ZED-2 – 60+ Years of Success L.R. Yaraskavitch Reactor Physicist, ZED-2 Nuclear Science Week 2020 ‐ CNS Lecture October 21, 2020

UNRESTRICTED / ILLIMITÉ -1- CW‐123110‐001‐000 ZED-2… Z-2… ZEEP-2 •ZEEP provides the why for ZED‐2 •Morgan Brown has set the stage last night: “The 75th Anniversary of ZEEP”

UNRESTRICTED / ILLIMITÉ -2- ZEEP Mark II Why? Limitations of ZEEP (6th UK- Technical Conference, 1957) • A number of outstanding problems in the way of determining optimum design for power reactor and ZEEP couldn’t address them because: • Size of ZEEP (small, calandria diameter 2.06m) best suited to more reactive lattices (e.g., metal) • Size of lattices desirable for power reactors was larger than ZEEP could accommodate • At the larger spacing to test power reactor lattices, substitution regions were necessary, but with a reactive outer ring. Subject to high uncertainty! • Too small to look at flux flattening (also desirable for power reactor lattices)

UNRESTRICTED / ILLIMITÉ -3- “A Proposal for Zed 2: A Large ZEEP Type Reactor” Jan 1958 (various authors) • To quote D. W. Hone (from CNS Bulletin Vol. 21 No.1): “An additional low power lattice testing reactor is required … to obtain rapidly more accurate experimental measurements on which to choose an optimum design of power reactor.” • Hone (Senior ZEEP Physicist) would later become first Senior ZED-2 Physicist • Zed-2: to designate ZEEP-2 • the backronym Zero Energy Deuterium followed, now designation ZED-2 is used.

UNRESTRICTED / ILLIMITÉ -4- “A Proposal for Zed 2: A Large ZEEP Type Reactor” • “Such a reactor would be used for the same type of measurements as are done in ZEEP, viz: • [reactivity] vs. lattice pitch … • critical size measurements … • fine structures through cells • temperature coefficients • void coefficients … [and] in addition • Flux distribution in rods in assemblies not necessarily uniform • Rapid measurements of the effect of various reflectors”

UNRESTRICTED / ILLIMITÉ -5- So what was designed? • Low power – 200 W nominal, but a larger power than ZEEP • Bigger calandria with a flat bottom – 335 cm versus 206 cm • Shutdown: three dump valves + cadmium absorber rods. • Other noteworthy features (AECL-1301, “ZED-2… Canada’s newest ”, A.E. Foster) • Cadmium control ring between calandria and graphite • Originally intended to have automatic power controller • Moderator heating capability • Channel heating capability • Lattice change mechanism – change lattice pitch remotely via mirrors and lights without opening lid/shielding • Removable graphite segments for reflector testing

UNRESTRICTED / ILLIMITÉ -6- UNRESTRICTED / ILLIMITÉ -7- Construction

• Foster-Wheeler chosen to construct the facility

February 6, 1959 June 8 1959

UNRESTRICTED / ILLIMITÉ -8- Reflector

• Assembly of 1277 graphite bricks • 90 cm thick axially, ~60 cm thick radially • Note penetrations

UNRESTRICTED / ILLIMITÉ -9- Vessel

• Cylindrical Al calandria • 3.36 m diameter • 3.35 m height

UNRESTRICTED / ILLIMITÉ -10- First Critical 7 September 1960, 13:15

• Using 7 element natural UO2 fuel bundles • 5 per channel, 55 channels • 24.56 cm pitch, hexagonal lattice • Estimated Hc: 164.3 cm/166 cm • Measured: 166.3 cm • Similar experiments described in AECL-1505

UNRESTRICTED / ILLIMITÉ -11- UNRESTRICTED / ILLIMITÉ -12- Circa 1970s ZED-2 • Open vessel – fuel support beams and hangers • Rolling top shields • Fuel storage racks • Control room

