ISO 18077:2018

INTERNATIONAL ISO
STANDARD 18077
First edition
2018-03
Reload startup physics tests for
pressurized water reactors
Essais physiques au redémarrage pour les réacteurs à eau préssurisée
Reference number
©
ISO 2018
© ISO 2018
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ii © ISO 2018 – All rights reserved

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Relation to other standards . 3
5 Physics test program and selection criteria . 3
5.1 Bases for startup physics test program . 3
5.2 Required minimum test program . 4
6 Test method requirements . 5
6.1 General test considerations . 6
6.1.1 Test objective . 6
6.1.2 Test purpose . 6
6.1.3 Initial conditions . 6
6.1.4 Test methods . 6
6.1.5 Evaluation . 6
6.2 Test criteria . 6
7 Requirements of this document . 7
Annex A (informative) User’s guide . 8
Bibliography .28
Foreword
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This document was prepared by Technical Committee ISO/TC 85, Nuclear energy, nuclear technologies
and radiation protection, Subcommittee SC 6, Reactor technology.
iv © ISO 2018 – All rights reserved

Introduction
In conjunction with each refuelling shutdown or other significant reactor core alteration, nuclear
design calculations are performed to ensure that the reactor physics characteristics of the new core
will be consistent with the safety limits. Prior to return to normal operation, successful execution of a
physics test program is required to determine if the operating characteristics of the core are consistent
with the design predictions and to ensure that the core can be operated as designed.
This document specifies the content of the minimum acceptable startup physics test program for
commercial pressurized water reactors (PWRs) and provides the bases for each test. Acceptable
methods for performing the individual tests are provided in Annex A. Alternate methods can be used as
long as they are shown to meet the requirements of Clause 6.
Successful completion of the physics test program is demonstrated when the test results agree with the
predicted results within predetermined test criteria. Successful completion of the physics test program
and successful completion of other tests that are performed after each refueling or significant reactor
core alteration provide assurance that the plant can be operated as designed.
INTERNATIONAL STANDARD ISO 18077:2018(E)
Reload startup physics tests for pressurized water reactors
1 Scope
This document applies to the reactor physics tests that are performed following a refuelling or other
core alteration of a PWR for which nuclear design calculations are required. This document does not
1)
address the physics test program for the initial core of a commercial PWR .
This document specifies the minimum acceptable startup reactor physics test program to determine
if the operating characteristics of the core are consistent with the design predictions, which provides
assurance that the core can be operated as designed. This document does not address surveillance of
reactor physics parameters during operation or other required tests such as mechanical tests of system
components (for example the rod drop time test), visual verification requirements for fuel assembly
loading, or the calibration of instrumentation or control systems (even though these tests are an
integral part of an overall program to ensure that the core behaves as designed).
This document assumes that the same previously accepted analytical methods are used for both the
design of the reactor core and the startup test predictions. It also assumes that the expected operation
of the core will fall within the historical database established for the plant and/or sister plants.
When major changes are made in the core design, the test program should be reviewed to determine
if more extensive testing is needed. Typical changes that might fall in this category include the initial
use of novel fuel cycle designs, significant changes in fuel enrichments, fuel assembly design changes,
burnable absorber design changes, and cores resulting from unplanned short cycles. Changes such as
these may lead to operation in regions outside of the plant's experience database and therefore may
necessitate expanding the test program.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
3.1
all rods out
ARO
all full-length control rods withdrawn
Note 1 to entry: Part-length rods may be inserted.
3.2
control rod
one or more reactivity control members mechanically attached to a single fixture
1) The good practices discussed in this document should be considered for use in the physics test program for the
initial core of a commercial PWR. One test that provides useful information (without additional test time) is the hot-
zero-power to hot-full-power reactivity measurement.
3.3
control rod group
one or more rods that are inserted or withdrawn simultaneously (also known as “control rod bank”)
Note 1 to entry: The term “all control rod groups” means all safety and regulating control rod groups. This term
may also be shortened to simply “rod group.”
