“АЕЦ КОЗЛОДУЙ” ЕАД, гр. Козлодуй
България, 3321, гр. Козлодуй, +359 973 7 2020, факс +359 973 80591
Start up physics tests of Units 5&6 (WWER1000) at
Kozloduy NPP by comparison with the calculated
neutron physics characteristics
Stoyanova I., I_STOIANOVA@npp.bg
Antov A., anantov@npp.bg
(Kozloduy NPP, Bulgaria)
ABSTRACT
In conjunction with each refuelling shutdown of the reactor core, nuclear design calculations
are performed to ensure that the reactor physics characteristics of the new core will be consistent with
the safety limits. Prior to return to normal operation, a physics test program is required to determine if
the operating characteristics of the core are consistent with the design predictions and to ensure that the
core can be operated as designed. Successful completion of the physics test program is demonstrated
when the test results agree with the predicted results within predetermined test criteria. Successful
completion of the physics test program and successful completion of other tests which are performed
after each refuelling provides assurance that the plant can be operated as designed.
The calculated neutron-physics characteristics values of Kozloduy NPP Unit 5 and Unit 6
(WWER 1000) obtained by the computer code package KASKAD [1] are compared with the obtained
results during the start up physics tests. The core fuel loading consists of 163 fuel assemblies (FAs).
The calculated values are given according to actual experimental conditions of the reactor
core during start up physics tests.
The report includes comparisons between calculation results by code package KASKAD
(BIPR7A) and experimental data values of main neutron-physics characteristics during start up physics
tests in selected recent cycles of Kozloduy NPP Unit 5 and Unit 6.
2
1. Boric acid concentration
The purpose of this measurement is to determine if the measured and predicted total core reactivity
are consistent.
Critical boric acid concentration at Hot Zero Power (HZP) measured at the beginning of the cycle
(BOC) is compared to calculated critical boric acid concentration. Table 1 shows the comparison
between the measured and calculated values. The difference between measured and calculated boric
acid concentration is about 0.3 g/kg.
Table 1. Comparison between measured and calculated critical boric acid concentration
(BOC, Хe=0, HZP)
Number
of
Unit/ cycle
Assemblies
TVSA
Т,
С
Р1к,
kg/сm2
Height of control
rods bank, %
Н 19
Н10
Снзвоз [g/kg]
Calc.- Meas.
[g/kg]
Measured Calculated
Unit 6/
cycle 10
12
279.8
159.8
100
20.0
8.65
8.88
0.23
Unit 6/
cycle 11
60
280.0
160.0
100
33.3
8.16
8.42
0.26
Unit 6/
cycle 12
97
277.6
160.0
100
33.3
8.40
8.72
0.32
Unit 5/
cycle 12
48
277.0
160.1
100
37.0
8.84
8.94
0.10
Unit 5/
cycle 13
91
277.3
159.1
100
32.0
8.65
8.72
0.07
279.7
160.7
100
35.0
8.55
8.58
0.03
273.3
160.0
100
24.0
8.78
8.60
-0.18
277.1
160.9
100
89.3
8.96
8.96
0.00
Unit 5/
cycle 14
133
The average difference between measured and calculated critical boric acid concentration is
lower than 0.3 g/kg.
3
2. Isothermal temperature coefficient (ITC)
The purpose of this measurement is to determine if the measured ITC of the reactor is
consistent with the predicted value.
The measurements are conducted in course of the processes of increasing and decreasing of
primary circuit coolant temperature in a slow and continuous manner with a stable coolant boron
concentration.
Table 2a. Comparison between measured and calculated ITC (BOC, Хe=0, HZP) Unit 6
Unit Cycle
10
6
11
12
H-10th control
rods bank
[%]
[cm]
28.0
28.5
31.5
31.5
99.1
100.9
111.5
111.5
29.5
26.4
29.0
33.0
29.0
31.0
34.0
104.4
93.5
102.7
116.8
102.7
109.7
120.4
27.0
27.0
30.0
95.6
95.6
106.2
СH3BO3
[g/kg]
8.59
8.16
8.34
ITC
Delta ITC
T1
[°C]
T2
[°C]
275.8
273.9
276.8
273.4
274.1
276.8
273.4
276.6
-9.485
-9.549
-9.376
-9.355
-6.80
-15.70
-4.60
-11.20
2.685
-6.151
4.776
-1.845
281.8
279.3
278.5
280.5
279.0
278.1
279.5
279.8
277.1
280.0
279.5
276.5
279.0
280.5
-11.571
-11.063
-11.214
-11.232
-10.878
-10.983
-11.188
-8.96
-6.98
-12.80
-8.96
-7.68
-11.37
-11.52
2.611
4.083
-1.586
2.272
3.198
-0.387
-0.332
275.5
272.9
275.0
273.5
274.5
276.0
-10.260
-10.101
-10.320
-7.56
-5.50
-5.67
2.700
4.601
4.650
Calculated
[pcm/°C]
Measured (Meas.-Calc.)
