ec6 design improvements and confirmatory testing

- Copyright -

EC6 Design Improvements and Confirmatory TestingPrepared By: Stephen Yu, Livia Drennan and Michael Soulard

35th Annual Conference of the Canadian Nuclear SocietySaint John, New Brunswick2015 May 31 –June 3

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Topics

• Introduction – Overview of the EC6 Confirmatory and Qualification testing Program

• Reactor Core Components

o Pressure Tubes and Rolled Joints

o Calandria Tubes and Rolled Joints

o Fuel Channel Annulus Spacer

o Shutoff Units in Shutdown Systems #1

• Instrumentation and Control Systems/Components

o EC6 Main Control Room Mock-up

• Summary

- Copyright - © 2015 SNC-Lavalin Inc. and its member companies. All rights reserved. Unauthorized use or reproduction is prohibited.

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Overview – EC6 Confirmatory & Qualification Testing

• EC6 Confirmatory Testing and Analysis Program is a fundamental component of the EC6 program to confirm design changes from the CANDU 6 Reference Qinshan plant

o Support the design and safety analysis of EC6 and address CANDU Generic Action Items (GAIs) and CANDU Category 3 Safety Items

• The confirmatory testing and analysis activities planned focuses on the first phase of testing needed to support the application for a construction licence


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Overview – EC6 Confirmatory & Qualification Testing

Major Focus Areas

• Verification of reactor core components design changes: design-basis and safety analysis data

• Address EC6 design safety performance specifications for various accident conditions as well as postulated severe accidents conditions such as calandria tube contact boiling; reactor vault refractory material; aircraft crash impact and calandria tube survivability in a spontaneous pressure tube rupture event.

• Validation or verification of computer codes, models & methodologies - Additional RD-14M testing on emergency core cooling injection will be done for CATHENA code verification

• Demonstration and performance testing work of new control computers and control centre equipment to address equipment obsolescence, OPEX feedback, and modernization of the control and display system to current standards


- Copyright - © 2015 SNC-Lavalin Inc. and its member companies. All rights reserved. Unauthorized use or reproduction is prohibited.5

EC6 Confirmatory & Qualification Testing Activities

Area SI Task Completion Status

Reactor Components

31110/31113 Pressure Tube Qualification and Rolled Joint 2014

31230 Calandria Tube Qualification 2015 (forecast)

31160 Fuel Channel Annulus Spacer 2014

31124 Position Assembly Before 2013

31730/31733 Shutdown System No.1 2014

Severe Accident 31230/03500 Calandria Tube Creep Rupture 2015 (forecast)

03665 Severe Accident Management –In-Vessel Retention Before 2013

21009 Refractory Vault Material Before 2013

03665 Calandria Tube Emissivity Before 2013

03500 ECC Injection –RD-14M 2015 (forecast)

Fuel 37100 Fuel Bundle Seismic Before 2013

Containment 21200 Aircraft Impact Crash Protection 2015 (forecast)

Instrumentation and Control

68000 Shutdown System Computers Before 2013

66900 Fuel Handling System Simulator Before 2013

66900 EC6 Analytical Dynamic Simulator Before 2013

66510 ACCIS Platform Readiness Before 2013

60300 Advanced Alarm Annunciation Before 2013

66190 Main Control Room Mock-up Before 2013

68500 Safety System On-line Monitoring Before 2013

66700 DCS Platform – vertical slice 2014


Enhancement of Reactor Core ComponentsDrivers for Design Change

• Reactor core physics design optimization.

• Safety-significant OPEX

• Full performance (no ROP degradation at end-of-life).

• Annulus spacer issues – material degradation.

• Improved spacer detectability throughout the life of the reactor

• Improved detection for leak-before-break.

• Generic Action Item GAI-95G02 - end fitting ejection.

• GAI-95G04 - positive void reactivity treatment in large loss of coolant accident (LLOCA) analysis.

• Upgraded reactor assembly: thicker pressure tube & calandria tube , strengthen positioning assembly, improve spacer design, reinforce step and increase end shield tube sheet thickness (60 year life; seismic); seamless calandria tube (instead of seam-welded) with thick ends.

