Scaling Factors Determination and Measurements’ Acceptance Criteria Deﬁnition

environments

Review Control Experiences Regarding Clearable Materials from Nuclear Power Plants and Nuclear Installations: Scaling Factors Determination and Measurements’ Acceptance Criteria Deﬁnition

Luca Albertone 1,*, Massimo Altavilla 2, Manuela Marga 1, Laura Porzio 1, Giuseppe Tozzi 1 and Pierangelo Tura 1

1 Arpa Piemonte, Dipartimento Rischi ﬁsici e tecnologici, Struttura Semplice Radiazioni ionizzanti e Siti Nucleari, Via Trino 89, 13100 Vercelli, Italy; [email protected] (M.M.); [email protected] (L.P.); [email protected] (G.T.); [email protected] (P.T.) 2 ISIN (Ispettorato Nazionale per la Sicurezza Nucleare e la Radioprotezione, National Inspectorate for Nuclear Safety and Radiation Protection), Via Capitan Bavastro 116, 00154 Roma, Italy; [email protected] * Correspondence: [email protected]

Received: 30 September 2019; Accepted: 14 November 2019; Published: 17 November 2019

Abstract: Arpa Piemonte has been carrying out, for a long time, controls on clearable materials from nuclear power plants to verify compliance with clearance levels set by ISIN (Ispettorato Nazionale per la Sicurezza Nucleare e la Radioprotezione - National Inspectorate for Nuclear Safety and Radiation Protection) in the technical prescriptions attached to the Ministerial Decree decommissioning authorization or into category A source authorization (higher level of associated risk, according to the categorization defined in the Italian Legislative Decree No. 230/95). After the experience undertaken at the “FN” (Fabbricazioni Nucleari) Bosco Marengo nuclear installation, some controls have been conducted at the Trino nuclear power plant “E. Fermi,” “LivaNova” nuclear installation based in Saluggia, and “EUREX” (Enriched Uranium Extraction) nuclear installation, also based in Saluggia, according to modalities that envisage, as a final control, the determination of γ-emitting radionuclides through in situ gamma spectrometry measurements. Clearance levels’ compliance verification should be performed for all radionuclides potentially present, including those that are not easily measurable (DTM, Difficult To Measure). It is therefore necessary to carry out upstream, based on a representative number of samples, those radionuclides’ determination in order to estimate scaling factors (SF), defined through the logarithmic average of the ratios between the i-th DTM radionuclide concentration and the related key nuclide. Specific radiochemistry is used for defining DTMs’ concentrations, such as Fe-55, Ni-59, Ni-63, Sr-90, Pu-238, and Pu-239/Pu-240. As a key nuclide, Co-60 was chosen for the activation products (Fe-55, Ni-59, Ni-63) and Cs-137 for fission products (Sr-90) and plutonium (Pu- 238, Pu-239/Pu-240, and Pu-241). The presence of very low radioactivity concentrations, often below the detection limits, can make it difficult to determine the related scaling factors. In this work, the results obtained and measurements’ acceptability criteria are presented, defined with ISIN, that can be used for confirming or excluding a radionuclide presence in the process of verifying clearance levels’ compliance. They are also exposed to evaluations regarding samples’ representativeness chosen for scaling factors’ assessment.

Keywords: clearance; scaling factor; decommissioning; nuclear power plant; nuclear installation

Environments 2019, 6, 120; doi:10.3390/environments6110120 www.mdpi.com/journal/environments Environments 2019, 6, 120x FOR PEER REVIEW 22 of of 14

1. Introduction 1. Introduction Until the early 2000s, it was noted that there were, within certain conditions, relatively constant ratios Until the early 2000s, it was noted that there were, within certain conditions, relatively constant among some radionuclides’ activity concentrations for each specific waste stream. For example, the ratios among some radionuclides’ activity concentrations for each specific waste stream. For example, “constant” ratio between the concentrations of Ce-144 and plutonium isotopes in the waste streams the “constant” ratio between the concentrations of Ce-144 and plutonium isotopes in the waste generated by a LWR (light water reactor) was proven [1]. The implication of this situation was immediate. streams generated by a LWR (light water reactor) was proven [1]. The implication of this situation It was indeed possible, once the above relationship would have been defined, to evaluate plutonium was immediate. It was indeed possible, once the above relationship would have been defined, to isotopes’ concentrations, which gave evident problems in terms of radiometric measurements, through evaluate plutonium isotopes’ concentrations, which gave evident problems in terms of radiometric the easier cerium determination. A large literature is available about this [1–3], essentially based on an measurements, through the easier cerium determination. A large literature is available about this [1–3], American origin which, limited to light water reactors, provides an extensive series of scaling factors essentially based on an American origin which, limited to light water reactors, provides an extensive (SF) for the different waste currents and different radionuclides of interest. However, using values series of scaling factors (SF) for the different waste currents and different radionuclides of interest. coming from literature has a limitation due to the fact that there is a wide variability of scaling factors, However, using values coming from literature has a limitation due to the fact that there is a wide as well as from waste stream, even from different nuclear installations and from the different way of variability of scaling factors, as well as from waste stream, even from different nuclear installations and operating on the same nuclear installation. From this, it follows that scaling factors’ values found in from the different way of operating on the same nuclear installation. From this, it follows that scaling the literature could find general applications from which general indications could be extracted. factors’ values found in the literature could find general applications from which general indications Nevertheless, it was necessary to establish specific evaluations regarding scaling factors, through could be extracted. Nevertheless, it was necessary to establish specific evaluations regarding scaling experimental investigations, when more precise technical information was necessary for defining, for factors, through experimental investigations, when more precise technical information was necessary example, a nuclear installation radioactivity inventory. for defining, for example, a nuclear installation radioactivity inventory. Nowadays in the international panorama, an average value is used for scaling factors’ Nowadays in the international panorama, an average value is used for scaling factors’ calculation, calculation, in some cases an arithmetic mean, while in other cases, a geometric (logarithmic) average, in some cases an arithmetic mean, while in other cases, a geometric (logarithmic) average, as in the case as in the case of Italy or the United States of America [4]. The concept of scaling factors is based on of Italy or the United States of America [4]. The concept of scaling factors is based on the assumption the assumption that the relationship between a key radionuclide and a radionuclide of difficult that the relationship between a key radionuclide and a radionuclide of difficult measurability is linear measurability is linear in the range of activities of interest (Figure 1). in the range of activities of interest (Figure1).

