ML082210118
| ML082210118 | |
| Person / Time | |
|---|---|
| Site: | Washington State University |
| Issue date: | 08/04/2008 |
| From: | Wall D Washington State Univ |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| Download: ML082210118 (21) | |
Text
WASHINGTON STATE r2UNIVERSITY Nuclear Radiation Center August 4, 2008 United States Nuclear Regulatory Commission Document Control Desk Washington D.C. 20555-0001 Docket Number 50-27 Facility License Number R-76 The purpose of this letter is to clarify the responses to RAI questions 6, 9, 15, 16, 28, 33, 36, and 40 that were provided in the June 13, 2008 letter from Washington State University to the U.S.
Nuclear Regulatory Commission.
The clarification information for RAI questions 6, 9, 15, 16, 28, 33, 36, and 40 is included with this letter as an attachment, titled, "REVISED RESPONSES TO QUESTIONS 6, 9, 15, 16, 28, 33, 36, AND 40 OF THE:': WASHINGTON STATE UNIVERSITY RESPONSE TO RAI SUBMITTAL TO NRC DATED JUNE 13, 2008."
I declare under penalty of perjury that the foregoing is true to the best of my knowledge.
Respectfully Submitted Donald Wall, Ph.D.
Director Nuclear Radiation Center Washington State University Enclosure P.O. Box641300, Pullman, WA 99164-1 300 509-335-8641
- Fax: 509-335-4433
- www.wsu.edu/nrc
REVISED RESPONSES TO QUESTIONS 6,9,15,16,28,33,36, AND 40 OF THE WASHINGTON STATE UNIVERSITY RESPONSE TO RAI SUBMITTAL TO NRC DATED JUNE 13,2008
- 6. Table 2 and Section 4.5.10. Table 2 has a calculated maximum pulsed reactivity insertion of $2.02 for mixed core 34A while the historical pulsing data has reactivity additions of
$2.15. Please explain Revised Response:
While regenerating the Axial Peaking Factors (APF) for all rod positions for Core 34A, one error was found in the IFE 2 - C4NW location listed in Table 16 of the August 2007 conversion safety analysis. The number 1.13 should be 1.43. Only the cold critical case had a wrong APF.
Some typos were found in the Table 16.
Some of the factors listed in the Table 16 had wrong factors. The Intra -Rod factors for the hot rod, IFE 1 - D6NW and IFE 2 - C4NW had wrong factors. However, in the previous pulsing calculations the correct Intra - Rod factors were used.
The old and the updated' Table 16 data are shown below.
Old Table 16 Power Peaking Factors -=WSU Mixed HEU Core 34A Current Operating Condition - Rods at Critical Positions Cold Critical - 23°C Hot Critical - 2800 C RPF APF Intra-Rod RPF APF Intra-Rod Hot Rod 2.56 1.27 2.01 2.49 1.29 1.99 Ave Rod 1.00 1.27 1.50 1.00 1.33 1.50 IFE 1 - D6NW 1.77 1.27 0.85 1.69 1.28 0.85 IFE 2-C4NW 1.39 1.13 0.85 1.51 1.44 0.85 Updated Table 16 Power Peaking Factors - WSU Mixed HEU Core 34A Current Operating Condition - Rods at Critical Positions Cold Critical - 230 C Hot Critical - 2800 C RPF APF Intra-Rod RPF APF Intra-Rod Hot Rod 2.56 1.27 1.23 2.49 1.29 1.21 Ave Rod 1.00 1.27 1.50 1.00 1.33 1.50 IFE 1 - D6NW 1.77 1.27 0.52 1.69 1.28 0.52 IFE 2 - C4NW 1.39 1.43 0.52 1.51 1.44 0.52 New pulsing calculations were performed for the IFE 2 - C4 NW case. The new results are shown in the updated Table 19.
The data presented in Table 19 from the SAR is for mixed core 34A, and is based upon calculations performed with the BLOOST code. New pulsing calculations were performed for the IFE 2 - C4 NW case. The new results are shown in the updated Table 19.
Table 20 from the SAR provides a larger pool of historical pulsing data. Both tables are reproduced below. The peak temperatures for rod position D4NE were also calculated and have been added to the reproduction of Table 20. A complete discussion of the calculation methodology is presented in the response for RAI Question 22. Comparison of the experimentally determined pulsing data and the modeled data demonstrate the model underestimates peak power, total energy release and peak temperatures.
