DE102022001349A1 - Use of Tc-99m for process description and quality control in material-removing surface treatment processes and for determining the filtering capacity of aerosol retention systems - Google Patents

Abstract

2.1 State of the art Abrasive processes are used to clean contaminated surfaces. As a measure of the cleaning quality, the deconfactor Kv/Kn is used to compare the quotient of contamination BEFORE Kv to residual contamination AFTER Kn. In nuclear/nuclear technology, typical nuclides are used, which cause radioactive residues and waste (long half-lives, such as Co-60: 5.3 a, Cs-137: 30.2 a). These nuclides are used to control and describe aerosol retention (= filter effectiveness). The affected components and systems are subsequently radioactively contaminated. They have to be decontaminated at great expense - which causes radioactive waste - or are themselves disposed of as radioactive waste.2.2 Improvement through patentInstead of the above. Tc-99m is used for nuclides. On the one hand, its short half-life (6.01 h) makes it possible to determine very precisely the cleaning effectiveness of the decontamination or cleaning processes and the aerosol retention of the filter systems. On the other hand, Tc-99m activity decays quickly, that is, the Tc-99m disappears. The components and accompanying materials used can i. A. can be easily measured. The measurable residual activity of all materials and components involved in the process and the checks is below the exemption limits of the Radiation Protection Ordinance. The use of Tc-99m has been standard in nuclear medicine for decades and the application is highly quality assured. Tc-99m can be used just as well in technical and nuclear technology applications.3 Areas of application3.1 Nuclear technology. Dismantling facility, dimensioning of deconstruction systems and procedures, quality assurance through recurring inspections (WKP). Checking the effectiveness and dimensioning of the exhaust air systems, aerosol retention of the filters.3.2 Other technologySurface processing processes (paint removal, chrome layers (chromate), corrosion layers): Checking the effectiveness. Checking the effectiveness and dimensioning of existing exhaust air systems, aerosol retention of the filters.

Description

Table of contents 1 Used abbreviations ................................................ ....................4 2 Background ................................................. ..........................................5 3 State of the art ............................................... ................................5 4 Use of Technetium 99m, Tc-99m .......................................... .......6 4.1 Principle ................................................ ................................................ .6 4.2 Background ................................................. ..........................................6 5 Technical application ................................................ ...................................7 6 Potential for improvement ................................................ ........................8th 6.1 Basic principle ................................................ .........................................8th 6.2 Conventional technology ................................................ ..........................8th 6.3 Nuclear, nuclear technology .......................................... ..............................8th 7 Conclusion ................................................. ................................................ .....9 1 Abbreviations used Expression Meaning Aerosol Heterogeneous mixture of solid or liquid suspended particles (aerosol particles) in air or gases. Size spectrum of suspended particles: down to the nanometer range (a few nm) Becquerel, Bq Radioactivity unit: decays per second ng Nanogram, 10 ^-9 g (0.000000001 g) nm Nanometer, 10 ^-9 m (1 nm corresponds to approx. 10 atom diameters, 0.000000001 m) pg Picogram, 10 ^-12 g (0.000000000001 g) StrlSchG Law to protect against the harmful effects of ionizing radiation (Radiation Protection Act - StrlSchG) StrlSchV Ordinance on protection against the harmful effects of ionizing radiation (Radiation Protection Ordinance - StrlSchV) Technetium Chemical element with atomic number 43; no stable isotopes, is produced artificially. Tc-99m: Used in medicine (nuclear medicine), with half-life of 6.01 hours; Daughter nuclide: Tc-99 Tracers, tracers Marking with a marker, here Tc-99m, ... “laying a track”

2 background

• • Innenoberflächen: Rohrleitungen und Behälterinnenflächen, Lüftungsschächte, die von Radioaktivität-führenden Medien durchströmt wurden,
• • Außenoberflächen: durch freigesetzte Radioaktivität kontaminierte Außenflächen.

During long-term operation of nuclear facilities, material surfaces become radioactively contaminated. These contaminations are radioactive deposits that are deposited on the surfaces of components and systems. Interior surfaces and exterior surfaces are affected:

• • Internal surfaces: pipes and inner surfaces of containers, ventilation shafts through which media carrying radioactivity flowed,
• • Exterior surfaces: exterior surfaces contaminated by released radioactivity.

