slides - INFN Sezione di Ferrara

Transcript

Corso di Formazione INFN, Energia Nucleare da Fissione
Ferrara, Italy
Incidents/Accidents at nuclear
facilities
Marco Calviani, CERN, 11th December 2009
Outline
• Overview of nuclear civilian and military incidents/accidents
together with some background, technical and situation-wide
• CIVILIAN PLANTS
• Chernobyl
• Three Mile Island
• Davis-Besse
• French and Japanese incidents/accidents
• Radiotherapy accidents
• MILITARY PLANTS
• Windscale
• Mayak/Kysthym accident
• Hanford nuclear reservation contamination
• BORAX-I
• SL-1
• Fallout from nuclear tests
• (Lost sources and reactors)
2
M. Calviani - Corso di formazione INFN Energia Nucleare da Fissione
11th December 2009
Basics of thermal reactor operation (I)
Effective multiplication factor of a
device (ratio of the number of neutrons produced
by fission in one generation to the number of
preceding one):
Thermal utilization factor
Leakage probability
keff = η ⋅ f ⋅ p ⋅ ε ⋅ PL
# fission
neutrons per
thermal
neutron
absorbed
Resonance
escape
probability
Fast
fission
factor
Thermalization of neutrons:
• fission neutrons emitted between 1-2 MeV
• does not induce fission in natural uranium
Æ Neutron’s energy reduced to thermal by elastic collisions in a moderator
Æ Thermalization should be performed in as few collisions as possible
• typical examples are H2O, D2O and C
For a constant power keff must be kept ~1
Æ key quantity is keff-1 Æ reactivity definition
3
ρ=
keff − 1
keff
11th December 2009
Basics of thermal reactor operation (II)
dφ (keff − 1)φ (t ) φ (t )
Reactor power is proportional to #
=
=
dt
l
T
fission events (neutron fluence)
For reactor safety T
(reactor period) should not
be too small…
In normal reactor operation criticality requires a
small number of fission events initiated by
delayed neutrons
• crucial for safely operating nuclear
reactors
Distinction could be made
between case where the
reactor is critical with or
without delayed neutrons
4
keff
mean neutron lifetime
l = (1 − β )l prompt + βldelayed
β ≈ 0.65%
Ex. lprompt~10-4 s, ldelayed~10 s
• ρ=0 Æ critical (delayed critical)
• 0<ρ<β Æ supercritical
• ρ=β Æ prompt critical
• ρ≥β Æ super prompt critical
Reactor protected
against changes of the
reaction on delayed
neutrons
11th December 2009
Reactor control
CONTROLS
• Insertion of a large negative reactivity in the core
• Intentional changes in reactor operating conditions / compensation for burnup / SCRAM
• 113Cd (σth~2x104 b), 10B (σth~3.8x103 b) as neutron absorbing control rods
• + soluble absorbers (chemical shim) (boric acid)
SCRAM –shutdown of a
Æ Reduction of thermal utilization factor
nuclear reactor (“safety
control rod (super-critical
reactor) axe man”)
XENON POISONING
135
Te (19.0s ) →135 I (6.6 h ) →135 Xe (9.1h ) →135 Cs ( 2.3e 6 yr )
σth ~2x106 b
• During normal operation 135Xe is in equilibrium between its production through
decay and depletion via neutron capture
• … if reactor is shut down (or running at low power for long period), 135Xe level
increases
• first discovered at Hanford during WW2, threatened production of 239Pu
• important contributor to the Chernobyl accident
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11th December 2009
Categories of reactor accidents
Potential major nuclear reactor accidents falls in two major categories:
Criticality accidents (Chernobyl - like)
a chain reaction builds up in uncontrolled manner (part of fuel)
improbable in LWR of normal design (negative feedbacks and shutdown
mechanisms + containment)
Loss-of-coolant accidents (Three Mile Island - like)
nuclear fuel has a continued heat output due to radioactive decay
without cooling fuel temp. rises Æ fuel cladding and fuel could melt Æ leak of
radioactive isotopes from pressure vessel
(*) Fuel handling or control rods mechanism fault
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11th December 2009
International Nuclear Event Scale (INES)
Introduced by IAEA in 1990 to enable prompt communication of safety significance
A large off-site impact, widespread
health and environmental effects.
