PLANNING OF ENVIRONMENTAL

Átírás

1 Theses of Ph.D dissertation PLANNING OF ENVIRONMENTAL RADIATION PROTECTION ACTIONS WITH REGARD TO DOSE REDUCTION AND DOSE OPTIMIZATION Written by: TÜNDE KATONA Supervisor: Prof. Béla Kanyár E NVIRONMENTAL S CIENCES P H D S CHOOL U NIVERSITY OF P ANNONIA D EPARTMENT OF RADIOCHEMISTRY Veszprém/Hungary,

2 INTRODUCTION, AIMS OF THE WORK Main objects of environmental radiation protection are determining, preventing and reducing the real and potential health detriment effects of the public due to radiation exposure. One has to find the optimum dose, which is as low as reasonably achievable considering the advantages and disadvantages of radioactivity. In order to apply radiation protection in practice numerical values have to be used, for example averted dose has to be given in monetary value to feature the benefit of the intervention action. This is the base of the application of radiation protection and determines its practical introduction. The cost-benefit analysis, the monetary needs of the averted dose, the personal compensation etc. are influenced by many today yet uncertain factors. During planning of radiation protection actions the first step is dose assessment as accurate as possible. A process to fulfil this requirement is developing existing measuring methods; an other method is computer simulation when long time scale predictions could be done and unmeasurable quantities can be analyzed. After dose assessment the next step during planning of intervention is dose optimization because the aim is to hold the dose contribution as low as reasonably achievable (ALARA-concept) and not to reduce it to the minimum. METHODS I. The dissertation presents a method to determine the parameters of the cost-benefit function in case of the public exposures. These parameters are the following: monetary value of the averted dose: α [MFt (person Sv) -1 ] and aversion coefficient: a [-]. The values of the parameters has been defined by a willingness to pay (WTP) questionnaire. These results are among the first ones in case of public radiation protection and their social benefit can be remarkable. II. The most significant part of natural radiation in case of public originates from the radioactive noble gas: radon, which causes inhalation dose. So determining, reducing and optimizing radon concentration in dwellings are important parts of the public radiation protection actions. An aim of the work was to study ventilation which is the simplest intervention to reduce radon concentration and inhalation dose taking into consideration the cost of the extra heating during heating period. For this analysis the previously determined parameters of the cost benefit function were needed. The method introduced computer simulations provided by the software MODELMAKER (Cherwell Scientific Ltd.) version 4.0 to model the time dependent radon concentration in a dwelling. 7

3 III. Considering inhalation dose due to radon not the radon gas itself is significant but its short-lived progenies: 218 Po, 214 Pb, 214 Bi. The metallic daughters may attach to aerosol particles in air and then deposited in the lung causing inhalation dose due to their radioactive decay. In order to study experimentally the concentration and activity of the aerosol attached radon daughters a relatively simple method was developed. A ZnS/plastic sandwich scintillation probe was used to detect parallel the gross-alpha and gross-beta intensities provided by all the progenies and then the gross-type intensity curves were decomposed by sum of exponentials using software MODELMAKER - and the individual activities of the progenies were assessed. This way the inhalation dose can be assessed more accurately in some special cases. The method provides an alternative to other methods and can be a better choice for some applications. IV. In relation to the work in modelling within the EU framework project BIOMOSA (Biospheric Modell. ) the aim was to assess the radiation exposure to members of a hypothetical population group living in the vicinity of a radioactive waste disposal. Altogether 5 groups of modellers from Europe were involved in comparison simulation results by use their national parameters and site specific data. The task was to assess public exposures using contaminated well water (including 38 Cl, 79 Se, 99 Tc, 129 I, 135 Cs, 226 Ra, 230 Th, 231 Pa, 237 Np, 238 U and 239 Pu) for drinking and irrigation at different geographical sites. Within BioMoSA, both, site-specific and generic biosphere models were derived by the Reference Biosphere Methodology. in order to ensure the development of consistent and scientifically justified biosphere models for application in long-term performance assessments for nuclear waste disposals. In our simulations the softwares MODELMAKER and MICROSHIELD were used. 8

4 THESES I. The parameters of the cost-benefit function for dose optimization were determined in case of public by adopting a willingness to pay (WTP) questionnaire. These values were: [P3] - the monetary value of the averted dose: α 0 = 2.5 MFt (person Sv) -1 and - the aversion coefficient: a = 2.51±0.39. II. Applying the parameters got from the willingness to pay method among the population the optimal radon concentration were determined in dwellings within the local (national) conditions. According to the computer simulations the optimal radon concentration should be 400 Bq m -3 taking into consideration the cost of extra heating and the benefit of the averted inhalation dose. [P2, P7] III. A new method for determining the individual activities of the short-lived 222 Rn daughters ( 218 Po, 214 Pb, 214 Bi) in air was developed The time dependent activity-curves of gross-α and gross-β intensities (measured by ZnS/plastic scintillation detector) were decomposed by sum of exponentials and the individual activities of the progenies were assessed. [P1] IV. In the framework of the BioMoSA project for the development of biosphere assessment models for radioactive waste disposal the Reference Biosphere Methodology was applied to develop models, to assess the hypothetical contamination of a range of agricultural and environmental pathways and the dose to individuals, following contamination of well water. Ingestion of drinking water and irrigated vegetables were found to be among the most important pathways for almost all radionuclide. Stochastic calculations revealed that distribution coefficient (Kd s ) has remarkable influence during long time assessments. [P4, P5, P6] 9

