Integrated Final Status Survey (Implementing the FSS) › RTWS › r2d2 › Shared Documents... · Reference Grids Indoors . Alternative coordinate systems for interior surveys: •

Integrated Final Status Survey (Implementing the FSS) Professional Training Programs

Contents

Reference Grids

Fundamental Survey Activities

Measurements and Samples

Scans

Sequence of Survey Activities

Investigation Levels

Survey Instrument Selection

Instrument Selection Case Study

Composite Sampling

2

Reference Grids

3

Reference Grids

General • Personnel should be trained and tested in the use of the

coordinate system.

• The training and testing should be documented.

• Part of the QA program might consist of testing personnel during the FSS.

4

Reference Grids

Outdoors • One reference grid might be adequate for an entire site.

• Multiple reference grids might be established (e.g., one for each survey unit).

• The reference grid might extend beyond the property boundary.

• It might, or might not, be established by professional surveyors. Professionals can be essential on complex/hilly terrain.

5

Reference Grids

Outdoors • The origin of the reference grid is usually in the southwest

corner.

• The spacing between the grid lines depends on the size of the property. Grid lines are usually 10–100 meters apart.

• The grid line intersections are usually marked with stakes.

• In some cases, locations are identified using GPS rather than a conventional reference grid.

6

North-south baseline runs through middle of the property! This can confuse personnel in the field.

Reference Grids

Outdoors

7

Reference Grids

Outdoors North and east coordinates identified as N and E respectively.

This can help personnel in the field.

8

Reference Grids

Indoors This is a two-dimensional reference grid for a three dimensional room! All locations are identified by two coordinates.

9

Reference Grids

Indoors Problems with the preceding system:

• Alpha-numeric coordinates can be confusing if the location being specified is not on one of the lines identified by letters (e.g., you are forced to specify coordinates in the following manner: 11.7m, D + 0.5m).

• When doing the survey, it can be hard to relate the real world to the coordinate system. Some coordinates don’t even exist (e.g., 2,B).

10

Reference Grids

Indoors Alternative coordinate systems for interior surveys:

• Establish a separate reference grid for each surface (i.e., floor, walls, and ceiling).

• Use a three coordinate system (x,y,z).

11


12


General There are two fundamental activities performed in the survey that involve data collection:

• Collect measurements and/or samples

– Unbiased (representative)

– Biased (non-representative)

• Perform scans

13

Soil Structural Surfaces

Scan yes yes Static

Measurements no1 yes

Samples collected yes no2

Fundamental Survey Activities General

1. In some cases measurements of contaminants in soil might be performed by in-situ gamma spec eliminating the need for soil samples.

2. Samples of structural surfaces might occasionally be collected (e.g., paint, smears)

14


15


Unbiased Measurements and Samples • Obtained to estimate the average and/or median

concentration of contamination in the survey unit. Might be assessed using a statistical test

• A secondary function of systematic measurements in Class 1 area is to locate “hot spots” (stumble upon the “hot spot” by accident).

• Locations are selected in a random or systematic pattern.

16


Biased Measurements and Samples • Obtained at locations of elevated activity identified in the

scan

These are obtained to quantify the concentration in a “hot spot” and/or determine its area.

• Obtained at locations chosen using professional judgment

These are obtained to locate “hot spots” that might be missed during the scan—the scan MDC is higher than the measurement MDC.

17


Biased Measurements and Samples • Example locations for judgmental biased sampling or

measurements:

Indoors: Floor drains, near work areas, cracks/joints, anchor bolts in floor, horizontal surfaces

Outdoors: Near loading docks, unusual depressions or mounds, animal burrows, fence line, areas where surface run-off could accumulate

18


Measurements —Structural Surfaces • Determine the alpha and/or beta concentration on

structural surfaces (e.g., dpm/100 cm2).

• MDC of instrument measurement system should be between 10 to 50% of DCGL.

• Fixed (static) measurements are performed often with a scalar using one minute counts.

19


Soil Sampling • Collect surface soil (usually the top 15 cm).

• For radiochemical analysis, 100 grams might be collected.

• For gamma spectroscopy analysis, 1 kg might be collected.

• If a particular vertical contamination profile is expected, standardizing the sampling method is important. For example, use core/plug samplers rather than trowels.

20

In-situ gamma spec using high purity germanium detector can eliminate/reduce the need for soil samples.

