Technical Meeting on Innovative Heat Exchanger and Steam Generator Designs for Fast Reactors

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1 Technical Meeting on Innovative Heat Exchanger and Steam Generator Designs for Fast Reactors Spiral-Tube Steam Generators for compact integrated reactors. The ELSY project Vienna, December 21-22,

2 The STSG is one of the key innovations which have been proposed during the ELSY project and which have contributed to its success. ELSY (European Lead-cooled System) is a three years project of the 6 th FP of EURATOM, started on ELSY aims at demonstrating the feasibility of a 600 MWe pool-type LFR, whilst fully complying with the Generation IV goals. ELSY is a breakthrough in the development of the LFR embodying innovations intended to overcome the alleged unfavourable properties of lead and even to exploit them as an advantage. Some of the ELSY innovations have already been engineered to confirm feasibility, whereas for others additional effort is necessary to transform a c o n c e p t u a l p r o p o s a l i n t o a r o b u s t e n g i n e e r e d d e s i g n. Note*: reference configuration of the primary system established in the first two years. 2

3 Main advantages and main drawbacks of HLM Atomic mass (g/mol) Chemical Reactivity (w/air and Water) Boiling Point ( C) Retention of fission products Density (Kg/m 3 C Cost Melting Point ( C) Compatibility with structural materials Opacity Lead- Bismuth (LBE) 208 Inert 1670 High High 125 Corrosive Yes Lead (Pb) Inert 1737 High Low 327 Corrosive Yes Note*: Several projects are based on the Lead-Bismuth Eutectic (LBE) which has a lower melting point (125 C), but several more impor tant inconveniences: - LBE is expensive - LBE expands at solid state - Under irradiation LBE produces large amount of polonium - LBE produces slag in the melt - LBE produces dust in the cover gas 3

4 Unique characteristics of lead make LFR very safe and contribute to reach the economic goal Atomic mass (g/mol) Chemical Reactivity (w/air and Water) Boiling Point ( C) Retention of fission products Density (Kg/m 3 C Cost Lead (Pb) Inert 1737 High Low Design impact -Fast reactor - No intermediate loop - Simple DHR system - No pressurized primary system - No risk of coolant boiling - Reduced risk of release of volatile contaminants in case of core damage. - Minimum/no risk of core compaction - Marginal cost of the coolant 4

5 Technological development and design provisions are necessary to overcome or mitigate the impact of the drawbacks. Lead drawbacks High Density Increased mechanical loads. Repair difficult in lead Opacity and High Melting Point Refueling difficult in lead. ISI difficult in lead. Risk of lead freezing Corrosion of structural materials Available hightemperature structural materials not adequate. 5

chemical reactivity of lead with air and water.

6 Reactor simplification and economical benefit of the elimination of the intermediate loop are the result of the low chemical reactivity of lead with air and water. but primary system can result larger than for sodium because of the reduced speed of lead. 6

7 Typical results of medium-size projects previous to ELSY height of the reactor vessel similar to that of a SFR with consequent unacceptable seismic loads; volume of the reactor vessel of about ~ 4 m3/mwe, twice as that of SFR offsetting the economic advantage of elimination of the intermediate loop; same or more difficult operation of refuelling and ISI To avoid those inconveniences, differently from previous LFR designs, ELSY relies on the sodium experience not to reproduce typical SFR configurations, but to identify solutions which fully exploit lead properties. 7

Main parameters of ELSY (solution with open square FA) ELSY Power, MWe 600 Thermal efficiency % 42 Primary coolant Primary coolant circulation (at power) Primary coolant circulation for DHR Pure lead

8 Main parameters of ELSY (solution with open square FA) ELSY Power, MWe 600 Thermal efficiency % 42 Primary coolant Primary coolant circulation (at power) Primary coolant circulation for DHR Pure lead Forced Natural Core inlet temperature ( C) 400 Core outlet temperature ( C) 480 Fuel Neutron spectrum MOX with and without MA Fast Fuel pin diameter, (mm) 10.5 Fuel cladding temperature (max) C ~ 550 Active core dimensions Height/ equivalent diameter, (m) 0.9/4.32 Fuel column height. (mm) 900 N Fuel Assemblies (FA) 162 FA geometry Open (wrapperless) FA pitch, (mm). 294 N fuel pins / FA 428 Fuel pin pitch at 20 C, (mm) Enrichment, (%wt HM) 13,9 square 14.54/17.63/20.61 Pu, three radial zones Power conversion system Water-superheated steam at 18 MPa, 450 C Primary/secondary heat transfer system Eight Spiral-Tube SGs 8

