Calibration standard for nuclear decommissioning.
Date: 2016-12-20
Institutions: Joint Research Centre
Subjects: cast-iron, decommissioning of power stations, decontamination, nuclear research, nuclear safety, research project, research report, scientific cooperation, tube

Calibration standard for nuclear 
decommissioning 

Grey cast iron tubes 
containing 60Co and 108mAg   

Raf Van Ammel, Faidra Tzika, Mikael Hult 

2016  

EUR 28276 EN  

 
 
 
 
 
 
 
 
 
This publication is a Technical report by the Joint Research Centre (JRC), the European Commission’s science and 
knowledge service. It aims to provide evidence-based scientific support to the European policy-making process. 
The scientific output expressed does not imply a policy position of the European Commission. Neither the 
European Commission nor any person acting on behalf of the Commission is responsible for the use which might 
be made of this publication. 

Contact information 
Name: Raf Van Ammel 
Address:  European  Commission,  Joint  Research  Centre,  Directorate  for  Nuclear  Safety  and  Security,  Unit  G.2  - 
Standards for Nuclear Safety, Security and Safeguards, Retieseweg 111, B-2440 Geel, Belgium 
E-mail: raf.van-ammel@ec.europa.eu 
Tel.: +32 14 571 267 

JRC Science Hub 
https://ec.europa.eu/jrc 

JRC104523 

EUR 28276 EN 

ISBN 978-92-79-64393-4 

ISSN 1831-9424 

doi:10.2789/936423 

© European Atomic Energy Community, 2016 

Reproduction is authorised provided the source is acknowledged. 

All images © European Atomic Energy Community, 2016 

How  to  cite:  Raf  Van  Ammel,  Faidra  Tzika,  Mikael  Hult;  Calibration  standard  for  nuclear  decommissioning; 
EUR 28276 EN; 10.2789/936423 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Abstract ............................................................................................................... 1 

Introduction ......................................................................................................... 2 

1  Requirements of the materials ........................................................................... 3 

1.1  Technical specifications ............................................................................... 3 

1.2  Sample numbering ..................................................................................... 5 

2  Production ...................................................................................................... 6 

3  Conclusion ...................................................................................................... 8 

References ........................................................................................................... 9 

List of figures ...................................................................................................... 10 

List of tables ....................................................................................................... 11 

 
 
 
 
Abstract  

In  the  frame  of  support  of  decommissioning  activities,  JRC-GEEL  produced  a  set  of  12 
grey cast iron tubes. These tubes contain known amounts of activity of 60Co  and 108mAg. 
The tubes are intended to be used  as a calibration standard for the detection efficiency 
of measurement facilities dealing with clearance (free release) and/or characterisation of 
waste  generated  from  decommissioning  of  nuclear  facilities/installations.  Following  to 
their  characterisation  the  SI-traceable  activity  standards  will  contribute  to  enhance 
reliability of these kinds of measurement systems. 

1 

 
 
 
Introduction 

In  Europe  and  even  globally  we  are  facing  the  challenges  of  decommissioning  of  old 
nuclear  power  plants  and  other  nuclear  installations.  After  the  removal  of  the  nuclear 
fuel, the nuclear installation needs to be decommissioned. The remaining materials need 
to be managed and/or cleared from regulatory control in a safe and reliable way. A lot of 
the  remaining  radioactivity  is  present  in  the  primary  circuit  of  the  reactor.  However, 
radioactivity is also encountered in the surroundings of the primary circuit. The levels of 
radioactivity  in  the  surroundings  are  lower  but  the  amount  of  the  material  to  be 
managed is much higher.  

The  two  most  important  streams  of  waste  are  concrete  and  metals.  As  an  example,  a 
Pressurised Water Reactor (PWR) built in 1970s, is constructed with around 75000 m3 of 
concrete  and  36000  metric  ton  of  steel  and  iron  [1].  The  vast  majority  of  this  material 
needs to be characterised before safe disposal or free release. 