The affected components and systems are located in the control areas of the nuclear power plants or nuclear facilities.

When these nuclear power plants or nuclear facilities are dismantled, these components and systems must be cleaned. The contaminants are removed from the surfaces; the surfaces are decontaminated.

The quality of surface cleaning/decontamination determines whether the treated materials can be recycled as valuable materials or whether they have to be separated and disposed of as radioactive waste. The classifications are described in legal regulations such as the Radiation Protection Ordinance.

When mechanically cleaning freely accessible surfaces, abrasive processes are used as standard (1 high-pressure water jets, high-pressure jets with dry abrasive, high-pressure jets with wet abrasive, LASER applications). When material is removed, aerosols are generated, finely dispersed solid or liquid particles suspended in the air. Because these aerosols are the radioactive contamination carriers, they must be effectively retained (2 particle size of the contamination carriers: a few µm down to the submicrometer range (a few nanometers)). This retention must be carried out quantitatively using suitable filter systems so that no radioactivity is released. The filter systems are classified and the retention levels are divided according to particle size.

3 State of the art

The classifications are carried out with synthetic dusts, which differ greatly from the dust actually produced in the filter systems used. The differences become even more significant when wet suspended matter is added to the dry suspended matter. In nuclear technology, radioactive aerosols are generated during decontamination processes; a quantitative description of the retention behavior is particularly important here.

4 Use of Technetium 99m, Tc-99m

4.1 Principle

• • vom Dekontaminationserfolg auf der Materialoberfläche bis hin zur
• • Rückhalte-Güte der Aerosol-rückhaltenden Filtersysteme.

By using Tc-99m, the process of abrasive decontamination can be specified and verified even more sensitively

• • from decontamination success on the material surface to
• • Retention quality of the aerosol-retaining filter systems.

This is done by radioactively marking/doping the material surfaces and tracking the activity loss of the process to be checked (see below, Chapter 5).

After completion of the investigations, Tc-99m activity subsided. The previously radioactively marked workpieces and all components that came into contact with Tc-99m are in principle free of activity again (decrease in activity and process progression see below, in ).

4.2 Background

Tc-99m is a nuclide that has been used in nuclear medicine (thyroid and whole body scintigraphy) for decades. For this purpose, Tc-99m is produced in high purity for human medical use and is available on an industrial scale in handy radionuclide generators.

Tc-99m has a half-life of 6.01 hours. It passes into the daughter nuclide Tc-99 by emitting a very easily measurable gamma signal at 141 keV (half-life Tc-99: 210,000 years) (Karlsruhe Nuclide Map, 7th edition 2006). In diagnostics, Tc-99m is measured via the gamma signal in the treated patient, and it decays very quickly with a half-life of 6.01 hours. In shows how 0.3 Bq of the daughter nuclide Tc-99 was created after seven days from the initially used 10 million Bq of Tc-99m.

5 Technical application

At the beginning of the process control, the aerosol source is doped/labeled with Tc-99m. In the example outlined in These are sample surfaces that are treated abrasive. 10 ⁺⁰⁸ Bq Tc-99m are used for doping/tracing.

At the beginning, during the implementation and after its completion, the relevant systems are sampled and the Tc-99m activities are determined. The Tc-99m concentrations are typically determined using appropriate gamma-sensitive measuring systems (spectrometers, counters), which can detect the 141 keV line of Tc-99m sensitively enough. The measurement results are corrected for decay time for evaluation (reference date and time).

This metrological tracking takes place in a control area. Seven days after the start of the investigations, the Tc-99m used “degraded” into Tc-99; all components, plant parts, materials and premises that initially came into contact with Tc-99m no longer show activity contamination, and the remaining 0.3 Bq

In terms of activity level, Tc-99 are below the exemption limits for the unrestricted release of solid and liquid substances (StrlSchV, Appendix 9, Table 1 “Exemption limits, release values for different types of release, values for highly radioactive radiation sources, surface contamination values”).