Figure 1. Ni-63~Co-60 correlation example for diﬀerent reactor types: pressurized water reactor (PWR) Figure 1. Ni-63~Co-60 correlation example for different reactor types: pressurized water reactor and boiling water reactor (BWR). Adapted from Determination and Use of Scaling Factors for Waste (PWR) and boiling water reactor (BWR). Adapted from Determination and Use of Scaling Factors for Characterization in Nuclear Power Plants, © IAEA, 2009 [5]. Waste Characterization in Nuclear Power Plants, © IAEA, 2009 [5]. The arithmetic mean will tend to produce a conservative value while the geometric mean will tendThe to produce arithmetic a more mean representative will tend to produce mean value a conservative when the data value is distributedwhile the geometric over several mean orders will tendof magnitude. to produce In a themore international representative panorama, mean value some when countries the data use logarithmicis distributed regression over several for scalingorders offactors magnitude. evaluation. In the In international this case, the samepanorama, correlation some factorscountries assume use logarithmic a non-linear regression relationship for between scaling factorsthe key evaluation. nuclide and In the this di case,ﬃcult the to measuresame correlati (DTM)on nuclide, factors assume and can a be non-linear used to more relationship accurately between model the key complex nuclide and and non-linear the difficult relationships to measure among (DTM) radionuclides. nuclide, and can be used to more accurately model the complex and non-linear relationships among radionuclides.

Environments 2019, 6, 120 3 of 14

2. Materials and Methods In the national context of scaling factors, referred to speciﬁc homogeneous groups, are determined through the application of the EPRI (Electric Power Research Institute) [1] method, which recognizes, in the calculation of the geometric mean and the dispersion associated with the distribution of the measured ratios (experimental scaling factors), the most eﬀective formalism in the statistical analysis of experimental data. Based on nuclear installation operational history, on the available radiometric data and on the systems, structures and radioactive waste subdivision in groups such as appropriate homogeneous radiological conditions are suitable, a minimum number of representative materials or waste samples [6] are taken (typically N = 20) for each one of the hypothesized homogeneous groups, so as to compute the i-th experimental scaling factor (SF) for each one of the N samples subjected to radiometric analysis: C SF = DTM , (1) CETM where, CDTM represents DTM concentration and CETM represents the easily (Table1) reference measurable radionuclide concentration (ETM, easy to measure).

Table 1. Reference key nuclide for diﬀerent DTMs.

DTM Radionuclide ETM Radionuclide Fe-55, Ni-59, Ni-63 Co-60 Sr-90, Pu-238, Pu239/240, Pu-241 Cs-137 Total-U U-238 DTM (diﬃcult to measure), ETM (easy to measure).

The determination of ETM radionuclides is performed by gamma spectrometry—in laboratory [7] and in situ [8], while for the DTM radionuclides, diﬀerent radiochemical methods are used [9–13]. Afterwards, the geometric mean ASF is calculated as:

P N ln SF i=1 i ASF = e N , (2) and the DSF dispersion parameter of the N experimental scaling factors is:

r P N (ln SF ln A )2 i=1 i− SF N 1 DSF = e − . (3)

The DSF deﬁnition [1,14] comes from the standard deviation (SD) meaning, applied to the logarithmic measurement distribution SFi. Given a value distribution ln(FSi), the probability that a new determination for ln(SF) gives a result belonging to the range ln(A ) – ln(D ) ln(SF) ln(A ) SF SF ≤ ≤ SF + ln(DSF) is 68.3%. Analogue probability, in the corresponding measurement distribution of SFi, results are associated with a new SF measurement whose value is in the range A /D SF A D . If SF SF ≤ ≤ SF· SF 2σ = 2ln(DSF), to the dispersion of distribution value ln(SFi) is associated, when there will be a new ln(SF) determination, a probability of 95.5% to assume a value in the range ln(A ) – 2ln(D ) ln(SF) SF SF ≤ ln(A ) + 2ln(D ), or A /D 2 SF A D 2 for SF measurements. ≤ SF SF SF SF ≤ ≤ SF· SF Scaling factor acceptability coming from the geometric mean of the N experimental scaling factors is therefore established coherently with conservative criteria, indicated by the EPRI [1] and NRC 2 (United States National Regulatory Commission) [15], relative to the 2σ dispersion (DSF ) of the distribution of experimental scaling factors. According to NRC [15], it can be considered an acceptable target that scaling factors are accurate within a factor of 10, or D 2 10. SF ≤ The nuclear regulatory body, ISIN, on the basis of indications, present in several international publications [1,5,15] and based on the solid materials radiological characterization, in particular relating Environments 2019, 6, 120 4 of 14

2 to the clearable solid materials, has adopted the criterion DSF 6 while, in the case of radioactive 2 ≤ wastes radiological characterization, the criterion DSF 8 has been adopted. 2 ≤ In the event that the 2σ dispersion (DSF ) of the distribution of the measurements satisﬁes the previous requirements, both in the case of clearable materials and radioactive wastes, the statistical consistency of the number of samples subjected to testing would be demonstrated and, consequently, the geometric mean would constitute a reliable estimate of the scaling factor for the generic nuclide representative of the set of materials or waste, constituting the homogeneous group under examination. Conversely, if the aforementioned requirements are not met, the deﬁnition of a valid scaling factor should be waived and any other criterion considered to be appropriately conservative should be used.

