ML111950452

From kanterella
Jump to navigation Jump to search
University of California, Irvine - *Redacted* Nuclear Analysis for Uci Triga Reactor, Report 911196, Rev. 0
ML111950452
Person / Time
Site: University of California - Irvine
Issue date: 06/07/2011
From:
General Atomics
To:
Office of Nuclear Reactor Regulation
Lynch, Steven - NRR/DPR/PRPB, 415-1524
Shared Package
ML120050026 List:
References
00096970, 39364 911196, Rev 0
Download: ML111950452 (27)
v • d • e


Text

University of California - Irvine (UCI)

License No. R-116 Docket No. 05000326 Nuclear Analysis of the UCI TRIGA Reactor Redacted Version*

Security-Related Information Removed

  • Redacted text and figures blacked out or denoted by brackets

911196 Revision 0 RELICENSING TASKS Nuclear Analysis of the University of California -

Irvine TRIGA Reactor Prepared by:

Address:

TRIGA Reactor Division of General Atomics PO Box 85608 San Diego, CA 92186-5608 Prepared under Contract No. 00096970 for the U.S. Department of Energy OFFICIAL USE ONLY This document contains information that may be exempt from public release under the Freedom of Information Act (5 U.S.C.552), Exemption 2. Approval by the U.S. Department of Energy, Idaho Operations Office, is required prior to public release.

GA PROJECT 39364

+ GENERAL ATONICS

+ GENERAL ATOMICS GA 1485 (REV. 08106E)

ISSUE/RELEASE

SUMMARY

0 R & D APPVL DISC QA LEVEL SYS DOC. TYPE PROJECT DOCUMENT NO.

REV El DV&S LEVEL 0] DESIGN C T&E 2

N IB NIA RGE 39364 911196 0

TITLE:

Nuclear Analysis of the University of California - Irvine TRIGA Reactor APPROVAL(S)

REVISION CM APPROVAL/

PREPARED DESCRIPTION/

DATE REV BY ENGINEERING QA PROJECT W.O. NO.

0 J. Crozier J. Bolin K. Partain T. Veca Initial Issue A39364.031 0 CONTINUE ON GA FORM 1485-1 NEXT INDENTURED DOCUMENT(S)

COMPUTER PROGRAM PIN(S)

El GA PROPRIETARY INFORMATION THIS DOCUMENT IS THE PROPERTY OF GENERAL ATOMICS. ANY TRANSMITTAL OF THIS DOCUMENT OUTSIDE GA WILL BE IN CONFIDENCE. EXCEPT WITH THE WRITTEN CONSENT OF GA, (1) THIS DOCUMENT MAY NOT BE COPIED IN WHOLE OR IN PART AND WILL BE RETURNED UPON REQUEST OR WHEN NO LONGER NEEDED BY RECIPIENT AND (2) INFORMATION CONTAINED HEREIN MAY NOT BE COMMUNICATED TO OTHERS AND MAY BE USED BY RECIPIENT ONLY FOR THE PURPOSE FOR WHICH IT WAS TRANSMITTED.

0 NO GA PROPRIETARY INFORMATION PAGE ii OF 29

Nuclear Analysis of the UCI TRIGA Reactor 911196-0 TABLE OF CONTENTS LIST O F ABBREVIATIO NS/ACRO NYM S............................................................................

vi I

Introduction...................................................................................................................

1 2

REACTO R DESCRIPTIO N.............................................................................................

1 2.1 Reactor Facility....................................................................................................

1 2.2 Reactor Core......................................................................................................

2 2.2.1 Fuel Elem ents............................................................................................

3 2.2.2 Control Rods.............................................

5 2.2.3 Neutron Reflector.......................................................................................

5 2.2.4 Reactor M aterials.......................................................................................

5 2.2.5 Calculation M odels; Nuclear Analysis Codes.............................................

6 2.2.6 Critical Core Configuration; Excess Reactivity...........................................

7 2.2.7 W orth of Control Rods.....................................................................................

9 2.2.8 Shutdown M argin........................................................................................

9 2.3 Additional Com puted Core Perform ance Param eters.........................................