[pcm/°C]
[pcm/°C]
The difference between measured and calculated ITC is in the range of (-6.2÷4.8) pcm/°C.
4
Table 2b. Comparison between measured and calculated ITC (BOC, Хe=0, HZP) Unit 5
Unit
H-10th control rods
СH3BO3
bank
Cycle
[g/kg]
[%]
[cm]
12
5
13
14
29.0
34.0
33.0
33.5
102.6
120.4
116.8
118.6
29.0
27.0
28.5
28.0
28.0
102.6
95.6
100.9
99.1
99.1
26.7
28.0
94.4
99.1
8.84
8.65
8.78
Delta ITC
(Meas.Calc.)
Calculated Measured
[pcm/°C] [pcm/°C] [pcm/°C]
ITC
T1
[°C]
T2
[°C]
274.5
271.5
275.5
270.7
271.0
275.5
271.5
273.0
-7.890
-7.809
-7.857
-7.528
-5.50
-7.70
-5.76
-7.26
2.390
0.109
2.097
0.268
277.5
275
273
275.5
271.5
275.5
273
276
272
274
-9.632
-9.217
-9.245
-9.119
-8.923
-7.70
-7.70
-10.70
-8.00
-9.20
1.932
1.517
-1.455
1.119
-0.277
273.3
274.3
276.5
276.5
-12.63
-12.74
-12.03
-11.68
0.600
1.060
The difference between measured and calculated ITC is in the range of (-1.5÷2.4) pcm/°C.
3. 10th control rods bank worth
The test objective is to measure the worth of selected control rod group. Experiments were
conducted in course of gradual decreasing of boric acid concentration in the primary circuit coolant
while inserting the control rod group from H-10th ~90% to the lower end of the core height.
The purpose is to determine if the worth of 10th control rod group is consistent with
prediction.
The measured and calculated integral and differential efficiencies of group 10th, HZP at BOC
are shown in Table 3 and Figures 1-5.
5
Table 3. Integral efficiencies of 10th control rod group
C H 3BO 3
T
Unit Cycle (mean)
[°C]
[g/kg]
5
H-10th control
rods bank
Hlow
Hup
[cm]
[cm]
Integral worth, 
Calculated
 [βeff]
Measured
 [βeff]
Relative error
 exp   calc
 exp
12
8.76
277.3
0
318
0.953
0.898
-6.1
13
8.77
277.3
88
322
0.999
1.015
1.6
14
8.75
277.1
94
316
0.840
0.907
7.4
11
8.28
277.3
74
318
0.822
0.844
2.6
12
8.59
277.6
10
326
0.980
1.080
9.3
*100%
6
The measured integral efficiencies differ from the calculated ones approximately by less than 10%.
CONCLUSION
The comparisons between calculation results by code package KASKAD (BIPR7A) and
experimental data values of main neutron-physics characteristics during start up physics tests in recent
cycles (fuel loading with TVSA) of Kozloduy NPP Unit 5 and Unit 6 show that:
-
the predicted values of the critical boric acid concentrations at BOC, HZP are of
accuracy ±0.3 g/kg;
-
the predicted values of the integral efficiencies of 10th control rod group at BOC, HZP
are of accuracy ± 10%;
-
the difference between measured and calculated ITC at BOC, HZP of Unit 5 is in the
range of (-1.5÷2.4) pcm/°C.
All these results are in agreement with the BIPR7A passport data.
The differences between measured and calculated ITC at BOC, HZP of Unit 6 differ from the
BIPR7A passport data. This needs additional analysis.
6
еff
х 10*2 [eff/cm]
1.20
1.20
1.15
1.15
1.10
1.10
1.05
1.05
1.00
1.00
0.95
0.95
0.90
0.90
0.85
0.85
0.80
0.80
0.75
0.75
0.70
0.70
0.65
0.65
0.60
0.60
0.55
0.55
0.50
0.50
0.45
0.45
0.40
0.40
0.35
0.35
0.30
0.30
0.25
0.25
0.20
0.20
0.15
0.15
0.10
0.10
0.05
0.05
0.00
0.00
0
20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 320 340 360
Haz[cm]
Fig.1. Measured and calculated differential and integral efficiency working
group control rod Cycle 12 of Unit5 ( BOC, Nt=0%).
