Andrew Hetherington University of Birmingham UNTF, April 2011

Characterisation of reactor graphite to inform strategies for disposal of reactor decommissioning waste

Andrew HetheringtonUniversity of Birmingham UNTF, April 2011

EC CARBOWASTE Project

CARBOWASTE: Treatment & Disposal of

Irradiated Graphite & Carbonaceous Waste

Co-ordinator: WERNER VON LENSA

Forschungszentrum Juelich GmbH (FZJ-ISR), Germany

EC CARBOWASTE Project Participants

Beneficiary Number *

Beneficiary name Beneficiary short name Country

1 Forschungszentrum Juelich GmbH FZJ Germany

2 AMEC-NNC Ltd AMEC-NNC United Kingdom

3 Agence nationale pour la gestion des déchets radioactifs ANDRA France

4 South African Nuclear Energy Corporation Limited NECSA South Africa

5 AREVA Nuclear Power AREVA NP France

6 Bradtec Decon Technologies Ltd. BRADTEC United Kingdom

7 Centro de Investigationes Energéticas Médioambientales y Tecnológicas

CIEMAT Spain

8 Commissariat à l’Énergie Atomique CEA France

9 Doosan Babcock DOOSAN BABCOCK United Kingdom

10 Electriceté de France SA EDF France

11 Ecole Normale Supérieure ENS France

12 Ente per le Nuove Tecnologie, l´Energia e l´Ambiente ENEA Italy

13 Empresa Nacional de Residous Radiactivos, S.A. ENRESA Spain

14 UCAR snc –Groupe GrafTech International Ltd. GRAFTECH France

15 Institute of Physics (Fizikos Institutas, FI) FI Lithuania

16 Regia Autonoma Pentru Activiati Nucleare – Sucursala Cercetari Nucleare Pitesti

INR Romania

17 Centre National de la Recherche Scientifique, Institut Natiopnal de Physique Nucléaire et de Physique des Particules

IPNL France

18 Commission of the European Communities - Joint Research Centre

JRC Belgium

19 Lithuanian Energy Institute LEI Lithuania

20 Nexia Solutions Limited NEXIA United Kingdom

21 Nuclear Decommissioning Authority – Radioactive Waste Management Directorate

NDA - RWMD United Kingdom

22 Nuclear Research and consultancy Group NRG The Netherlands

23 Studiecentrum voor Kernenergie–Centre d’Étude de l’Énergie Nucléaire

SCK.CEN Belgium

24 SGL-Carbon GmbH SGLGROUP Germany

25 Studsvik AB STUDSVIK Sweden

26 Assotiation pour la Recherche et le Développement des Méthodes et Processus Industriels

SUBATECH France

27 The University of Manchester UNIMAN United Kingdom

28 Pebble Bed Modular Reactor (Pty) Ltd PBMR South Africa

EC CARBOWASTE ProjectFramework

WP1 Integrated Waste Management Approach

Work Package Leader: 20 Partners: 1,2,3,5,6,7,8,9,10,13,15,26,28



WP2 Retrieval & Segregation Work Package Leader: 8

Partners: 1,2,4,5,9,10,13,15,16,19,20,27,29


Partners: 1,2,4,5,9,10,13,15,16,19,20,27,29

WP4 Treatment & Purification

Work Package Leader: 1 Partners: 6,7,9,12,14,16,18,19,

20,23,24,25,27,28,29



20,23,24,25,27,28,29

WP3 Characterisation & Modelling

Work Package Leader: 7 Partners: 1,8,10,11,12,13,15 16,19,

20,21,22,23,24,26,27



20,21,22,23,24,26,27

WP5 Recycling & New Products

Work Package Leader: 6 Partners: 1,5,8,14,22,24,

25,26,27,28,29



25,26,27,28,29

WP6 Disposal Behaviour

Work Package Leader: 26 Partners: 1,2,3,5,7,8,10,13,16,17,19,20,21,22



Requirements assessment


Product assessment

assessment Requirements

samples characterisation

samples data

characterisation

samples

Product for waste management


Product assessment

samples

Product quality




Work Package Leader: 20 Partners: 1,2,3,9,10,13,15,16,19,28


Partners: 1,2,4,5,9,10,13,15,16,19,20,27,29


Partners: 1, 2, 4, 5, 9, 10, 13, 15, 16, 19, 20



20,23,24,25,27,28,29


Work Package Leader: 1 Partners: 4,5,6,7,9,12,14,16,18,

23,24,25,27,28



20,21,22,23,24,26,27


Work Package Leader: 7 Partners: 1, 8,10,11,12,13,15 16,19,

22,23,24,26,27



25,26,27,28,29


Work Package Leader: 6 Partners: 1, 4, 514,22,24,

25,26,27,28




Work Package Leader: 26 Partners: 1, 2,3, 4, 5,8,10,13,16,17,19,20,21,22



Product assessment

assessment Requirements

samples characterisation

samples data

characterisation

samples

Product for waste management


Product assessment

samples

Product quality

Context of work

• Reactor decommissioning in the UK will give rise to some 90,000 tonnes of graphite

