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aged concrete, Alkali Silica Reaction, ASME, ASR, ASR damage, chloride damage, concrete containment, concrete structures, cracked concrete, crystalline structure, earthquake hazards, gamma radiation, hydrogen damage, hydrogen gas, hydroxyl, material testing, nuclear containment, nuclear power, Nuclear Power Stations, nuclear radiation, nuclear reactors, nuclear waste, nuclear waste hazard, potassium chloride, radiation damage, radioactive waste, radiolysis, Safety, salt, salt damage, sodium chloride, USNRC
[The problem of concrete degradation at nuclear power stations, including spent fuel pools and dry cask storage remains, even though the comment period for which this was written is past.]
Comment deadline was on March 30th, for whether the US NRC should use proper methods to detect concrete degradation at Nuclear Power Stations: “The petitioner requests that the NRC amend its regulations to improve identification techniques against ASR concrete degradation at U.S. nuclear power plants. The petitioner suggests that the reliance on a visual inspection does not ‘adequately identify Alkali-Silica Reaction (ASR), does not confirm ASR, or provide the current state of ASR damage (if present) without petrographic analysis under current existing code.” http://www.regulations.gov/#!docketDetail;D=NRC-2014-0257 The need for ultrasonic testing for damage to the nuclear reactor pressure vessel is critically important, though it was strangely not on the docket. See: https://miningawareness.wordpress.com/2015/03/03/nuclear-reactor-cracks-widespread-disease-scourge-warns-nobel-in-chemistry-nominee/
William et.al.-NRC, 2013
“NRC Chairman Allison Macfarlane uses a flashlight to closely examine cracks in a concrete wall at the Seabrook nuclear plant in New Hampshire. The cracks are caused by a chemical reaction in the components of the concrete…” (USNRC-Flickr)
The average age of US commercial nuclear reactors is 34 years with the oldest being over 45 years old (EIA, 2015). Even in the best of circumstances, concrete suffers age related damage. But, nuclear power stations suffer from extreme conditions. According to William et. al., for the NRC (2013):
“All commercial NPPs in the United States contain concrete structures whose performance and function are necessary for protection of the safety of plant operating personnel and the general public as well as the environment. A myriad of concrete-based structures are contained as a part of a light-water reactor (LWR) plant to provide foundation, support, shielding, and containment functions. Typical safety-related concrete structures contained in LWR plants may be grouped into four general categories: primary containments, containment internal structures, secondary containments/reactor buildings, and other structures… there may be a coupling effect between radiation and ASR that can potentially accelerate ASR activity or cause ASR to occur with aggregates that are not normally reactive. As plants age, the potential of ASR to occur in structures forming the biological shield or support for the reactor pressure vessel may increase as these structures are located in areas in which they are subjected to moderate elevated temperature in combination with radiation… ASR capable of being detected visually, however, is probably in a fairly advanced stage of development“. (William et. al. NRC, 2013, p. 83, pp. 88-89)
Unfortunately, the problem of concrete and radiation isn’t going away on 11.59 pm Monday. Not only is concrete used in nuclear power stations, but it is also an issue for spent fuel pools, dry cask storage, burial of nuclear waste – whether a “facility” like WIPP, or burying it in concrete lined trenches or burying concrete casks in unlined trenches. Also it may be used for above ground temporary storage of nuclear waste. For these other problems one must also take into consideration high LET alpha radiation-bombardment, along with low LET gamma radiation and high LET neutron bombardment. Worse, someone had the stupid idea of putting concrete in some nuclear waste storage drums with the waste.
Additionally, if you replace the silicon (Si) in concrete with carbon, not only can you start to think about the damage to carbon steel, but also radiation damage to all known living beings on earth, since they have carbon as their base. Because of its randomness, damage from very low levels of ionizing radiation in living beings can sometimes be repaired, but the risk is that repair can be faulty, leading to mutations and genetic damage and possibly cancer or other diseases. Thus, there is no safe dose of ionizing radiation. Still there is active repair, which is lacking in non-living materials.
Yesterday we discussed mostly about generic ASR, and how it impacts nuclear power stations and some theory of radiation impacts: https://miningawareness.wordpress.com/2015/03/28/nuclear-power-stations-need-testing-for-concrete-damage-comment-deadline-monday-march-30th-11-59-et/
Except as otherwise noted, the following is highlights-extracts from a document prepared for the US NRC, which deals more specifically with the impacts of radiation on concrete. (If you are a US taxpayer, you paid for it.) We only found it yesterday. It’s more interesting than the title would have you believe.
