FUNDAMENTAL SAFETY OVERVIEW VOLUME 2: DESIGN AND SAFETY CHAPTER S: RISK REDUCTION CATEGORIES 3. RADIOLOGICAL CONSEQUENCES OF SEVERE ACCIDENTS

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1 PAGE : 1 / RADIOLOGICAL CONSEQUENCES OF SEVERE ACCIDENTS 3.1. SAFETY REQUIREMENTS Safety objectives The safety approach for EPR reactors is deterministic, complemented by probabilistic analyses, based on the concept of defence in depth. Within this framework, a number of design provisions (depressurisation of the primary system, installation of recombiner units, core catcher, EVU [CHRS]) are made to preserve the integrity of the containment in severe accidents and hence reduce the accident consequences. The objective of the radiological consequence calculations for RRC-B core melt accidents is to show that taking account of the above design provisions, the release of radioactive products outside the plant remains within the limits set out below Radiological objectives The radiological objectives associated with RRC-B accidents are expressed on the basis that only very limited countermeasures should be necessary in such situations i.e.: - limited sheltering duration for the public, - no need for emergency evacuation beyond the immediate vicinity of the plant, - no permanent relocation, - no long term restrictions on the consumption of foodstuffs. These countermeasures, which are those laid down in the ICRP 63 (see Ref. /1/), relate to both the short term phase (sheltering and evacuation) and the medium and long term phases, (absence of permanent relocation). The ICRP associates dose bands or dose rates with these protective measures, as follows: - sheltering: 5 50 msv (effective dose), - evacuation; msv (effective dose), - issue of iodine tablets: msv (thyroid dose), - permanent relocation: 5 15 msv/month for prolonged exposure (dose rate from contaminated ground), the value proposed by the ICRP, being 10 msv/month. The ICRP also recommends permanent relocation in case of excess of 1 Sv (effective averted dose). The thresholds of 10 and 50 msv (effective dose) have been adopted by the French General Health Directorate for, respectively, population sheltering and evacuation, and a threshold of 100 msv in equivalent thyroid dose for issuing iodine tablets. The French General Health Directorate also recommends limiting any sheltering of more than 48 hours.

2 PAGE : 2 / 10 Possible restrictions of the consumption of foodstuffs from the vicinity of the power plant are in line with European regulations that establish limits for marketing these foodstuffs in the case of nuclear accident or other radiological emergency (see Ref. /2/). Taking these various elements into account, the assumed thresholds associated with the different countermeasures for population protection are: - short term measures: o o o imposition of sheltering: 10 msv (effective dose), evacuation; 50 msv (effective dose), issue of iodine tablets: 100 msv (equivalent thyroid dose). - medium and long term measures: o relocation: 10 msv/month for prolonged exposure (irradiation dose rate by the ground) or 1 Sv (effective dose). The assessment of the effective dose takes account of the 4 exposure routes (exposure to the plume, inhalation, ingestion and exposure to deposits) It also takes account, if appropriate, of foodstuff restrictions arising from European marketing legislation (see Ref. /2/). In general, dose calculation results will normally be presented for adults and for a 1-year-old infant at the site boundary (500 m) over 7 days, and for an adult at a of 2 km from the point of release over 50 years. The equivalent thyroid dose will also be assessed for these two population groups. This presentation will be supplemented as required by explaining, in each case, how the radiological objectives are met (limited sheltering, evacuation only to the site boundary, absence of permanent relocation) taking account of the thresholds mentioned above PRINCIPAL METHODS AND ASSUMPTIONS Background The EPR reactor is a French-German design and the original method used to assess the radiation consequences of accidents was German. Constructing the EPR in France made it necessary to adopt a common methodology applicable to EPR and reactors operating in France. In fact, despite design improvements such as design measures against severe accidents, in terms of its functional principles the EPR reactor is close to the reactors currently in operation in France. Methods and assumptions adopted for evaluating the radiological consequences of Design Basis Accidents for the French NPPs in operation are applied, except for some identified design differences. A simplified implementation of this common assessment method has been used for this safety report. This approach will be reviewed to address UK specific requirements later in the licensing process.

