Dose Assessment for Tritium Releases During Normal Operation of NPP - - PowerPoint PPT Presentation

Dose Assessment for Tritium Releases During Normal Operation of NPP

Irena Malátová*, Juraj Ďúran **

*NRPI, Praha, Czech Republic, VÚJE, a.s. Trnava, Slovakia.** 4th Meeting WG7, 6 – 9 September 2010, Aix-en-Provence, France

Main source of tritium in the Czech republic are NPPs Dukovany and Temelín, both PWR Type. Doses to population from tritium and other radionuclides in the discharges from NPPs are very low, much lower than authorized limits However, calculation of doses from tritium has some problems from the point of view of its RBE and therefore, often it is a target of anti-nuclear activists. Aim of this work was to find out how realistic are the estimation of doses to public, and if too conservative, to suggest more realistic approach.

Dose constraint for total discharge of radionuclides – 250µSv per year for a representative individual from public (200µSv for airborne discharges, 50µSv for liquid discharges) On the basis of optimization process, site specific authorized limits are set for NPP NPP Dukovany: 40µSv airborne and 6µSv liquid discharges NPP Temelín: 40µSv airborne and 3µSv liquid discharges

Dose constraint and authorized limits for discharges of radionuclides into environment in the Czech Republic

Characteristics of the NPPs in the Czech republic and doses to public from their releases.

Nuclear Power Plant Dukovany Temelín Power output 4x440MW 2X1000MW Releases to atmosphere (Sv) 1.6E-08 8.0E-09 Releases of tritium (Sv) 3.20E-10 6.40E-11 Releases to hydrosphere (Sv) 1.80E-06 1.10E-06 Releases of tritium (Sv) 1.80E-06 1.10E-06 Doses from liquid releases during normal operation are 2 to 3 order

• f magnitude higher than from airborne releases. In liquid effluents

and therefore in overall dose to population, dose from tritium is

• dominant. Tritium is the only one radionuclide measurable in the

environment (in the rivers) Doses to public are calculated using models of transport of radionuclides in environment in combination with measured released activity of radionuclides into air and water.

Austria Slovakia Germany Germany

Hřensko,river Elbe

0.1 1 10 100 1.1.1994 0:00 1.1.1996 0:00 31.12.1997 0:00 31.12.1999 0:00 30.12.2001 0:00 30.12.2003 0:00 29.12.2005 0:00 29.12.2007 0:00 28.12.2009 0:00

Volum e activity H -3 [B q/l]

Poland NPP Temelin NPP Dukovany Praha

Pohansko, river Dyje

1.E+10 1.E+11 1.E+12 1.E+13 1.E+14 1985 1990 1995 2000 2005 2010

Bq EDU hydrosphere EDU atmosphere ETE atmosphere ETE hydrosphere

Annual releases to atmosphere and hydrosphere from the Czech Nuclear Power Plants Dukovany and Temelín

Annual releases of tritium, normalized to power output, from NPP PWR to air and water (geom.mean)

1 10 100 1000 10000 100000 Loviisa (Finn.) Belleville (France) Cruas (France) Biblis B (Germ.) Emsland (Germ.) Neckarwestheim 2 Ringhals (Sweden) Sizewell B (GB) Krško (Slovenia) Paks (Hungary) EDU (CR] ETE (CR) GBq/GWe Air Water

The old model calculation of population doses took into account releases through ventilation stacks into atmosphere and liquid effluents into hydrosphere only. However, in Dukovany NPP the source of cooling water is water from the river dam with the outfall of liquid effluents from NPP. Significant activity of tritium is escaping into air by the way of the cooling towers, contributing thus to the dose from air releases and diminishing dose from hydrosphere. Activity of radionuclides in cooling water is measured periodically in NPP, amount of water vapours is calculated from flow rate above and below NPP.

Old model for calculation of doses to the public

Ventilation stacks (HTO,HT) 5.7E+11Bq Cooling towers To the dam: 8.9E+12Bq , Cooling towers To cooling towers is returning 3.99E+12Bq Net to river: 4.9E+12Bq 0.5* (3.99E+12)Bq (HTO vapor and drop 0.5* (3.99E+12)Bq (HTO vapor and drops)

A computer code PTM_HTO has been developed to assess the dose to general public. It takes into account HTO, HT and water drops (1 – 3 % of the released activity of 3H). Oxidation of HT to HTO and reemission of HTO from soil to the atmosphere are included too. Organically bound tritium (OBT) in vegetations, milk and beef is taken into account. In the same way as in the old model local consumption is assumed (e.g. that all products consumed are locally produced – very conservative approach)

Modifications in the new model

0.0 50.0 100.0 150.0 200.0 250.0 0.0 50.0 100.0 150.0 200.0 250.0 300.0 Measured concentrations of HTO [Bq/m3] Calculated concentration of HTO [Bq/m3]

1.0E+04 2.1E+05 4.1E+05 6.1E+05 8.1E+05 1.0E+06 1.2E+06 1.4E+06 1.6E+06 1.8E+06 1.0E+04 5.1E+05 1.0E+06 1.5E+06 Measured concentration HT [Bq/m3] Calculated concentration HT [Bq/m3]

Validation of PTM_HTO Model on the data from field experiment

R.M.Brown,G.L.Ogram And F.S.Spencer: Field Studies of HT Oxidation and Dispersion in the Experiment II, the 1987 June experiment at Chalk River, Canadian Fusion Fuels Techn.

• Project. CFFTP Report No CFFTP –

G – 88007, October 1988

Experimental vs. Theoretical Data HTO HT

0.10 1.00 10.00 100.00 A2/A1 B1/A1 B2/A1 ratio of doses

Ratio of doses to individual from released 3H calculated by modified transport models to the

• riginal one

hydro,i hydro,a atm,i atm, a

Doses to individual per unit of released 3H activity

1.0E-22 1.0E-21 1.0E-20 1.0E-19 1.0E-18 A1 A2 B1 B2 type of model Sv/Bq

hydrosphere, infant Hydrosphere, adult atmosphere, infant atmosphere, adult

A1 – without OBT, without releases through cooling towers A2 – with OBT, without releases through cooling towers B1 – without OBT, with releases through cooling towers B2 – with OBT, with releases through cooling towers

Example for releases in 2008

Change of normalized doses from tritium with modification of transport model

0.00 0.20 0.40 0.60 0.80 1.00 1.20 1.40 1.60 1.80 hydro, i hydro, a atm,i atm,a exposure patway, representative individual ratio of normalized doses to individual A2/A1 B1/A1 B2/A1

A1 – without OBT, without releases through cooling towers A2 – with OBT, without releases through cooling towers B1 – without OBT, with releases through cooling towers B2 – with OBT, with releases through cooling towers

Doses from tritium to population from the Czech NPP are very low (below 2µSv), When OBT is included, doses from airborne discharges increase by about 30 %. Increase of doses from water discharges, which are dominant, is less than 10% Taking into account recirculation of cooling water, overall doses from tritium from NPP Dukovany decreased about 50%. Such approach would be not practical for limitation purposes as the amount of water evaporated through cooling towers is known ex post only. However, for reporting annual doses, a realistic approach would be appropriate.

Conclusions.