• Major source is core moderator and reflector from decommissioning stage 3 but also fuel element components

• Baseline plan to package and consign to deep geological disposal but

not yet shown that this represents the optimum solution

• Packaging and disposal costs >£2bn

• NDA commitment to ‘explore management/treatment options for graphite waste taking account of worldwide developments’

Inventory

UK has largest irradiated graphite inventory of any country• Magnox

~56,000 tonnes ~20% LLW, 80% ILW

• AGR ~22,000 tonnes 30% LLW, 70% ILW

• 100,000 m3 of packaged material • 25% by volume of the total waste inventory destined for

geological disposal

Overall View of Issues for Graphite Wastes• Graphite has characteristics that make it different from other

radioactive wastes

• Radioactivity arises from activation of impurities

• Significant amounts of long-lived radionuclides 14C from 14N, nitrides and absorbed N2

36Cl from 35Cl left behind on purification of graphite from neutron poisons

• Wigner energy Stored energy – function of neutron flux, exposure time and

irradiation history Potentially releasable

Management options

• No internationally accepted solution for dealing with graphite waste

• Most plans involve burial as the favoured option

• A proportion of graphite is LLW but waste acceptance criteria precludes disposal of large quantities to the LLWR near Drigg

• Direct disposal (Baseline)

• Disposal following treatment/cleaning to reduce long-lived radionuclide content

• Gasification followed by discharge to atmosphere or CO2 sequestration

• In principle LLW-type disposal is a possibility

Context of Issues – 14C

• 14C occurs in a number of waste streams, around 80% of the inventory is in graphite (on basis of analysis of 2007 National Inventory)

• Half-life 5730 years

• Readily assimilated in living organisms

• Could be transported to the biosphere either as a gas or by groundwater

• Gas potentially significant during post-closure phase

• Need to improve confidence in disposal inventory for this radionuclide

Routes of 14C generation in nuclear graphite

• Nitrogen route dominates production, for example - 60% for a Magnox reactor

Reaction Capture Cross-Section (barns)

Abundance of Isotope in Natural Element (%)

14N(n,p)14C 1.8 99.63

13C(n,γ)14C 0.0009 1.07

17O(n,α)14C 0.235 0.04

Context of Issues – 36Cl

• Current reference case based on the 2007 Inventory has a total 36Cl inventory of 31 TBq of which approximately 75% (23 TBq) arises in graphite from Final Stage Decommissioning

• Half-life 301,000 years

• Highly mobile

• Transported to the biosphere by groundwater

• One of the key radionuclides in repository post-closure performance assessments

Radiological characterisation of graphite waste

• Modelling production of radionuclides requires knowledge of:• Neutron flux levels in the graphite• Operational history of the reactor• Any incidents which occurred during operation• Concentrations of impurities in the original graphite and

coolant

• Dialogue underway to progress understanding of uncertainties in the 14C content of graphite calculated by waste producer.

• Emerging evidence to suggest that operational factors may reduce 14C content.

Reactor modelling

• Multiple models used to give diversity of approach

• Modelling based on “Pippa” reactor type at Chapelcross• WIMS • TRAIL• FISPIN

- Preliminary results indicate 14C levels of ~25 kBq/gram- 36Cl levels of ~500 Bq/gram

• MCNP whole core model under development

• Tracking the reactions which are of interest

Cross-section through x-y plane

Pin cell

fuel

graphite block

control rod channel

fuel cladding

coolant

~ 1.2m

Outputs

• Aim to determine activity of whole core

• Map of flux across core showing proportions with activation of ‘x’

• Understand degree of segregation of graphite according to activation levels

• Help inform NDA strategy

Validation of results

• Results of predictive methods need to be backed up by analysis of representative samples

• Major question marks over errors on impurity levels in virgin material

• Samples of Magnox and AGR graphite available from NNL’s graphite handling facility in B13 at Sellafield

• Spectral gamma scanning inappropriate for the long-lived nuclides of interest

Summary

• Graphite treatment/disposal a major challenge to the nuclear industry

• Research required in order to move forward with strategy development

• Accurate characterisation of graphite waste is very important for interim storage and disposal safety cases

• But…..can predictive methods deliver results that are representative of the true radiological inventory?

Documents

Andrew Hetherington University of Birmingham UNTF, April 2011