IEC/IEEE 63113:2021

IEC/IEEE 63113 ®
Edition 1.0 2021-04
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Nuclear facilities – Instrumentation important to safety – Spent fuel pool
instrumentation
Installations nucléaires – Instrumentation importante pour la sûreté –
Instrumentation des piscines de refroidissement et de stockage du combustible

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IEC/IEEE 63113 ®
Edition 1.0 2021-04
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Nuclear facilities – Instrumentation important to safety – Spent fuel pool

instrumentation
Installations nucléaires – Instrumentation importante pour la sûreté –

Instrumentation des piscines de refroidissement et de stockage du combustible

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 27.120.20 ISBN 978-2-8322-9624-0

– 2 – IEC/IEEE 63113:2021 © IEC/IEEE 2021
CONTENTS
FOREWORD . 4
INTRODUCTION . 6
1 Scope . 9
1.1 General . 9
1.2 Purpose . 9
1.3 Application . 9
2 Normative references . 9
3 Terms and definitions . 10
4 Symbols and abbreviated terms . 12
5 Functional requirements . 12
6 Performance criteria . 14
6.1 Range . 14
6.2 Accuracy . 15
6.2.1 General . 15
6.2.2 Additional criteria for DEC spent fuel pool monitoring instrumentation . 15
6.3 Response time . 15
6.4 Required accident operating time . 15
6.5 Reliability . 15
6.6 Documentation of performance criteria . 15
6.6.1 General . 15
6.6.2 Additional criteria for DEC spent fuel pool monitoring instrumentation . 15
7 Design criteria . 16
7.1 Redundancy . 16
7.2 Common cause failure . 16
7.3 Physical independence and separation . 16
7.4 Electrical isolation . 17
7.5 Information ambiguity . 17
7.6 Power supply . 17
7.6.1 General . 17
7.6.2 Additional criteria for DEC spent fuel pool monitoring instrumentation . 18
7.7 Calibration . 18
7.7.1 General . 18
7.7.2 Additional criteria for DEC spent fuel pool monitoring instrumentation . 18
7.8 Testability . 18
7.8.1 General . 18
7.8.2 Additional criteria for DEC spent fuel pool monitoring instrumentation . 18
7.9 Direct measurement . 18
7.10 Control of access . 19
7.11 Maintenance and repair . 19
7.12 Supporting features . 19
8 Qualification criteria . 19
8.1 General . 19
8.2 Seismic qualification . 19
8.3 Environmental qualification . 19
8.4 Shock and vibration qualification . 20
9 Display criteria . 20

9.1 Human factors . 20
9.2 Trend or rate information . 20
9.3 Continuous versus on-demand displays . 20
9.3.1 General . 20
9.3.2 Additional criteria for DEC spent fuel pool monitoring instrumentation . 20
9.4 Display identification . 20
9.5 Display location . 20
9.5.1 General . 20
9.5.2 Additional criteria for DEC spent fuel pool monitoring instrumentation . 21
10 Quality assurance . 21
Annex A (informative)  Typical bases for identifying spent fuel pool conditions to be
detected. 22
Bibliography . 25

Figure A.1 – Spent fuel pool monitoring instrumentation . 22

Table 1 – Relationship of functional groups used in this document . 14

– 4 – IEC/IEEE 63113:2021 © IEC/IEEE 2021
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
NUCLEAR FACILITIES –
INSTRUMENTATION IMPORTANT TO SAFETY –
SPENT FUEL POOL INSTRUMENTATION

FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
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International Standard IEC/IEEE 63113 has been prepared by subcommittee 45A:
Instrumentation, control and electrical power systems of nuclear facilities, of IEC technical
committee 45: Nuclear instrumentation, in cooperation with Nuclear Power Engineering
Committee of the IEEE, under the IEC/IEEE Dual Logo Agreement.
The text of this standard is based on the following IEC documents:
FDIS Report on voting
45A/1373/FDIS 45A/1382/RVD
Full information on the voting for the approval of this standard can be found in the report on
voting indicated in the above table.
International standards are drafted in accordance with the rules given in the International
Organization for Standardization (ISO) / IEC Directives, Part 2.
The IEC Technical Committee and IEEE Technical Committee have decided that the contents
of this publication will remain unchanged until the stability date indicated on the IEC web site
under "http://webstore.iec.ch" in the data related to the specific publication. At this date, the
publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
IMPORTANT – The 'colour inside' logo on the cover page of this publication indicates
that it contains colours which are considered to be useful for the correct understanding
of its contents. Users should therefore print this document using a colour printer.