UNRESTRICTED / ILLIMITÉ -13- 2014 ZED-2 Operations

UNRESTRICTED / ILLIMITÉ -14- Graphite Reflector

UNRESTRICTED / ILLIMITÉ -15- Dump Valves

UNRESTRICTED / ILLIMITÉ -16- Dump Tanks

UNRESTRICTED / ILLIMITÉ -17- UNRESTRICTED / ILLIMITÉ -17- ZED-2 Control Room

UNRESTRICTED / ILLIMITÉ -18- Fuel

• Natural UO2 Bundles • 7-, 18-, 19-, 28-, 37- and 43-element • Other NU flavours • Carbide • Silicide • Metal (ZEEP rods, 19-el, 36-el) • Mixed oxides • Pu-U (Depleted) (simulated mid-burnup) • 233U-Th • Pu-Th • 235U-Th • Bundles with absorber elements (LVRF)

• Enriched UO2 bundles (LEU, SEU, RU) • Booster rods (LEU/HEU + Zr/Al)

UNRESTRICTED / ILLIMITÉ -19- To reproduce materials and geometry, not to ‘cool’

• D2O (incl. bubbled) (supported CANDU-PHWR)

• H2O (incl. bubbled) (supported CANDU-BLW) • HB-40 (terphenyl, organic ) (supported CANDU-OCR) • Helium

• CO2 • Pb-Bi • Highest temperature (electrically heated): 300 °C • Bonus fact, lowest temperature reached: -196.15 °C (liquid nitrogen cryostat used to cool wax moderator to measure eff. cross sections at very low temperatures)

UNRESTRICTED / ILLIMITÉ -20- Fuel Lattices in ZED-2

UNRESTRICTED / ILLIMITÉ -21- Timeline

• 60’s – Metal and oxide fuels, D2O, air, He, organic coolants, pitches from 20 cm to 40 cm (CANDU support). Carbide measurements in international collaboration. • 70’s – simulated boiling light water (CANDU BLW), enriched U booster rods, liquid absorbers, coupled cores, kinetics

measurements, (Pu, U)O2, shutoff rod materials and shapes, reactor regulating systems, Self Powered Flux Detectors, NRU loop site

simulation, adjuster rods, 37 el. lattice physics, Th-UO2, NRX, 99 • 80’s – Co and Cd absorber rods, (Pu, Th)O2, Mo for NRU, simulated 233 NRU loop, simulated burned up fuel, ( U, Th)O2 • 90’s – Coolant Void Reactivity (fresh and mid-burnup), delayed , Low Void Reactivity Fuel, 43 element CANFLEX • 00’s – Advanced CANDU Reactor 233 • 10’s – Reactor kinetics, (Pu, Th)O2, ( U, Th)O2

UNRESTRICTED / ILLIMITÉ -22- Evolution of Use • 60’s – Lattice recipes, two energy group calculations, four factor formula – driven by obtaining experimental data (and training reactor physicists)! • Included buckling, 238U/235U fission ratios, reaction rates, fine structure, etc.

… Increasing computational power, availability of computational tools, increase in quality of available nuclear data, increasing experience …

• 10’s – Verification/validation of nuclear data and computer codes, especially at the edges of the existing parameter space! • And calibrations + irradiations

UNRESTRICTED / ILLIMITÉ -23- The 10s: ZED-2 School 9 iterations, 154 attendees, 24 different organizations

• Outcome of 50th Anniversary • Focus on education • A week of lectures, demonstrations, and sharing ideas.

UNRESTRICTED / ILLIMITÉ -24- The 10s: Transients

Zeller and Atfield, CNL Nucl. Rev., Vol. 4 No. 1 (2015)

UNRESTRICTED / ILLIMITÉ -25- The 10s: Advanced Fuel Cycles

• First such transients in ZED-2 with nuclides other than 235U and 238U • Most fissions due to Pu and 233U ever in ZED-2 “Kinetics experiments in ZED-2 using heterogeneous cores of advanced nuclear fuels”, Annals of Nuclear Energy, 121 (2018) 36-49.

