Radiation endurance of piezoelectric ultrasonic transducers--a review.

Ultrasonics xxx (2014) xxx–xxx

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Radiation endurance of piezoelectric ultrasonic transducers – A review A.N. Sinclair a,⇑, A.M. Chertov b,1 a b

Department of Mechanical and Industrial Engineering, University of Toronto, Ontario M5S 3G8, Canada Institute for Diagnostic Imaging Research, University of Windsor, Ontario N9A 5R5, Canada

a r t i c l e

i n f o

Article history: Received 5 June 2014 Received in revised form 28 October 2014 Accepted 30 October 2014 Available online xxxx Keywords: Ultrasonic NDT Piezoelectric transducers Nuclear reactor inspection Radiation endurance Transducer failure

a b s t r a c t A literature survey is presented on the radiation endurance of piezoelectric ultrasonic transducer components and complete transducer assemblies, as functions of cumulative gamma dose and neutron fluence. The most extensive data on this topic has been acquired in CANDU electrical generating stations, which use piezoelectric ultrasonic transducers manufactured commercially with minor accommodation for high radiation fields. They have been found to be reliable for cumulative gamma doses of up to approximately 2 MegaGrays; a brief summary is made of the associated accommodations required to the transducer design, and the ultimate expected failure modes. Outside of the CANDU experience, endurance data have been acquired under a diverse spectrum of operating conditions; this can impede a direct comparison of the information from different sources. Much of this data is associated with transducers immersed in liquid metal coolants associated with advanced reactor designs. Significant modifications to conventional designs have led to the availability of custom transducers that can endure well over 100 MegaGrays of cumulative gamma dose. Published data on transducer endurance against neutron fluence are reviewed, but are either insufficient, or were reported with inadequate description of test conditions, to make general conclusions on transducer endurance with high confidence. Several test projects are planned or are already underway by major laboratories and research consortia to augment the store of transducer endurance data with respect to both gamma and neutron radiation. Ó 2014 Elsevier B.V. All rights reserved.

Contents 1. 2.

3. 4. 5. 6.

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.1. Scope of literature review. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Gamma interaction with individual transducer components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1. Effects of gamma irradiation on the piezoelectric element . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2. Effects of gamma irradiation on organically-based components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3. Effects of gamma radiation on transducer housing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.4. Effects of gamma radiation on electric cabling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Failure modes and associated gamma dose levels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Transducer design for cumulative gamma doses up to 1–2 MGy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Neutron irradiation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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⇑ Corresponding author. Tel.: +1 416 978 6953. 1

E-mail addresses: [email protected] (A.N. Sinclair), [email protected] (A.M. Chertov). Tel.: +1 (519) 991 6546.

http://dx.doi.org/10.1016/j.ultras.2014.10.024 0041-624X/Ó 2014 Elsevier B.V. All rights reserved.

Please cite this article in press as: A.N. Sinclair, A.M. Chertov, Radiation endurance of piezoelectric ultrasonic transducers – A review, Ultrasonics (2014), http://dx.doi.org/10.1016/j.ultras.2014.10.024

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A.N. Sinclair, A.M. Chertov / Ultrasonics xxx (2014) xxx–xxx

1. Introduction There is considerable demand for ultrasonic nondestructive evaluation (NDE) at locations where there are substantial radiation fields, e.g., periodic inspection of nuclear reactor components, or ultrasonic scanning for potential leakage sites on irradiated fuel assemblies. This raises the possibility of degradation or even complete failure of ultrasonic transducers. Much has been written about the effects of gamma radiation (and combined neutron and gamma radiation) on individual materials used in transducer components, such as the piezoelectric element. However, less has been documented regarding the precise failure mechanisms and projected lifetimes of entire transducer assemblies. Most of the literature on that topic tends to be in the form of isolated observations under unique operating conditions on various types of sensors and piezoelectric materials – some of the work in this area is briefly summarized in several technical articles, e.g., [1–9]. However, the limited extent of these transducer studies makes it difficult to get an overall picture of expected lifetime reduction of a transducer as a function of radiation dose. In addition, some of the relevant data have never been published in the open literature, but have been acquired through operational experience and kept as internal information at nuclear generating stations or research facilities. In this review paper, we draw on operational experience to provide the link between studies on individual transducer component materials exposed to gamma radiation, and expected lifetimes of ultrasonic transducers. Experience at CANDU heavy-water moderated nuclear reactors is particularly useful, where extensive ultrasonic inspections are routinely performed of fuel channels and other reactor components during maintenance shutdowns, using a sophisticated robotic delivery system to enable remote scanning. In such instances where the nuclear reactor is shut down, the neutron flux is negligible and the effects of gamma radiation alone can be studied. Other operational experience and research data include that acquired in liquid metal-cooled research reactors, [4,10–14], or current US government-sponsored programs on Advanced Sensors and Technologies in Nuclear Environments [7,15]. The total amount of data acquired under such conditions, in terms of number of irradiated transducers or total radiation dose, is far less than for CANDU reactor inspections, and many of the transducers have specialized designs to match unique operating environments. Under these conditions, it is difficult to draw definitive conclusions with a sound statistical basis. There is the added possibility in some experiments to examine the effects of neutron radiation on transducer lifetimes. However, these data often feature a gamma–neutron mixture; some of these data correspond to an unknown elevated temperature, and the spectrum of neutron energies is generally not precisely described. This complicates the task of comparing results of different studies on neutron irradiation of piezoelectric transducers, and determining a precise correlation between cause and effect. The end result is a somewhat ambiguous overall picture of the relative effects of neutron radiation compared to gamma radiation on transducer lifetimes. 1.1. Scope of literature review The scope of this review is as follows: Identify the most common failure mechanisms and associated cumulative radiation doses of individual ultrasonic piezoelectric transducer components in gamma fields. The review is limited to transducers containing conventional piezoelectric elements – composite piezoelectric elements are not included

due to their vast number and frequent lack of detailed published information regarding their exact structure. Identify degradation and failure mechanisms of entire transducer assemblies in radiation fields, and associated dose levels. Describe minor modifications to commercial transducer manufacturing steps that have been adopted to improve gamma radiation resistance. Characterize operating experience and expected transducer lifetimes with such modified commercial transducers in contemporary electrical power generating stations. Review the published data regarding lifetimes of transducers and their components exposed to neutron radiation fields, or combinations of neutron and gamma radiation. The data are far less definitive than those corresponding to gamma irradiation, due to the limited amount of data, variety of test conditions under which measurements have been made, and lack of information regarding the role of neutron energy. Note: The measurement unit for gamma radiation dose is the Gray, equal to 1 Joule of absorbed energy per kg of material; the data relevant to this literature review are generally in the MegaGray (MGy) range. Due to the very strong dependence of the attenuation coefficient for gamma rays on the atomic number Z of the target [16], the various components of a transducer will experience vastly different radiation doses that are difficult to estimate. It is therefore common practice [17] to express radiation dose in terms of the number of Grays that would be absorbed by light elements with atomic numbers similar to those of biological tissue. Materials used in such dosimeters include dyed polymethylmethacrylate [14], ferrous sulfate and sodium chloride mixed with sulfuric acid and water used in the Fricke dosimeter [18], silicon [19], and air [20]. The key point is that the actual energy absorption (plus associated heating effect) in a high-Z piezoelectric element such as PZT will be far higher than that indicated by the quoted nominal dose applicable to biological tissue. This can cause high temperature excursions that could damage a transducer. For perspective on the relative magnitudes of gamma radiation doses, a few key examples are shown in Table 1. Neutron radiation exposure is usually expressed in terms of neutron fluence, equal to the cumulative track length swept out by neutrons per unit volume of material integrated over time. Neutron fluence is commonly expressed in the non-S.I. unit of cm 2.

