GENERATION AND INITIAL VALIDATION OF A NEW CASMO5 ENDF/B-VIII.0 NUCLEAR DATA LIBRARY

Abstract

A new nuclear data library for the CASMO5 advanced lattice physics code has been generated based on the recently-released ENDF/B-VIII.0 evaluation. The ENDF/B-VIII.0 evaluation represents the state-of-the-art in nuclear data and features new evaluations from the CIELO project for 1 H, 16 O, 56 Fe, 235 U, 238 U and 239 Pu. A description of the library generation procedure used to process these data into the CASMO5 586 energy group structure is provided. Initial validation of the new ENDF/B-VIII.0-based library, referred to as the E8R0 library, is also presented and involves the comparison of predicted criticality and fission rate distributions to measurements from various critical experiments. The critical experiments used in the initial validation of the E8R0 library consist of the B&W 1810 series, B&W 1484 series, DIMPLE S06A/B, and TCA reflector experiment with iron plates. The results from the initial validation indicate that the new E8R0 library provides a satisfactory performance in terms of CASMO5 predicted eigenvalue and fission distributions.

Full text

PHYSOR 2020: Transition to a Scalable Nuclear Future
Cambridge, United Kingdom, March 29th-April 2nd, 2020
GENERATION AND INITIAL VALIDATION OF A NEW CASMO5
ENDF/B-VIII.0 NUCLEAR DATA LIBRARY
Rodolfo Ferrer and Joel Rhodes
Studsvik Scandpower
1070 Riverwalk Dr., Suite 150
Idaho Falls, ID 83402
rodolfo.ferrer@studsvik.com, joel.rhodes@studsvik.com
ABSTRACT
A new nuclear data library for the CASMO5 advanced lattice physics code has been
generated based on the recently-released ENDF/B-VIII.0 evaluation. The ENDF/B-VIII.0
evaluation represents the state-of-the-art in nuclear data and features new evaluations from
the CIELO project for 1H, 16O, 56Fe, 235U, 238U and 239Pu. A description of the library
generation procedure used to process these data into the CASMO5 586 energy group
structure is provided. Initial validation of the new ENDF/B-VIII.0-based library, referred to
as the E8R0 library, is also presented and involves the comparison of predicted k–eff and
fission rate distributions to measurements from various critical experiments. The critical
experiments used in the initial validation of the E8R0 library consist of the B&W 1810
series, B&W 1484 series, DIMPLE S06A/B, and TCA reflector experiment with iron plates.
The results from the initial validation indicate that the new E8R0 library provides a
satisfactory performance in terms of CASMO5 predicted k–eff and fission distributions.
KEYWORDS: CASMO, ENDF/B-VIII.0, lattice physics, critical experiments
1. INTRODUCTION
The fundamental nuclear data used in the generation of multi-group, incident-neutron cross sections is the
starting point and foundation of all nuclear reactor simulation and analysis. Advanced in-core fuel
management tools, such as Studsvik’s Core Management System 5 (CMS5), rely on the two-step scheme
for production-level efficient design, analysis and optimization of Light Water Reactors (LWRs). The
CMS5 two-step scheme involves the use of the CASMO5 [1] advanced lattice physics code for the
generation of homogenized data for downstream use by the SIMULATE5 [2] advanced three-dimensional
nodal simulator, which supports the analysis of Boiling Water Reactors (BWRs), Pressurized Water
Reactors (PWRs) [3] and VVERs [4,5].
The release of a new nuclear data evaluation affords the opportunity to use the best-available data to
possibly reduce biases and improve predictions in LWR analysis. However, experience indicates that
careful testing and validation are necessary to determine whether the new and updated data may be
regarded as an improvement. Furthermore, the processing of the basic nuclear data evaluation may require
changes to the library generation procedure.