Taking  into  consideration  the  large  amount  of  material  and  the  high  cost  of  safe 
issued  Council  Directive 
radioactive  waste  disposal,  the  European  commission 
2011/70/Euratom  [1]  stating  that:  "Generation  of  radioactive  waste  shall  be  kept  to  a 
minimum which is reasonably practicable in volume and activity by means of appropriate 
design measures and of operating and decommissioning practices including the recycling 
and reuse of materials."  

The activity concentration (expressed in Bq kg-1) values for clearance of materials which 
can  be  applied  by  default  to  any  amount  and  to  any  type  of  solid  material  during  the 
decommissioning  of  a  power  plant  are  laid  down  in  Council  Directive  2013/59/Euratom 
[3]. These values are set per radionuclide.  

In order to comply with legislation a lot of measurements need to be carried out for the 
segregation/characterisation  and/or  free  release  of  all  the  materials  present  on  the 
nuclear  sites.  To  validate  and  calibrate  the  various  systems/set-ups  used  to  perform 
such measurements, SI-traceable activity standards are needed. Such standards need to 
represent,  as  much  as  possible,  the  geometries,  matrices,  radionuclide  content  of 
interest in the practice. The routine free release involves normally measurement of bulk 
quantities of materials (often placed in europallet sized containers for measurement)  of 
three  types:  metal,  concrete  or  light  materials.  It  is  therefore  critical  to  have  suitable 
calibration  standards  of  such  types  available.  The  need  for  a  resembling  reference 
standard  is  even  more  pronounced  for  metals  due  to  the  strong  effects  of  self-
attenuation  of  radiation.  Such  a  standard  should  resemble  in  matrix  and  geometrical 
configuration the routinely measured metal waste.  

A NPP has to manage large components and in particular a lot of piping system parts. In 
order  to  fill  the  gap  in  availability  of  such  standards  to  the  European  community,  JRC-
Geel  has  included  in  its  work-programme  the  development  of  a  standard  consisting  of 
metal tubes.  

The feasibility of the production and characterisation of this material has been proven by 
previous  work  led  by  JRC-Geel.  This  work  had  been  carried  out  in  the  context  of  the 
MetroRWM  project.  The  outcome  was  a  traceable  activity  standard,  for  free  release 
measurement facilities, consisting of iron tubes [4], [5] (and references therein).  

These  tubes  contained  60Co  and  110mAg.  Silver-110m  has  a  major  drawback  in  this 
context that its short half-life, only 250 days, limits the time during which the calibration 
standard  can  be  used.  There  was  a  concern  that  the  activity  of  110mAg  would  not  be 
sufficiently homogeneously distributed, as silver does not form a solid solution with iron 
as  cobalt  does.  In  the  MetroRWM  project  we  showed  that  indeed  there  is  a  small 
inhomogeneity of about 2% of the 110mAg  in the radial direction. However the nuclide is 
homogeneously  distributed  along  the  major  axis  of  the  tubes.  Thereby  the  activity 

2 

 
 
 
 
 
 
distribution 
homogenously distributed.  

fulfilled 

the  requirements.  Cobalt-60  was,  as  predicted,  perfectly 

The radionuclide 108mAg has the same chemical properties as 110mAg. It also emits several 
intense gamma-rays of suitable energy. It has a longer half-life, 438 years, compared to 
110mAg. Therefore, it is more suitable for this type of calibration standard. 

1  Requirements of the materials 

1.1  Technical specifications 

JRC-Geel  set  up  a  contract  with  an  industrial  metal  melting  facility  to  produce  the 
material  for  the  metallic  standard:  a  set  of  12  grey  cast  iron  tubes  containing 
homogeneously distributed radionuclides: 60Co and 108mAg.The tubes were produced from 
a  batch  of  grey  cast  iron  (Standard  DIN  1691  GG10,  GG15,  GG20  or  GG25)  [4] 
contaminated  with  60Co  and  108mAg.  The  homogeneity  of  the  batch  material  in  density 
and  radioactivity  distribution  was  specified.  In  addition,  representative  samples,  of  the 
raw  material  and  of  the  individual  tubes,  were  requested.  These  samples  were  in  the 
shape of disks and machining swarfs. These samples will be used for the characterisation 
of the standard.  