Table 1 Approximate gamma dose rates and cumulative doses [21–24]. Gamma radiation source

Dose rate (Gy/h)a

Cumulative dose in one year (Gy)

Interior of a commercial nuclear reactor, at full power Interior of a commercial nuclear reactor, shutdown Adjacent to nuclear fuel in spent fuel storage ponds

107

1011

0.5

4000

103

107

Gamma doses to the human body Short-term dose yielding 50% death probability Typical background radiation from rocks, cosmic rays One full-body CT Scan Maximum legal dose to the public from nonmedical nuclear activities (Canadian Nuclear Safety Commission regulations)

2.5–5 10

7

10

3

10 10

2 3

a The biological effect of a dose of radiation is expressed in Sieverts, where 1 Sievert is equal to the dose (expressed in Grays) multiplied by a Quality Factor. The Quality Factor is 1 for gamma radiation, such that Grays or Sieverts are used interchangeably for gamma.



The equivalent cumulative dose in Sieverts can be estimated by multiplying neutron fluence by a factor ranging from 10 11 up to 4 10 10 [25,26], although many variables can greatly distort this conversion factor. 2. Gamma interaction with individual transducer components The basic components of a generic immersion ultrasonic transducer (Fig. 1) are the active piezoelectric element; backing (damper); 1/4 wave matching layer (often featuring a focusing lens); a bonding agent to hold the layers together; external housing; and cabling/electrical leads [27,28]. Contact transducers operate on similar principles, although the focusing lens is normally absent, and a frontal plate protects the transducer from wear. 2.1. Effects of gamma irradiation on the piezoelectric element Piezoelectric properties of several candidate materials are tabulated in [10]. Gamma rays interact with such materials primarily via ionization, i.e., creation of electron–hole pairs [16,29]. In general, the prevailing assumption is that the consequences of gamma radiation absorption by the piezoelectric element in a transducer depend only on the cumulative dose [30]; the damage is assumed to be independent of the dose rate provided that the elevated temperatures caused by high dose rates are well below the Curie temperature. The major mechanisms for piezomaterial performance degradation via gamma ray interaction are as follows [24,31]: 1. The primary degradation mechanism is depoling, which may be reduced somewhat by using a piezomaterial with a high Curie temperature such as lithium niobate [31–34]. A general review of the temperature dependence of piezomaterials is presented in [35]. More details on this topic as applied to several types of PZT are presented in [36–38] and examine the sensitivity to temperature of hard vs soft PZT. 2. Accumulated exposure to ionizing radiation can cause gradual crystal dielectric loss and thus a reduction of the piezo effect [17,31,39,40]. 3. Radiation-induced charges can be trapped near the electrodes. Such a concentration of charge could potentially affect polarizability of individual dipoles or their domains [19]. Considerable work has been done to measure the effects of various doses of gamma radiation on samples of piezoelectric material. It is not our intent to review all of these many studies here, although results from several representative tests are listed in Table 2. Although the data from various sources show considerable

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variation, general results have been noted, such as hard piezoelectrics generally have higher Curie temperature [41] and greater radiation resistance than soft piezoelectrics [1,7,32]. For a further look at this topic, the reader is referred to key publications that each contains substantial reviews on radiation resistance of piezoelectric materials [1,2,7,8]. These data can then be compared with the gamma dose levels to be encountered near nuclear reactor components or spent fuel, such as those tabulated in [24]. PZT is the preferred choice for ultrasonic transducers in low temperature environments and moderate radiation doses, due to its high value of d33, relatively low cost, and easy availability [12,42]. PZT comes in various types [43]; PZT-5A is relatively resilient with a Curie temperature of up to 365 °C [44], but is rarely used above 200 °C in radiation environments due to deteriorating performance. Substantial radiation fields will tend to elevate the temperature inside a transducer, such that PZT will no longer be an option [32]. Under conditions of significantly elevated temperature or high accumulated radiation dose, PZT can be replaced by other piezoelectrics (Table 2); although pricier and generally less efficient (lower d33) than PZT, these materials have a higher Curie temperature and generally higher tolerance to gamma radiation. Lead metaniobate is a popular choice up to about 250–300 °C [2]; above this limit, Kazys et al. suggest that bismuth titanate offers the best combination of thermal and radiation stability up to 550 °C [45]. At even higher temperatures, aluminum nitride has good temperature and radiation endurance, although sensitivity is relatively low. An alternative choice at high temperatures and gamma fields is lithium niobate, although its use is not recommended in high neutron fields. 2.2. Effects of gamma irradiation on organically-based components Several transducer components may be organically based. These include the backing element, 1/4-wave matching layer, focusing lens or protective face plate, bonding agent, potting agent, and in some cases a delay line. In general, plastics have the advantages over metals of low material & fabrication costs. In addition, key mechanical properties of plastics or plastic-based composites such as impedance and attenuation can be tailored to desired values. Although metals would essentially eliminate practical concerns regarding degradation of these transducer components from gamma radiation, plastics may give superior performance at low cost if the degradation issue can be managed. An ultrasonic transducer’s backing layer is selected to have an impedance Z that is compatible with the piezoelement, and a high attenuation coefficient [11,52]. These conditions may be met by

Fig. 1. Basic components of a generic immersion transducer.


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Table 2 Gamma resistance of common piezoelectric materials at moderate temperatures. Piezo material

Curie temp. (°C)

PZT (several types)

250–360

Reported behaviour Reliable operation after doses of 1.5 MGy [46] Ionization damage threshold of 400 MGy of gamma, but only if temperature and neutron fluence are kept low [1,8,29] Sub-critical damage at accumulated gamma dose of 0.01 MGy in sol–gel based PZT thin films [17] Gradually increasing damage to PZT sol–gel films in the range 0.05–1 MGy of gamma, but damage is recoverable via post-irradiation bias cycling [40]

Lithium niobate

1142–1210

No significant performance degradation at 100 MGy [47] Some decrease in d33, but no serious performance degradation at a dose of 40 MGy [33] No effect from 4 MGy on accelerometers that employ lithium niobate P15 piezoelectric elements [3,32] Slight degradation in the range of 35–88 MGy [1,8] ‘‘Good’’ resistance to a radiation dose of 22 MGy [14] No effect from 0.4 MGy of Co-60 gamma [34]

Aluminum nitride

>1100

No significant performance degradation at a dose of 27 MGy gamma (in combination with neutron fluence) [15,31] No significant performance degradation at 18.7 MGy [14]

Bismuth titanate

670

Slight reduction of piezoelectric coefficient at 22.7 MGy [12,14,48]

Lead metaniobate

400

A moderate decrease in piezoelectric voltage coefficient g33 at 1 MGy absorbed gamma dose [8]

Barium titanate

120

Gallium orthophosphate

Phase transition at 970 °C

Signal amplitude decrease of 13% after dose of 22.7 MGy in a customized transducer assembly; drop is believed to be due to a change in piezoelectric efficiency [14]

95 kGy threshold for permanent damage [8,29] Drop in polarization above 1 MGy for single crystals [49] At 1 MGy gamma plus neutron flux: decreased coercive field, and increase of spontaneous polarization [50] Changes in piezoelectric properties after exposure to ‘‘low’’ pile radiation (mixed neutrons and gamma fields) [51]

some epoxies and plastics, but the effects of radiation exposure on such materials varies widely; plastics such as Teflon that are highly susceptible to radiation should be avoided [24,29,53–56]. A general trend is that radiation may increase the amount of cross-linking [57], leading to a decrease in flexibility and toughness of the plastic material, plus some discoloration [58]. Swelling and gas production may also be seen, leading to interfacial stresses. The relative radiation resistance of several common polymers is shown in Table 3; more complete lists showing radiation sensitivities of many organically-based materials are available in [24,29,54– 56,59]. There are no published reports on direct observation of damage or total failure of the bulk material that makes up the backing of an irradiated transducer – that would require a very delicate disassembly operation on a radioactive item. The issue of a delamination failure at the piezoelement-backing interface is considered in the section on transducer assemblies.