“A Review of the Effects of Radiation on Microstructure and Properties of Concretes Used in Nuclear Power Plants“, by William et. al. NRC, 2013, NUREG/CR-7171 ORNL/TM-2013/263
(Full citation and link at bottom; note author affiliations).
“8.2 SPECIFIC CONDITIONS RELATED TO THE EFFECT OF RADIATION ON CONCRETE
NPP concrete structures, particularly those related to the biological shield or support for the reactor pressure vessel, can be subjected to neutron and gamma radiation during their service lives. As the service lifetimes of these plants are being extended, the impact of radiation on the concrete structures may have increased significance that can affect their functional and performance requirements. Irradiation of concrete has the potential to impact the concrete’s microstructure as well as its mechanical and physical properties. An assessment of the impact of radiation on the concrete microstructure and properties would require removal of concrete samples from the areas of interest and application of techniques such as identified in Tables 8.1 and 8.2.
In addition to the impacts of radiation on the microstructure and properties of concrete, radiation can contribute to elevated temperatures in the concrete as well as increased potential for ASR and concrete carbonation to occur. Techniques associated with identification of concrete that has experienced or is experiencing elevated temperatures, ASR, or carbonation may also provide indications that the concrete has been affected by radiation.” (William et. al. NRC p. 87)
“Under nuclear radiation, the internal structure of some aggregates can be converted from an ordered crystalline structure to a disordered structure, resulting in a decrease in specific gravity and an increase in volume.” ( William et. al. NRC p. 93)
The US Dept. of Transportation offers an illustration of how a disorderly structure is more prone to Alkali Silica Reaction (ASR). Radiolysis of water provides hydroxyl radicals needed for ASR to occur.
Si is silicon; Na is sodium; K is potassium, O is oxygen, OH is the hydroxyl. Silica “reactivity depends on the crystal structure of the silica rather than its chemical composition. For example both quartz and opal are silica minerals and are predominantly composed of silica (SiO2); i.e., they are of similar composition (although opal has varying proportion of water, usually 3 to 9 percent). Quartz has a well-ordered crystal structure (figure 7) and is very stable in concrete at normal temperatures. Opal, on the other hand, has an internal structure consisting of more-or-less densely packed aggregate of spheres of silica (cristobalite and/or tridymite) and is highly reactive in concrete.” US Dept. of Transportation:
http://www.fhwa.dot.gov/publications/research/infrastructure/pavements/concrete/06133/002.cfm
William et. al.-NRC, 2013 restarts here:
“3.2 IMPACT OF IRRADIATION ON THE CRYSTALLINE STRUCTURE OF AGGREGATES
Under nuclear irradiation, the atomic structure of some aggregates can be converted from crystalline structure to distorted amorphous structure with a decrease in specific gravity and an increase in volume (Kontani et al. 2010). Two negative impacts are associated with the conversion. One is that the distorted internal structure leads to higher reactivity of the converted aggregates, which may make the aggregates more reactive to certain aggressive chemicals. A typical example is the ASR of concrete, which is discussed in detail in Section 6. The other negative impact is that the increase in volume can cause microcracking of concrete.” (p. 11)
“5. THE EFFECTS OF NUCLEAR RADIATION ON PROPERTIES OF CONCRETE
5.1 INTERACTION BETWEEN NUCLEAR RADIATION AND THE INTERNAL STRUCTURE OF CONCRETE
There are two types of interactions between nuclear radiation and the internal structure of concrete. One is related to geometric changes of the structure resulting from displacements of atoms from their lattice sites. The other is related to phase transformations of the constituents in concrete, resulting in reduction in porosity and/or formation of microcracks. As a result, the geometric changes and phase transformations can produce changes in properties of concrete. The geometric changes to the internal structure of concrete will be discussed first, followed by the phase transformations.