9 ELSY Extended-stem Fuel Assemblies Spiral-tube SG Primary Pump Core 9

10 Spiral-tube SG (STSG) is made of superposed plane tube-spirals 10

11 The STSG for a compact LFR STSG For a given volume the cross section of the STSG perpendicular to the lead flow path is at least 3 time that of a Generic SG (GSG), ½*Π*(D+d)*h ¾*Π*D^2 ( d~1/2*d and in general D<h) ¼*Π*(D^2) and the length of the lead flow path inside the bundle of the STSG is about 4 times shorter than that of a GSG. GSG ½*(D-d) ~ ¼*D h 1*D 1) The STSG features a small tube-pitch resulting in a tube bundle with half the volume of a helical-tube bundle Smaller diameter and shorter reactor vessel 2) while limiting the primary pressure loss to half the pressure loss of a helical-tube SG. Shorter reactor vessel 11

12 The STSG for a compact LFR, cont.d ELSY SPX1 3) The free space inside the inner shell of the STSG can be used to locate the primary pump. Smaller diameter of the reactor vessel 4) The outlet of the cold lead all along the outer shell of the STSG keeps the reactor vessel at uniform cold temperature without need of insulation, deversoir, heat exchangers Smaller diameter of the reactor vessel 12

13 The STSG for a compact LFR, cont.d ELSY SPX1 5) A short STSG can be positioned high in the reactor vessel because: - fed from the bottom, does not present risks of gas entrainment. - the radial flow path is not interrupted by a lowered lead free level in case of reactor vessel leakage. Shorter reactor vessel 13

14 The STSG for safety a) Feed water and steam collectors are installed outside the reactor vessel. No risk of catastrophic primary system pressurization. 14

15 The STSG for safety, cont.d b) The tube bundle of the STSG is positioned up in the reactor vessel. In case of Steam Generator Tube Rupture steam leaks near the lead free level reducing lead displacement. c) The casing of tube bundle is bottom-closed. In case of Steam Generator Tube Rupture no downward steam jet is possible and only small bubbles can be entrained into the core. 15

16 The STSG for safety, cont.d d) The tube bundle of the STSG is made of long tubes (high water-side pressure loss). Superheated or supercritical steam can be generated. In case of Steam Generator Tube Rupture the water-steam leak rate is limited. e) The tube bundle is made of few tubes with excess flow valves at feed water inlet and check valves at steam outlet. In case of Steam Generator Tube Rupture feed of the water-steam leak is timely blocked. 16

17 The STSG for safety, cont.d R 6 4 R f) In a STSG each tube is surrounded by only two tubes. In case of Steam Generator Tube Rupture, a ruptured tube inside the spiral-tube bundle can damage at most two other tubes. 17

18 The STSG for safety, cont.d g) the STSG tube bundle is positioned at higher level than the core. lead natural circulation is possible in case of decay heat removal trough the water-steam loops. 18

core cooling by natural circulation is possible by RVACS and/or Dip

19 The STSG for safety cont.d SFR h) The STSG outlet is positioned well above the core mid level. core cooling by natural circulation is possible by RVACS and/or Dip Coolers in case of unavailable water-steam loops, even in a primary system with cylindrical inner vessel configuration. 19

20 The STSG for a LFR with removable internals 1st 2nd 3rd 4th b a d c First condition: a>b, Second condition: c>d The STSG is fed from the bottom. all in-vessel components are removable, including the Cylindrical Inner Vessel and the SG that can be disengaged from the Inner Vessel by a combination of radial and vertical displacements (investment protection). 20

21 Spiral-tube SG of ELSY Ф i of the SG inner shell (mm) 1120 Ф e of the SG inner shell (mm) 1220 Ф i of the inner companion shell (mm) 1230 Ф e of the inner companion shell (mm) 1240 Porosity of the inner shells (%) 30 Ф i of the outer companion shell (mm) 2420 Ф e of the outer companion shell (mm) 2430 Фi of the SG outer shell (mm) 2440 Ф e of the SG outer shell (mm) 2540 Porosity of the outer shells (%) 15 Number of tubes 218 Length of the tubes (m) 55 Number of tubes per layer 2 O.D. of the tubes (mm) 22,22 Thickness of the tubes (mm) 2,5 Radial pitch (mm) 24 Axial pitch (mm) 24 Height (coils only) (mm)

