NUCLEAR FUEL FOR VVER-1000 REACTORS
Fast breeder reactor BN-600 is the world’s largest currently operating fast breeder reactor that has been showcasing accident-free operation for 25 years running.
Fuel for fast breeder reactor BN-600 is manufactured as FAs supplied to unit 3 of Beloyarsk NPP (Russia). The FAs are manufactured by JSC Mashinostroitelny Zavod (JSC MSZ). The core comprises three FA types containing the fuel of different enrichments (U235 content – 17%, 21%, and 26%). FAs for the core are designed for thermal energy generation in order to pass it over to the coolant flow.
FA design includes head- and tailpieces as well as the central part. Headpiece serves for coupling with the refuelling machine during FA (un)loading. Headpieces are equipped with the axial slots for coolant exit. The central part consists of a hexagonal tube with the installed fuel rod (FR) bundle inside (total 127 FRs). Tailpiece ensures that an FA is loaded into the reactor and securely fixed there; it also ensures the required coolant flow rate through FA. FRs are loaded with fuel pellets manufactured from uranium dioxide powder enriched by U235 in central zone and blankets of depleted uranium dioxide situated at FR ends. FAs of the breeding blanket are intended to ensure reliable heat removal and recovery of fertile material. Their design and outer dimensions are identical to the FAs loaded in the reactor core, the differences relate only to their number (total 37 pieces) and FR design. FRs of the breeding blanket are loaded with fuel pellets of depleted uranium dioxide.
FRs by design are tubes made of special steel alloys, loaded with fuel material and hermetically sealed with end plugs by welding. FR-to-FR distances and FR-to-shroud-tube distances are ensured by wire wound around the FR with the required pitch. FRs are manufactured using the automated production line with the integrated state-of-the-art inspection and control equipment that can guarantee product quality and reliability. The use of materials with low swelling for FA shroud tubes and FR claddings, the use of the three enrichments for fuel fabrication as well as further development of FR and FA design and manufacturing process made it possible to improve FA in-pile behaviour and reliable operation in BN-600 reactor. The manufacturer makes continuous efforts for FR material improvement in order to reach higher fuel burnups and better FA performance. At present fuel burnup in FA reaches 11.3% ha – the world’s best obtained burnup to date. The reactor has now been transferred to 11.3% burnup level, and currently further efforts are being made to increase it to 15%.
Specifications
BN-600 fuel zones
Number of FAs in core, pieces 369
Number of FAs in breeding blanket, pieces 378
Fuel type uranium dioxide
Coolant type liquid sodium
Coolant pressure, MPa 0.9
Coolant temperature, °С, at core inlet 368
Coolant temperature, °С, at core outlet 533
FA specifications (in core)
FA maximum thermal power, MWt 4.7
Design service life, years 4
Number of FRs per FA 127
Mass, kg 103
Uranium mass per FA, kg:
enriched 28.9
depleted 19.8
Enrichment (U235 content in U), %
enriched zone 17,21,26
axial blankets (depleted uranium) <0.7
Dimensions, mm
FA length 3500
width across flats 96
Maximum specified thermal power generation, by enrichment, MWt·day/KgU:
17% 95
21% 100
26% 107
Power start-up of unit 4 (fast breeder reactor BN-800) of Beloyarsk NPP in Russia took place in 2015. Hot on the heels of NB-800 reactor it is intended to erect a BN‑1200 reactor of even larger power capacity. The core at the startup load is made up of several FA types – with uranium oxide fuel of different enrichments (U235 content – 18.5%, 21%, and 24%), with mixed uranium-plutonium oxide (MOX) pellet fuel, and with vibropac MOX fuel. All types of FAs are designed for thermal energy generation in order to pass it over to the coolant flow. Around the FAs in the core there are also FAs of radial blanket intended to ensure reliable heat removal and recovery of fertile material as well as steel and boron shield assemblies. The heart of the core comprises the startup neutron source as well as control rods incerted into the Control and Protection System (CPS) seats. JSC MSZ manufactures FAs with uranium oxide fuel, FAs of radial blanket, steel and boron shield assemblies, deliverables for FRs and FAs with MOX fuel, vessel of the startup neutron source, control rods as well as CPS seats.