– 6 – IEC/IEEE 63113:2021 © IEC/IEEE 2021
INTRODUCTION
a) Technical background, main issues and organization of the Standard
This IEC/IEEE standard sets out the requirements for instrumentation to monitor spent fuel pool
water level and temperature in nuclear facilities as well as radiation monitoring in the vicinity of
the pool.
Prior to the accident at Fukushima Daiichi, spent fuel pool monitoring in nuclear power plants
was provided mainly to enable operators to monitor pool temperature at a location near the top
of the pool. It was also used to determine that the water level remained below the point where
flooding of operational areas would be a concern and above the level assumed in safety
analyses that evaluated the release of fission products from the pool in the event of a fuel
handling accident.
In general, robust spent fuel pools protect the fuel from physical damage and use highly reliable
coolant systems that ensure continuous decay heat removal. Monitoring of the pool cooling
system and drain taps at the bottom of the pool were considered sufficient to confirm pool
cooling under operational states and design basis accidents. Because these are straightforward
measurements, neither IEC SC 45A nor IEEE NPEC considered that a standard on this topic
was necessary.
During the accident at Fukushima Daiichi, explosions occurred in the reactor buildings of units
1, 3, and 4. Hydrogen release from fuel in the spent fuel pool, due to loss of water inventory,
had to be considered as a possible cause of the explosions. Instrumentation suitable for
checking this hypothesis was not installed and operators could not directly check pool
conditions because of radiation dose rates and other hazards in the reactor buildings.
Consequently, plant operators had to take action on the assumption that the spent fuel was no
longer fully covered by water.
Eventually, it was confirmed that the many extraordinary actions taken by site personnel
succeeded in averting a greater release of radioactive material from the spent fuel pools.
Nevertheless, the lack of real time information about pool conditions created significant
difficulties in responding to the accidents, increased public anxiety, and diverted resources
away from activities to restore core cooling.
Subsequent analysis, however, determined that if the water in the reactor well and dryer-
separator pits in Unit 4 had not leaked into the spent fuel pool as water in the pool evaporated,
the spent fuel in Unit 4 may have become uncovered. [6], [8]
This experience points to a need to provide plant operators with instrumentation to enable them
to understand the state of spent fuel cooling under design extension conditions (DEC). To
support the design of such instrumentation, the expected pool conditions must be defined and
the instruments should be designed considering any special characteristics needed to ensure
their high reliability and operability in the presence of hazards that might exist during design
extension conditions.
It is also necessary to monitor spent fuel pools during normal operations in order to: detect a
potential loss of heat removal from the pool, detect high pool levels that risk pool overflow,
confirm the pool contains sufficient water to shield operators from the radiation from fission
products contained in the spent fuel, and ensure safety analysis assumptions are met
concerning pool water hold-up of fission products in the event of a fuel handling accident.
___________
Numbers in square brackets refer to the Bibliography.