3.4
decades per minute
DPM
unit used to measure a rate of change in flux as measured by the ex-core detectors
3.5
hot full power
HFP
full power
rated thermal power
licensed core thermal power level
3.6
hot zero power
HZP
reactor operating state where the core is essentially critical but is not producing measurable heat from
nuclear fission, the reactivity due to xenon is negligible, and the primary coolant system is at design
temperature and pressure for zero power
Note 1 to entry: At HZP, the flux signal should be high enough so that the reactivity computer can account for
contamination sources such as noise, gamma background, and leakage.
3.7
isothermal temperature coefficient
ITC
change in reactivity per unit change in the fuel and moderator temperature when the fuel and moderator
are at the same temperature
3.8
part-length rod
control rod whose primary absorber material does not extend the entire length of the control rod
(typically the lower half of the control rod’s active length)
Note 1 to entry: Used for axial shape control. For the purposes of this document, the term “part-length rod” can
also represent a “part-strength” control rod.
3.9
percent milli-rho
pcm
−3
unit of reactivity worth equivalent to 10 %Δρ
Note 1 to entry: See definition of “reactivity worth” below.
Note 2 to entry: Throughout this document, pcm is the unit of reactivity to be used.
3.10
reactivity computer
analog or digital device that calculates the core reactivity by using an external signal that is proportional
to the core neutron flux
3.11
reactivity worth
2 © ISO 2018 – All rights reserved

change in reactivity expressed in terms of percent as follows:
%(Δρ=−kk )/×100 kk
21 12
where:
k is the effective multiplication constant for reactor state 1;
k is the effective multiplication constant for reactor state 2.
3.12
regulating control rod group
group of control rods that may be partially or fully inserted in the core during normal operation
3.13
safety control rod group
shutdown rod group
shutdown bank
control rod group that remains withdrawn from the core during normal operation
3.14
test criterion
review criterion
predetermined value for evaluating the result of each test
Note 1 to entry: The value is based on differences between calculations and measurements that would suggest
a problem with the as-built core, the measurement, or the prediction. The value is not based on safety analysis
assumptions. See the Annex for a more complete discussion of test (review) criteria used in this document.
4 Relation to other standards
[2]
American National Standard ANSI/ANS-3.2-2012 (R2017) , provides requirements and
recommendations for an administrative control and quality assurance program for the safe and
efficient operation of nuclear power plants. Provisions for test and applicable test equipment control
required by this document are also included in ANSI/ANS-3.2-2012 (R2017). American National
[3]
Standard ANSI/ANS-3.1-2014 , provides for the selection, qualification, and training of personnel for
nuclear power plants, including personnel responsible for startup testing.
[4]
American National Standard ANSI/ANS-19.4-1976 (R2000) (W2010) , and American National
[5]
Standard ANSI/ANS-19.5-1995 (W2005) , address reactor physics measurements that are intended to
yield documented data of both the type and quality required for validating nuclear analysis methods.
[6]
American National Standard ANSI/ANS-19.11-2017 , describes how to calculate and measure the
moderator temperature coefficient of reactivity. American National Standard ANSI/ANS-19.6.1-2011
[7]
(R2016) , defines the minimum acceptable startup physics test program and acceptable test methods
(7)
to determine if the reactor core operating characteristics are consistent with the design predictions .
ANSI/ANS-19.6.1-2011 (R2016) was used as the basis for this standard (ISO 18077).
5 Physics test program and selection criteria
5.1 Bases for startup physics test program
During the reload design process, the reactor safety is determined by analysis. Following the reload,
specific core characteristics shall be confirmed by measurement to ensure that the reconstructed core
is accurately represented by that analysis and is operating as designed. Thus, the testing results seek to
confirm that the reactor can be operated within the bounds of the technical specifications, that there
is sufficient operational flexibility, and that the plant can be expected to safely deliver the designed
power output.