Rodolfo Ferrer et al., Generation and Initial Validation of New CASMO5 Nuclear Data Library
Proceedings of the PHYSOR 2020, Cambridge, United Kingdom
The objectives of this work are to provide a description of the library generation procedure used to
process the recently-released ENDF/B-VIII.0 [6] evaluation into a new commercially available CASMO5
586 energy-group library, referred to henceforth as the E8R0 library, and present the initial validation of
the E8R0 library using several critical experiments.
2. ENDF/B-VIII.0 NUCLEAR DATA EVALUATION
The ENDF/B-VIII.0 nuclear data evaluation was released by the Cross Section Evaluation Working
Group (CSEWG) on February 2, 2018. ENDF/B-VIII.0 represents the state-of-the-art in nuclear data, and
the neutron sub-library features the following highlights:
• New CIELO evaluations for 1H, 16O, 56Fe, 235U, 238U and 239Pu, including prompt fission spectra.
• New evaluated data for light nuclides such as 3He, 6Li, 10B, 12C and 13C.
• New evaluated data for structural materials such as 54,56-58Fe, 58-62,64Ni, 59Co, 63,65Cu, 174-182Hf, and
182-186W.
• Updated evaluated data for minor actinide nuclides such as 236mNp, 240Pu, and 241,243Am.
• Revised or reevaluated thermal scattering law for UO2, light water, and graphite.
• New data for fission energy release and radioactive decay data.
All major nuclides present in current-generation LWR fuel, coolant, absorber and structural materials
possess new evaluations in the ENDF/B-VIII.0 release. Consequently, this new evaluation may impact the
prediction of core parameters such as k–eff, temperature coefficients, cycle length, reflector savings,
activation and spent fuel characterization. Although the delayed neutron data remains relatively
unchanged from the previous release, reactor kinetics predictions may also be indirectly impacted by the
new evaluation, primarily due to changes in the fuel temperature (Doppler) coefficient [7]. A detailed
description of the ENDF/B-VIII.0 library may be found in reference [6].
Although the total number of nuclides available in the ENDF/B-VIII.0 neutron sub-library has increased
significantly from those present in the ENDF/B-VII.1 release, many short-lived nuclides represented in
the CASMO5 data library may not possess an evaluation. Therefore, the TALYS-based Evaluated Nuclear
Data Library 2017 (TENDL-2017) [8,9] is used to supplement the ENDF/B-VIII.0 evaluation.
3. UPDATED CASMO5 LIBRARY GENERATION PROCESS
A depiction of the CASMO5 library generation procedure is shown in Fig. 1, which has been adapted
from reference [10]. The ENDF/B-VIII.0 neutron cross section, thermal scattering (TSL), radioactive
decay and fission yield sub-libraries are depicted near the top of Fig. 1. The neutron and TSL sub-libraries
are processed through a sequence of NJOY2016 [11] modules: MODER, RECONR, BROADR, HEATR,
PURR, THERMR, and GROUPR. The NJOY2016 sequence is repeated for each individual nuclide
present in the CASMO5 library. Once neutron data for a nuclide has been processed with NJOY2016, a
modified version of the NJOY94 POWR module is used to read the NJOY2016 output tape and generate
an ASCII text file in the expected format. After all nuclides have been processed with NJOY2016 and
NJOY94, a utility program (NJXMRG) is used to generate pre-mixed materials available in the CASMO5
library. The resulting ASCII files are concatenated by the NJXLIB utility into a single file, labeled as the
ASCII Library in Fig. 1. The ASCII Library is structured into seven sub-files, each of which corresponds
to certain type of data for all nuclides, e.g., all resonance data for resonant nuclides is grouped together
into a single sub-file for efficiency. Finally, the ASCII Library is converted into a binary file using the
CASLIB utility code. Since Transport-Corrected P0 (TCP0) cross sections are written by the CASLIB
code into the final library, a dedicated infinite-medium  calculation must be performed by CASMO5
using a preliminary library. The output TCP0 cross sections from this calculation are subsequently
embedded into CASLIB and the final CASMO5 library is generated.

Physics of Reactors Transition to a Scalable Nuclear Future
Proceedings of the PHYSOR 2020, Cambridge, United Kingdom
Figure 1. Updated CASMO5 library generation procedure. Codes highlighted in gray required
updating to process ENDF/B-VIII.0 data.
The radioactive decay and fission yield sub-libraries are processed by the RDDFYD utility code. Either
cumulative or independent fission yields can be used, which in turn depends on the depletion chains
implemented in the CASMO5 code. The explicit representation (or omission) of metastable states of a
certain nuclide in the CASMO5 depletion chains is also handled by RDDFYD. Finally, the determination
of a representative incident-neutron energy is determined by RDDFYD when processing the fission yield
data.
The generation of Intermediate Resonance (IR) λ factors and Resonance Upscatter (RUP) corrections are
performed by the RABBLE [12] and MCSD [13] codes, respectively. Delayed neutron data and fission
spectra χ are extracted from the NJOY94 output via the CHICALC utility code.
Data →
Code →
Decay/Yield
Sub-libraries
IR λ and RUP
Data
χ and Delayed
Neutron Data
Neutron/TSL
Sub-libraries
ASCII Library
Final CASMO5
Library
NJOY2016
NJOY94
CASLIB
RDDFYD
RABBLE
CHICALC
CASMO5
NJXLIB
NJXMERG
MCSD

