ASTM E2956-21

Standard Guide for Monitoring the Neutron Exposure of LWR Reactor Pressure Vessels

SIGNIFICANCE AND USE
4.1 Regulatory Requirements—The USA Code of Federal Regulations (10CFR Part 50, Appendix H) requires the implementation of a reactor vessel materials surveillance program for all operating LWRs. Other countries have similar regulations. The purpose of the program is to (1) monitor changes in the fracture toughness properties of ferritic materials in the reactor vessel beltline6 resulting from exposure to neutron irradiation and the thermal environment, and (2) make use of the data obtained from surveillance programs to determine the conditions under which the vessel can be operated with adequate margins of safety throughout its service life. Practice E185, derived mechanical property data, and (r, θ, z) physics-dosimetry data (derived from the calculations and reactor cavity and surveillance capsule measurements (1) using physics-dosimetry standards) can be used together with information in Guide E900 and Refs. 4, 11-18 to provide a relation between property degradation and neutron exposure, commonly called a “trend curve.” To obtain this trend curve at all points in the pressure vessel wall requires that the selected trend curve be used together with the appropriate (r, θ, z) neutron field information derived by use of this guide to accomplish the necessary interpolations and extrapolations in space and time.  
4.2 Neutron Field Characterization—The tasks required to satisfy the second part of the objective of 4.1 are complex and are summarized in Practice E853. In doing this, it is necessary to describe the neutron field at selected (r, θ, z) points within the pressure vessel wall. The description can be either time dependent or time averaged over the reactor service period of interest. This description can best be obtained by combining neutron transport calculations with plant measurements such as reactor cavity (ex-vessel) and surveillance capsule or RPV cladding (in-vessel) measurements, benchmark irradiations of dosimeter sensor materials, and knowledge of th...
SCOPE
1.1 This guide establishes the means and frequency of monitoring the neutron exposure of the LWR reactor pressure vessel throughout its operating life.  
1.2 The physics-dosimetry relationships determined from this guide may be used to estimate reactor pressure vessel damage through the application of Practice E693 and Guide E900, using fast neutron fluence (E > 1.0 MeV and E > 0.1 MeV), displacements per atom – dpa, or damage-function-correlated exposure parameters as independent exposure variables. Supporting the application of these standards are the E853, E944, E1005, and E1018 standards, identified in 2.1.  
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.  
1.4 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

General Information

• Status: Historical
• Publication Date: 31-Jan-2021
• ICS: 27.120.10 - Reactor engineering
• Technical Committee: E10 - Nuclear Technology and Applications
• Drafting Committee: E10.05 - Nuclear Radiation Metrology

Standards Content (Sample)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation: E2956 − 21
Standard Guide for
Monitoring the Neutron Exposure of LWR Reactor Pressure
1
Vessels
This standard is issued under the fixed designation E2956; 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 (´) indicates an editorial change since the last revision or reapproval.
INTRODUCTION
Light Water Reactor (LWR) power plant safety analysis reports and subsequent neutron exposure
parameter calculations for the reactor pressure vessel (RPV) wall and critical welds need to be verified
using modern codes and information from surveillance dosimetry. The location of critical welds
relative to the axial and azimuthal fluence rate map should be taken into account, as well as changes
in fuel loading during periods when surveillance capsules are exposed and beyond to the end of the
reactor’s operating license. For many reactors today this is a 60-year-long interval. In the nuclear
industry, there is active consideration and evaluation of an 80-year-long operating interval. Most
reactor surveillance programs were designed based on the guidance of Practice E185 with a 40-year
operating life in mind. The Practice E185 surveillance programs are designed to select and irradiate
the RPV material test specimens. The dosimetry in the surveillance capsule is there primarily to
measure the neutron fluence to which the capsule’s material specimens have been exposed.
In addition, those programs were based on the operating assumptions in place at the time; typically
annual out-in core loading patterns and base load operation at a fixed reactor power level. Reactor
3
operations have evolved so that low-leakage core loading patterns (L P) are the norm as are 18- and
24-month-long fuel cycles and reactor power up-ratings of up to 20 %. Many reactors have now
installed flux suppression features such as natural uranium fuel rods, full or part-length hafnium or
B C rods, or stainless steel rods to minimize the neutron exposure of critical areas of the RPV. Such
4
developments increase the need to comprehensively monitor the RPV accrued fluence through the
extended operation period.
This guide is intended to be used together with other Standards to provide best estimates of the
neutron exposure and exposure rate (together with uncertainties) at positions at the inner diameter and
within the pressure vessel wall of a light water reactor. Also provided will be estimates of gamma-ray
exposure and exposure rates to interpret dosimetry sensor photo-reaction and other gamma-ray
induced effects. Information used to make these estimates is obtained from coupled neutron-gamma
ray transport calculations and from neutron and gamma-ray sensors located in surveillance positions
2
on the core side of the vessel and in the reactor cavity outside the vessel wall (1). Benchmark field
irradiations of similar monitors also provide valuable information used in the verification of the
accuracy of the calculations (1).
Knowledge of the time-dependent relationship between exposure parameters at surveillance
locations and selected (r, θ, z) locations within the pressure vessel wall is required to allow
determination of the time-dependent radiation damage to the RPV. The time dependency must be
known to allow proper accounting for complications due to burn-up, as well as changes in core loading
configurations (2-5). An estimate of the uncertainty in the neutron exposure parameter values at
selected (r, θ, z) points in the vessel wall (1) is also needed to place an upper bound on the allowable
operating lifetime of the reactor vessel without remedial action (6-9). (See Guide E509.)
1. Scope
1.1 This guide establishes the means and frequency of
2
monitoring the neutron exposure of the LWR reactor pressure
The boldface numbers in parentheses refer to the list of references appended to
this guide. vessel throughout its operating life.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
1