Old Table 19 Pulse performance: Measured and Calculated, WSU Mixed HEU Core 34A Parameter Pulse
$1.50 $1.75 $2.00 $2.30 $ 2.50 Measured Data (a)
P (MW) 240 440 1030 E(MW -sec) 16 20 25 N/A N/A 0
T .3(OC)
D6NW 279 310 344 C4NW 254 281 313 BLOOST-calculation fi (MW) . 649 1321 2206 3537 4580 E(MW- sec) 19 26 32 40 45 T (-C) (D4NE) 558 701 820 954 1030 Tcore (°C) 201 252 300 356 387 T (°C)
D6NW 260 313 358 405 436 C4NW 201 241 276 316 341 (a) Pulse data taken from test pulses performed on November 21, 2005 2
Updated Table 19 Pulse performance: Measured and Calculated, WSU Mixed HEU Core 34A Pulse Parameter
$1.50 $1.75 $2.00 $2.30 $ 2.50 Measured Data (a)
P (MW) 240 440 1030 E(MW -sec) 16 20 25 N/A N/A 0.3(oC)
D6NW 279 310 344 C4NW 254 281 313 BLOOST-calculation
/(MW) 649 1321 2206 3537 4580 E(MW - sec) 19 26 32 40 45 T(-C) (D4NE) 558 701 820 954 1030 Tcore (°C) 201 252 300 356 387 10.3 (C)
D6NW 260 313 358 405 436 C4NW 238 286 328 373 400 (a) Pulse data taken from test pulses performed on November 21, 2005 3
Historical Pulsing Data for WSU Core 34A Ptlse Date Reactivity 10.3 10.3 Peak Energy Peak number added D6NW C4NW Power (MWos) temperature (MW) D4NE 1040 11/21/2005 1.25 242 227 60 11.5 414 1041 11/21/2005 2.00 332 317 1200 24 702 1043 11/21/2005 1.50 279 254 16 527 1044 11/21/2005 1.50 279 254 240 16 527 1045 11/21/2005 1.75 310 281 440 20 618 1046 11/21/2005 2.00 344 313 1030 25 722 1047 12/5/2005 1.25 241 217 120 12.4 438 1048 5/31/2006 1.25 246 223 120 11.6 417 1049 5/31/2006 1.75 305 279 500 17.2 555 1050 5/31/2006 2.00 378 309 1000 20 618 1051 11/6/2006 1.25 259 230 160 12 427 1052 11/6/2006 1.50 292 252 260 13 453 1053 11/6/2006 1.75 319 286 480 17.2 555 1054 11/6/2006 2.00 355 317 ---- 21 640 1055 11/6/2006 2.15 375 334 1420 25 722 1056 11/6/2006 2.15 382 340 1420 24 702 1057 12/14/2006 1.75 317 281 1200 ........
1058 1/29/2007 1.25 261 228 190 11.9 425 1059 1/29/2007 2.15 376 335 1420 24.8 718 1060 1/29/2007 2.00 355 315 1000 22 661 1061 1/29/2007 0.75 92 78 0 0 ....
1062 1/29/2007 1.01 218 188 399 7.8 310 1063 1/29/2007 1.03 222 193 399 8.3 325 1064 5/14/2007 1.25 256 160 11 401 1065 5/14/2007 2.00 354 316 1000 21.5 650 1066 5/14/2007 1.50 292 259 220 14.3 486 1067 5/14/2007 1.75 320 284 440 16.8 546 1068 5/14/2007 1.25 257 229 ---- 10.5 387 1069 5/14/2007 1.50 290 257 210 14.2 484 1070 8/7/2007 1.50 294 260 300 15 503 4
The following table compares calculated data in updated Table 19 above with measured historical pulsing data in IFE locations D6NW and C4NW for a reactivity insertion of $2.00.
IFE-1 IFE-2 Hot Rod D6NW C4NW D4NE T, -C T, -C T,- C Calculated in Table 19 358 328 820 using BLOOST code Average of 6 Historical 351 +/- 17 315 +/- 3 666 + 39 Pulses of $2.00 Insertion Measured Measured Calculated*
- Calculated using the Nordheim-Fuchs model as described in the response to Question 22.
Temperatures calculated using the BLOOST code agree well with the measured temperatures in IFE locations D6NW and C4NW. However, the temperature in the hot rod in location D4NE is considerably higher when calculated using the BLOOST code rather than the Nordheim-Fuchs variable heat capacity model for a reactivity insertion of $2.00. As a result, the BLOOST calculations in Table 19 are considered to be conservative in that a smaller maximum pulsed reactivity insertion of $2.02 is needed to reach the limiting temperature of 830 0 C for pulse operation.
For a reactivity addition of $2.15, the average of two measured temperatures in IFE locations D6NW and C4NW were 379 +/- 5 'C and 337 +/-4 'C, respectively. The corresponding average peak temperature in the hot rod location D4NE calculated using the Nordheim-Fuchs variable heat capacity model was 712 +/- 14 'C. This temperature is well below the limiting temperature of 830°C for pulse operation.
