ALLEGRO project challenges Petr DALEK Radoslav ZAJAC darilekvuje

ALLEGRO project challenges Petr DAŘÍLEK, Radoslav ZAJAC darilek@vuje. sk AER Working Group F Meeting „Spent Fuel Transmutations“ Konferenční centrum AV ČR – zámek Liblice, Czech Republic April 10 -13, 2012 VUJE , Inc. , Okružná 5, 918 64 Trnava, Slovakia

Content q ALLEGRO reactor recall q ALLEGRO safety q Selected challenges VUJE , Inc. , Okružná 5, SK 918 64 Trnava, Slovakia

ALLEGRO reactor recall [1] General frame: Gas-cooled Fast Reactor (GFR) development Main motivations of GFR : The use of He as primary coolant: - Neutronics transparency With an innovative fuel - Fast N - Without phase change (no cliff edge effects) - Chemical inertness - Optical transparency - Opening the gate to high temperatures - Robust and refractory - High level of Fission Products confinement - Increased resistance to severe accidents Possible use of high temperatures with Sustainable resources management

ALLEGRO reactor recall [1] General frame: Gas-cooled Fast Reactor (GFR) development GFR R&D : challenges è Self-sustainable cores è A robust safety approach è An attractive power density ~100 MW/m 3 è An innovative fuel (FPs confinement, fast neutrons, high HM content, high temperature) è Reactor design and safety systems / management of the decay heat removal And together with the SFR: In common with the VHTR : è Fuel recycling technologies è Technology of He circuits and components And possibly …: è Power conversion, Fuel materials and design? è High temperature materials è Power conversion

ALLEGRO reactor recall [2] Objectives 1. Pilot scale demonstration of key GFR technologies demonstration (core behavior and control, refractory fuel qualification, gas reactor technologies) and dispose of a first validated Safety reference Framework 2. Fast flux irradiation and contribution to the development of future fuels (innovative or heavily loaded in Minor Actinides) 3. Potential test capacity of high temperature components or heat processes A necessary step towards an electricity generating GFR prototype, for the demonstration of the chosen solutions and the whole reactor system merits confirmation

ALLEGRO reactor recall [2] ALLEGRO main reference options Reduced scale, power about 75 MWth, loop concept, GFR type primary Helium circuit, Same as GFR core power density 100 MW/m 3 No energy conversion, 2 nd pressurized water circuit, atmospheric final heat sink Step by step approach for the core, with 2 successive configurations: – Mox core, Tinlet/Toutlet He = 260/530 °C, with some GFR advanced refractory S/As (T max MOX # 1050 °C ) – Full refractory core , Tinlet/Toutlet He = 400/850°C, representative of the GFR core Reservation for a HT test circuit (about 10 MWth) MOX Carbide Control Shutdown Reflector Shield

ALLEGRO reactor recall [2] The 75 MWth MOX core Studies for a 75 MW core (5 rows) MOX ~25 %Pu Frequency 1, 3 at%, 660 EFPD For one GFR Sub. Assembly (U, Pu)C , per year* GFR 2400 F Core ALLEGRO Mox 75 MW Frequency 1 GFR S/A Pu enrichment 17. 3% 30. 5% X 1. 8 12. 4 1014 8. 4 1014 -32% 2. at% 1. 8 at% -10% 22 15 -32% 11. 0 8. 3 -25% Fast Φ max n/cm²/s, E > 0. 1 Me. V Experiment Burn-up max MOX Control Shutdown Reflector Shield Dose max dpa Si. C R = Dose/Burn-up. dpa Si. C/at% *1 year = 365 EFPD

q ALLEGRO reactor recall q ALLEGRO safety q Selected challenges VUJE , Inc. , Okružná 5, SK 918 64 Trnava, Slovakia

ALLEGRO safety [2] Preliminary safety analysis - background Initial strategy relying on 3 DHR loops + guard containment ( medium backup Pressure) - for pressurized situations, natural circulation is possible if the blowers fail GFR CEA PSA(2007) studies led to add an additional level for pressurized situations use primary circuits at the 1 st level and DHR loops as backup systems (2 nd and 3 rd level) Same conclusions are anticipated for ALLEGRO à Primary circuits were doubled ( 2* 37 MWth) à Addition of pony motors to primary blowers (20% nom. speed for pressurized , 80 -100% for depressurized cases) fed by diesels/batteries Possibility of main water secondary circuits nat. Circulation in case of water pump failure

