Atmospheric input of 137Cs and 239,240Pu isotopes in Korea after theFukushima nuclear power plant accident

Jung-Suk Oh, Sang-Han Lee n, Jong-Ki Choi, Jong-Man Lee, Kyung-Bum Lee, Tae-Soon ParkKorea Research Institute of Standards and Science, Daejeon 305-340, Republic of Korea

H I G H L I G H T S

� Atmospheric samples have been collected for the analysis of 137Cs and Pu isotopes.� Current levels of 137Cs and 239,240Pu in Korean rainwater are reported.� The monthly depositional fluxes of 239,240Pu and 137Cs are evaluated.� The Fukushima Daiichi NPP accident caused no significant impact in Korea.

a r t i c l e i n f o

Available online 1 December 2013

Keywords:FukushimaRainwater137Cs239,240PuDry deposition

a b s t r a c t

Caesium isotopes (134Cs and 137Cs) and 239,240Pu in rainwater and dry deposition have been analyzed byKorea Research Institute of Standards and Science (KRISS) since the Fukushima nuclear power plant(NPP) accident in March 2011. The concentrations of 239,240Pu and 137Cs in the rainwater are 2.671.0 to1573 mBq/kg and 0.01 to 0.36 mBq/kg, respectively. The concentrations are concordant to thoseobserved before the Fukushima NPP accident, on the other hand, the monthly depositional flux of239,240Pu and 137Cs are much lower than the amounts observed after Fukushima NPP accident and inMonaco in 1998–2001. This confirms that the Fukushima NPP accident caused no significant impactin Korea.

& 2013 Elsevier Ltd. All rights reserved.

1. Introduction

Plutonium in the environment mainly consists of four isotopes;238Pu (t1/2¼87.74y), 239Pu (t1/2¼2.4100�104y), 240Pu (t1/2¼6.561�103y) and 241Pu (t1/2¼14.33y). 239Pu and 240Pu are themost important isotopes because of their very long half-lives andhigh abundance. 137Cs is a fallout radionuclide characterized asa high toxicity element with a reasonably long half-life (t1/2¼30.05y) and a long residence time in biological circulation,particularly affecting muscles (Laboratoire National HenriBecquerel (LNHB), 2013; Lee et al., 2013a, 2013b).

Majority of 137Cs and 239,240Pu in the environment wereoriginated from the atmospheric weapons testing conducted bythe USA and the former Soviet Union in the mid-1950s to early1960s and from accidents at nuclear power plants, such asChernobyl in 1986. On March 11th, 2011, a nuclear accidentoccurred at the Fukushima Dai-ichi Nuclear Power Plant (NPP) asa result of a large scale earthquake. The earthquake recorded the

magnitude 9.0 with 500 km long and 200 kmwide and an ensuingtsunami (Doi et al., 2013).

The Fukushima Daiichi NPP accident caused the releaseof a large amount of radioactive fission products such as 131I(T1/2: 8.02d), 134Cs (T1/2: 2.06y), and 137Cs to the atmosphere andto the marine environment. The artificial radionuclides releasedinto the environment are suspended in the air and are depositedon the ground as global fallout by either wet or dry precipitation(Lee et al., 2002). Various studies on the 134Cs, 137Cs and 131I inthe rainwater and aerosol samples have been immediatelycarried out after the Fukushima Daiichi NPP accident to evaluatethe degree of artificial radionuclide contamination in the envir-onment. (Pham et al., 2012; Povinec et al., 2012; Lujanienė et al.,2012; Kim et al., 2012). However, the little information on theseisotopes in rainwater samples is known and the further studieson plutonium in rainwater and dry deposition samples have notbeen conducted because of the complexity of radiochemical andsample preparation techniques due to its low activity in theenvironment.

The objectives of this study are to introduce an analytical methodof low level artificial radionuclides and to evaluate an impact of theFukushima Daiichi NPP accident by carrying out the analysis of 137Csand 239,240Pu in rainwater sample and dry deposition.