The following tables in the August 2007 conversion safety analysis are also updated here.
The power peaking factors for WSU mixed LEU core 35A at BOL are listed in Table 17. The APF for IFE 2 - C4NW at cold critical case had a wrong factor; 1.17 should be 1.46.
Old Table 17 Power Peaking Factors - WSU Mixed LEU Core 35A - BOL Beginning of Life Rods at Critical Positions Cold Critical - 23 0 C Hot Critical - 2801C RPF APF Intra-Rod RPF APF Intra-Rod Hot Rod 2.56 1.27 1.35 2.47 1.29 1.19 Ave Rod 1.00 1.29 1.55 1.00 1.33 1.55 IFE 1 - D6NW 1.73 1.26 0.51 1.64 1.27 0.45 IFE.2 - C4NW 1.43 1.17 0.51 1.56 1.44 0.45 5
Updated Table 17 Power Peaking Factors - WSU Mixed LEU Core 35A - BOL Beginning of Life _ Rods at Critical Positions Cold Critical - 23 0 C Hot Critical - 280 0 C RPF APF Intra-Rod RPF APF Intra-Rod Hot Rod 2.56 1.27 1.35 2.47 1.29 1.19 Ave Rod 1.00 1.29 1.55 1.00 1.33 1.55 IFE 1 - D6NW 1.73 1.26 0.51 1.64 1.27 0.45 IFE 2 - C4NW 1.43 1.46 0.51 1.56 1.45 0.45 New pulsing calculations were performed for the IFE 2 - C4NW location, and the updated results are listed in the updated Tables 20 and 21.
6
OLD Table 20 Calculated Pulse Performance for WSU Mixed HEU Core 34A, Current Performance, and WSU Mixed Core 35A, BOL WSU Mixed LIEU Core 34A - WSU Mixed LEU Core 35A - BOL Parameter Current
$1.50 $1.75 $2.00 $2.30 $2.50 $1.50 $1.75 $2.00 $2.30 $2.50 $2.75 $3.19
/(MW) 649 1321 2206 3537 4580 546 1143 1969 3222 4210 5506 6686 E (MW-sec) 41 19 26 32 40 45 16 22 29 36 46 52 T (-C) (D4NE) 558 701 820 954 1030 533 683 812 961 1046 1132 1234
.ore ( 0C) 201 252 300 356 387 174 227 276 334 367 401 442 T03 (0 C)
D6NW 260 313 358 405 436 232 285 331 379 405 437 479 C4NW 201 241 276 316 341 192 236 275 318 345 375 403 Updated Table 20 Calculated Pulse Performance for WSU Mixed HEU Core 34A, Current Performance, and WSU Mixed Core 35A, BOL WSU Mixed lIEU Core 34A - WSU MixedLEU Core 35A - BOL Parameter Current
$1.50 $1.75 $2.00 $2.30 $2.50 $1.50 $1.75 $2.00 $2.30 $2.50 $2.75 $3.19 P(MW) 649 1321 2206 3537 4580 546 1143 1969 3222 4210 5506 6686 E (MW-sec) 19 26 32 40 45 16 22 29 36 41 46 52
(*(C)(D4NE) 558 701 820 954 1030 533 683 812 961 1046 1132 1234 T.re (0 C) 201 252 300 356 387 174 227 276 334 367 401 442 To.3 (°C)
D6NW 260 313 358 405 436 232 285 331 379 405 437 479 C4NW 238 286 328 373 400 226 277 322 370 397 424 465
OLD Table 21 Calculated Pulse Performance for WSU Mixed LEU Core 35A, BOL, and WSU Mixed Core 35A, EOL WSU Mixed LEU Core 35A - BOL WSU Mixed LEU Core 35A - EOL Parameter
.$1.50 $1.75 $2.00 $2.30 $2.50 $2.75 $3.19 $1.50 $1.75 $2.00 $2.30 $2.50 $3.00 $3.19 P(MW) 546 1143 1969 3222 4210 5506 6686 506 1099 1914 3172 4202 6373 6816 E(MW-sec) 16 22 29 36 41 46 52 16 22 29 36 42 52 55
(-C) (D4NE) 533 683 812 961 1046 1132 1234 465 608 733 878 961 1119 1154 re(C) 0(o 174 227 276 334 367 401 442 168 224 275 337 373 441 455 T03 (°c)
D6NW 232 285 331 379 405 437 479 206 256 301 350 379 430 444 C4NW 192 236 275 318 345 375 403 227 281 330 381 408 473 489 Updated Table 21 Calculated Pulse Performance for WSU Mixed LEU Core 35A, BOL, and WSU Mixed Core 35A, EOL WSU Mixed LEU Core 35A - BOL WSU Mixed LEU Core 35A - EOL Parameter
$1.50 $1.75 $2.00 $2.30 $2.50 $2.75 $3.19 $1.50 $1.75 $2.00 $2.30 $2.50 $3.00 $3.19
/(MW) 546 1143 1969 3222 4210 5506 6686 506 1099 1914 3172 4202 6373 6816 E (MW-sec) 16 22 29 36 41 46 52 16 22 29 36 42 52 55 T(°C) (D4NE) 533 683 812 961 1046 1132 1234 465 608 733 878 961 1119 1154 (0ore(C) 174 227 276 334 367 401 442 168 224 275 337 373 441 455 T03 (°C)
D6NW 232 285 331 379 405 437 479 206 256 301 350 379 430 444 C4NW 226 277 322 370 397 424 465 227 281 330 381 408 473 489 8
- 9. Table 9. The individual calculated rod worths differ from the measured values by 28%
for Blade 4 and 111 % for Blade 5. Please explain these differences? What are the estimated (uncertainties) for the measurements of the rod worths?
