Environmental Monitoring Programs and Equipment Flashcards
What are the purposes of environmental monitoring?
- Measure and/or reconstruct (estimate) human population doses
- Determine radiological impact of a facility
- Detect and quantify accidental off-site radionuclide releases
- Meet specific license requirements
- Obtain pathway data to refine models
- Study air and water mixing patterns
Define
Pathway
(Environmental Monitoring)
Any route that radioactivity can follow in passing from a licensed facility to a person in the general population.
Define
Critical pathway
(Environmental Monitoring)
The route taken by a critical nuclide from point of release to body entry.
Compare and Contrast
Preoperational vs. and Postoperational Monitoring Programs
Preoperational Monitoring Program
- Put in place prior to the use of radioactivity at the site, and typically run for one year.
- Comprehensiveness ⇒ Determines a baseline analysis of environmental radioactivity over any possible areas of concern.
Postoperational Monitoring Program
- Sensitivity ⇒ Corresponds to a concentration of 1% to 10% of the applicable limits set for by federal or state radiation protection standards.
- Selectivity ⇒ Ability to select the radionuclide out of background.
Define
Critical nuclide
(Environmental Monitoring)
Those nuclei which cause the largest dose contribution to the actual population at risk near the facility.
What are the objectives of a preoperational monitoring program?
- Locate radiation anomalies
- Document ambient levels
- Identify critical nuclides and pathways
- Document seasonal meteorology patterns
What questions are to be answered by a preoperational monitoring program?
- What radioisotopes should be measured?
- Where should the samplers be located?
- How often should a sample be collected?
- Which equation is used to calculate population dose?
What is this plume pattern?
Looping
What is this plume pattern?
Coning
What is this plume pattern?
Fanning
What is this plume pattern?
Lofting
What is this plume pattern?
Fumigation
What are two practical techniques to overcome radon interference in environmental alpha monitors?
- Introduce a delay time between sample collection and counting to account for the short half-life of radon and its daughters.
- Use a detector such as a surface barrier diodide which have excellent energy resolution. Then use a single channel pulse height analyzer to eliminate the interference of the alphas particular to radon.
What questions need to be addressed in setting up a program to monitor the environmental levels of radioactivity?
- Which isotopes?
- Collection frequency?
- Sampling location?
- Sample preparation?
- Sampling medium?
- Counting equipment?
- Sample size?
- Calculational model?
How are environmental levels of external gamma radiation (“direct radiation”) measured?
- Using thermoluminescent dosimeters.
- Calcium fluoride and calcium sulphate TLDs are commonly used which can measure doses below 1 mrem per month.
What is a good TLD for environemental monitoring that represents human tissue?
- Use a carbon-doped aluminum oxide (Al2O3:C) phosphor which has an effective atomic number of 10.2. This is much closer to 7.5 than calcium phosphors.
- It has maximum fading of 10% in three months at extreme environmental temperatures, with no fading at room temperature for up to 9 months.
- Minimum detectable dose is 0.1 mrem.
How do you measure real time “direct exposure” gamma radiation?
- Use a pressurized ion chamber.
- Fill gas is pressurized to 600 psi with argon gas.
- The extra loading of gas molecules makes the chamber more sensitive.
- It can then detect a gamma ray background of as little as 1 mrem per year.
- This is good for plume detection.
What are some techniques and examples for monitoring airborne particulates?
- Sedimentation (Flypaper)
- Inertial Separation (Cascade Impactor)
- Filtration (High Volume Sampler)
- Electrostasis (Precipitator)
What are two factors to consider in operating a filter sampler?
- The accumulation of nonradioactive material on the filter element as time passes (dust loading). Problem in dusty environments.
- Change in efficiency of a filter matrix as the airflow velocity changes.
Graph
Collection Efficiency vs. Incoming Particle Velocity
(in reference to Air Filter Sampler for Environmental Monitoring)
Define
Stack sampling
- Sampling of particulates in a moving air stream.
- A stack is a vent pipe or duct carrying a stream of air molecules and particulates, possibly for release into the enviornment.