3. Results This paper does not claim to provide an overview of all the experiences regarding the determination of scaling factors for clearable materials, but only a brief report of the experiences carried out by Arpa Piemonte at:

Bosco Marengo “FN” nuclear installation; • Trino “E. Fermi” nuclear power plant; • Saluggia “LivaNova” nuclear installation; • Saluggia “EUREX” nuclear installation. • 3.1. Bosco Marengo ”FN” Nuclear Installation Experiences The Bosco Marengo “FN” nuclear installation carried out its activity in the nuclear fuel cycle field from 1972 to 1990 as the only national nuclear fuel manufacturer for ENEL’s (Ente Nazionale per l’Energia Elettrica) nuclear power plants. Currently, following the issue of Ministerial Decree 27 November 2008 for decommissioning authorization, the plant is completing the decommissioning operations, an activity that has involved the production, in addition to radioactive wastes, of considerable quantities of metallic materials, building materials, and various other materials intended for clearance. The nuclear fuel produced during the operation of the plant consisted of natural and low enriched uranium; therefore, the radionuclides potentially present are: U-238 and U-235 in percentages by mass equal to the enrichment values worked (in the range 0.2–5%) and U-234 in variable proportions depending on the enrichment values. Following the plant characteristics and the production cycle, the liquid effluents have been considered as characteristic of the average contamination of all the plant components. Scaling factors were therefore updated [16] through a statistical analysis of the isotopic composition—obtained by alpha spectrometry after radiochemical separation—of the liquid effluents collected during the period 2006–2018. In particular, it was possible to observe an average enrichment of about 2% with an approximately normal distribution. In this case, therefore, there is a statistically significant correlation (Figure2) between U-238’s and total uranium (Total-U) concentrations. It was therefore established to take the U-238 as reference radionuclide (key nuclide). In the 2013–2017 period, an amount of 12 lots, part of a total of 22 lots, consisting of cleared metallic materials, were subjected to control by Arpa Piemonte using the clearance levels contained in the technical prescriptions of the decommissioning authorization attached to the 27 November, 2008 Ministerial Decree (Tables2 and3).

Table 2. Metallic materials clearance levels.

Metallic Materials Radionuclide Direct Reuse Recycle Direct Reuse/Recycle α emitters 0.1 Bq/cm2 0.1 Bq/cm2 1 Bq/g Environments 2019, 6, 120 5 of 14 Environments 2019, 6, x FOR PEER REVIEW 5 of 14

Total-U~U-238 correlation 500

450 ASF=3.91 D 2=1.23 400 SF N=87

350

300

250 Total-U (Bq/l) Total-U 200

150

100

0 0 20406080100120 U-238 (Bq/l)

FigureFigure 2. 2. Total-U~U-238Total-U~U-238 correlationcorrelation inin thethe BoscoBosco MarengoMarengo “FN”“FN” nuclearnuclear installation’sinstallation’s liquidliquid eeffluents.ﬄuents. OnOn the the x-axis, x-axis, the the concentrationconcentration of of U-238U-238 as as determineddeterminedby byalpha alphaspectrometry spectrometry [ 10[10],], on on the the y-axis, y-axis, the the sumsum ofof the the concentrations concentrations ofof U-238, U-238, U-234, U-234, and and U-235, U-235, also also determined determined byby alpha alpha spectrometry. spectrometry. TheThe scalingscaling factor factorA ASFSF isis thethe slopeslope ofof thethe lineline shownshown inin thethe graph.graph.

Table 3. Non-metallic materials clearance levels. In the 2013–2017 period, an amount of 12 lots, part of a total of 22 lots, consisting of cleared metallic materials, were subjected to control byCementitious Arpa Piemonte Materials using the clearance Variouslevels Materialscontained in the technicalRadionuclide prescriptions of the decommissioning authorizationDemolition attached to the 27 November, Buildings Reuse Mass 2008 Ministerial Decree (Tables 2 and 3). Surface Building Rubble Concentration α emitters 0.1 Bq/cm2 1 Bq/cm2 0.1 Bq/g 0.1 Bq/g Table 2. Metallic materials clearance levels. Other U-238 and U-235 decay 2 2 products different from Legislative 0.1 Bq/cm Metallic0.1 Bq Materials/cm 0.1 Bq/g 0.01 Bq/g Decree n. 230/1995 TableRadionuclide I-2, Annex I Direct Reuse Recycle Direct Reuse/Recycle α emitters 0.1 Bq/cm2 0.1 Bq/cm2 1 Bq/g A total of 376 tons of iron and steel were cleared and all the γ spectrometry measurements confirmed the respect of the clearance levelsTable (Figure 3. Non-metallic3). U-238 materials was determined clearance by levels. direct γ spectrometry [8], while Total-U was estimated using the above scaling factor. Various Cementitious Materials 3.2. Trino “E. Fermi” Nuclear Power Plant Experiences Materials Radionuclide Demolition Buildings Mass In the case of Trino “E. Fermi” nuclear power plant, the analysis ofBuilding the discharges (Figure4) Reuse Surface Concentration did not allow us to identify scaling factors because the resulting dispersionRubble did not result to be in compliance with EPRIα emitters criteria. This circumstance 0.1 Bq/cm is not2 surprising1 Bq/cm2since 0.1 the Bq/g effl uents derive 0.1 Bq/g from a mixingOther of U-238 all the and waste U-235 streams decay products coming from the different systems of the plant, so that results are hardlydifferent traceable from Legislative to a single Decree homogeneous n. 230/1995 group. 0.1 Bq/cm2 0.1 Bq/cm2 0.1 Bq/g 0.01 Bq/g Table I-2, Annex I