Table 3 Relative resistance to radiation of several common polymers (from [24,54]). Radiation resistance

Polymer

Highest radiation resistance

Glass fiber phenolics Asbestos filled phenolics Epoxy systems Polyurethane Polystyrene Mineral filled polyester Mineral filled silicones Furane-type resins Polyvinyl carbazole

Moderate radiation resistance

Poor radiation resistance

Polyethylene Melamine–formaldehyde resins Urea formaldehyde resins Aniline formaldehyde resins Unfilled phenolic resins Silicone resins Methyl metacrylate Unfilled polyesters Cellulosic Polyamides Teflon

The transducer matching layer and wearplate can be made from a variety of low-attenuation materials, including plastics, metals, epoxy-based composites, and glass. Significant deterioration of the plastics used in the matching layer and wearplate (blistering, bubbling, discoloration and deformation) has been observed during ultrasonic inspections of CANDU reactor components when cumulative doses exceed 2 MGy [60–62]; such NDE inspections are typically conducted a few days following reactor shutdown. These UTX-type transducers incorporate minor modifications to standard commercial designs to avoid materials that are particularly susceptible to radiation. (UTX Inc., Holmes, NY [63]) Similar endurance test results with respect to organic components of commercial ultrasonic piezoelectric transducers were reported by Smilie [64]. To bond the layers of the transducer together, an adhesive with good radiation resistance is required that will maintain its strength and flexibility. Several such recommended adhesives are listed in [24,54]; a few examples are provided in Table 4. Alternative methods of bonding [12], such as dry coupling under high pressure, or liquid coupling, may mitigate the problems of radiation damage but can lead to a significant increase in the cost of the transducer, and may still not lead to stable coupling in highly adverse environments [35,65]. At very elevated temperatures, soldering [44] or special high-temperature adhesives are required. 2.3. Effects of gamma radiation on transducer housing The metal casing itself (often stainless steel) will not suffer significant radiation damage in terms of its functionality within the

Table 4 Radiation damage threshold of common adhesives (from [24,54]). Adhesive

Threshold damage level at room temperature (MGy)

Neoprene–nylon–phenolic Neoprene–phenolic Epoxy, epoxy–thiokol, nitrile–phenolic Epoxy–phenolic, vinyl–phenolic, nylon–phenolic

0.5 1.0 5 10



lifetime of the transducer. However, if the gamma fields feature relatively low-energy photons, then a stainless steel housing could offer minor shielding to the interior of the transducer, and might serve to extend the transducer lifetime. Curiously, Smilie et al. [58,64] noticed the opposite effect: performance of steel-encased transducers deteriorated well before that of similar transducers enclosed in an aluminum casing that would provide inferior shielding. He reasoned that the secondary electrons produced by gamma rays interacting with the stainless steel casing served to irradiate the adjacent epoxy material inside the transducer, approximately doubling the absorbed dose to the peripheral epoxy. Provided that the energy spectrum of the gamma radiation field is approximately known, calculations can be performed to evaluate the shielding effects, and secondary radiation effects, of an aluminum vs steel housing [16]. No corroboration of this effect observed by Smilie could be found in other published material. 2.4. Effects of gamma radiation on electric cabling For transducers destined for use in substantial radiation fields, electrical circuitry such as an impedance matching network should not be included inside the housing, due to the relatively low gamma radiation resistance of circuit components [24,66,67]. However, cabling is still needed between the transducer and pulser/receiver. The transducer and its associated cable can be purchased as a single integrated unit for use in high radiation fields; this implies that when the cable’s performance deteriorates below a threshold value, the transducer and cable must both be discarded. In non-harsh environments, standard co-axial cable with 50ohm impedance is often used. These use plastic materials as an insulator and outer sheath. Many of these plastics will eventually harden, become brittle, and crack, such that the transducer/cable assemble must be discarded after absorbing a dose of gamma radiation of the order of 1 MGy [60]. Alternatively, the good radiation tolerance of PEEK and polyimide for these applications is well known [59,66,68,69]. Cables utilizing polyurethane rubbers or a PEEK/polyimide combination can survive gamma doses of 50– 70 MGy [24]. A variety of radiation-hardened RF coaxial cables are available for which deterioration in cable performance with radiation exposure is minimized [7,24,54,70–72]. If high cable flexibility is important, e.g., for connection to a moving ultrasonic scanning system, one route is to form the cable into an extendable coil as in a home telephone line [24,60]. Using inorganic materials such as glass, ceramics or mica as insulators in a cable can yield much higher radiation endurance, although flexibility is sacrificed and the cost is much higher. One popular choice is two-conductor mineral cable [7,12,66]. Mineral-insulated inserts are used to maintain the separation between the rod conductors, and this assembly is inserted into a sheath. The open space is filled with magnesium oxide, which acts as a seal and fireproof insulator. Special electrical connectors and factory terminations on the cable are required to keep water out of the sheath. A second type of cable with no organic components used extensively in high-radiation (and high temperature) environments is specialized coaxial cable [7,72]. This cable uses SiO2 as the annular dielectric and can be obtained commercially with standard 50 X impedance in various diameters. Larger diameters are less flexible while smaller diameters exhibit higher insertion loss. Once again, this cable must be hermetically sealed to maintain electrical integrity; this requires factory termination. By selection of an appropriate radiation-hardened cable, failure of a transducer/cable assembly should no longer be precipitated by failure of the cable itself, i.e., the cable does not play a role in limiting the assembly lifetime. A variety of radiation-hardened connectors are also available [7,68].

