Modification of fuel for increasing the power of Paks units Botond Beliczai PA Zrt. NUFO RFO 2009.

Increasing the lattice pitch and its effect Profiled enrichment 4th unit 23rd cycle subchannel outlet temperature values applying fuel assemblies with different lattice pitch Assembly 12.2 mm lattice pitch 12.3 mm lattice pitch Difference C312.9 C C C313.4 C C C307.3 C C C287.1 C C

Geometry of Hf-layer in the CFA

Effect of applying Hf- layer in the CFA Decreasing the power peak in the pin next to the CFA

Purpose of modification: helping in the increase of heat power Increasing the subchannel outlet temperature reserve for 8 % heat power increase: 5 ( 4+1) C Sources of increasing the subchannel outlet temperature reserve : Change in the pressure control:1 C VERONA upgrade + modified engineering limits 1.5 C Modified fuel 1.5 C Alltogether4 C Other sources: More conservative reload pattern Reduced pressure in the secondary circuit Applying a mixing modell inside the FA

Measured characteristics of reload pattern of unit 4 _____________________________________________________________________________ |Mintavetel: :14:40 >>> IRIS <<< 4.bl. 20.kamp eff. nap| |_____________________________________________________________________________| |Telj. |SZBV 6cs.|Cborsav |T hideg|T meleg|DeltaT|R.forgalom |By pass|Pr.nyom.| | 96.1%|218.07cm | 6.5g/kg|265.50C|296.73C|31.23C| t/h| 3.80%| b| |_____________________________________________________________________________| |MAX3 : Osszefoglalo naplo a tartalekok alapjan legterheltebb kazettakrol | |_____________________________________________________________________________| | Reaktorfizikai feldolgozas alapjan szubcsatorna kilepo homerseklet | | tartalek (TS-t) minimum, futoelem linearis teljesitmeny tartalek (NL-t) | | minimum, futoelem teljesitmeny tartalek (PP-t) minimum es kazetta | | teljesitmeny tartalek (AP-t) minimum szerint kivalasztva. | |=============================================================================| | 1. legterheltebb kazettak | |Kiv|koord/sz| TS-t ( Tsub) | NL-t ( Nlin) |PP-t (Ppin) |AP-t (Pass) | |===|========|===============|==================|==============|==============| TS-t:11-28/ (313.3) C 45.2 (240.8) W/cm 6.6 ( 45.4) kW 0.90 (5.38) MW NL-t:19-34/ (313.0) C 45.1 (240.9) W/cm 6.5 ( 45.5) kW 0.88 (5.40) MW PP-t:15-52/ (310.0) C 54.4 (231.6) W/cm 6.5 ( 45.5) kW 0.91 (5.37) MW AP-t:19-34/ (313.0) C 45.1 (240.9) W/cm 6.5 ( 45.5) kW 0.88 (5.40) MW |=============================================================================| | Maximalisan elerheto teljesitmenyek az alapveto korlatok szerint | |=============================================================================| Szubcsatorna kilepo homerseklet szerint: % Futoelem linearis teljesitmeny szerint: % Futoelem teljesitmeny szerint : % Kazetta teljesitmeny szerint : % |=============================================================================| | Maximalisan elerheto teljesitmeny : % |=============================================================================|

Characteristics of reload patterns Before increasing the heat power: 90 FAs/cycle, 4-year usage of working FAs 1485 MW power, unchanged average enrichment: 102 FAs/cycle, higher relative fuel cost (Ft/kWh) Enhancing the economy: higher enriched FAs with burnable poison –Boric acid conc. at BOC, moderator temperature coefficient –Subcriticality under the conditions of storing-transporting

Opportunities for fuel development Present or modified geometry Enrichment ( 4.2 – 4.4) Annual number of FAs, 4 or 5-year usage of FAS, maximum burnup Pins with Gd-burnable poison (number, arrangement) CFA follower (with burnable poison ?)

Different perspectives of investigations Economy ( Ft / kWh ) Maximum burnup (licensing, reliability) Storage subcriticality Planning capabilities for reload patterns – equlibrium, transient – reserves to the limits ( 1485 MW ! )

Fuel costs CycleFAs / cycleFuel cost / kWh Present / 1485 MW 1021 Gd-1 / 1485 MW % Gd-2 / 1485 MW %

Present and expected burnups

Higher enriched fuel (3 Gd pins)

6 Gd or 3 Gd pins

Limits during the cycle (examples) 6 Gd pins 3 Gd pins

Storage subcriticality 6 Gd pins: deep subcriticality for all cases 3 Gd pins : Gd-1 o.k., Gd-2 New calculations: –Modified geometry with 3 Gd-pins: o.k.

Ultimate common proposal/ 1 - Diameter of fuel pin - 9,07 mm; - Height of fuel pin in the working FA mm; - Height of fuel pin in the working control FA mm; - Outer diameter of fuel pellet - 7,6 mm; - Inner diameter of fuel pellet - 1,20 mm; - Lattice pitch of fuel pins- 12,3 mm; - Thickness of the shroud of working and control FAs - 1,5 mm; - Outer „diameter” of working and control FAs mm; - Average enrichment of working and control FAs kb 4,25 %;

Ultimate proposal / 2

Higher enriched fuel (Russian proposal)

Features of equilibrium cycle/1 FUEL DESCRIPTION 1ST C. 2ND C. 3RD C. 4TH C. 5TH C. 3-gd pins working FA gd pins.Hf fol. FA %-os follower FA

Features of equilibrium cycle/2 teff power rodh6 tin flow cb apmax s po ppmax s po pin tsmax s po cha nlmax nllim nltar s po le pin

Process of works 2006 second half: decision making (Hungarian – Russian) 2006 end : contracts for the analysis (TVEL, KFKI, etc. ) 2007 –2008: safety analyses 2009 : Test FAs to Paks 2010 : FAs for the whole core (84 pieces)

One main problem: mixing in the FA-head

Test FA for hydraulical measurement

Process of solution Buying the measured results from TVEL CFD program validataion Parametrization of temperature difference Introduction of its results into VERONA system Check on the test FAs, corrections