A total of 376 tons of iron and steel were cleared and all the γ spectrometry measurements confirmed the respect of the clearance levels (Figure 3). U-238 was determined by direct γ spectrometry [8], while Total-U was estimated using the above scaling factor.

Environments 2019, 6, 120 6 of 14 Environments 2019, 6, x FOR PEER REVIEW 6 of 14

FigureFigure 3. 3.Performed Performed radiometric radiometric measurements measurements on metallic on metallic materials materials to be cleared to be fromcleared Bosco from Marengo Bosco Environments“FN”Marengo nuclear 2019 “FN”, 6, installation. x FORnuclear PEER installation. REVIEW 7 of 14

3.2. Trino “E. Fermi” Nuclear Power PlantSr-90~Cs-137 Experiences correlation 18 In the case of Trino “E. Fermi” nuclear power plant, the analysis of the discharges (Figure 4) did not allow us to identify scaling factors because the resulting dispersion did not result to be in 16 compliance with EPRI criteria. This circumstance is not surprising since the effluents derive from a mixing of all the waste streams coming from the different systems of the plant, so that results are 14 hardly traceable to a single homogeneous group. ASF=0.05 D 2=9.82 12 SF N=27

8 Sr-90 (Bq/l)

0 0 20406080100120 Cs-137 (Bq/l)

FigureFigure 4.4. Sr-90~Cs-137Sr-90~Cs-137 correlationcorrelation inin thethe TrinoTrino “E.“E. Fermi”Fermi” nuclearnuclear powerpower plant’splant’s liquidliquide effluents.ﬄuents.

However,However, aa moremore detaileddetailed analysis—carriedanalysis—carried outout byby meansmeans ofof simplesimple samplesample groupinggrouping cyclescycles usingusing RR softwaresoftware scripts—madescripts—made itit possiblepossible toto identifyidentify twotwo statisticallystatistically signiﬁcantsignificant groupsgroups (Figure(Figure5 5),), both with DSF2 ≤ 6, indicating the presence of at least two different waste streams. The highest point concentration of Cs-137 (~ 110 Bq/l) does not significantly influence the correlation.

Sr-90~Cs-137 correlation 18

ASF=0.46 D 2=3.41 16 SF N=5

8 Sr-90 (Bq/l)

ASF=0.03 D 2=2.16 6 SF N=22

0 0 20406080100120 Cs-137 (Bq/l)

Environments 2019, 6, x FOR PEER REVIEW 7 of 14

Sr-90~Cs-137 correlation 18

14 ASF=0.05 D 2=9.82 12 SF N=27

8 Sr-90 (Bq/l)

0 0 20406080100120 Cs-137 (Bq/l)

Figure 4. Sr-90~Cs-137 correlation in the Trino “E. Fermi” nuclear power plant’s liquid effluents. Environments 2019, 6, 120 7 of 14 However, a more detailed analysis—carried out by means of simple sample grouping cycles using R software scripts—made it possible to identify two statistically significant groups (Figure 5), 2 both with D 2 6, indicating the presence of at least two different waste streams. The highest point both with DSFSF ≤ 6, indicating the presence of at least two different waste streams. The highest point concentrationconcentration ofof Cs-137Cs-137 (~(~ 110110 BqBq/l)/l) doesdoes notnot significantlysignificantly influenceinfluence thethe correlation.correlation.

Sr-90~Cs-137 correlation 18

ASF=0.46 D 2=3.41 16 SF N=5

8 Sr-90 (Bq/l)

ASF=0.03 D 2=2.16 6 SF N=22

0 0 20406080100120 Cs-137 (Bq/l)

Figure 5. Sr-90~Cs-137 correlation in the Trino “E. Fermi” nuclear power plant’s liquid eﬄuents—identiﬁed groupings have been highlighted.

During 2018, Trino “E. Fermi” nuclear power plant started a treatment activity for part of the potentially clearable radioactive waste, split into three lots. These wastes were made of material carried out from processing in controlled areas, even though they did not belong to any plant system, classified as radioactive waste at the time of production and that had become clearable over time. Arpa Piemonte witnessed the initial treatment of some of the samples taken by the operator (10%) and subsequently analyzed the aqueous extracts obtained according to UNI (Ente Nazionale Italiano di Unificazione) standard UNI 11194 [7] in order to make assessments on the scaling factors. The first analysis of the nature of these samples (sand, cement, earth, metallic material, and clothing) could make one suspect the absence of homogeneity in the composition of the contamination of the waste. The laboratory analyses, carried out both on ETM and DTM radionuclides, confirmed the absence of homogeneity:

In wastes with lower contamination (lot 1), the presence of Cs-137, Co-60, and Ni-63 was observed • only in half of the samples, and Sr-90 in a single sample. The presence of alpha emitters was not observed. In the wastes with high contamination (lot 3), the presence of Cs-137 was observed beyond the • clearance levels (Table4), Co-60, Ni-63, and Sr-90 in only half of the samples, and alpha emitters in only two samples. Environments 2019, 6, 120 8 of 14

Table 4. Metallic materials and various materials clearance levels. Technical prescriptions attached to the Ministerial Decree 2 August, 2012 of the decommissioning authorization.