After a corresponding waiting period (Tc-99m decay window), the Tc-99m has completely decayed. The systems, components, rooms (= control area) previously exposed to Tc-99m and also the waste generated during the implementation (cleaning cloths, papers, protective suits, masks) are then free of Tc-99m again. They can be released accordingly, taking into account the applicable regulations (StrlSchV).

6 Potential for improvement

6.1 Basic principle

The quality of the abrasive removal behavior as well as the checking and description of the filtration behavior/process is done by gamma measurement of the Tc-99m tracer, which has decayed after the test series has been completed. In principle, the examinations can be carried out in temporary control areas and under radiation protection control. After the Tc-99m activity has subsided, the components can be released inactive again, as can the resulting waste. The temporary control area can be dissolved again. There is no radioactive waste from the test series.

6.2 Conventional technology

For non-nuclear, non-nuclear technology, the use of the Tc-99m tracer or doping technology is technically advantageous especially when designing or specifying aerosol containment systems when the exact nature of the aerosols is not known or is not stable (Aerosol size distribution, dry to wet aerosol ratios).

6.3 Nuclear, nuclear technology

To describe the aerosol retention capacity of filter systems, a variety of “real” nuclides are used, as they also occur in system operation and dismantling (e.g. Co-60, Mn-54, Cs-137, Ag-110m, others); These nuclides all have long half-lives, well above the 6.01 hours of the Tc-99m (several 100 day to decade ranges). As a result, all examined components are permanently contaminated. They must either be decontaminated in a laborious process or be taken into the interim storage facilities as radioactive waste (currently: Federal Ministry for Economic Affairs and Energy (now: BMWK) - “Announcement of research funding for nuclear safety” from October 14, 2021) - which is the basic goal of nuclear Disposal contradicts. There are no final storage facilities for radioactive residues and waste.

7 Conclusion

• • neue Verfahren
  • ◯ schneller,
  • ◯ wirtschaftlicher und
  • ◯ kostengünstiger konzipieren, verifizieren zu können und
  • ◯ schneller zum Einsatz zu bringen,
• • wird dem vom Bundesministerium für Wirtschaft und Energie (jetzt:
  • BMWK) gesetzten Ziel der Minimierung radioaktiven Abfalls für die Verlängerung der Zwischenlagerung Rechnung getragen (Reduzierung der Auslastung des Zwischenlagers, siehe Fußnote⁵),
• • Die Personendosisbelastung bei der Durchführung der Messungen mit Tc-99m durch die kurze Halbwertszeit minimiert.

Through the process of
“Use of Tc-99m
for process description and quality control in material-removing surface treatment processes
and to determine the
Filtering capacity of aerosol retention systems
There is a tool available in the field of nuclear technology to

• • new procedures
  • ◯ faster,
  • ◯ more economical and
  • ◯ be able to design, verify and more cost-effectively
  • ◯ to be deployed more quickly,
• • is approved by the Federal Ministry for Economic Affairs and Energy (now:
  • The BMWK) goal of minimizing radioactive waste was taken into account for the extension of interim storage (reduction in the utilization of the interim storage facility, see footnote ⁵ ).
• • The personal dose exposure when carrying out measurements with Tc-99m is minimized due to the short half-life.

The process can also be used in the field of conventional technology.

• • hochgenau, einfach und sauber, und ebenfalls mit
• • realen Aerosolen durchgeführt werden.

After setting up temporary control areas, measurements can be carried out

• • highly accurate, simple and clean, and also with
• • real aerosols are carried out.

Claims (2)

Determination of the deconstruction or removal behavior in surface-removing processes such as 1.1. Abrasive techniques, which are: 1.1.1. Water pressure process (high-pressure cleaner) 1.1.2. Liquid printing process (high-pressure cleaner) 1.1.3. Liquid-air or liquid-gas mixtures under high pressure (up to 1000 MPa), and with the addition of abrasive solids, carbon dioxide (dry ice) 1.2. Use of laser systems, typically 1.2.1. continuously or 1.2.2. operated in a pulsed manner. Determination of aerosol retention, filter effect and effectiveness of filter systems and filter combinations, such as 2.1. Particle-retaining filters 2.2. Activated carbon/carbon filter 2.3. Gas scrubbing filters