Лист 1

Trial operation of TVS-2 at Balakovo NPP.Analysis of results and further modernization.

Authors: I. N. Vasilchenko, S. B. Ryzhov, U. G. Dragunov, S. N. Kobelev,V. S. Medvedev (FSUE EDO “GIDROPRESS”); V. V. Molchanov,V. M. Trojanov, S. E. Volkov (JSC TVEL); A. M. Pavlovichev (RRC KI);V. V. Novikov (VNIINM); A. A. Enin, V. V. Rozhkov (JSC NZHK);J. J. Lihachev (JPPE); A. V. Mikhalchuk (Balakovo NPP).

Abstract.

In the report [1] the causes, premises of development, basic characteristics and the firstresults of trial operation of TVS-2, which is an essentially new design of WWER-1000 FA, arepresented.

In this report the more detailed specifications of TVS-2 considering modifications ofseparate units, and also the conditions and results of its operation at Balakovo NPP on the basisof three fuel loads are presented.

Implementation of TVS-2 at power units of Balakovo NPP in the fuel cycle 3×350 eff.days has been started in 2003 and the reactor core full loading at Balakovo NPP, Unit 1 hasbeen achieved in 2005.

Considering positive operational experience of TVS-2 at Unit 1 implementation ofTVS-2 by full make-ups has been started at other units of Balakovo NPP.

The results of operation confirm the predicted essential increase in reliability of reactorscram, possibility of implementation of new design restrictions, which enable to form the fuelloadings with small neutron leakage. Besides, the favorable results on performance of transport- technological procedures enabling to reduce time of PM has been obtained.

On the basis of this structure the detailed project report of a new FA modification withlengthened fuel stack has been developed, the necessary calculational and experimental justifi-cations have been performed, materials for obtaining a license to trial operation of the first lotof such fuel assemblies beginning from 2006 are being prepared.

Лист 2

1. Design features of TVS - 2

The general view of TVS-2, consisting of a skeleton, fuel rod bundle, capand tail-piece is presented in fig.1.

The skeleton serves as a bearing structure of TVS-2. The skeleton isassembled of 18 guiding channels (GCh), a central channel (CCh) and spacinggrids (SGr) welded to them and is formed to provide resistance to bending andtorque loads, irrespective of the forces of interaction of fuel rods with SGrcells during operation.

A SGr is welded toGCh by contact spot welding,as shown in fig. 2, in twoplaces along the height of acell.

GCh serve as a load-bearing element of skeletonand as guides for displace-ment of CPS AR in them. Thecentral channel serves as aguide for displacement of neutron flux sensors in it.

GCh and the CCh are made of alloy Э635, having increased stress-strain properties for geometrical stability during long-term operation.

Bending rigidity of SGr is enhanced (the height of cell field is in-creased up to 30 mm and cell tube thickness is increased up to 0,3 mm) toprovide for the absence of SGr warping and for slipping of fuel rods in SGrcells at temperature and irradiation elongation.

- geometry of SGr cells is optimized to provide for the necessaryforces of fuel rod slipping, ensuring decrease in thermo-mechanical loads onthe components of fuel rod bundle, with preservation of fuel rod resistance tovibrofretting-deterioration during operation.

The easy-off cap of TVS-2 enables to withdraw failed fuel rods, en-sures TVS-2 maintainability in the NPP conditions.

Installation and removal of caps is carried out by means of collet chuck, without anyadditional parts.

To increase cross rigidity and decrease the friction force between movable and fixedcomponents of TVS-2 cap the guiding shroud is introduced into the design of the cap.

The spring unit of the cap enables to damp CPS CR drop completely. Rigidity and op-erating forces of the cap spring unit are reduced to increase TVS-2 stability during operation.

The lower supporting grid has holes to fasten fuel rods, guiding channels, the centralchannel and has through slots for coolant flow in inter-fuel rod space of the bundle of fuel rodsand gadolinium fuel rods.