10 2.3.1 Effective Delayed Neutron Fraction, eff........................................................ 10 2.3.2 Prom pt Neutron Life (t).........................................................................

11 2.3.3 Prom pt Fuel Tem perature Coefficient of Reactivity (afuel)............................. 11 2.3.4 Void Coefficient, (c(void)................................................................................. 13 2.3.5 M oderator Coefficient, (Oamod)....................................................................... 14 2.3.6 Power Peaking Results.............................................................................

15 3

REFERENCES..............................................................................................................

17 Appendix A: Fuel Rod Num ber Densities..................................................................

A-1 iii

Nuclear Analysis of the UCI TRIGA Reactor 911196-0 LIST OF FIGURES Figure 2-1 UCI Core Configuration.......................................................................................

3 Figure 2-2 Fuel E lem ent D etails............................................................................................

4 Figure 2-3 Radial Initial Model for Monte Carlo (MCNPX) Transport Calculations Full C ore -

.. 7 Figure 2-4 Initial Axial Model for Monte Carlo (MCNPX) Transport Calculations Just Critical Full Core -

8 Figure 2-5 Prompt Fuel Temperature Coefficient for TRIGA LEU (8.5% wt.) Fuel, BOL........ 13 Figure 2-6: Reactivity Worth as a Function of Percent Coolant Void.................................... 14 Figure 2-7: Moderator Temperature Coefficient as a Function of Temperature..................... 15 Figure 2-8 Hot Critical - Core Power Map............................................................................

16 iv

Nuclear Analysis of the UCI TRIGA Reactor 911196-0 LIST OF TABLES Table 2-1 LEU Design Data, Core Physics, and Safety Parameters......................................

2 Table 2-2 Description of the Averaged UCI Fuel Elements....................................................

5 Table 2-3 Material Composition Used in the MCNPX Models...............................................

6 Table 2-4 UCI Unrodded Full Core Results (eff

= 0.0079)......................................................

8 Table 2-5 Summary of UCI Control Rod Worths.....................................................................

9 Table 2-6 Reactivity Change with Fuel Temperature, BOL..................................................

12 v

Nuclear Analysis of the UCI TRIGA Reactor 911196-0 LIST OF ABBREVIATIONSIACRONYMS APF Axial Peaking Factor ARI All Rods In ARO All Rods Out BOL Beginning of Life GA General Atomics kW kilowatt LEU Low Enriched Uranium MCNP Monte Carlo N-Particle Code MW Megawatt PTS Pneumatic Transfer System RPF Radial Peaking Factor SAR Safety Analysis Report TRIGA Training Research Isotope General Atomics UCI University of California-Irvine vi

Nuclear Analysis of the UCI TRIGA Reactor 911196-0 I

INTRODUCTION This report provides an overview of the nuclear characteristics of the University of California -

Irvine (UCI) TRIGA Reactor.

2 REACTOR DESCRIPTION 2.1 Reactor Facility Table 2-1 provides a comparison of the key design safety features of the

, along with a comparison of the key reactor and safety parameters that were calculated for the core. As discussed in Sections 2.2.7 and 2.2.8, there is sufficient shutdown margin combined with a negative power coefficient to show that the UCI reactor facility can be operated safely with The computations produced operational parameters to be compared with the actual measured values from the operations conducted by the UCI staff for the UCI TRIGA core loaded with that GA manufactured. The experimentally measured parameters included the reactivity for the fully loaded core (

) and the control rod calibration values.

In addition, the computations produced results for the prompt, negative temperature coefficient of reactivity (Ak/k-0C) versus reactor fuel temperature that can be compared with current values, as well as the moderator coefficient, void coefficient, and power peaking profiles.