Contents lists available at ScienceDirect

journal homepage: www.elsevier.com/locate/apradiso

Applied Radiation and Isotopes

0969-8043/$ - see front matter & 2013 Elsevier Ltd. All rights reserved.http://dx.doi.org/10.1016/j.apradiso.2013.11.099

n Corresponding author. Tel.: þ82 428 685 812; fax: þ82 428 685 671.E-mail address: s.lee@kriss.re.kr (S.-H. Lee).

Applied Radiation and Isotopes 87 (2014) 53–56

2. Materials and methods

2.1. Rainwater and dry deposition sampling

The rainwater and the dry deposition sampling systems wereplaced on the roof of the KRISS building in Daejeon, Korea after theFukushima Daiichi NPP accident. The rainwater sampling wasperformed by using a 1�1 m plastic collector. The collector,designed to prevent evaporation of rainfall, consists of 4 parallelpolyethylene containers (each with a capacity of 20 L). Aftercollecting rainwater from the container, the samples were acidifiedwith concentrated HCl (ca. pH 1), (Lee et al., 2013a). The drydeposition samples were collected at the end of each month byusing a 1�1 m plastic collector. The radiochemical separation wasconducted in the laboratory. The sensitivity for Cs and plutoniumisotope (239,240Pu) is improved by analyzing large volumes ofrainwater sample. The detailed radiochemical procedures for Csand Pu isotopes in rainwater sample were described elsewhere(Lee et al., 2002, 2013a).

2.2. Preconcentration of 137Cs and 239,240Pu in rainwater

Stable Cs and 242Pu tracers were added and the samples werethoroughly mixed to achieve equilibrium between the tracers andthe rainwater samples. An appropriate amount (0.5 mL/1 L ofsample) of saturated KMnO4 were added and mixed with 10 MNaOH solution to obtain pH 9–10. Then 0.5 M MnCl2 was added,adjusting pH to 9 to co-precipitate the plutoniumwith manganeseoxide. The precipitates (Pu) were dissolved by using a reducingagent (0.1 g/mL NH2OH�HCl) with HCl. After the Pu oxidation statewas converted from Pu(III) to Pu(IV) with NaNO2, plutonium wereco-precipitated with 50 mg of iron. The residues were dissolved inconcentrated HCl and evaporated to dryness. The sample wasredissolved in 8 M HNO3, followed by a radiochemical separationprocedure for plutonium using an anion exchange column.

The supernatants from MnO2 precipitation were transferred toanother container for caesium isotope (134Cs and 137Cs) analysis.The pH of Cs-containing supernatant previously described wasadjusted to pH 1–2 using 10 M HCl. An appropriate amount of AMP(ammonium molybdophosphate) was added to the sample andstirred for 1 h to adsorb Cs onto the AMP. The AMP precipitate wasre-dissolved with 5 mL of 10 M NaOH and was transferred to astandardized container for a well-type HPGe detector (Ortec) with

a relative efficiency of 90%. The chemical recoveries obtained fromthis procedure, which ranged from 40 to 50%, were measuredusing an inductively coupled plasma-mass spectrometry (ICP-MS)by measuring the stable Cs (Lee et al., 2013a).

2.3. Radiochemical procedure for the separation of 239,240Pu in thedry deposition sample

The dry deposition sample after 137Cs estimation was dissolvedin concentrated HNO3, HCl and HF, and evaporated to dryness.The sample was redissolved in 8 M HNO3. The sample solution(8 M HNO3) was passed through a Bio Rad (1-X8, 100–200 mesh,Cl� form) anion exchange column (10 mm dia.�120 mm).The columnwas washed with 100 mL of 8 M HNO3 and thenwashedwith 100 mL of 10 M HCl. Finally, Pu was eluted with 100 mL of 0.1 MNH4I-9 M HCl. The eluent was evaporated to dryness and NH4I wasremoved using H2O2 and concentrated HNO3. The acids wereevaporated to dryness again and Pu isotopes were electroplatedusing Na2SO4 as an electrolyte onto a 27 mm stainless steel disk(SSD) for 1 h at a constant current of 1 A. The Pu isotopes electro-plated on the SSD were counted by alpha spectrometry.

