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ALLEGRO project challenges

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 , 201 2. Content. ALLEGRO reactor recall ALLEGRO safety Selected challenges.

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ALLEGRO project challenges

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  1. ALLEGROproject challenges Petr DAŘÍLEK, Radoslav ZAJACdarilek@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

  2. Content • ALLEGRO reactorrecall • ALLEGRO safety • Selectedchallenges VUJE , Inc., Okružná 5, SK 918 64 Trnava, Slovakia

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

  4. ALLEGRO reactor recall [1] General frame: Gas-cooled Fast Reactor (GFR) development GFR R&D : challenges • Self-sustainable cores • A robust safety approach • An attractive power density ~100 MW/m3 • An innovative fuel (FPs confinement, fast neutrons, high HM content, high temperature) • Reactor design and safety systems / management of the decay heat removal • In common with the VHTR : • Technology of He circuits and components • High temperature materials • Power conversion • And together with the SFR: • Fuel recycling technologies • And possibly …: • Power conversion, Fuel materials and design?

  5. ALLEGRO reactor recall [2] • Objectives • 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 • Fast flux irradiation and contribution to the development of future fuels (innovative or heavily loaded in Minor Actinides) • 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

  6. ALLEGRO reactor recall [2] MOX Carbide Control Shutdown Reflector Shield 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/m3 • No energy conversion, 2nd 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)

  7. ALLEGRO reactor recall [2] Experiment MOX Control Shutdown Reflector Shield The 75 MWth MOX core • Studies for a 75 MW core (5 rows) • MOX ~25 %Pu • Frequency 1, 3at%, 660 EFPD *1 year = 365 EFPD

  8. ALLEGRO reactorrecall • ALLEGRO safety • Selectedchallenges VUJE , Inc., Okružná 5, SK 918 64 Trnava, Slovakia

  9. 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 1st level and DHR loops as backup systems (2nd and 3rd level) • Same conclusions are anticipated for ALLEGRO • Primary circuits were doubled ( 2* 37 MWth) • 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

  10. ALLEGRO safety [2] ALLEGRO DHR Strategy • Global principle • 1st level : use of primary blowers with pony motors for pressurized and depressurized situations • 2nd level : DHR loops with forced circulation for pressurized and depressurized situations • 3rd level : DHR loops with natural circulation for pressurized situations only • 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)

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

  12. ALLEGRO safety [2] ALLEGRO – Provisional safety conclusions • Situation of the transient analysis for ALLEGRO MOX core • (Deliverable D1.4-1 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 • The results of the Prevention phase are useful to define scenarios for MOX core severe accidents

  13. ALLEGRO reactorrecall • ALLEGRO safety • Selectedchallenges VUJE , Inc., Okružná 5, SK 918 64 Trnava, Slovakia

  14. Selected challenges – He purification [3] Specification for Primary Coolant Chemistry Example : control of the oxidizing potential in the coolant for HTR/VHTR Water injection and Control of H2O/H2 ratio 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,…). Protect metallic materials against corrosion (oxide layer) Limit the oxidation of carbon based material

  15. Selected challenges – He purification [3] Maintenance operation Fuel elements, reflector replacement, loading and unloading operations Graphite degassing O2, N2 H2, CO, CO2, N2, H2O CH4, CO2, CO, H2, H20 Fission and activation products Thermal insulator degassing H20, CO2, N2, O2 N2, O2, H2, H2O O2, N2 Metallic structure degassing Welding, junctions Particles : Graphite, thermal insulator Source of impurities in primary coolant PRIMARY CIRCUIT

  16. Selected challenges – He purification [3] HTR10 purification unit Primary circuit 30 Bar, 210 kg/h Activated carbon bed -160°C Filtration < 5 mm Molecular sieve bed Ambient T CuO Oxidation bed 250°C 30 Bar, 10.5 kg/h Filtration

  17. 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)

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

  19. Selected challenges – He purification [3] HPC – Main characteristics • For inlet impurities concentration of 40ppmV, regeneration frequency: • Oxidation column : 5 days • Molecular sieve column : 12 hours • Activated carbon column: 24 hours

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

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

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

  23. Selected challenges – Coaxial tubes [1] External liner Spring Internal liner Upper Flange Lower flange. "S" seal He tightness • HETIQ : • 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 : • Helicoflex type • SPG type Imposed deformation Imposed load

  24. Selected challenges – Coaxial tubes [1] He tightness • HETIQ : • Outlook : • 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 APX2 (flexible graphite with low oxidation at high temperature • Seals behavior in dynamic loop. Ultraseal • June2002 : Patent FD 355 « Smooth graphite seal with metallic liner for high temperature»

  25. 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

  26. 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/cm3) Water just under the fissile zone: Reactivity decrease ALLEGRO Safety Meeting, Budapest, 28-29 March 2012

  27. 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

  28. Selected challenges – Refractory fuel evolution [6] • Evolutionofpininternals: • linermadeof Ta/Nb (W/Rhatpreviousdesign) • gapfilled by porous C or fibrousSiCf VUJE , Inc., Okružná 5, 918 64 Trnava, Slovakia

  29. REFERENCES VUJE , Inc., Okružná 5, 918 64 Trnava, Slovakia

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