Rodolfo Ferrer et al., Generation and Initial Validation of New CASMO5 Nuclear Data Library
Proceedings of the PHYSOR 2020, Cambridge, United Kingdom
These data are not placed in the CASMO5 library and instead are embedded into the source code, as
depicted in Fig. 1, which allows for greater versatility when testing options, such as RUP [7].
4. NEW CASMO5 ENDF/B-VIII.0-BASED E8R0 LIBRARY
Various advanced numerical schemes and features have been implemented into CASMO5 since the
original release [1]. The CASMO5 neutron data library has also been updated from the original ENDF/B-
VII.1-based E7R1 200-series library [10] to the current E7R1 202-series library. The new E8R0 300-
series library shares the following features with the E7R1 202-series library:
• 586 energy groups with 128 fast groups (20 MeV to 9.118 keV), 41 resonance groups (9.118 keV
to 10 eV), 375 fine groups (10 eV to 0.625 eV), and 42 thermal groups (below 0.625 eV).
• 1095 nuclides and materials with cross section data (full or absorption-only).
• Over 2300 nuclear reactions models including (n,2n), (n,3n) and (n,4n) reactions.
• A total of 119 heavy nuclides (from 221Rn to 255Fm) and 491 fission products available in the
library.
• Explicit transmutation chains for heavy nuclides (from 229Th to 252Cf), fission products (from 76Ge
to 165Ho), burnable absorbers (AIC, Sm, Eu, Gd, Tb, Dy, Ho, Er, Hf, and W chains) and light
nuclides (1H to 20O unified chain).
• Shielded resonance data tabulated at 19 background cross sections and up to 10 temperatures
ranging from 239 K to 2700 K.
• High-order scattering matrices supporting 2D transport calculation with anisotropic sources.
• No ad hoc adjustment to 238U resonance absorption as done for ENDF/B-VI data [10].
The new E8R0 300-series library features the following updated data from the ENDF/B-VIII.0 release:
• Absorption, fission, transport, and scattering (including ) cross sections.
• Radioactive decay and fission yield.
• Prompt and delayed neutron fission spectra, along with IR λ factors and RUP correction.
• Energy release per fission and capture data.
5. INITIAL VALIDATION OF NEW CASMO5 E8R0 LIBRARY
A summary of the initial validation of the new CASMO5 E8R0 library is presented in this section. All
CASMO5 calculations were performed using a 95 energy-group structure. Energy condensation from the
586-group library structure to the 95 groups is performed through a set of one-dimensional pin cell
calculations. The 2D transport solution uses the default Linear Source (LS) Method of Characteristics
(MOC) scheme and angular quadrature (64 azimuthal angles, 3 polar angles and a 0.05 cm ray spacing).
All numerical results use the TCP0 unless otherwise noted. The problem-specific axial bucklings, used to
model the axial leakage effects, have been gleaned from the various critical experiment reports.
3.1. B&W 1810 Critical Experiment Series
The Babcock & Wilcox 1810 critical experiments [14] represent realistic PWR reactor configurations.
The core configurations consist of 55 arrays of Westinghouse, or Babcock & Wilcox, 1515 assemblies
(Cores 1 through 17) and Combustion Engineering 1616 assemblies (Cores 18 through 20), as depicted
in Fig. 2. Cores 1 through 10 consist of uniform fuel enrichment, whereas Cores 12 through 17 consist of
a high enriched central area surrounded by a low enriched zone. The central pseudo-assembly is modified
by introducing gadolinium fuel pins, Ag-In-Cd (AIC) or B4C control rods, or even hollow tubes. Cores 18
through 20 also consist of a high enriched central area surrounded by a low enriched zone. These cores
only differ in the number of gadolinium fuel pins present. All measurements are reported at a facility
temperature of 25 ˚C. Tables I and II show the k–eff and Fission Rate (FR) results, respectively.

Physics of Reactors Transition to a Scalable Nuclear Future
Proceedings of the PHYSOR 2020, Cambridge, United Kingdom
Figure 2. CASMO5 multi-assembly depiction of B&W 1810 Core 1 (left) and Core 18 (right). Core
1 is similar to cores 2-17 and Core 18 is similar to cores 19-20.
Table I. CASMO5 B&W 1810 critical experiments: k–eff results.
Core
Boron (ppm)
Lattice
Central Region
4 % Gd1 Pins
AIC Rods
  
