Transcript Low Level Waste Management and Decommissioning of Nu

Decommissioning of
Nuclear Facilities
Decommissioning
Definition:
The process of safely closing a facility from service where
nuclear materials are used at the end of the facilities’
useful life.
Reasons for decommissioning:
• Too expensive to operate, maintain, or repair to maintain
operational compliance
• Lack of necessity for nuclear facility
• Risk to Benefit ratio is too low (congressional wisdom)
NRC: 10 CFR 50.82
Termination of License
Purpose:
The purpose of decommissioning is to remove the nuclear
facility from service and to reduce the residual radioactivity so
that the operating license may be terminated and the property
may be released under restricted or unrestricted conditions.
Facilities Effected:
• Nuclear Power Plants (the most difficult)
• Chemical Plants (that handle nuclear products)
• Conversion plants
• Reprocessing plants
• Fabrication Plants
( these facilities decommissioning equate to decontamination)
Beginning Decommissioning
Process
• When it has been determined to cease operation of a nuclear
power facility, a written certification, license termination plan
(LTC), must be written within 30 days of the determination to
the NRC consistent with guidelines of 10 CFR 50.4(b)(8)
• Once all of the fuel has been removed from the core, another
written certification (LTC) must be submitted under guidelines
10 CFR 50.4(b)(9)
• Written certification can be made for cease of operation with
retention of fuel in the core
• Decommissioning is addressed in 10 CFR 50. Some parts are
addressed in parts 20, 30, 40, 51 ,70, 72, and the
“Decommissioning Resource Manuel”
Beginning Decommissioning
Process
cont.
• Upon docket of permanent cessation of operation and
removal of fuel or legal order to cease operation, the postlicensee has 2 years to submit a post-shutdown
decommissioning activity report (PSDAR) to the NRC and the
affected state.
• No major decommissioning activity may start until 90 days
after PSDAR submittal (i.e. removal of hazardous materials)
• Nuclear power facilities with multiple reactors may apply for a
partial site release. The NRC will have to approve the license
termination plan (LTC)
PSDAR
• A description of planned decommissioning activities and
completions
• Estimation of expected cost
• A report that concludes that previous environmental reports
will substantiate the current environmental report parameters
associated with the decommissioning site. It will discuss the
appropriate activities associated with the decommissioning of
the site
• Decommissioning will be completed in 60 yrs. Extensions may
be granted by NRC if public health and safety are a
consideration
Key points of
Decommissioning Plan
• Hazardous LLW’s removal procedure
• Return to unrestricted use plan (unless site has more than one
reactor, a partial site release is required )
• Safety procedures and protocols (i.e. disposal of radioactive
waste procedures/methods and disposal locations)
• Financial plan of decommissioning (includes removal of spent
fuel and removal of nonessential equipment necessary to
license termination.
• Record keeping and time management
• ALARA
Decommission Completion
• Radioactive components have been removed from the site
• Site Decontamination performed (if necessary)
• Total Effective Dose Equivalent (TEDE) to an average member
of the critical group is less than .25 mSv/yr
• Critical Group - the group of individuals expected to receive
the greatest exposure to residual radioactivity for any
applicable set of circumstances (one or several groups
considered)
• TEDE for restricted use must be .25 mSv with institutional
controls and 1 mSv with no institutional control.
Institutional control – fences, restriction of use of site(i.e.
parking, farming), access restriction
Total Effective Dose Equivalent
International Commission on Radiological Protection (ICRP)
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Leading agency that provides recommendations for radiological safety
Introduce detailed technical regulations
Develop codes of practice best suited for countries to protect their citizens
ICRP Publication 60 recommends EDE limits for exposure
ICRP Basic Radiation Safety Criteria (Groups)
• Occupational exposure
• Pregnant women
• Radiation workers
• General public exposure
• Medical Exposure (diagnostic and therapeutic)
Total Effective Dose Equivalent
ICRP Basic Radiation Safety Criteria (Groups)
• Occupational exposure
• Pregnant women
• Radiation workers
• General public exposure
• Medical Exposure (diagnostic and therapeutic)
Dose Limit System
• Non-stochastic Effect – assumes a radiological dose has a threshold before
an effect takes place
• Stochastic Effect – assumes that any radiological dose has the capacity : the
to have an effect; the only safe radiological dose is zero .
Total Effective Dose Equivalent
ALI (Annual Limit of Intake)
The derived upper bound of allowed radiological dosage that
may not be exceeded per year. (workers = 2000 hours)
• Compliance is determined when the summation of the
effective dose equivalent plus the committed effective dose
equivalent value is less than 1.