3 PAGE : 3 / Principles The principles involved in assessing the radiological consequences associated with severe accidents are listed below: - the evaluation of the activity released is based on a reference source term, calculated with reasonably conservative bounding assumptions, independent of the accident scenario, - the assumptions used in calculating radiological consequences (dose evaluation) are fixed realistically to give a reasonably conservative evaluation of the radiological consequences. The calculation of the effective dose includes all potential exposure routes: external exposure to radiation plumes and deposits, internal exposure by inhalation and ingestion of contaminated foodstuffs. The dose is assessed over a period of up to 50 years. The results are presented: - At 7 days: The doses at 7 days correspond to the exposure of an individual located in the immediate vicinity of the site at the time of the release. The effective doses received via inhalation and external exposure to the plume and to deposits on the ground are calculated at 500 m from the reactor. In addition. The thyroid dose due to radio-iodine inhalation is evaluated for an adult and a 1-year-old infant at the same ; - At 50 years: The 50 year dose represents the effects integrated over the life of an individual. In addition to the doses received during the passage of a radioactive cloud, the doses received during this phase are those due to the persistency of the contamination deposited on the ground. Individuals living close to the power plant are subjected to external exposure to deposits on the ground and to internal exposure by ingesting contaminated foodstuffs, over a duration of 50 years. These doses are evaluated 2km from the point of release Dose calculation hypotheses Atmospheric diffusion of fission products released into the environment: The atmospheric concentration integrated during the passage of the plume is obtained by the differential equation of atmospheric diffusion. The model used is a Gaussian plume model with a standard deviation evaluated by the 2 class Doury model. The calculations are performed taking into account standard meteorological conditions which ensure a broad coverage in accordance with their effects on atmospheric dispersion. The conditions of weak diffusion with a wind of 2 m/sec are taken here. It can be noticed that they cover around 90% of the conditions encountered whichever the French NPP site is considered (even if located on seashore, Flamanville for instance). Changes in meteorological conditions such as wind speed, wind direction and diffusion are taken into account according to the release duration with a correction factor, ranging from 1 to 5, applied to the horizontal standard deviation. Conversion factors for dosage, respiratory flow rate: A respiratory volume of 29m 3 per day has been used for adults, and 5m 3 per day for children.

4 PAGE : 4 / 10 The conversion factors into doses are as follows (cf. Ref [3] and [4]): FD plume : FD inhalation : Federal Guidance ICRP 71 and European Directive 96/29/EURATOM FD inhalation thyroid : ICRP 71 FD deposits: FD ingestion : Federal Guidance ICRP 72 and European Directive 96/29/EURATOM As regards life habits, exposure conditions, integration time and transfer of radionuclides into the environment, the values proposed in the EDF methodology are realistic in terms of all French sites. The preliminary dose calculations from applying the EDF methodology, and presented here, are considered to be generic in nature REFERENCE SOURCE TERM The design options available to EPR are such that the risks of core melt are highly unlikely. With a reinforced defence-in-depth procedure, design provisions were adopted which make it possible to exclude severe accident phenomena which could lead to large early releases. Low pressure core melt sequences are dealt with in the design by specific provisions aimed at ensuring the integrity of the containment under such situations. An examination of RRC-B conditions should show that, taking account of the design provisions adopted, the radiological objectives associated with these situations (see within this Subchapter) are met. The main assumptions of the reference source term are as follows: - 100% core melt, - release rates of the most significant radionuclides, from the point of view of radiological consequences on populations (noble gases, iodine and caesium), have been maximised (100% release in the containment vessel), - quantity of aerosols in suspension in the containment falls because of natural deposition. The effectiveness of the containment spray system has not been taken into consideration, - iodine is mainly released in the containment in the form of aerosols. Airborne organic iodine is taken into account from the beginning of the accident representing 0.15% of the iodine initial core inventory. This value bounds that measured in the long term phase of the Three Mile Island accident. During a severe accident in an EPR, the integrity of the containment vessel is ensured by specific provisions which justify the use of the PCC assumptions to assess releases into the environment: - an internal containment leak rate of 0.3% vol/day (maximum internal containment leak rate at its absolute design pressure of 5.5 bar),

5 PAGE : 5 / 10 - filtration which allows 99.9% of the aerosols and molecular iodine and 99% of the organic iodine to be retained. Noble gases cannot be filtered. Given the conservative assumptions taken, the reference source term bounds that from low pressure core melt accidents RESULTS Release fraction The EPR reference source term, calculated using these assumptions, is shown in the table below. It is expressed as fractions of the initial core activity released to the environment (as percentages) for some radionuclides. Radionuclides 133 Xe 131 I 137 Cs 132 Te 90 Sr 106 Ru 141 Ce 241 Pu Source Term (% C.I.) 1 1.5x x x x x x x x10-8 I.C.: Initial core inventory Radiological consequences From the fractions discharged into the environment and the methods and assumptions described in 3.2 within this Sub-chapter, the short term and long term doses as a function of the around the reactor have been evaluated (see FIG 1 to FIG 4). These results confirm that the main radiological objectives are met: - evacuation or relocation of the population is not necessary: only limited sheltering in the very close vicinity of the site boundary is envisaged; - the dose rate due to irradiation from the radionuclides deposited on the ground and the effective dose are much lower than the long term objectives. 1 % C.I. : percentage of initial Core Inventory