- If the particulates can possibly be radioactive their concentration must be measured before release.
Why would a stack monitor have a logarithmic readout?
- To allow coverage of levels from below background to disaster concentrations without range switching.
- A 30-day strip chart recorder gives a continuious record and makes it possible to calculate the amount of radioactivity released during any kind of evolution.
What are three considerations for a stack sampling?
- Type of nozzle
- The placement of the nozzle in the air stream
- The transport of the particulates to your collection point.
What design criteria must the nozzle meet?
(in reference to Stack Sampling)
- The nozzle must be designed to meet the conditions of isokinetic sampling.
- These conditions are met if the velocity of the air steam entering the nozzle is exactly equal to the velocity in the duct at the sampling point.
Define
Adsorption vs. Absorption
- Adsorption is the process in which atoms, ions, or molecules from a substance (it could be gas, liquid or dissolved solid) adhere to a surface of the adsorbent.
- Absorption is the process in which a fluid is dissolved by a liquid or a solid (absorbent).
What are some air sampling techniques for gases and examples?
- Continuous Flow (Stack Monitor)
- Grab Sample (Lucas Cell)
- Adsorption (Charcoal Canister)
- Condensation (Tritium Monitor)
How is a DAC value generated?
DAC (μCi mL-1) = ALI (μCi) ÷ 2.4 x 109 mL
- 2.4 x 109 mL is derived from the total volume of air (2,400 m3) breathed during a 2000 hour work year.
Define
Derived Air Concentration (DAC)
- If the air concentration is exactly equal to the DAC for one year, a worker will just reach the legal intake of radioactivity, one ALI, on December 31st.
- A worker not receiving any other radiation doses except by inhalation would be allowed a cumulative exposure of 2,000 DAC-hours in one working year.
What is an inexpensive method for screening houses for radon levels?
- A charcoal canister (3” in diameter and 1” high).
- A hole in the lid is covered by a “diffusion barrier” to increase the average sampling time, and holds about 25 grams of activated charcoal.
- Over the course of several days’ exposure, radon gas diffuses into the canister and adsorbs onto the charcoal.
- At the end of the exposure period, the canister is resealed and mailed back to an analytical lab for counting.
What are the alpha emissions from the 222Rn decay chain?
222Rn → 218Po
218Po → 214Pb
// 214Pb → 214Bi → 214Po (beta decay)
214Po → 210Pb
// 210Pb → 210Bi → 210Po (beta decay)
210Po → 206Pb (stable)
Define
Working level
- Any combination of short-lived radon daughters in one liter of air that will result in the emission of 1.3 x 105 MeV of potential alpha energy.
- If radon gas was present at a concentration of 100 pCi L-1, and if the daughter products were all in equilibrium, then the decay through the first 4 daughters would release exactly 1.3 x 105 MeV of alpha particle energy.
- The DAC for Rn-222 is 1/3 the working level.
How does an electret chamber work when measuring for radon?
- An electret is a material that can hold a permanent electrostatic charge.
- A teflon disk holds a charge through both humidity and temperature changes.
- Radon diffuses into a chamber containing the electret and the ionization caused by the radon gas decays and cancels some of the electrostatic charge on the positively charged electret.
- The surface voltage of the electret is measured before and after radon exposure.
- The voltage drop reveals the average radon concentration.
- Can be reused (cost is low) and insensitive to humidity and temperature.
NRC Regulatory Guide 1.97
What 3 levels of radioiondine monitoring are required?
- Reactor plant ⇒ The inplant air must be sampled during normal operations.
- Environmental ⇒ The environs outside the plant must be sampled periodicially.
- Accident monitoring ⇒ The plant must have special high range instruments available for post-accident monitoring.
How is routine monitoring accomplished for radioiodine?
- Sucking air through a collection medium with a high or low volume sampler.
- The collection medium is activated charcoal or silver impregnated zeolite.
- Charcoal cartidges are several times cheaper.
NRC Regulatory Guide 1.97
Monitoring equipment must be able to detect radioiodine in what range?