UNRESTRICTED / ILLIMITÉ -26- The 10s: Fast Rod Recommissioning capability • ‘Transformer Rod’ of U- metal from 1960’s of interest once more for fast neutron irradiation and spectrum manipulation. • Fast flux on order of 108 nv

• Thermal flux trimmed with Cd • Appreciable dose to biological samples

UNRESTRICTED / ILLIMITÉ -27- Other Heavy Water Moderated ZPRs

• USA: Process Development Pile (1953), Pawling (1958) • France: Aquilon (1956) • Belgium: VENUS (1964) (Now VENUS-F) • UK: DIMPLE (1954), DAPHNE (1962), JUNO (1964) • Serbia: RB (1958) • Sweden: R-0 (1959) • Norway: NORA (1961) • India: Zerlina (1961), Facility for AHWR/PHWR (2008) • Italy: ECO (1965), RB-3 (1971) • South Africa: Penlinduna-0 (1967) • Japan: Deuterium Critical Assembly (1969) • Czech Republic: TR-0 (1972) (Now LR-0) • Iran: HWZPR (1995) Legend: • Russia: MAKET (1976) Decommissioned/Shutdown Still Operating

UNRESTRICTED / ILLIMITÉ -28- How do we stand in 2020?

• American Nuclear Society Nuclear Historic Landmark (awarded 2010) • 2529 cores, 196+ of them unique, and counting • On core designation GN – started at A, but subscripts seem to have been used sometimes… • Building on the work of multiple generations of operators and experimenters, a dedicated team of operations staff and experimenters continue to use ZED-2 for Federal Science & Technology work for Government of Canada and commercial projects. • Take away: ZED-2 is an integral part of the reactor physics design of all Canadian power reactors, and much more!

UNRESTRICTED / ILLIMITÉ -29- Looking to the future…

• A.G. Ward, The Role of Critical Experiments in the Chalk River Power Programme, Proc., Exponential and Critical Experiments, Amsterdam 2-6 Sept. 1963, IAEA “Although one may hope for the day when the reactor-physics calculations are confidently based on computer programmes, with no recourse to experimental or critical facilities, it seems likely this happy time will only arrive when new reactor designs are no longer of interest” • Currently working towards understanding role that can be played in validation of reactor physics of SMR designs (e.g., press release on Terrestrial Energy integral )

UNRESTRICTED / ILLIMITÉ -30- Acknowledgements ZED-2 Facility: D. Brushey, J. Horner, S. Mirault, D. Trudeau, G. Hamilton, K. Thomson, M. Crowe Applied Physics: J. Atfield, J. Chow, N. Lee, L. Li, X. Wang, E. Rand, S. Livingstone, R. Rogge Computational Techniques: K. Hartling, B. Bromley, F. Adams

UNRESTRICTED / ILLIMITÉ -31- Useful Websites http://www.cnl.ca Canadian Nuclear Laboratories http://www.cns-snc.ca Canadian Nuclear Society http://www.nuclearfaq.ca Canadian Nuclear FAQ http://canteach.candu.org CANDU Owners Group Inc. (COG) CANTEACH Project http://inis.iaea.org IAEA International Nuclear Information System http://www.nuceng.ca/candu/ The Essential CANDU textbook http://www.nuclearheritage.ca The Society for the Preservation of Canada’s Nuclear Heritage https://www.osti.gov/ U.S. DOE Office of Scientific and Technical Information http://science-libraries.canada.ca/eng/national-science-library/

