ENVIRONMENTAL RADIOLOGICAL IMPACT ASSESSMENT AFTER TEN YEARS OF OPERATION AT CERNAVODA NUCLEAR POWER PLANT

1
TRITIUM MANAGEMENT AT CERNAVODA NUCLEAR POWER
PLANT
S. GHELBEREU, I. POPESCU, R. NANIS CNE CERNAVODA,
ROMANIA sghelbereu_at_cne.ro, ipopescu_at_cne.ro,
rnanis_at_cne.ro
29 to 31 October, Râmnicu Vâlcea
2
WHY TRITIUM MANAGEMENT IS NECESSARY?
3H is continuously produced in Moderator and PHT
circuits
3
WHY TRITIUM MANAGEMENT IS NECESSARY?

• At Cernavoda NPP 3H emissions account for
• majority of public dose (about 80)
• an important fraction of the professional
  exposure.
• CNE Cernavoda management is commited to
  maintain ALARA both population and personnel
  doses and, consequently, to take appropriate
  measures to reasonably reduce doses.

4
WHY TRITIUM MANAGEMENT IS NECESSARY?
Internal dose trend - from total exposure
5
WHY TRITIUM MANAGEMENT IS NECESSARY?

• Moderator is the main tritium source in a CANDU
  reactor
• Several barriers should be provided to reduce
  tritium doses in CANDU reactors, most of them
  being related to Moderator circuit.

6
CONCEPTUAL BARRIERS FOR 3H CONTROL
vapor recovery
vapor recovery
vapor recovery
vapor recovery
vapor recovery
leak tightness
leak tightness
leak tightness
leak tightness
Detritiation
Detritiation
Detritiation
confinement and local ventilation control
confinement and local ventilation control
purge dilution
7
CONCEPTUAL BARRIERS FOR 3H CONTROL

• The most fundamental method to reduce 3H
  concentration in heavy water is detritiation.
• The efficiencies of the following barriers
• leak tightness
• DTO recovery (water and vapor)
• confinement and local ventilation control
• purge ventilation.
• are progressively less effective in this order.

8
TRITIUM EMISSION REDUCTION STRATEGY

• 1. Identify ALARA requirements
• 2. Leak tightness
• 3. Contain capture escaped DTO vapour
• Multidisciplinary team with focus on tritium
  reduction
• Utilize OPEX Operational Experience
• 4. Reduce the source - DETRITIATION

9
TRITIUM EMISSION REDUCTION STRATEGYIdentify
ALARA requirements

• Reducing internal 3H exposure of personnel and 3H
  emissions are important ALARA objectives of the
  Plant Management
• Performance indicators are established and
  reported twice a month
• Corrective actions are initiated when necessary.

10
TRITIUM EMISSION REDUCTION STRATEGY Leak
Tightness

• Between 2000 and 2007 most of the technological
  fluids leaks were usually treated in a corrective
  manner. Due to the careful management the leak
  number was significantly lower than in similar
  plants but a systematic approach was considered
  necessary.
• Technological fluids leak reduction program was
  initated at CNE Cernavoda in 2008.
• EPRI LeakTrak Data Base is used

11
TRITIUM EMISSION REDUCTION STRATEGY Leak
Tightness main achievments

• 1-32710, Moderator liquid poison, AG1/AG2.
• 1-32710, Moderator liquid poison, SG25/SG
  (R-011).
• 1-32510 Moderator D2O collection SG14, STR1
• 1-32220, Moderator dueteration and dedeuteration
  V51
• 1-3381 PHT D2O collection SGs
• 1-63432 Emergency core cooling and recovery
  system FI 203

12
Optimization of adsorption / regeneration cycle
for Unit1 Vapor Recovery System Dryers
TRITIUM EMISSION REDUCTION STRATEGY Contain
capture escaped DTO vapor

• DR1 4 Boiler Room R-501/R-601 and Reactor
  Faces R-107 and R-108
• DR7DR8 Moderator EnclosureR-112
• DR9DR10 Reactor Building accessible areas
• DR5 to maintain zoning between areas Vapor
  recovery and Ventilation System areas
• DR11 when in service to increase drying capacity
  of DR1 4 if tritium leaks appear in R-501 are
  or during Outages.

13
TRITIUM EMISSION REDUCTION STRATEGY Contain
capture escaped DTO vapor
Optimization of adsorption / regeneration cycle
for Unit1 Vapor Recovery System Dryers

• Optimization is necessary to operate Dryers
• providing high adsorption capacity of molecular
  sieve and
• not reducing the life time because of a too
  high frequency of adsorption / regeneration
  cycles.

Based on design considerations and operating
experience we developed the following operation
schedule for dryers
14
Optimization of adsorption / regeneration cycle
for Unit1 Vapor Recovery System Dryers
15
TRITIUM EMISSION REDUCTION STRATEGY Contain
capture escaped DTO vapor
Optimization of adsorption / regeneration cycle
for Unit1 Vapor Recovery System Dryers

• The schedule for dryers operation was made
  based on the following principles
• The same adsorption time for similar dryers
• 49h pentru DR14 DR7/DR8 and 10h
  pentru DR9/DR10
• NO simultaneous regeneration for two Boiler Room
  dryers
• The same regeneration time for DR1 and DR2
  during absorption time for DR3 and DR4 and
  reciprocal (one pair at 13h after the other)
• The same time 4 h between regenerations of the
  same dryers pair DR1 DR2, and DR3 DR4
  respectively.
• The same time between DR7 DR8 regeneration
  (22h after the other) and between DR9 DR10
  (3h after the other).

16
TRITIUM EMISSION REDUCTION STRATEGY Contain
capture escaped DTO vapor

• This operation schedule provides
• An absorption period of about 2 days for dryers
  DR1 DR4 and DR7 DR8 and about 20h,
  cumulated per day, for DR9 DR10
• An acceptable compromise between adsorption
  efficiency (molecular sieve far from saturation)
  and dryers operation cycling
• Potential for tritium in air sampling in similar
  operating conditions to identify eventual DTO
  leaks
• Balanced cycling of D2O recovery system dryers.

17
TRITIUM MANAGEMENT MAIN RESULTS Tritium
Emissions in Air
18
TRITIUM MANAGEMENT MAIN RESULTS Tritium
Emissions in Water
19
TRITIUM MANAGEMENT MAIN RESULTS Professional
Exposure
Significant improvements in internal dose
performance
20
TRITIUM MANAGEMENT MAIN RESULTS Tritium Public
Doses
Legal dose limit 1000 ?Sv/year CNE Cernavoda
license dose constraint 100 ?Sv/year Mean
natural exposure in Romania 2400 ?Sv/year