1

Nuclear Analysis of the UCI TRIGA Reactor 911196-0 Table 2-1 LEU Design Data, Core Physics, and Safety Parameters DESIGN DATA Number of Fuel Rods Fuel Type Uranium Enrichment, %

Zirconium Rod Outer Diameter, mm Fuel Meat Outer Diameter, mm Fuel Meat Length, mm Clad Thickness, mm Clad Material REACTOR PARAMETERS Reactor Steady State Operation, kW Cold Clean Excess Reactivity, Ak/kp ($)

Measured Cold Clean Excess Reactivity, Ak/kp ($)

Prompt Fuel Temperature Coefficient of Reactivity (BOL), Ak/k-°C, 23-10000C (x 10-4)

Coolant Void Coefficient, Ak/k-% void, 0 - 10%,

(x 10-4)

Moderator Coefficient, Ak/k -°C, 23-1 000°C, (x 10-4)

Maximum Rod Power at 250 kW, kW/element Average Rod Power at 250 kW, kW/element Prompt Neutron Lifetime, psec Effective Delayed Neutron Fraction ARI cold, clean core, Ak/kp ($)

Shutdown Margin, Ak/kp ($) (with most reactive rod out)

Additional Shutdown case, Ak/kp3 ($) (with most reactive rod out and next most reactive rod stuck 50% out)

UZrH 19.79 250 2.82 2.66

-0.70 to -1.11

-7.40 to -3.68 0.884 to 0.396 4.519 3.125 98.5 0.0079

-5.88

-2.03

-1.27 2.2 Reactor Core This section provides a detailed description of the components and structures in the reactor core. The UCI reactor is a primarily homogeneous, light water moderated and cooled, tank-type reactor fueled with a full core of LEU (19.79% enriched UZrHx) TRIGA fuel in a cylindrical lattice configuration. The fuel clusters are supported by a 19.05mm thick aluminum grid plate.

The UCI core configuration is shown in Figure 2-1; it contains each with a central zirconium rod for structural integrity, a fuel-followed shim control rod, a fuel-followed regulating control rod, an air-followed adjustable transient control rod, and an air-followed fast transient rod. A graphite reflector block, located on the periphery of the grid plate, is used for reflection of neutrons.

2

Nuclear Analysis,f the UCI TRIGA Reactor 911196-0 Figure 2-1 UCI Core Configuration The core configuration is a circular arrangement of core elements consisting of fuel, control, reflector, and testing elements. The grid-plate consists of 6 circular rings of elements, A for the central ring and G for the outer ring. The individual locations for the elements are numerically ordered in a clockwise direction. The design of the grid-plate will allow it to accept up to a total of 2.2.1 Fuel Elements The LEU (8.5% wt) TRIGA fuel installed in the UCI core consists of Figure 2-2 shows a detailed illustration of the fuel, graphite, and zirconium rod regions. The zirconium rod is manufactured to a diameter of but the hole for the zirconium rod has a diameter of 3

Nuclear Analysis of the UCI TRIGA Reactor 911196-0 Figure 2-2 Fuel Element Details An aluminum grid plate (19.1 mm thick) is used to support the fuel clusters on the bottom of the reactor. In addition, an aluminum grid plate (16.1 mm thick) is located at the top of the core to provide lateral restraint for the core components. The reactor is controlled by poison rods supported by a bridge mounted at the top of the biological shield.

4

Nuclear Analysis of the UCI TRIGA Reactor 911196-0 The core is positioned above the bottom of the reactor tank, and it is support by an aluminum core support structure which is bolted to the floor of the reactor tank.

The geometries, materials, and fissile loadings of the current fuel elements are summarized in Table 2-2.

Table 2-2 Description of the Averaged UCI Fuel Elements Design Data Number of Fuel Elements Full Load Fuel Type UZrH Enrichment, %

19.79 Uranium Density, g/cm3 0.59 Wt-%

8.5 235U per Fuel Element, g Zirconium Rod Outer Diameter, mm.

Fuel Meat Outer Diameter, mm.

Fuel Meat Length, mm.

Cladding Thickness, mm.

Cladding Material 2.2.2 Control Rods The UCI reactivity control system consists of four standard TRIGA control rods; one fuel-followed shim rod, one fuel-followed regulating rod, one air-followed adjustable transient rod, and one air-followed fast transient rod as shown in Figure 2-1. All four control rods are supported from the bridge structure at the top of the biological shield.

2.2.3 Neutron Reflector The primary reflector for UCI reactor consists of nuclear-grade graphite designed in a ring shaped block around the core as shown in Figure 2-1. The graphite block is placed in a leak-tight, welded, aluminum container.

It is thick radially with an inside diameter of and high.