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3. Failure modes and associated gamma dose levels Provided that ‘‘radiation-soft’’ materials are avoided, then bulk failure of individual components is not normally the direct cause of catastrophic transducer failure. To identify the most common degradation and failure mechanisms of the entire transducer assembly, the very limited experimental and operational data from piezoelectric-based accelerometers, acoustic emission sensors, piezoresistive sensors, and ultrasonic transducers may be collectively considered, given the overlap in many of their system components, [1,2,8,18,32,34,58,64,73]. For water-immersion transducers, a key consideration is that the various active layers (backing, piezoelectric element, 1/4 wave matching layer, protective wearplate) must maintain intimate physical contact to allow efficient transfer of ultrasound energy between layers [2,65]. Radiation exposure can lead to production of gases, bulging and thermal expansion in organic transducer components and bonding agents [58,64]; this can cause interfacial stresses and inter-layer debonding that can impede or block ultrasound transmission. Other observed failure mechanisms of transducers are loss of electrical connection; internal stress that causes cracking of one of the transducer layers (usually the piezoelement); gases collecting at a weakened interface that impede the passage of ultrasound; distortion and swelling of organic materials, which then allow water to leak into the transducer [19,61,63,64]. Debonding of the backing layer from the piezoelement does not lead to complete transducer failure, but to an unacceptable distortion of the signal characterized by excessive ‘‘ringing’’; this loss-ofperformance mechanism has been indirectly inferred from a reduction of bandwidth, and degradation of timing resolution in ultrasonic echoes [62]. These are the most common routes reported in operational settings for serious degradation of water-immersion transducer performance in high radiation fields, ultimately leading to the need for transducer replacement. It is noted that these failure modes bear considerable resemblance to transducer breakdowns at high temperature [65]. To establish the gamma dose levels that would lead to such failures, several PZT-based commercial immersion transducers were tested at the MDS Nordion gamma irradiation facility in Laval, Quebec to cumulative gamma doses of 1–2 MGy [74]. Subsequent examination and analysis revealed blistering of the matching layer, probe discoloration, loss of bandwidth (detachment of backing layer), and loss of sensitivity of 3–13 dB, but no complete catastrophic failures [61,62]. However, performance degradation and water leakage into some of the tested transducers were sufficiently severe to make further use of the transducers questionable. Based on the MDS Nordion results, Ontario Power Generation and Atomic Energy of Canada Limited routinely retire their ultrasonic transducers once they have received a maximum of 2 MGy of gamma radiation [60–62], at which point they see only a minor drop in piezoelectric efficiency; the efficiency drop is accommodated through periodic recalibration. This loss of sensitivity might be recoverable by a post-irradiation biased anneal [8,17,19,29,30,40], but accumulated damage in plastic components of the transducer (bulging/distortion of faceplate, matching layer, backing) preclude such efforts. Radiation resistant materials are used in the manufacturing process, although the overall design is very similar to that for standard transducers [61,63]. Lead metaniobate is employed as the piezoelectric element, largely due to its superior temperature stability compared to PZT. Roughly consistent with the above findings, PCB Piezotronics currently markets accelerometers rated for accumulated gamma doses of 1 MGy, although the piezoelectric element is not specified [75]. Smilie noted similar dose limits for unmodified commercial transducers: he found considerable deformation of the faceplates


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and matching layers after 0.46–0.65 MGy of absorbed dose, but no details regarding the construction of his piezoelectric transducers construction were provided [58,64]. Fourmental et al. found that PZT-based transducers designed for nuclear reactor use could withstand 1.5 MGrays of gamma radiation without measurable loss of performance [76]. Further corroboration on this range of threshold gamma dose level for piezoelectric transducers is provided in 1971 tests conducted by Aerojet Nuclear Systems: a 40% drop in sensitivity was noted in PZT-based accelerometers after a dose of 4 MGy in conjunction with a neutron fluence of 2.5 1018 n/cm2. Although cited frequently, e.g., [8,32], the Aerojet report T102-FHT08-W150f8 is not readily available. The International Thermonuclear Experimental Reactor (ITER) organization has created a Radiation Hardness Manual [72] to provide guidelines and a database of test results on components that might be used in radiation environments, including ultrasonic transducers. Although no manufacturing details nor failure criteria are provided, dose levels of 0.5–10 MGy are listed for several different gamma radiation tests. The suggested maximum gamma dose level of the order of 1–2 MGy is subject to considerable variation. Beeson and Pepper found that some of their PAC acoustic emission sensors with bismuth titanate piezoelements [77] failed at 0.03 MGy due to deterioration of the organic bonding agent [18]. By contrast, Kazys et al. reported minimal drop in efficiency of their PZT, bismuth titanate, and silver nitride transducers carefully customized for high radiation exposure at cumulative doses of approximately 20 MGy [14]. Meggit Sensing Systems now manufactures high-temperature radiation hardened accelerometers, some of which are rated to a total gamma dose of up to 600 MGy [71]; it is inferred that there are no plastics in these sensors, as they can be used both at high doses and at temperatures of up to 482 °C.

4. Transducer design for cumulative gamma doses up to 1–2 MGy Recent test results indicate that for gamma dose rates up to 10,000 Grays/h, single-element water-immersion ultrasonic transducers are serviceable for accumulated doses of approximately 1–2 MGy. These findings are predicated on minor adjustments to conventional transducer design [63], summarized as follows: (i) Use PZT for the piezoelectric element if ambient temperatures are under 200 °C. Some grades of PZT have Curie temperatures over 300 °C [43] . However, radiation heating can elevate the temperature inside the piezoelectric element well beyond that of the ambient environment. Griffin suggests a maximum ambient temperature of 260 °C in very low radiation fields [10]; Tittmann et al. recommend a maximum temperature of 150–250 °C for PZT-based transducers [78]. The combined effects of elevated temperature and radiation on PZT are not yet thoroughly documented and indicate a conservative design approach [65]. For moderately higher temperatures and gamma doses, lead metaniobate is a less efficient piezoelectric, but more stable. Above 300 °C, bismuth titanate, aluminum nitride or lithium niobate are preferred choices depending on the temperature range. Composite piezoelectrics (beyond the scope of this review) may also be an alternative. (ii) Minimize the use of any circuitry, such as impedance matching networks, inside the transducer. Integrated circuits and other types of electronics can be the weak link for sensors and machinery operating in significant radiation fields [66,67,69]. (iii) If plastics are to be used for the damper, 1/4-wave matching layer, or protective face, they need to be selected to have strong radiation resistance; several types of epoxy are suitable.

Blistering, swelling, peeling, and other types of deformation of the protective plastic layer or 1/4-wave matching layer are frequently seen on transducers after accumulated doses of 106 Grays; this is often accompanied by a drop in transducer sensitivity. Frequent recalibration of the transducer may make this efficiency drop acceptable [60–62]. (iv) To bond the layers of the transducer together, use an adhesive with good radiation resistance that will maintain its strength and flexibility. An epoxy-based adhesive is generally a good choice [24,54]. Thermal mismatch between transducer layers should be avoided during the design stage, as it can stress the interfacial bond and precipitate transducer failure. High-pressure contact and brazing are alternative joining methods. (v) Use commercially available electric cables, connectors, and leads designed for the appropriate radiation dose level [72]. The cable and transducer may be marketed as an integrated unit. (vi) Design the transducer system for both the expected radiation exposure and expected temperature (including the effects of radiation heating) [65].

5. Neutron irradiation NDE of conventional in-service nuclear reactors is normally pursued only during shutdown periods, when the neutron flux is expected to be very low and damage to ultrasonic transducers would be primarily from gamma radiation. The same applies to stored irradiated fuel, such that the susceptibility of transducers to time integrated neutron flux (fluence) is of limited interest in most conventional nuclear power stations. However, research facilities where advanced reactor concepts (often employing liquid metal coolants) are being investigated have an interest in on-line measurements. In such cases, the neutron fluence to ultrasonic transducers may be substantial [9], delivered either continuously or in pulsed form [79,80]. Unlike gamma rays that interact with an atom’s electrons and cause ionization, neutrons interact with the atomic nuclei themselves [29]. This may cause fission, transmutation or excitation of the nucleus. Absorption of a neutron by a nucleus (leading to the creation of a different isotope, or even transmutation to a different element) is strongly dependent on the neutron absorption cross section ra of the element. A case in point is lithium niobate: natural lithium consists primarily of two isotopes – 3Li6 and 3Li7. The large value of ra in 3Li6 leads to quick disintegration of transducers containing natural lithium niobate piezoelements through a (n, a) interaction when exposed to a significant neutron flux [1,2]. Although this issue can be avoided with lithium niobate by using only the isotope 3Li7, alternative piezoelectric elements may offer a simpler solution for use in neutron fields. Neutron absorption can lead to activation of a material, such that it becomes dangerous to handle. Elastic or inelastic scattering of a neutron may also knock an atom out of its lattice position. It is the lighter atoms (low atomic weight) such as those in plastic components and certain adhesives that are most prone to picking up large amounts of energy via the scattering of neutron radiation [16]; such materials can efficiently moderate fast and epithermal neutrons to lower energies where the neutron capture cross section is greatest. Plastics can then become distorted, or flexibility and ductility can decrease to the point that they become unusable [56]. A summary of test results on neutron damage to piezoelectric materials and entire transducer assemblies is presented in Table 5. One study of particular relevance to the topic at hand is an experimental evaluation of the effect of neutron dose on piezoelectric transducer assemblies, conducted as the main focus of a 2004



