ML21193A076

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ITAAC Related to Incore Instrument Thimble Assembly (Iita)
ML21193A076
Person / Time
Site: Vogtle  Southern Nuclear icon.png
Issue date: 07/08/2021
From:
Southern Nuclear Company
To:
NRC/NRR/VPOB
Santos C
References
Download: ML21193A076 (13)
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Text

Vogtle 3&4 ITAAC Related to Incore Instrument Thimble Assembly (IITA)

July 8, 2021

Background

  • 6/24/21SNC discussion regarding draft ICN for ITAAC 515

- Added manufacturer inspections to draft ICN in accordance with NEI 08-01, Section 9.5, because the DAS core exit temperature sensors (located within the IITA) cant be installed in final as-built location until core fuel load

- NRC requests additional discussion

  • 7/8/21Follow-up discussion agenda:

- IITA Design & Installation

- Related ITAAC 2

IITA Design

  • IITA cables are inserted into 8 Quickloc assemblies which penetrate the upper head of the reactor vessel
  • IITA cables from 8 reactor vessel head penetrations are connected to the 42 IITAs which are supported by the Instrumentation Grid Assembly (IGA)
  • 42 IITAs are inserted into the fuel assemblies during operation (38 PMS & 4 DAS)
  • The 42 IITAs each contain multiple fixed incore flux detectors and one Core Exit Thermocouple (CET) 3

Refueling Operations

  • Prior to removal of the IHP and reactor vessel head for refueling the IITA cables are disconnected at the Quickloc nozzle
  • The Quickloc device is removed and the IHP with the reactor vessel head are both removed and transported to the head storage stand
  • The Upper Reactor Vessel Internals assembly is prepared for moving to the upper internals stand by lifting the Instrumentation Grid Assembly (IGA) plate and with it lifting the IITAs out of the fuel assemblies
  • The Upper Reactor Vessel Internals assembly, including the IGA, is then placed on the Upper Reactor Vessel Internals assembly stand within the refueling cavity 4

Initial Fuel Load

  • Following initial core fuel load the Upper Reactor Vessel Internals assembly is installed in the Reactor Vessel
  • Upper Reactor Vessel Internals assembly houses the IGA containing the 42 IITAs
  • IGA is then lowered into its seated position
  • IHP with the reactor vessel head are both installed
  • Quickloc device installed
  • IITA cables are connected at the Quickloc nozzle 5

Incore Instrumentation System Precritical Verification

  • Verifications performed after initial fuel load and IITAs installed
  • Electrical continuity checks made at the incore instrumentation system panel to verify proper installation and connection of the incore sensor strings
  • Incore thermocouple data compared with the measured reactor coolant system temperature to verify proper operation of the incore thermocouples and signal processing
  • Confirms that the incore instrumentation thimbles have been installed correctly following initial fuel load
  • Confirms proper operation of the incore thermocouples prior to plant heatup 6

IITA ITAAC Discussion

- Requires inspection of as-built Diverse Actual System (DAS) sensor inputs

>> Demonstrate DAS sensor inputs are separate from those used by Protection and Safety Monitoring System (PMS) and Plant Control System (PLS)

>> DAS Core Exit Temperature (CET) sensors are located in 4 of the 42 IITAs (other 38 IITAs are for PMS) and therefore cannot be installed until after fuel is loaded in core

  • Utilized NEI 08-01 section 9.5 to credit inspection of IITAs and their DAS CET sensors performed at manufacturer prior to shipment to the plant site, since sensors will be not installed in their final as-built location until core fuel load.
  • Utilized construction drawings and work packages to demonstrate remainder of DAS CET sensor installation outside of the IITAs

- Preparation of ITAAC Principal Closure Document led to review of other ITAACs associated with incore instrumentation 7

Other IITA Related ITAACs

- Deleted in License Amendment 85 based on the Function Arrangement being verified by other ITAAC

- Not impacted since the basis for deleting ITAAC 505 remains valid, i.e., ITAAC 506 preserves the Design Commitment, Inspection Tests, Analyses (ITA), and Acceptance criteria for ITAAC 505.

  • ITAAC 564 (Incore Instrumentation System (IIS) Functional Arrangement)

- Deleted in License Amendment 170 based on the Function Arrangement being verified by other ITAAC

- Not impacted since the basis for deleting ITAAC 564 remains valid, i.e., ITAACs 565, 570 and 572 remain 8

Other IITA Related ITAACs

  • ITAAC 556 (Data Display Processing System (DDS) Functional Arrangement)

- Unit 3 ICN documents review of the DDS Network and Workstation Cabinets.

- Not impacted since individual IITA sensor inputs were not within the scope of the ITA or AC.

  • ITAAC 570 (IIS cable sheaths)

- Similar to the approach for ITAAC 515, U3 ICN for ITAAC 570 documents inspections performed both at manufacturer and on-site.

  • ITAAC 572 (IIS Core Exit Temperature (CET) safety-related displays in MCR)

- Not impacted. As described in UIN this ITAAC injects a test signal for CET and visually confirms that when each of the safety-related displays for CET is summoned from a Main Control Room PMS Visual Display Unit (VDU), the summoned CET appears on the PMS VDU.

9

Other IITA Related ITAACs

- 2.i (CET displays in Remote Shutdown Workstation (RSW))

>> Not impacted. Testing forces the Data Display System CET input parameter from an engineering workstation and CET display data recorded from RSW.

- 2.ii (CET visual Alerts at RSW)

>> Not impacted. As described in UIN, a combination of factory acceptance and on-site testing is performed. Testing forces the applicable Data Display System CET input parameter from an engineering workstation and visually confirms that when each of the plant parameters is used to generate visual alerts that identify challenges to Critical Safety Functions, the summoned plant visual alert appears on a display monitor at the RSW.

- Not impacted. Test signal will be used to inspect and record CET display data.

10

Other IITA Related ITAACs

- Not impacted. Test signal will be used to inspect and record CET display data.

- Not impacted. Testing is performed by simulating an analog signal and then inspection is performed to check that appropriate indication is retrieved in the MCR.

- Not impacted. Test signal will be used to inspect and record CET display data.

11

Other IITA Related ITAACs

- Not impacted. Factory Acceptance Testing is used following the guidance of NEI 08-01 Section 9.4 for as-built tests performed at other than the final installed location.

>> Plant parameters are simulated and adjusted to create applicable alert conditions, PMS outputs monitored, and confirmed that visual alerts were generated that identify challenges to critical safety functions

  • ITAAC 565 (IITA Seismic and Equipment Qualification)

- As-built installation Acceptance Criteria will likely utilize NEI 08-01 section 9.5 to document inspections performed by the manufacturer prior to shipment to the plant site, where necessary and justifiable, since IITAs can not be installed in their final as-built location until core fuel load

>> Draft ICN will be provided to NRC when its available 12

Conclusions

  • This approach is consistent with ITAAC 570, which was already submitted and accepted for Unit 3.
  • SNC will likely use a similar approach for ITAAC 565 also.

13

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