2.2.4 Reactor Materials Table 2-3 presents the material composition of components other than the fuel used in the computational models.

5

Nuclear Analysis of the UCI TRIGA Reactor 911196-0 Table 2-3 Material Composition Used in the MCNPX Models Nuc. Den.

Physical Density Material Nuclide 1 (atoms/b-cm)

(glcc)

(clad)

Cr-50 0.000778 7.98 Cr-52 0.015003 Cr-53 0.001701 Fe-56 0.056730 Ni-58 0.007939 Mn-55 0.001697 Graphite C

(reflector in fuel) 0.087745 1.75 (reflector blocks) 0.078719 1.57 Zirconium Zr 0.034790 5.27 (rod w/ 60 ppm Hf) 6061 Al AI-27 0.058693 2.70 (upper grid plate, lower Fe-56 0.000502 grid plate, and control rod clad) 90% B4C (control rod)

B-10 0.020950 2.30 B-11 0.084310 C

0.026320 Water 1.0 Air 0.000123 2.2.5 Calculation Models; Nuclear Analysis Codes Three-dimensional calculations are performed using Monte Carlo codes. The Monte Carlo calculations are used to evaluate the facilities around the core and also to compute the worth of core components and different core configurations.

2.2.5.1 MCNPX Monte Carlo Code Reactor calculations were performed in three dimensions for the initial criticality of the UCI core using the continuous energy Monte Carlo code MCNPX, Version 2.6d for the calculations (Ref.

1).

The nuclide cross sections for the core were based on ENDF/B VII.O data for the final model, included in the library MCNP5 DATA (CCC-710). For the core calculations, most of the nuclide cross sections used ENDF/B VII.0, excluding minor impurities that were not available.

The fuel meats were derived from material estimates supplied by UCI, and the fuel meat nuclide densities used in the MCNPX model are shown in Appendix A. Since the fuel meats lack fission 1 Other isotopes were reviewed in the process, but they were determined to have an insignificant impact on the results.

6

Nuclear Analysis o: t.

UCI TRIGA Reactor 911196-0 products the reactivity estimates and shutdown margins will be conservative. The other materials besides the fuel used in the UCI MCNPX models are listed in Table 2-3.

2.2.5.2 Geometrical Models Each fuel element was explicitly modeled such that 19 cells and 13 surface cards were constructed to properly represent one fuel element. A total of and were made for the for the cold critical case (Ref. 2).

2.2.6 Critical Core Configuration; Excess Reactivity 2.2.6.1 UCI Full Core; Cold Unrodded A detailed MCNPX model of the UCI reactor full, cold, unrodded core was made including (8.5% wt.) fuel elements, a fuel-followed shim control rod, a fuel-followed regulating control rod, an air-followed adjustable transient control rod, an air-followed fast transient rod, and a graphite block around the core (Ref. 2). Figure 2-3 and Figure 2-4 are the radial and axial plots, respectively, of the MCNP model for the UCI full core cases.

Figure 2-3 Radial Initial Model for Monte Carlo (MCNPX) Transport Calculations Full Core -

7

Nuclear Analysis of the UCI TRIGA Reactor 911196-0 Z axis LZ Graphite ZAir Water Fuel B4C x - axis Figure 2-4 Initial Axial Model for Monte Carlo (MCNPX) Transport Calculations Just Critical Full Core -

Table 2-4 summarizes the computational analysis for the UCI full core, all rods out, case modeled using MCNPX.

Table 2-4 UCI Unrodded Full Core Results (

= 0.0079)

Reactor keff I

Reactivity Measured No. of Elements UCI Full Core Cold Unre keff = 1.0230 1(Y = 0.0001

+$2.82

+$2.66 Cold, Unrodded Since a complete burnup estimate of the fuel was not completed for this analysis, the difference in the modeled fuel elements and actual fuel elements is sufficient to provide a discrepancy of 6%. Thus the unrodded full core results, $2.82, are within a reasonable estimate of the measured value, $2.66.