UNRESTRICTED / ILLIMITÉ -32- Other References • “ZEEP: The Little Reactor that Could”, by R.E. Green and A. Okazaki, from CNS Bulletin Vol. 16 No. 3, Autumn 1995 • “ZED-2, the first 40 years”, by F. Boyd, from CNS Bulletin Vol. 21 No. 1, May 2000 • “ZED-2… Canada’s newest research reactor”, A.E. Foster, AECL-1301 • A history of ZED-2, Jones, R., Canadian Nuclear Society Bulletin; v. 31(4); p. 5-7; 2010 • The Role of Critical Experiments in the Chalk River Power Programme, Proc., Exponential and Critical Experiments, Amsterdam 2-6 Sept. 1963, IAEA • B. Bromley, Joint ICTP-IAEA Workshop on Nuclear Reaction Data for Advanced Reactor Technologies, 19-30 May 2008 • A. Okazaki and R.T. Jones, IAEA-TECDOC-491

UNRESTRICTED / ILLIMITÉ -33- Thank you. Merci. Questions? Luke Yaraskavitch Applied Physics Branch Canadian Nuclear Laboratories [email protected]

UNRESTRICTED / ILLIMITÉ -34- Quick Facts Power: up to ~200 W (thermal) Peak Neutron Flux: 1x109 n/cm2 s thermal, 5x108 n/cm2 s fast Calandria: 3.36 m in diameter, 3.35 m in height Fuel: Various types and assemblies

Moderator: Heavy water (99.8 to 97.5 weight% D2O), soluble poison capability, temperatures up to 90°C, and variable core height (criticality achieved by pumping moderator into calandria) Core Geometry: flexible, typically square and hexagonal lattices, with variable pitch

Coolant: H e a v y w a t e r, l i g h t w a t e r, a i r, C O 2, organics, Pb-Bi, etc. (not active). Temperatures up to 300°C in some channels. Flexibility: We can operate with new fuels/coolants/materials as required

UNRESTRICTED / ILLIMITÉ -35- What does a reactor do?

• Objective is to create a self-sustaining chain reaction • That is, # of neutrons lost or absorbed = # created

• Effective multiplication constant, keff of 1: critical • What can you do if you’re supercritical/subcritical? • Make reactor smaller/bigger • Change reactor materials – make it more absorptive/less absorptive, or fewer neutrons per fission/more neutrons per fission

UNRESTRICTED / ILLIMITÉ -36- Facility Cross-Section

Control Room Top Shields

Support Beams (15)

Core Vessel

Reflector

Dump Valves (3)

Dump Tanks (3)

UNRESTRICTED / ILLIMITÉ -37- CANDU Calandria

UNRESTRICTED / ILLIMITÉ -38- UNRESTRICTED / ILLIMITÉ -38- 37-element Fuel Bundle

• Length = 0.5 m • Weight = 24 kg • Diameter = 10 cm

UNRESTRICTED / ILLIMITÉ -39- ZED-2 Control Room

UNRESTRICTED / ILLIMITÉ -40- View from the Calandria Floor

UNRESTRICTED / ILLIMITÉ -41- ZEEP – Zero Energy Experimental

• Decision made to build for Pileresearch/assist in design and start- up of National Research eXperimental • Photo is Spring 1945, pre-April 10

Picture: www.nuclearheritage.ca UNRESTRICTED / ILLIMITÉ -42- • Construction complete 4 September 1945 • 16 months after conception of the reactor

Picture: www.nuclearheritage.ca UNRESTRICTED / ILLIMITÉ -43- • Natural U-metal fuel (to start), heavy water moderator • 5 September 1945, first critical! • 1st reactor outside of U.S. • 3.5 W, 30 W for short periods

UNRESTRICTED / ILLIMITÉ -44- Pictures: NRC National Science Library • Flurry of activity to support

NRX, after which D2O was used to start NRX • Tested NRU rod design • Lattice physics for power reactors • 25 years of service

UNRESTRICTED / ILLIMITÉ -45- ZED-2 Research in Support of CANDU Physics

• Carrying on probing spatial variation from Advanced Fuels work • More in-core detectors to track flux shape real time • Reactor transfer function measurement and model development • Flux perturber(s) • Even delayed neutron effectiveness carries some spatial dependence • All good tests for 3D analysis methods

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