A crystalline structure can be visualized as a three-dimensional lattice or grid formed by an orderly arrangement of atoms. During gamma and neutron irradiation of concrete, the atoms in the lattice structure of some constituents in the concrete are displaced from their lattice sites. This displacement results in a new formation that is less stable than the previous one. This type of defect is known as a dislocation, or a lattice defect, and has an effect on the mechanical properties of materials, including strength and ductility. Dislocations can also contribute to macroscopic swelling, or geometric expansion, leading to an increase in internal stresses and strains…. The phase transformation noted above is similar to the natural carbonation reaction in concrete, a reaction of portlandite with CO2 to form calcite and water. The difference is that the natural carbonation reaction takes place at the surface layer of concrete, where CO2 comes from the environment and penetrates into the concrete through diffusion, whereas the radiation-induced carbonation occurs in the concrete that has been irradiated and THUS IS NOT LIMITED TO THE SURFACE OF A CONCRETE STRUCTURE.” (pp. 39-40 Caps added)
“… The effects of radiation on the components of concrete (aggregate and cement paste) translate to effects on properties of concrete itself, such as compressive strength, tensile strength, modulus of elasticity, and thermal expansion….” (p. 43)
“Water in the concrete can be decomposed by gamma rays by a process called radiolysis and can be converted to hydrogen, oxygen, and hydrogen peroxide. Water can also be removed from the concrete by evaporation due to heat generated by gamma radiation. Because most of the water in concrete is contained in the cement paste, gamma radiation has a greater effect on the cement paste than it has on the aggregate materials.
In the instance of neutron irradiation, the neutrons do not interact with the electrons but with the nuclei of atoms. Because neutrons interact with the nuclei of atoms, the lattice spacing within the material may change after the collisions. Therefore, the neutrons have a more significant effect on dense and well-crystallized materials (e.g., aggregates) than on randomly structured materials with high porosity (e.g., cement paste). Interactions between nuclear radiation and the internal structure of concrete produce geometric changes of the structure resulting from displacements of atoms from their lattice sites and phase transformations of the concrete constituents resulting in a reduction in porosity and/or formation of microcracks. These interactions result in changes in the various concrete properties.
A summary of the effects of neutron and gamma radiation on the mechanical and physical properties of concrete is provided. Information is presented on thermal effects due to gamma heating of the concrete. Coupling effects of mechanical loading, thermal effect, moisture content, and radiation are described” (p. xv)
“… concrete is widely used for primary and secondary containment structures of nuclear power plants (NPPs) exposed to radiation and elevated temperatures. Besides being a basic infrastructure material, concrete is used to build shielding structures and interim storage facilities for spent nuclear fuel. Radiation and temperature effects on the properties of concrete depend on a range of variables, such as the intensity of the radiation field, the temperature level, and the period of exposure. In addition to the separate effects of radiation and temperature, there is also a one-way coupling effect between the two (i.e., a radiation-induced thermal effect).
There are two types of radiation in NPPs” [Ed. note: assuming that alpha stays mostly in the reactor pressure vessel and that alpha emissions do not come into contact with concrete], “neutron radiation and gamma rays. Neutron radiation is the emission of neutrons; gamma rays are a special form of photon radiation. The two types of radiation interact with concrete in different ways. A variety of concrete materials, with different types of cement, aggregates, and additives, have been used in NPPs. Some concretes are more susceptible to gamma radiation, and others are more susceptible to neutron radiation, depending on the constituent materials used in the mix.
Elevated temperatures have two different effects on concrete. One involves phase transformations of the concrete constituents under high temperatures; the other refers to mechanical damage in the form of spalling. Both effects may result in significant deterioration of the stiffness, strength, and ductility of concrete and concomitant loss of load-bearing capacity. Phase transformations depend primarily on the temperature level, but not on the rate of temperature changes. Spalling damage occurs under high heating or cooling rates. A moderate elevation in temperature can occur in concrete exposed to gamma radiation.“(p. 1)
“Nuclear reactions are driven by the transformation of atoms; typically, atoms of one element are converted into atoms of another element. This process is different from chemical reactions. Chemical reactions usually involve electrons being shared, or transferred, to form compounds.” (p.3)
“3.5 THE STATES OF WATER IN CONCRETE…
The water content in cement paste is important to the effect of radiation on the properties of concrete….” p. 20
“The change of water content in concrete is important for radiation shielding because the loss of adsorbed water and interlayer water, by change of temperature and/or relative humidity, is one of the causes for drying shrinkage, which can result in shrinkage cracking. The loss of adsorbed water by a change of loading is one of the causes for creep; the loss of chemically combined water through dehydration reduces both the strength and stiffness of concrete.
The energy transfer during the collision of a neutron and a nucleus is proportional to the mass of the neutron and the mass of the nucleus. If the mass of the nucleus is similar to the mass of the neutron, larger energy transfer will occur.