8

Nuclear Analysis of the UCI TRIGA Reactor 911196-0 2.2.7 Worth of Control Rods 2.2.7.1 UCI Full Core Loading; All Control Rods Inserted The full core loading in the UCI reactor contains and includes the aforementioned fuel-followed shim control rod, fuel-followed regulating control rod, air-followed adjustable transient control rod, air-followed fast transient rod, and graphite ring around the core. The MCNPX calculation with all control rods inserted gives a keff value with one sigma uncertainty:

keff = 0.9376 +/- 0.0001 This is equivalent to reactivity shutdown of -$5.88 (Peff =0.0079), which is calculated as the difference between the ratio of the reactivity for the all rods out case and all rods in case, ARO/ARI, and the core excess (i.e., $8.70 - $2.82). As shown in Table 2-5, the four control rods have a combined reactivity worth of $8.70 when comparing ARO to ARI calculations.

An additional analysis, relative to cold critical, of the individual control rod worths in the UCI core gave values for the shim rod, regulating rod, adjustable transient rod (ATR), and fast transient rod (FTR) respectively $3.85, $3.15, $1.88, and $0.64 for the shim rod, regulating rod, adjustable transient rod (ATR), and fast transient rod (FTR) respectively. These values sum to

$9.52, which is approximately 9% more than the ARO/ARI calculation. Further, these values relative to critical values are only $0.45 more (-5%) than the measured control rod worths from the most recent control rod measurement. Table 2-5 summarizes the control rod worth calculations and measurements for the UCI core based upon the model.

Table 2-5 Summary of UCI Control Rod Worths Calculated Value Calculated Value Measured Value in Control Rod ARO/ARI Relative to Critical LEU Core 5129/10 Difference Shim

$3.85

$3.60

+6.9%

Regulating

$3.15

$2.96

+6.4%

ATR

$1.88

$1.81

+3.9%

FTR

$0.64

$0.70

-8.6%

TOTAL

$8.70

$9.52

$9.07

+5.0%

2.2.8 Shutdown Margin As stated in the UCI Technical Specifications (Ref. 3), the reactor shall be placed in the Shutdown Mode unless the reactor can be demonstrated to be subcritical by more than $0.50 with the following conditions:

a. The most reactive rod fully withdrawn 9

Nuclear Analysis of the UCI TRIGA Reactor 911196-0

b. The reactor is experiment free
c. The reactor is xenon free The MCNPX calculations for a cold, clean core were used to evaluate the individual worth of the four control rods. The maximum worth control rod is the Shim Rod with a calculated worth of

$3.85. The reactor shutdown margin for the Shim Rod withdrawn, a cold excess of $2.82, and an ARI/ARO of $8.70 is conservatively estimated to be -$2.03 ($2.82 + $3.85 - $8.70). In addition, the reactor is required to be subcritical by at least $1.00 for the ARI case.

The calculated ARI reactivity has been calculated to be -$5.88 ($2.82 - $8.70). Therefore, the Shutdown Margin meets the UCI Technical Specification requirements for the current core configuration.

To test for an additional margin of safety, the reactor is shown to be subcritical with the maximum worth rod fully withdrawn and the second most reactive rod withdrawn 50%. The second most reactive rod by calculation is the Regulating Rod with a worth of $3.15. By adding

$3.85 from the Shim Rod worth and $1.58 from the Regulating Rod 50% worth, to the ARI reactivity -$5.88, the reactor is calculated to remain subcritical by $0.45.

An additional MCNPX model of the UCI cold, clean core was run to verify this additional conservative estimate of the shutdown margin. This run was of the core modeled with the rods in the actual position specified rather than adding individual rod worths to the ARI reactivity case. For this case, the Shim Rod was fully withdrawn, the Regulating Rod was withdrawn 50%,

and the ATR and FTR were fully inserted. The modeled keff with one sigma uncertainty for this shutdown core was:

Shim Rod 100%, Reg. Rod 50%, ATR 0%, FTR 0% withdrawn - keff = 0.9901 +/- 0.0001 This keff values corresponds to a reactivity of -$1.27.

2.3 Additional Computed Core Performance Parameters 2.3.1 Effective Delayed Neutron Fraction, IPeff The effective delayed neutron fraction, fPeff for UCI was also derived from Monte Carlo calculations of the UCI core with all control rods out.