The important analysis characteristics that shall be confirmed by measurement are the following:
a) Reactivity balance: Reactivity balance neutronically demonstrates that the total amount of fuel
loaded in the core is consistent with design. The boron end point measurements confirm that the
amount of various fissionable materials in the core, as well as the reactivity effects of various fixed
poisons (e.g. burnable absorbers) and transient poisons (e.g. samarium), is consistent with the
design calculations.
b) Reactivity control: Reactivity control refers to the reactor core parameters that have an impact on
the ability of the operators to control the plant. The primary parameter that confirms this is the
isothermal temperature coefficient.
c) Power distribution: Power distribution is a measurement (check) that the core is loaded properly
and will perform as designed. When the measured power distributions agree with predictions,
there is high confidence that the as-built core and the designed core are the same. In addition,
there is increased confidence that the conclusions of the safety analyses are correct. Finally, close
agreement between measured and predicted power distributions increases the confidence that
reactivity control parameters will perform as designed.
d) Capability to shutdown: Capability to shutdown is demonstrated by showing that the measured
control rod worths are consistent with the calculated values. The shutdown margin calculations
are based upon design values, which shall be confirmed.
e) Requirements to shutdown: The requirements to shutdown are the reactivity elements that the safety
and regulating control rods shall overcome in a reactor trip. The shutdown margin calculations are
based upon design values, which shall be confirmed.
Any new testing process or program of tests that are not described in Annex A shall specify how the
above parameters are to be confirmed.
The reload startup testing program is constructed such that as the power ascension proceeds, the level
of confidence in confirmed reactor characteristics continues to improve. Similarly, the results of testing
at a given power level shall provide reasonable assurance that the next proposed power level can be
achieved without risk of violating the design or licensing bases of the plant.
A minimum test program is designed to ensure a complete certification, assuming no anomalies were
identified during the test program. When results show deviations from predictions that are beyond the
experience base, supplementary actions shall be identified and performed, as necessary. A complete
design verification test program should identify the minimum testing that will be performed and the
supplementary actions that may be performed.
5.2 Required minimum test program
The characteristics required to be confirmed by this document, example measured parameters used
for confirmation, and power levels before which they shall be confirmed are provided by Table 1. The
parameters were selected by considering the following requirements:
a) The information obtained from the parameter cannot be inferred from other tests that will be
performed. This requirement means that redundant tests can be excluded. In the event that a
particular parameter fails to pass the test criteria, however, other (redundant) tests should be
performed to help resolve the discrepancy.
b) Each test shall be able to quantitatively measure an important physics characteristic of the reactor
core. This requirement means that the following types of measurements were excluded (although
they may be performed for other reasons):
1) mechanical tests of system components (rod drop time, etc.);
2) tests used solely for instrument calibration;
4 © ISO 2018 – All rights reserved

3) tests used to benchmark computer models.
b) Each measurement shall be accurate, and an accurate prediction shall be available. This requirement
means that the expected difference between the measured result and the prediction shall be small
so that if the measurement and the prediction agree, there is confidence that the core will behave
as predicted. Conversely, if there actually is a design discrepancy in the core, the measurement will
reveal it (the measurement and prediction will not agree).
c) The test program shall be designed to not violate the plant's shutdown margin requirements. This
requirement means that the plant shutdown margin requirements shall not be violated while
performing startup physics testing.
Table 1 — Required physics characteristics to be confirmed
Power level
Characteristic(s) Example measured parameter to use for confirmation
%
Reactivity balance All-rods-out boron concentration <5
Capability to shutdown,
Control rod worths <5
a
power distribution
Reactivity control Isothermal temperature coefficient <5
Flux symmetry or direct power distribution measurement
Power distribution 0 to 30
between 0 and 30 % of full power
If a direct low-power distribution measurement has yet to be
Power distribution confirmed, then it shall be confirmed (compared to predictions) 30 to 50
b
prior to exceeding 50 % power .
Power distribution measurement results shall be assessed
Power distribution collectively to ensure that local and global core characteristic 50 to 80
trends are acceptable prior to exceeding 80 % power.
Power distribution Direct power distribution measurement at full power >90
Reactivity balance,
Hot-zero-power to hot-full-power reactivity measurement >90
requirement to shutdown
a
Although the power distribution may not be directly measured at <5 % power, an indirect measurement such as
control rod worths provides the first indication that the power distribution is consistent with predictions. Such an indirect
measurement is not required to be performed prior to exceeding 5 % power but may be used to support an increase in power
from 30 % to 50 % by which the first direct power distribution needs to be measured. This indirect power distribution
measurement may have tighter test criteria than that for control rod worths.
b
See A.3.4.6 for a discussion of direct and indirect power distribution measurements.