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Table 5 Neutron fluence damage. Because of the limited amount of relevant published data, results are shown both for isolated piezoelectric elements, and for entire transducer assemblies (where so indicated). Piezoelectric element

Gamma dose (MGy)

Time-integrated neutron flux (fluence) (n/cm2)

Lithium niobate

4 N/av N/av

3 1018 2 1021 2.7 1018 fast

No significant damage [32,3] Disintegration due to neutron capture of Li-6 [1,2] No discernible effect on entire accelerometer [34]

Barium titanate

0.095 N/av N/av N/av N/av N/av

7.6 1010 2.1 1020 pile radiation 1 1018 fast 1.8 1020 fast 8 1019 thermal 2.8 1016

Lead zirconate titanate

N/av

2.5 1020 1.5 1020 1.5 1015 1.6 1017 1.6 1016 3.5 1019 1.4 1019 3.6 1018 2 1018

60 dB drop in pulse-echo signal magnitude, but only slight damage at 1/10 this fluence [2] Minor degradation to thin films [84] Measurable drop in response amplitude, but piezoelectric element was still operable [46] Measurable drop in electromechanical coupling [85]

N/av 0.5 (estimated) N/av Low N/av 0.6 4

thermal, plus fast thermal, plus fast thermal, plus fast

1.7 1019 thermal, 1.6 1018 fast 2.5 1018

Damage description

Permanent damage threshold for entire transducer assembly [3,29] 50% reduction in dielectric constant [81] No longer able to support reversible dielectric polarization [51] Fundamental changes in structure of single crystals [82] Relative permittivity drops, but is recoverable by post-irradiation annealing [83] Approximately 14% drop in coercive field [50]

Permanent damage threshold for a pressure transducer [3,29] ‘‘Critical’’ value for neutron damage in lanthanum-modified PZT. A post-irradiation anneal is helpful at lower fluence levels [86] Complete transducer breakdown, with sharp drop in electrical resistance [87] 40% drop in accelerometer output [32] No change in d33 [31,15,88,89]

N/av

5.8 1018 thermal plus 1.85 1018 fast 1.94 1022 fast

Lead metaniobate

N/av

1 1011 to 2.4 1012

Frequency response degradation ranged from 16% to 92% for entire acoustic emission transducer assembly [91]

Bismuth titanate

N/av

1 1020 fast

Lost 60% of one-way piezoelectric response [7,15]

Aluminum nitride

26.8

Master’s thesis by Severson at the Wright-Patterson Air Force Base in Ohio [91]. He focused on transducers employed for acoustic emission NDT; their principal components and frequency range were similar to those of commercial ultrasonic transducers. Severson’s study included a number of transducers, with a variety of exposure rates and total time-integrated neutron flux (fluence) of up to 1.5 1017 neutron/cm2. His conclusion was that prolonged exposure to neutron radiation at this level does not lead to catastrophic failure of the transducers, but rather a significant drop in their sensitivity. This drop started to become noticeable at a fluence of the order of 1015 neutron/cm2, although there was considerable variation depending on the dose rate and neutron energy [10,91]. Severson speculated that the efficiency drop was due to damage in the lead metaniobate piezoelectric material, but it was not feasible for him to verify this. At fluence levels over 1017 neutrons/cm2, he saw transducer efficiency losses that were on average 40–80% compared to non-irradiated transducers. Similar results were noted in separate studies at the BR1 research reactor at SCKCEN in Belgium [46]. A drop in efficiency might be accommodated with frequent recalibrations of transducers during use, but eventually transducer replacement would be required. Overall, the data of Table 5 are difficult to compare or interpret, due to (i) the strong dependence of irradiation damage on neutron energy [16]; (ii) the presence of mixed gamma and neutron fields; (iii) some tests performed using radiation bursts as opposed to time-invariant radiation fields [79,80], and (iv) the lack of documentation regarding possible elevated temperatures in many reported test results. The limited number of test results, and the large number of input parameters make it impossible at this point to provide comprehensive conclusions regarding transducer damage as a function of neutron fluence. However, Parks and Tittmann [88] suggest that AlN and ZnO offer the best prospects for

Damage is dependent on extent of isotope enrichment between N14 (high neutron capture cross section) and N15 (low cross section) [90]

endurance of the piezoelement if substantial levels of fast neutron flux (and gamma radiation) are encountered (Table 5). A series of tests on transducer assemblies sponsored by the US Department of Energy illustrates the inherent difficulties in measuring neutron irradiation endurance limits for ultrasonic transducers: The projected environment for a portion of the tests includes a thermal neutron flux of 3.6 1013 n/cm2 s, fast neutron flux of 1.2 1014 n/cm2 s, and gamma dose rate of 10 MGy/h, all at an elevated temperature of 350–400 °C. [15]. The mix of radiation types, elevated temperature and difficulties in conducting detailed examination of failed irradiated transducers will make interpretation of test results challenging. 6. Conclusion Although there have been several studies conducted on the expected lifetime of ultrasonic transducers in radiation fields, the different test conditions in each study and lack of detail make the results difficult to compare. Results of some tests have not been published, but combined with extensive operational experience in the nuclear power industry have led to a series of assumptions and manufacturing practises: (a) It is assumed that the damage caused by gamma rays to ultrasonic transducers is dependent only on the total accumulated dose, and not the dose rate, provided that the radiation causes no significant temperature rise in the transducer. (b) In conventional water-immersion ultrasonic transducers, it is the organically-based components that are most susceptible to radiation damage. These include the backing material, 1/4 wave matching layer, protective wearplate, adhesives, and plastic components in the cables. In addition, the


8


(c)

(d)

(e)

(f)

(g)

generation of gases in the plastic components during irradiation can lead to swelling, peeling, and generation of internal stresses, particularly at the interfaces between transducer layers. Secondary effects of this damage can be delaminations, cracking of the piezoelement, and water ingress. Radiation damage in conventional transducers normally leads first to degradation of performance, but not immediately to catastrophic failure. This damage is manifested by a drop in transducer sensitivity, and sometimes a narrowing of the bandwidth (probably due to separation of the backing layer from the piezoelement). Several moderately-priced modifications can be taken to the design of conventional transducers to make them more radiation resistant. These include the avoidance of certain plastics, use of radiation-hardened cables, selection of a strong adhesive that will not easily embrittle, removal of circuit elements from inside the casing, appropriate selection of a piezoelement compatible with both the expected cumulative dose level and temperature. Upon the adoption of the above-mentioned modifications to a standard transducer design, the expected lifetime is 1–2 MGy of gamma irradiation. Over this lifetime, the transducer may experience sub-lethal distortion and peeling of the wearplate or 1/4 wave matching layer, but moderate degradation in performance can be compensated by periodic recalibration. Additional tests on ultrasonic transducers of various types are currently underway or planned, e.g., [7,74,89]. Many such tests are on transducers featuring composite piezoelements with high radiation and temperature resistance. Dose limits well in excess of 100 MGy are claimed to be achievable provided organically based materials are excluded, and a manufacturing procedure is in place that minimizes the damage caused by any thermal mismatch of transducer components. It is not possible to make comprehensive conclusions regarding transducer damage caused by neutron radiation fluence, based on the limited amount and format of published data on the topic. The published data cannot be readily correlated, as measurements were conducted under a variety of test conditions. Some of the published data have limited value due to insufficient information regarding the neutron energy spectrum, concurrent gamma fields, and details on the types of plastics and adhesives used.

