Definition
As the indicators, collective radiation exposure by plant site and plant unit is monitored, as well as the average of the 10 highest yearly radiation ex-posures.
Source of data
The data on collective radiation exposure is ob-tained from quarterly and annual reports. The data on individual radiation doses is obtained from the national dose register.
Purpose of the indicator
The indicators are used to control the radiation ex-posure of employees. In addition, compliance with the YVL Guide’s calculated threshold for one plant
unit’s collective dose averaged over two successive years is followed. The threshold value, 2.5 manSv per one gigawatt of net electrical power, means a radiation dose of 1.22 manSv for one Loviisa plant unit and 2.15 manSv for one Olkiluoto plant unit.
The collective radiation doses describe the success of the plant’s ALARA programme. The average of the 10 highest doses indicates how close to the 20 manSv dose limit the individual occupational doses at the plants are, at the same time indicating the effectiveness of the plant’s radiation protection unit.
Responsible unit/person Radiation protection (SÄT) Antti Tynkkynen
STUK-B 147 STUK’SSafeTyperformanceindicaTorSfor nppSin 2011 APPENDIX 1 Interpretation of the indicator
Loviisa
Most doses are incurred through work done dur-ing outages. Thus outage duration and the amount of work having significance on radiation protec-tion affect the yearly radiaprotec-tion doses. Both Loviisa plant units have more extensive annual outages every four and eight years (the four-year annual maintenance and the eight-year annual mainte-nance) so that both plant units never have a major annual maintenance outage in the same year. The four-year and eight-year outages have been held in even years and normal annual outages in odd years. The effect of annual outages on collective doses can be seen on the Collective radiation dose, Loviisa graph. In 2011, the Loviisa 1 and 2 plant units had refuelling outages. The time used for annual maintenance outages was short, and there were few operations of significance for radiation protection, which resulted in the total collective dose of the Loviisa power plant being the lowest ever in the history of the Loviisa NPP. The previ-ous lowest collective dose ever was recorded in 2007.
Collective occupational radiation dose (manSv), Loviisa NPP
2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2.61 0.94 2.49 0.81 1.66 0.72 1.55 0.75 1.57 0.71
manSv
Average of the ten highest doses (mSv), Loviisa NPP
2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 18.54 9.01 14.93 10.48 13 7.76 11.99 7.11 14.55 6.56
mSv
Collective dose per 1 GW of net electrical capacity averaged over two succesive years,
Loviisa NPP
2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 1.85 1.69 2.68 2.53 1.18 1.12 1.57 1.58 1.11 0.98 1.99 1.95 0.84 0.85 1.36 1.33 0.76 0.78 1.27 1.36
manSv/GW
Reporting threshold 2.5 manSv/GW according to the Guide YVL 7.9
The radiation doses for nuclear power plant workers were below the individual dose limits. In 2011, the average of the 10 highest radiation doses was the lowest ever recorded at the Loviisa power plant. The trend of the 10 highest radiation doses has been a declining one with the exception of 2010 when the individual doses were higher due to the extensive eight-year maintenance. The Radiation Decree (1512/1991) stipulates that the effective dose for a worker from radiation work must not exceed the 20 manSv/year average over any period of five years, or 50 manSv in any one year.
0.0
Collective occupational radiation dose (manSv) quarterly, Loviisa NPP
Average of the ten highest doses (mSv) quarterly, Loviisa NPP
I/10 II/10 III/10 IV/10 I/11 II/11 III/11 IV/11 0.44 0.42 11.32 6.53 0.70 0.54 6.27 1.00 LO
mSv
STUK-B 147 APPENDIX 1 STUK’SSafeTyperformanceindicaTorSfor nppSin 2011
Furthermore, the threshold set for the collective occupational dose was not exceeded in 2011. If, at one plant unit, the collective occupational radiation dose average over two successive years exceeds 2.5 manSv per one GW of net electrical power, the util-ity is to report the causes of this to STUK, and any measures possibly required to improve radiation safety (Guide YVL 7.9).
Interpretation of the indicator Olkiluoto
Most doses are incurred through work done dur-ing outages. Thus outage duration and the amount of work having significance on radiation protec-tion affect the yearly radiaprotec-tion doses. The annual outages for the Olkiluoto power plant units are divided into two groups: the refuelling outages and the maintenance outages. The refuelling outage is shorter in duration (approx. 7 days). The length of the maintenance outage depends on the amount of work (2–3 weeks). Annual outages are scheduled so that in the same year, one plant unit has a mainte-nance outage and the other a refuelling outage. In 2011, the collective radiation dose at the Olkiluoto
Collective dose per 1 GW of net electrical capacity averaged over two succesive years,
Olkiluoto NPP
2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 0.70 0.64 0.80 0.90 1.37 1.25 0.69 0.77 0.64 0.53 0.67 0.64 0.92 1.36 1.28 0.73 0.66 0.58 0.57 0.54
Reporting threshold 2.5 manSv/GW according to the Guide YVL 7.9
manSv/GW
Average of the ten highest doses (mSv), Olkiluoto NPP
2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 8.41 6.20 7.96 10.32 10.30 7.63 7.28 8.27 7.68 6.65
mSv
Collective occupational radiation dose (manSv), Olkiluoto NPP
2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 1.12 1.03 1.51 2.22 2.20 1.18 0.94 1.19 0.90 0.96
Collective occupational radiation dose (manSv) quarterly, Olkiluoto NPP
Average of the ten highest doses (mSv) quarterly, Olkiluoto NPP
I/10 II/10 III/10 IV/10 I/11 II/11 III/11 IV/11 1.08 7,00 1.46 1.41 1.63 5.73 1.61 1.25 OL
mSv
power plant was the fourth-lowest recorded during the plant’s history, in spite of the maintenance out-age of Olkiluoto 2 that was extensive both in terms of the personnel involved and the amount of work carried out. The lowest-ever collective radiation dose was recorded at the power plant in 2010. The new steam dryers installed at the plant units in 2005–2006 have reduced the radiation levels and collective doses at the turbine plant.
In 2011, the average of the 10 highest radia-tion doses was lower than average. The prescribed dose limits (Radiation Decree 1512/1991) were not exceeded.
STUK-B 147 STUK’SSafeTyperformanceindicaTorSfor nppSin 2011 APPENDIX 1