Revised Response:
A review comment was made that the reactivity worth of the transient rod moved in the wrong direction between the control blade reactivity worths shown in Table 9 of the August 2007 conversion safety analysis report and the recalculated control blade reactivity worths shown in the response to Question 9 in the June 2008 responses to the RAI. Inputs to both the original MCNP calculations and the MCNP recalculated values were reviewed and found to be as the calculations had intended. The transient rod is a cylindrical rod located near the center of the core and could have a different effect on the core radial power distribution when inserted into a core with no control rods than do the large flat control blades.
The estimated uncertainties in the measurements of the rod worths are shown in the following figures and tables:
1.80 1.60 -
1.40 /
1.20 I-. . . .
[ 20045
>1.0 I__ 20054
. 0.80 --.-. 20061
- 20071 0.60 .
0.40 0.20 0.00 0 5 10 15 20 blade withdrawal height (inches)
Blade I Calibrations for the years 2004, 2005, 2006 and 2007.
4.00 3.50 3.00 2.50 !--2004
-_--2005 2.00
2006 2007 1.50 1.00 0.50 0.00 0 10 15 20 blade withdrawal height (inches)
Blade2 Calibrations for the years 2004, 2005, 2006 and 2007.
3.50 3.00 2.50 12.00 1.50 1.00 0.50 0.00 0 2 4 6 8 10 12 14 16 blade withdrawal height (inches)
Rod 3 Calibrations for the years 2004. 2005. 2006 and 2007.
10
4.50 4.00 3.50 3.00 2004 2.50 U 2005 2.00 ----. 2006
.- 2007 1.50 1.00 0.50 0.00 0 5 10 15 20 blade withdrawal height (inches)
Blade 4 Calibrations for the years 2004, 2005, 2006 and 2007.
0.25 0.20 0.15 ---- 2004 2005
. 2006 0.10 2007i -
0.05 0.00 0 5 10 15 20 25 blade withdrawal height (inches)
Blade 5 Calibrations for the years 2004, 2005, 2006 and 2007.
11
Control Element Reactivity Worths at Half Withdrawal Control Withdrawal Height Average Integral Percentl Relative Element (inches) Reactivity Worth () Standard Deviation 1 9 0.82_+/-0.03_
2 91.7+/-0009 3 7.5 1.66 +/-0.008 0.5_______
4 9 1.88 0.08__4 5 11 0.07_______ 0___01___19 _
Control Element Reactivity Worths at Full Withdrawal Control Withdrawal Height Average Integral Percent Relative Element (inches) Reactivity Worth () Standard Deviation 1 18 1.62++/-0.04 3 2 18 3.52 +/-0.03 0.9 3 15 3.10 +/-0.01 0.5 4 18 3.93 +/-0.08 2 5 22 0.17++/-0.03 21
- 15. Section 4.5.4. It says that calculated shutdown worth is the excess reactivity minus the worth of rods 1, 2, and 3. Shouldn't it be rods 1, 2, and 4?
Revised Response:
Blades 1, 2, and 3 should be used to calculate the shutdown margin based on measured data because Blade 4 in Table 9 on page 37 of the August 2007 conversion safety analysis report is the blade with the maximum measured reactivity worth. Blade 5, the servo or regulating blade, is excluded from the shutdown margin calculation because it is not fully scrammable.
Blades 1, 2, and 4 should be used to calculate the shutdown margin based on calculated data because Transient Rod 3 (Blade 3) in the same Table 9 is the blade with the maximum calculated blade worth. Blade 5, the servo or regulating blade, is excluded from the shutdown margin calculation because it is not fully scrarnmable.
- 16. Section 4.5.4. Explain why the shutdown margin calculation does not take into account the removal of the experiment with the maximum non-secured reactivity worth.
