CANDUCANDU SafetySafety #1#1 -- CANDUCANDU NuclearNuclear PowerPower PlantPlant DesignDesign

Dr. V.G. Snell Director Safety & Licensing

24/05/01 8:14 AM CANDU Safety - #1 - CANDU Design.ppt Rev. 1 vgs 1 WhatWhat AccidentAccident isis This?This?

28 killed, 36 injured, 1821 homes and 167 buildings destroyed

24/05/01 8:14 AM CANDU Safety - #1 - CANDU Design.ppt Rev. 1 vgs 2 OrOr this?this? “It could take months to determine what caused an explosion early Wednesday at Hawthorn power plant. The generating plant, which produces 15 percent of Kansas City Power & Light's electricity, will be out of operation for an extended period of time” 24/05/01 8:14 AM CANDU Safety - #1 - CANDU Design.ppt Rev. 1 vgs 3 WhatWhat isis CANDU?CANDU?

λ CANada Deuterium - the name gives the design λ started as the Canadian contribution to the War effort: to produce using natural uranium and λ the first reactor to go critical outside the U.S. was ZEEP in 1945 - too late for the War but started the Canadian nuclear civilian power programme

24/05/01 8:14 AM CANDU Safety - #1 - CANDU Design.ppt Rev. 1 vgs 4 ZEEPZEEP -- Canada’sCanada’s FirstFirst ReactorReactor

Right - ZEEP building at Laboratories near Chalk River, , as it appeared around the time of the first startup in 1945.

Left - ZEEP taken during the 1950s. Experiments were conducted on fuel for early CANDU designs, including NPD and Douglas Point

24/05/01 8:14 AM CANDU Safety - #1 - CANDU Design.ppt Rev. 1 vgs 5 CANDUCANDU GenealogyGenealogy

Darlington

900 900 MW Class CANDU 9 Reactors 800 Bruce A Bruce B

700 Pt Lepreau Embalse Qinshan 1&2 Wolsong 600 MW Class 2,3,4 600 Gentilly 2 Wolsong 1 Cernavoda Reactors

Power (MWe) 500 Pickering A Pickering B

- RAPP 1,2

200 Douglas Point Research &

KANUPP Prototype 100 NRU Reactors

ZEEP NRX NPD

19501960 1970 1980 1990 2000 2010 Years 24/05/01 8:14 AM CANDU Safety - #1 - CANDU Design.ppt Rev. 1 vgs 6 ReactorReactor PWR CANDU

24/05/01 8:14 AM CANDU Safety - #1 - CANDU Design.ppt Rev. 1 vgs 7 ReactorReactor

λ CANDU λ PWR – 380 small diameter (10 cm), thin – 1 large diameter, thick pressure (4.2 mm) pressure tubes vessel – horizontal orientation – vertical orientation – heavy water coolant (312°C) – light water coolant (329°C) – separate heavy water – coolant is the same as the moderator (65°C) moderator, both hot – reactivity devices in low – reactivity devices in high pressure moderator pressure coolant / moderator – large core, low energy density – small core, high energy density (11 MW / m3) (60 MW / m3)

24/05/01 8:14 AM CANDU Safety - #1 - CANDU Design.ppt Rev. 1 vgs 8 FuelFuel CANDU PWR

24/05/01 8:14 AM CANDU Safety - #1 - CANDU Design.ppt Rev. 1 vgs 9 FuelFuel

λ CANDU λ PWR – natural uranium – enriched uranium – low burnup – high burnup – short bundles (0.5 metres) – long bundles (3.8 metres) – on-power refuelling – shut down to refuel – remove defected fuel during – remove defective fuel only operation when shut down to refuel

24/05/01 8:14 AM CANDU Safety - #1 - CANDU Design.ppt Rev. 1 vgs 10 FuelFuel ChannelChannel

λ CANDU fuel bundles lie inside the pressure tube λ a calandria tube separates the pressure tube from the moderator λ a gas gap between the pressure tube and the calandria tube provides thermal insulation

