Radiation protection at a reprocessing plant. Jim Bishop Head of Radiological Protection Sellafield

Transcription

1 Radiation protection at a reprocessing plant Jim Bishop Head of Radiological Protection Sellafield

2 Sellafield 2 km long 1, employees 3, contractors 7, classified (Cat A) workers. 2 Nuclear facilities Complex interactions between facilities Facilities close together 5 different isotopic fingerprints

3 Sellafield Wide range of different processes. Construction, Operation and Decommissioning side by side. Facilities of very different ages >6yrs 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

4 msv per year msv per year Average Sellafield radiation exposure 1951 to Internal External 2 Includes Calder Hall and Contractors

5 People receiving more than 1mSv and 15mSv per year at Sellafield 1986 to Numbers > 1mSv Numbers > 15mSv > 1 msv > 15 msv BNFL and Contractors

6 Risk ALARA Balance of Risk Perception of Risk Short term vs Long term Risks Optioneering Hazard and Operabilitity Studies ALARA Checklists Time Do Nothing Intervention 4 December 214 6

7 Cumulative Dose in millisieverts per Calendar Year Stargate control levels Actual w ritten dose Cumulative Projected Jan-11 Feb-11 Mar-11 Apr-11 May-11 Jun-11 Jul-11 Aug-11 Sep-11 Oct-11 Nov-11 Dec-11 Jan Main Contractor: Full Name of Person: Feb Mar Apr SLF Contractor's Personnel: Annual Dose Management Info supplied up to w/e: Status of radiation worker: May Zone 5 Jun Zone 1 Month Jul Zone 2 Aug Peoplesoft Number DOB: Current cumulative dose:. Zone 3 Sep Oct Employer: Zone 4 Nov Dec Current radiological training or SQEP assessment date: Competence reassessment due: Current Medical date (C/P's only): Respirator Fit Test Date: Radiation Passbook No: "Fit w ith conditions"

8 Legacy PCM filters ALARA example 1 B3s Series B3 series the older of the PCM Stores built and commissioned in the late 197 s exist and still contain PCM Waste. These stores are in the process of being systematically emptied LI Date? Transfer of 5 items from B3 Series Stores to Engineered Drum Stores was achieved safely and to time. Removal of 2 items high crate and drum 8% of items moved, only difficult items left Main projects 28/29 Roofing project (care and maintenance of the building water ingress and fire systems) Leaking filter stillage (initiator for repacking of filters) Repacking filter stillages (43 repack safe state) Crate and brake down facility (large items) PCM Stores 3 April 28 6 >2 Filter stillages Dating back to the 196s Dose rates up to 1 msv/h Filters loaded with Pu Oxide as a fine powder Containment deteriorating Stored in old building No ventilation 4 December 214 8

9 Legacy PCM filters ALARA example 1

10 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.

11 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 8%. New culture was established, workers were proud of the new conditions.

12 Radiological Rollback ALARA example 4 Before After

13 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.