Revised Response:
The shutdown margin calculation should take into account the possibility that non-secured 12
experiments in the core have their maximum reactivity worth of+ $1.00 because the Technical Specifications allow the maximum reactivity worth of the non-secured experiments to be either positive or negative.
Shutdown margins taking into account the maximum reactivity worth of the non-secured experiments are calculated below for WSU mixed HEU Core 34A using both calculated and measured excess reactivities and control blade/rod worths. The difference between the calculated and measured shutdown margins for core 34A represents a reactivity bias that will be utilized in calculating the shutdown margin for LEU mixed core 35A.
Table 9 on page 16 of the June 2008 RAI submittal provides the following control rod worths for core 34A:
Table 9 WSU Mixed HEU Core 34A - Control Rod Worth MCNP MCNP Measured Calculated Recalculated Blade 1 (Shim) $1.32 0.03 $ 1.46 +/- 0.03 $1.68 Blade 2 (Shim) $2.89 +/- 0.03 $ 3.64 + 0.03 $ 3.56 Transient Rod 3 $3.22 +/- 0.03 $ 3.86 +/- 0.03 $3.11 Blade 4 (Shim) $2.86 + 0.03 $ 3.82 +/- 0.03 $ 3.99 Blade 5 (Servo) $0:40 +/- 0.03 $ 0.46 +/- 0.03 $ 0.19.
Total $10.68+/- 0.07 $ 13.24+/- 0.07 $12.53 Shutdown margins based on measured and MCNP recalculated control blade/rod reactivity worths are:
Calculation of Shutdown Margin for WSU Mixed Core 34A MCNP Recalculated Measured Core Excess Reactivity without Control $ 6.31 $ 6.65 Blades and Experiments*
Reactivity Worth of Non-Secured + $1.00 + $1.00 Experiments Total Excess Reactivity $ 7.31 $ 7.65 Reactivity Worth of 3 Blades with Smallest - $ 8.92 - $ 8.35 Worth, excluding Blade 5 (Servo)
Shutdown Margin -$1.61 -- $0.70 See page 35 of the August 2007 conversion safety analysis.
These calculations demonstrate that the magnitude of the shutdown margin is greater than $0.25 under the conditions stated in the WSU Technical Specifications - that is, with the highest worth non-secured experiment in its most reactive state, the highest worth control rod and the regulating rod fully-withdrawn, and the reactor in the cold critical condition without xenon. It also shows that the magnitude of the reactivity bias between the measured and calculated shutdown margin is $0.91 for Core 34A.
13
The recalculated values for reactivity worth of the control blades/rods for WSU Mixed Core 35A from Question 14, Table 10 of the WSU June 2008 RAI submittal are:
Table 10 WSU Mixed LEU Core 35A - Control Rod Worths MCNP Recalculated Blade 1 (Shim) $ 1.56 + 0.03 Blade 2 (Shim) $ 3.79 + 0.03 Transient Rod 3 $ 3.84 +/- 0.03 Blade 4 (Shim) $ 4.01 + 0.03 Blade 5 (Servo) $ 0.44 + 0.03 Total $ 13.64 + 0.07 The shutdown margin for LEU Mixed Core 35A based on the calculated excess reactivity and MCNP recalculated control blade/rod reactivity worths, including the measured-to-calculated shutdown margin bias determined above for Core 34A are:
Calculation of Shutdown Margin for WSU LEU Mixed Core 35A MCNP Recalculated Core Excess Reactivity without Control $ 6.37 Blades and Experiments Reactivity Worth of Non-Secured + $1.00 Experiments Total Excess Reactivity $ 7.37 Reactivity Worth of 3 Blades with Smallest - $ 9.19 Worth, excluding Blade 5 (Servo)
Measured to Calculated Reactivity Bias from + $0.91 Core 34A Shutdown Margin -$0.91 This calculation demonstrates that the magnitude of the shutdown margin in LEU Mixed Core 35A is calculated to be greater than $0.25 under the conditions stated in the WSU Technical Specifications - that is, with the highest worth non-secured experiment in its most reactive state, the highest worth control rod and the regulating rod fully-withdrawn, and the reactor in the cold critical condition without xenon.
- 28. Section 4.8.1. The thermal hydraulic analysis was performed with an assumed water inlet temperature of 30 C. Based on this analysis, please propose a TS limiting condition on water temperature or explain why a limit on water temperature is not needed.
Response
Washington State University currently has an administrative limit of 50' C for maximum pool 14
water temperature-the reactor must be shutdown and may not be operated if pool water temperatures reach 500 C. The reactor pool water cooling system has been shown to be capable of indefinitely maintaining the pool water temperature below 500 C when operating at full licensed power, under all ambient weather conditions.