To address the specific lessons learned from the Fukushima Daiichi accident and to give an
overall view of the requirements for spent fuel pool monitoring, this document establishes
criteria for the performance, design, qualification, display, and quality assurance of instruments
for monitoring spent fuel pool conditions during both operational states and accident conditions
(including design extension conditions) at nuclear facilities.
b) Situation of the current Standard in the structure of the IEC SC 45A standard series
IEC 63113 is at the third level in the hierarchy of SC 45A standards.
IEC 61513 is the first level standard of SC 45A standards, and provides general requirements
for I&C systems and equipment that are used to perform functions important to safety in Nuclear
Power Plants (NPPs). IEC/IEEE 60780-323 provides the standard for environmental
qualification. IEC 62003 provides the requirements for electromagnetic compatibility testing.
IEC 63147/IEEE Std 497™ provides criteria for accident monitoring instrumentation. IEEE Std
497™ was directly adopted as a joint logo standard and a technical report, IEC TR 63123, was
prepared to discuss the application of the joint standard within the IEC context.
The structure of this standard is adapted from the structure of IEC 63147/IEEE Std 497™, and
the technical requirements of this standard are consistent with the requirements given in
IEC 63147/IEEE Std 497™ together with the application guidance given in IEC TR 63123. This
standard deals with instrumentation intended to help plant operators avoid severe accidents in
spent fuel pools. The introduction to IEEE Std 497™ notes that design extension conditions that
are not severe accidents are not covered by that standard. For more details on the structure of
the IEC SC 45A standard series, see item d) of this introduction.
c) Recommendations and limitations regarding the application of the Standard
It is important to note that this standard establishes no additional functional requirements for
safety systems.
This standard is directed at facilities in which loss of spent fuel pool inventory makes possible
a significant fission product release to the environment. Thus, the standard applies only to spent
fuel pools at which the water fill is necessary to prevent a release of fission products that
exceeds allowed operational limits.
d) Description of the structure of the IEC SC 45A standard series and relationships with
other IEC documents and other bodies’ documents (e.g., IAEA, ISO)
The top-level documents of the IEC SC 45A standard series are IEC 61513 and IEC 63046.
IEC 61513 provides general requirements for I&C systems and equipment that are used to
perform functions important to safety in NPPs. IEC 63046 covers power supply systems
including the supply systems of the I&C systems. IEC 61513 and IEC 63046 are to be
considered in conjunction and at the same level. IEC 61513 and IEC 63046 structure the IEC
SC 45A standard series and shape a complete framework establishing general requirements
for instrumentation, control and electrical systems for nuclear power plants.
IEC 61513 and IEC 63046 refer directly to other IEC SC 45A standards for general topics
related to categorization of functions and classification of systems, qualification, separation,
defence against common cause failure, control room design, electromagnetic compatibility,
cybersecurity, software and hardware aspects for programmable digital systems, coordination
of safety and security requirements and management of aging. The standards referenced
directly at this second level should be considered together with IEC 61513 and IEC 63046 as a
consistent document set.
– 8 – IEC/IEEE 63113:2021 © IEC/IEEE 2021
At a third level, IEC SC 45A standards not directly referenced by IEC 61513 or by IEC 63046
are standards related to specific equipment, technical methods, or specific activities. Usually
these documents, which make reference to second-level documents for general topics, can be
used on their own.
A fourth level extending the IEC SC 45 standard series, corresponds to the Technical Reports,
which are not normative.
The IEC SC 45A standards series consistently implements and details the safety and security
principles and basic aspects provided in the relevant IAEA safety standards and in the relevant
documents of the IAEA nuclear security series (NSS). In particular this includes the IAEA
requirements SSR-2/1, establishing safety requirements related to the design of NPPs, the
IAEA safety guide SSG-30 dealing with the safety classification of structures, systems and
components in NPPs, the IAEA safety guide SSG-39 dealing with the design of instrumentation
and control systems for NPPs, the IAEA safety guide SSG-34 dealing with the design of
electrical power systems for NPPs and the implementing guide NSS17 for computer security at
nuclear facilities. The safety and security terminology and definitions used by SC 45A standards
are consistent with those used by the IAEA.
IEC 61513 and IEC 63046 have adopted a presentation format similar to the basic safety
publication IEC 61508 with an overall life-cycle framework and a system life-cycle framework.
Regarding nuclear safety, IEC 61513 and IEC 63046 provide the interpretation of the general
requirements of IEC 61508-1, IEC 61508-2 and IEC 61508-4, for the nuclear application sector.
In this framework IEC 60880, IEC 62138 and IEC 62566 correspond to IEC 61508-3 for the
nuclear application sector. IEC 61513 and IEC 63046 refer to ISO as well as to IAEA GS-R part
2 and IAEA GS-G-3.1 and IAEA GS-G-3.5 for topics related to quality assurance (QA).
At level 2, regarding nuclear security, IEC 62645 is the entry document for the IEC/SC 45A
security standards. It builds upon the valid high level principles and main concepts of the
generic security standards, in particular ISO/IEC 27001 and ISO/IEC 27002; it adapts them and
completes them to fit the nuclear context and coordinates with the IEC 62443 series. At level
2, IEC 60964 is the entry document for the IEC/SC 45A control rooms standards and IEC 62342
is the entry document for the aging management standards.
NOTE It is assumed that for the design of I&C systems in NPPs that implement conventional safety functions (e.g.
to address worker safety, asset protection, chemical hazards, process energy hazards) international or national
standards would be applied.
NUCLEAR FACILITIES –
INSTRUMENTATION IMPORTANT TO SAFETY –
SPENT FUEL POOL INSTRUMENTATION