6 Test method requirements
Established test methods for the confirmation of each characteristic required by this document are
described in the Appendix. Whether one of these methods or a different method is used, the user shall
verify that the following requirements are met:
a) The intent, content, purpose, and other requirements of the overall startup program as outlined in
this document are met.
b) The method unambiguously confirms one or more of the five physics characteristics described in 5.1.
c) The method has been validated by successful benchmarking.
d) The method has withstood independent peer review.
6.1 General test considerations
6.1.1 Test objective
The general objective of each test is to measure a reactor physics parameter.
6.1.2 Test purpose
The general purpose of each test is to determine if the measured reactor physics parameter is consistent
with the predicted value. Data from the test results may also be used to establish appropriate operating
limits or to determine compliance with appropriate Technical Specifications.
6.1.3 Initial conditions
In general, initial conditions are specified for each test such that an accurate measurement can be
performed at the same or nearly the same conditions assumed in the prediction. So, the test results or
predictions shall be adjusted to account for any difference between the specified conditions and those
that were present at the time of measurement. Except for unusual circumstances, each adjustment
due to different conditions shall have a negligible effect on the uncertainty in the measured-versus-
predicted comparison. All adjustments shall be documented.
6.1.4 Test methods
For each test, Annex A provides abstracts of acceptable methods for performing the test. Alternate
methods can be used as long as they are shown to be acceptable by meeting the requirements of this
clause. In general, the stated initial core conditions shall be achieved as closely as practical, and the
reactor physics parameter shall be measured accurately (i.e. consistent with the assumptions used to
establish the test criteria). To ensure that the measurement uncertainty is minimized, precautions are
provided in Annex A. During each test, the appropriate core conditions shall be recorded, and those
conditions shall be maintained within the specified range for the test.
6.1.5 Evaluation
In general, each test is considered to be successful if the difference between the prediction and the
measurement (or, for some tests, the physics parameter inferred from the measurement) is less than a
predetermined criterion. This difference shall be evaluated after appropriate adjustments have been
made to account for any differences between the specified core conditions and those that were present
at the time of measurement.
The predetermined criteria shall be developed with adequate allowance for uncertainties in both
the measurement and prediction. Typical criteria based on current technology and best practices are
provided in Annex A.
6.2 Test criteria
If the difference between the measured and predicted values for a physics parameter exceeds the
predetermined criterion, the measurements shall be reviewed, and if necessary, a thorough review of the
predictions shall be performed. If a measurement is repeated, either the same measurement technique
or an approved alternate technique shall be used. If these actions do not resolve the discrepancy, the
impact on plant safety shall be evaluated, and if necessary, appropriate operating restrictions shall be
established.
The test criteria are flexible since it is unknown what problems or deficiencies might be encountered
during testing and to what extent test conditions may vary from those assumed in developing the
test predictions and criteria. The test criteria shall, therefore, be applied along with common sense
and historical perspective (previous cycles, sister plants, etc.) to establish whether or not the reactor
core has satisfactorily passed the test program. The simple meeting or failing a test criterion does not
definitively establish whether or not a core is deficient in a given area. The results should be reviewed
6 © ISO 2018 – All rights reserved

not only as individual tests but also as related sets and in light of results from previous cycles and
results from similar cores. Most problems will cause deviations from expected results in more than one
parameter. By reviewing the results in a global sense, considerably more assurance can be given that
the reactor core is functioning as expected.
The physics test program results should be evaluated along with the results of other tests performed
during startup. The failure of one or more of the physics test results to meet the test criteria shall be
evaluated relative to the implications on plant safety. The results of this evaluation shall be employed
as a guide for continued plant operation.
7 Requirements of this document
Compliance with this document shall be demonstrated by meeting the following requirements:
a) Test program: Have ability to accurately confirm the required physics characteristics listed in
Table 1.
b) Test methods: Perform each test using a verified and validated procedure (examples are given in the
Appendix).
c) Test acceptance: Compare the results of each test to predetermined test criteria.
d) Test documentation: Document the results of the test program including, as a minimum, the
following items:
1) the test methods employed;
2) the measured parameters;
3) the predicted parameters and any corrections made to account for different core conditions;
4) the predetermined test criteria for test acceptance;
5) an evaluation of the test results based on a comparison between the measured and predicted
parameters, taking into account the uncertainties in both the measurements and predictions.