… using w/c as an experimental parameter resulted in other major changes in the concretes. The concrete strength was reduced by increasing w/c,… increase in w/c reduces the strength of concrete because the porosity of concrete increases…” p. 21 [w/c is water concrete ratio]
“4. HEAT OF RADIATION AND THE THERMAL STRESS DUE TO RADIATION
Irradiation of concrete by neutron and gamma radiation can lead to an increase in temperature of up 250°C (Fillmore 2004). Such a large increase in temperature can have significant impacts on the mechanical and radiation-shielding properties of concrete. Granata and Montagnint (1972) and Acevedo and Serrato (2010) reported that concrete samples were heavily damaged when heated to 280°C (a temperature commonly reached in heavy-water reactors) and at a fluence of 1020 n/cm2.
In general, high temperature causes two forms of damage in concrete. One is the deterioration in mechanical properties of concrete, such as physico-chemical changes of the cement paste and aggregate (so-called phase transformations), and thermal incompatibility between the aggregate and the cement paste. The other one is spalling of concrete. Spalling can result in severe reduction of cross-sectional area, leading to the exposure of the interior concrete to excessive temperatures, which in turn causes further spalling damage, called progressive spalling damage. There are several theories explaining the spalling mechanisms of concrete under high temperature, which will not be discussed here (See Willam et al., 2009). Experimental results have shown that spalling damage occurs under a high heating rate in the temperature range of 200°C to 350°C… Spalling of concrete typically occurs near the concrete surface, but may occur at depths up to 50% its cross section thickness…
The heat of radiation affects properties of concrete at two levels: the structural level and the microstructural level. At the structural level, the thermal gradient due to the heat of radiation results in thermal stress, which may be high enough to create damage in concrete. At the microstructural level, the mismatch of thermal strains in cement paste and in aggregate responding to the heat of radiation may cause a large stress at the interface between the aggregate and cement paste, which may cause microcracking in the cement paste.
4.1 HEAT GENERATED BY GAMMA AND NEUTRON IRRADIATION
Radiation energy is converted to heat when absorbed by a shield. The heat generated by irradiation can reach quite high temperatures, depending on the shielding material used and the configuration of the shielding structure. Hilsdorf et al. (1978) noted a temperature as high as 250°C was developed in some of the investigations he summarized, which is high enough to generate considerable damage in shielding materials. Therefore, the heat generated by gamma and neutron radiation is very important in that it can impact the functional and performance requirements of the shield…“(p. 25)
“… In the case of neutron irradiation, the heat generated by the process can be divided into direct and indirect heat. For elastic scattering, no gamma ray is generated, and the heat generated by the interaction of neutrons and nuclei is deposited at the site of interaction. For inelastic scattering, the heat generated by the interaction is deposited on site (direct heat), but the gamma rays produced by the interaction deposit their energies at various distances from the site of reaction (indirect heat)…“(p.26)
“4.2 TEMPERATURE VARIATION DUE TO THE HEAT OF RADIATION
After the heat generated by the irradiation is determined, the temperature field in a shielding structure can be evaluated by considering the heat of radiation as a heat source in a thermal analysis for the shielding structure. Because the irradiation effect is a long-term effect and shielding structures are usually very large (such as a thick wall of a biological shield), a one-dimensional steady-state thermal conduction equation with a heat source can be used for evaluating temperature distribution due to irradiation by gamma rays…“(pp. 27-28)
“4.3 MACROSCOPIC THERMAL STRESS IN SHIELDING STRUCTURES DUE TO RADIATION
Thermal stresses occur in a shielding material due to the heat of radiation at two different scale levels. One, which is due to the temperature gradient as noted in Eq. (4.12), may be called macroscopic thermal stress.. The other one, which is due to the differential thermal expansions of the constituent phases in the shielding material that occur even under a uniform heating of radiation, may be called microscopic thermal stress. The macroscopic thermal stress due to the gamma and neutron irradiation is discussed in this section. Microscopic thermal stress is discussed in the Section 4.4…. The thermal stress calculated this way is the thermal stress induced by the heat of radiation. The effect of irradiation on transport and mechanical properties of shielding materials must also be considered. For example, gamma and neutron radiation can have an impact on the thermal conductivity, coefficient of thermal expansion, modulus of elasticity, and Poisson’s ratio. These effects will be discussed in the following chapters.