3. Results and discussion

3.1. Temporal variations of 239,240Pu and 137Cs in rainwater

After the Fukushima Daiichi NPP accident, the presence of Puisotopes originated from the Fukushima NPP was reported(Lujanienė et al., 2012). However, in the previous study performedby the KRISS the concentrations of 239,240Pu in rainwater werebelow the LLD (low limit of detection as defined by Currie, 1968) of0.1 μBq/kg, suggesting no detectable impact of 239,240Pu from theFukushima Daiichi NPP accident to Korea Peninsular (Lee et al.,2013a). Nevertheless, the study of Pu in rainwater is worthwhileand important because of its radiological toxicity. As shown inTable 1, the Pu isotopes were positively reported in severalsamples, but most of rainwater samples did not show any Pucoinciding with the earlier study (Lee et al., 2013a). The temporalvariations of Pu concentration in rainwater are presented in Fig. 1,including results of other previous studies (Thein et al., 1980;Ballestra et al., 1987; Rubio-Montero and Martin Sanchez, 2001;Lee et al., 2002; This study).

Table 1The monthly depositional fluxes of 137Cs and 239,240Pu in Daejeon in Korea from. November 2011 to February 2013.

Precipitation(mm/month)

Particledepositionweight (g)

137Cs(mBq/m2/month)

Unc.(k¼1)

239,240Pu(mBq/m2/month)

Unc.(k¼1)

Nov. 2011 103.2 0.774 o1.00 – 0.14 0.10December 11.5 0.291 o1.00 – 0.15 0.09Jan. 2012 16.4 0.724 6.08 0.19 0.25 0.10February 2.5 0.254 3.93 0.26 o0.07 –

March 54.6 2.91 25.13 0.59 0.68 0.17April 66.2 3.02 22.46 0.55 0.67 0.20May 24.0 1.76 10.96 0.45 o0.07 –

June 57.8 2.33 15.06 0.30 0.48 0.17July 277.6 1.06 2.95 0.19 0.12 0.08August 463.6 0.77 4.26 0.27 o0.07 –

September 242.5 0.18 1.65 0.30 o0.07 –

October 81.3 0.35 o1.00 – o0.07 –

November 58.4 1.24 o1.00 – o0.07 –

December 64.6 1.44 o1.00 – 0.34 0.08Jan. 2013 46.2 0.28 1.68 0.86 0.09 0.05February 54.2 1.21 11.1 2.2 0.19 0.06

LLD (low level of detection) for 137Cs:o1.0 (mBq/m2/month).LLD (low level of detection) for 239,240Pu:o0.07 (mBq/m2/month).

J.-S. Oh et al. / Applied Radiation and Isotopes 87 (2014) 53–5654

This figure suggests that the Pu concentrations in rainwater aredecreasing exponentially and the current concentrations of Pu(2.671.0 to 1573 mBq/kg) are concordant to those observedbefore the Fukushima Daiichi NPP accident (Lee et al., 2002;Hong et al., 2006). These findings confirm that the FukushimaDaiichi NPP accident caused no significant impact in Korea.

The temporal variations of 137Cs concentrations in rainwater arepresented in Fig. 2. In the previous study conducted after theFukushima Daiichi NPP accident, the highest concentration of134Cs in rainwater was estimated to be 334774 mBq/kg and thelevel of 134Cs in rainwater rapidly decreased with time andeventually became an LLD (o0.01 mBq/kg) in August 2011 (Leeet al., 2013a). An effort was made to identify 134Cs in rainwatersamples because the half-life of 134Cs (2.06y) is comparativelylonger than other isotope discharged from the Fukushima DaiichiNPP accident, i.e., 131I. However, no 134Cs was measured in rain-water samples from this study. Therefore, the source of 137Cs inrainwater observed in this study is thought be resuspended fromthe past fallout and not from the Fukushima Daiichi NPP accident.