ALLEGRO safety [2] ALLEGRO DHR Strategy Global principle 1 st level : use of primary blowers with pony motors for pressurized and depressurized situations 2 nd level : DHR loops with forced circulation for pressurized and depressurized situations 3 rd level : DHR loops with natural circulation for pressurized situations only à Principle extended for unprotected transients Pressurized: use of primary blowers at nom. speed, secondary and tertiary circuits forced circulation Depressurized : (large breaks excluded) use of primary blowers at nom. speed combined with nitrogen injection (to be investigated)

ALLEGRO safety [2] Preliminary safety analysis - ALLEGRO DHR Strategy Graphic illustration of the (D)HR strategy proposed by CEA

ALLEGRO safety [2] ALLEGRO – Provisional safety conclusions Situation of the transient analysis for ALLEGRO MOX core (Deliverable D 1. 4 -1 of GOFASTR project) Pressurized situations can be managed using the proposed DHR strategy even with aggravating failures or combined failures (complex sequences) Depressurized situations can be controlled with 2 main loops operating over the whole break size spectrum, Small-break LOCAS could be controlled with one main loop active (single failure criterion) with broken loop closed, Cooling strategy needs to be tested and refined for unprotected transients à The results of the Prevention phase are useful to define scenarios for MOX core severe accidents

q ALLEGRO reactor recall q ALLEGRO safety q Selected challenges VUJE , Inc. , Okružná 5, SK 918 64 Trnava, Slovakia

Selected challenges – He purification [3] Purpose of Helium chemistry control Ensure safety during operation and in case of accident : limit the inventory of particles, fission products and activated species, Increase service life : minimize the interactions between gas and structures (graphite, stainless steel, …). Specification for Primary Coolant Chemistry Example : control of the oxidizing potential in the coolant for HTR/VHTR Protect metallic materials against corrosion (oxide layer) Limit the oxidation of carbon based material Water injection and Control of H 2 O/H 2 ratio

Selected challenges – He purification [3] Source of impurities in primary coolant Fuel elements, reflector replacement, loading and unloading operations Maintenance operation Graphite degassing H O 2, N 2 2 , CO , C O 2 , N 2 , H 2 O 0 2 , H 2 H , O , C O 2 , C 4 CH Thermal insulator degassing H 20, CO 2, N 2, O 2 , O Fission and activation products PRIMARY CIRCUIT O , H 2 , 2 H 2 O 2 , N 2 Metallic structure degassing Welding, junctions Particles : Graphite, thermal insulator

Selected challenges – He purification [3] HTR 10 purification unit 30 Bar, 210 kg/h Activated carbon bed -160°C Filtration < 5 mm Cu. O Oxidation bed 250°C 30 Bar, 10. 5 kg/h Molecular sieve bed Ambient T Filtration Amount before and after purification unit (ppm. V) H 2 O CO N 2 H 2 CH 4 CO 2 1 9 2 9 3 1 1 <0. 2 <0. 1

Selected challenges – He purification [3] HPC - objectives Demonstration of the feasibility of an integrated process for the purification of Helium Purpose: Demonstrate the efficiency of purification using industrial processes, Demonstrate the feasibility of primary coolant composition control through purification and controlled injection of selected impurities, Ensure the coolant chemistry quality control for a technological loop in reactor conditions (pressure and materials)

Selected challenges – He purification [3] Oxidation HPC loop Adsorption Molecular sieve Adsorption Activated carbon

Selected challenges – He purification [3] HPC – Main characteristics Flow rate (g/s) Pressure (bars abs. ) Temperature (°C) Volume (L) Oxidation (Cu. O) 5 - 20 25 - 80 300 Regeneration: 350°C 10 Molecular sieve 5 – 20 25 – 80 25 Regeneration: 250°C 50 (x 2) Activated carbon 5 – 20 25 – 80 -180 Regeneration: 150°C 20 For inlet impurities concentration of 40 ppm. V, regeneration frequency: • Oxidation column : • Molecular sieve column : • Activated carbon column: 5 days 12 hours 24 hours

Selected challenges – He purification [3] HPC – 3 D view

Selected challenges – Coaxial tubes [2] ALLEGRO Primary System Overview DHR IHX DHR loops Main vessel Main IHX #2 x 40 MW) Main blower HT IHX (10 MW)