1
1337.9
1515
Uniform
--
--
1.00125
2
1250
1515
Uniform
--
16
1.00088
3
1239.3
1515
Uniform
20
--
1.00111
4
1171.7
1515
Uniform
20
16
1.00174
5
1208
1515
Uniform
28
--
1.00073
5A
1191.3
1515
Uniform
32
--
1.00075
5B
1207.1
1515
Uniform
28
--
1.00087
6
1155.8
1515
Uniform
28
16
1.00102
6A
1135.6
1515
Uniform
32
16
1.00101
7
1208.8
1515
Uniform
28 (annular)
--
1.00083
8
1170.7
1515
Uniform
36
--
1.00093
9
1130.5
1515
Uniform
36
16
1.00085
10
1177.1
1515
Uniform
36
16
1.00076
12
1899.3
1515
2-Region
--
--
1.00162
13
1635.4
1515
2-Region
--
16
1.00204
14
1653.8
1515
2-Region
28
16
1.00143
15
1479.7
1515
2-Region
28
16
1.00194
16
1579.4
1515
2-Region
36
--
1.00153
17
1432.1
1515
2-Region
36
16
1.00158
18
1776.8
1616
2-Region
--
--
1.00221
19
1628.3
1616
2-Region
16
--
1.00209
20
1499
1616
2-Region
32
--
1.00199
Average
1.00133
Stand. Dev. (pcm)
49.3
1
% Gd indicates the mass fraction of Gd relative to Gd2O3 in a mixture of Gd2O3+UO2 in percentage.

Rodolfo Ferrer et al., Generation and Initial Validation of New CASMO5 Nuclear Data Library
Proceedings of the PHYSOR 2020, Cambridge, United Kingdom
Table II. CASMO5 B&W 1810 critical experiments: FR results for Central Assembly (CA) and
Diagonal Pins (DP).
Core
4 % Gd Pins
AIC Rods
CA FR RMS
DP FR RMS
1
--
--
0.57
5
28
--
0.74
2.26
12
--
--
0.84
14
28
16
1.46
5.76
18
--
--
0.84
20
32
--
1.53
3.99
The average CASMO5 calculated k–eff using the E8R0 library is 133 pcm higher than unity over a wide
range of burnable absorber types and loadings. The FR statistics indicate a Root-Mean-Square (RMS)
difference of less than 2 % relative to the Central Assembly and less than 6 % relative to diagonal pins.
The CASMO5 E8R0 predictions are comparable to those obtained with the E7R1 library.
3.2. B&W 1484 Critical Experiment Series
The Babcock & Wilcox 1484 critical experiments [15] consist of twenty-one configurations involving low
and high leakage cores, as well as PWR fuel storage configurations. A depiction of the Core I through VI
configuration is shown in Fig. 3 and Core X and XI in Fig. 4. k–eff results are given in Table III.
Figure 3. CASMO5 multi-assembly depiction of B&W 1484 Cores I through VI (left to right, top to
bottom). Absorber rods containing B4C are depicted as red pins.

Physics of Reactors Transition to a Scalable Nuclear Future
Proceedings of the PHYSOR 2020, Cambridge, United Kingdom
Figure 4. CASMO5 multi-assembly depiction of B&W 1484 Core X (left) and XI (right). Isolation
sheets are depicted as vertical and horizontal slabs.
Table III. CASMO5 B&W 1484 critical experiments: k–eff results.
Core
k
Core
  
I
1.00031
X
1.00270
II
1.00071
XIa
1.00122
IIIa
1.00025
XIb
1.00117
IIIb
1.00063
XIc
1.00117
IIIc
1.00022
XId
1.00123
IIId
1.00021
XIe
1.00167
IIIe
1.00033
XIf
1.00153
IIIf
1.00062
XIg
1.00279
IIIg
1.00059
XII
1.00082
IV
0.99968
XIII
0.99906
V
0.99887
XIIIa
0.99668
VI
0.99903
XIV
0.99554
VII
0.99958
XV
0.99182
VIII
0.99965
XVI
0.99247
IX
1.00028
XVII
0.99545
XVIII
0.99558
XIX
0.99715
XX
0.99692
XXI
0.99708
Mean
1.00006
Mean
0.99853
St. dev. (pcm)
56
St. dev. (pcm)
330
Cores I and II do not involve any heterogeneity and only differ in size and shape. Core I consists of
2.459 % enriched (by mass) 235U fuel pins arranged in a high leakage circular core. Core II consists of the
same fuel enrichment as Core I, but the core is arranged in a low-leakage configuration. Cores III through
IX represent various hypothetical fuel storage configurations where 1515 fuel assemblies are ranged in
33 space lattices. The spacing between the assemblies and interstitial absorber pin configuration is
varied. Cores X through XXI also represent fuel storage configurations. Unlike the previous
configurations, isolating/absorbing plates are introduced between the fuel assemblies.