𝐸𝑥𝑡𝑒𝑟𝑛𝑎𝑙 𝑒𝑓𝑓𝑒𝑐𝑡𝑖𝑣𝑒 𝑑𝑜𝑠𝑒
5 𝑟𝑒𝑚𝑠
+
𝐶𝑗
𝑗 𝐷𝐴𝐶
𝑗
𝑡 ℎ𝑜𝑢𝑟𝑠
x 2000 ℎ𝑜𝑢𝑟𝑠 < 1
Decommission Completion
Steps to a successful Decommissioning:
1. Create an advisory committee with local people
participation
2. Calculate the residual radiation level as closely as
possible
3. Model and compute the exposure probabilities of
workers and the public.
4. ALARA
5. Protect the ground water per EPA guidelines
Decommissioning Methods
• Decommissioning doesn’t include used nuclear fuel
• Disposal of LLW’s and TRU leaked into coolant from fuel rods
• Cost and exposure risk are major contributors to method
decision
Three methods
• DECON – dismantle; all materials, equipment, machinery,
radiological sources, etc. are removed. Upon completion, the
license is terminated and the site is released as unrestricted
• SAFSTOR – mothballing; radioactive material are removed.
Equipment and machinery is secured and monitored. The site
is licensed as restricted use until the plant is dismantle.
• ENTOMB – entombment; the site is encased in concrete and
monitored until the radiological levels reduce to unrestricted
levels
Decommissioning Methods
Major Considerations for deciding decommissioning
method
• Whether or not other nuclear generating facilities are on site
• Current and projected waste facility site availability
• Current and projected cost of decommissioning and funding
availability
• Regulatory outlook
Decommissioning Methods
• Two types of waste for disposal during process
• Leaked transuranic (TRU) in the fuel
• Contaminated equipment due to neutron absorption (i.e. heat
exchangers, instrumentation cables, steam generators, reactor
coolant pumps, pressurizer, and the reactor pressure vessel )
• Both inside and outside of the reactor
• Most Important Isotope to dispose – Co-60, Ni-59, Nb-94, and Eu152 due to long half life and radiological concentrations
Decommissioning Methods
Decommissioning Methods
Decommissioning Methods
Decontamination Methods
The process of transferring radioactive material from one
surfaces to another for disposal
Benefits:
• Lowers the volume of LLW and decreases cost of disposal
• Lowers radiation exposure to workers
4 methods of decontamination
• Chemical
• Physical
• Electropolishing
• Ultrasonic
Janitorial methods are done prior to these methods
Decontamination Methods
Chemical
• Chemical solution used to remove radioactive materials
• Solution type depends on the radioactive material and the
surface
Physical
• Pressure washing, jack hammering, pneumatic disk, etc. are
used to remove radioactive materials
• Debris is package and shipped to a LLW repository
Electropolishing
• Radiactive metal surfaces are put in an phosphoric acid. The
surface creates a negatively charged terminal. Electric current
is applied to metal surface. A atomic layer is removed with
the electrical current which carries the radionuclide.
Decontamination Method
Ultrasonic Method
• Used on valves and pumps
• Items are placed in a bath of liquid. Ultrasonic waves are
applied to the bath. Waves create a pressure of 10,000 psi
and dislodge the material from the item
• Abrasives and chemicals may be added to the liquid to
increase effectiveness of process.
Assurance of Funds for
Decontamination
Prepayment (preferred)
External Sinking Fund
• Trust
• Escrow Account
• Govt. funds
Certificate of Deposit
• Deposit of Govt. Security
Surety Method, insurance, or other guarantee method
• Surety bond (open ended and automatically renewable)
• Must close surety in writingZ
• Letter of credit (
• Line of Credit
Cost depends on plant size, plant design, and local labor markets
Assurance of Funds for
Decontamination
Assurance of Funds for
Decontamination
Assurance of Funds for
Decontamination
Assurance of Funds for
Decontamination
Obstacles to Decommissioning
Affecting Cost
• LLW’s Facilities in the long term for storage
• Transition personnel from operation professional to
shutdown/dismantlement professionals
• Regulatory transition
• Government uncertainty
• SNF/HLW remaining on site issues (i.e. transportability,
canister licensing)
• Aging Management
• Operating margins no longer supporting operation due to:
• Environmental hurdles
• Aging facilities too costly to repair
• Independent Spent Fuel Storage Installation (ISFSI)
• Safety (exposure)
Obstacles to Decommissioning
Affecting Cost (cont.)
