IAEA-TECDOC-482 PREVENTION AND MITIGATION OF GROUNDWATER CONTAMINATION FROM RADIOACTIVE RELEASES

Transcription

1 IAEA-TECDOC-482 PREVENTION AND MITIGATION OF GROUNDWATER CONTAMINATION FROM RADIOACTIVE RELEASES A TECHNICAL DOCUMENT ISSUED BY THE INTERNATIONAL ATOMIC ENERGY AGENCY, VIENNA, 1988

2 PREVENTION AND MITIGATION OF GROUNDWATER CONTAMINATION FROM RADIOACTIVE RELEASES IAEA, VIENNA, 1988 IAEA-TECDOC-482 ISSN Printed by the IAEA in Austria October 1988

3 ALL PLEASE BE AWARE THAT

4

5 FOREWORD The Agency's plans for establishing safety standards for nuclear power plants referred

6 In preparing this material EDITORIAL NOTE

7 1. INTRODUCTION CONTENTS

8

9 Caps Applicability...

10

11 overview

12 It is known that most gaseous elements and compounds released directly to the ground can diffuse through natural features back to the surface. It is believed that serious groundwater contamination cannot occur in this manner. The penetration of solid material into the aquifer followed by

13 surface water pathways. In many cases this characteristic permits radionuclides

14 2. CHARACTERISTICS OF THE RELEASES 2.1 General Leaks and spills of small, limited amounts of radioactive liquids due to equipment leaks or operator failure may not represent a hazard to the operating personnel

15 Among nuclides with high radiotoxicity 90 Sr exhibits

16 Table

17 Another reason

18 It is highly unlikely that a severe reactor accident, resulting in groundwater contamination

19 The total inventories of the three radionuclides do not differ very much from those presented

20

21 Among

22 Advection/dispersion processes The evaluation of groundwater contamination depends primarily on the hydrodynamic parameters of the aquifer units, principally advection (groundwater velocity) and dispersion. The velocity of groundwater flow may be determined from (1) Darcy's equation, (2) the use of tracers placed in the groundwater,

23 Chemical

24 may be better described as stratified flow or channeling than as a normal Fickian dispersion. Although transport capacity

25

26 particle tracking methods in velocity fields of a known statistical structure is a useful complement to analytical approaches which can become very complex and even unsoluble

27 Since

28 conductivity and the specific yield. the groundwater flow, neglecting For a one dimensional approximation of

29 required data, both at regional and local scales, can be classified into the following groups: plants located at sites having a thick (>50m) unsaturated zone, plants located

30 C. Data for transport source, solute, and chemistry: o Waste from leach rates and contaminant decay constants. o Adsorption data such as K^, bulk density and effective porosity, adsorption-desorption isotherm, mineral charge density, and mineral surface density. o Precipitation-dissolution data such as: solid phase solubility limits, ion activity coefficients, and kinetic coefficients, o Specification data such as chemical equilibrium constants, activity coefficients, and kinetic coefficients. This includes an assessment of the interaction of contaminants with fire retardants

31 o Data on pumping and recharge wells such as location, owner, well design

32 Comparison

33 To avoid some of the difficulties mentioned above, it is recommended to perform the appropriate laboratory measurements with samples of groundwater taken from the boreholes, existing wells or springs. In this context

34

35 o Maps showing isoconcentration contours of various chemical constituents

36 Saturated Zone Sources of uncertainties and technical issues that need to be addressed when assessing water flow

37 Finally, it has to be emphasized that anthropogenic infringement of subsurface flow

38 4. PREVENTION AND MITIGATION TECHNIQUES 4.1 General Owners of nuclear power plant reactors should assess the options of selecting, designing, installing and operating either (1) preventive systems to contain any accidental onsite or offsite release of radioactive material into

39 Active groundwater systems generally can be adjusted better as far as locations and number of installations to respond to changes in groundwater conditions than

40 required volumes

41 o Formations that extend to depths considerably below the depth of

42 An advantage of wells is that construction methods are relatively simple and there is a high degree of design and operational flexibility. However, extreme caution must

43 Design Altering

44

45 Performance considerations Some

46 slurry well construction technique.

47 drain. If a drain is placed at the midpoint between the water table and an impervious layer,

48 o Maintenance of infiltration galleries may be difficult, depending on the configuration of the screen and where it is placed. Therefore,

49 Ground freezing is an energy intensive active system technique that may provide a permanent protection system but would most likely be used for temporary mitigation while more permanent measures

50 Construction Construction of a freeze wall requires the vertical installation in the host medium of a series of steel refrigeration or freeze pipes. Drilling of the freeze holes must be carefully controlled to assure verticality. This is important

51 4.4 Passive systems The passive system consists of various types of engineered barriers. These barriers may be constructed:

52 typically used

53 equipment (walls have been constructed to depths of 80m). The design width of the wall depends on (1) the length of time the wall is to function (i.e. the life of the contaminants to be contained), (2) the permeability of the material used

54 it is extremely important to prevent sloughing of the trench walls during excavation. Accumulation of sloughed material could results in "windows" at the base of the wall.

55

56 is important that

57 Chemical grouts. Chemical grouts usually involve two reagents which when mixed set-up into a gel. The original Joosten two shot process utilized sodium silicate which was pumped into the soil, and followed by calcium chloride. The subsequent reaction

58 Variations

59

60 The material through which the sheet piles are to be driven should have density characteristics that permit the piles to be driven and should be free of boulders which

61 temporary or short-term corrective measure while more long-term or permanent solutions

62 The cap should be keyed into barrier walls surrounding contaminated areas to prevent infiltration of precipitation or escape of gases along the margin Performance considerations Some important performance considerations for caps are: o The required design life of the cap to provide protection for

63 Table

64 Table 5 (cont) o groundwater users in area throughout the operation of the facility a) owner of system b) location

65 5. MONITORING AND SAMPLING

66 From this information, the following maps and cross-sections should be prepared:

67 Monitoring locations should be distributed throughout the site to permit detection

68 Steel

69 Table 6 Examples of methods and frequencies of measurements within the monitoring programme Groundwater Methods Frequency-*- Water table level Piezometric analysis Monthly Chemistry Chemical analysis Monthly Radioactivity Radiometrie analysis Monthly Direction

70 At

71 EPA Recommendations Table 8

72 Table

73 Table 8 (cont) Measurement Vol. Req. (ml) Container^) Preservative'-^' Holding Time Specific Conductance 100 P.G.T Field determined Sulfate 50 P.G.T Cool, Total dissolved solids (TDS) 100 P,G Uranium 200 P,G Vanadium 200 P,G Zinc 200 P,G NOTES: (1) (2)

74 6. QUALITY ASSURANCE

75 Appendix SUGGESTED GROUNDWATER MODELS UNSATURATED FLOW Training Course

76 REFERENCES

77 BIBLIOGRAPHY o Freeze, R.A., Cherry, J.A., "Groundwater" Prentice Hall, Englewood Cliffs, o Bauer, L.D., Gardner, W.H., Gardner, W.R., "Soil Physics",

78 Working Group LIST OF PARTICIPANTS

79 HOW TO ORDER IAEA PUBLICATIONS An exclusive sales agent for IAEA publications, to whom all orders and inquiries should be addressed, has been appointed in