There are inadequate statistics to form general conclusions on the endurance limits of transducers designed for immersion in liquid metals used for cooling in advanced nuclear reactors, often liquid sodium or lead bismuth. Temperatures typically reach 600 °C at full power in liquid sodium reactors, with gamma fields of 30 kGy/h [13]; even systems designed for hot shutdown encounter temperatures of the order of 250 °C [11]. Additional key challenges are that the transducer must be able to resist the corrosive action of the coolant, while maintaining good ultrasonic coupling [10,35,44] – issues that lead to significant departures from transducers designed for water immersion. Protective membranes [45] and cabling structure represent additional departures from conventional transducer design such that the endurance statistics accumulated for water immersion transducers have no applicability. Acknowledgement Funding for this work was provided by the Canadian Nuclear Waste Management Organization (NWMO), under Contract # 00760 A-TDS.

References [1] K.E. Holbert, S. Sankaranarayanan, S.S. McCready, D.R. Spearing, A.S. Heger, Response of piezoelectric acoustic emission sensors to gamma radiation, in: Proceedings of the 7th European Conference on Radiation and Its Effects on Components and System, RADECS 2003, Noordwijk, Netherlands, September 2003. [2] G.H. Broomfield, The effects of temperature and irradiation on piezoelectric acoustic transducers and materials, UKAEA Report AERE-R 11 942, Harwell, UK, 1985. [3] K.E. Holbert, S.S. McCready, A.S. Heger, T.H. Harlow, D.R. Spearing, Performance of piezoresistive and piezoelectric sensors in pulsed reactor experiments, in: Proceedings of Fourth American Nuclear Society International Topical Meeting on Nuclear Plant Instrumentation, Controls and Human-Machine Interface Technologies, Columbus, OH, September 2004. [4] J. Rempe, J. Daw, D. Knudson, R. Schley, T. Unruh, B. Chase, J. Palmer, In-Pile Instrumentation to Support Fuel Cycle Research and Development – FY12 Status Report, Idaho National Laboratory Report INL/EXT-12-26921, 2012. [5] A.N. Sinclair, A. Chertov, Ultrasonic Inspection Development In High Radiation Fields, Contract Report DS-262 R002 Submitted to Nuclear Waste Management Organization, 2013. [6] K.E. Holbert, J.A. Nessel, S.S. McCready, A.Sharif Heger, T.H. Harlow, Response of piezoresistive MEMS accelerometers and pressure transducers to high gamma dose, IEEE Trans. Nucl. Sci. 50 (2003) 1852–1859. [7] J. Daw, J. Rempe, J. Palmer, P. Ramuhalli, R. Montgomery, H.-T. Chien, B. Tittmann, B. Reinhardt, G. Kohse, NEET In-Pile Ultrasonic Sensor EnablementFY-2013 Status Report, Idaho National Laboratory Report INL/EXT-13-29-144, 2013. [8] K.E. Holbert, S. Sankaranarayanan, S.S. McCready, D.R. Spearing, Response of lead metaniobate acoustic emission sensors to gamma irradiation, IEEE Trans. Nucl. Sci. 52 (2005) 2583–2590. [9] J. Rempe, H. MacLean, E. Schley, D. Hurley, J. Daw, S. Taylor, J. Smith, J. Svoboda, D. Kotter, D. Knudson, S.C. Wilkins, M. Guers, L. Bond, L. Ott, J. McDuffee, E. Parma, and G. Rochau, New In-Pile Instrumentation to Support Fuel Cycle Research and Development, Idaho National Laboratory Report INL/EXT-1019149, 2011. [10] J.W. Griffin, T.J. Peters, G.J. Posakony, H.T. Chien, L.J. Bond, K.M. Denslow, S.H. Sheen, A.C. Raptis, Under-Sodium Viewing: A Review of Ultrasonic Imaging Technology for Liquid Metal Fast Reactors, Prepared by Pacific Northwest National Laboratory for the U.S. Department of Energy, Contract DE-AC0576RL01830 Report PNNL-18292, Richland, WA, 2009. [11] L.J. Bond, J.W. Griffin, G.J. Posakony, R.V. Harris, D.L. Baldwin, Materials issues in high temperature ultrasonic transducers for under-sodium testing, AIP Conf. Proc. 1430 (2012) 1617–1624, http://dx.doi.org/10.1063/1.4716407. [12] R. Kazˇys, A. Voleišis, R. Šliteris, B. Voleišiene, L. Mazˇeika, H.A. Abderrahim, Research and development of radiation resistant ultrasonic sensors for quasiimage forming systems in a liquid lead–bismuth, Ultragarsas (Ultrasound) 62 (2007) 7–15. niene˙, Ultrasonic imaging techniques for non-destructive testing of [13] E. Jasiu nuclear reactors, cooled by liquid metals: review, Ultragarsas (Ultrasound) 62 (2007) 39–43. [14] R. Kazys, A. Voleišis, R. Šliteris, R. Reimondas, L. Mazeika, R. Van Nieuwenhove, P. Kupschus, H.A. Abderrahim, High temperature ultrasonic transducers for imaging and measurements in liquid Pb/Bi eutectic alloy, IEEE Trans Ultras. Ferro. Freq. Cont. 52 (2005) 525–537. [15] J. Daw, B. Tittmann, B. Reinhardt, G. Kohse, P. Ramuhalli, R. Montgomery, H.-T. Chien, J.-F. Villard, J. Palmer, J. Rempe, Irradiation testing of ultrasonic transducers, in: Proceedings of 3rd International Conference on Advancements in Nuclear Instrumentation Measurement Methods and Their Applications (ANIMMA), June 2013, doi: http://dx.doi.org/10.1109/ANIMMA. 2013.6728097. [16] G. Knoll, Radiation Detection and Measurement, John Wiley & Sons, 1979, ISBN 0-471-49545-X. [17] S.C. Lee, G. Teowee, R.D. Schrimpf, D.P. Birnie, D.R. Uhlmann, K.F. Galloway, Total-dose radiation effects on sol–gel derived PZT thin films, IEEE Trans. Nucl. Sci. 39 (1992) 2036–2043. [18] K.M. Beeson, C.E. Pepper, Acoustic Emission Sensor Radiation Damage Threshold Experiment, in Waste Management ’94: Working Towards a Cleaner Environment, Tucson, Feb–Mar 1994. [19] J.R. Schwank, R.D. Nasby, S.L. Miller, M.S. Rodgers, P.V. Dressendorfer, Totaldose radiation-induced degradation of thin film ferroelectric capacitors, IEEE Trans. Nucl. Sci. 37 (1990) 1703–1712. [20] K.E. Holbert, Personal Communication to A.N. Sinclair, 2014. [21] Sources and Effects of Ionizing Radiation, United Nations Scientific Committee on the Effects of Atomic Radiation, Report UNSCEAR 2008 to the General Assembly, 2010, ISBN: 978-92-1-142274-0. [22] R.J. Halstead, Radiation Exposures from Spent Nuclear Fuel and High-Level Nuclear Waste Transportation to Geological Depository or Interim Storage Facility in Nevada, (accessed 01.10.14). [23] A.G. Croff, O.W. Hermann, C.W. Alexander, Calculated, Two-Dimensional Dose Rates from a PWR Fuel Assembly, Oak Ridge National Laboratory Report ORNL/ TM-6754, March 1979. [24] L.P. Houssay, Robotics and Radiation Hardening in the Nuclear Industry, M.Sc. Thesis, Univ. of Florida, 2000.


