Radiation protection at a reprocessing plant Jim Bishop Head of Radiological Protection Sellafield
Sellafield • 2 km long • 10,000 employees • 3,000 contractors • 7,000 classified (Cat A) workers. • 200 Nuclear facilities • Complex interactions between facilities • Facilities close together • 50 different isotopic fingerprints
Sellafield • Wide range of different processes. • Construction, Operation and Decommissioning side by side. • Facilities of very different ages >60yrs • Design standards have evolved. • ALARA and a flexible approach is essential. Start of nuclear defence work Civil nuclear power (Magnox and AGR) Start of modern design standards Commercial Reprocessing Waste treatment and storage Decommissioning
mSv per year 1951 to 2013 Average Sellafield radiation exposure 10 15 20 25 0 5 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 External Internal 66 67 68 69 70 71 72 73 74 75 76 mSv per year 77 0.5 1.5 2.5 78 0 1 2 79 1991 80 81 1992 82 1993 83 84 1994 85 1995 86 1996 87 88 1997 89 1998 90 91 1999 92 Includes Calder Hall and Contractors 2000 93 94 2001 95 2002 96 97 2003 98 2004 99 00 2005 01 2006 02 03 2007 04 2008 05 2009 06 07 2010 08 2011 09 10 2012 11 2013 12 13
People receiving more than 10mSv and 15mSv per year at Sellafield 1986 to 2013 2500 Numbers > 10mSv Numbers > 15mSv 400 2000 350 > 10 mSv 300 > 15 mSv 250 1500 200 150 BNFL and Contractors 100 1000 50 0 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 500 0 86 87 88 89 90 91 92 93 94 95 96 97 98 99 00 01 02 03 04 05 06 07 08 09 10 11 12 13
ALARA • Balance of Risk • Perception of Risk • Short term vs Long term Risks • Optioneering Risk • Hazard and Operabilitity Studies • ALARA Checklists Time Do Nothing Intervention 04 December 2014 6
Stargate control levels SLF 2.03.100 Contractor's Personnel: Annual Dose Management Info supplied up to w/e: Status of radiation 0 Peoplesoft Number Current radiological Main Contractor: worker: training or SQEP Full Name of Person: DOB: Employer: assessment date: 15 14 Current cumulative dose: 0.00 Cumulative Dose in milliSieverts per Calendar Year 13 Zone 5 Competence re- 12 assessment due: 11 Cumulative 10 Current Medical date Projected Zone 4 9 (C/P's only): 8 Zone 3 7 Respirator Fit Test Date: 6 5 Zone 2 Radiation Passbook No: 4 3 2 Zone 1 "Fit w ith conditions" 1 0 Jan-11 Feb-11 Mar-11 Apr-11 May-11 Jun-11 Jul-11 Aug-11 Sep-11 Oct-11 Nov-11 Dec-11 Month Actual w ritten Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec dose 0 0 0 0 0 0 0 0 0 0 0 0
Legacy PCM filters – ALARA example 1 • >200 Filter stillages B300s Series • Dating back to the 1960s B300 series the older of the PCM Stores built and commissioned in the late 1970 ’ s exist and still contain PCM Waste. These stores are in the process of being systematically emptied LI Date ? • Dose rates up to 1 mSv/h • Transfer of 50 items from B300 Series Stores to Engineered Drum Stores was achieved safely and to time. • Removal of 2 items high crate and drum • • Filters loaded with Pu 80% of items moved, only difficult items left Main projects 2008/2009 • Roofing project (care and maintenance of the building Oxide as a fine powder water ingress and fire systems) • Leaking filter stillage (initiator for repacking of filters) • Repacking filter stillages (430 repack safe state) • Crate and brake down facility (large items) • Containment deteriorating • Stored in old building PCM Stores • No ventilation 03 April 2008 6 04 December 2014 8
Legacy PCM filters – ALARA example 1
Retrieval and treatment of waste – ALARA example 2 • New plant needed to retrieve waste from the older facilities and process it for long term storage. • Limited space and have to be built around existing plant / equipment. • Mock ups to test new equipment.
Glovebox Cleaning – ALARA example 3 • Perceived wisdom that internal decontamination of glovebox would result in significant dose uptake and could not be maintained. • Decision was to carry out the work. Gloveboxes were cleaned and doses reduced by 80%. • New culture was established, workers were proud of the new conditions.
Radiological Rollback – ALARA example 4 Before After
Key Messages • Judgement of what is ALARA is subjective and coloured by individuals perception of risk which depends upon their experience / knowledge, level of control of the risk and perceived benefits from taking that risk. • Sometimes it is necessary to accept increased risk in the short term to reduce risk in the long term. Waiting for a perfect solution can increase risk. • Dose estimates need to be realistic as pessimistic dose predictions can rule out good solutions. • A flexible approach and a range of different techniques and needed to deliver risk reduction.
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