10-9 to 10-3 µCi cm-3
How do you accomplish tritium air sampling?
- Suck ambient air through an ioniziation chamber.
- Due to the very low energy of the tritium betas, a very sensitive electrometer circuit must be used to detect the tiny current produced inside the chamber by tritium decays.
Which is a higher concern: tritiated water vapor or tritium gas?
- Tritiated water vapor
- Tritiated water vapor can be absorbed easily through the skin while tritium gas produces no skin dose from the extremely weak betas emitted.
What are two problems encountered in water sampling?
- If the water has a high silt level (it’s muddy), then the clay in the silt will act as an ion exchange medium and trap radioactivity when the water is passed through a filter to remove the silt. Dealt with by providing two results, filtered and non-filtered.
- Need to assure that water sample is a representative sample that exists through a large body of water. Due to variations (e.g., temperature, depth), this can be addresssed by collection of multiple sample points.
Safe Drinking Water Act of 1974 (EPA)
What are MCLs for alpha emitters?
- Uranium ⇒ 30 μg L-1
- 226Ra / 228Ra ⇒ 5 pCi L-1
- Adjusted gross alpha activity ⇒ 15 pCi L-1
// Excluding radon and U
Safe Drinking Water Act of 1974 (EPA)
What are MCLs for beta/gamma emitters?
Established by limiting the annual effective dose equivalent to 4 mrem yr-1 for the total body or any single organ.
Why is milk sampled for radioactivity for environmental monitoring?
- Grass is an excellent collection medium for the fallout of fission products.
- Radioactivity can be seen after the grass is processed and fission products are passed to the milk.
Define
Working level month
- An exposure to 1 working level for 170 hours.
- 2,000 working hours per year over 12 months per year equals 170 hours per month.
What is the occupational limit for radon exposure in the United States?
- 4 WLM year-1
- One working level-month produces about one rem CEDE.
Describe
Unattached fraction
- Used by the EPA to estimate the amount of actual radon progeny present.
- Also called the “equilibrium factor”
- Typical value ⇒ 0.5
Radon gas can be found in which naturally occurring decay chains?
All of them
- Actinium (Rn-219)
- Thorium (Rn-220)
- Uranium (Rn-222)
Where do radon daughters inhaled during uranium mining normally deposit?
The lungs
What is the suggested action level for Radon concentrations in homes?
4 pCi L-1
What report is titled BEIR VI 1999?
“The Health Effects of Exposure to Indoor Radon”
Is the oxygen effect significant with radon exposure? Why or why not?
- The effect is not significant for radon exposure because alpha radiation released from radon is high-LET radiation.
- The oxygen effect describes the enhanced biological damage that occurs in the cells when dissolved oxygen is present as a result of the formation of long-lived free radicals.
- This is more significant in low-LET radiation events as they are likely to produce more free-radicals.
What is the best estimate for absorbed dose to the lungs from exposure to radon progeny?
500 mrad WLM-1
List two important radon and radon progeny aerosol properties.
- Radon is a chemically inert gas, so it is primarily exhaled when taken into the lungs while breathing.
- Progeny exist as solid aerosol particles comprised of ions, atoms, and atoms attached to condensation nuclei. This affects their diffusion and deposition on various surfaces of respiratory tract when inhaled.
List three important physiological characteristics of the respiratory tract.
- Thickness of mucous sheet.
- Action of the cilia on the flow of the mucous sheet in clearing particles.
- Thickness and mass of critical target tissue (e.g., basal cells of the bronchial epithelium).
What is a grab sample?
Give an example of a grab measurement for both radon and radon progeny.
Measurements of a radon sample are taken over a relatively short period of time.
- Radon ⇒ Concentration in air is collected in a ZnS(Ag) scintillation cell.
- Radon progeny ⇒ Determined by 3 separate counts of a 5-minute air filter sample (short half-life).
What is an integrated radon sample?
Give an example of an integrated measurement for both radon and radon progeny.
Integrated measurements are proportional to the integrated exposure from radon and radon progeny.