4.4 MICROSCOPIC THERMAL STRESS IN CONCRETE DUE TO RADIATION
When exposed to neutron irradiation, concrete increases in volume, with the increase mainly due to a change in volume of the aggregate in the concrete (Kontani et al. 2010). When subjected to fast neutron irradiation, the lattice structure of the minerals in aggregates is disturbed, leading to an increase in volume. The crystalline lattice structure present in the aggregates is much more affected by neutrons than the more-amorphous lattice structure of the cement paste. On the other hand, the volume of cement paste decreases, exhibiting shrinkage that is due to the evaporation of pore water under the heat of radiation and due to the phase change of water under irradiation. The mismatch of expansion in aggregate and shrinkage of cement paste may cause damage in the interface between the two phases…
Microscopic thermal stress analysis is more complicated than macroscopic thermal stress analysis. The damage development depends on both the size and shape of the aggregates….”
pp. 30-31
“5.2 COMPRESSIVE STRENGTH
A general assessment is that compressive strength of concrete decreases under gamma and neutron radiation exposure… reduction in strength may be due to the combined effect of neutron and gamma radiation instead of only gamma radiation” (p.45-46)
“5.3 TENSILE STRENGTH
… The results indicate that for a neutron fluence of 5 × 1019 n/cm2, the tensile strength of irradiated specimens can be 20% to 80% less than the strength of unirradiated and unheated specimens, as shown in Figure 5.12. Thus, depending on the test conditions and the radiation level, the tensile strength of concrete can be reduced significantly. (p. 53)
“5.4 MODULUS OF ELASTICITY
Similar to the strengths of concrete, the stiffness, or modulus of elasticity, of concrete is reduced under nuclear radiation, as shown in Figure 5.15 (Hilsdorf et al. 1978). In the figure, “Ec/Eco” is the ratio of the modulus of elasticity after irradiation and heating to the modulus of elasticity before irradiation and heating. A neutron fluence in the range of 1 × 1019 n/cm2 leads to a slight decrease of the modulus of elasticity. When the fluence was larger than 5 × 1019 n/cm2, the reduction can be as high as 30% of the original stiffness“. ( p. 55) [Ed. note: 19 is a superscript so x 10 to the 19th]
“5.5 CREEP, SHRINKAGE, AND VOLUMETRIC VARIATION
… elasticity of irradiated concrete is expected to be lower than that of regular concrete, and thus the creep of irradiated concrete would be expected to be higher… The cement paste undergoes shrinkage while the aggregate expands under neutron radiation. Thus, the amount of shrinkage of cement paste and the amount of expansion of aggregate determine the overall volumetric variation of the concrete.“(p. 56-57)
“…With increasing age of nuclear reactors in service in the United States and around the world, deformation properties of concrete, such as creep and shrinkage, have increased importance for long-term performance evaluation of the concrete structures…
The creep test data in Figure 5.19 indicate that (1) the creep rates (the slopes of the curves) of dry-stored concrete samples decreased at about one year after loading, the rates remained the same all the way to 30 years, and there was no sign for the asymptotic trend of the ultimate creep; and (2) the rates of wet-stored concrete samples started to increase after about 10 years. The range of the measured 30 year creep coefficient was from 1.2 to 9.2, depending on the water/cement ratio (or strength) and aggregate type. For those test data, specific creep and creep compliance were underestimated by all methods of prediction“. (p. 58)
“5.7 EFFECT OF LOW TEMPERATURE…
Under a low temperature, ice may form in concrete and the volume expansion associated with the ice formation may cause damage in concrete. The damage induced by low temperatures will have an impact on the shielding capacity of concrete…the results are important from the perspective of indicating the potential impact of damage (i.e., cracking) on the attenuation of shielding concretes.” (p.61)
“6.1 ASR AND THE COUPLING EFFECT BETWEEN ASR AND RADIATION
Ichikawa and Koizumi (2002) and Ichikawa and Kimura (2007) showed that ASR nonreactive aggregates can become reactive (or ASR-sensitive) under irradiation, depending on the intensity of the radiation, the reactivity of the aggregate, and the alkali content of the cement. Therefore, ASR and the possible coupling effect between ASR and nuclear radiation have become important research topics.
6.1.1 ASR of Concrete
The alkali-silica reaction (ASR) in concrete can be described as a chemical reaction involving alkali cations and hydroxyl ions from concrete pore solutions (Hobbs 1987). ASR will produce a gel that swells with the absorption of moisture. The amount of ASR gel and the swelling pressure vary depending on the reaction temperature, type and proportions of the reacting materials, gel composition, gradation of aggregates, and other factors. Sometimes the pressure generated by ASR gel in concrete is sufficient to generate and propagate microcracks in the concrete.” p. 63
“the aggregates may react with surrounding cement paste in concrete to generate greater expansion due to neutron radiation than that experienced by the aggregate alone. Ichikawa and Koizumi (2002) considered this additional expansion as possibly occurring as a result of a coupling effect between ASR and radiation.