Chernobyl disaster (1986)
Significant off-site release
Mayak accident (1957)
Limited off-site release
Windscale fire (1957)
Or severe damage to a reactor core
Three Mile Island accident (1979)
Anomaly beyond authorized operating regime
A very small off-site impact, public exposure
at levels below the prescribed limits, or
severe spread of contamination on-site
and/or acute health effects to one or more
workers
THORP plant, Sellafield (UK) (2005)
7
Incident with no off-site
impact, significant spread of
contamination on-site may
have occurred or
overexposure of worker or
incidents with significant
failures in safety provisions
Minor off-site impact public
exposure of the order of the
prescribed limits or significant
damage to a reactor core
Saint-Laurent NPP (1980),
Tokaimura (Japan) (1999)
11th December 2009
Civilian plants accidents
8
11th December 2009
Chernobyl
RBMK reactors: light water cooled, graphite moderated, direct cycle
Individual pressurized fuel channels Æ removal of fuel when reactor on
Evolved from reactors designed for weapons grade 239Pu production
4 units, 3.2 GWth each, 1 GWel
RBMK reactors lack external containment
9
11th December 2009
Chernobyl (1986) – The accident
Sequence of events 26th April 1986 – Chernobyl Unit 4:
¾ “Safety” test was planned Æ power requested to be <50%
INES = 7
Worst nuclear
accident ever
¾ Electricity grid asked to maintain reactor on for an additional day Æ low power
¾ Xenon poison buildup due to lack for neutrons in the core
¾ Removed control rods completely out of the core to maintain power output
(more than proper operating guidelines) Æ small reactivity margin
¾ At 1h23m on 26th April 1986 the safety test began
¾ Cut electricity to remaining turbine to see if inertia in rotating blades was sufficient to
keep turbines spinning and therefore power to cooling pumps for a few seconds until
emergency power (UPS) started
¾ Emergency cooling system off (to maintain reactor at low power)
¾ Turned off steam to one of the turbines
¾ This lead to a slight drop in water flow to steam generators
¾ Less heat now extracted from core Æ water began to boil in the reactor
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11th December 2009
Chernobyl (1986) – void coefficient effect
INES = 7
¾ Chernobyl reactor: coolant is light water, moderator is graphite
¾ Light water is also a poison for neutrons, therefore slowing down the reaction
¾ Can act as a moderator but moderation is dominated by graphite
¾ When bubbles form (as heat increase) fewer neutrons are absorbed Æ reaction rate
increase! Æ thermal feedback loop
¾ More heat lead to more “bubbles” – this feedback is called positive void coefficient
¾ The net outcome depends on the relative amount and arrangement of U, C and H2O in the reactor.
¾ This behavior is not the same of PWR/BWR/AGR
The following sequence of events has been strongly influenced by the
peculiar design of the RBMK reactor:
ÆPOSITIVE VOID COEFFICIENT
(reactor is overmoderated)
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11th December 2009
Chernobyl (1986) – The accident
INES = 7
¾ 1:23:04 on 26th April 1986 safety test began Æ steam to turbine shut-off
¾ 1:23:40 to control the effect of the positive void coefficient (local boiling) operators
inserted control rods (emergency shutdown attempted)
¾ BUT: bottom of the control rods were made of graphite Æ when control rods were
inserted was an increase in reactor rate
¾ The full motion of the CR was slow, by the time the control rod properly entered into the
core, it was late (0.4 m/s Æ 20 s for 7 m)
¾1:23:40/45 the reactor went superprompt critical
¾ > 40 s two large explosions
¾ steam explosion that exposed the reactor fuel to the air
¾ explosion due to exothermic reactions
¾ Hydrogen produced by Zr/steam reaction or reaction between red-hot graphite
with steam produced O and H or of nuclear nature due to positive void coefficient
¾ Explosions breached reactor building
¾ burning fragments Æ fires outside Unit 4 and on top of Unit 3
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11th December 2009
Chernobyl (1986) – released radionuclides
Thyroid
gland
deposition
Potassium
like
Isotope
t1/2
Core content
(MCi)
Released
(MCi)
Fraction
85Kr
10.8 years
0.89
0.89
1.0
133Xe
5.24 days
176
176
1.0
131I
8.02 days
86
48
0.6
134Cs
2.07 years
4.1
1.5
0.36
137Cs
30.1 years
7.0
2.3
0.33
90Sr
28.8 years
5.9
0.27
0.05
Biochemical behavior
similar to Ca
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11th December 2009
United Nations Scientific Committee on the Effects of Atomic Radiation, UNSCEAR (2000)
INES = 7
Releases:
• 24% 1st day, 28% over the next 5 days and 48% over the following 4 days
• mainly of the volatile elements (noble gases, iodine, cesium)
• incident was not immediately made public
• radioactive cloud was detected by the Sweden Forsmark NPP April 28th
Chernobyl (1986) - Aftermath
INES = 7
• Prompt radiation dose: in some part of the reactors the readings were estimated
(*) to be close to 200 Sv/h (lethal ~1 Sv/h) Æ most operators died within minutes
• Fire containment:
• extinguish fires on the roof and the area around the building containing Unit 4
to protect Unit 3 and keep its core cooling systems intact Æ until 5:00 AM