Metallic Materials Various Materials Radionuclide Reuse Surface Recycle Surface Reuse/Recycle Reuse/Recycle (Bq/cm2) (Bq/cm2) Mass (Bq/g) Mass (Bq/g) H-3 10,000 100,000 1 1 C-14 1000 1000 1 1 Mn-54 10 10 1 0.1 Fe-55 1000 10,000 1 1 Co-60 1 10 1 0.1 Ni-59 10,000 10,000 1 1 Ni-63 1000 10,000 1 1 Sr-90 10 10 1 1 Sb-125 10 100 1 1 Cs-134 1 10 0.1 0.1 Cs-137 10 100 1 1 Eu-152 1 10 1 0.1 Eu-154 1 10 1 0.1 α emitters 0.1 0.1 0.1 0.01 Pu-241 10 10 1 1

In particular, in addition to the impossibility of estimating DTM radionuclides scaling factors in manyEnvironments samples, 2019, the 6, x EPRIFOR PEER criteria REVIEW were never respected (Figure6). 9 of 14

Ni-63~Co-60 correlation 300

250

200

150 Ni-63 (Bq/l) Ni-63

100

0 012345678 Co-60 (Bq/l)

FigureFigure 6.6.Ni-63~Co-60 Ni-63~Co-60 correlationcorrelation presentpresent inin thethe TrinoTrino“E. “E.Fermi” Fermi” clearable clearable materials. materials.

However, it is possible to highlight the fact that some of the samples belong to one of the two Ni-63~Co-60 correlation waste streams present in the liquid eﬄuents (Figure7), conﬁrming that these materials do not form a 500 single homogeneous lot. The condition of homogeneity is a necessary condition for estimating the scaling450 factors.

400

350

300 ASF=3.82 D 2=4.88 250 SF N=7 Ni-63 (Bq/l) Ni-63 200 Clearable materials 150

100

0 0 5 10 15 20 25 30 35 40 45 50 Co-60 (Bq/l)

Figure 7. Ni-63~Co-60 correlation present in the Trino “E. Fermi” nuclear power plant’s liquid effluents, in red, and in some clearable materials samples, in blue.

3.3. Saluggia “LivaNova” Nuclear Installation Experiences At the “LivaNova” nuclear installation based in Saluggia—category A source authorization— for a long time, a hydrocarbon contamination of portions of soil, within the controlled area in which

Environments 2019, 6, x FOR PEER REVIEW 9 of 14

Ni-63~Co-60 correlation 300

250

200

150 Ni-63 (Bq/l) Ni-63

100

0 012345678 Co-60 (Bq/l)

Environments 2019, 6, 120 9 of 14 Figure 6. Ni-63~Co-60 correlation present in the Trino “E. Fermi” clearable materials.

Ni-63~Co-60 correlation 500

450

400

350

300 ASF=3.82 D 2=4.88 250 SF N=7 Ni-63 (Bq/l) Ni-63 200 Clearable materials 150

100

0 0 5 10 15 20 25 30 35 40 45 50 Co-60 (Bq/l)

FigureFigure 7. 7.Ni-63~Co-60 Ni-63~Co-60 correlation correlation present present in the in Trinothe Trin “E. Fermi”o “E. Fermi” nuclear nuclear power plant’s power liquid plant’s eﬄ uents,liquid ineffluents, red, and in in red, some and clearable in some materials clearable samples, materials in samples, blue. in blue.

3.3.3.3. SaluggiaSaluggia “LivaNova” “LivaNova” Nuclear Nuclear Installation Installation Experiences Experiences AtAt thethe “LivaNova” “LivaNova” nuclear nuclear installation installation based based in in Saluggia—category Saluggia—category A sourceA source authorization—for authorization— afor long a long time, time, a hydrocarbon a hydrocarbon contamination contamination of portionsof portions of of soil, soil, within within the the controlled controlled area area in in which which radioactive wastes were also placed, had been highlighted. In this area, during the past years, diesel tanks were placed for supplying an incineration plant, which is now dismantled. For the purpose of conventional remediation, ISIN has, in any case, requested the radiological characterization of the soil to correctly deﬁne its management. In particular, the several possibilities are:

Soil contaminated by radionuclides (regardless of any hydrocarbon contamination) to be managed • as cleared materials or, if the relevant clearance levels are not respected, as radioactive waste. Soil without any radiological constraints but contaminated by hydrocarbons to be managed as • “special” waste. Soil not contaminated by either radionuclides or hydrocarbons. • Soil radiological characterization showed the presence—with considerable inhomogeneities—of the following radionuclides: Cs-137, Sr-90, Am-241, and plutonium. These kinds of radioisotopes had already been identiﬁed in 2012 in the contaminated sediments of the radioactive eﬄuent management plant (now decontaminated), in the same ratios. In this case, therefore, by integrating the two datasets, it was possible to preliminarily estimate a complete set of scaling factors characteristic of a single main source of contamination (Figure8). Environments 2019, 6, x FOR PEER REVIEW 10 of 14 radioactive wastes were also placed, had been highlighted. In this area, during the past years, diesel tanks were placed for supplying an incineration plant, which is now dismantled. For the purpose of conventional remediation, ISIN has, in any case, requested the radiological characterization of the soil to correctly define its management. In particular, the several possibilities are: • Soil contaminated by radionuclides (regardless of any hydrocarbon contamination) to be managed as cleared materials or, if the relevant clearance levels are not respected, as radioactive waste. • Soil without any radiological constraints but contaminated by hydrocarbons to be managed as “special” waste. • Soil not contaminated by either radionuclides or hydrocarbons. Soil radiological characterization showed the presence—with considerable inhomogeneities—of the following radionuclides: Cs-137, Sr-90, Am-241, and plutonium. These kinds of radioisotopes had already been identified in 2012 in the contaminated sediments of the radioactive effluent management plant (now decontaminated), in the same ratios. In this case, therefore, by integrating Environmentsthe two datasets,2019, 6, 120 it was possible to preliminarily estimate a complete set of scaling 10factors of 14 characteristic of a single main source of contamination (Figure 8).

Sr-90/Am+Pu~Cs-137 correlation 1,000.00

ASF=0.20 2 DSF =2.94 N=6 100.00

ASF=0.16 2 DSF =2.69 N=6 10.00

Sr-90 (Bq/g) Sediments Am+Pu (Bq/g) 1.00

Soils 0.10

0.01 0.1 1.0 10.0 100.0 1,000.0 10,000.0 Cs-137 (Bq/g)

Environments 2019, 6, x FOR PEER REVIEW 11 of 14 FigureFigure 8.8.Sr-90 Sr-90/Am/Am + + Pu~Cs-137Pu~Cs-137 correlationcorrelation presentpresent inin thethe SaluggiaSaluggia “LivaNova”“LivaNova” nuclearnuclear installationinstallation clearancesoilssoils andandlevel sedimentssediments (Table samples.5) samples.—in particular less than 1%—the detection limits for plutonium isotopes were only in the order of ten times smaller than the corresponding clearance level (Figure 10). 3.4. Saluggia “EUREX” Nuclear Installation Experiences 3.4. SaluggiaIf for the “EUREX”Sr-90 it can Nuclea be consideredr Installation acceptable Experiences setting the scaling factor to zero, for plutonium isotopes,AtAt thethe it “EUREX”is“EUREX” more precautionary nuclearnuclear installation,installation,—also considering basedbased inin Saluggia—nuclearSaluggia the characteristics—nuclear fuelfuel of reprocessingreprocessing the plant—to plant—inplant estimate—in thethe a yearnon-zeroyear 2017,2017, scaling thethe radiologicalradiological factor, assuming contaminationcontamination a rectangular ofof thethe distribution soilsoil surroundingsurrounding between aa portion portionzero and ofof the thethe pertinent liquidliquid radioactiveradioactive detection limits.eeffluentﬄuent managementmanagement plant plant was was highlighted highlighted (Figure (Figure9 ).9). The correct management of the excavation soil, also in this case, has interested a complete radiological characterization of the soil itself, which showed the presence of only Cs-137. Specifically, however, while for the Sr-90 radionuclide the detection limit was much lower than the relevant

Figure 9. Contaminated area.

Table 5. Cementitious and various materials clearance levels. Ministerial Decree 12 August 2009. Technical management prescriptions.

Building Demolition Various Materials Radionuclide Surface (Bq/cm2) Mass (Bq/g) Mass (Bq/g) H-3 10,000 1 1 Ni-59 100,000 1 1 Ni-63 100,000 1 1 Co-60 1 0.1 0.1 Sr-90 100 1 1 Tc-99 100 1 1 Sb-125 10 1 1 Cs-134 10 0.1 0.1 Cs-137 10 1 1 Pm-147 10,000 1 1 Sm-151 10,000 1 1 Eu-152 10 1 0.1 Eu-154 10 1 0.1 Eu-155 100 1 1 α emitters 1 0.1 0.01 Other U-238 and U-235 decay products different from 0.1 0.1 0.01 Legislative Decree n. 230/1995 Table I-2, Annex I

Environments 2019, 6, 120 11 of 14

The correct management of the excavation soil, also in this case, has interested a complete radiological characterization of the soil itself, which showed the presence of only Cs-137. Speciﬁcally, however, while for the Sr-90 radionuclide the detection limit was much lower than the relevant clearance level (Table5)—in particular less than 1%—the detection limits for plutonium isotopes were only in the order of ten times smaller than the corresponding clearance level (Figure 10).

Table 5. Cementitious and various materials clearance levels. Ministerial Decree 12 August 2009. Technical management prescriptions.

Building Demolition Various Materials Radionuclide Surface (Bq/cm2) Mass (Bq/g) Mass (Bq/g) H-3 10,000 1 1 Ni-59 100,000 1 1 Ni-63 100,000 1 1 Co-60 1 0.1 0.1 Sr-90 100 1 1 Tc-99 100 1 1 Sb-125 10 1 1 Cs-134 10 0.1 0.1 Cs-137 10 1 1 Pm-147 10,000 1 1 Sm-151 10,000 1 1 Eu-152 10 1 0.1 Eu-154 10 1 0.1 Eu-155 100 1 1 α emitters 1 0.1 0.01 Other U-238 and U-235 decay products diﬀerent from Legislative Decree 0.1 0.1 0.01 n. 230/1995Environments Table 2019 I-2,, 6, x FOR PEER REVIEW 12 of 14 Annex I Pu-241Pu-241 100100 11 1 1