Twelve  disks  were  made  from  the  smelts  used  to  cast  the  tubes.  These  disks  should 
have  the  same  homogeneity  in  density  and  activity  distribution  as  the  tubes.  From  the 
12  tubes,  36  samples  of  swarfs  were  collected  (3  samples  per  tube  each  sampled  at  a 
different  height)  during  machining.  All  the  specifications  of  the  tubes,  disks  and  swarfs 
are listed in Table 1.  

The  contaminated  waste  metal,  obtained  from  the  tubes/disks  machining  process,  was 
re-melted  in  order  reduce  the  amount  of  radioactive  waste.  From  this  smelt  20  iron 
waste-disks were produced. These disks are to be characterised as an activity standard 
for  other  applications  (e.g.  radioactivity  monitoring  in  the  metallurgical  sector).  The 
massic activity concentration of the two radionuclides in the waste-disks is expected to 
be  slightly  lower,  compared  to  the  one  of  the  disks,  and/or  swarfs  obtained  during  the 
tubes' production. The specifications of the 20 waste-disks are listed in Table 2.  

3 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Table 1 Specification of the iron tubes, disks and swarfs 

A. 

B. 

C. 

D. 

Parameter 
One tube/casting data 
Length 

Diameter (outer) 

Mass 

Thickness 

Tubes/casting set of 12 data 
Mass 
Total Activity 108mAg 
Total Activity 60Co 
Average density in occupied 
container volume 
Batch material 

Density homogeneity 

Homogeneity in specific activity 

Disks from tubes 
Diameter (outer) 

Thickness 

Unit 

Value 

mm 

mm 

kg 

mm 

kg 

kBq 

kBq 

400 +0 -0.2 

200 +0 -0.2 

20.5  0.5 

12  0.4 

246  6 

100 40 

1800 400 

g/cm3 

1.28  0.03 

% 
variation 
% 
variation 

2 

108mAg: 7 
60Co: 2 

mm 

mm 

80  1 

10  1 

E. 

Swarfs ( specs. for one sample) 

mass 

g 

10-20 

Table 2: Specifications of waste-disks 

Parameter 

Diameter (outer) 

Thickness 

Contents of radionuclides 

Homogeneity in specific activity 

Unit 

mm 

mm 

- 
% 
Variation 

Value 

35 ± 0.5 

10 ± 0.5 
60Co, 108mAg 
60Co: 2 
108mAg: 10 

4 

 
 
  
  
  
  
  
  
  
  
  
  
  
 
  
  
  
  
  
  
  
  
  
  
  
  
  
 
 
 
 
 
1.2  Sample numbering 

For  the  production  of  the  contaminated  tubes,  disks  and  swarfs,  it  is  of  utmost 
importance that all items produced are uniquely identified and traceable to their origin. A 
schedule  for  numbering  the  items  was  agreed  upon  with  the  contractor  producing  the 
material. The schedule is shown in Figure 1.  

Figure 1: Numbering of the samples during the production of the tubes 

5 

 
 
 
 
 
 
 
The  20  waste-disks  also  need  to  be  uniquely  numbered  according  to  the  schedule  in 
Figure 2.  

Figure 2: Numbering of the 20 waste-disks 

2  Production 
The production of the tubes and the collection of the samples took place in the industrial 
melting facility of VUHZ in Trebic, Czech Republic [7]. For the production of the tubes it 
was not possible to use conventional technologies due to the fact  that high amounts of 
materials are needed causing contamination in the production plant. Centrifugal casting 
was  considered  the  most  suitable  for  producing  the  material  as  it  needs  less  material 
input and generates relatively small amounts of waste.  

In centrifugal casting, a permanent mold is rotated continuously around its axis at high 
speeds  as  the  molten  metal  is  poured  on.  The  molten  metal  is  centrifugally  thrown 
towards  the  inside  mold  wall,  where  it  solidifies  after  cooling.  The  casting  is  usually  a 
fine-grained  casting  with  a  very  fine-grained  outer  diameter,  owing  to  chilling  against 
the mould surface. A schematic view of the production process is shown in Figure 3. 