• Number of adjusters is reduced, moderator isotopic is increased, guide-tube tensioning springs are relocated to above the calandria shell; reference power shape is revised to meet core performance characteristics at End of Life (EOL)

• Improved LOCA margin: heavier SOR accelerator springs, lighter SORs, increasing coolant isotopic, reducing the flux tilt limit, providing contour parking for the shutoff rods, limiting the moderator poison concentration, adding full-size SORs, replacing ion chambers with fission chambers and adding two new fast linear rate trips.

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Pressure Tubes (PT) and PT Rolled Joints

›Improve Regional Overpower Protection (ROP) Margin by Reducing Diametral Strain

• Increased PT wall thickness

• Existing tight tolerance controls during the manufacturing process were utilized to add additional control to the average diameter of the pressure tube.

The EC6 pressure tube design with these enhancements achieves approximately 20% reduction in peak diametral strain and, thus will result in a minimum of 245,000 EFPH of reactor operation without de-rating.

• The inside diameter of the end fitting in the PT rolled joint region has been increased to accommodate thicker pressure tube.


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PT and PT Rolled Joint Test Program• Qualification of pressure tube material by verifying material properties for

code compliance for a thicker tube in EC6o Chemical analysis; Microstructure characterization and Mechanical property

testing• Pressure tube rolled joint qualification testing with representative thicker EC6

pressure tubes to demonstrate that the joints meet the CSA N285.2 requirements for helium leakage, pull out strength, and pressure tube residual stresseso Testing was also used to show various joint characteristics after the rolling

process and to further understand the end of life behaviour. o During the testing, the wall reduction of the test joints and diametral fit between

the EF hub ID and the PT OD were varied so that the effect of these variables on the performance of the joint could be reviewed

• Feasibility of DynaloyTM application to the end fitting in the rolled joint region to reduce hydrogen ingress - lower hydrogen ingress will result in increased pressure tube lifetimeo Results of the PT rolled joint development testing with C6 zero clearance rolled

joints using Dynaloy coated EF hubs show higher than acceptable helium leak rates for some joints. Hence, Candu decided not to use Dynaloy coating for EC6 pressure tube rolled joints


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PT and PT Rolled Joint Test Program Results

›EC6 pressure tube qualification: supplier fabricated pressure tube to EC6 PT technical specifications and examinations conducted by Canadian Nuclear Laboratories at Chalk River:

• The concentrations of niobium, hydrogen and nitrogen were within the specification.

• The α-grain thickness, texture and dislocation results were within the specification.

• The UTS and 0.2% yield strength for tensile testing satisfied the specified minimum standard values.

Based on the above, the EC6 pressure tubes manufactured with an increase in thickness met the technical specifications

Qualification testing of the EF-PT rolled joint using the EC6 pressure tube sections with increased thickness - same batch of pressure tube used in above material qualifications

• All of the test joints had acceptable helium leak rates before and after thermal soak and cycle testing and also after the accelerated stress relation (EOL).

• As well all the test joints achieved pull out forces higher than the acceptance level. This was true even for the test joints that completed the end of life behaviour simulation.

• The residual stresses measured during this testing are similar to the results found in previous testing


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Calandria Tubes (CT) and CT Rolled Joints

›Address GAI – 95G02 and CSI –AA07 related to pressure tube failure with consequential loss of moderator followed by end fitting ejection

• Seamless calandria tube (CT) with thickened ends and improved rolled joints (RJ) are expected to survive pressure tube rupture to help mitigate core damage.

• A seamless calandria tube prevents the impact of in-core LOCA and provides the operator with adequate time to cool down the reactor.

• Target for core damage frequency (CDF) less than 10-6 per reactor year


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CT and CT Rolled Joint Test Program

Confirm that the manufactured EC6 calandria tube and the new rolled joint design meet the design requirements

• Material Qualification Testing

o Development of a manufacturing process in collaboration with supplier

o Material characterization of calandria tubes to establish that the material meets the acceptance criteria of the appropriate standard and design requirements.

