DOSE RATES EVALUATION ON ENVIRONMENT AROUND ALMIRANTE ALVARO ALBERTO NUCLEAR POWER STATION AFTER ANGRA 2 NUCLEAR POWER PLANT S OPERATION

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1 2007 International Nuclear Atlantic Conference INAC 2007 Santos, SP, Brazil, September 29 to October 5, 2007 ASSOCIAÇÃO BRASILEIRA DE ENERGIA NUCLEAR ABEN DOSE RATES EVALUATION ON ENVIRONMENT AROUND ALMIRANTE ALVARO ALBERTO NUCLEAR POWER STATION AFTER ANGRA 2 NUCLEAR POWER PLANT S OPERATION Orlando C. Ferreira, Elenilson Barboza and Sergio Ney M. Cardoso Eletrobrás Termonuclear S.A. Eletronuclear Rodovia Rio-Santos (BR-101) Km. 522 Itaorna Angra dos Reis, RJ landocf@eletronuclear.gov.br barboza@eletronuclear.gov.br sergion@eletronuclear.gov.br ABSTRACT Six years after Angra 2 Nuclear Power Plant has began operating, the dose rates on the environment around it remain the same. This report s purpose is to present pre and post-operational dosimetric data during the last seven years ( ) to evaluate the real plant s operation radiological impact on the environmet between Angra dos Reis and Paraty. The results obtained in these analysis, show that there is no radiological impact to the environment around Almirante Alvaro Alberto NPS after the beginning of Angra 2 operation. 1. INTRODUCTION Since 1978, the Environmental Monitoring Laboratory (EML) monitores the environment around Almirante Alvaro Alberto Nuclear Power Station (AAANPS) to verify the potential environmental impact which can be caused by Angra 1 and Angra 2 Nuclear Power Plants operation. From 1978 to 1982, a preliminary radiometric measurement of the area was done and composed the pre-operational report. From 1982 to 2000, the monitoring goes on with the operation of Angra 1 and was the pre-operational time to Angra 2. Since 2000, the monitoring includes the operation of both units. This work s purpose is to present the pre and post-operational dosimetric data during the last 7 years of Angra 1 and Angra 2 s operations ( ) to evaluate the real radiologic impact on environment, caused by the Nuclear Power Plant s operations. Thermoluminescent dosimeters (TLD) are displaced in 41 points between Angra dos Reis and Paraty cities. The results obtained show that, even with the beginning of Angra 2 NPP s operation of, there was no impact to the environment around Angra Nuclear Station. 2. THE ENVIRONMENT MONITORING LABORATORY

2 The Environmental Monitoring Laboratory is a radioactive installation belonging to Eletrobras Termonuclear S.A. ELETRONUCLEAR, owner of Angra 1 and Angra 2 NPP, and is located in Mambucaba Village, 12 Km away from Nuclear Station, in Angra dos Reis. Its purpose is to monitore all the environment around the Nuclear Power Plants to verify the possible impact caused by the operation of the two units. This monitoration is done by radiometric analysis of several environmental samples, from marine, terrestrial and aerial sources, colected in points stablished in pre-operational time of Angra 1 ( ). Besides these samplings, the environment monitoring is done by direct measurement of dose rate in several points between Angra dos Reis and Paraty. Another study, made by EML biologist team, is to verify the possible impact to marine fauna and flora in Saco de Piraquara de Fora bay, due the thermal impact caused by the NPP s discharges. All EML s analysis follow the reference parameters stablished on Brazil s legislation. Any anormality must be reported to the policy (CNEN and IBAMA). 3.1 Principle of the Method 3. METHODOLOGY The thermoluminescent dosimetry is based on the energy absorption, due to environmental radiation, by the electrons in the atoms of the elements which the dosimeters cristals are made and in its release like a luminous energy, by heating of these cristals. The eletronic levels of the cristals work like traps and they can capture the electrons with less energy when these electrons gain more energy by absorption of the incident radiation energy, and change its fundamental level by a more energetic state (excited state). When the excitation stop, the electrons remain in these levels for an indetermined time. During the analysis, the cristals are heated and the electrons gain suficient energy to scape out of the trap and return to the fundamental state, releasing all the absorbed energy like a light. This is called thermoluminescence. The dosimeters used in EML are apropriate to environmental monitoring due to their efficient response to low dose rates. The response of the thermoluminescent cristals, for all types of radiations, is linear with the dose. The least detectable dose for environmental dosimetry depends of several variables, including: thermoluminescent cristal sensibility; TLD Reader sensibility; cristal preparation; the time between the irradiation and the reading; the combination of the radiations like a mixture of beta particules e γ-rays; the radiation incidence angle;

