ISO 10645:2022

INTERNATIONAL ISO
STANDARD 10645
Second edition
2022-04
Nuclear energy — Light water reactors
— Decay heat power in non-recycled
nuclear fuels
Énergie nucléaire — Réacteurs à eau légère — Puissance résiduelle
des combustibles nucléaires non recyclés
Reference number
© ISO 2022
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols and subscripts . 2
4.1 Symbols . 2
4.2 Subscripts . . 3
5 Calculation of decay heat power .3
5.1 General . 3
5.2 Power histogram . 3
5.3 Contribution of fission products . 4
5.4 Contribution of actinides . 6
239 239
5.4.1 Contribution of U and Np . 6
5.4.2 Contribution of other actinides . 7
5.5 Contribution by neutron capture in fission products . 7
5.5.1 Contribution of Cs . 7
5.5.2 Contribution of other fission products . 9
5.6 Total decay heat power . 9
Annex A (informative) Example of a calculation.16
Bibliography .20
iii
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national Standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www.iso.org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to
the World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see
www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 85, Nuclear energy, nuclear technologies,
and radiological protection, Subcommittee SC 6, Reactor technology.
This second edition cancels and replaces the first edition (ISO 10645:1992), which has been technically
revised.
The main changes compared to the previous edition are as follows:
235 238 239 241
— The decay heat curves for U, U, Pu, and Pu are revised using data adopted from the
[1]
American National Standard ANS-5.1-2014 .
— These curves are based on fits to experimental spectroscopic and calorimetric measurements of
fission product decay heat at short cooling times less than ~10 seconds, and on measurements and
[2]
simulations for longer times .
— Nuclear data constants are updated to reflect modern evaluated values.
— The range of initial U enrichment is extended beyond 4,1 % (mass fraction) to 5 %.
— Burnup range is extended to 62 GWd/t, an increase from 52 GWd/t in the previous 1992 edition.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
iv
Introduction
The decay heat power of nuclear fuels is the thermal power produced by radioactive decay of fission and
activation products of the nuclear fuel. Decay heat is one of the contributors to the total heat emitted
from the nuclear fuel during the reactor operation, representing about <7 % of the total heat. As decay
heat continues to be released after shutdown of a nuclear reactor, it is an important physical quantity
for the design of systems in which the decay heat power should be taken into consideration as a heat
source.
This document provides an alternative to dedicated and validated calculation codes, as it provides values
for the local generation of decay heat power as a function of the thermal fuel power during operation.
The values for the fission product component of decay heat are based on fits to measured data for short
5 [2]
cooling times less than ~10 s , and on measurements and computational simulations for longer times.
Values for other components of decay heat are developed to provide conservative estimates. Therefore,
at longer cooling times where fission products represent an increasingly smaller relative contribution
to total decay heat, this document becomes increasing conservative, and alternative methods such as
dedicated computer codes may provide more accurate estimates. The spatial distribution of the energy
conversion into heat, e.g. γ-radiation, is not considered. If required, evaluation of this is left to the user.
The calculation procedure used has the advantage of enabling the estimation of the decay heat power
without the need for a validated dedicated calculation code. Nevertheless, the calculation requires the
fission fractions of each fissile isotope. These values are not given in this document but can be obtained
[3][4]
from literature or computer codes.
The power generated by residual fission induced by delayed neutrons after shutdown and activated
structural materials is not considered in this document. Delayed neutrons are generally negligible
several minutes after core shutdown, and the activated structural materials generally have a minor
effect on the global decay heat. Analyses of delayed neutron heating is configuration specific and may
require more detailed models. Similarly, analysis of structural activation heating requires separate
evaluations.
v
INTERNATIONAL STANDARD ISO 10645:2022(E)
Nuclear energy — Light water reactors — Decay heat
power in non-recycled nuclear fuels
1 Scope
This document provides the basis for calculating the decay heat power of non-recycled nuclear fuel of
light water reactors. For this purpose the following components are considered:
— the contribution of the fission products from nuclear fission;
— the contribution of the actinides;
— the contribution of isotopes resulting from neutron capture in fission products.
This document applies to light water reactors (pressurized water and boiling water reactors) loaded
235 238
with a nuclear fuel mixture consisting of U and U. Application of the fission product contribution
to decay heat developed using this document to other thermal reactor designs, including heavy water
reactors, is permissible provided that the other contributions from actinides and neutron capture are
determined for the specific reactor type. Its application to recycled nuclear fuel, like mixed-oxide or
reprocessed uranium, is not permissible.
The calculation procedures apply to decay heat periods from 0 s to 10 s.
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 https:// www .electropedia .org/
3.1
decay heat power
thermal power produced by radioactive decay of fission and activation products of the nuclear fuel,
following shutdown of a nuclear fission reactor, excluding prompt radiation emissions
3.2
operating time
entire period of irradiation from the first loading of the considered fuel into the reactor until the final
shutdown and removal of the fuel
3.3
decay time
time elapsing after the operating time (3.2)
3.4
power histogram
approximation of the true continuous variation of power with time, by subdividing the variation into
intervals of constant power output
4 Symbols and subscripts
4.1 Symbols
Table 1 shows the symbols used in this document.
Table 1 — Symbols
Symbol Quantity Unit
A(t) Factor to be applied to the decay heat power of the fission products P, Unitless
for calculating the contribution P of the actinides (excluding U and
A
Np)
f (t) Decay heat power of the fission products at time t after a single nuclear (MeV/s)/fission
i
fission of the fissile nuclide i
Δf (t) Standard deviation of f (t) (MeV/s)/fission
i i
F (t ,T ) Decay heat power of the fission products of the fissile nuclide i at time t, (MeV/s)/(fission/s)
i k k
after the irradiation time interval, T , referred to one fission per second
k
ΔF (t ,T ) Standard deviation of F (t) (MeV/s)/(fission/s)
i k k i
H(t) Factor to be applied to the decay heat power of the fission products P, for Unitless
calculating the contribution P from neutron capture in fission products
E
(excluding capture in Cs)
th a
P Total thermal power of the fuel during the k time interval T
k k
b
P Contribution of the fissile nuclide i to the thermal power of the fuel dur-
ik
th
ing the k time interval T
k
b
P (t,T) Total decay heat power at time t after the end of operating time, T
N
b
P (t,T) Summed decay heat power on the basis of fission product decays
S
b
ΔP (t,T) Standard deviation of P (t,T)
S S
b
P (t,T) Contribution of fissile nuclide i to the decay heat power P (t,T)
Si S
b
ΔP (t,T) Standard deviation of P (t,T)
Si Si
b
P (t,T) Contribution to the decay heat power due to neutron capture in fission
E
products other than Cs
239 239 b
P (t,T) Contribution of actinides U and Np to the decay heat power
B
239 239 b
P (t,T) Contribution of actinides other tha
...