Selected challenges – Coaxial tubes [4] ALLEGRO Safety Reference Design Safety valve ( DP, p, K) in cold DHR branch ON Natural position 50 MW Design 1 PCS OFF Forced convection from other blowers Safety valve ( DP, p, K) in cold main branch OFF Natural position and from other blowers 75 MW Design 2 PCS ON Forced convection from main own blower Coaxial branch design of loop circuits

Selected challenges – Coaxial tubes [1] HETIQ : He tightness – Seals design & qualification in GCR conditions : • Economic aspect : Reduce the leaks to 10 % of the He inventory • Safety : reduce contamination due to leaks. – 2 seals type tested : Imposed deformation • Helicoflex type External liner Spring Internal liner Imposed load Upper Flange • SPG type Lower flange. "S" seal

Selected challenges – Coaxial tubes [1] HETIQ : – Outlook : He tightness • Improvement of Helicoflex seal : – Liner material modification (Monel, Tantale, …) – Bonding issue : used of coatings, – New seals flat seals with : » Thermiculite 866 (vermiculite exfoliated & laminated) » Sigraflex APX or APX 2 (flexible graphite with low oxidation at high temperature Ultraseal • June 2002 : Patent FD 355 « Smooth graphite seal with metallic liner for high temperature» • Seals behavior in dynamic loop.

Selected challenges – Water in the core [5] Water ingress • Water leaking to the primary and the core from the connected water-based system • Heat exchangers • Decay heat removal • Relatively slow leaking rate, operating conditions, nominal pressure and temperature kept, vaporized water • Ideal gas assumption for vapor + helium • ECCO+ERANOS RZ transport (BISTRO Sn ) calculation for different cores ALLEGRO Safety Meeting, Budapest, 28 -29 March 2012 25

Selected challenges – Water in the core [5] Water flood • Cooling the core in emergency situation by water. Is it possible to cool the shutdown core by water without boron? • Hot shutdown condition, below the saturation temperature of the water, inserted control rods • 260 ˚C, 70 bars, reference calculation without water • Water in liquid phase (0. 787 g/cm 3) Water just under the fissile zone: Reactivity decrease Core type Δρ 0 efpd MOX+6 GFR -626. 7 0 efpd MOX+6 STEEL -625. 5 660 efpd MOX+6 GFR -671. 6 660 efpd MOX+6 STEEL -668. 2 ALLEGRO Safety Meeting, Budapest, 28 -29 March 2012 26

Selected challenges – Water in the core [5] Water in the core - conclusions The water related accidents have no negative impact on the safety. The core will remain subcritical when water in vapor or in liquid phase enters the core. • In case of the water ingress – above the saturation temperature of the water - the reactivity increase remains very low, and if the vapor content is significant, than it will cause a reactivity decrease. • In case of flooding – below the saturation temperature - the reactivity increase is smaller than the absolute value of the shut down reactivity, consequently the reactor remains subcritical even in case of using not borated water. Question of the presenter: Before an unintentional flooding, can the reactor be critical below the saturation temperature of the water? Are there technical solutions or/and operational rules to avoid this situation? ALLEGRO Safety Meeting, Budapest, 28 -29 March 2012 27

Selected challenges – Refractory fuel evolution [6] Evolution of pin internals: • liner made of Ta/Nb (W/Rh at previous design) • gap filled by porous C or fibrous Si. Cf VUJE , Inc. , Okružná 5, 918 64 Trnava, Slovakia

REFERENCES [1] L. Cachon: Helium technology & components design, Presentation at Allegro technical meeting, 28. -29. February 2012, Cadarache [2] Ch. Poette: Recall of ALLEGRO main design&safety options from past CEA studies, Presentation at Allegro technical meeting, 28. -29. February 2012, Cadarache [3] K. Liger: Helium chemistry control and monitoring for Gas Cooled Reactors, Presentation at Allegro technical meeting, 28. -29. February 2012, Cadarache [4] ALLEGRO Design, CEA presentation at Allegro technical meeting, 28. -29. February 2012, Cadarache [5] Z. Elter, V. Brun-Magaud, D. Blanchet: Analysis of reactivity effects in the ALLEGRO reactor, Presentation at ALLEGRO Safety Meeting, 28. 29. 3. 2012, Budapest [6] M. Zabiego: Task 2. 2: Modelling results and updated pin design, Go. Fast. R 3 rd Progress Meeting, 27 -28 March 2012, Budapest VUJE , Inc. , Okružná 5, 918 64 Trnava, Slovakia