Sr-90/Pu~Cs-137 correlation 10,000.00

cSr-90< 1% climit Sr-90 → ASF=0 1,000.00

100.00

2 cPu< 10% climit Pu → ASF=0.0044 DSF =5.90 10.00

1.00

0.10 0 50 100 150 200 250 300 350 400 450 500 Cs-137 (Bq/kg)

Sr-90 (Bq/kg) Sr-90 limit (Bq/kg) Pu (Bq/kg) Pu limit (Bq/kg) Linear [Sr-90 (Bq/kg)] Linear [Pu (Bq/kg)]

Figure 10.FigureSr-90 10. /Pu~Cs-137Sr-90/Pu~Cs-137 correlation correlation pres presentent in the in Saluggia the Saluggia “EUREX” “EUREX” nuclear installation nuclear soils installation samples. soils samples. 4. Discussion Clearance levels’ compliance verification should be performed for all radionuclides potentially present, including DTM. It is therefore necessary to carry out upstream, based on a representative number of samples, those radionuclides’ determination in order to estimate scaling factors (SF). Specific radiochemistry is used for defining DTMs’ concentrations, such as Fe-55, Ni-59, Ni-63, Sr-90, Pu-238, and Pu-239/Pu-240. As a key nuclide, Co-60 was chosen for the activation products (Fe-55, Ni-59, and Ni-63) and Cs-137 for the fission products (Sr-90) and plutonium (Pu- 238, Pu-239/Pu-240, and Pu-241). The presence of very low radioactivity concentrations, often below the detection limits, can make it difficult to determine the related scaling factors. The different technical experiences carried out so far allows us to formulate the following observations on methods and measurement acceptability performance requirements: • The homogeneity of a clearable lot of material should always be verified with experimental measurements. • All available information can be useful for the purposes of estimating scaling factors. • In all samples used to estimate scaling factors, at least one ETM radionuclide must be detectable. • It is appropriate to define an exclusion level, for example a detection limit – for the detection limit definition and, more generally, for the definition of the characteristic limits, the reference is represented by the ISO (International Standard Organization) standard ISO 11929 [17] – in the range 1–10% of the relevant clearance level, in order to be able to exclude the presence of DTM radionuclides in the sample. • It is appropriate to define an acceptability level (for example a detection limit in the range 10– 50% of the relevant clearance level) in order to establish whether the sample can be used to estimating scaling factors.

Environments 2019, 6, 120 12 of 14

If for the Sr-90 it can be considered acceptable setting the scaling factor to zero, for plutonium isotopes, it is more precautionary—also considering the characteristics of the plant—to estimate a non-zero scaling factor, assuming a rectangular distribution between zero and the pertinent detection limits.

4. Discussion Clearance levels’ compliance verification should be performed for all radionuclides potentially present, including DTM. It is therefore necessary to carry out upstream, based on a representative number of samples, those radionuclides’ determination in order to estimate scaling factors (SF). Specific radiochemistry is used for defining DTMs’ concentrations, such as Fe-55, Ni-59, Ni-63, Sr-90, Pu-238, and Pu-239/Pu-240. As a key nuclide, Co-60 was chosen for the activation products (Fe-55, Ni-59, and Ni-63) and Cs-137 for the fission products (Sr-90) and plutonium (Pu- 238, Pu-239/Pu-240, and Pu-241). The presence of very low radioactivity concentrations, often below the detection limits, can make it difficult to determine the related scaling factors. The different technical experiences carried out so far allows us to formulate the following observations on methods and measurement acceptability performance requirements:

The homogeneity of a clearable lot of material should always be verified with • experimental measurements. All available information can be useful for the purposes of estimating scaling factors. • In all samples used to estimate scaling factors, at least one ETM radionuclide must be detectable. • It is appropriate to define an exclusion level, for example a detection limit – for the detection • limit definition and, more generally, for the definition of the characteristic limits, the reference is represented by the ISO (International Standard Organization) standard ISO 11929 [17] – in the range 1–10% of the relevant clearance level, in order to be able to exclude the presence of DTM radionuclides in the sample. It is appropriate to define an acceptability level (for example a detection limit in the range 10–50% • of the relevant clearance level) in order to establish whether the sample can be used to estimating scaling factors.

In particular, if radiometric measurements provide for the DTM radionuclide a CDTM activity concentration lower than the corresponding detection limit DLDTM, this last detection limit may be prudently adopted for the estimation of the scaling factor (a more cautious assumption from the radiation protection point of view). Alternatively, a rectangular distribution in the range 0–DLDTM could be taken as a reference, adopting DLDTM/2 for the purposes of estimating the scaling factor (a less cautious assumption from the radiation protection point of view, perhaps more realistic). The above criteria, due to preliminary considerations, will have to be evaluated case-by-case, depending on the plant, the speciﬁc context, and the speciﬁc radionuclide. In summary, the decisional scheme of Figure 11 may be adopted. Environments 2019, 6, x FOR PEER REVIEW 13 of 14

In particular, if radiometric measurements provide for the DTM radionuclide a CDTM activity concentration lower than the corresponding detection limit DLDTM, this last detection limit may be prudently adopted for the estimation of the scaling factor (a more cautious assumption from the radiation protection point of view). Alternatively, a rectangular distribution in the range 0–DLDTM could be taken as a reference, adopting DLDTM/2 for the purposes of estimating the scaling factor (a less cautious assumption from the radiation protection point of view, perhaps more realistic). The above criteria, due to preliminary considerations, will have to be evaluated case-by-case, depending on the plant, the specific context, and the specific radionuclide. EnvironmentsIn summary,2019, 6, 120 the decisional scheme of Figure 11 may be adopted. 13 of 14

