ASTM E2005-99
(Guide)Standard Guide for Benchmark Testing of Reactor Dosimetry in Standard and Reference Neutron Fields
Standard Guide for Benchmark Testing of Reactor Dosimetry in Standard and Reference Neutron Fields
SCOPE
1.1 This guide covers facilities and procedures for benchmarking neutron measurements and calculations. Particular sections of the guide discuss: the use of well-characterized benchmark neutron fields to calibrate integral neutron sensors; the use of certified-neutron-fluence standards to calibrate radiometric counting equipment or to determine interlaboratory measurement consistency; development of special benchmark fields to test neutron transport calculations; use of well-known fission spectra to benchmark spectrum-averaged cross sections; and the use of benchmarked data and calculations to determine the uncertainties in derived neutron dosimetry results.
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Designation:E2005–99
Standard Guide for
Benchmark Testing of Reactor Dosimetry in Standard and
Reference Neutron Fields
This standard is issued under the fixed designation E 2005; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope E 526 Test Methods for Measuring Fast-Neutron Reaction
Rates by Radioactivation of Titanium
1.1 This guide covers facilities and procedures for bench-
E 704 Test Methods for Measuring Fast-Neutron Reaction
marking neutron measurements and calculations. Particular
Rates by Radioactivation of Uranium-238
sections of the guide discuss: the use of well-characterized
E 705 Test Methods for Measuring Fast-Neutron Reaction
benchmark neutron fields to calibrate integral neutron sensors;
Rates by Radioactivation of Neptunium-237
the use of certified-neutron-fluence standards to calibrate
E 706 Master Matrix for Light-Water Reactor Pressure
radiometriccountingequipmentortodetermineinterlaboratory
Vessel Surveillance Standards
measurement consistency; development of special benchmark
E 706 (IIE2) Guide for Benchmark Testing of Light Water
fields to test neutron transport calculations; use of well-known
Reactor Calculations
fissionspectratobenchmarkspectrum-averagedcrosssections;
E 844 Guide for Sensor Set Design and Irradiation for
and the use of benchmarked data and calculations to determine
Reactor Surveillance, E 706 (IIC)
the uncertainties in derived neutron dosimetry results.
E 854 Test Method for Application and Analysis of Solid
2. Referenced Documents State Track Recorder (SSTR) Monitors for Reactor Sur-
veillance, E 706 (IIIB)
2.1 ASTM Standards:
E 910 Test Method forApplication andAnalysis of Helium
E 170 Terminology Relating to Radiation Measurements
Accumulation Fluence Monitors for Reactor Vessel Sur-
and Dosimetry
veillance, E 706 (IIIC)
E 261 Practice for Determining Neutron Fluence Rate, and
E 1297 Test Method for Measuring Fast-Neutron Reaction
Spectra by Radioactivation Techniques
Rates by Radioactivation of Niobium
E 263 Test Methods for Measuring Fast-Neutron Reaction
Rates by Radioactivation of Iron
3. Significance and Use
E 264 Test Methods for Measuring Fast-Neutron Reaction
3.1 This guide describes approaches for using neutron fields
Rates by Radioactivation of Nickel
with well known characteristics to perform calibrations of
E 265 Test Methods for Measuring Fast-Neutron Reaction
neutron sensors, to intercompare different methods of dosim-
Rates by Radioactivation of Sulfur-32
etry, and to corroborate procedures used to derive neutron field
E 266 Test Methods for Measuring Fast-Neutron Reaction
information from measurements of neutron sensor response.
Rates by Radioactivation of Aluminum
3.2 This guide discusses only selected standard and refer-
E 343 Test Methods for Measuring Reaction Rates by
ence neutron fields which are appropriate for benchmark
Analysis of Molybdenum 99Activity from Fission Dosim-
2 testing of light-water reactor dosimetry. The Standard Fields
eters
considered are neutron source environments that closely ap-
E 393 Test Methods for Measuring Reaction Rates by
proximate the unscattered neutron spectra from Cf sponta-
Analysis of Barium-140 from Fission Dosimeters
neous fission and U thermal neutron induced fission. These
E 482 Guide forApplication of Neutron Transport Methods
standard fields were chosen for their spectral similarity to the
for Reactor Vessel Surveillance, E 706 (IID)
high energy region (E > 2 MeV) of reactor spectra. The
E 523 Test Methods for Measuring Fast-Neutron Reaction
reference field considered in detail is the Materials Dosimetry
Rates by Radioactivation of Copper
Reference Facility, which has a spectral shape similar to the
neutrons impinging on a pressurized water reactor vessel. The
various categories of benchmark fields are defined in Termi-
This practice is under the jurisdiction of ASTM Committee E-10 on Nuclear
nology E 170.
Technology and Applications and is the direct responsibility of Subcommittee
3.3 There are other well known neutron fields that have
E10.05 on Nuclear Radiation Metrology.
been designed to mockup special environments, such as
Current edition approved Feb. 10, 1999. Published April 1999.