The computed values for Kt and Kp are used in the following expression to obtain 3eff Peff = 1 - [Kp / Kt]

where:

Kp = core reactivity using prompt fission spectrum Kt = core reactivity using prompt and delayed fission spectrum The values of Kp and Kt calculated using MCNPX are:

Kp = 0.99228 +/- 0.0001 Kt = 1.00014 +/- 0.0001 10

Nuclear Analysis of the UCI TRIGA Reactor 911196-0 Using these values the result for the UCI core is:

f3eff=0. 0 07 9 (l1 = 0.0001) 2.3.2 Prompt Neutron Life (ý)

The prompt neutron lifetime, i, was computed by the 1/v absorber method where a very small amount of boron is distributed homogeneously throughout the system and the resulting change in reactivity is related to the neutron lifetime. The boron cross sections used in the core were generated over a homogenized core spectrum. Boron cross sections used in all other zones were generated over a water spectrum.

The neutron lifetime, i, is defined as follows:

= 1/ (6o vo NB )*(Akeff) where NB = boron density = 6.0180 x 10-7 atoms/b-cm Vo = 2200 m/sec, 60 = 755 barns = 6 aB at 2200 m/sec kbase= 1.00014 kseed = 0.99029 Akeff kbase - kseed = 0.00985 (the change in reactivity due to the addition of boron)

The result for the prompt neutron life (i) in the BOL UCI core is the following:

98.5 psec 2.3.3 Prompt Fuel Temperature Coefficient of Reactivity ( afuel)

The definition of afuel, the prompt fuel temperature coefficient of reactivity, is given as dp dT where p = reactivity

= (k-1)/k k = multiplication factor T = reactor temperature (°C) 1 dk k 2 dT To evaluate (A p) from reactivity as a function of reactor fuel temperature, the finite differences can be written as follows:

11

Nuclear Analysis of the UCI TRIGA Reactor 911196-0 A I2 k2 - 1 kI -I1 k2 k-

_k2 - kI k]k2 a2k2 - k1 I

ki k2 AT7,2

Thus, The data in Table 2-6 were produced by MCNPX for the listed fuel temperatures.

Table 2-6 Reactivity Change with Fuel Temperature, BOL Avg. Fuel k2 -ka, 2

Temperature keff Akeff kk 2 (Ak/k--C)

(oC) k__k_(

__-_C 20 1.00014 0.00746

-0.00751

-7.02E-05 127 0.99268 0.02106

-0.02183

-1.09E-04 327 0.97162 0.02045

-0.02213

-1.11E-04 527 0.95117 0.01752

-0.01973

-9.86E-05 727 0.93365 0.01509

-0.01760

-8.80E-05 927 0.91856 Figure 2-5 is a histogram plot of the computed values for a in Table 2-6 as a function of the reactor core temperature for BOL.

12

Nuclear Analysis c" the UCI TRIGA Reactor 911196-0 Prompt Fuel Temperature Coefficient as a Function of Temperature 0.00E+00

.a -2.OOE-05 IE 00

-4.OOE-05 CL -6.00E-05 E

I-

  • -8.00E-05 LL 4-0J.

E 2 -1.00E-04

-1.20E-04 0

200 400 600 800 1000 Temperature (C)

Figure 2-5 Prompt Fuel Temperature Coefficient for TRIGA LEU (8.5% wt.) Fuel, BOL 2.3.4 Void Coefficient, (U.void)

The void coefficient was calculated for 1%, 5%, and 10% and the results are plotted in Figure 2-6. The void coefficient for the UCI reactor ranges from -7.40 x 1 0 - for 0% void to -3.68 x 10-4 with 10% void. The overall estimated worth calculates out to be roughly -$0.06 per 1% water void.

13

Nucleur Analysis of the UCI TRIGA Reactor 91 1196-0 Void Coefficient as a Function of Void Percentage 0.OOE+O0

-1.OOE-04

-2.OOE-04

  • -3.O0E-04 0

o -5.OOE-04

-6.OOE-04

-7.OOE-04

-8.0OE-04 0

2 4

6 8

10 Void Fraction (%)

12 Figure 2-6: Reactivity Worth as a Function of Percent Coolant Void Fraction 2.3.5 Moderator Coefficient, (am..d)

The moderator coefficient, amd, was calculated using MCNPX through a series of cases with the moderator (both water and graphite) having a temperature of 297K, 400K, 600K, 800K, and 1000K; the results are plotted in Figure 2-7.