FA comprises head- and tailpieces as well as the central part. Headpiece serves for coupling with the refuelling machine during FA (un)loading. Headpieces are equipped with the axial slots for coolant exit. The central part consists of a hexagonal tube with the installed FR bundle inside (total 127 FRs). Tailpiece ensures that an FA is loaded into the reactor and securely fixed there; it also ensures the required coolant flow rate through an FA. FRs are loaded with fuel pellets manufactured from uranium dioxide powder enriched by U235 in central zone and blankets of depleted uranium dioxide situated at FR ends. Design and outer dimensions of the FAs of radial blanket are identical to the FAs with uranium oxide fuel. FRs of the breeding blanket FAs are loaded with fuel pellets of depleted uranium dioxide. FA components with MOX fuel are dismountable allowing the FA manufacturer to insert FR bundles inside the shrouds with welded tailpieces. FRs in FAs of radial blanket are remotely threaded onto the profiled sheets without welding. As of the upper FA components with MOX fuel pellets, the headpiece in this case is connected to a bundle of absorber rods (ARs). This AR bundle is placed inside a hexagonal tube above the FR bundle, as it is intended to protect the permanent structural elements of the reactor. ARs of an FA are loaded with hot-pressed boron carbide inserts of natural enrichment.
FRs by design are tubes made of special steel alloys loaded with fuel material and hermetically sealed with end plugs by welding. FR-to-FR distances and FR-to-shroud-tube distances are ensured by wire wound around the FR with the required pitch. FRs are manufactured using the automated production line with the integrated state-of-the-art inspection and control equipment that can guarantee product quality and reliability. The use of materials with low swelling for FA shroud tubes and FR claddings, further development of FR and FA design and manufacturing process makes it possible to predict reliable FA operation in BN‑800 reactor with the specified characteristics for burnup and damaging dose per FR cladding.
Maximum specified thermal power generation in FAs with uranium oxide fuel for BN-800 reactor is somewhat lower that in BN-600 FAs. This is explaned by the purpose of the startup load of BN-800 reactor system that is seen as a temporary transient configuration prior to formation of the equilibrium zone completely comprised of FAs with MOX pellet fuel. In order to exclude additional transient modes when forming the equilibrium zone, reloading of FAs with uranium oxide fuel pertaining to the startup load of BN-800 reactor is initially set to be the same as for the FAs with MOX pellet fuel – after 3 microcampaigns, 465 eff.days in total (provided there is a substantial stress-strain margin for structural materials of FAs with uranium oxide fuel). For comparison, BN‑600 FAs are operated during four microcampaigns, 560 eff.days in total. Thus, given that the planned operation period is shorter ‑ the specific power generation for BN‑800 FAs with uranium oxide fuel is also a bit lower.
Specifications
|
BN-800 fuel zones | |
|
Number of FAs (with uranium oxide fuel) in core, pieces |
468 |
|
Number of FAs (with MOX pellet fuel) in core, pieces |
54 |
|
Number of FAs (with MOX vibropac fuel) in core, pieces |
36 |
|
Number of FAs in breeding blanket, pieces |
90 |
|
Coolant type |
liquid sodium |
|
Coolant pressure, MPa |
0.77 |
|
Coolant temperature, °С, at core inlet |
354 |
|
Coolant temperature, °С, at core outlet |
547 |
|
FA with uranium oxide fuel, specifications | |
|
FA maximum thermal power, MWt |
4.8 |
|
Design service life, years |
2 |
|
Number of FRs per FA |
127 |
|
Mass, kg |
103 |
|
Uranium dioxide mass per FA with uranium oxide fuel, kg: | |
|
enriched zone |
29.1 |
|
axial blankets |
27.2 |
|
Enrichment (U235 content in U), %: | |
|
enriched zones: - low enrichment zone - average enrichment zone - high enrichment zone |
18.5 21 24 |
|
axial blankets |
0.7 |
|
Dimensions, mm: | |
|
FA length |
3500 |
|
width across flats |
96 |
|
Maximum specific thermal power generation, by enrichment, MWt·day/kgU: | |
|
18.5% |
78 |
|
21% |
79 |
|
24% |
75 |