Annex A
(informative)
User’s guide
2)
NOTE This annex is not a set of requirements. This annex is not to be used as a detailed procedure for
performing each test.
A.1 Introduction
The purpose of this annex is to provide the users of this document a set of acceptable or target methods,
general guidelines, precautions, and suggestions for each test. Also included in this user’s guide are
values of test criteria based on industry experience at the time of its writing. Users should develop their
own test criteria based on expected differences between measurements and predictions. This user’s
guide should help the user formulate a startup physics test program that will meet the requirements
of the document. This user’s guide is not a set of requirements nor should it be used as a detailed
procedure for performing each test.
A.2 Acronyms
Following are definitions of acronyms used in this annex.
ARO all rods out
CBC critical boron concentration
DBW differential boron worth
DPM decades per minute
DRWM dynamic rod worth measurement
FP full power
HFP hot full power
HZP hot zero power
ITC isothermal temperature coefficient
M/D movable detector
pcm percent milli-rho
ppm parts per million by weight or grams of boron per tonne of water
psi pounds per square inch (1 psi = 6 895 Pa)
PWR pressurized water reactor
RCS reactor coolant system
2) This annex to the standard is the user's guide, which provides acceptable methods, guidelines, precautions,
suggestions, and typical test criteria for each required test.
8 © ISO 2018 – All rights reserved

rms root-mean-square (square root of the average squared difference)
RPD relative power density
VCT volume control tank (also known as letdown storage tank)
A.3 Typical criteria and bases
A.3.1 Overview of criteria
The use of criteria for evaluation of test results is a long-standing practice in industry. This method
allows for on-the-spot evaluation of the test results against the nuclear design predictions. The ideal
criterion to be used is tight enough such that no design anomaly would go unnoticed but loose enough
such that typical differences would not violate the criterion. Some of the factors that enter into the
determination of the criteria are the design model limitations, the measurement limitations, and
the compatibility between the design and measurement methods. The criteria are established by
differences between calculations and measurements that would suggest a problem with the as-built
core, the measurement, or the prediction. The criteria are not established by rigorous analysis of the
test methods or design models.
Another long-standing practice in the industry is the establishment of two level criteria for the
evaluation of the test results. These two criteria are often referred to as “Test (Review) Criteria”
and “Acceptance Criteria.” The differences in these two criteria are better defined in the following
descriptions.
A.3.2 Test (review) criteria
Test (review) criteria are based on differences between calculations and measurements as discussed
above and are not based on the safety analysis. Therefore, these criteria typically have two-sided
tolerances. These criteria are used to identify measurement or design errors. Failure of any one test
criterion does not necessarily warrant stopping the testing process or power ascension. ANSI/ANS-
[7]
19.6.1-2011 (R2016) states that it is prudent to address these test criteria as part of a continuing
evaluation of the design and measurement processes.
A.3.3 Acceptance criteria
Acceptance criteria are those criteria that have a direct link to the safety analysis or are defined by
Technical Specifications. These criteria are typically one sided and are constructed from safety analysis
or related assumptions. Failure of these criteria should not prevent further testing at the current power
plateau for supporting information. Failure of these criteria, however, should prevent power ascension
until the issue is resolved. Resolution of a failure is often performed under established procedures
(e.g. Technical Specification action statements). The established procedures will typically stipulate the
power ascension requirements.
For the purposes of this User’s Guide, all criteria referenced herein are test (review) criteria. It is outside
the scope of this User’s Guide to define or require acceptance criteria because the safety analysis basis
is plant specific. Typical test criteria for each test are shown in Table A.1. These values are guidelines
only and represent about twice the expected differences between measurements and predictions being
seen by the industry as of the writing of this User’s guide.
Table A.1 — Typical test criteria
Test parameters Test criteria
HZP critical boron ±50 ppm or ±500 pcm equivalent
a
Control rod worth ±15 % or ± 100 pcm, whichever is
greater (For rod swap, the
Individual group or user-specified group
reference group should be
within 10 %.)
a
Sum of groups or total integral of measured worths ±10 % (For DRWM, the total worth
should be within 8 %.)