24/05/01 8:14 AM CANDU Safety - #1 - CANDU Design.ppt Rev. 1 vgs 11 FuelFuel channelchannel

24/05/01 8:14 AM CANDU Safety - #1 - CANDU Design.ppt Rev. 1 vgs 12 HeatHeat TransportTransport SystemSystem COMPARISON OF HEAT TRANSPORT SYSTEMS PHWR PWR

Headers

* SMALL PIPING - LOW STRESSES * SIMPLE PIPING, LARGE PRESSURE VESSEL * SAFETY RODS IN MODERATOR * SIMPLE FUELLING - ONCE PER YEAR * ON-POWER FUELLING * LARGE REACTIVITY CHANGE IN OPERATION * FULL-PRESSURE RHR LOOPS * ECC NEEDED TO STOP MELTING AFTER LOCA 24/05/01 8:14 AM CANDU Safety - #1 - CANDU Design.ppt Rev. 1 vgs 13 HeatHeat TransportTransport SystemSystem

λ CANDU λ PWR – each channel is individually – the pressure vessel is a large connected to collectors pot containing all the core (headers) above the core water in one place – pumps, steam generators – pumps, steam generators above the core above the core – each particle of fluid goes – each particle of fluid goes through the core twice before it through the core once before it gets back to where it started gets back to where it started – one or two loops – two, three or four loops – operating pressure ~10 MPa – operating pressure ~15.5 MPa

24/05/01 8:14 AM CANDU Safety - #1 - CANDU Design.ppt Rev. 1 vgs 14 ModeratorModerator Relief Pipe λ cold: 65°C heavy water, large inventory: ~260 Mg λ cooling capacity: 100 MW(th) or about 4.6% of full power Calandria Calandria Vault

Pump

24/05/01 8:14 AM CANDU Safety - #1 - CANDU Design.ppt Rev. 1 vgs 15 ReactivityReactivity ControlControl

λ short-term: in-core devices (absorber & adjuster rods, light water) λ long-term: on-power refuelling λ no absorber in coolant λ little absorber in moderatormoderator exceptexcept duringduring startup after a long shutdown λ routine control: dual redundant digital computers

24/05/01 8:14 AM CANDU Safety - #1 - CANDU Design.ppt Rev. 1 vgs 16 ReactivityReactivity ControlControl

Slave Master

24/05/01 8:14 AM CANDU Safety - #1 - CANDU Design.ppt Rev. 1 vgs 17 Secondary Side Manway Main steam Secondary Side Secondary nozzle Separators λ conventional nuclear steam Primary generators and turbine / generator Separators λ the steam generators have heavy Shroud cone the steam generators have heavy U-Bend water on the primary side Tube bundle λ steam conditions: 4.7 MPa and Shroud 260°C Support Plate Cold leg Hot leg

Preheater Feedwater Inlet Tubesheet D O Outlet 2 D2O Inlet

24/05/01 8:14 AM CANDU Safety - #1 - CANDU Design.ppt Rev. 1 vgs 18 AuxiliaryAuxiliary SystemsSystems

λ CANDU has systems not found in PWRs – automated refuelling & fuel handling system – annulus gas system (leak-before-break) – shield cooling system – heavy water vapour and liquid recovery λ and systems that are found in PWRs – primary pressure & inventory control – shutdown cooling system – shutdown systems, Emergency Core Cooling, containment, emergency power etc.

24/05/01 8:14 AM CANDU Safety - #1 - CANDU Design.ppt Rev. 1 vgs 19 SystemsSystems CANDUCANDU DoesDoes NotNot NeedNeed

λ Some PWR systems are not needed in CANDU or are much simpler – no boron control system in the coolant – no boron addition to ECC water – no criticality concerns outside the reactor for new or used fuel – simpler core, reactivity devices

24/05/01 8:14 AM CANDU Safety - #1 - CANDU Design.ppt Rev. 1 vgs 20 SummarySummary

24/05/01 8:14 AM CANDU Safety - #1 - CANDU Design.ppt Rev. 1 vgs 21