More data can be obtained and more quickly.

Makes assumptions about the depth and aerial extent of the contamination.


In Situ Isotopic Analysis

21


Class 1 Areas • Collect the number of data points needed for the purpose

of the statistical tests.

More data points will be needed if the scan MDC is greater than the DCGLEMC.

• Measurements/samples are obtained on a random- start systematic pattern (e.g., triangular pattern).

22


Class 2 Areas • Collect the number of data points needed for the statistical

test (chances are, it won’t be necessary to perform the Sign test or WRS test in a Class 2 survey unit).

• Measurements/samples are obtained on a random-start systematic pattern (e.g., triangular pattern) as in a Class 1 survey unit.

23


Class 3 Areas • Collect the number of data points necessary for the

statistical tests (it should never be necessary to perform the Sign test or WRS test in a Class 3 survey unit).

• MARSSIM recommends that all the measurements and samples in Class 3 areas be taken at random locations. Nevertheless, there is no apparent reason why they could not be obtained systematically given a random start.

24

Scans

25

Scans

General • Scans are performed to identify small areas of elevated

activity (hot spots) that could exceed the release criteria.

• Detector is moved over the potentially contaminated surface.

26

Scans

General • Monitor audible output of meter for detectable changes in

count rate.

• Mark locations of elevated radiation (count rates exceeding the investigation level).

• Document scan results.

• In Class 1 areas, the scan MDC should be less than or equal to the DCGLEMC.

27

Scans

Structural Surfaces • Structure surfaces are scanned for alpha and/or beta

contamination

• Probe should be less than 0.5–1 cm above surface

• Speed should be one half to one full probe width per second

• Usually a good idea to also perform a simple gamma scan indoors

28

Scans

Soil • Land areas scanned for gamma radiation

• Probe (usually 1.5–2 inch NaI) swung over ground

• Probe within 10–15 cm of surface

• Surveyor moving at 0.5 m/s

29

Scans

Computerized Systems • The detector output and location are stored electronically

as the detector scans the surface.

• The detector location might be determined via GPS, laser ranging, or some other method.

• The scan is perfectly documented. Unlike people, computers don’t lose concentration.

30

Scans

Computerized Systems • If the detector to surface distance and the scan speed are

fixed, the regulator might allow the data to be considered quantitative in nature.

• In this case, the scan and the fixed measurements are effectively combined into a single activity.

• Since the contamination in the survey unit is completely characterized, there might be no need to obtain fixed measurements or samples.

31

Scans

Computerized Systems • In many cases, the computerized scan will not be

considered sufficiently quantitative to bypass the need for fixed measurements or samples.

• Nevertheless, the quality of the data and the documentation are far superior to those of a conventional scan where the data is recorded manually.

32

Laser ranging system

Scans

Computerized Systems

33

Shonka Position Sensitive Proportional Counter. Data and detector location transmitted to computer. Location of contamination determined mechanically and electronically.

Scans


34

Gamma scan data and surveyor location (determined by GPS) logged then downloaded to computer for display and data analysis. Soil samples are still needed.

Scans


35

Scans

Scan Coverage Class 1: 100% surface coverage

Class 2: 10–100% coverage; effort should be proportional to contamination potential, with judgmental scans in areas with highest probability of elevated activity

Class 3: Judgmental (<10%); scan areas with highest potential for contamination based on professional judgment

36


37


General • Investigation levels are radionuclide-specific.

• They might be expressed as a count or count rate.

• They can also be expressed as a concentration (e.g., pCi/g, Bq/kg, dpm/100 cm2).

38


General • The investigation level is expressed as a count rate (e.g.,

cpm) so that the surveyor performing a scan on a structural surface or soil will know when an investigation is necessary.

• The investigation level might be expressed as a count so that the surveyor performing a measurement on a structural surface will immediately know when an investigation is required.

39


General • The investigation level might also be expressed as a

concentration (e.g., pCi/g, Bq/kg) so that the person reviewing the data (rather than the surveyor) will know when an investigation is required.

40


General • When an observed count, count rate, or concentration

exceeds the investigation level, an investigation is required.

• The first step in the investigation is to confirm the measurement.

• Results of each investigation and corresponding actions (e.g., remediation) must be documented.

41


MARSSIM Recommendations

Class 1 Area • MARSSIM recommends that the investigation level be set at

the counts or count rate that equate to levels > DCGLEMC.