The analysis was repeated for a power level of 1 MW, to show that thermal hydraulic results are still acceptable at 50' C. Results are presented below for the hottest fuel element.
Parameter Inlet Temp. Inlet Temp.
30°C (86-F) 50°C (122-F)
Exit Coolant Temperature. 'C (°F) 84.06 (183.3) 98.3 (208.9)
Maximum Wall Temperature, 'C (°F) 142.6 (288.6) 142 (288)
Peak Fuel Temperature, 0 C (OF) 500 (932) 499 (931)
Minimum DNB Ratio 2.50 2.20 Channel Mass Flow Rate, kg_/sec 0.0919 0.103 Maximum Flow Velocity, cm/sec 18.90 21.3 Exit Clad Temperature, 0 C 130.9 131
-The results show a reduction in the DNB ratio but very little change in fuel or cladding temperatures. A slight increase in natural circulation flow helps to offset the effect of the higher coolant inlet and exit temperatures.
The 500 C pool water temperature limit is specified in the WSU Nuclear Radiation Center Standard Operating Procedure, "Standard Procedure for Startup, Operation, and Shutdown of the Reactor," section C, (Steady State Operation) subsection 2 (At Power Operation) step e, which states, "If the pool water temperature becomes greater than 50' C, rundown the reactor."
The Washington State University Administrative Procedure, "Approval, Revision, and Review of Standard Operating Procedures" stipulates the following conditions:
- Substantive changes to the above procedures shall be made only with the approval of the licensed senior reactor operator directly in charge of the facility
" All SOP's and associated forms for the WSU Nuclear Radiation Center TRIGA reactor shall be reviewed and approved by the Reactor Supervisor and the Director prior to the implementation of the procedure or the implementation of revisions and/or additions to existing SOP's and associated forms
" All SOP's and the revisions or additions thereto shall be reviewed by the Reactor Safeguards Committee The pool water temperature limit has been examined as a part of the Safety Analysis for conversion of the Washington State University reactor from HEU to LEU fuel, the Request for Additional Information (RAI), and the Responses to the RAI's. Any change to the pool water temperature limit in the WSU SOP "Standard Procedure for Startup, Operation, and Shutdown of the Reactor," will require the above described approvals, followed by submission to the U.S.
NRC under 10 CFR 50.59, describing the relevant analysis and implementation of such a change.
There is no case under which changes to the pool water temperature limit would be permitted outside the framework of 10 CFR 50.59.
15
- 33. Section 13.3. The IFE contains three thermocouples at different locations. What impact will the choice of thermocouple have on the LSSS.
This section states that at 1.3 MW, peak fuel temperature in the core is 520 C. Table 29 indicates a peak fuel temperature of 541 C. Please explain.
The factors listed (items i-iv) to be taken into account when setting the LSSS are termed the "safety margin". However, you discuss a peak core temperature of 950 C representing a safety margin of 200 C. Given this, do the factors really represent a safety margin?
Response
Of the three thermocouples, the bottom one tends to be the highest due to power tilting toward the lower half of the core from control blade insertion. As an example, for Core 35A at 1 MW, the IFE in D6NW reads 4270 C at the bottom, 424* C at the middle, and 414' C at the top thermocouple locations.
The peak fuel temperature at 1.3 MW is 541' C and the text in section 13.3 should be corrected.
The factors do not represent a safety margin and should not be identified as such. The text in Section 13.3 near the middle of page 73 of the August 2007 conversion safety analysis should be revised to remove the large bracket and the words "Safety Margin" and should read:
- i. Accuracy of the temperature calibration ii. Precision of electronic readout/scram circuitry iii. Account taken of location of sensing tip of thermocouple 0.3 inch from axial center line of IFE iv. Difference in peak temperature in IFE compared to that in the hottest fuel element
- 36. Section 13.5.2. Please submit a stand-alone evaluation for the LOCA stating all assumptions and showing calculations. Also, please state what is the margin to clad yield strength with a power density of 22.9 kW/rod.
Revised Response:
A standalone evaluation for the LOCA has been prepared, and is included with this document as Appendix LOCA: Analysis of Loss-of-Coolant Accident (LOCA).
However, the first sentence at the top of page 60 in the Appendix should be revised to read:
"This power density is above the maximum power density of 20.8 kW/element for the WSU reactor operating at 1 MW."
16
- 40. Section 14.2.2. Section 13.3 of the SAR evaluates the LSSS for two specific IFE locations. However, the TS allows the IFE to be located anywhere in the 30/20 fuel region. Please repeat the analysis for the worse case to show that the LSSS as proposed protects the safety limit.
Revised Response:
The worst IFE location would be E6SE which has an RPF of 1.224 and a maximum APF of 1.47. The rod power is lowest among the 30/20 LEU fuel because it is in the far SE corner.