The mold used for the production of the castings had a diameter of 170 mm and a length 
of  1131  mm.  One  smelt  (basin)  per  casting  was  prepared.  From  each  casting  2  tubes 
were produced by machining them to their final dimensions.  

Figure 3: Schematic view of horizontal casting 

6 

 
 
 
 
 
 
 
 
 
 
 
 
Two disks were produced from each smelt (basin). Each disk was casted in a mold and 
machined  to  its  specified  dimensions.  In  total  12  disks  were  produced  from  6  smelts 
(basins). Pictures of the tubes and disks are shown in Figures 4 and 5. 

Figure 4: 12 cast iron tubes 

Figure 5: 12 cast iron disks 

7 

 
 
 
 
 
 
 
 
JRC-Geel  supplied  VUHZ  with  two  standard  solutions  of  108mAg  containing  in  total  an 
activity of 740 KBq in the total volume of 10 mL [8]. The  60Co in the tubes was readily 
available  at  VUHZ.  A  master  alloy  containing  both  radionuclides,  60Co  and  108mAg,  was 
prepared. This master alloy was distributed over each smelt (basin) of production of the 
individual raw castings.   

From the collection of all the  swarfs an additional  smelt was made. From this  smelt 20 
additional disks were made. 

3  Conclusion 
In the frame of the support to nuclear decommissioning, a set of 12 grey cast iron tubes, 
containing  known  amounts  of  60Co  and  108mAg,  was  produced.  Disk-shaped  and  swarfs 
samples  were  produced  in  order  to  be  used  for  the  characterisation  of  the  material.  All 
the produced materials were identified by a unique code.  

The produced materials will be tested against their specifications. Activity measurements 
of  the  tubes,  disks  and  swarfs  will  lead  to  a  new  SI-traceable  metal  standard  in  the 
shape  of  tubes.  The  standard  will  contribute  to  enhance  reliability  of  free  release  and 
waste characterisation measurements in the field of nuclear decommissioning.  

8 

 
 
 
   
 
 
 
 
 
References 

[1] Metal and concrete inputs for several nuclear power plants, Peterson P., Zhao 

H., Petroski R., Report UCBTH-05-001. 

[2] Council Directive 2011/70/Euratom of 19 July 2011 establishing a Community 

framework for the responsible and safe management of spent fuel and 
radioactive waste 

[3] Council Directive 2013/59/Euratom of 5 December 2013 laying down basic 

safety standards for protection against the dangers arising from exposure to 
ionising radiation 

[4] A new large-volume metal reference standard for radioactive waste 

management, Tzika F., Hult M., Stroh H., Marissens G., Arnold D., Burda O., 
Kovář P., Suran J., Listkowska A., Tyminski Z., Radiat Prot Dosimetry. 2016 
Mar;168(3):293-9 

[5] Distribution of radionuclides in an iron calibration standard for a free release 
measurement facility. Hult M., Stroh H., Marissens G., Tzika F., Lutter G., 
Šurán J., Kovar P., Skala L., Sud J., Appl Radiat Isot. 2016 Mar;109:96-100 

[6] Standard DIN 1691 Flake graphite cast iron (grey cast iron) Properties 
[7]  VÚHŽ a.s., 739 51 Dobrá 240, Czech Republic 
[8] Certificates of calibration gamma standard solution, Eckert&ziegler ref 1867-

17, 1827-38 

9 

 
 
 
 
 
 
List of figures 

Figure 1: Numbering of the samples during the production of the tubes ....................... 5 

Figure 2: Numbering of the 20 waste-disks .............................................................. 6 

Figure 3: Schematic view of horizontal casting .......................................................... 6 

Figure 4: 12 cast iron tubes .................................................................................... 7 

Figure 5: 12 cast iron disks .................................................................................... 7 

10 

 
 
 
 
 
 
List of tables 

Table 1 Specification of the iron tubes, disks and swarfs ............................................ 4 

Table 2: Specifications of waste-disks ...................................................................... 4 

11 

 
 
 
 
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doi:10.2789/936423 

ISBN 978-92-79-64393-4