ITC ±2 pcm/°F (3,6 pcm/°C)
Flux symmetry
b
±10 % (Meas versus Meas) depend-
Deviation between the highest and lowest values in the symmetric
ing on power level
locations
±0,10 RPD for each measured
c
Power distribution assembly power rms
(radial) <0,05
±50 ppm or ±500 pcm equivalent
HZP to HFP reactivity measurement
a
or ±10 %
a
For calculating percent differences use (Meas − Pred) × 100 /Pred, where Meas indicates the measured value and
Pred indicates the predicted value. Having percent difference defined with Pred (i.e. predicted) in the denominator is
consistent with comparisons of measured-versus-predicted data for safety-related purposes (e.g. total control rod worth
and peaking). This definition of percent difference simply recognizes that PWR reload cores are licensed with calculated
(predicted) data.
b
Percent difference is (Highest − Lowest) × 100/Avg, where Highest is the largest measured value in a particular
symmetric location, Lowest is the smallest measured value, and Avg is the average of all the measured values in the same
symmetric location (which could be 2, 4, or 8 values).
ΔRPD
N ()
i
c
The rms is defined as ∑ .
N
i=1
A.3.4 Bases
A.3.4.1 Bases for test criteria
The test criteria shown in this User’s Guide are indicative of industry experience at the time of this
writing. As industry experience changes, the criteria should change with it. Also, new technology, more
advanced fuel cycles, etc., may necessitate different criteria until industry experience is gained.
The test criteria are based on differences between calculations and measurements. The intent of each
test criterion is to provide a value that, if exceeded, suggests that something may be wrong. When a
test result falls outside of the test criteria, it means that there may be a problem with the as-built core,
the measurement itself, the test equipment, or the design calculations or that the conditions during the
measurement were significantly different from the conditions assumed for the prediction.
The test criteria are established assuming that known biases are accounted for in the predictions
before comparisons are made.
A.3.4.2 Bases for critical boron concentration measurement
The objective of this test is to confirm the reactivity balance. This test measures the overall reactivity of
the reactor and validates the accuracy of the predicted criticality calculations. This test is performed at
a nearly all rods out (ARO) configuration to minimize error from the use of control rod worth to correct
for any control rod insertion that may exist. This test provides a verification of the design models used
to perform reactivity balance calculations and to provide operators with estimated critical conditions.
This verification ensures that predicted shutdown boron concentrations provide the necessary margin
to criticality to meet operability requirements.
10 © ISO 2018 – All rights reserved

This test provides verification that soluble boron sources provide adequate negative reactivity as
modelled in the accident analyses.
A.3.4.3 Bases for control rod worth measurement
The objective of the control rod worth measurement is to confirm the capability to shut down and
control reactivity. It demonstrates that the reactivity worth of the safety and regulating control rods is
consistent with predictions. This test provides a level of assurance that the fuel and core components
are configured consistent with design assumptions. The total safety and regulating control rod worth
verifies adequate shutdown margin capability. Control rod group worths and shapes provide initial
indication of an acceptable power distribution. Also, the rod group shapes provide an indication of the
reactivity control characteristics of the core.
Since control rod worth cannot be inferred from other operating parameters, this test represents the
only opportunity to verify that the rod worths are consistent with those assumed in the shutdown
margin calculations and in the safety analyses for the core. This test is performed prior to power
ascension to maximize available design margin in case some problem with the rod worths exists.
Also, this test helps ensure the integrity of the rods and that the rods are latched. Several different
methods are available for the measurement of control rod worths. Each method has its own inherent
measurement process control issues that are to be addressed to obtain reliable results.
A.3.4.4 Bases for isothermal temperature coefficient measurement
The objective of the isothermal temperature coefficient (ITC) measurement is to confirm the reactivity
control characteristic. The test demonstrates that the reactivity response to temperature changes in
the reactor core is consistent with design predictions. This measurement is performed at a nearly ARO
condition, thus maximizing the boron concentration for the test and resulting in the most positive ITC
for comparison with beginning of core life moderator temperature coefficient (MTC) limits. Since the
MTC cannot be directly measured, the MTC is verified via measurement of the ITC, which includes both
moderator and Doppler coefficients. This measurement is performed at hot zero power (HZP) to ensure
that the ITC is consistent with design and operational expectations before power ascension.