1 Scope
1.1 General
This document provides criteria for spent fuel pool instrumentation for nuclear power generating
stations and other nuclear facilities. The document applies to water filled spent fuel pools where
the water volume is necessary to prevent a release of fission products that exceeds allowed
operational limits.
1.2 Purpose
The purpose of this document is to establish design, performance, qualification, and display
criteria for spent fuel pool instrumentation for normal operation, anticipated operational
occurrences, design basis events, and design extension conditions (including severe accident
conditions).
1.3 Application
This document applies only to instrumentation for monitoring the condition of the spent fuel
pool, i.e., pool level, pool temperature, and area radiation. It does not apply to control systems
that are related to the spent fuel pool such as: the pool cooling systems, isolation valve control,
crane instrumentation and control, or refuelling machine instrumentation and control.
In some plant designs some of the instruments covered by this document also provide inputs
to protection system functions. Such instruments must also comply with requirements for
protection systems that are given elsewhere.
The requirements applied to the systems and components performing these functions depend
on how they contribute to the safety of the spent fuel pool.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies.
For undated references, the latest edition of the referenced document (including any
amendments) applies.
IEC 60709:2018, Nuclear power plants – Instrumentation, control and electrical power systems
important to safety – Separation
IEC/IEEE 60780-323, Nuclear power plants – Electrical equipment important to safety –
Qualification
IEC/IEEE 60980-344, Nuclear facilities – Equipment important to safety – Seismic qualification
IEC 61226, Nuclear power plants – Instrumentation and control important to safety –
Classification of instrumentation and control functions
NOTE 1 The use of IEC 61226 should take account of the discussion given in IEC TR 63123 [19].

– 10 – IEC/IEEE 63113:2021 © IEC/IEEE 2021
IEC 61513, Nuclear power plants – Instrumentation and control important to safety – General
requirements for systems
IEC 63046, Nuclear power plants – Electrical power system – General requirements
IEEE 384™, 2018, IEEE Standard Criteria for Independence of Class 1E Equipment and Circuits
NOTE 2 This document can be used with either IEEE and/or IEC normative references, but one coherent and
consistent set of references shall be defined at the beginning of the project and used as a whole as the basis for the
design and for all the project.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO, IEC and IEEE maintain terminological databases for use in standardization at the following
addresses:
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp
• IEEE Standards Dictionary Online: available at http://dictionary.ieee.org
3.1
accident conditions
deviations from normal operation that are less frequent and more severe than anticipated
operational occurrences
[SOURCE: IAEA Safety Glossary, 2018 Edition]
3.2
anticipated operational occurrence
deviation of an operational process from normal operation that is expected to occur at least
once during the operating lifetime of a facility but which, in the view of appropriate design
provisions, does not cause any significant damage to items important to safety or lead to
accident conditions
[SOURCE: IAEA Safety Glossary, 2018 Edition]
3.3
common cause failure
failures of two or more structures, systems or components due to a single event or cause
Note 1 to entry: Common causes may be internal or external to an instrumentation and control (I&C) system.
Note 2 to entry: The IEC definition differs from the IAEA in that the term "specific" was deleted because this
additional word is not necessary to understand the definition.
[SOURCE: IAEA Safety Glossary, 2018 Edition, modified: see Note 2 to entry.]
3.4
design basis accident
postulated accident leading to accident conditions for which a facility is designed in accordance
with established design criteria and conservative methodology, and for which releases of
radioactive material are kept within acceptable limits
[SOURCE: IAEA Safety Glossary, 2018 Edition]