The APF is high because it is located adjacent to a control blade. Thermocouple sensing tips are located 6.5", 7.5", and 8.5" from the bottom of the fuel. TAC2D calculations of this location gave the following values for the highest and lowest temperatures of the three thermocouple sensing tips if the IFE were to be located there.
Highest and Lowest Temperatures of Thermocouple Sensing Tips of an IFE in Core Position E6SE as a Function of Reactor Power Reactor Highest Temperature Lowest Temperature Power, MW Thermocouple Thermocouple Sensing Tip, 'C Sensing Tip, 'C 1.0 408 382 1.3 440 412 1.8 512 478 2.0 - 491 2.2 504 These calculations predict that the lowest temperature thermocouple at 8.5" from the bottom of the fuel would read 491'C at a reactor power of 2.0 MW and 504'C at a reactor power of 2.2 MW. Thus, a reactor power of 2.14 MW (interpolated) would be needed to reach an LSSS temperature of 500'C. At 2.2 MW, the maximum powered rod in position D4NE would have a peak fuel temperature of 836°C. Since the response to Question 28 of the June 2008 RAI submittal shows that departure from nucleate boiling (DNB) as predicted by the Bemath correlation is expected to occur at a power level of 2.2 MW, if the pool water inlet temperature were 50'C, position E6SE is not an acceptable location for the IFE because the IFE would not protect the safety limit of 11 50'C if DNB were to occur in the hottest rod.
Actually, the safety limit would be protected by the redundant high power trips at 1.2 MW and an IFE in position E6SE would not be relevant. An approach to using the IFEs to protect the safety limit if both power trips were to fail is to select IFE locations where the reactor power
,level would be low enough to remain far below the power level (2.2 MW) at which DNB is predicted to occur in the hottest rod. A maximum reactor power level of 1.7 MW was selected as reasonable for this purpose.
The product of the reactor power level, the rod power peaking factor, and the axial power peaking factor at the level of the thermocouple being considered uniquely defines the thermocouple temperature reading. The TAC2D calculations described above indicated that a reactor power of 2.14 MW, a rod power peaking factor of 1.22, and an axial power peaking factor of 1.15 for the lowest temperature thermocouple produced a thermocouple reading of 17
500'C. Therefore, the product 2.14 MW x 1.22 x 1.15, which equals 3.00 MW, will correspond to a thermocouple reading of 500'C.
Table 40-1 shows the rod power peaking factors for LEU Mixed Core 35A under BOL hot conditions. All of the candidate core positions for the IFE are in the white region, which is located between the control blades where the LEU 30/20 fuel is planned to be inserted. Table 40-2 shows the maximum axial power peaking factor and the axial power peaking factors for the IFE thermocouples located at 6.5", 7.5", and 8.5" from the bottom of the fuel.
Table 40-3 shows the product of the rod power peaking factors in Table 40-1 and selected axial power peaking factors in Table 40-2 for the planned 30/20 fuel positions in LEU Mixed Core 35A. The upper value for each rod position is the product of the rod peaking factor and the axial peaking factor for the thermocouple located at 6.5" from the bottom of the fuel (hottest axial location). The lower value for each rod position is the product of the rod power peaking factor and the axial peaking factor for the thermocouple located at 8.5" from the bottom of the fuel (coldest axial location).
Table 40-4 shows the reactor power level (in MW) at which the hottest and the coldest thermocouples are predicted to reach 500'C in each fuel rod. These power levels are 3.0 MW/(Factors in Table 40-3).
For both the hottest and the coldest thermocouples, an IFE located in the rod positions shown in green would protect the fuel temperature safety limit of 115 OT0 for reactor power levels that are less than 1.7 MW. The positions shown in red are excluded as possible IFE locations because power levels greater than 1.7 MW would be required to reach 5000'C in the coldest thermocouple.
The positions shown in orange would also protect the fuel temperature safety limit, but could cause the reactor to trip at a temperature of 500'C on the hottest or the coldest thermocouple before the redundant power level trips at 1.2 MW. Thus, the positions shown in orange are excluded for practical operational reasons and not for safety reasons.