3 the stress of the thermoluminescent cristal in extreme conditions of temperature and humidity. The EML dosimeter s detection limit is about mrem. 3.2 Description of the Method To measure the dose rates in environment, the EML uses thermoluminescent dosimeters (TLD), model UD-814 Panasonic, composed of 4 cristals: one is Lithium Borate cristal (Li 2 B 4 O 7 :Cu) and 3 Calcium Sulfate cristals (CaSO 4 :Tm) with the same Lead shielding in each cristal. Due to this fact, the TLD has a good sensibility to very low dose rates (environmental doses). These dosimeters are placed in 41 points under influence of the Nuclear Station, between Angra dos Reis and Paraty (Table 1). They are changed each 3 months and analysed in the Dosimeter Reader UD-716 Panasonic. They are placed 1 m height and protected from the rain to avoid humidity. These dosimeters are not affected by light. Before they are placed at the monitoring points, the dosimeters are inicially cleaned of any energy previously absorbed (natural radiation). Control dosimeters are used, to provide the background results. During environmental dosimeters readings, reference dosimeters are used. These dosimeters are irradiated with known dose values and are read with the field dosimeters, in turns. Table 1. Localization of the monitoring points with TLD POINT LOCAL ANGRA 1 ANGRA 2 SECTION DIST. (m) SECTION DIST. (m) A01 Ponta Fina S 610 S 700 A02 Mamede s Hill SSE 640 SSE 780 A03 Mamede s Hill SE 200 SE 390 A04 Mamede s Hill ESE 340 ESE 560 A05 Rio-Santos s Road E 450 ESE 660 A06 Rio-Santos s Road ENE 430 E 570 A07 Rio-Santos s Road NE 520 ENE 620 A08 Rio-Santos s Road NNE 720 NE 700 A09 Rio-Santos s Road N 600 N 470 A10 Rio-Santos s Road NNW 700 NNW 500 A11 Rio-Santos s Road NW 790 NW 570 A12 Information Center WNW 970 WNW 750 A13 Rio-Santos s Road W W C14 Environment M. Laboratory WSW WSW

4 B15 Rio-Santos s School NE ENE B16 Piraquara (Velho Beach) SE SE B17 Praia Brava (Centro Náutico) W W B18 Praia Brava (Hospedagem I) W W B19 Sítio Beach (Pingo D Água) ENE ENE B21 Vermelha Beach WSW WSW B22 Frade Hotel NNE NNE C23 Paqueta Island ENE ENE C24 Sandri Island SW SW C25 Mambucaba (Vila Histórica) WSW WSW C26 Brandao Island ESE ESE C27 Gratau Farmer NNE NNE C28 Mambucaba (Eletronuclear) WSW WSW C29 Colégio Naval (Angra)* E E C30 Praia Hotel* ENE ENE C31 Tarituba* WSW WSW C32 Paraty* SW SW A33 Ponta Fina SSW 980 S A34 Micro-wave Tower ENE 810 ENE 950 B35 Pump s House (Frade) N/NNE NNE C36 Bracuy Port NE NE C37 Ribeira Beach (Angra) E E C38 Madezatti Village W W A46 Molhe de Itaorna WSW 480 SW 380 A47 Molhe de Itaorna SW 430 SSW 460 A48 Molhe de Itaorna W 580 WSW 410 A49 Road to Itaorna Angra 1 N 430 NNE 340 * Points located in control area. The other points are located in impact área. 4. RESULTS The dose rates values, during the seven years of environmental monitoring with TLD, are presented in Table 2. It s presented the anual average values, as much to the impact area as to the control area. Impact area is defined like been the area in which is allowed to expect to be affected by NPP s operation. Control area is defined like been the area in which is not allowed to expect to be affected by NPP s operation.

5 YEARS Table 2. Direct measures results of TLD dose rates AREAS IMPACT CONTROL (msv/30 days) (msv/30 days) ,11 0, ,09 0, ,11 0, ,10 0, ,07 0, ,08 0, ,07 0,06 The Fig. 1 below shows a graphic view of the data from the table above. We can notice that the values of dose rate are maintained statistically the same since DOSE RATES (msv/30 days) 0,12 0,1 0,08 0,06 0,04 0, YEARS IMPACT CONTROL Figure 1. Dose rate variation from 2000 to CONCLUSIONS It can be noted, in Fig. 2, that the values of the dose rates do not show any significant changes since the pre-operational time of Angra 1 ( ) to 2006, with two units in operation. It means that the environment did not suffer any radiological impact with the beginning of Angra 2 operation.

6 When Angra 3 starts its operation, the environment monitoring will goes on and the EML will verifies if anything will changes. DOSE RATES (msv/30 days) 0,12 0,1 0,08 0,06 0,04 0,02 0 PRE YEARS IMPACT CONTROL Figure 2. Dose rate variation since pre-operational time of Angra 1. REFERENCES 1. Cardoso, S. N. M., Programa de Monitoração Ambiental Radiológico Operacional, Relatórios Anuais, Volume 1, Eletrobrás Termonuclear S.A. (1982 a 2006). 2. Miklos, J. A., Theory and Operation of a Thermoluminescent Dosimetry Program Using the Panasonic System, Training Course, Eletrobrás Termonuclear S.A. (1999). 3. UD-716 Panasonic Reader Manual.