Fig. 1

Fig. 2

GCh

SGr

Лист 3

The lower grid slots, shown in fig. 3, have triangular form and are located symmetri-cally relative to holes for fastening the fuel rod lower tail-pieces.

The size of a turn-key TVS-2 is approached to theupper design limit for reduction of the gap around of TVS-2 and restriction of maximum bowings of TVS-2 in thecore during operation.

As to the number of SGr, two modifications ofTVS-2 have been developed. The first one has 15 SGr, thesecond one has 12 SGr. The first modification has greaterrigidity and is used in the first transitional loading withTVS-2. In all subsequent loadings, down to the stationaryone, the second modification of TVS-2 having smaller hydraulic resistance and more compati-ble with the prototype structure is used. SGr arrangement in this modification is made with thepitch of 340 mm in such a manner that boundary spacing grids and every fourth SGr in themiddle part are at the level of SGr of the prototype. The calculational pre-reactor tests haveshown sufficiency of bending rigidity, both in the stationary and transitional loading of TVS-2.

Fig. 3

Лист 4

2. Basic parameters of TVS - 2 operationat Balakovo NPP

Unit 1 of Balakovo NPP has been chosen as the basic unit for TVS-2 trial operation.The trial operation at Balakovo NPP, Unit 1 is performed according to a special pro-

gram which basic sections determine acquisition of data on:– core physical identification from the point of view of neutron - physical charac-

teristics;– compliance with thermal-hydraulic parameters;– mechanical reliability of structure.Unit 1 of Balakovo NPP contains the reactor plant of B-320 type. The reactor operates

under base load with imposing dispatcher restrictions within the ranges allowed by fuel speci-fications.

The diagram of thermal load is shown in fig. 4.

0

800

1600

2400

3200

0 100 200 300

Lifetime duration, eff. days

Ther

mal

pow

er, M

W

during fuel life 13

0

800

1600

2400

3200

0 100 200 300

Lifetime duration, eff.days

Ther

mal

pow

er, M

W

during fuel life 14Fig. 4 – Diagram of thermal load at Balakovo NPP, Unit 1

Coolant flowrate through the reactor is 86830 and 88163 m3/h (average and max. offuel load 13 ); 87425 and 88342 m3/h (average and max. of fuel load 14)

Temperature at the core outlet 316,1 and 317,6 °С (average and max. of fuel load 13);316,2 и 317,5 (average and max. of fuel load 14)°С.

Specific character of multiunit plant consists in that for units of such NPPs the decid-ing index is availability factor, therefore fuel cycles with large duration between refuelings arecalled for. However restrictions to duration of a cycle are imposed now by the established pe-riodicity of survey of the equipment and carrying out of repair work. In this connection TVS-2are operated in the following fuel cycle:

Duration of lifetime ......................................................... ~ 350 eff. days.Number of loaded FA ...................................................... 54 / 55 pcs.Average enrichment of loaded fuel .................................. 4,12 %Achievable burn-up of fuel

- average .............................................................. ~ 44,5 MVt⋅days / kg U- maximum .......................................................... ~ 47,5 MVt⋅days / kg U

Лист 5

3. Results of TVS - 2 trial operationat Balakovo NPP

The trial operation of TVS - 2 at Balakovo NPP has been started in 2003 from loadingof the test batch of 54 pcs in number into the reactor core of Unit 1and operation during fuel life 13.

Dynamics of TVS - 2 implementation at Unit 1 of Balakovo NPP is presented in fig. 5.

Fig. 5

Installation of TVS - 2 into the core, completed with 2/3 fuel assemblies of previousdesign (AFA), was accompanied by increased efforts since at the same time the flattening ofthe core was performed. The further additional loading of TVS - 2 has improved the conditionsof transport - technological procedures.

During start-up of the unit after PM and during its shut-down for PM the tests forchecking of time of CPS CR drop at RP in the hot state were carried out.

