the reactor O feed drive turbines has been lowered. This allows turbine speed level control at lower flow rates. The startup flow control valve is closed earlier result-ing in less time that the valve is utilized for low flow level control and fewer thermal cycles are experienced. This mode of operation will continue O until replacement of the startup flow control valve with one of appropriate design and application. Replacement is currently scheduled for the upcoming refueling outage in Spring 1987.

O In light of the on/off operation of the startup level control valve, the Supply System has perfonned an analysis of the cyclic thermal load on the feedwater nozzle fatigue integrity. The analysis was based on the total number of startups since fuel load and estimated cycling during each startup.
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l FEE 0 WATER N0ZZLE INSPECTION REPORT PAGE 4 of 7 g ,

O The analysis compared the present WNP-2 feedwater system thermal transients with General Electric's generic transients described in " Boiling Water Reactor o Feedwater Nozzle /Sparger", Final Report, NEDE-21821-A, Class III, February 1980 Based on this comparison the estimated feedwater nozzle life exceeds forty years with the present WNP-2 feedwater system design.

g STARTUP/ SHUTDOWN CYCLES WNP-2 has experienced 45 startup/ shutdown cycles between initial heatup

( April 1984) and shutdown for refueling outage RF86A ( April 1986). The data 1 g was compiled from the Final Startup Report and Monthly Core Energy Output Worksheets.

NEXT SCHEDULED EXAMINATION O

The Supply System will perform an ultrasonic examination from the OD of the reactor vessel on one reactor feedwater nozzle inner radius, bore and safe end per the committment in FSAR section 5.2.4.10 and the Inservice Inspection Pro-gram Plan section 5.3.2 during the refueling outage scheduled for Spring 1987.

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O FEEDWATER N0ZZLE INSPECTION REPORT PAGE 5 of 7 O

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APPENDIX I

g. Procedure QCI '6-4, revision 3 Procedure QCI 6-13, revision 3 O

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O g 'FEEDWATER N0ZZLE INSPECTION REPORT PAGE 6 of 7

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