• Calandria Tube Integrity Testing - confirm that the calandria tube survives a spontaneous pressure tube rupture event thus preventing subsequent in core damage and potential ejection of the end-fitting. Two stage approach:

o Hydrostatic test of short calandria tube spools to evaluate burst and creep behaviour independently from the rolled joint.

o Leak tightness and pullout strength tests with rolled joints using EC6 seamless qualification tubes


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CT and CT Rolled Joint Test Program ResultsCalandria Tube Material Qualification Testing

• The manufacturing of the full length EC6 seamless CTs for material qualification testing and the various CT sections to be used for the two stages of CT integrity testing have been delivered based on the EC6 technical specification for seamless calandria tubeso Material qualification tests have been completed at CNL confirming compliance

Calandria Tube Integrity Testing - EC6 seamless CT sections (flanges welded at the ends of the spools)

• Hydrostatic tests of short calandria tube spools to evaluate burst and creep behaviour independently from the rolled joint

o EC6 seamless CT with increase thickness shows no signs of CT pressure boundary leakage when subjected to internal pressures of up to 13 MPa (g).

o When subjected to constant internal pressure in range of 10 to 11 MPa(g) at high temperature during staged increase of hydraulic pressure, the creep rate of the EC6 CT spools is much slower than that for current CANDU 6 CT;

Therefore , the expected time to rupture at these pressures surpassed the acceptance criteria with a significant margin.


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CT and CT Rolled Joint Test Program ResultsEC6 Calandria Tube sections Integrity Testing with rolled joints - in progress• Integrity testing at CNL will be repeat for a seamless CT with rolled joint (RJ)• The first test section with seamless CT with RJ has been delivered to CNL• Creep rupture confirmatory testing at CNL to be completed by August

EC6 Seamless Calandria Tube Rolled Joint Qualification Testing• Qualification testing including Load Cycle, Leak tightness and Pullout Strength Tests

are planned at Candu lab SP3• All the qualification testing on 1st assembly is being completed this week• CT RJ Qualification testing for all the assemblies will be completed in June.


EC6 CTRJ Assembly with CT spool piece – side view

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Fuel Channel Annulus Spacer

›The key drivers for the design change include the followings:

• Elimination of concerns with the ability of nickel alloy X-750 to be suitable for extended operation as a result of material degradation mechanisms such as embrittlement and void swelling (caused by irradiation induced transmutation chain of 58Ni).

• Prevent in service mobility of the spacer by making it a tight-fitting design,

• Achieve detectability using Eddy Current to facilitate PIP & ISI and enhanced compliance with CSA N285.4, and

• GAI – 89G04 related to spacer location and repositioning.

→ Change to stronger, tight fitting Zr 2.5Nb 0.5Cu with welded girdle wire


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EC6 Annulus Spacer Test Program›Two Stage Program

• Development Stage – Manufacturability and Feedback to Design

o Examine manufacturability of non-reactor grade material (Zr-2.5Nb) spacer regarding simulation of in-reactor relaxation and spacer mobility

Several low tensioned springs are fabricated to simulate the in-reactor relaxation due to thermal and irradiation creep and to examine mobility of the spacers under these conditions.

In addition, a series of testing were performed to assess resistance of the spacer to free rolling, simulating an end-of-life effect of increase in pressure tube diameter which causes the closed-loop welded girdle wire to become tight against the spacer coil

• Qualification Stage – annulus spacer fabrication per EC6 Technical Specification (same material and standard as a reactor order)

o Spacer integrity under cyclic loading and PT & CT wear evaluation

o Spacer relaxation and mobility testing- Copyright - © 2015 SNC-Lavalin Inc. and its member companies. All rights reserved. Unauthorized use or reproduction is prohibited.

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EC6 Annulus Spacer Test Program

›Two Stage Program

• Qualification Stage – annulus spacer fabrication per EC6 Technical Specification (same material and standard as a reactor order)

o Spacer integrity under cyclic loading and PT & CT wear evaluation

Several spacers were subjected to simulated in reactor loading conditions (with the exception of radiation) to evaluate spacer integrity under repeated (cyclic) loading

o Spacer relaxation and mobility testing

More spacers with very high values of relaxations (higher relaxation rate than what was already tested during the development process) were subjected to vibration and interaction with calandria tube to evaluate mobility under simulated vibration excitation


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EC6 Annulus Spacer Test Program Results›Qualification Test results demonstrated that

• The contact wear in the pressure tube, calandria tube and spacer are insignificant and the spacer meets the fatigue requirements.

• Vibration testing also confirmed that the fully relaxed spacers, as long as they are not loose on the pressure tube they are installed on, would not become mobile under acceptable excitation amplitudes.