18
Table 40-1. Rod Peaking Factors for LEU Mixed Core 35A at BOL, HOT 1 2 3 4 5 6 7 0.23 0.27 0.35 0.42 0.46 0.52 0.49 0.42 B 0.28 0.33 0.45 0.55 0.60 0.65 0.63 0.55 0.40 0.50 0.65 0.70 1.58 1.51 1.44 1.37 0.55 0.51 C 0.47 0.62 0.70 0.73 1.72 11.68 I 1.76 11.86 2.22 11.73 1 1.49 1.42 0.62 0.58 0.50 0.60 115 1.67 11 1.73 11.881 1.98 12.47 1 TR_12.30 1.64 1.56 0.67 0.63 D 0.50 0.59 154
.7311.7 1.6 1 1.7 1.071 241 1.8 11.62 1.54 0.67 0.62 E
0.46 0.61 0.68 0.71 1.70 11.65 1.74 1.76 1.72 11.61 I 1.43 1.37 0.59 0.55 0.38 0.48 0.62 0.66 1.52 11.52 I 1.47 1.40 1.28 1.22 0.49 0.45 0.28 0.32 0.41 0.50 0.55 0.61 0.56 0.48 0.39 0.31 F 0.22 0.25 0.31 0.37 0.45 0.52 0.45 0.38 0.30 0.24 Table 40-2. Axial Power Peaking Factors for the WSU LEU Mixed Core 35A, BOL, HOT 2 3 4 5 6 Max 1.475 1.470 1.454 1.433 1.374 1.336 1.342 1.341 6.5" 1.461 1.457 1.443 1.424 1.368 1.333 1.342 1.341 7.5" 1.371 1.369 1.361 1.352 1.312 1.295 1.322 1.327 8.5" 1.153 1.151 1.155 1.162 1.175 1.211 1.259 1.270 C
1.301 1.296 1.292 1.289 1.288 1.277 1.272 1.271 1.301 1.296 1.292 1.289 1.288 1.277 1.271 1.269 1.274 1.270 1.269 1.268 1.272 1.264 1.261 1.262 1.209 1.208 1.209 1.213 1.222 1.218 1.219 1.221 1.284 1.286 1.284 1.283 1.282 1.286 - 1.283 1.274 1.273 1.284 1.286 1.284 1.283 1.282 1.285 - 1.282 1.273 1.272 1.268 1.269 1.267 1.267 1.267 1.273 - 1.272 1.264 1.264 1.219 1.218 1.217 1.218 1.219 1.226 - 1.229 1.223 1.224 D
1.284 1.286 1.284 1.283 1.282 1.281 1.285 1.279 1.278 1.278 1.284 1.286 1.284 1.283 1.282 1.281 1.285 1.279 1.277 1.278 1.268 1.269 1.267 1.267 1.267 1.267 1.272 1.267 1.265 1.266 1.220 1.218 1.217 1.218 1.218 1.220 1.227 1.222 1.220 1.221 1.301 1.296 1.293 1.290 1.288 1.288 1.290 1.294 1.300 1.296 1.293 1.290 1.288 1.288 1.290 1.294 1.273 1.270 1.269 1.267 1.266 1.266 1.267 1.270 1.209 1.207 1.208 1.208 1.209 1.209 1.208 1.208 E
1.472 1.468 1.454 1.438 1.400 1.404 1.454 1.469 1.459 1.455 1.442 1.426 1.385 1.389 1.442 1.455 1.369 1.366 1.358 1.348 1.310 1.312 1.358 1.366 1.153 1.150 1.151 1.153 1.152 1.151 1.152 1.150 19
Table 40-3. Product of Rod and Axial Power Peaking Factors for Thermocouples with the Lowest and the Highest Axial Peaking Factors for WSU LEU Mixed Core 35A, BOL, HOT 2 3 4 5 6 RPF x APF 6.5" 2.31 2.20 2.25 2.24 2.13 2.041 1.93 1.84 RPF x APF 8.5" 1.82 1.74 1.80 1.82 1.83 1.85 1.81 1.74 C
2.24 2.18 2.27 2.40 2.86 2.21 1.89 1.80 2.08 2.03 2.13 2.26 2.71 2.11 1.82 1.73 1.99 2.15 2.22 2.41 2.54 3.17 TR 2.95 2.09 1.98 1.892.0312.11 2.29 2.41 3.03 2.83 2.01 1.91 D
1.98 2.13 2.22 2.40 2.53 2.65 3.10 2.42 2.07 1.97 1.8 , . 2.11 2.28 2.40 2.53 , 2.96 2.31 1.98 1.88 2.21 2.14 2.25 2.27 2.21 2.07 1.84 1.77 2.06 1.99 2.10 2.13 2.08 1.95 1.73 1.66 E
2.25 2.14 2.19 2.17 2.04 1.94 1.85 1.78 1.78 1.69 1.75 1.75 1.69 [ 1.69 1.47 1.40 Table 40-4. Reactor Power Levels (in MW) at Which the Hottest (top value) and Coldest (bottom value) Thermocouples Reach 500*C in Each 30/20 Fuel Rod in LEU Mixed Core 35A, BOL, HOT. The Current IFE Are Located in Positions C4NW and D6NW.
2 34 6 RPF x APF 6.5" C RPF x APF 8.5" D
E 20