Annual Book of ASTM Standards, Vol 12.02. pressure vessel mockups in which it is possible to make
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
E2005
dosimetry measurements inside of the steel volume of the measured and calculated spectrum-averaged cross sections are
“vessel.” When such mockups are suitably characterized they all given in a compendium, see Ref. (5).
are also referred to as benchmark fields. A variety of these
5.2.2 The NIST Cf sources have a very nearly unper-
engineering benchmark fields have been developed, or pressed
turbed spontaneous fission spectrum, because of the light-
into service, to improve the accuracy of neutron dosimetry
weight encapsulations, fabricated at the Oak Ridge National
measurement techniques. These special benchmark experi-
Laboratory (ORNL), see Ref. (6).
ments are discussed in Guide E 706 (IIE2), and in Refs. (1)
5.2.3 Foracomprehensiveviewofthecalibrationanduseof
and (2).
a special (32 mg) Cf source employed to measure the
spectrum-averaged cross section of the Nb(n,n8) reaction, see
4. Neutron Field Benchmarking
Ref. (7).
4.1 To accomplish neutron field “benchmarking,” one must 5.3 U Fission Spectrum—Standard Neutron Field:
perform irradiations in a well-characterized neutron environ-
5.3.1 Because U fission is the principal source of neu-
ment, with the required level of accuracy established by a
trons in present nuclear reactors, the U fission spectrum is a
sufficient quantity and quality of results supported by a
fundamental neutron field for benchmark referencing or do-
rigorous uncertainty analysis. What constitutes sufficient re-
simetry accomplished in reactor environments. This remains
sultsandtheirrequiredaccuracylevelfrequentlydependsupon
true even for low-enrichment cores which have up to 30 %
the situation. For example:
burnup.
4.1.1 Benchmarking to test the capabilities of a new dosim-
5.3.2 Therearecurrentlytwo Ustandardfissionspectrum
eter;
facilities available, one in the thermal column of the NIST
4.1.2 Benchmarking to ensure long-term stability, or conti-
Research Reactor (8) and one at CEN/SCK, Mol, Belgium (9).
nuity, of procedures that are influenced by changes of person-
5.3.3 A standard U neutron field is obtained by driving
nel and equipment;
(fissioning) U in a field of thermal neutrons. Therefore, the
4.1.3 Benchmarking measurements that will serve as the
fluence rate depends upon the power level of the driving
basis of intercomparison of results from different laboratories;
reactor, which is frequently not well known or particularly
4.1.4 Benchmarking to determine the accuracy of newly
stable. Time dependent fluence rate, or total fluence, monitor-
established benchmark fields; and
ing is necessary in the U field. Certified fluence irradiations
58 58
4.1.5 Benchmarking to validate certain ASTM standard
are monitored with the Ni(n,p) Co activation reaction. The
methods or practices which derive exposure parameters (for
fluence-monitor calibration must be benchmarked.
example, fluence > 1 MeV or dpa) from dosimetry measure- 235 252
5.3.4 For U, as for Cf irradiations, small (nominally
ments and calculations.
< 3 %) scattering and absorption corrections are necessary. In
addition, for U, gradient corrections of the measured fluence
5. Description of Standard and Reference Fields
which do not simply depend upon distance are necessary. The
5.1 There are a few facilities which can provide certified
scattering and gradient corrections are determined by Monte
“free field” fluence irradiations. The following provides a list
Carlo calculations. Field characteristics of the NIST U
of such facilities. The emphasis is on facilities that have a
Fission Spectrum Facility and associated measured and calcu-
long-lived commitment to development, maintenance, re-
lated cross sections are given in Ref. (5).
search, and international interlaboratory comparison calibra-
5.4 Materials Dosimetry Reference Facility (MDRF)—
tions. As such, discussion is limited to presently existing
Reference Neutron Field:
facilities.
5.4.1 Anew, high-intensity reference-neutron field for reac-
5.2 Cf Fission Spectrum—Standard Neutron Field:
tor dosimetry has been placed into operation, by NIST, in the
5.2.1 The standard fission-spectrum fluence from a suitably
pool adjacent to the Ford Nuclear Reactor (FNR) at the
encapsulated Cf source is characterized by its source
UniversityofMichigan.Neutronspectrumcharacterizationhas
strength, the distance from the source, and the irradiation time.