Endurance and Wear Test RigVibration Test Rig

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EC6 Shutdown System #1 Shutoff Units

›Improve SDS1 performance to improve the safety margins for the Large LOCA design basis accident

• Shutoff rod was lightened and the rod accelerator spring was redesigned to give a higher preload force and longer compression/extension stroke.

o Lighter shutoff rods require thinner stainless steel cladding, thinner neutron absorbing cadmium material, and change in the push rod material from stainless steel to titanium.

o The EC6 rod accelerator spring will be fabricated from Inconel X750 (the same as is used in other CANDU plants), but has a similar stroke and preload

• Change to the drive is required to address obsolescence issues with the traditional drive mechanism. The EC6 adopted the ACR drive assembly since the manufacturing of the ACR drive assembly was already completed.

o The new drive mechanism, while using key components proven designs, has a smaller footprint on the RM Deck, is simpler to maintain and is less expensive to produce.


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SDS1 Test Program• Investigative wear test for the high-force long-stroke spring to confirm the

acceptability of the accelerator spring, spring seat and spring housing selected for qualification testing

• Seismic qualification testing of the drive assembly and basic seismic testing of the shutoff unit guide assembly to validate seismic analysis and models

o Functional capability following and during a design basis earthquake (DBE) event.- survive without compromising the ability to effect a shutoff rod insertion

• Qualification testing to demonstrate (1) the shutoff rod time-to-distance travel under expected nominal moderator conditions and (2) durability through endurance testing

o Testing comprises of basic performance testing to verify that time to distance performance requirements are met under normal operating conditions.

• Environmental qualification testing to verify rod release function of shutoff unit drive mechanism during adverse environmental conditions

o Testing to prove that the shutoff unit drive mechanism satisfies requirements for external environmental conditions and expected peak internal pressures


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Test Conditions• Components were manufactured

to reactor-grade standards and assembled in a test tank for performance testing

• The tests run simulated nominal reactor conditions for moderator level and temperature and local flow conditions around the guide tube.

• In addition, a group of high moderator level tests were run to approximate the worst-case conditions for a shutoff unit outside the expected damage zone during an in-core LOCA.

• Correction factors were applied to account for the use of light water instead of heavy water for the moderator in these tests.



EC6 SOU Performance curve (Rod position vs time in seconds)

• Observed average performance results closely matched predicted values and provided a significant performance improvement, reducing the Gate 1 time by over 20 percent as compared to the existing CANDU 6 design.

• EC6 Safety performance objectives were met in all cases, even with the in-core LOCA simulation.

Operating C6 Average Performance

Average EC6 Performance (Nominal Moderator Level)

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Drivers for Design Changes to Instrumentation and Control Systems/Components

Licensing

• New systems such as EHRS and SARHRS• Safety Parameter Display System• MCR Safety Panel Changes• Shutdown System No. 1

o Computerize neutronic trips for EC6 to improve Large LOCA safety margins and to address OPEX feedback for the CANDU 6 reactors in operation.

o To further improve trip computer platform diversity between SDS1 and SDS2, an FPGA based digital platform is being evaluated for use as SDS1 trip computers

Modern I&C - MCR shall employ modern digital technology to enhance human performance

• The DCC control computers in the reference design are being replaced (due to obsolescence)with a modern Distributed Control System (DCS) for EC6. Part of the testing is to demonstrate the control software can be ported to function correctly on the new hardware

• The Advanced Control Centre Information System (ACCIS) developed by Candu, has been qualified and configured for EC6 implementation; provide organized, hierarchical access to displays, controls, alarms

• Computerized safety system testing• Computerized procedures



EC6 MCR Mock-upprovides facility to perform such design activities and to conduct Integrated System Validation for Control Centre design (HFE) as part of design process

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Summary

• The EC6 design is also based on the extensive knowledge base of CANDU® technology gained over many decades of operation and supporting Research and Development studies.

• Performance testing and material qualification testing of improved EC6 reactor components show improved robustness and performance of the shutoff units, the higher operating life margin for the pressure tubes, the improved safety margin for the seamless calandria tubes and successful verification of the enhanced EC6 spacer behaviour with new materials.

• The confirmatory testing and analysis activities are near completion to ensure EC6 product readiness for new build or refurbishment project implementation.

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ec6 design improvements and confirmatory testing

Engineering

ec6 program

calandria tube qualification

safety analysis of ec6

phase of testing

pressure tube qualification

calandria tube survivability

calandria tube emissivity

calandria tube creep