- Radon ⇒ Exposure is determined by the measurement of alpha tracks in a plastic detector.
- Radon progeny ⇒ From integrated TLD response from radiation emitted by progeny collected on a filter paper in a continuous air sampler.
What is a continuous radon sample?
Give an example of a continuous sample for both radon and radon progeny.
A continuous measurement is related to the instantaneous concentrations, or the short-term average concentrations over an extended monitoring period.
- Radon ⇒ Concentration of sampled air that continuously passes through a ZnS(Ag) scintillation cell.
- Radon progeny ⇒ Alpha counts of a filter in a constant air particulate monitor.
List three reasons apparent releases may end up considerably less than expected
- Condensation of radionuclide and subsequent chemical reactions on surfaces including duct work and the stack itself.
- Building ventilation is likely to be filtered.
- Chemical reaction with radionuclide with constituents in the air and formation of particles that settle to surfaces especially if the mean residence time is long.
Assume a release through a pipe to the bottom and in the middle of a wide, shallow, straight river
What is the effect on liquid radioactivity concentration if the temperature of the discharge is increase?
Centerline concentration is expected to increase as the temperature of the discharge is increased because the density of the discharged water is less.
Assume a release through a pipe to the bottom and in the middle of a wide, shallow, straight river
What is the effect on liquid radioactivity concentration from an increased velocity of the discharge?
If release rate Q (Ci sec-1) increases with increased velocity of discharge, assuming the released concentration does not change, the concentration everywhere in the river will increase.
Assume a release through a pipe to the bottom and in the middle of a wide, shallow, straight river
What is the effect on the liquid radioactivity concentration from an increase in the river current?
If the river current F (m3 sec-1) increases, then average concentration C in the river will decrease.
Assume a release through a pipe to the bottom and in the middle of a wide, shallow, straight river
What effect does time have on the concentration of radioactive material in the sediment on the river bottom?
As time (t) increases, the activity concentration C(t) in sediment on the river bottom will decrease with depth in the sediment if the activity release rate Q and sedimentation rate do not change with time.
List five ways to improve the dose estimate for off-site individuals exposed to airborne concentrations of 239Pu.
- Determine particle size distribution and AMAD of collected 239Pu aerosol particles on the filter.
- Correct for the actual AMAD.
- Correcting the calculated respiratory tract deposition for the actual AMAD.
- Determine the inhalation compound classes for 239Pu aerosol particles and take into account when revising.
- Collecting and analyzing deposited plutonium aerosol particles at various downwind locations and take this information into account for number 1-4.
List five ways to reduce the potential long term dose to individuals from brush fires or other high re-suspension events.
- Defoliation agents ⇒ Limit the amount of brush on top of contaminated lands.
- Fire breaks ⇒ Separates contaminated from clean land areas that have a significant amount of brush/fire potential.
- Decontamination ⇒ Remove contamination from areas where the potential exists for a re-suspension of radioactive materials.
- Shelter-in-Place ⇒ Early warning of individuals in downwind locations to shelter themselves and close ventilation (if appropriate for exposure levels).
- Evacuation ⇒ Early warning of individuals in downwind locations to evacuate area (if appropriate for exposure levels).
List four sources of uncertainty in the application of the results from epidemiological studies of populations of underground miners to health effects in the general population.
- Miners were heavy smokers and their data may overestimate the risk to non-smokers (especially if radon & smoke act synergistically)
- Miners may have been exposed to other carcinogens (e.g., diesel smoke) not normally present in the home
- The unattached radon progeny cause most of the dose to the bronchial epithelium. The fraction of progeny unattached to condensation nuclei and other aerosol particles in a mine differ from that in a home.
- The breathing pattern of miners differs from that of occupants of homes.
List four sources of uncertainty when using the respiratory tract as applied to risk estimates from radon exposures
- Unattached fraction ⇒ Fraction of radon progeny unattached to condensation nuclei and other aerosol particles can greatly alter the deposition and dose to the critical bronchial epithelium tissue.
