Activation of equipment - overviewChris Theis, Helmut Vincke - DGS/RP

Contents

• How does material become activated and what drives activation levels?

• Legal criteria to classify material as “conventional” or as “radioactive”

• How can we minimize the amount of activated material?

Creation of radioactivity

• Material being placed in an accelerator environment can become radioactive undesirable but unavoidable

• Interaction with the beam produces lot of different radioisotopes which have different levels of radiotoxicity and different half-lives

• Radioactivity decays but this depends on the half-life of the produced isotopes

Creation of radioactivity

Energy (machine)& beam loss

Position in accelerator

Radioactivity levelsa1, a2, a3,…

for different isotopes

Time of material present in accelerator & in storage

Chemical composition

When is a material legally radioactive?

• Surface contamination:1 Bq/cm2 in case of unidentified beta- and gamma emitters and 0.1 Bq/cm2 in case of unidentified alpha emitters. Once a radio-nuclide has been identified then the CS-values given in Table 4 of EDMS doc 942170 can be used.

• Activity: Specific activity exceeds the CH exemption limits as given in Table 2 (column 2) of EDMS doc 942170

ANDtotal activity exceeds the CH exemption limits as given in Table 2 (column 2) of EDMS doc 942170

OR

• Dose rate: ( additional criterion used for practical reasons)Ambient dose equivalent rate measured in 10 cm distance of the item exceeds 0.1 uSv/h after subtraction of the background.

Safety code F:

Design studies... the minimum of the exemption limits proposed in Refs. [5,7,8] which will be adopted by future European Directives and national legislations.

When is a material legally radioactive?

When is a material legally radioactive?

• Legally it is ONLY the ratio of activity / LE which defines if a material is conventional or radioactive*:

• The dose rate criterion > 100 nSv/h is an auxiliary practical criterion. Equipment might be radioactive even if the dose rate is < 100 nSv/h!

*surface contamination is not considered here as equipment can often be decontaminated

How do you determine the activity levels?

Dose rate measurementa) If DR > 100 nSv/h radioactive

b) If DR < 100 nSv/h requires detailed analysis with gamma spectroscopy which yields activity levels

Gamma spectroscopy is very accurate but time consuming and usuallyrequires destructive sampling!

Why detailed material composition data is crucial for rad. waste characterization?

Example – 3 types of steel used @ CERN

Stainless steel 304LDensity: 8 g/cm3CARBON 0.03 wt%CHROMIUM 18.5 wt%COBALT 0.1 wt%IRON 67.1 wt%MANGANESE 2.0 wt%NICKEL 11.3 wt%PHOSPHORUS 0.0225 wt%SILICON 1.0 wt%SULFUR 0.015 wt%

Magnet steel - MAGNETILDensity: 7.8 g/cm3CARBON 0.0025 wt%IRON 99.7 wt%MANGANESE 0.235 wt%PHOSPHORUS 0.0115 wt%SILICON 0.0035 wt%SULFUR 0.00901wt%

Exposed as magnets in the SPS for 20 years

Storage time % of isotopes contributing to radiotoxicity that cannot be directly measured via dose rate or gamma spec

5 years 29% - stainless steel,93% - MAGNETIL steel,76% - KHMN steel,

10 years 19% - stainless steel,95% - MAGNETIL steel,77% - KHMN steel,

20 years 10% - stainless steel, 68% - MAGNETIL steel,41% - KHMN steel,

Steel KHMN – LHC endyoke laminationsDensity: 8 g/cm3CARBON 0.1 wt%CHROMIUM 6.7 wt%IRON 63.6 wt%MANGANESE 28 wt%MOLYBDENUM 0.1 wt%NICKEL 0.82 wt%NITROGEN 0.1 wt%PHOSPHORUS 0.022 wt%SILICON 0.6 wt%SULFUR 0.004 wt%

Different steel types show considerable differences in radiotoxicity & measurable dose rate

Cooling time dependence

Ti-44 dominant,Fe-55 is disappearing

Fe-55 dominant

Cooling time dependence

Radiological characterization without detailed knowledge about chemical composition and radiation history is like searching a haystack to prove that there is no needle.

What can we do to avoid or minimize activation?

Reduction of radioactive waste

Safety benefit

• Lower dose rates and committed doses

Operational benefit

• Reduced downtime due to faster access

• Less restrictions for manipulation & access

End of life-cycle benefit

• Smaller amount and less critical radioactive waste

• Smaller financial burden

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• Optimization already crucial during the design phase

• Beside other aspects also the radiological consequences of the implementation of a material have to be considered

• Level of activation depends on the type of the material

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Material catalogue

Material catalogueproduced with ActiWiz

EDMS 1184236 or http://rpactiweb.cern.ch

Classification of most common materials by the use of global operational and waste hazard factors

Catalogue provides guidelines for selection of materials to be used in CERN’s accelerator environment

Authors: Robert Froeschl, Stefano Sgobba, Chris Theis, Francesco La Torre, Helmut Vincke and Nick WalterAcknowledgements: J. Gulley, D. Forkel-Wirth, S. Roesler, M. Silari and M. Magistris

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• Catalogue consists of three parts:

Catalogue for the radiological hazard classification of materials

Introduction

List of critical materials in terms of

handling & waste disposal*

Appendix with data

* Many thanks to Luisa Ulrici (DGS-RP-RW) for elaborating and providing the waste disposal guidelines

Materials not contained can be very easily assessed by the equipment designer/producerwith the ActiWiz software – http://www.cern.ch/actiwiz

Thank you for your attention