Figure 11. Scaling factors’ decisional flow chart. Figure 11. Scaling factors’ decisional flow chart. Funding: This research received no external funding. Funding: This research received no external funding. Conflicts of Interest: The authors declare no conflict of interest. Conflicts of Interest: The authors declare no conflict of interest. References References 1. Electric Power Research Institute (EPRI). Low Level Waste Characterization Guidelines (EPRI TR-107201); EPRI: 1. Electric Power Research Institute (EPRI). Low Level Waste Characterization Guidelines (EPRI TR-107201); Palo Alto, CA, USA, 1996. EPRI: Palo Alto, CA, USA, 1996. 2. Hong, S.B.; Kang, M.J.; Lee, K.W.; Chung, U.S. Development of scaling factors for the activated concrete of 2. Hong, S.B.; Kang, M.J.; Lee, K.W.; Chung, U.S. Development of scaling factors for the activated concrete of the KRR-2. Appl. Radiat. Isot. 2009, 67, 1530–1533. [CrossRef][PubMed] the KRR-2. Appl. Radiat. Isot. 2009, 67, 1530–1533. 3. Niese, S.; Gleisberg, B. Determination of radioisotopes of Ce, Eu, Pu, Am and Cm in low-level wastes from 3. Niese, S.; Gleisberg, B. Determination of radioisotopes of Ce, Eu, Pu, Am and Cm in low-level wastes from power reactors using low-level measuring techniques. Appl. Radiat. Isot. 1996, 47, 1113–1114. [CrossRef] power reactors using low-level measuring techniques. Appl. Radiat. Isot. 1996, 47, 1113–1114. 4. International Standard Organization (ISO). ISO 21238 Nuclear Energy—Nuclear Fuel Technology—Scaling Factor Method to Determine the Radioactivity of Low-And Intermediate-Level Radioactive Waste Packages Generated at Nuclear Power Plants; ISO: Geneva, Switzerland, 2007. 5. International Atomic Energy Agency (IAEA). Determination and Use of Scaling Factors for Waste Characterization in Nuclear Power Plants (IAEA NW-T-1.18); IAEA: Vienna, Austria, 2009. 6. Zaffora, B.; Magistris, M.; Saporta, G.; La Torre, F.P. Statistical sampling applied to the radiological characterization of historical waste. EPJ Nucl. Sci. Technol. 2016, 2.[CrossRef] 7. Ente Nazionale Italiano di Unificazione (UNI). UNI 11665 Determinazione di Radionuclidi Gamma Emettitori Mediante Spettrometria Gamma ad Alta Risoluzione. Determination of Gamma Emitting Radionuclides by High-Resolution Gamma Spectrometry; UNI: Milano, Italy, 2017. Environments 2019, 6, 120 14 of 14

8. International Standard Organization (ISO). ISO 18589-7 Measurement of Radioactivity in the Environment—Soil—Part 7: In Situ Measurement of Gamma-Emitting Radionuclides; ISO: Geneva, Switzerland, 2013. 9. International Standard Organization (ISO). ISO 13160 Water Quality—Strontium 90 and Strontium 89—Test Methods Using Liquid Scintillation Counting or Proportional Counting; ISO: Geneva, Switzerland, 2012. 10. International Standard Organization (ISO). ISO 13166 Water Quality—Uranium Isotopes—Test Method Using Alpha-Spectrometry; ISO: Geneva, Switzerland, 2014. 11. International Standard Organization (ISO). ISO 13167 Water Quality—Plutonium, Americium, Curium and Neptunium—Test Method Using Alpha Spectrometry; ISO: Geneva, Switzerland, 1992. 12. International Standard Organization (ISO). ISO/DIS 22515 Water Quality—Iron-55—Test Method Using Liquid Scintillation Counting; ISO: Geneva, Switzerland, 2019. 13. International Standard Organization (ISO). ISO/CD 23655-1 Water Quality—Nickel-59 and Nickel-63—Part 1: Test. Method Using Liquid Scintillation Counting; ISO: Geneva, Switzerland, 2019. 14. Ente Nazionale Italiano di Unificazione (UNI). UNI 11194 Manufatti di Rifiuti Radioattivi Condizionati-Caratterizzazione Radiologica di Manufatti Appartenenti Alla Categoria 2 ai Fini del Conferimento al Deposito Finale. Radiological Characterization of Category 2 Packages for the Purpose of Disposal in the Final Repository; UNI: Milano, Italy, 2006. 15. United States National Regulatory Commission. Low-Level Waste Licensing Branch Technical Position on Radioactive Waste Classification; NRC: Rockville, MD, USA, 1983. 16. Albertone, L.; Marga, M.; Porzio, L. Esperienze di Controllo dei Materiali Allontanabili Dagli Impianti Nucleari Tramite Misure di Spettrometria Gamma in Situ, Atti del XXXVII Convegno AIRP “Le radiazioni: Valori, Conoscenza Scientifica e Aspetti Operativi”; Aosta 15-17/10/2014; AIRP: Roma, Italy, 2014; ISBN 978-88-88648-40-8. 17. International Standard Organization (ISO). ISO 11929 Determination of the Characteristic Limits (Decision Threshold, Detection Limit and Limits of the Confidence Interval) for Measurements of Ionizing Radiation–Fundamentals and Application; ISO: Geneva, Switzerland, 2019.

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