Are radioactivity measurements of building materials justifiable? Finnish data from the
2000s
Tuukka Turtiainen Radon and Health, STUK
First survey at STUK
• In the early 1980s, Raimo Mustonen measured natural radioactivity in 369 samples of Finnish building materials. Health Phys 46(6),1984
Material N 226Ra (Bq/kg)
mean (max)
232Th (Bq/kg) mean (max)
40K (Bq/kg) mean (max) Concrete ballast material 266 34 (146) 39 (225) 960 (1860)
Concrete 15 53 (70) 38 (53) 840 (960)
Clay brick 38 80 (134) 62 (92) 990 (1190)
White brick 4 23 (25) 21 (29) 620 (700)
Wood 2 0.4 (0.5) 0.7 (1.5) 9.6 (12)
Siporex exp. concrete 2 49 (53) 63 (40) 360 (390)
Cement 11 40 (84) 20 (55) 250 (340)
Blast‐furnace slag 5 120 (130) 79 (100) 180 (210) By‐product gypsum 17 310 (830) 23 (120) 17 (30)
Natural gypsum 1 7 1.5 25
First survey, radon exhalation from BMs
• Radon exhalation was measured from 19 materials
• Radon concentration was measured in 34 flats in which radon from soil and household water was negligible
• Traditional concrete had higher normalized exhalation rates than by‐gypsum or slag‐aggregate concrete
• Rn concentration in the indoor air was 17 – 149 Bq/m3. This was also dependent of ventilation rates
Assessment of doses from building materials
• Mustonen presented a model flat (72 m3) which was used for assessing doses Radiat Prot Dosim 7(1‐4),1985
Nordic flag book 1986 – Recommendations
• For existing houses: External radiation from building materials usually cause effective doses below 5 mSv/a. A reduction seldom justifies actions to bring the rate down.
• For planned houses: The upper bound of exposure should correspond to a dose rate in air of 0.5 µGy/h (3 mSv/a)
• Exemption level for building materials as a source for radon should be 100 Bq/kg of radium‐226
• Exemption level for building materials as a source for gamma radiation should be determined by mγ < 1
3000 200 200
Guide ST 12.2 (February 1993)
• Radiation act (592/91) and Radiation decree (1512/91) set stricter criteria for exposure to natural radioactivity
• The Guide: “The Radioactivity of Construction Materials, Fuel Peat and Peat Ash”
• Fall‐out from Chernobyl resulted in high concentrations of cesium‐
137 in peat ash
• Fly ash has been used as supplementary cementitious material in concrete since the 1930s a new radionuclide in building materials
• The radiation act stipulates that the party running a radiation practice is responsible for the safety of the operations. The responsible party is obliged to ensure that the level of safety specified in the ST Guides is attained and maintained
Guide ST 12.1 (1993)
• Building materials (action level 1 mSv/a)
200 300 3000
• Materials used in road, street and related construction work (action level 0.1 mSv/a)
500 700 8000 2000
• Materials used in landfill and landscaping (action level 0.1 mSv/a) 1500 2000 20000 5000
STUK‐B‐STO‐32 (in 1995)
• Radiation Dose Assessments for Materials with Elevated Natural Radioactivity by Mika Markkanen
• A guide book by which external doses can be assessed
European Commission 1999
• Radiological Protection Principles concerning the Natural Radioactivity of Building Materials. Radiation Protection 112
300 200 3000
Dose Criterion 0.3 mSv/a 1 mSv/a
Materials used in bulk amounts, e.g.
concrete
I ≤ 0.5 I ≤ 1
Superficial and other materials with restricted use:
tiles, boards, etc.
I ≤ 2 I ≤ 6
Nordic flag book 2000 – Recommendations
• For existing buildings: 1 µSv/h
• For planned buildings: 0.5 µSv/h
• Exemption level: 100 Bq/kg of radium‐226 (radon source)
• Upper level: 200 Bq/kg of radium‐226 (radon source)
• Exemption level for building materials as a source for gamma radiation should be determined by mγ < 1
• Upper level for building materials as a source for gamma radiation should be determined by mγ < 2
3000 300 200
• Exemption level ~1 mSv/a, upper level ~2 mSv/a
Natural stones 1999 – 2002
• A project about environmental impact during the life cycle of Finnish natural stone production
• Impacts: ground water, noise, vibration, radiation, dust, by‐
products, waste
• Natural stones are used as tiles, boards, gravestones, etc.
• Exposure of workers (dust, direct gamma rays, radon)
• Exposure for end‐users (buildings)
• Sample 23 natural stones produced in Finland, and 5 from abroad
Natural stones
• All samples exhibiting index value I > 1 were granites or migmatites
• Calculations were perforemd for end‐users in homes and work places assumin that all floors were clad with tiles
• Effective doses were well below 1 mSv/a for all cases
Beneficial project for all partners
• Ra‐226: 0.9 –170 Bq/kg
• Th‐232: 0.8 – 380 Bq/kg
• K‐40: 14 – 1700 Bq/kg
0%
25%
50%
75%
100%
0 1 2 3 4
Index
data
cumulative
Gypsum boards + new materials, 2003
• Most gypsum boards were of FGD‐gypsum (no phosphogypsym or natural gypsum)
• Flue gas desulphurization by lime
• New materials: Fiber cement boards, Calcium silicate boards, mineral wool boards
• 18 gypsum boards the index I value
– Mean: 0.07 Max: 0.15 Min: 0.03
• 7 new materials:
– Mean: 0.28 Max: 0.53 Min: <0.03
Aggregate samples from the companies 2000 – 2006
• Measurement services had been provided by STUK since introduction of ST 12.2 in 1993
• About 70 customers (producers, consultancies) sending concrete aggregates
• 356 samples of concrete aggregate (sand, gravel, crushed stone)
• Only aggregates are presented, Markkanen showed in 1992 that aggregate concentrations are good enough estimate for concrete concentrations
Index
0,0 0,2 0,4 0,6 0,8 1,0 1,2 1,4
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
0 1 2 3 4 5 6
Density
Cumulative (%)
Index
data cumul.