The experimental study by Ichikawa and Koizumi (2002) showed that the reactivity of silica-rich quartz to alkali may be significantly increased by nuclear radiation.” (p.64)
“When the combination of aggregate and cement is quite close to the critical condition for a detrimental ASR, then the increase in aggregate reactivity due to nuclear radiation could become a very important factor, making a nonreactive aggregate ASR-sensitive.” (p. 65)
“6.3 RADIOLYSIS AND EVAPORATION OF WATER
The decomposition of water under radiation is called radiolysis. It is different from vaporization of water under elevated temperature, as shown in Figure 6.3. Both interstitial water and water in the pore structure of concrete may participate in the radiolysis process. One of the products of radiolysis is hydrogen gas, H2. In addition to the effects of radiolysis resulting from radiation noted in Chapter 2, water radiolysis is important for dry storage facilities and for radioactive waste conditioning. For long-lived wastes, concrete materials are used as an immobilization matrix undergoing mixed irradiation (i.e., a combination of alpha, beta, and gamma radiation) (Bouniol and Aspart 1998, Bouniol 2011). The two main outcomes resulting from water radiolysis are (1) buildup of internal overpressure that may lead to cracking of the waste form and (2) the accumulation of hydrogen gas in a storage area, hence, the buildup of an explosive gas mixture when mixed with atmospheric oxygen (Bar-Nes et al. 2008)“. pp. 67- 68 [Ed. note: hydrogen gas within pores causing hydrogen damage as in metals, as well?]
“The rust formation during rebar corrosion generates a high interface pressure between the rebar and the surrounding concrete. The level of pressure depends on many factors, such as the volume ratio of rust to steel and the thickness of the concrete cover. If the pressure is high enough, cracks may form in the concrete and the concrete cover may spall“. (p. 70)
“8. DETECTION AND EVALUATION OF RADIATION DAMAGE IN NPP CONCRETE STRUCTURES
All commercial NPPs in the United States contain concrete structures whose performance and function are necessary for protection of the safety of plant operating personnel and the general public as well as the environment. A myriad of concrete-based structures are contained as a part of a light-water reactor (LWR) plant to provide foundation, support, shielding, and containment functions. Typical safety-related concrete structures contained in LWR plants may be grouped into four general categories: primary containments, containment internal structures, secondary containments/reactor buildings, and other structures.
The primary containment is a vital engineered safety feature of an NPP that is subjected to various operating and environmental stressors (e.g., ambient pressure fluctuations, temperature variations, and earthquakes). Concrete containments are metal-lined, reinforced concrete pressure-retaining structures that in some cases may be post-tensioned. The concrete containment includes the concrete shell and shell components, shell metallic liners, and penetration liners that extend the containment liner through the surrounding shell concrete. The reinforced concrete shell, which generally consists of a cylindrical wall with a hemispherical or ellipsoidal dome and flat base slab, provides the necessary structural support and resistance to pressure-induced forces. Leak tightness is provided by a steel liner fabricated from relatively thin plate material (e.g., 6 mm thick) that is anchored to the concrete shell by studs, structural steel shapes, or other steel products. In addition to the containment, a number of other concrete structures are contained as part of a light-water plant to support and protect safety-related systems and components. The other structures are primary, secondary, and biological shield walls as well as floors and supporting structures in the containments, reactor buildings, auxiliary (or intermediate) buildings, diesel generator buildings, intake structures, and service-water pump houses. The exterior walls and roofs, shield walls and buildings, interior floors that support heavy equipment and piping, and foundation mats are constructed of reinforced concrete. Some of the interior walls of these structures are constructed of (reinforced or unreinforced) masonry blocks. Beams and columns that support the floors are either of structural steel or reinforced concrete. Of these concrete structures, the structures most susceptible to the potential effects of radiation exposure would be those that provide biological shielding and support for the reactor pressure vessel. The presence of concrete degradation in these structures resulting from nuclear radiation could be determined through visual examination for signs of distress (e.g., cracking, volume change, and misalignment), application of nondestructive test methods, or removal and evaluation of concrete samples…
8.1 NONDESTRUCTIVE TEST METHODS FOR CONCRETE AND REINFORCED CONCRETE STRUCTURES
Nondestructive testing (NDT) is a branch of materials science that utilizes noninvasive techniques to determine the integrity of a material, component, or structure or to quantitatively measure some characteristic of an object. Objectives of NDT are to:
• determine material properties;
• detect, characterize, locate, and size discontinuities/defects; p. 83
• determine the quality of manufacturing or fabrication of a component or structure; and
• check for deterioration after a period of service for a component or structure.