A.3.4.5 Bases for flux symmetry measurement
The objective of this measurement is to confirm that the power distribution in the core is consistent with
design predictions at low power prior to escalating to higher power. The flux symmetry measurement
is applicable only to plants that choose to not perform a complete power distribution measurement at
low power (such as those with a fixed in-core detector system). While fixed in-core detector systems
can provide continuous power distribution indication during power ascension, the accuracy may not
be sufficient to perform a complete power distribution measurement below 30 % power. The flux
symmetry measurement may reveal core anomalies (e.g. dropped rods, detached rod fingers, fuel
misloadings, flow anomalies) prior to complete power distribution tests at higher power levels.
A.3.4.6 Bases for power distribution measurements
The objective of the power distribution measurements is to confirm that the power distribution is
consistent with design predictions at low, intermediate, and high power levels. The measurements
verify that the power distribution is within its design and licensing bases, and they may identify any
power distribution anomalies. These measurements provide comprehensive assurance that the fuel
and core components are configured consistent with design assumptions.
The power distribution is confirmed by measurement at various power conditions during power
ascension. Confirmation may be direct (e.g. in-core detectors) or indirect (e.g. all bank worths). The
level of confidence in the power distribution results is minimal with the bank worth results, good
with the flux symmetry results, and best with a direct power distribution measurement using in-
core detectors. A direct power distribution measurement is necessary before exceeding 50 % of full
power (FP) to provide a high level of confidence that unforeseen power distribution anomalies will not
result in violations of design assumptions. All of the power distribution measurement results are to be
assessed collectively to ensure that local and global core characteristic trends are evaluated during
power ascension.
Startup power distribution measurements using in-core detectors should be taken using as many
detector locations that cover as much of the core as practical. Thus, any core configuration anomaly
(e.g. misloaded fuel assembly or dropped rod) will have a higher chance of being detected.
A.3.4.7 Bases for HZP to HFP reactivity measurement
The objective of the HZP to hot full power (HFP) reactivity measurement is to confirm the requirement
to shutdown. The test demonstrates that the reactivity deficit resulting from the increase in reactor
power from zero to near FP (>90 %) is consistent with design predictions. While this test incorporates
a number of reactivity effects (xenon, moderator temperature, fuel temperature, soluble boron
worth), it is the only measurement that provides verification of the calculated total power defect.
This measurement is performed to ensure the power deficit is consistent with design predictions and
operability requirements for shutdown margin.
Measurement of the power deficit verifies the reactivity requirements of the safety and regulating
control rod system to ensure adequate shutdown margin is maintained.
A.4 Acceptable test methods
The following sections provide, for each test, acceptable methods for performing the test. Alternate
methods may be used as long as they are shown to meet the requirements of Sec. Six of this document.
In addition, there is a set of guidelines, precautions, and suggestions that will help the user perform
the test and evaluate the results. Typical values for rates of change and stability requirements are also
included.
A.4.1 Critical boron concentration
A.4.1.1 Test objective
To measure the HZP critical boron concentration (CBC) with all rods fully withdrawn (part-length rods
may be inserted).
A.4.1.2 Purpose
To determine if the measured and predicted total core reactivities are consistent.
A.4.1.3 Initial conditions
The reactor core is at HZP with all full-length rods withdrawn except that the lead regulating rod group
may be inserted (but not more than 200 pcm or 20 % of the worth of the lead group). Specific guidelines
are as follows:
a) Power: HZP;
b) Reactor coolant system (RCS) temperature: within 2 °F (1 °C) of the reference temperature;
c) RCS pressure: within 50 psi (0,345 MPa) of the reference pressure;
d) Rod groups: ARO except the lead regulating rod group may be inserted in the core but not more
than 200 pcm or 20 % of the total worth.
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A.4.1.4 Test method
Measure the CBC and record the appropriate reactor conditions. Adjust the measured value for
differences between th
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