• If found, such areas should be remediated and resurveyed.

42



Class 2 Area • MARSSIM recommends that the investigation level be set at

the count or count rate that equate to levels > DCGLW

• If found, the survey unit might be reclassified as Class 1.

43



Class 3 Area • Establishing the investigation level can be problematic for a

Class 3 area since the scan MDC might be above the DCGLw (let alone the boundary between a Class 2 and Class 3 area).

• The lowest value that can be lived with might be used.

44



Class 3 Area • Measurements exceeding the DCGLW indicate that the area

should be remediated as necessary. The area should then be reclassified as Class 1 (some portions might remain Class 3).

• If significant contamination is identified, but at a level below the DCGLW, the area might be reclassified as Class 2.

45


46


Recommended Instruments for Alpha and Beta Scans and Measurements Alpha

• Gas flow proportional

• ZnS scintillator

Beta

• Gas flow proportional

• Pancake GM

• Beta plastic scintillator

47


Advantages of Gas Flow Proportional Counters for Alpha and Beta Scans and Measurements: • The probe areas can be much greater than those of a

pancake GM. This allows them to scan large areas much quicker.

• The window thickness (ca. 0.8 mg/cm2) is typically one half the window thickness of a pancake GM (ca. 1.5 mg/cm2). This gives them superior efficiency, especially for low-energy beta emitters.

48


Recommended Instruments for Gamma Scans: • NaI gamma scintillator (2” × 2” standard)

• FIDLER (for low energy photons)

• In some cases, multiple vehicle mounted NaI detectors or large plastic scintillators are employed

49

50


51


Scenario We will evaluate the effect of instrument selection on our project budget.

The two possible instruments are being considered for scanning the survey unit.

Soil samples are also taken in the survey unit to allow a statistical assessment of the contamination.

52


Given: • Contaminant is Am-241, a low energy gamma emitter (59.5

keV)

• Class 1 survey unit

• Survey unit area is 1,300 m2

• DCGLW for Am-241 is 10 pCi/g (370 Bq/kg)

• 25 soil samples must be analyzed for the purpose of the statistical tests

53

25 systematic sampling locations


54


To find potential hotspots, we must scan 100% of the survey unit.

We have two instruments to choose from for the scan:

• A standard 2” × 2” NaI detector

• A more costly and more sensitive FIDLER

55


Sodium Iodide (NaI ) Scintillator • Standard 2” × 2” crystal

• Scan MDC of 31.5 pCi/g (1166 Bq/kg)

• Since the scan MDC is greater than the DCGLW of 10 pCi/g (370 Bq/kg), it is possible that the scan MDC also exceeds the DCGLEMC.

• If the scan MDC exceeds the DCGLEMC, additional samples will be required.

56


Sodium Iodide (NaI ) Scintillator • We must calculate the DCGLEMC for the area bounded by

four measurement points:

The area bounded by four measurement points is the survey unit area divided by the number of samples: 1300 m2/25 = 52 m2

Assume that the area factor (AF) for 52 m2 is 2.4. Therefore, the DCGLEMC is 24 pCi/g or 888 Bq/kg (DCGLW × AF).

57

Hotspot with lowest DCGLEMC that would not be identified by systematic soil samples

52 m2


58

52 m2

Hotspot at DCGLEMC of 24 pCi/g delivers 25

mrem


• This hotspot cannot be detected by the scan because the scan MDC is 31.5 pCi/g.

This is a big problem.

We have to do something. What?

59


Sodium Iodide (NaI) Scintillator • We must increase the number of samples so that the

DCGLEMC for the new (smaller) area bounded by four measurement points equals the actual scan MDC (31.5 pCi/g or 1166 Bq/kg).

• Determining the new required number of samples involves three steps:

60


Sodium Iodide (NaI) Scintillator Step 1. Determine the required area factor for the new

(smaller) area bounded by four measurement points.

To do this, divide the actual scan MDC (31.5 pCi/g) by the DCGLW (10 pCi/g).

The required area factor for this area is 3.15 (31.5/10).

61


Sodium Iodide (NaI) Scintillator Step 2. Determine the area that has the required area factor.

Assume that our table/graph of area factors indicates that 11.1 m2 has an area factor of 3.15.

62


Sodium Iodide (NaI) Scintillator Step 3. Determine the required number of samples.