With respect to application of NDT methods to concrete, they can indicate strength, density and quality; locate and characterize voids or cracks; locate steel reinforcement and indicate depth of concrete cover; and indicate corrosion of reinforcing materials. Tables 8.1 and 8.2 present NDT methods to determine structural properties and to assess conditions of concrete and to determine material properties of hardened concrete in existing structures, respectively“. p. 84 [Tables 8.1 and 8.2 are on pp. 84-87]
“Table 8.1. Nondestructive test methods to determine structural properties and assess conditions of concrete (ACI 2013)
Table 8.2. Nondestructive test methods for determining material properties of hardened concrete in existing structures (ACI 2013)
Visual and NDT methods are effective in identifying areas of concrete exhibiting distress but often cannot quantify the extent or nature of the distress. Quantifying and determining the nature of distress in concrete are generally accomplished through removal of cores or other samples using an established procedure. When core samples are removed from areas exhibiting distress, a great deal can be learned about the cause and extent of deterioration through property determinations and petrographic studies. Additional uses of concrete core samples include calibration of NDT devices, conduct of chemical analyses, visual examinations, determination of steel reinforcement corrosion, and detection of the presence of voids or cracks. Information on methods for examining hardened concrete to characterize materials and to identify and quantify degradation is available (Walker et al. 2006). Qualitative or quantitative characterization of the microstructure can be done using techniques such as nanoindentation, mercury intrusion porosimetry, XRD, thermal gravimetric analysis, nuclear magnetic resonance, SEM, and energy-dispersive spectroscopy.
8.2 SPECIFIC CONDITIONS RELATED TO THE EFFECT OF RADIATION ON CONCRETE
NPP concrete structures, particularly those related to the biological shield or support for the reactor pressure vessel, can be subjected to neutron and gamma radiation during their service lives. As the service lifetimes of these plants are being extended, the impact of radiation on the concrete structures may have increased significance that can affect their functional and performance requirements. Irradiation of concrete has the potential to impact the concrete’s microstructure as well as its mechanical and physical properties. An assessment of the impact of radiation on the concrete microstructure and properties would require removal of concrete samples from the areas of interest and application of techniques such as identified in Tables 8.1 and 8.2.
In addition to the impacts of radiation on the microstructure and properties of concrete, radiation can contribute to elevated temperatures in the concrete as well as increased potential for ASR and concrete carbonation to occur. Techniques associated with identification of concrete that has experienced or is experiencing elevated temperatures, ASR, or carbonation may also provide indications that the concrete has been affected by radiation. (p. 87)
“8.2.1 Temperature effects
Gamma and neutron radiation can produce elevated temperatures and thermal gradients in concrete structures. Thermal loading of reinforced concrete can result in damage ranging from cosmetic blemishes to more serious effects (e.g., misalignment and distortions). Heating of concrete may result in a variety of structural changes such as cracking, spalling, debonding of aggregate, expansion, and mineralogical or chemical changes such as discoloration, dehydration, and dissociation. With respect to the cement paste, evaporation may occur as well as dissolution, dehydration, and dissociation of ettringite, gypsum, calcium hydroxide, calcium carbonate, and other phases, such as calcium silicate hydrates…
Nondestructive approaches identified for application to fire-damaged concrete can also be utilized as part of the assessment process. Table 8.3 presents a listing of possible NDT approaches. Examples of approaches that have been used in the field include: rebound hammer, impact echo, indirect ultrasonic pulse measurements based on refraction of longitudinal waves to identify depth of damage,…
Table 8.3. Listing of possible nondestructive approaches for use in assessment of fire-damaged concrete (Columbo and Felicetti 2007) …
8.2.2 ASR potential of existing concrete and detection
[…]
ASR has been identified at one U.S. NPP (i.e., Seabrook). It was noted in Section 6.1 of this report that there may be a coupling effect between radiation and ASR that can potentially accelerate ASR activity or cause ASR to occur with aggregates that are not normally reactive. As plants age, the potential of ASR to occur in structures forming the biological shield or support for the reactor pressure vessel may increase as these structures are located in areas in which they are subjected to moderate elevated temperature in combination with radiation.“( p. 88)
“The primary method utilized for detection of ASR is through visual examinations indicating evidence of expansion, relative movements between structural elements, and cracking. ASR capable of being detected visually, however, is probably in a fairly advanced stage of development. Removal, examination, and testing of concrete samples from suspect areas can be used to confirm the presence of ASR. Petrographic examinations of thin sections of aggregate materials, and tests developed for identification of ASR reactivity products (e.g., use of sodium cobalt nitrite solution to detect potassium and uranyl acetate to detect sodium) are examples of examination and testing methods (Walker et al. 2006)….