- Mucous sheet ⇒ Thickness can greatly influence the dose to the underlying basal cells. Consequently, thickness varies from smoker to non-smoker and the degree of any respiratory disease present.
- Breathing pattern ⇒ The deposition of radon progeny in various regions of the respiratory tract can vary with breathing pattern (e.g., nose vs. mouth breathing).
- Clearance rate ⇒ The clearance rate of deposited radon progeny aerosols may vary considerably from individual to individual or default values to those in dosimetric model.
List four methods to reduce the radon entry into a home or building
- Seal cracks in foundation.
- Ventilate crawl spaces with outdoor air.
- Maintain a positive pressure in the basement relative to that of soil/gas (use outdoor air for combustion of fuel).
- Strip high levels of radon from well water or absorb radon on charcoal filters before well water is used in the house.
What is the reduction in concentration (“transfer factor”) of radon in water (pCi L-1) to the indoor air concentration (pCi L-1)?
10000 : 1
Define
Derived Concentration Guidance Level
- Action level based on a specific release criterion, exposure pathway, and measurement
- A predicted or measured concentration of a contaminant that would cause a dose or risk equal to the release criterion for a specific exposure pathway
- DCGLs are based on possible exposure pathways, therefore the planned use or reuse of structures does affect the determination of DCGLs
List four factors that must be considered in converting field instrument reading to a specific DCGL
- Detector background counting rate
- Scanning speed and geometry
- Detector intrinsic gamma detection efficiency
- The effect of photon absorption and scatter in soils
Describe five pathways by which radioactivity in soil can contribute to human dose.
- Direct terrestrial exposure to penetrating radiations.
- Transfer of radioactivity from soil to water and subsequent ingestion of water.
- Transfer of radioactivity to air by evaporation, emanation, or other physical airborne entrainment, with subsequent inhalation of radioactive aerosols.
- Absorption of radioactivity from soil by plants and subsequent ingestion.
- Transfer of radioactivity to grazing livestock and subsequent ingestion of milk and other animal byproducts.
What are two parameters that are important to know when conducting a dose assessment from contaminated soil?
- Specific activity of the soil, which determines the mass of suspended soil per unit volume of air that is required to reach a given airborne concentration.
- AMAD and geometric standard deviation of the suspended soil particles, which influence their respiration, deposition, and clearance from compartments within the respiratory tract.
What does trace A represent?
A short term “puff” release of a long-lived radionuclide with no additional releases during the sampling period.
What does trace C represent?
The presence of an exponentially increasing concentration of a long-lived radionuclide.
What does trace D represent?
The presence of a nuclide with a half-life of approximately 20 minutes.
List 3 potential sources of radon in a home
- Radon in soil gas from an open sump
- Unfinished basement, radon in soil gas enters through various pathways (e.g., cracks in the floor)
- Radon in well water escapes into air when water is used in the home
List two radon remediation techniques for an open sump in a home’s basement
- Fill and cap sump hole if not needed
- Cap sump and connect pipe to cap that fans to outside the house ⇒ This maintains a negative pressure in the sump and under the basement floor
List two radon remediation techniques for soil gas emanating from an unfinished basement
- Seal all pathways with plastic sealant
- Put in a subfloor suction system to create a negative pressure
List two radon remediation techniques for well water
- Use aeration system on water intake line, which will strip radon from water
- Place activated charcoal in intake line to absorb radon
Define
Unattached fraction
The fraction of any given radon progeny unattached to condensation nuclei in the air and existing as free atoms or ions, which have a much higher diffusion coefficient than the attached species.
The figure represents the variation of mean dose to the tracheobronchial region of the lung with percent unattached fraction. Explain the reason for the increase in dose with the percent increase in unattached fraction.
- These free atoms and ions quickly diffuse and deposit on walls of the tracheobronchi where they decay and deliver most of the dose.
- The activity of the inhaled air that deposits by diffusion deposition on the bronchial epithelium is essentially independent of breathing rate.