To do this, divide the survey unit area (1,300 m2) by the new area (11.1 m2).

The number of required soil samples is 117 (1,300 m2/11.1 m2).

63

Sodium Iodide (NaI) Scintillator

• An 11.1 m2 hotspot at the DCGLEMC of 31.5 pCi/g can be detected by the scan because the scan MDC is 31.5 pCi/g.

Good!

Hotspot (11.1 m2) at 31.5 pCi/g

delivers 25 mrem


64


• But, if the hotspot were larger (e.g., 30 m2), the DCGLEMC (e.g., 28 pCi/g) would be less than 31.5 pCi/g, and the hotspot would be missed by the scan.

• Is this a big problem?

Hotspot (30 m2) at 28 pCi/g delivers

25 mrem


65


• No, it is not a major problem because the analysis of the soil samples (the white dots) would indicate elevated concentrations that would hopefully trigger an investigation.

Hotspot (30 m2) at 28 pCi/g delivers

25 mrem


66


Consider the FIDLER for the Scan • The other detector sometimes used to scan for Am-241 is

the FIDLER

• Compared to the NaI detector, the FIDLER has both advantages and disadvantages.

67


FIDLER • A FIDLER (Field Instrument for the

Detection of Low Energy Radiation) is a large-area thin-crystal NaI scintillator with a thin window.

• Fairly heavy and fragile.

• Primarily intended for low energy gammas and x-rays (e.g., Am-241 59.5 keV gamma).

68


FIDLER • The FIDLER’s scan MDC of 6 pCi/g or 222 Bq/kg is less than

the DCGLW (10 pCi/g or 370 Bq/kg), let alone the DCGLEMC of 31.5.

• No additional samples would be needed above the 25 required for the purpose of the statistical tests!

69

Item NaI (2” × 2”) FIDLER Scan MDC 31.5 pCi/g 6.0 pCi/g

Equipment cost $2,000 $5,000

Scan rate 0.5 m/s 0.25 m/s

Time to scan survey unit 0.7 hours 1.4 hours

Cost for scan ($50/hour) $35 $70

Number of samples 117 27 Sample cost $14,625 $3,375

Total cost $16,660 $8,445


Cost Comparison

70

Composite Sampling

71

Composite Sampling

Scenario Contaminant is Am-241

DCGLW is 10

Class 1 survey unit

Ten samples are needed for the statistical tests

Scan MDC is above the DCGLEMC. As such, the number of soil samples must be increased to 18.

72

But 18 samples are needed to allow for poor scan MDC!

Only 10 samples needed for purpose of statistical tests

Each extra sample that has to be analyzed by the lab increases our costs. There is a solution: composite sampling.

Composite Sampling

73

Composite 16 of the 18 samples in pairs. There are now 10 samples to send to the lab for analysis—enough to meet the needs of the statistical tests!

Composite Sampling

74

4

4 5

5

2

2 3

7

11

10

Composite Sampling

The concentrations are indicated in red.

The DCGLEMC is 12.

Is there a problem?

75

4

4 5

5

2

2 3

7

11

10

These samples will have to be analyzed separately.

Composite Sampling

Is there a problem?

YES!

One of the two samples used in this composite might have exceeded the DCGLEMC of 12!

76

Composite Sampling

The trigger concentration (T) that will require the samples used in a composite to be analyzed separately is:

𝑻𝑻𝑻𝑻𝑻𝑻𝑻𝑻𝑻𝑻𝑻𝑻𝑻𝑻 𝑻𝑻 =𝑫𝑫𝑫𝑫𝑫𝑫𝑫𝑫𝑬𝑬𝑬𝑬𝑫𝑫

𝑵𝑵𝑵𝑵𝑵𝑵𝑵𝑵𝑻𝑻𝑻𝑻 𝒐𝒐𝒐𝒐 𝒔𝒔𝒔𝒔𝑵𝑵𝒔𝒔𝒔𝒔𝑻𝑻𝒔𝒔 𝑻𝑻𝒊𝒊 𝒄𝒄𝒐𝒐𝑵𝑵𝒔𝒔𝒐𝒐𝒔𝒔𝑻𝑻𝒄𝒄𝑻𝑻

In the previous example, the trigger was 6.

For a discussion of composite sampling, see Section 14.3 in NUREG 1505.

77