Before start-up of the unit after PM and after its shut-down for PM the measurementsof displacement forces of AR coupled with the extension shafts of CPS CR drives from thecompacted upper unit were carried out.

In the period of PM during fuel life preparation the measurements of straightness ofFA guiding channels before and after refueling were performed. Data on FA bowings and gapfields between them were obtained.

During refueling the measurements of forces of FA withdrawal - installation in the re-actor core and cooling pond were carried out.

In the beginning of fuel life the measurements of neutron - physical characteristics andthermal-hydraulic characteristics of the RP under the conditions with two, three and fourworking RCPs were performed.

During fuel life the radiochemical inspection of primary coolant specific activity wascarried out.

During refueling the TVS - 2 state was subject to examination in fuel-handling ma-chine (FHM) mast.

PM-2003Batch 1 (54 pcs.)TVS-2 with 15 SGr

PM-2004Batch 2 (54 pcs.)TVS-2 with 12 SGr

PM-2005Batch 3 (55 pcs.)TVS-2 with 12 SGr

Лист 6

The results of measurements performed at Balakovo NPP, which are presented below,characterize normal serviceability of the new structure and confirm the compliance of its char-acteristics to those of the design.

3.1 Checking of time of CPS CR drop

The regulation value of time of CPS CR drop is 1,2-4 s.Data on time of drop from the moment of TVS - 2 implementation are presented in

fig. 6. It shows that time of drop is stabilized at the level of 2 s. From the data presented it fol-lows, that during operation of the unit the changes worsening the conditions of CPS AR dropdo not occur and installation of a lot of fresh fuel assemblies is not a necessary condition forthis purpose as it has been earlier and as it has been felt even during TVS – 2 implementation.

2,1

2 2,1 2,2

1,85 2,

1

1,7

2,3

2,75

2,2

2,2

1,9

1,7

2,12,2 2,

4

2,2

3,4

1,7

2,1

1,7

0

0,5

1

1,5

2

2,5

3

3,5

4

begi

nnin

g

end

begi

nnin

g

end

begi

nnin

g

end

begi

nnin

g

fuel life 12 fuel life 13 fuel life 14 fuel life15

1-year FA 2-year FA 3-year FA

Fig. 6 – Time of CPS CR drop

3.2 Measurement of forces of CPS CR pushing

The change of forces of CPS AR pushing from the compacted upper unit in the begin-ning of fuel life shall not exceed ± 10 kg-force.

Data on forces of CPS AR pushing over the last 10 years are presented in fig. 7. Theupper values show the forces of pushing before refueling, the lower values – after refueling. Inthe diagram two groups of values are specified: the maximum (unit) value for all CPS CR andthe average value for all CPS CR. And the average value is determined as average from themaximum forces.

Лист 7

02468

101214161820222426283032

1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006PM

Fric

tion

forc

es o

f CPS

CR

,kg-

forc

e

Average Maximum

PM Load Stage Averagevalue Maximum value Quantity of

AFA Quantity of

TVS-22002 11 Before refueling 14,24 21,00 1482002 12 After refueling 5,24 10,00 1612003 12 Before refueling 14,82 29,30 1612003 13 After refueling 4,52 10,01 107 542004 13 Before refueling 8,11 26,00 107 542004 14 After refueling 2,27 5,30 55 1082005 14 Before refueling 2,24 7,50 55 108

Лист 8

2005 15 After refueling 2,18 4,00 1 162

Fig. 7 – Change of the average and maximum values of the maximum friction forces at CPSCR pushing from the compacted upper unit before and after refueling depending on the year ofoperation

Data on forces at the beginning and at the end of fuel life from the moment of imple-mentation of TVS - 2 for three groups of FA are presented in fig. 8. The diagram indicates thatin TVS-2 the forces of CPS AR pushing at the beginning of fuel life 13 do not exceed thevalue of 2 kg-force, in AFA they are at the level of 10 kg-force, and in TVS-2 the forces ofpushing at the end of fuel life do not exceed the value of 4 kg-force, in AFA they exceed thevalue of 10 kg-force.