- Therefore, for a fixed unattached fraction, the total dose is directly proportional to the total radon progeny exposure in WLM.
Define
Isokinetic sampling
- Vent, stack, or duct is used to assure that a representative sample of contaminant aerosols is collected.
- This is achieved when the velocity of air entering the sample probe (vS) is the same as the velocity of the exhaust gases (vE) at the sampling location in the exhaust.
When do anisokinetic conditions exist?
When the velocity of air entering the sample probe (vS) does not equal the velocity of the exhaust gases (vE)
vS ≠ vE
What effect do sampling conditions (i.e., vS compared to vE) have on the size of collected sample particles?
- vS > vE ⇒ The sample will have a deficit of larger particles.
- vS < vE ⇒ The sample will have an excess of larger particles.
List five factors that lead to sample line losses.
- Diffusion deposition ⇒ Particles diffuse and deposit on the walls of the sampling system.
- Chemical reaction ⇒ Contaminant aerosols (e.g., radioiodine) react chemically with walls.
- Piping bends ⇒ Impaction of particles at bends in the sampling lines.
- Condensation ⇒ Contaminants condense on walls.
- Electrostatic attraction ⇒ Contaminant ions are electrically attracted to charged wall surfaces.
If copper tubing is used for the sampling line in an air-sampling system, what effect would radioiodine have on the system?
Radioiodine would react chemically with copper.
What additional information would you request in order to confirm a release scenario and reduce the uncertainty in the release estimate?
Request stack monitoring data for
- Analyses of stack filter samples
- Stack gas exhaust flow rate
List five tasks that should be routinely perform to assure the quality of a counting system
- Electronics ⇒ Check integrity of all electronics prior to use
- χ2 test with a standard ⇒ in a fixed position to evaluate counter operation.
- χ2 test without a standard ⇒ Placed in a pre-determined specific position for each count to determine the extra Poisson variance associated with the sample changer.
- Background count of a blank ⇒ Conduct before each sample count and plot on a control chart.
- Standard source check ⇒ Confirms counting efficiency and plot of counting data on a control chart.
Describe one type of hand-held instrument routinely used for detection of uranium contamination on personnel as they leave contaminated areas. Include advantages and disadvantages
Thin window (2 mg cm-2) pancake type GM detector and rate meter.
Advantage
- Low cost
- Durability
- Sensitive to the α/β radiation associated with the decay of uranium & progeny
Disadvantage
- Relatively high background
- Window can easily be punctured/damaged
- Lack of α/β/γ discrimination prevents use when checking for α-emitting contamination in external radiation fields.
List two important Rn/Rn progeny aerosol properties
- Radon is a chemically inert gas, so it is primarily exhaled when taken into the lungs while breathing.
- Progeny exist as solid aerosol particles comprised of ions, atoms, and atoms attached to condensation nuclei.
These properties affect their diffusion and deposition on various surfaces of the respiratory tract when inhaled.
List three important physiological characteristics of the respiratory tract
- Mucous sheet ⇒ Thickness of mucous sheet
- Cilia ⇒ Affects the flow of particles on the mucous sheet in clearing particles.
- Critical target tissue ⇒ Thickness and mass of critical target tissue (e.g., basal cells of the bronchial epithelium)
Define and State an Example
Grab sample
A measurement of a sample taken over a short period of time.
Examples
- Radon concentration in air collected in a ZnS(Ag) scintillation cell.
- Short-lived radon progeny concentration from 3 counts of a 5-minute air sample.
Define and State an Example
Integrated sample
A measurement proportional to the integrated exposure
Examples
- Radon exposure from alpha tracks in a plastic detector exposed over a period of time.
- Radon progeny exposure from integrated TLD response to radiation emitted by radon progeny collected on filter paper in a continuous air sampler
Define and State an Example
Continuous sample
A measurement that can be related to the instantaneous concentration (short term average concentration) over an extended monitoring period
Examples
- Radon concentration of sampled air that continuously passes through a ZnS(Ag) scintillation cell
- Radon progeny from alpha counts of a filter in a constant air particulate monitor