3.5
design extension conditions
postulated accident conditions that are not considered for design basis accidents, but that are
considered in the design process of the facility in accordance with best estimate methodology,
and for which releases of radioactive material are kept within acceptable limits
[SOURCE: IAEA Safety Glossary, 2018 Edition]
3.6
monitoring channel
arrangement of components, from sensors to displays, as required to generate a signal from a
plant condition and present the signal to the end user
3.7
operational states
states defined under normal operation and anticipated operational occurrences
Note 1 to entry: Some States and organizations use the term operating conditions (in contrast with accident
conditions) for this concept.
[SOURCE: IAEA Safety Glossary, 2018 Edition]
3.8
periodic testing
performance of tests at predetermined time points to demonstrate that the functional capabilities
of the I&C systems and equipment important to safety are retained and that the characteristics
relevant to the claims of safety analysis are satisfied
[SOURCE: IEC 60671:2007, 3.7]
3.9
pond sludge
undesired debris material that originates from the storage of items in the spent fuel pool
3.10
redundancy
provision of alternative (identical or diverse) structures, systems and components, so that any
single structure, system or component can perform the required function regardless of the state
of operation or failure of any other
[SOURCE: IAEA Safety Glossary, 2018 Edition]
3.11
response time
period of time necessary for a component to achieve a specified output state from the time that
it receives a signal requiring it to assume that output state
[SOURCE: IAEA Safety Glossary, 2018 Edition]
3.12
severe accident
subset of design extension conditions during which fuel damage has occurred
[SOURCE: IEC 63147 / IEEE Std 497™, 3]

– 12 – IEC/IEEE 63113:2021 © IEC/IEEE 2021
3.13
supporting features
systems or components that provide services (such as cooling, lubrication and energy supply)
required for the systems to accomplish their intended functions
Note 1 to entry: Some countries use the term "auxiliary features".
4 Symbols and abbreviated terms
AOO Anticipated Operating Occurrence
CANDU Canada Deuterium Uranium (Reactor)
CCF Common Cause Failure
DBA Design Basis Accident
DEC Design Extension Conditions
SFP Spent Fuel Pool
5 Functional requirements
Spent fuel pools within the scope of this document shall be provided with monitoring
instrumentation that enables the plant staff to recognize the following conditions.
a) Thermodynamic conditions in the pool. Pool thermodynamic conditions may be determined
by measurement of pool temperature. Higher than normal temperatures may indicate an
abnormally high rate of pool water evaporation. Normal temperatures in combination with
unexpected loss of inventory may indicate that the pool is leaking.
b) Maximum water level. Pool inventory has approached the point where there is a risk of water
overflowing the top of the pool.
c) Minimum water level for moving fuel. Pool inventory less than this level would be insufficient
to comply with accident analysis assumptions of iodine decontamination factors following a
fuel handling accident.
d) Minimum active cooling water level. Pool inventory has approached the point where there
is a risk that operation of the normal fuel pool cooling system cannot be supported.
e) Minimum shielding water level. Pool inventory has approached the point where the coolant
cannot provide substantial shielding for a person standing on the spent fuel pool operating
deck.
f) Top of fuel water level. Pool inventory has reached the point where the fuel remains covered
but actions to implement make-up water addition should no longer be deferred.
g) Air dose rate above the pool. Gamma radiation dose rates in the pool building are at a level
that indicates that significant loss of shielding has occurred.
Functional requirements for conditions a), d), e), f) and g) are intended to monitor design
extension conditions that do not involve fuel damage. There is reason to believe that information
about those conditions will enable the operators to restore pool cooling before fuel in the pool
is damaged. Nevertheless, provisions should also be made to enable the plant staff to
recognize the following severe accident conditions:
h) Fuel damage water level. Pool inventory has approached the point where fuel damage is
expected.
___________
Extending the range of fuel pool water level measurement is necessary only if specific injection modes are needed
under the fuel rack level to ensure fuel integrity or to maintain fuel pool tightness in at least one accident scenario
(DEC included). Detection of these conditions becomes more important if robust means to provide makeup water
to the spent fuel pool have not been separately implemented. For example: portable pumps that are not dependent
upon plant power sources for makeup to the SFP and primary and alternative delivery points for makeup water.