Since the second loading of TVS - 2 the situation with forces of CPS AR pushing hasimproved. So at the beginning of fuel life 14 the forces in TVS-2 do not exceed 4 kg-force, inAFA– 6 kg-force, and at the end of fuel life the forces do not exceed 4 kg-force, in AFA – 8kg-force. At the beginning of fuel life 15 the forces of pushing do not exceed 4 kg-force.

Лист 9

1,75 3,

55

3 2,5

1,9

10

26

4 3,5

3,6

10

23,5

5,3 7,

5

4

0

5

10

15

20

25

30

beginning end beginning end beginning

fuel life 13 fuel life 14 fuel life15

1-year FA 2-year FA 3-year FA

Fig. 8 – Maximum values of forces of CPS AR pushing in FA groups

3.3 Results of measurements of TVS – 2 straightness

The results of measurements of FA deflections from straightness for two levels alongthe height in the core of Unit 1 of Balakovo NPP are presented in fig. 9. For fuel assemblies ofAFA type (by the results of calculation researches) straightness depends on the reactor state,namely straightness in the free state is not kept during installation of PTU and during the sub-sequent compacting the reactor. For fuel assemblies with rigid skeleton this dependence ispractically absent and it is possible to assert, that the measured straightness is kept during op-eration of the reactor.

From data presented it follows, that by 2005 the core has come practically to the initialstate from the point of view of straightness. It is confirmed also by data on actuation time andforces of CPS AR pushing.

The change of the maximum and average values of TVS - 2 bowings at two levelsalong the height is shown in fig. 9. The upper values correspond to bowing before refueling,the lower values – after refueling.

26,9

5,2

13,9

8,9

4,36,1

12,55

2,01 1,952,714,213,49

0

5

10

15

20

25

30

2002 2003 2004 2005 2006PM

FA b

owin

g, m

m

at height of 1400 mm from the core bottom

8,78

6,8

4,07

2,50

4,79

3,18

2,2

5,5

4,0

6,5

2,81

0

1

2

3

4

5

6

7

8

9

10

2002 2003 2004 2005 2006РM

FA b

owin

g, m

m

at height of 2400 mm from the core bottom

– maximum bowing – average bowingFig. 9 – Change of the maximum and average FA bowing

at two levels along the core height

Лист 10

The data on FA groups are presented in fig. 10.

26,9

6,3

4,6

2,1

4,8

3,2

26,8

13,9

8,6

4,3 6,

1

4,9

23,2

8,4 8,9

3,9 5,

4

5,2

0

5

10

15

20

25

30

before after before after before after

РM-2003 PM-2004 PM-2005

FA b

owin

g, m

m

1-year 2-year 3-year

at height of 1400 mm from the core bottom

8,4

5,6

5,4

2,5

5,5

4

7 6,5 8

4

6

3,1

8,7

6,4 6,7

5,5 6,

8

3,6

0

5

10

15

20

25

30

before after before after before after

РM-2003 PM-2004 PM-2005

FA b

owin

g, m

m

1-year 2-year 3-year

at height of 2400 mm from the core bottom

Fig. 10 – Maximum bowings of FA at two levels of the core height

Fig. 11 gives general representation of change of the FA form in the core. From thefigure the conclusion about improvement of situation with geometry of the core with TVS - 2is made up.

Fig. 11 – Change of the average value of FA axis bowing after refueling by the years

FA height, mm

FA b

owin

g, m

m

Лист 11

3.4 Transport - technological procedures at TVS – 2 refueling

The parameters established for TTP at FA refueling do not reflect directly the state ofRP safety, however they determine convenience and velocity of refueling and that, finally, in-fluences availability factor.