• Unit 4 core burned until 10th May: 5000 ton of Pb, clay and 10B poured inside
the open pit
• Steam explosion risk: “corium” at 1200 C interacting
with water at the bottom of reactor Æ drain of
radioactive water
• Debris removal: liquidators, very acute level of
radiation
Æ Trucks and machines still in the Chernobyl area
nowadays: 100-300 mSv/h
http://www.progettohumus.it/chernobyl.php
14
* Most dosimeters were off-scale – 40 mSv/h max
11th December 2009
Chernobyl (1986) - Aftermath
Steam pipe
Lava flow
(corium)
Electrical
equipment
Concrete
• Chernobyl lava-flows formed by fuel-containing mass in the basement of the plant Æ
risk of an additional steam explosion
• 4-5 days after the accident the corium started to solidify, losing capabilities to other
structure
Formation and spread of Chernobyl Lavas, Radiochemistry 50, 650-654 (2008)
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11th December 2009
Chernobyl (1986)
INES = 7
Total fuel: ~190 ton
• lower region of reactor building
~135 ton
• upper level: ~38 ton
• fuel release beyond RB: ~7 ton
• unaccounted: ~11 ton
Upper biological
shield (15° tilt)
Uncovered reactor after the accident
16
11th December 2009
A. Sarcophagus built around the
reactor open core
B. Concrete injected into the
basement to reduce
possibilities for the radioactive
material to come in contact
with the ground water
C. Definitive structure to be built
in 2011 under EBRD Æ New
Safe Confinement
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11th December 2009
Chernobyl (1986) - Conclusions
Chernobyl wouldn’t have exploded if it didn’t have a positive void INES = 7
coefficient – poor reactor design
Chernobyl wouldn’t have exploded if the control rods didn’t have moderator
displacer at the bottom – poor safety design
Chernobyl wouldn’t have exploded if managers had waited for normal
operating conditions before starting the test – poor management and
safety culture
Exposures and Effects of the Chernobyl Accident, UNSCEAR (2000)
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11th December 2009
Bodansky (2004)
Estimated for total expected fatalities vary enormously
projected fatalities vary from 1000 to 200000
Two groups unambiguously harmed by radiation:
plant workers and firemen Æ 69 direct deaths
childhood thyroid cancer: as of 2002 UNSCEAR ~2000 cases, predicted
8000-10000 in coming years
Overall radiation exposure: ~9000 excess fatalities predicted in worst case
scenario (delayed cancer fatalities), if linear behavior is true also at low exposures
Three Mile Island 2 (1979) – Pennsylvania,
USA
Three Mile Island Nuclear Generating Station (TMI)
• Civilian nuclear power plant located on the Three Mile Island, Harrisburg, Pennsylvania
• Hosts two units, TMI-1 (802 MWe) and TMI-2 (906 MWe)
• PWR reactors
INES = 5
¾ TMI-2 suffered a partial
core meltdown 28th March
1979
¾Worst accident of US civilian
nuclear industry
¾ Release of
¾ <20 Ci of 131I
¾ ~MCi of other noble gases
¾ The accident was followed by a
cessation of new nuclear plant
construction in the US
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11th December 2009
Three Mile Island 2 (1979) – PWR design
INES = 5
Primary loop
Secondary loop
Tertiary loop
Tin ~ 275 C, Tout~315 C, pressure~150 atm
20
Russell D. Hoffman (2002)
11th December 2009
Three Mile Island 2 (1979) – sequence of
events
INES = 5
Initial problem was an interruption of the flow of water to the secondary side of steam
generator
Due to human error one of the main feedwater pump failed (critical for cool
primary circuit)
Backup system opens emergency feedwater system BUT two block valves were
closed Æ no water flowing to the secondary side of steam generator
No one noticed the red warning lights in the CR (violation 1)
Cooling water in the core overheated Æ
control rods inserted in the core due to
overpressure
PORV valves (in hot leg) opened
automatically to release pressure
Normal pressure restored … PORV should
have closed but it didn’t Æ control light
in the CR said it had (violation 2)
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11th December 2009
Three Mile Island 2 (1979) – sequence of
events
• Fission stopped by the control rod insertion but β-decay continue in
the fuel Æ steam generators started to boiled dry
• All water evaporated through PORV
• steam bubbles cause the water level in the pressurizer to rise Æ thought
that there was no LOCA Æ overpressure fear Æ shut off the ECCS
• 04:14 AM water in the drain tank began to leak in the containment
• ~05:20 AM primary pumps began to cavitate
• steam interacted with the zirconium cladding Æ hydrogen bubble
• PORV was closed at 6:22 AM through a block valve Æ
• substantial core melt (@ bottom of the vessel)
• some release of radioactivity
• 13 MCi of Kr + ~20 Ci of 131I
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11th December 2009
INES = 5
• At this stage operators had to cope with unusual condition without
knowing the actual status of the system (4:00 AM)
Three Mile Island 2 (1979)
INES = 5
Some “surprised” by the fact that vessel withstood molten fuel at bottom
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11th December 2009
http://www.washingtonpost.com/wp-srv/national/longterm/tmi/gallery/photo10.htm
Photo image (1983) of TMI-2 core.