5 PUBLICATIONS REFERRED PERIODICALS P1 T. Katona, B. Kanyár, J. Somlai, Á. Molnár: Determining 222 Rn daughter activities by simultaneous alpha- and beta-counting and modelling Journal of Radioanalytical and Nuclear Chemistry, 2006 (in press) P2 T. Katona, B. Kanyár, J. Somlai: Cost assessment of ventilation and averted dose due to radon in dwellings Journal of Environmental Radioactivity 79: ; 2005 P3 T. Katona, B. Kanyár, K. Eged, Z. Kis, Á. Nényei, R. Bodnár: The monetary value of the averted dose for public exposure assesssed by the willingness to pay Health Physics 84(5): ; 2003 P4 G. Pröhl, G. Olyslaegers, B. Kanyar, P. Pinedo, U. Bergström, S. Mobbs, K. Eged, T. Katona, I. Simón, U. B. Hallberg, Q. Chen, R. Kowe and T. Zeevaert: Development and comparison of five site-specific biosphere models for safety assessment of radioactive waste disposal Journal of Radiological Protection 25: ; 2005 P5 G. Olyslaegers, T. Zeevaert, P. Pinedo, I. Simon, G. Pröhl, R. Kowe, Q. Chen, S. Mobbs, U. Bergström, B. Hallberg, T. Katona, K. Eged and B. Kanyar: A comparative radiological assessment of five European biosphere systems in the context of potential contamination of well water from the hypothetical disposal of radioactive waste Journal of Radiological Protection 25: ; 2005 P6 B. Kanyár, G. Pröhl, U. Bergström, B. Hallberg, S. Mobbs, G. Olyslaegers, P. Pinedo, I. Simon, T. Zeevaert, K. Eged, T. Katona: Modelling of the radioactive daughter elements in soil to assess radiation impact due to contaminated irrigation water by parents of Pa- 231, Ra-226, U-238, Np-237 and Pu-239 Academic and Applied Research in Military Science, AARMS 3(5): ;2004 P7 Kanyár B., Katona T., Somlai J.: A radonból eredő lakótéri sugárterhelés csökkentésének költségei és a radon cselekvési szint Egészségtudomány, 48: 72-80;

6 PRESENTATIONS PUBLISHED IN CONFERENCE PROCEEDINGS International: T. Katona, B. Kanyár, V. Jobbágy, N. Kávási, Á. Molnár, K. Imre: Determination of radon daughter activities of different aerosol fractions by gross-alpha and gross-beta measurements (full tex) 4th European Conference on Protection against Radon; Prague, 2004 T. Katona, B. Kanyar: Cost-benefit of ventilation and averted radon in dwellings Regional International Radiation Protection Association (IRPA) Congress in Central Europe; Bratislava, 2003 T. Katona, K. Eged, B. Kanyar, Z. Kis and A. Nenyei: The monetary value of the averted dose for public exposure European International Radiation Protection Association (IRPA) Congress; Florence, 2002 Hungarian: Katona T., Kanyár B.: Radon leányelemek kötődése aeroszol részecskékhez: mérés és modellezés XXX. Sugárvédelmi Továbbképző Tanfolyam; Keszthely, 2005; best young lecturer prize Katona T., Kanyár B., Somlai J., Kávási N., Jobbágy V.: Radon leányelemek aktivitásának meghatározása különböző méretfrakciójú aeroszol mintákban összes-alfa és összes-béta típusú mérésekkel (full text) A Környezeti Ártalmak és a Légzőrendszer XIV. Országos Konferenciája; Hévíz, 2004 Katona T., Kanyár B., Kávási N., Jobbágy V., Somlai J., Kovács T.: Aeroszol részecskékhez kötött radon leányelem aktivitások nuklid-specifikus meghatározása Őszi Radiokémiai Napok; Eger, 2004 Katona T., Kanyár B., Kovács T., Kávási N., Jobbágy V.: Radon-leányelem aktivitások nuklidspecifikus meghatározása az aeroszol minták összes-alfa és -béta típusú mérésekkel XXIX. Sugárvédelmi Továbbképző Tanfolyam; Balatonkenese, 2004 B. Kanyár, G. Pröhl, U. Bergström, B. Hallberg, S. Mobbs, G. Olyslaegers, P. Pinedo, I. Simon, T. Zeevaert, K. Eged, T. Katona: Modelling of the radioactive daughter elements in soil to assess radiation impact due to contaminated irrigation water by parents of Pa-231, Ra-226, U-238, Np-237 and Pu-239 VII. szimpózium Sugárzástechnika a mezőgazdaságban, élelmiszeriparban és ökológiában; Veszprém, 2003 Katona T., Kanyár B.: Radon, szellőztetés és fűtési költség XXVIII. Sugárvédelmi Továbbképző Tanfolyam; Mátrafüred, 2003; best young lecturer prize Katona T.: A sugárdózis elkerüléséből eredő haszon és averzió meghatározása a lakosság körében XXVI. Országos Tudományos Diákköri Konferencia; Budapest, 2003 Kanyár B., Katona T.: Sugárvédelmi optimálás Magyar Geofizikusok Egyesületének Mecseki Csoportjának Ankétja; Pécs, 2002 Katona T., Kanyár B., Eged K., Kis Z., Bodnár R.: A dózis elkerüléséből eredő haszon és averzió a lakosság körében XXVII. Sugárvédelmi Továbbképző Tanfolyam; Mátrafüred, 2002; best young lecturer prize Katona T.: A lakossági radioaktív sugárzás elleni averziójának meghatározása sugárvédelmi optimáláshoz VIII. Országos Környezettudományi Diákkonferencia; Veszprém, 2002; Katona T.: A sugárdózis elkerüléséből eredő haszon és averzió meghatározása a lakosság körében Intézményi Tudományos Diákköri Konferencia; Veszprém, 2001; 2nd prize 11