Distortion of FA has been resulted not only in exceeding of the established criteria ofrefueling (friction force of FA – 75 kg-force, CPS AR – 13 kg-forces), but also in problemswith installation of FA or CPS AR in the specified cell. For each case of that kind it has beenrequired to make non-standard solution either concerning the fact of increase in some setpoint,or concerning the change of situation around of the installed FA. More than 50 % of cases ofinstallation or withdrawals passed not standardly.

During operation of cores on the basis of TVS - 2 from refueling to refueling there wasan improvement of conditions and performance of the established parameters. The followingstatistics, which has been carried out by the results of PM - 2005 at Unit 1 of Balakovo NPP,indicates it.

484 operations of withdrawal and installation of FA have been performed during PM –2005, including withdrawals from the core at FA unloading, at refueling, unloading of freshfuel from casks, at installation into the core, racks of spent fuel pond.

From these 484 cases 435 operations within the ranges of 75 kg-forces, 14 caseswithin the ranges up to 100 kg-forces, 33 cases – up to 150 kg-forces and two cases – up to200 kg-forces have been fixed, only ~ 10 % of cases of nonstandard loading, considering theacquired experience, have not caused difficulties and have been overcome by simple increasein interlocking.

Thus, conditions for increase in velocity of FA vertical displacement up to 4 m / min.tested on the assembling bench are created.

Similar improvement of conditions of refueling has taken place also for CPS AR. Asagainst the previous loadings, CPS AR refueling has been performed without deviations fromregular conditions, it is also confirmed by the fact of flattening of the core.

It is necessary to note, that compactness of installation of FA and the increased rigidityof structure cannot guarantee loading of the core absolutely without problems, however it maybe easily overcome, as it has been already marked. In addition CPS AR refueling reflects thestate with reliability of CPS CR injection in EP mode, and carrying out of refueling withoutproblems is a priority condition.

3.5 Analysis of the state of springs and TVS-2 GCh

Consideration of value of springs relaxation and radiation elongation of GCh is im-portant for non-buoyancy of FA and elimination of their pinching.

In TVS - 2 design the springs made of alloy ХН77ТЮР which by the results pre-reactor and reactor tests as a part AFA have shown stability of force characteristics are applied.

In behavior of made of alloys Э110 and Э635 essential differences are determined. Infig. 12 scheme of dimensional changes of GCh made of these alloys up to burn-up ~ 50 MVt⋅days / kg U by the results post-reactor researches is shown.

Лист 12

GCh(E110)

CТ(E110)

GCh(E635)

nominal size

CТ(E110)

Fig. 12

From fig. 12 it follows, that Gch made of alloy Э100 which is under action of com-pressing force due to of irradiation-thermal creeping not only "does not grow", but also is re-duced in length while the central tube, established freely, is lengthened under action of radia-tion elongation.

The length of GCh made of alloy Э635 is practically not changed. It predeterminesalso the position of PTU in the WWER-1000 core.

In fig. 13 change of position of the PTU installed on reactor FA for two versions offuel assemblies is shown: AFA ( Volgodonsk NPP) and TVS - 2 (Balakovo NPP).

Лист 13

15,2

16,55

15,4

16,1

14,25

17,2517,0517,1

10

11

12

13

14

15

16

17

18

19

20

2000 2001 2002 2003 2004 2005 2006PM

PTU

pad

pro

ject

ion,

mm

Volgodonsk NPP

15,564 15,783

16,75

19,111

17,789

15,139

14,13913,344

10

11

12

13

14

15

16

17

18

19

20

2001 2002 2003 2004 2005 2006PM

PTU

pad

pro

ject

ion,

mm

Balakovo NPP

Fig. 13In case of installations of PTU on the fuel assemblies containing GCh made of alloy

Э110, during the cycle of operation PTU lowers by the size of GCh shortening. At installationof it onto TVS-2 the PTU practically preserves the position. In figure the process of transitionfrom one type of fuel assemblies (alloy Э110) to another type (alloy Э635) is shown. It isshown, that after loading of two lots of TVS - 2 the tendency to decrease of PTU level isstopped and during the cycle of operation there was some rise of PTU by the value of GChelongation. Later on it allows decrease of the hold-down force onto FA due to design debug-ging of PTU adjusting pads. Thus, all done measurements show positive dynamics in behaviorof fuel assemblies of the core at Balakovo NPP, Unit 1.