Rodolfo Ferrer et al., Generation and Initial Validation of New CASMO5 Nuclear Data Library
Proceedings of the PHYSOR 2020, Cambridge, United Kingdom
The CASMO5 average predicted k–eff for Cores I through IX is only 6 pcm higher than unity and -147
pcm lower for Cores X through XXI. The second set of cores exhibits greater spatial non-uniformity with
the presence of the absorber plates, where boron/aluminum isolation plates are present in Cores XIII
through XXI. The CASMO5 E8R0 300 library predictions for the B&W 1484 critical experiments are
comparable to results obtained with the E7R1 202 library.
3.3. DIMPLE S06A/B Critical Experiments
The AEA Winfrith DIMPLE experimental program [16] conducted critical experiments involving a
cruciform core configuration, which resembles a rectangular corner of a PWR core, and consists of five
1616 PWR assemblies with 3 % 235U enriched UO2 fuel pins. The DIMPLE S06A configuration is
surrounded by a water reflector region, whereas the DIMPLE S06B configuration involves a 2.67 cm
stainless steel baffle region between the fuel and water reflector regions. The DIMPLE critical
experiments indicate the CASMO5 performance for multi-assembly calculations routinely performed to
generate PWR reflector data. The geometry of critical experiments is depicted in Fig. 5.
Figure 5. CASMO5 multi-assembly depiction of DIMPLE S06A (left) and S06B (right).
The k–eff for each core configuration are given in Table IV. Fission rates for 235U and 238U were also
measured in select fuel pins. Table IV also provides descriptive statistics for the relative error in the
CASMO5 fission rates compared to the measured values.
Table IV. CASMO5 DIMPLE critical experiments: k–eff and fission rate (relative difference in
percent) results.
S06A
S06B
  
0.99888
0.99909
Statistic
235U
238U
235U
238U
Mean
0.093
0.003
-0.935
-1.137
Standard Deviation
0.779
2.24
1.43
1.904
RMS
0.784
2.24
1.708
2.217
The DIMPLE results indicate that the new CASMO5 E8R0 library performs well in predicting k–eff and
fission rates for the generation of PWR reflector data involving baffle regions. Relative to the previous
E7R1 202 library, the E8R0 library yields comparable results.

Physics of Reactors Transition to a Scalable Nuclear Future
Proceedings of the PHYSOR 2020, Cambridge, United Kingdom
3.3. TCA Iron Reflector Critical Experiments
The Tokai Research Establishment of JAERI conducted critical experiments using a Tank-type Critical
Assembly (TCA) while varying the thickness of the steel or steel-water reflector slabs [17]. The fuel
assembly consists of a 1515 PWR design and 2.6 % 235U enriched fuel. The objective of the experiment
was to measure the reactivity effect of two reflector types: steel-only and steel-water reflector containing
about 90 % steel and 10 % water. The TCA geometry for a steel-only reflector case is shown in Fig. 6 and
a comparison of the CASMO5 predicted and measured reactivity effect [17] is shown in Fig. 7.
Figure 6. CASMO5 multi-assembly depiction of TCA steel-only reflector with 15.12 cm thickness.
Figure 7. Reactivity effect of steel (left) and steel-water (right) reflectors in TCA experiment.
The reactivity effect is the change in reactivity from the reference critical water height, which is taken
from the assembly with the steel replaced by water, to the critical height with the reflector present. The
ratio of the effective delayed neutron yield and mean neutron lifetime, , is also provided for the
bare TCA configuration. The CASMO5 E8R0 computed  is 162.8 , as compared to a measured
value of 161.5  ± 5.0 . The CASMO5 results using the E8R0 library are comparable to those
obtained using the E7R1 202 library.

Rodolfo Ferrer et al., Generation and Initial Validation of New CASMO5 Nuclear Data Library
Proceedings of the PHYSOR 2020, Cambridge, United Kingdom
6. CONCLUSIONS
A new commercially available CASMO5 nuclear data library has been generated based on the recently-
released ENDF/B-VIII.0 evaluation. A summary of the library generation procedure and main features of
the new CASMO5 586-group library (referred to as E8R0) is provided in this work. Initial validation of
the E8R0 library versus the B&W 1810, B&W 1484, DIMPLE and TCA critical experiments indicate
comparable accuracy relative to the previous E7R1 202 library. Although changes were made to Fe cross
sections in ENDF/B-VIII.0, they do not have a significant impact in terms of core k–eff, such as in the
TCA reflector experiments. Future work involves further validation against MOX critical experiments and
comparisons to Post Irradiation Examination (PIE) isotopic data.
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