+
#
- eff] - BIPR7A
- eff ] - exp.
o -  10*2 [beff /cm] - BIPR7A
* - 10*2 [beff /cm] - exp.
7
 х 10*2 [eff/cm]
  еff
1.20
1.20
1.15
1.15
1.10
1.10
1.05
1.05
1.00
1.00
0.95
0.95
0.90
0.90
0.85
0.85
0.80
0.80
0.75
0.75
0.70
0.70
0.65
0.65
0.60
0.60
0.55
0.55
0.50
0.50
0.45
0.45
0.40
0.40
0.35
0.35
0.30
0.30
0.25
0.25
0.20
0.20
0.15
0.15
0.10
0.10
0.05
0.05
0.00
0.00
0
20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 320 340 360
Haz[cm]
Fig.2. Measured and calculated differential and integral efficiency working
group control rod Cycle 13 of Unit5 ( BOC, Nt=0%).
+ -  eff] - BIP R7A
# -  eff ] - exp.
o * -
  10*2 [beff /cm] - BIP R7A
  10*2 [beff /cm] - exp.
8
 х 10*2 [eff/cm]
  еff
1.20
1.20
1.15
1.15
1.10
1.10
1.05
1.05
1.00
1.00
0.95
0.95
0.90
0.90
0.85
0.85
0.80
0.80
0.75
0.75
0.70
0.70
0.65
0.65
0.60
0.60
0.55
0.55
0.50
0.50
0.45
0.45
0.40
0.40
0.35
0.35
0.30
0.30
0.25
0.25
0.20
0.20
0.15
0.15
0.10
0.10
0.05
0.05
0.00
0.00
0
20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 320 340 360
Haz[cm]
Fig.3. Measured and calculated differential and integral efficiency working
group control rod Cycle 14 of Unit5 ( BOC, Nt=0%).
+ -  eff] - BIP R7A
# -  eff ] - exp.
o * -
  10*2 [beff /cm] - BIP R7A
  10*2 [beff /cm] - exp.
9
 х 10*2 [eff/cm]
  еff
1.20
1.20
1.15
1.15
1.10
1.10
1.05
1.05
1.00
1.00
0.95
0.95
0.90
0.90
0.85
0.85
0.80
0.80
0.75
0.75
0.70
0.70
0.65
0.65
0.60
0.60
0.55
0.55
0.50
0.50
0.45
0.45
0.40
0.40
0.35
0.35
0.30
0.30
0.25
0.25
0.20
0.20
0.15
0.15
0.10
0.10
0.05
0.05
0.00
0.00
0
20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 320 340 360
Haz[cm]
Fig.4. Measured and calculated differential and integral efficiency working
group control rod Cycle 11 of Unit 6 ( BOC, Nt=0%).
+ -  eff] - BIP R7A
# -  eff ] - exp.
o * -
  10*2 [beff /cm] - BIP R7A
  10*2 [beff /cm] - exp.
10
 х 10*2 [eff/cm]
  еff
1.20
1.20
1.15
1.15
1.10
1.10
1.05
1.05
1.00
1.00
0.95
0.95
0.90
0.90
0.85
0.85
0.80
0.80
0.75
0.75
0.70
0.70
0.65
0.65
0.60
0.60
0.55
0.55
0.50
0.50
0.45
0.45
0.40
0.40
0.35
0.35
0.30
0.30
0.25
0.25
0.20
0.20
0.15
0.15
0.10
0.10
0.05
0.05
0.00
0.00
0
20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 320 340 360
Haz[cm]
Fig.5. Measured and calculated differential and integral efficiency working
group control rod Cycle 12 of Unit 6 ( BOC, Nt=0%).
+ -  eff] - BIP R7A
# -  eff ] - exp.
o * -
  10*2 [beff /cm] - BIP R7A
  10*2 [beff /cm] - exp.
REFERENCES
1. Комплекс программ нейтронно-физических расчетов РНЦКИ Комплекс программ
КАСКАД
Инструкция по използованию графического интерфейса комплекса КАСКАД -
Бычкова Н.А., Томилов М.Ю., Москва 2002.
2. Комплекс программ нейтронно-физических расчетов РНЦКИ Комплекс программ
КАСКАД Программа БИПР-7А - Суслов А.А., Шишков Л.К., Большагин С.Н., Москва 2002.
3. Комплекс программ нейтронно-физических расчетов РНЦ КИ. Программа
ПЕРМАК-А. Описание алгоритма и инструкция для пользователя. Алешин С.С., Большагин
С.Н., Томилов М.Ю.
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