Management of Transition between Shut Down and Decommissioning

Management of Transition between Shut Down and Decommissioning of Research Reactor Cirus R. C. Sharma Director, Reactor Group, BARC, Mumbai, India

BHABHA ATOMIC RESEARCH CENTRE • BARC – a multidisciplinary research centre • Research Reactor Cirus was first large reactor for production of radioisotopes, testing of materials, fundamental research in the area of science and technology and human resource development.

CIRUS 40 MW, heavy water moderated, light water cooled tank type reactor with natural metallic uranium fuel 1956 -1960: Construction 1960 -1997: Operational with 70% AF 1997 -2003: Shut down for refurbishment and safety up-gradation 2003 -2010: Operational with 85% AF December 31, 2010: Shut down permanently

RV: Cyl. Alcon 6056 tank. Graphite Reflector: about 45 T Concrete biological shields Fuel : Nat. U metal rods Moderator – Heavy water, SS pipeline Coolant – DM water, CS pipelines Sea water secondary coolant Metal containment

THE DECISION Reactor operation was at its Peak (high availability factor, higher safety margins and effective utilization after refurbishment) when decision was taken to shut it down permanently as a part of Indo-US agreement. Time available for planning : about two years Objectives: Ø Bring the facility to safe and stable condition with SSCs in preservation mode. Ø Emphasis on Radiological and Industrial Safety to eliminate tendency for complacency. Ø Smooth transition from the operating organization to the decommissioning organization.

PRE-REQUISITES Planning with option for revival kept open/closed. Completion of planned experiments and tests. Optimum utilization of fuel Plan for core unloading and bringing SSCs to safe state. Management of resources including manpower and spares. Regulatory approval – Technical Specifications. Documentation. Preparatory work for permanent shut down and decommissioning.

PREPARATIONS Utilization of Irradiation Facilities Ø Neutron radiography set up installed, commissioned and utilized. Decided to shift it to Dhruva. Ø Re-irradiation of Thorium based fuel pins along with fresh fuel pins was carried out in pressurized water loop. Ø All other irradiations completed with proper planning, co-ordination and excellent synergy between stake holders. Fuel Utilization: Ø Maximize the average irradiation level of fuel assemblies to be discharged from the core after permanent shutdown. Ø Minimize the requirement of fresh fuel assemblies. Ø Minimize the downtime, radiation exposure and efforts. This was achieved by shuffling the fuel assemblies within core in a planned manner over a period of about 15 months.

PREPARATIONS Management of O & M: Residual Life Assessment and replacement requirements revisited. Plan for procurement of spares curtailed with out compromising availability and safety. Components for re-use identified. Induction of fresh manpower curtailed. Redeployment of manpower planned – New RR projects and existing facilities in BARC. Plan for permanent shut down - preparation of procedures, technical specifications and regulatory approval.

CORE UNLOADING • Removal of spent fuel from the core completed with radiation exposure of 39% of the budgeted amount by elimination of hot spots and delaying the core unloading by a few weeks. • Spent fuel assemblies reprocessed. • All in-core assemblies except primary shut down devices; removed, dismantled and disposed off as radioactive waste. • In-Core Test Section of Pressurized Water Loop not removed to minimize radiation exposure. Shielding provided as necessary. • Tritiated heavy water (Moderator) removed from system and transferred to a separate storage tank which was physically isolated from rest of the system with independent venting and recirculation arrangement. • Primary shut down devices removed after removal of heavy water from reactor vessel and kept under safe storage.

STATUS OF SSCs Continued in Operation: Ø Containment and ventilation (at low capacity to conserve energy). Ø Thermal Shield Recirculation System – to reduce radiation field in area of work. Ø Other auxiliary support systems like power supply, service air, service water, waste disposal, fire detection, etc. § Rest of the systems brought to truncated state (preservation mode). § Civil structures ensured to be fit for use till dismantling except stack, for which action for repairs was initiated and work to commence shortly.

MODERATOR AND COVER GAS § Heavy Water completely removed from system and transferred for utilization in Dhruva. § Helium was replaced with Nitrogen shortly after permanent shut down. § Drying of HW pipelines, tanks, heat exchangers etc going on to recover HW traces and to reduce tritium activity in the system has been completed. § Nitrogen will be replaced with air after regulatory clearance. § Instrumentation and other components to be utilized in Dhruva. § Decontamination of tanks and piping to be taken up shortly.

PRIMARY COOLANT SYSTEM § Maintained in preservation mode with periodic recirculation for few hours to assess change in water chemistry. § On line polishing system kept out of service. § Stagnancy period enhanced from one week to two months. No significant change in chemistry parameters. § Coolant activity below detectable limits. § System to be drained and dried after regulatory clearance. § Decontamination of a representative sample on hand.

