Application of ALARA at Tihange NPP ISOE EUROPEAN

Application of « ALARA » at Tihange NPP ISOE EUROPEAN SYMPOSIUM Ir. Philippe Petit – Deputy head of SRP department 26 June 2008

The Tihange Nuclear Power Plant Net output: 2985 MWe n Unit 1: 962 Mwe n Unit 2: 1008 Mwe n Unit 3: 1015 Mwe n PWRs 3 loops Application of the ALARA principle at the Tihange nuclear power plant 3 3

Introduction n 2 ALARA procedures are used at TNPP: - General procedure: defines the optimisation method and the role of the people involved - Application procedure: describes the ALARA procedure for workshops outside and during unit outages Observation Radiological risk management only makes sense when ALL risks are being managed. Application of the ALARA principle at the Tihange nuclear power plant 4 4

The ALARA general procedure n METHOD: Reduce as much as possible the collective dose by acting on: the ambiant doserate AD the duration of the intervention AD x Duration of exposure = INDIVIDUAL DOSE x Number of persons = COLLECTIVE DOSE R. D. 20/07/2001 ALARA Application of the ALARA principle at the Tihange nuclear power plant 5 5

The ALARA general procedure The ALARA principle goes further than merely limiting doses n Reduce as much as possible individual and collective doses. n The departments involved: CARE MAINTENANCE AD x Duration of exposure Means of action • • • PRIMARY CHEMISTRY CHOICE OF MATERIAL SHIELDING DECONTAMINATION DISTANCE = INDIVIDUAL DOSE Means of action CHOICE OF THE METHOD CHOICE OF CONTRACTOR TRAINING PREPARATION ERGONOMICS CARE Application of the ALARA principle at the Tihange nuclear power plant MAINTENANCE 6 6

The ALARA procedure An EFFICIENT ALARA procedure starts BEFORE the beginning of an activity and includes the following phases: • IDENTIFICATION of the risk of high radiological exposure • QUANTITATIVE EVALUATION of the identified risk • ANALYSIS and DETERMINATION of prevention and protection measures • SURVEILLANCE of procedure conditions • ADAPTATION of prevention and protection measures • EVALUATION and REGISTRATION RE-EVALUATION based on the evolution of the organisation, qualifications, feedback, results of the registration, individual and collective dosimetry data, etc. Application of the ALARA principle at the Tihange nuclear power plant 7 7

The ALARA procedure THE AVAILABLE MEANS IDENTIFICATION of the risk of high radiological exposure Based on: - Results from the surveillance programme (job reports, feedback, databases, etc. ) - Description of projects (study dossier, Health, Safety and Environment Prevention Plan, etc. ) - Programme and description of activities and interventions (state of the circuits, etc. ). - Meeting at start or opening of workshop Application of the ALARA principle at the Tihange nuclear power plant 8 8

The ALARA procedure THE AVAILABLE MEANS QUANTITATIVE EVALUATION of the identified risk Availability to the people involved of a data base containing the dose rates per equipment and per location. Application of the ALARA principle at the Tihange nuclear power plant 9 9

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The ALARA procedure ORGANISATIONAL CHART (1 st part) CARE WORK IN CONTROLLED ZONE ESTIMATION OF THE RAW D < 0. 1 M. m. Sv: MAINTENANCE COLLECTIVE DOSE Work granted – standard workshop Normal surveillance 0, 1 < D < 0. 5 M. m. Sv: ACTION 1 Primary chenistry, decontamination, rinsing, distance, Preparation using a model, ergonomics, others. D > 0. 5 M. m. Sv ACTION 2 Idem ACTION 1 + definition of at least 3 work zones Application of the ALARA principle at the Tihange nuclear power plant 12 12

The ALARA procedure ORGANISATIONAL CHART (cont’d) MAINTENANCE CARE NET COLLECTIVE DOSE D < 0. 5 M. m. Sv: ACTION 1 - ESTIMATE of the Work granted ALARA WORKSHOP – Normal surveillance Dosimetry monitoring of the workshop 0. 5 < D < 5 M. m. Sv: ACTION 2 - Work granted ALARA WORKSHOP – Normal surveillance Dosimetry monitoring of the workshop + RP INSPECTIONS D > 5 M. m. Sv: ACTION 3 TRANSFER OF DOSSIER TO THE ALARA COMMITTEE Application of the ALARA principle at the Tihange nuclear power plant 13 13

Application of ALARA PREVENTIVE AND PROTECTIVE ACTIONS TO REDUCE THE DOSE a) RAW DOSE LESS THAN 5 M. m. Sv: - Simple shielding (lead blanket) - 3 areas (work, assistance, withdrawal) - Ergonomics of the workshop (work in height, accessibility, lighting, …) b) RAW DOSE HIGHER THAN 5 M. m. Sv: -Additional shielding - Rinsing or decontamination of the equipment - Preparation of work on a model - Use of post-preparation forms Application of the ALARA principle at the Tihange nuclear power plant 14 14

Application of ALARA CALCULATING THE NET DOSE After determining the means to reduce the dose, a new estimate is made. The result is the NET DOSE that is used as a basis for the dosimetry monitoring DOSIMETRY MONITORING There are 3 TYPES of ALARA jobs: * ALARA 1: net collective dose between 0. 1 and 0. 5 M. m. Sv * ALARA 2: net collective dose between 0. 5 and 5 M. m. Sv * ALARA 3: net collective dose higher than 5 M. m. Sv Application of the ALARA principle at the Tihange nuclear power plant 15 15

Application of ALARA • ALARA 1: net collective dose between 0. 1 and 0. 5 M. m. Sv Work granted Normal surveillance Dosimetry monitoring completed by workers and controlled by RP • ALARA 2: net collective dose between 0. 5 and 5 M. m. Sv Idem ALARA 1 Use of Preparation forms Additional RP inspections • ALARA 3: net collective dose greater than 5 M. m. Sv The job can’t start Approval of the ALARA committee needed Use of preparation forms Dosimetry monitoring on specific ALARA job’s form HOLD POINT if 75% of the estimated collective dose is reached Application of the ALARA principle at the Tihange nuclear power plant 16 16

Application of ALARA REGISTRATION OF THE ALARA DOSSIER • At the end of the job. • By the responsible for the job with participation of RP. • If the collective dose is exceeded by more than 25% in relation to the estimated dose, then the reasons for the overrun must be analysed. • The ALARA dossier of a job indicating a collective dose of > 5 M. m. Sv must be transmitted to the ALARA committee. Application of the ALARA principle at the Tihange nuclear power plant 17 17

Application of ALARA PREPARATION DOCUMENTS Application of the ALARA principle at the Tihange nuclear power plant 18 18

Annual collective dose “target” • Target 2006: 1, 4 Man. Sv and achieved: 1, 372 M. Sv • Target 2007: 1, 3 Man. Sv and achieved: 1, 047 M. Sv Application of the ALARA principle at the Tihange nuclear power plant 19 19

Application of ALARA Specific cases (Tihange 3 – January 2007) Application of the ALARA principle at the Tihange nuclear power plant 20 20

Application of ALARA Fixed supports for shielding A good practice recognised by IAEA experts Application of the ALARA principle at the Tihange nuclear power plant 21 21

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