1 ALARA at the Borssele nuclear power plant

2 ALARA at the Borssele P Borssele  NPP Borssele  In the delta in the Southwest of the Netherlands  KWU design PWR  Design of the 60’s, commisioned 1973 (->2033)  2 loop 480 MW electrical output

3  Introduction  Dose rates  Collective dose  Individual dose  ALARA considerations  Conclusions  Last word Summary

4 Introduction 1979 dose rates went up Extensive investigations Wet sipping the fuel elements Also activited corrosion products where measured Trending showed new fuel cause of Co-60 ingress

5 Dose rates  Nickel coating of spacers elements  Fifth cycle >>1% Co  Trhee cycles with these elements  Dose rates gradually decreased  Strict specifications for Co  Dose up to 5000 mSv/y

6 Dose rates The dose rates decreased because of the decay of Co-60 and the following measures taken:  More time for cleaning the primary water before the outage  Changing ion exchange filters more often, mainly due to applying on the criterion of breakthrough for of certain nuclides important for avoiding dose rate build-up  Spent fuel basin cleaned through powder resin and a “Balduf” micro filter  Pores of mechanical filters in the supporting primary systems were reduced from 3 micrometer to 0.3 micrometer  The pH is kept very constant on 7.0, with dosage of LiOH in dependence on boron grade content

7 Collective dose

8 Besides the reduction of the dose rates, the collective dose is reduced as a result of the following measures taken:  Improving shielding  Different maintenance jobs were combined  Periodical maintenance and periodic inspections reduced  More consequent RP supervision  Commitment of the maintenance department

9 Collective dose  Better planning and preparation during normal operation  Careful outage planning, evaluation  Mockup training  Lowering the threshold for working without a proper dose estimate and dose reduction plan.  Shortening the yearly outages.  Limiting the individual allowed day dose

10 Collective dose

11 Individual dose  Dose rates primary chambers SG 600mSv/h  Manipulators

12 Individual dose  KCB limit always under legal limit  mSv/y (5y av.)  Limited day dose lowered from 1 to 0.5 to 0.2 mSv/day in 2006

13 Individual dose  A very helpfull tool to discuss the individual dose is the “life time dose graph”  Made every year

14 Individual dose

15 Individual dose

16 ALARA considerations  Alfa value € 500-€ 1000 Dependent on individual dose.  > 10 mSv collective or 2 mSv individual dose : ALARA report.  > 1 mSv coll. or 0.5 mSv individual dose : written dose estimate.

17 ALARA considerations Some proposed ALARA measures are implemented others are not. Implemented Decontamination of residual heat removing system Saving 750 mSv cost €105,000 ( 950 mSv => 200 mSv) Result 77 mSv because decontfactor 17 instead of 8

18 ALARA considerations Not implemented ALARA measure : Zinc injection Considerations:  Influence of Zinc on the installation  Dose rates of primary loops still falling  Investments costs ( once-only)  The yearly enriched zinc costs  Yearly implemantation costs id extra work  Extra waste costs and dose  Planned maintenance work  Calculation period 10 years

19 ALARA considerations Not implemented ALARA measure : Zinc injection Considerations:  Influence of Zinc on the installation  Dose rates of primary loops still falling  Investments costs ( once-only)  The yearly enriched zinc costs  Yearly implemantation costs id extra work  Extra waste costs and dose  Planned maintenance work  Calculation period 10 years

20 Conclusions = Construction materials = Extra ingress of Co- 60 = High collective dose (one of the worst) in the 80s = now low (amoung the best) = Small measures substantial results

21 Last Word Money is a scarce commodity and it can be spent only once, it is very important to consider ALARA measures very thoroughly.