been accomplished by measurement of spectral indexes (see
In the U.S., neutron source emission rate calibrations are all
Section 7.) and DORT neutron transport calculations. The fast
referenced to source calibrations at the National Institute of
neutron fluence rate has been determined by means of the
Standards and Technology (NIST) accomplished by the
fluencetransferprocedure(see6.2)fromaNIST Cfstandard
MnSO technique (3). Corrections for neutron absorption,
neutron field and by other means (Ref.(10)). MDRF certified
58 58
scattering, and other than point-geometry conditions may, by
neutron fluences are monitored with the Ni(n,p) Co activa-
careful experimental design, be held to less than 3 %. Associ-
tion reaction.The fast neutron spectrum is similar to that at the
ated uncertainties for the NIST Cf irradiation facility are
inside surface of the pressure vessel in a PWR reactor with a
discussed in Ref. (4). The principal uncertainties, which only
thermal shield. Spectral monitoring measurements during
total about 2.5 %, come from the source strength determina-
changes in nearest neighbors in the pool and fuel element
tion, scattering corrections, and distance measurements. Exten-
changes at the nearest edge of the core indicated fluence rate
sive details of standard field characteristics and values of
level variations but very small (< 5 %) changes in the spectrum
(for example, no significant changes in various reaction rate
ratios).
5.4.2 The MDRF is employed for calibration and validation
The boldface numbers given in parentheses refer to a list of references at the
end of the text. experiments in support of materials neutron dosimetry for the
E2005
nuclear reactor industry and for the metallurgical community frequently large, leading to a less accurate determination of f
engaged in estimating radiation damage in steel. Field charac- than desired. However, if one can make an additional irradia-
terization and user operation of the facility is a joint effort by tion of the same type of dosimeter in a standard neutron field
the NIST and the Phoenix Memorial Laboratory of the Uni- with known fluence rate, then one may apply Eq 2 to both
versity of Michigan. This reference field is a natural extension irradiations and write
of a long-term NIST program to develop standard and refer-
f 5f ~R /R !~s¯ /s¯ ! (3)
A B A B B A
ence neutron fields for measurement assurance applications
where “A” denotes the field of interest and “B” denotes the
and for testing new detectors and techniques.
standard neutron field benchmark. In Eq 3 the ratios of spectral
5.4.3 The MDRF complements the Cavity Fission Source at
average cross section, will have a small uncertainty if the
the NIST reactor by providing a tenfold increase in the
spectral shapes f (E) and f (E) are fairly similar.There may
A B
fast-neutronfluencerate,amuchlargerirradiationvolumewith
also be important cancellation of poorly known factors in the
modest gradients, and a neutron spectrum similar to that at the
ratio R /R , which will contribute to the better accuracy of Eq
A B
inner surface of a PWR pressure vessel. An option to alter the
3. Whether f is better determined by Eq 3 or Eq 2 must be
intermediate-energy neutron rate is afforded by installation of a
10 11 evaluated on a case by case basis. Often the fluence rate from
B filter liner. The fluence rate (E > 1 MeV) is 2.7 3 10
Eq 3 is substantially more accurate and provides a very useful
–2 –1
neutrons cm s and the neutron-to-gamma fluence ratio is
validation of other dosimetry. The use of a benchmark neutron
0.35 (dimensionless).
field irradiation and Eq 3 is called fluence rate transfer.
6.2.1 Certified Fluence or Fluence Rate Irradiations—The
6. Applications of Benchmark Fields
primary benefit from carefully-made irradiations in a standard
6.1 Notation—Reaction Rate, Fluence Rate, and Fluence—
neutron field is that of knowing the neutron fluence rate.
The notation employed in this section will follow that in E 261 252
Considerthecaseofalightlyencapsulated Cfsintered-oxide
(Standard Practice for Determining Neutron Fluence Rate, and
bead, which has an emission rate known to about 6 1.5 % by
Spectra by Radioactivation Techniques) except as noted. The
calibration in a manganese bath (MnSO solution). Further,
reaction rate, R, for some neutron-nuclear reaction {reactions/
consider a dosimeter pair irradiated in compensated beam
[(dosimeter target nucleus)(second)]} is given by
geometry (with each member of the pair equidistant from, and
`
on opposite sides of, the Cf source). For such an irradiation
R 5 s~E! f~E! dE (1)
in a large room (where very little room return occurs), the
*
o
fluence rate – with a Cf fission spectrum – is known to
or: within 63 % from the source strength, and the average
distance of the dosimeter pair from the center of the source.
R5s¯ f (2)
Questions concerning in- and out-scattering by source encap-
where:
sulation, source and foil holders, and foil thicknesses may be
s(E) 5 the dosimeter reaction cross section at energy E
accurately investigated by Monte Carlo calculations. There is
–24 2
(typically of the order of 10 cm ),
no other neutron-irradiation situation that can approach this
f(E) 5 the differential neutron fluence rate, that is the
level of accuracy in determination of the fluence or fluence
fluence per unit time and unit energy for neutrons
rate.
with energies between E and E +dE (neutrons
6.2.2 Fluence Transfer Calibrations of Reference Fields—
–2
–1 –1
cm s MeV ),
The benefit of irradiating with a source of known emission rate
–2 –1
f5 the total fluence rate (neutrons cm s ), the integral
is lost when one
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