A.N. Sinclair, A.M. Chertov / Ultrasonics xxx (2014) xxx–xxx [25] S.-G. Kwon, K.-E. Kim, C.-W. Ha, P.S. Moon, C.-C. Yook, Calculation of neutron and gamma-ray flux-to-dose-rate conversion factors, J. Korean Nucl. Soc. 12 (1980) 171–179. [26] J.K. Shultis, Radiation Analysis of a Spent-Fuel Storage Cask, Kansas State University, Engineering Experiment Station Report #290, 2000. [27] M.G. Silk, Ultrasonic Transducers for Nondestructive Testing, Nondestructive Testing Center at AERE Harwell, Adam Hilger Ltd., Bristol, 1984, ISBN 0-85274436-6. [28] D. Ensminger, L.J. Bond, Ultrasonics – Fundamentals, Technologies, and Applications, third ed., CRC Press, Berlin, 2012, ISBN 978-0-8247-5889-9. [29] A. Holmes-Siedle, L. Adams, Handbook of Radiation Effects, second ed., Oxford University Press, London, 2002. [30] D.V. Boychenko, A.Y. Nikiforov, P.K. Skorobogatov, A.V. Sogoyan, Radiation Effects in Piezoelectric Sensor, in: 9th European Conference on Radiation and Its Effects on Components and Systems, Deauville, France, September 2007. [31] D.A. Parks, B.R. Tittmann, Ultrasonic NDE in a reactor core, in: IEEE International Instrumentation and Measurement Technology Conference, Graz, Austria, May 2012, doi: http://dx.doi.org/10.1109/ULTSYM.2011.0188. [32] R.L. Thomas, Vibration instrumentation for nuclear reactors, in: International Symposium on Vibration Problems in Industry, Keswick, UK, April 1973. [33] S.L. Halverson, T.T. Anderson, A.P. Gavin, T. Grate, Radiation exposure of a lithium niobate crystal at high temperatures, IEEE Trans. Nucl. Sci. 17 (1970) 335–340. [34] T.K. Bierney, Instrumentation for the measurement of vibration in severe environments such as nuclear reactors, Endevo Technical Report TP272, Endevco–Meggit Sensing Systems, Irvine, CA, 1977. [35] R. Kazys, A. Voleisis, B. Voleisiene, High temperature ultrasonic transducers: review, Ultragarsas (Ultrasound) 63 (2008) 7–17. [36] Z. Gubinyi, C. Batur, A. Sayir, F. Dynys, Electrical properties of PZT piezoelectric ceramic at high temperatures, J. Electrochem. 20 (2008) 95–105. [37] R.G. Sabat, B.K. Mukherjee, W. Ren, G. Yang, Temperature dependence of the complete material coefficients matrix of soft and hard doped piezoelectric lead zirconate titanate ceramics, J. Appl. Phys. 101 (2007) 064111, http:// dx.doi.org/10.1063/1.2560441. [38] F. Li, Z. Xu, X. Wei, X. Yao, Determination of temperature dependence of piezoelectric coefficients matrix of lead zirconate titanate ceramics by quasistatic and resonance method, J. Phys. D: Appl. Phys. 42 (2007) 095417, http:// dx.doi.org/10.1088/0022-3727/42/9/095417. [39] C. Claeys, E. Simoen, Radiation Effects in Advanced Semiconductor Materials and Devices, Springer-Verlag, Berlin, 2002, ISBN 3-540-43393-7. [40] J.M. Benedetto, R.A. Moore, F.B. McLean, P.S. Brody, S.K. Dey, S.K. The, Effect of ionizing radiation on sol–gel ferroelectric PZT capacitors, IEEE Trans. Nucl. Sci. 37 (1990) 1713–1717. [41] Piezoelectric Ceramics: Principles and Applications, APC International Limited, 2002, ISBN: 0-9718744-09. [42] F.S. Foster, L.K. Ryan, D.H. Turnbull, Characterization of lead zirconate titanate ceramics for use in miniature high-frequency (20–80 MHz) transducers, IEEE Trans. UFFC 38 (1991) 446–453. [43] PZT5A & 5H materials technical data (typical values), CTS Corporation, , (accessed 22.04.14). [44] J.W. Griffin, G.J. Posakony, R.V. Harris, D.L. Baldwin, A.M. Jones, L.J. Bond, High temperature ultrasonic transducers for in-service inspection of liquid metal fast reactors, in: IEEE Ultrasonics Symposium (IUS), 2011, pp. 1924–1927, doi: http://dx.doi.org/10.1109/ULTSYM.2011.0479. niene˙, A. Voleišis, Ultrasonic evaluation of status of [45] R. Kazˇys, L. Mazˇeika, E. Jasiu nuclear reactors cooled by liquid metal, in: 9th European Conference on NDT, Berlin, ECNDT 2006 – We.1.2.4, September 2006. [46] F.P.J. Augereau, J.Y. Ferrandis, J.F. Villard, D. Fourmentel, M. Dierckx, J. Wagemans, Effect of intense neutron dose radiation on piezoceramics, Acoustics-08, Paris, June July, 2008, pp. 6473–6477. [47] R.W. Smith, Gamma radiation effects in lithium niobate, Proc. IEEE 59 (1971) 712–713. [48] M. Dierckx, Development of ultrasonic sensor for visualisation under heavy liquid metal, in: Coolants and Innovative Reactor Technologies, Aix-enProvence, 2009. [49] J.J. Keating, G. Murphy, Gamma-irradiation effects in single-crystal barium titanate, Phys. Rev. 1969 (1844) 476–480. [50] I. Lefkowitz, T. Mitsui, Effect of gamma-ray and pile radiation on the coercive field of BaTiO3, J. Appl. Phys. 30 (1959) 269, http://dx.doi.org/10.1063/ 1.1735149. [51] I. Lefkowitz, Radiation induced changes in the ferroelectric properties of some barium titanate type materials, J. Phys. Chem. Solids 10 (1959) 169–173. [52] H. Wang, T. Ritter, W. Cao, K.K. Shung, Passive materials for high frequency ultrasound transducers, in: SPIE Conference on Ultrasonic Transducer Engineering, SPIE 3664, 1992, pp. 35–42. [53] S.M. Milkovich, C.T. Herakovich, G.F. Sykes, Space radiation effects on the thermo-mechanical behavior of graphite–epoxy composites, J. Compos. Mater. 20 (1986) 579–593. [54] K.U. Vandergriff, Designing equipment for use in gamma environments, ORNL Oak Ridge National Laboratory Report ONRL/TM-11175, 1990, p. 25. [55] M.H. Van de Voorde, C. Restat, Selection Guide To Organic Materials For Nuclear Engineering, European Organization for Nuclear Research, CERN-72-7, Geneva, 1972. [56] W.W. Parkinson, O. Sisman, The use of plastics and elastomers in nuclear radiation, Nucl. Eng. Des. 17 (1971) 247–280.