PRESSURIZED WATER LOOP § System isolation, draining and drying completed. § Some equipment (safety valves, instruments) shifted to Dhruva for commissioning of In-Pile Loop. § Power supply scheme simplified. Redundant equipment have been electrically isolated to reduce power consumption as well as fire hazards and surveillance. § Action on hand for removal of representative samples from Zircalloy test section and recirculation system equipment and piping (SS 347) for generation of data on irradition damage and corrosion respectively and development of chemicals for decontamination.

REDUCTION IN MANPOWER Operational Manpower strength Current Manpower strength Engineer including RS & ARS Supervisors 19 Engineer including DS 03 9 Supervisors 8 Technicians 55 Technicians 21 Trainee Technicians 15 Trainee Technicians Nil Attendants 16 Attendants 11 Total 114 Total 43

SAFETY AND SECURITY § Access control to radioactive areas (reactor building and SFSB) maintained as it was. § Turnstile gates installed at the entrance and Perimeter intrusion detection system kept functional. § Radiological safety aspects reviewed and revised to cater to reduced requirements. Dhruva RSO entrusted with responsibility to look after safety requirements. SWP system continues to be in place. § Approved Technical Specifications in force. § Technical audit and QA checks in place. § Regular safety and security audit including periodic inspections continued.

DOCUMENTATION AND TRAINING § The present staff: a mix of young and old and re-trained to familiarized with change in duties and responsibilities considering decommissioning aspects also. § Qualified and authorized with regulatory approval. § Procedures and practices reviewed, modified and approved. § Relevant records pertaining to operation phase preserved. § All drawings and documents which will be needed for preparation of decommissioning plan and execution of dismantling activities have been maintained. Redundant documents have been identified and disposed off. § Preparation of documentation for dismantling and disposal has been initiated.

ORGANISATIONAL SET UP Decommissioning task Force Ø Decommissioning Apex Committee Decomm. Superintendent (DS) as Convener Ø Director, Reactor Group as convener with experts in O & M and design as memebrs and DS as member-secretary Expert members from waste management, RHC, maintenance & services, decontamination, remote handling. Preparations procedures. of plans Decommissioning Plan and Ø Provides guidance to Task Froce and approval of proposals. Ø Reviews of decommissioning plans.

RADIOACTIVE WASTE Theoretical estimate of radioactivity content in structural components due to activation by neutrons Radiation mapping of reactor vessel and structural components carried out in refurbishment outage. Further data generation taken up soon after permanent shut down. Estimation of radioactivity content in accessible components by measurements on representative samples.

PRELIMINARY RADIOLOGICAL CHARACTERIZATION Reactor Structure Co-60, Zn-65, Mn-54, Cd-109 Cs-137 Primary Coolant Water System Eu-152, Ce-144, Sb-125, Cs-137, Ru-106, Mn-54, Co-60 Heavy Water System Traces of Co-60 and 3 H in D 2 O and He lines Pressurized Water Loop Co-60, Ag-110 m Cs-137 (trace) Ventilation System Co-60 and Eu-152 (in traces) Waste Disposal System Co-60, Cs-137, Sb-125

WASTE VOLUME As an approximation § about 500 cubic meter of category-I solid waste, § 25 cubic meter of category-II solid waste § A few cubic meter of category-III solid waste would need to be managed. § Preparatory work for this has been initiated. Waste management facility at site available and required space has been earmarked. Emphasis is laid on minimization of waste volume by all means including decontamination techniques. Waste compaction and incinerator facility available.

Development of Decontamination Techniques It is planned to (a) convert category-I or very low active or potentially active materials into inactive materials (b) convert category-II/III waste into category-I/II waste by using suitable decontamination techniques. (c) A set up has been created for trials at real scale on samples drawn from the components. (d) This will be reviewed taking into consideration factors like generation of large quantities of secondary waste, overall economics of disposal and optimization of radiation exposure aspects.

DECOMMISSIONING Strategy - Deferred decommissioning. Dismantling of reactor structure and core components is envisaged after about 15 - 20 years when the dominant radionuclide Co-60 will decay to acceptable levels. Short term plans – To gradually bring systems to conducive state with progressive reduction in maintenance and surveillance efforts. Planning, scheduling and Preparatory work. Mid-term plans - Disposal of out of core components. Long term plans – dismantling of core and structural components and safe disposal. Site release - No release in public domain. May be used for some Lab / other facility.

CONCLUSION CIRUS was brought to a safe shut down state by proper planning and execution of several useful schemes. Transition from operation to decommissioning phase being utilized well with reduction in cost and efforts without compromising with safety and security. Deferred dismantling has been opted as the optimal decommissioning strategy. Cirus being the first major nuclear facility under decommissioning in India, it will provide valuable experience feedback for decommissioning of similar facilities in future.

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