• Competitive price of natural gas (“fracking” lower cost of
natural gas extrusion from 12.50 per thousand cubic ft. to
4.85 per thousand cubic ft.)
Transport of LLW’s
(Containers)
• LSA material (low specific activity) – non-fisslie material that
have an activity set below those prescribed by 10 CFR 71.75
• May be packaged in a “essentially” Type A packaging if
determined “nonexclusive use”
• Essentially – not having to meet all of the testing for Type A
packaging
• Guarantee of loading procedures must be presented and adhered to
• Dose rates of packaging must meet guidelines
cont.
Stability Requirements
• Must be able to maintain structural integrity under
disposal conditions
• Must be noncorrosive at 1% waste volume or .5% of
waste volume in stable form
• No void spaces in packaging
• Clearly identified in designated
• classes
Transport of LLW’s
(Containers)
Nonexclusive LSA Type A container transport criteria
• 2mSv/h at any point of packaging
• If higher, an exclusive vehicle must transport the material and
satisfy additional criteria
• 10 mSv if shipment is in a closed vehicle
• 10 mSv if materials are secures to avoid material movement during
transport
• 10 mSv if materials are not unloaded and loaded during the trip
• 2 mSv/h at any point on external surface of vehicle
• 0.1 mSv/h at any point 2 meters from surface of the vehicle
• 0.02 mSv/h in any normally occupied space (i.e. driver cab)
Calculating Package Classification
with Several Radionuclides
The Fraction Rule
𝐶𝑖 (Package)
𝑖 𝐶 (𝑇𝑎𝑏𝑙𝑒)
𝑖
<1
Apply this equation when there are more than one isotope in a package
• If the isotopes are in the same column of Table 1 or Table 2, add the
summation to find if their sums equal more than or less than one. If more
than one, the next higher class is designated for the class.
• The isotope of the most restrictive class designates the class of the package
if two isotopes of different Tables and/or columns are in the LLW package.
Transport of LLW’s
(Containers)
• Covered in 10 CFR 71 and 49 CFR 173
• Packages must pass test to satisfy shipping requirements
• Three type of containers allowed for shipping
• Type A package – capable of withstanding normal conditions of
transport without leaking of radioactive contents.
• Class A radionuclides or a mix thereof may be packaged into Type A
packaging
• Examples (fiberboard box, wooden box, steel drum
Transport of LLW’s
(Containers)
• Type B package – capable of withstanding normal and accidental
transport conditions without leaking radioactive contents.
• Class B radionuclides must be transported in in Type B packaging
• Examples (Steel drum outer layer, shielded inner layer, thermal
insulation between layers)
Examples of Low Level Waste
Examples of radioisotopes contaminated items like:
• Clothing
• Tools
• Swipes
• Trash
• Liquids
Low Level Waste sources include:
• Nuclear plants
• *Research Laboratories
• *Hospitals
• Radiopharmaceutical Laboratories
• *Industrial Facilities
Classification of LLW’s
(Near surface burial disposal site permitted for LLW packages)
Class A – This class has the least amount of radioactivity
• Radionuclides not listed in Table 1 or Table 2
• Radionuclides of Table 1 at 10% or less of concentration listed in Table 1
• Radionuclides of Table 2 at concentrations equal to or less than the value in Col.1 of
Table 2
Class B
• Radionuclides of Table 2 that have concentration values greater than Col. 1 yet less
than Col.2
Class C
• Radionuclides of Table 1 with concentrations greater than 10% of the value listed in
Table 1
• Radionuclides of Table B with concentration values greater than Col. 2 and less than
values listed in Col.3
Class GTCC (greater than class C)
• Radionuclides of Table 1 with concentrations greater than the value listed in Table 1
• Radionuclides of Table 2 with concentrations greater than the values listed in Col.3
Classification of LLW’s
(Near surface burial disposal site permitted for LLW packages)
Examples of GTCC’s
• Activated metals from reactors (decommissioning)
• Reactor control rods
• Cladding
• Sealed sources
• Medical (sterilizing products)
• Industrial ( xrays to detect flaws in welds)
• Radionuclides found in GTCC
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Cs137Cl
Pu238
Pu240
Am241, Am243
Cm244
LLW Disposal Requirements
Minimum Requirements
• Packaging in cardboard or fiberboard is prohibited
• Liquid waste must be solidified (made not to leak)
• In absorbent material
• Liquid must not exceed 1% of waste
• Waste must not be explosive
• Waste must not be pyrophoric
• Waste activity must be less than 100 Ci/container and
contained at a pressure of less than 1.5 atm @ 20 degree Cel.
Questions?