9

[57] H.W. Bonin, V.T. Bui, H. Pak, E. Poirier, H. Harris, Radiation effects on aluminum–epoxy adhesive joints, J. Appl. Polym. Sci. 67 (1998) 37–47. [58] R.W. Smilie, F.A. Iddings, Mechanisms of transducer failure in a gamma radiation field, Mater. Evaluat. 11 (1983) 1409–1411. [59] D.W. Clegg, A.A. Collyer, Irradiation Effects on Polymers, Elsevier Applied Science, London, 1991. [60] K. Chaplin, A.N. Sinclair, Personal Communication, AECL, Chalk River, ON, 2013. [61] A. Karpelson, A.N. Sinclair, Personal Communication, Kinectrics, Toronto, ON, 2013. [62] M. Trelinski, A.N. Sinclair, Personal Communication, Ontario Power Generation, Whitby, ON, 2013. [63] W. Hatcher, A.N. Sinclair, Personal Communication, UTX Inc., Holmes, NY, 2013. [64] R.W. Smilie, Gamma Radiation Effects on Ultrasonic Transducers, Master of Science Thesis, Department of Nuclear Engineering, Louisiana State University and Agricultural and Mechanical College, 1978. [65] A. Karpelson, M. Trelinski, Operation of highly focussed immersion ultrasonic transducers at elevated temperatures, NDTNet (9), , 2004. [66] R. Sharp, M. Decreton, Radiation tolerance of components and materials in nuclear robot applications, Reliab. Eng. Syst. Safe. 53 (1996) 291–299. [67] P. Leszkow, M. Decreton, Radiation tolerant techniques of multiplexing analog signals in nuclear environments. in: First European Conference on Radiation and its Effects on Devices and Systems, RADECS 91, La Grande-Motte, France, September 1991. [68] M. Decreton, S. Coenen, J. de Geeter, J. Implementing radiation hardened sensors for computer aided teleoperation in a nuclear environment, in: Proceedings of the IEEE International Symposium on Industrial Electronics, vol. 1, 1997, pp. SS278–SS284, doi: http://dx.doi.org/10.1109/ISIE.1997. 651776. [69] M. Decreton, Position sensing in nuclear remote operation, Measurement 15 (1995) 43–51. [70] W. Bonivento, E. Collet, P. Imbert, C. de LA Taille, Radiation hard micro-coaxial cables for the atlas liquid argon calorimeters, Nucl. Instrum. Methods Phys. Res. A 451 (2000) 492–505. [71] Endevco Piezoelectric Accelerometer Model 2248, Meggitt Sensing Systems, Irvine, CA, , (accessed 24.04.14). [72] Radiation Hardness Manual (Rad) (Volume II Gamma Irradiation), International Thermonuclear Experimental Reactor (ITER) Report N 23 MA 35 01–04-12 W 0.1, 2012. [73] Model D9215 High Temperature Sensor, Physical Acoustics Corporation/ Mistras Group, , (accessed 1.10.14). [74] Radiation certificates, Lot # 108971, 115571, & 125571. Nordion Gamma Center of Excellence, Laval, Quebec, 2001. [75] High Temperature, Radiation-Hardened, Single Axis Accelerometers, Models 357B53 & 357b54, PCB Piezotronics, , (accessed 12.05.14). [76] D. Fourmental, J.-F. Villard, J.-Y. Ferrandis, F. Augereau, E. Rosenkrantz, M. Dierckx, Acoustic sensor for in-pile fuel rod fission gas release measurement, IEEE Trans. Nucl. Sci. 58 (2011) 151–155. [77] S. Momeni, A.N. Sinclair, Personal Communication, Physical Acoustics Corporation, Princeton Junction, NJ, 2014. [78] B.R. Tittmann, D.A. Parks, S.O. Zhang, High temperature piezoelectrics – a comparison, in: 13th Intl Symposium on Nondestructive Characterization of Materials (NDCM-XIII) 20–24 May 2013, le Mans, France, , (accessed 12.05.14). [79] S.S. McCready, T.H. Harlow, A.S. Heger, K.E. Holbert, Piezoresistive micromechanical transducer operation in a pulsed neutron and gamma ray environment, in: IEEE 39th Annual International Nuclear and Space Radiation Effects Conference (NSREC), Data Workshop Record, July 2002, pp. 181–186. [80] K.E. Holbert, A. Sharif Heger, S.S. McCready, Performance of commercial offthe-shelf microelectro mechanical systems sensors in a pulsed reactor environment, in: IEEE Radiation Effects Data Proceedings, Denver, CO, July 2010, pp. 129–136. [81] F.T. Rogers, Effect of pile irradiation on the dielectric constant of ceramic BaTiO, J. Appl. Phys. 27 (1956) 1066–1067. [82] M.C. Wittels, F.A. Sherrill, Fast neutron effects in tetragonal barium titanate, J. Appl. Phys. 28 (1957) 606–609. [83] Kobayashi, Effect of neutron irradiation on dielectric properties of barium titanate ceramics, Electric. Eng. Jpn. 94 (1974) 213–219. [84] R.A. Moore, J.M. Benedetto, J.M. McGarrity, F.B. McLean, Neutron irradiation effects on PZT thin films for nonvolatile-memory applications, IEEE Trans. Nucl. Soc. 38 (1991) 1078–1082. [85] G.H. Broomfield, The effect of low-fluence neutron irradiation on silverelectroded lead–zirconate–titanate piezoelectric ceramics, J. Nucl. Mater. 91 (1980) 23–34. [86] A. Sternberg, A. Spule, L. Shebanovs, E. Birks, H.W. Weber, H. Klima, F. Sauerzopf, Phase state and structure of ferroelectric ceramics under irradiation, Key Eng. Mater. 132–136 (1997) 1096–1099. [87] V.M. Baranov, S.P. Martynenko, A.I. Sharapa, Durability of ZTL piezoceramic under the action of reactor radiation, Soviet Atom. Energy 53 (1982) 803–804.


10


[88] D. Parks, B. Tittmann, Radiation tolerance of piezoelectric bulk single-crystal aluminum nitride, IEEE Trans. UFFC 61 (2014) 1216–1222. [89] J. Daw, B. Tittmann, B. Reinhardt, G. Kohse, P. Ramuhalli, R. Montgomery, H.-T. Chien, J.-F. Villard, J. Palmer, J. Rempe, Irradiation testing of ultrasonic transducers, IEEE Trans. Nucl. Sci. 61 (2014) 2279–2284. [90] T. Yano, K. Inokuchi, M. Shikama, J. Ukai, S. Onose, T. Maruyama, Maruyama, neutron irradiation effects on isotope tailored aluminum nitride ceramics by a

fast reactor up to 2 l026 n/m2, J. Nucl. Mater. 329–333 (Pt. B) (2004) 1471– 1475. [91] M.R. Severson, An experimental design for measuring in situ radiation damage to a piezoelectric transducer, Master’s Thesis submitted to Air Force Institute of Technology, Wright Patterson Air Force Base, Ohio, AFIT/GNE/ENP/04-06, 2004.


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