8.2.3 Carbonation
In Section 5.1, it was indicated that radiation can produce carbonation of concrete that is internal to the concrete (i.e., it does not start at exposed concrete surface)“. (p. 89)
…
“Thresholds were set by various national standards for radiation exposure in 1960s, 1970s, and 1980s to reduce risk of shielding concrete property degradation due to radiation.” (p. 91)
“10. SUMMARY AND CONCLUSION
…
Gamma rays … can result in the destruction of anisotropic chemical bonds such as covalent bonds. Water in the concrete can be decomposed by gamma rays by a process called radiolysis and can be converted to hydrogen, oxygen, and hydrogen peroxide. Water can also be removed from the concrete by evaporation due to heat generated by gamma radiation. Because most of the water in concrete is contained in the cement paste, gamma radiation has a greater effect on the cement paste than it has on the aggregate materials.
In the instance of neutron irradiation, the neutrons do not interact with the electrons but with the nuclei of atoms… Because neutrons interact with the nuclei of atoms, the lattice spacing within the material may change after the collisions. Therefore, the neutrons have a more significant effect on dense and well-crystallized materials (e.g., aggregates) than on randomly structured materials with high porosity (e.g., cement paste). Under nuclear radiation, the internal structure of some aggregates can be converted from an ordered crystalline structure to a disordered structure, resulting in a decrease in specific gravity and an increase in volume.
Interactions between nuclear radiation and the internal structure of concrete produce geometric changes of the structure resulting from displacements of atoms from their lattice sites and phase transformations of the concrete constituents resulting in a reduction in porosity and/or formation of microcracks. These interactions result in changes in the various concrete properties. As the gamma radiation dose increases, the specific pore surface and the porosity of the Portland cement paste have been shown to decrease. It also has been shown that as the gamma radiation dose increases the concentration of calcite increases resulting in carbonation of the concrete. Experimental studies have shown that the reactivity of silica-rich quartz to alkali can be significantly increased by exposure to nuclear radiation. As a result, irradiation can produce ASR in concretes containing aggregates that are typically nonreactive.“(p. 93)
Excerpted from: “A Review of the Effects of Radiation on Microstructure and Properties of Concretes Used in Nuclear Power Plants” Manuscript Completed: August 2013 Date Published: November 2013
Prepared by: Kaspar William University of Houston Department of Civil and Environmental Engineering Houston, TX 77204-4003
Yunping Xi University of Colorado Department of Civil, Environmental and Architectural Engineering Boulder, CO 80309-0428
Dan Naus Oak Ridge National Laboratory Materials Science and Technology Division Oak Ridge, TN 37831-6069
Herman L. Graves, III, NRC Technical Monitor
NRC Job Code N6978
Prepared for: Division of Engineering Office of Nuclear Regulatory Research U.S. Nuclear Regulatory Commission Washington, DC 20555-0001
NUREG/CR-7171 ORNL/TM-2013/263″
Emphasis added throughout. Ed. note in brackets is our comment. IF YOU READ THE ORIGINAL YOU MAY NOTE THAT THERE APPEARS TO BE A PRO-NUCLEAR AUTHOR OPPOSED TO NUCLEAR SAFETY WHO GOES THROUGH HERE AND THERE AND MAKES STATEMENTS WHICH CONTRADICT THE INFORMATION AND NUMBERS GIVEN IN THE STUDY. BE ALERT! http://permanent.access.gpo.gov/gpo42084/ML13325B077.pdf
ANOTHER STRANGE THING IS THAT THEY SAID THAT FREEZING WOULDN’T IMPACT CONTAINMENT AND YET THERE WERE REPORTS OF A LOT OF SNOW BUILD-UP ON TOP OF DAVIS BESSE NUCLEAR POWER STATION. WASN’T THE OWNER BLAMING THE SNOW FOR CRACKS IN DAVIS BESSEE CONTAINMENT? IF SNOW BUILDS UP THEN THERE MUST BE SOME CHANCE OF FREEZE THAW EFFECT, ESPECIALLY WITH GREAT LAKES SNOWS.
Mining Awareness + 
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