Application of « ALARA » at Tihange NPP ISOE EUROPEAN SYMPOSIUM 26 June 2008 Ir. Philippe Petit – Deputy head of SRP department 2 2

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

Application of the ALARA principle at the Tihange nuclear power plant 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. Introduction

Application of the ALARA principle at the Tihange nuclear power plant 5 5 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 INDIVIDUAL DOSE x Number of persons = COLLECTIVE DOSE The ALARA general procedure R.D. 20/07/2001 ALARA

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

Application of the ALARA principle at the Tihange nuclear power plant 7 7 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. The ALARA procedure

Application of the ALARA principle at the Tihange nuclear power plant 8 8 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 The ALARA procedure

Application of the ALARA principle at the Tihange nuclear power plant 9 9 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 10

Application of the ALARA principle at the Tihange nuclear power plant 11

Application of the ALARA principle at the Tihange nuclear power plant 12 ORGANISATIONAL CHART (1st part) The ALARA procedure WORK IN CONTROLLED ZONE ESTIMATION OF THE RAW COLLECTIVE DOSE CARE MAINTENANCE D < 0.1 M.mSv : Work granted – standard workshop Normal surveillance 0,1 < D < 0.5 M.mSv: ACTION 1 Primary chenistry, decontamination, rinsing, distance, Preparation using a model, ergonomics, others. D > 0.5 M.mSv ACTION 2 Idem ACTION 1 + definition of at least 3 work zones

Application of the ALARA principle at the Tihange nuclear power plant 13 ORGANISATIONAL CHART (cont’d) The ALARA procedure ESTIMATE of the NET COLLECTIVE DOSE CARE MAINTENANCE D < 0.5 M.mSv : ACTION 1 - Work granted ALARA WORKSHOP – Normal surveillance Dosimetry monitoring of the workshop 0.5 < D < 5 M.mSv: ACTION 2 - Work granted ALARA WORKSHOP – Normal surveillance Dosimetry monitoring of the workshop + RP INSPECTIONS D > 5 M.mSv: ACTION 3 TRANSFER OF DOSSIER TO THE ALARA COMMITTEE

Application of the ALARA principle at the Tihange nuclear power plant 14 Application of ALARA PREVENTIVE AND PROTECTIVE ACTIONS TO REDUCE THE DOSE a) RAW DOSE LESS THAN 5 M.mSv: - 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.mSv: -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 15 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.mSv * ALARA 2: net collective dose between 0.5 and 5 M.mSv * ALARA 3: net collective dose higher than 5 M.mSv

Application of the ALARA principle at the Tihange nuclear power plant 16 Application of ALARA ALARA 1: net collective dose between 0.1 and 0.5 M.mSv  Work granted  Normal surveillance  Dosimetry monitoring completed by workers and controlled by RP ALARA 2: net collective dose between 0.5 and 5 M.mSv  Idem ALARA 1  Use of Preparation forms  Additional RP inspections ALARA 3: net collective dose greater than 5 M.mSv  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 17 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.mSv must be transmitted to the ALARA committee.

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

Application of the ALARA principle at the Tihange nuclear power plant 19 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 20 Application of ALARA Specific cases (Tihange 3 – January 2007)

Application of the ALARA principle at the Tihange nuclear power plant 21 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 22