LEAD is compatible with air and water Water and air are used as

(RVACS) 4 Water Direct Reactor Cooling (W-DRC) systems 4 Condensers

Double-wall, helium-bonded-outer-tube bayonet tubes with continuously

22 LEAD is compatible with air and water Water and air are used as cooling fluids for the DHR loops A Reactor Vessel Air-Cooling System (RVACS) 4 Water Direct Reactor Cooling (W-DRC) systems 4 Condensers on the main steam lines. Double-wall, helium-bonded-outer-tube bayonet tubes with continuously monitored double barrier between primary system and outside. (A 800 kw dip cooler has been successfully tested by ENEA) 22

23 LEAD has high density The Fuel Assemblies (FA), extended with a stem above the lead free level, are sustained by buoyancy and kept in the vertical position by a support system in gas. Reactor Roof FA support system Extended-stem Fuel Elements 23

24 Lead is opaque and has high melting point The Refueling machine operates in gas. All reactor structures which constitute the vertical support of the fuel elements can be inspected, from outside, in gas space. Handling Mechanisms Heat transfer fluid (hot lead) Fuel element stem (cold) Operator Heat transfer fluid (hot oil) Handle (cold end) Nuclear fuel Vessel Special fuel Vessel 24

25 Lead has high melting point Wrapperless fuel elements to cool the core even in case of frozen primary loop 25

26 ELSY has a low core outlet temperature Effective corrosion protection Compact stable oxide barrier on ferrite/martensite and austenite Transition zone Oxide layer growth on ferrite/martensite Mixed corrosion mechanism: oxidation / dissolution on austenite Additional protection needed Oxide layer unstable FeAl alloy coating stable Main ongoing activities to address the material technology gaps. Material screening in Japan and Korea Functionally Graded Composite (FGC) under development at MIT, in the US. Fe-Al coating with DC-sputtering technique at the University of Trento, Italy 400 C 480 C- 500 o C 550 o C 600 o C Temperature C 650 Technology gap Critical Parameter Technological Limits 480 C 400 C Pumps V outlet Core inlet 480 ~ Vessel Internals Cladding Negligible few ~ 100 O 2 control + alluminization O 2 control Low [O] activity Material embrittlement Lead Freezing T, dpa dpa 26

27 LEAD is corrosive ELSY has a low core outlet temperature Advantages Drawbacks 400 C core inlet temperature 480 C core outlet temperature Enough above the melting point of lead (no risk of freezing) Sufficiently high, to reduce steel embrittlement in fast neutron flux. Sufficiently high, for an efficient thermal cycle ( 42% net efficiency). Low, to use as much as possible proven steels. Low, to rely as much as possible on the experience on LBE. Increased flowrate, larger core and primary system dimensions Coolant Core inlet T ( C) Core oulet T ( C) SVBR-75/100 LBE ELSY Lead 480 BREST

28 Primary boundary Cold collector level Level at refuelling Hot collector level ELSY has no intermediate loops and a low Primary System specific volume ELSY m3/mwe ~1,5 SFR, pool m3/mwe ~2 Most LFR projects m3/mwe ~4 B C B C L. Cinotti Spiral-Tube Steam Generators for compact integrated reactors. 28 Vienna, December 21-22, 2011

Innovative solutions in ELSY allow a compact primary system The result is a reactor with very short vessel (~ 9 m) Preliminary mechanical analyses confirm the

29 Innovative solutions in ELSY allow a compact primary system The result is a reactor with very short vessel (~ 9 m) Preliminary mechanical analyses confirm the feasibility of the 600MWe reactor. Prospective corrosion resistant materials would allow to increase the core T and to reduce the flow rate, opening the way for a larger reactor 29

30 In spite of the low core outlet temperature, efficiency is high because the thermal cycle is not degraded by the intermediate loop. EMPRESARIOS AGROUPADOS evaluation Lead temperature at SG inlet 480 C Lead temperature at SG outlet 400 C Steam generator feedwater temperature 335ºC Steam temperature at SG outlet 450ºC Steam generator outlet pressure 18 MPa Steam Generator Power 1388 MW Condensate pump Consumption 0,51 MW Feed-water Pump Consumption 23,5 MW Cycle Efficiency 43,05% 30