density
• 30% of the samples exceeded index value of 1 Arithmetic mean 0.93
Radium‐226
• About 10% of samples exceeded 100 Bq/kg
0,0 % 0,2 % 0,4 % 0,6 % 0,8 % 1,0 % 1,2 % 1,4 %
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
0 200 400 600 800 1000 1200
Density (%)
Cumulative (%)
Ra‐226 (Bq/kg) data
cumulative density
Worst‐case scenario
• Crushed stone from southern Finland intended for i.a. concrete production
– K‐40: 1740 ± 170 Bq/kg 1520 ± 150 Bq/kg – Ra‐226: 1190 ± 120 Bq/kg 1040 ± 210 Bq/kg – Th‐232: 150 ± 10 Bq/kg 130 ± 13 Bq/kg
• The index value is 5.3 ± 0.4
• For the model apartment building this would have caused ~5 mSv/a dose from gamma radiation
• Based on generic 0.39 (Bq.m–2.h–1)/(Bq.kg–1),and ventilation rate of 0.5 h–1, the projected concentration in 72 m2 flat’s indoor air would be ~1000 Bq/m3 (ref: Mustonen, 1992) 17 mSv/a
Customer satisfaction survey 2007
Score (1–5) Ease of placing an order 4.4 Staff’s readiness to help 4.2 Intelligibility of instructions 3.8 Intelligibility of results 4.3
Service times 4.4
Price 3.4
• Open answers from customers:
– We were glad that STUK considered exceeding index values as their own/mutual problem and pursued to solve it
– We were surprised that STUK’s attitude was not the same as that of many other ”authorities”
– When we have started to have our stone materials measured during the
Survey 2012
• Survey data: 52 samples from 9 companies
• 34 produced in Finland, 18 imported
– blast furnace slag – blast furnace sand
– Prefabricated slab (concrete elements) – Cement chemical admixtures
– Cement render, putty, float (surface finishing materials) – Building stone
– Decorative tiles – Cement
– Building board
– Gypsum and gypsum boards
Results from the survey
• 17% of samples exceeded Index value of 1
– 6 building stones – 1 prefabricated slab – 1 blast furnace slag
Conclusion of the survey
• The building stones intended for surface materials or pavements
• The furnace sand and slag become enough diluted if used in production of concrete
Results from measurement service 2007 – 2013
• 543 building material samples:
– 222 soil, natural gravels, fillers and sand
– 158 other stone materials (not specified)
– 133 stone material derived from rock
– 23 other building materials
Samples from 2007 – 2013
N Mean I I > 1 (%)
Natural soils, gravel, sand 222 0.83 19%
Other stone material 156 0.87 30%
Rock materials 133 1.01 44%
Other building materials 23 0.39 5%
All measured materials 534 0.87 28%
• Activity indices very similar to the data from 2000 – 2006 (mean 0.93, exceeding 30%)
• Aggregate measurements 73 samples per year (compared to 51 per year between 2000 – 2006)
Conclusion based on the samples 2007 – 2013
• Companies order measurements from areas where they suspect risk of high activities
• The samples are not representative of situation in all Finland
• Large variations were observed, also in smaller regions
• Decision of the use of material may be made based on the results (if index value is exceeded, the material is used e.g. for road
construction)
In 2015
• 80 orders for building material measurement
• One order may contain several samples
• Index exceeded in 19 samples inspection reports have been sent
• The companies have sent clarification and assessment of doses for 6 cases already
• Companies can do simple assessments by themselves with a help from a calculation tool created by Mika Markkanen
Lessons learned, potential risks
• Law on Extractable Land Resources 1982
• Latest decree on Extractable Land Resources 2005 sets strict limits on extraction of natural gravel and sand (protection of eskers and ground water)
• During this period, extraction has shifted from extraction of gravel to extraction of rock
• Most aggregates are made from crushed stone
• Rock materials exhibit higher radioactivity than natural gravel
• Risk of exceeding 1 mSv/a would be relatively high if measurements were not carried out (30–40% of the measured crushed stone
samples exceeded the index value of 1)
Lessons learned, potential risks
• After STUK had enough large sample of results, a memorandum was sent to the industry associations 2005:
• Measurements must be carried out for the following:
– Aggregate materials used for concrete production
– Materials used in small quantities which may have high activity concentrations such as fly ash or blast furnace slag
– Imported phosphogypsum
• Measurements are generally not needed for:
– Materials with low activity concentrations such as timber, white bricks, metal constructions
– Rock mineral with low activity concentrations such as gabro, diabase – When only small amounts of material is used (e.g. ceramic tiles, natural
stone tiles, surface materials)
– Materials that are used in places where little exposure can take place
Lessons learned
• Buildings are very expensive and have a long life‐span
• Too high concentrations of NORM in buiding materials would cause big financial losses
• High dose rates found in a building would create bad publicity
• Consumers reactions are often strong (example: granite kitchen table tops a few of years ago)
• There are ~6000 permits for extraction, not everything can be measured, optimization
Lessons learned
• Companies have been cooperative and their opinion on measurements have been positive
• Some small companies have had trouble understanding why
measurements are made, inspectors have given guidance to them
• CE marking in 2013 resulted high measurement activity