i) Bottom of fuel water level. Pool inventory has reached the point where air cooling is the
dominant cooling mechanism for the fuel.
When functions to detect conditions h) or i) are implemented they shall comply with the
requirements given in this document.
In this document the term "spent fuel pool monitoring instrumentation" refers to any monitoring
instrumentation that is specifically intended to detect one or more of the conditions listed above.
Annex A provides further discussion of conditions a) through i) above and the spent fuel pool
monitoring instrumentation functions intended to detect these conditions. It also gives a diagram
showing an example of how the measurements might physically relate to each other and the
spent fuel pool itself.
The specific values corresponding to the above conditions shall be determined based upon
plant-specific design information. Instruments that are intended to detect conditions a), d), e)
and f) shall accurately indicate the water level when the water is both below and above its
saturation temperature.
Instruments that are intended to detect conditions a), b), and c) are meant for use in plant
operational states.
Instruments that are intended to detect conditions a), d), e), f), and g) are meant for use during
accident conditions to alert operators to situations that may jeopardize the cooling of spent fuel
under DEC.
Instruments that are intended to detect conditions g), h), and i) are meant for use during severe
accident conditions to alert the operators to situations that may immediately result in or have
already resulted in fuel damage.
A spent fuel pool that contains two or more sections that are connected by normally open gates
may be treated as a single spent fuel pool. If the isolable sections of the pool are not used for
long-term storage of significant quantities of fuel (as defined by local regulations), sensors for
level and temperature monitoring channels shall be located in the main pool. Administrative
provisions shall be put into place to ensure that these instruments are operable before pools
are isolated from each other.
If, however, the multiple pool sections are normally isolated and used for long-term storage of
significant fuel quantities, each section shall be treated as an individual spent fuel pool.
Criteria for spent fuel pool monitoring instrumentation apply to all instruments that are intended
to detect conditions a) through i). Additional criteria are given for DEC spent fuel pool monitoring
instrumentation, and these apply only to instruments that are intended to detect conditions a)
and d) through i).
The terms used for the different functions and functional groups intended to detect the
conditions identified above and their relationship to plant states are shown in Table 1.

– 14 – IEC/IEEE 63113:2021 © IEC/IEEE 2021
Table 1 – Relationship of functional groups used in this document
Operational states Accident conditions
Plant state Normal Anticipated Design basis Design extension conditions (DEC)
operation operational accidents
DEC without significant Severe
occurrence (DBA)
fuel degradation accidents
(AOO)
Conditions a), b) and c) see Note 1 a), d), e), f) and g) g), h) and i)
Terms used for Spent fuel pool monitoring instrumentation
functional groups
DEC spent fuel pool monitoring
(see Note 2)
instrumentation
NOTE 1 Typically, there are no DBAs
associated with pool water level,
temperature and radiation dose rates;
therefore, this document does not specify
spent fuel pool monitoring instrumentation
for DBAs.
NOTE 2 One or more monitoring
channels make up a functional group of
monitoring instrumentation.
Some fa
...