6 PAGE : 6 / 10 LIST OF REFERENCES [1] Publication ICRP 63 Principles of intervention for the protection of the public in cases of radiological emergency. A report by a working group from Committee 4 of the CIP, adopted by the ICRP in November Oxford, New York, Seoul, Tokyo, 1993 [2] Council decree dated December , specifying the maximum values for radioactivity in food products and animal feedstuffs in the case of nuclear accident or other radiological emergency, Official Journal of the European Community No. L37/11, as amended on July , Official Journal of the European Communities No. L211/1.] [3] International Commission on Radiological Protection: Recommendations de la International Commission on Radiological Protection; Publications No: 56 (Age-Dependent Doses to the Public from Intake of Radionuclides; Part 1; 1990), 60 (1990 Recommendations of the International Commission on Radiological Protection, 1992), 67 (Age-Dependent Doses to Members of the Public from Intake of Radionuclides; Part 2; Ingestion Dose Coefficients 1990; 1994), 69 (Age-Dependent Doses to Members of the Public from Intake of Radionuclides; Part 3; Ingestion Dose Coefficients ;1995), 71 (Age- Dependent Doses to Members of the Public from Intake of Radionuclides; Part 4; Ingestion Dose Coefficients ;1996), 72 (Age-Dependent Doses to Members of the Public from Intake of Radionuclides; Part 5; Compilation of Ingestion and Inhalation Dose Coefficients ;1996) [4] Council Directive 96/29/Euratom dated May which sets out the basic standards relating to the health protection of the population and worked against the dangers arising from ionising radiation. Official Journal of the European Communities, L159; Vol. 39; June 1996

7 FIGURE : 1 PAGE : 7 / 10 FIG 1: EFFECTIVE SHORT TERM DOSE IN THE CASE OF SEVERE ACCIDENT Doses court terme (7 jours) en accident grave 100 Dose efficace (msv) 10 1 Dose efficace Adulte Dose efficace Enfant confinement Evacuation (km) French Doses court terme (7 jours) en accident grave Dose efficace adulte Dose efficace enfant confinement Evacuation Doses efficaces (msv) English Short term doses (7 days) in case of severe accidents Effective adult dose Effective dose for 1 yr-old infant sheltering Evacuation Effective doses (msv)

8 FIGURE : 2 PAGE : 8 / 10 FIG 2: SHORT TERM THYROID DOSE IN THE CASE OF SEVERE ACCIDENT Doses court terme (7 jours) en accident grave 1000 Dose thyroïde (msv) Dose Thyroïde Adulte Dose Thyroïde Enfant Prophylaxie iode (km) French Doses court terme (7 jours) en accident grave Dose Thyroïde Adulte Dose Thyroïde Enfant Prophylaxie iode Dose thyroïde (msv) Doses efficaces (msv) English Short term doses (7 days) in case of severe accidents Thyroid Dose Adult Thyroid Dose 1 yr-old infant Iodine prophylaxis Thyroid Dose (msv) Effective doses (msv)

9 FIGURE : 3 PAGE : 9 / 10 FIG 3:EFFECTIVE LONG TERM DOSE IN THE CASE OF SEVERE ACCIDENT Doses long terme (50 ans) en accident grave Dose efficace (msv) Dose efficace Adulte Dose panache Dose Ingestion + dépôt Relogement (km) French Doses long terme (50 ans) en accident grave Dose efficace adulte Dose panache Dose ingestion + dépôt Relogement Doses efficaces (msv) English Long-term doses (50 years) in case of severe accident effective adult dose Plume dose Ingestion & deposit dose Relocation Effective doses (msv)

10 FIGURE : 4 PAGE : 10 / 10 FIG 4: LONG TERM THYROID DOSE IN THE CASE OF SEVERE ACCIDENT Doses long terme (50 ans) en accident grave 1000 Dose thyroïde (msv) Dose Thyroïde Adulte Dose Thyroïde Enfant Prophylaxie iode (km) French Doses long terme (50 ans) en accident grave Dose Thyroïde Adulte Dose Thyroïde Enfant Prophylaxie iode Dose thyroïde (msv) Doses efficaces (msv) English Long-term doses (50 years) in case of severe accident Thyroid Dose Adulte Thyroid Dose 1 yr-old infant Iodine prophylaxis Thyroid Dose (msv) Effective doses (msv)