The present level of 137Cs concentration in rainwater rangedfrom 0.01 to 0.36 mBq/kg. Although the 137Cs concentration variedwith time (Fig. 2), its concentration level is comparable to thosereported in the previous study (Hong et al., 2006), i.e., before theFukushima Daiichi NPP accident. It seems that the variation of137Cs reported in this study is attributable to a precipitation rate.The higher concentration of 137Cs observed was concordant to dry

season, while the lower concentration of 137Cs was shown in heavyrainfall season in Korea (Korea Metrological Administration (KMA),2011–2013). Similar phenomena have been reported elsewhere(Lee et al., 2002; Hong et al., 2006).

3.2. Depositional fluxes of 239,240Pu and 137Cs

The results of monthly depositional fluxes of 239,240Pu and 137Cswere presented in Table 1 and Fig. 3. The high depositional fluxesof 239,240Pu appear from March to April. The periods of highdeposition coincide with periods of dry season. Although theprecipitation has been known as the main factor controllingdepositional fluxes of radionuclides (Lee et al., 2002), the impactof precipitation was not shown in this study. The temporalvariation of monthly depositional fluxes of 239,240Pu was shownin Fig. 4. The results are comparable to those reported by Lee et al.(2002) in Monaco and Hong et al. (2006) in Korea, respectively.Therefore, the 239,240Pu input from the Fukushima Daiichi NPPaccident is thought be very little over Korea.

In addition to the 239,240Pu, the Cs isotopes were measured indry deposition samples because the 134Cs and 137Cs have beenknown as main isotopes discharged from the Fukushima DaiichiNPP accident together with 131I. The 134Cs was not measured in drydeposition samples because of low activity. The 134Cs was reportedless than low limit of detection (LLD:o1 mB/kg) like the rainwatersamples.

The variation of monthly depositional fluxes of 137Cs is similarto the pattern of the 239,240Pu, indicating that the high depositionalfluxes appeared from March to April. The present amounts ofmonthly 137Cs depositional fluxes are one or two orders ofmagnitude lower than those observed in April and May after theFukushima Daiichi NPP accident and in Monaco in 1998–2001 (Leeet al., 2002; Kim et al., 2012).

Fig. 1. Temporal variation of 239,240Pu concentrations in rainwater (▲: Thein et al.,1980; Δ: Ballestra et al., 1987; ■: Rubio-Montero and Martin Sanchez, 2001; □: Leeet al., 2002; �: this study).

Fig. 2. Temporal variation of 137Cs in the rainwater in Daejeon and JejuIsland, Korea.

Fig. 3. Temporal variation of monthly deposition fluxes of 239,240Pu.

Fig. 4. Temporal variation of 239,240Pu and 137Cs in rainwater with precipitation inDaejeon, Korea.

J.-S. Oh et al. / Applied Radiation and Isotopes 87 (2014) 53–56 55

4. Conclusions

(i) The higher concentration of 137Cs is concordant to dry season,while the lower concentration of 137Cs were shown in heavyrainfall season.

(ii) The Pu concentration in rainwater is decreasing exponentiallywith time and the current concentration of Pu is similar tothose observed before the Fukushima Daiichi NPP accident,confirming that the Fukushima Daiichi NPP accident causedno impact..

(iii) The monthly depositional fluxes of 239,240Pu and 137Cs aremuch lower than the amounts observed after Fukushima NPPaccident and in Monaco in 1998–2001.

Acknowledgement

This work was supported by the Korea Research Institute ofStandards and Science under the project “Establishment of IonizingRadiation Measurement Standards”, Grant 13011026.