Лист 14

4. New modification TVS-2M

Plans to increase availability factor of Balakovo NPP have demanded elaboration of anew modification TVS - 2M. Basically this elaboration is connected to increase in fuel loadingin fuel rods and, respectively, in FA due to lengthening of stack. In fig. 14 various version ofsheathless fuel assemblies are shown.

Bundle(rigid skeleton,ZSGr with increased height and cell with wall thickness 0.3 mm,Channels of alloy Э635, number of ZSGr is optimized, fuel stack height is increased by 150mm)

Lower grid(collet chuck of fuel rods/gadolinium fuel rods)

Tail-piece(shortened)

100 мм

Bundle(rigid skeleton,ZSGr with increased height and cell with wall thickness 0.3 mm,Channels of alloy E635)

Lower grid Lower grid

50 мм

Shortened cap

50 мм

Bundle

Cap,Rigidity of shroud is increased,Improved thermal control)Cap

Fig. 14 – Versions of sheathless fuel assemblies for WWER-1000

Version TVS - 2M due to reductions of end pieces has the lengthened fuel stack and,respectively, the lengthened fuel rods. At the bottom the thirteenth SGr located closer to a tail-piece, than in prototypes, is entered. It provides additional counteraction of fuel rod bundle tovibrational loads at the inlet of fuel assembly.

Characteristics of fuel cycles of the cores on the basis of TVS - 2M with face blanketsand without them are shown in Table 1.

Table 112 months 18 months.

Fuel cycle TVS-2 TVS –2M(with blankets)

TVS –2M(without blankets)

TVS-2 TVS –2M(with

blankets)

TVS –2M(withoutblankets)

Number of make-up FA 42 42 36 42 36 70 60 60Average enrichment of FA,% 4,26 4,27 4,63 4,45 4,83 4,54 4,68 4,88

Number of burnt-out FA atthe core periphery, % 43 86 86 86 86 57 71 71

Lifetime duration 293 327,9 314,8 337 324 464 465,3 479Burn-up in the unloaded FAaverage 48,4 50,8 56,9 52,2 58,5 46,1 50,6 52,0maximum 51,5 52,4 60,0 53,9 61,1 52,1 58,7 60,3Specific consumption ofnatural uranium 0,199 0,190 0,185 0,193 0,188 0,224 0,211 0,214

Relative specific consump-tion of natural uranium 1,000 0.955 0,930 0,972 0,946 1,000 0,941 0,958

Лист 15

Finally, the presented cycle with duration ~ 480 eff. days can be used to provide forhigh availability factor. Transition to such cycle demands additional modernizations of CPSCR and sensors of in-core instrumentation system.

In 2005 the detailed project report of TVS - 2M with face blankets is developed andthe proving documentation is developed for obtaining a license to installation the first lot ofsuch fuel assemblies for trial operation in 2006.

Лист 16

Conclusion

1. As a result of hard works on modernization of FA design a new type of sheathlessTVS - 2 with the increased rigidity ensuring geometrical stability of the core, is devel-oped and has successfully passed trial operation in the reactor.

2. On the basis of the new design of TVS - 2 modification TVS - 2M with increased load-ing of the fuel stack, ensuring the lengthened fuel cycles is developed.

Лист 17

References

1. «New requirements for the WWER fuel and their consideration in designing thefuel assemblies», I. N. Vasilchenko, Yu. A. Ananyev, 5th International Conference on WWERFuel Performance, Modelling and Experimental Support, Albena, 2003.