31 OPEN SQUARE CORE Core configuration (one quarter) Pb FA cross section at level of the fuel pins 32,0 30,8 30,6 B4C SS box 35,3 38,3 291,9 mm (FA size at 20 C) 13,9 41,7 (= 3 pitches) B 4 C Finger + SS BOX (Void) + 3 SPACERS + Pb B4C Hom. Region: - 3,00 % Void 13,9 * 3 (Real Void - 3 spacers) - 42,79 % SS (Box+Spacers+Finger Clad) - 35,08 % B4C - 19,13 % Pb Fuel Inner (56) Fuel Interm. (50) Fuel Outer (56) B4C CR Barrel Dummy Fuel wt % HM Inner 14,54 Intermediate 17,63 Outer 20,61 Core av. 17,59 Power MWth 1500 Fuel column height (mm) 900 N Fuel Assemblies (FA) 162 FA geometry Open square FA pitch (mm) 294 N fuel pins / FA 428 Fuel rod pitch (at 20 C) (mm) 13,9 Fuel rod outer diameter (mm) 10,5 31

32 An adiabatic core (it burns its own MA) with BR 1 is feasibile 1,0E ,0E ,0E+03 1,0E+02 [ kg ] 1,0E+01 U (-9,6% at FA EoL) 1,0E+00 1,0E-01 [ days ] Pu (-1,7% at FA EoL) MAs MA equilibrium content (at equilibrium): 310 [kg] ~ 4,8% Pu BOL ~ 0,9% HM BOL, BUav. (5 years) 78,1 MWd kg -1 (HM) BUmax (5 years) 94 MWd kg -1 (HM) 32

33 Clad peak temperature of 552 C in case of Station Blackout (PLOF+PLOH) Lead Flowrate at Core Inlet 600 Core Temperatures Core flow 550 Core inlet Core outlet Max clad Flowrate (kg/s) Temperature ( C) Time (s) Time (s) Natural circulation in the primary circuit stabilizes at 6% of nominal value after primary pumps trip. Clad peak temperature of 502 C at t = 1005 s; pump inertia = 3000 kg-m 2 and t(1/2ω )=2,1 s 33 33

34 The ELSY project has demonstrated: ELSY Results (1/2) 1. A mid-size LFR is feasible. Main lead drawbacks have been solved at design level or are under solution at technological level. Lead drawbacks High Density Increased mechanica l loads. Repair in lead difficult. Opacity and High Melting Point Refueling in lead difficult. ISI in lead difficult. Corrosion of structural materials Available structural materials not adequate. Proposed solutions Shortheight vessel. Replaceable components. Made possible by the STSG which also makes LFR Refueling machine operating in gas. FA are sustained by buoyancy, kept in the vertical position by structures which can be inspected from outside in gas space. New materials. Corrosion protection of structural materials. economic and improves its safety. 34

35 ELSY Results (2/2) 2. A LFR is sustainable. - Adiabatic core 3. A LFR is safe. - Physical properties of lead - Forgiving design 4. A LFR is economic - Suppression of the intermediate loops - Simple DHR systems - Compact design (if a STSG is adopted) 35

36 Potential for other applications of STSG Sodium fast reactors Compactness Reduction of heat transfer surface Wastage limitation X (1) X (2) Integrated LWR XX (3) X Renewable energies X XX (4) Note: (1) STSG is a compact solution for SFR, but compactness is not a key feature for a SG located outside the reactor vessel. (2) The tube disposition reduces the risk of wastage, the effect of the different tube pitch has not been evaluated. (3) Reduction of the reactor vessel dimensions of 20-30% is important for integrated LWR (4) Renewable energy systems rely on coolants (molten salts, diathermic fluids, gas...) with low heat transfer properties. 36

37 Conclusion & perspectives STSG is an interesting innovation and a key component for safety and economics of the LFR (reduction of the primary system volume by about factor 2). A request of contribution to the development of a STSG for different applications has been addressed on 2010 to the Italian Ministero dello Sviluppo economico. Next design and experimental activities on STSG will be devoted to renewable energies. 37

ELSY The European Lead Fast Reactor

Le competenze industriali ELSY The European Lead Fast Reactor Alessandro.Alemberti@ann.ansaldo.it FR09 - International Conference on Fast Reactors and Related Fuel Cycles - Challenges and Opportunities