14

Nuclear Anclysis of the UCI TRIGA Reactor 911196-0 Moderator Temperature Coefficient as a Function of Tem peratu re y = -7E-08x + 9E-05 4-C.2 0

0 0U 4-(V 1..a; 0.E 0I-I...

0 4-(U 1~

0 0

9.OOE-05~

9.OOE-05 7.QOE-05 6.OOE-05 5.00 E-05 4.OOE-05 3.00 E-05 2.OOE-05 1.OOE-05 0.OOE+00 0

100 200 3

300 500 700 800 400 Temperature (C) 600 Figure 2-7: Moderator Temperature Coefficient as a Function of Temperature 2.3.6 Power Peaking Results Power peaking in the BOL core is analyzed on the basis of the following component values:

1.

T, / I.,,,e: rod power factor, the power generation in a fuel rod (element) relative to the core averaged rod power generation.

2.

(P/P),, axial peak-to-average power ratio within a fuel rod (element).

3.

(Pr,"

/ -rd)radlal: rod peaking factor, the peak-to-average power in a radial plane within a fuel rod (element).

Since maximum fuel temperature is the limiting operational parameter for the core, the peaking factor of greatest importance for steady-state operation is Pr,,/re, The maximum value of this factor for the hottest rod, the hot-rod factor, [( 15,d / P.o,, )max = hot-rod factor], determines the power generation in the hottest fuel element. The hot rod power factor is calculated to be 1.446, which can be found in fuel element C6. When combined with the axial power distribution, the hot-rod factor is used in the thermal analysis for determination of the maximum fuel 15

Nuclear Analysis of thE UCI TRIGA Reactor 911196-0 temperature. The axial power peaking factor, (P/P )....i, is calculated to be 1.352, and at BOL it is relatively independent of fuel temperatures or radial position in the core. The radial power distribution within the element has only a small effect on the peak temperature, but it is also used in the steady-state thermal analysis.

The rod peaking factor, (Pd /.,,d) radial, is of importance in the transient analysis for calculating maximum fuel temperatures in the time range where the heat transfer is not yet significant, and was calculated to not exceed 1.717. It is used in the safety analysis to calculate the peak fuel temperature under adiabatic conditions, where temperature distribution is the same as power distribution.

The reactor radial power peaking map for the UCI core is shown in Figure 2-8.

Figure 2-8 Hot Critical - Core Power Map 16 9

Nuclear Analysis of the LJCI TRIGA Reactor 911196-0 3

SUMMARY

Based on the nuclear analysis performed the UCI TRIGA reactor is considered to be safely operating under steady-state conditions. The UCI full, cold, unrodded core has an excess reactivity of $2.82; the reactivity of the core for the ARI case shows that the core is subcritical by

$5.88. The Shutdown Margin for the most reactive rod withdrawn from the core shows that the reactor is subcritical by $2.03. Also, it has been demonstrated that the reactor has both a negative void coefficient and negative prompt, fuel temperature coefficient, which provide for a controllable reactor. In addition, the highest rod factor shows a peak value of 1.446, which leads to a maximum power per fuel rod of 4.519 kW. Hence, it has been demonstrated through thorough analysis that the neutronic behavior of the UCI reactor meets the necessary operating requirements.

4 REFERENCES

1.

"MCNPX 2.6D Code Verification Report," General Atomics, April 2008

2.

Chiu, H., "Support Calculations for the Nuclear Analysis of the UCI TRIGA Reactor,"

General Atomics, GA 911197, November 2010

3.

UCI Technical Specification, July 2010 17

APPENDIX A: FUEL ROD NUMBER DENSITIES NOT INCLUDED IN THIS COPY A-1

A-2

OFFICAL USE ONLY

+ GENERAL ATOMICS P.O. BOX 85608 SAN DIEGO, CA 92186-5608 (858) 455-3000

Retrieved from "https://kanterella.com/w/index.php?title=ML111950452&oldid=5276316"