EC6 design improvements and confirmatory testing

- Copyright -
EC6 Design Improvements
and Confirmatory Testing
Prepared By: Stephen Yu, Livia Drennan and Michael Soulard
35th Annual Conference of the Canadian
Nuclear Society
Saint John, New Brunswick
2015 May 31 –June 3

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
2
- Copyright - © 2015 SNC-Lavalin Inc. and its member companies. All rights reserved. Unauthorized use or reproduction is prohibited.

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
oSupport 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
3

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
4

EC6 Confirmatory & Qualification Testing Activities
5
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 Components
6
Drivers 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.

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.
7

PT and PT Rolled Joint Test Program
• Qualification of pressure tube material by verifying material properties for
code compliance for a thicker tube in EC6
o 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 stresses
o 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 lifetime
o 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
8

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
9

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
10

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
11

CT and CT Rolled Joint Test Program Results
Calandria 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 tubes
o 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.
12

CT and CT Rolled Joint Test Program Results
EC6 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.
13
EC6 CTRJ
Assembly
with CT
spool
piece –
side view

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
14

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
15

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
16

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.
17
Endurance and Wear Test RigVibration Test Rig

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.
18

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
19

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.
20

EC6 SOU Performance curve
(Rod position vs time in seconds)
21
• 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)

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
22

EC6 MCR Mock-up
provides facility to perform such design activities and to conduct Integrated System
Validation for Control Centre design (HFE) as part of design process
23

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.
›
24

THANK YOU
25

EC6 design improvements and confirmatory testing

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