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E2956 − 21
1.2 The physics-dosimetry relationships determined from E2215 Practice for Evaluation of Surveillance Capsules
this guide may be used to estimate reactor pressure vessel from Light-Water Moderated Nuclear Power Reactor Ves-
damage through the application of Practice E693 and Guide sels
E900, using fast neutron fluence (E > 1.0 MeV and E > 0.1
2.2 American Society of Mechanical Engineers Standard:
4
MeV), displacements per atom – dpa, or damage-function-
Boiler and Pressure Vessel Code, Sections III and XI
correlated exposure parameters as independent exposure vari-
2.3 Nuclear Regulatory Document:
a
...

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: E2956 − 14 E2956 − 21
Standard Guide for
Monitoring the Neutron Exposure of LWR Reactor Pressure
1
Vessels
This standard is issued under the fixed designation E2956; 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 (´) indicates an editorial change since the last revision or reapproval.
INTRODUCTION
Light Water Reactor (LWR) power plant safety analysis reports and subsequent neutron exposure
parameter calculations for the reactor pressure vessel (RPV) wall and critical welds need to be verified
using modern codes and information from surveillance dosimetry. The location of critical welds
relative to the axial and azimuthal fluence rate map should be taken into account, as well as changes
in fuel loading during periods when surveillance capsules are exposed and beyond to the end of the
reactor’s operating license. For many reactors today this is a 60-year-long interval. In the nuclear
industry, there is active consideration and evaluation of an 80-year-long operating interval. Most
reactor surveillance programs were designed based on the guidance of Practice E185 with a 40-year
operating life in mind. The Practice E185 surveillance programs are designed to select and irradiate
the RPV material test specimens. The dosimetry in the surveillance capsule is there primarily to
measure the neutron fluence to which the capsule’s material specimens have been exposed.
In addition, those programs were based on the operating assumptions in place at the time; typically
annual out-in core loading patterns and base load operation at a fixed reactor power level. Reactor
3
operations have evolved so that low-leakage core loading patterns (L P) are the norm as are 18- and
24-month-long fuel cycles and reactor power up-ratings of up to 20 %. Many reactors have now
installed flux suppression features such as natural uranium fuel rods, full or part-length hafnium or
B C rods, or stainless steel rods to minimize the neutron exposure of critical areas of the RPV. Such
4
developments increase the need to comprehensively monitor the RPV accrued fluence through the
extended operation period.
This guide is intended to be used together with other Standards to provide best estimates of the
neutron exposure and exposure rate (together with uncertainties) at positions at the inner diameter and
within the pressure vessel wall of a light water reactor. Also provided will be estimates of gamma-ray
exposure and exposure rates to interpret dosimetry sensor photo-reaction and other gamma-ray
induced effects. Information used to make these estimates is obtained from coupled neutron-gamma
ray transport calculations and from neutron and gamma-ray sensors located in surveillance positions
2
on the core side of the vessel and in the reactor cavity outside the vessel wall (1). Benchmark field
irradiations of similar monitors also provide valuable information used in the verification of the
accuracy of the calculations (1).
Knowledge of the time-dependent relationship between exposure parameters at surveillance
locations and selected (r, θ, z) locations within the pressure vessel wall is required to allow
determination of the time-dependent radiation damage to the RPV. The time dependency must be
known to allow proper accounting for complications due to burn-up, as well as changes in core loading
configurations (2-5). An estimate of the uncertainty in the neutron exposure parameter values at
1
This guide is under the jurisdiction of ASTM Committee E10 on Nuclear Technology and Applications and is the direct responsibility of Subcommittee E10.05 on Nuclear
Radiation Metrology.
Current edition approved Feb. 1, 2014Feb. 1, 2021. Published March 2014March 2021. DOI: 10.1520/E2956-14.Originally approved in 2014. Last previous edition
approved in 2014 as E2956-14. DOI: 10.1520/E2956-21.
2
The boldface numbers in parentheses refer to the list of references appended to this guide.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
1

---------------------- Page: 1 ----------------------
E2956 − 21
selected (r, θ, z) points in the vessel wall (1) is also needed to place an upper bound on the allowable
operating lifetime of the reactor vessel without remedial action (6-9). (See Guide E509.)
1. Scope
1.1 This guide establishes the means and frequency of monitoring the neutron expo
...