References

Ballestra, S., Holm, E., Walton, A., Whitehead, N.E., 1987. Fallout deposition atMonaco following the Chernobyl accident. J. Environ. Radioact. 5, 391–400.

Currie, L.A., 1968. Limits for qualitative detection and quantitative determination;application to radiochemistry. Anal. Chem. 40, 586–593.

Doi, T., Masumoto, K., Toyoda, A., Tanaka, A., Shibata, Y., Hirose, K., 2013. Anthro-pogenic radionuclides in the atmosphere observed at Tsukuba: characteristicsof the radionuclides derived from Fukushima. J. Environ. Radioact. 122, 55–62.

Hong, G.H., Chung, C.S., Lee, S.H., Kim, S.H., Baskaran, M., Lee, H.M., Kim, Y.I., Yang,D.B., Kim., C.K., 2006. Artificial radionuclides in the Yellow Sea: inputs andredistribution. In: Povinec, P.P., Sanchez-Cabeza, J.A (Eds.), Radioactivity in theEnvironment. Elsevier, Amsterdam, pp. 96–133.

Kim, C.K., Byun, j.I., Chae, J.S., Choi, H.Y., Choi, S.W., Kim, D.J., Kim, Y.J., Lee, D.M.,Park, W.J., Yim, S.A., Yun, J.Y., 2012. Radiological impact in Korea following theFukushima nuclear accident. J. Environ. Radioact. 111, 70–82.

Korea Metrological Administration (KMA), 2011, 2012, 2013. Monthly PrecipitationRate. ⟨http://www.kma.go.kr/weather/climate/average_30years.jsp⟩.

Laboratoire National Henri Becquerel (LNHB), 2013. Decay Data Evaluation Project(DDEP) ⟨http://www.nucleide.org/DDEP_WG/DDEPdata.htm⟩.

Lee, S.H., Heo, D.H., Kang, H.B., Oh, P.J., Lee, J.M., Park, T.S., Lee, K.B., Oh, J.S., Suh, J.K.,2013a. Distribution of 131I, 134Cs, 137Cs and 239,240Pu concentrations in Koreanrainwater after the Fukushima nuclear power plant accident. J. Radioanal. Nucl.Chem. 296, 727–731.

Lee, Sang-Han, Lee, Sun Ah., Lee, Jong Man., Park, Tae Soon., Lee, K.B., 2013b.Measurement of 137Cs in the soil in Korea by low-level background gamma-rayspectrometer. J. Radioanal. Nucl. Chem. 296, 721–725.

Lee, S.H., Pham, M.K., Povinec, P.P., 2002. Radionuclide variations in the air overMonaco. J. Radioanal. Nucl. Chem. 254, 445–453.

Lujanienė, G., Byčenkienė, S., Povinec, P.P., Gera, M., 2012. Radionuclides from theFukushima accident in the air over Lithuania: measurement and modellingapproaches. J. Environ. Radioact. 114, 71–80.

Pham, M.K., Eriksson, M., Levy, I., Nies, H., Osvath, I., Betti, M., 2012. Detection ofFukushima Daiichi nuclear power plant accident radioactive traces in Monaco.J. Environ. Radioact. 114, 131–137.

Povinec, P.P., Sýkora, I., Holý, K., Gera, M., Kováčik, A., Brest’áková, L., 2012. Aerosolradioactivity record in Bratislava/Slovakia following the Fukushima accident—acomparison with global fallout and the Chernobyl accident. J. Environ. Radioact.114, 81–88.

Rubio-Montero, M.P., Martin Sanchez, A., 2001. Activity of 239þ240Pu and 238Pu inatmospheric deposits. Appl. Radiat. Isot 55, 97–102.

Thein, M., Ballestra, S., Yamato, A., Fukai, R., 1980. Delivery of transuranic elementsby rain to the Mediterranean Sea. Geochim. Cosmochim. Acta 44, 1091–1097.

J.-S. Oh et al. / Applied Radiation and Isotopes 87 (2014) 53–5656