Shows damage to U fuel rods, more
extensive than initially thought. Core
meltdown with temperature ~4700 C
Three Mile Island 2 (1979) – Current Status
TMI-2 reactor is permanently shutdown and defueled:
reactor coolant system drained
radioactive water decontaminated and evaporated
reactor fuel and core debris shipped to DOE facility (Hanford, SRS?)
… remainder of the site being monitored and waiting for TMI-1
decommissioning (2034 after license extension)
worst accident to a commercial US unit Æ brought an halt to
order of reactors
Exposures were too small to have produced any observable effects
assuming official accounts of the magnitude of releases
… despite persistent claims: Pennsylvania DOH found “no excess” of
spontaneous abortions and stillbirths
Bodansky (2004) and references therein
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11th December 2009
TMI-1 in the news (very recently…)
INES = 1
Limit for nuclear workers Æ 20 msV
Normal annual natural dose is ~ 1 msV
Dose received by the worker = 0.16 mSv
25
11th December 2009
Davis-Besse nuclear power plant
• Davis-Besse NPP is a 879 MWel single reactor in Ohio, US
• Complex story of failures (stuck open PORV, loss of feedwater)
INES = 3
before and after TMI
• March 2002: discovered that boric acid had caused extensive
and rapid degradation of carbon steel components
• cavity of 250 cm2 through the 17 cm steel vessel
• generated by leakages of B in the control rods nozzles
• primary pressure kept only by stainless steel inner liner
• if undetected and uncorrected, leakage could potentially have
propagated and resultd in a loss-of-coolant accident
DAVIS-BESSE REACTOR VESSEL
HEAD DEGRADATION LESSONSLEARNED TASK FORCE REPORT,
US NRC
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11th December 2009
Davis-Besse nuclear power plant
Reactor vessel head
INES = 3
Erosion of the 17 cm thick carbon
steel reactor head, caused by a
persistent leak of borated water.
Boric acid crystals
27
Plant was switched off for >1 year
and from 2004 is operating again
11th December 2009
Tricastin Nuclear Power Center
Tricastin is one of the most important nuclear
technology industrial site in the world, located
~70 north of Avignon, France
• jointly operated by EDF, Areva, CEA
Several facilities operate at Tricastin:
• CEA Pierrelatte – a DAM nuclear weapons
research center
• EDF Tricastin – 4 PWR power reactors, ~915
MWe each
• EURODIF George Besse + George Besse II
(under construction) – uranium enrichment
facility
• COMURHEX - UF conversion facility
• SOCATRI - Uranium Recovery and Cleanup
Facility
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11th December 2009
Recent French plants incidents at Tricastin
INES = 1
Uranium solution spill, July 2008
th
• 7-8 July 2008, 18’000 liters of uranium solution containing natural uranium accidentally released
– SOCATRI facility
• The fluid overflowed from one tank into another one
• 75 kg of natural uranium in the two rivers at site borders
• Precautionary stop of drinking water for 3 days…
• … Ce bilan permet de confirmer l’absence de pollution persistante dans l’environnement liée
au rejet d'uranium du 7 juillet (IRSN-DIR-2008-481, 28 August 2008)
Tricastin reactor contamination
• 23rd July 2008, Tricastin NPP: during reactor
4 outage, a contamination incident occurred
• during maintenance on primary system
pipes, monitors detected air
contamination:.
• ~100 workers was contaminated at
levels < 0.5 mSv (1/40 regulatory limit at
20 mSv)
http://www.asn.fr/index.php/content/view/full/104460
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11th December 2009
Tokai (1999) criticality excursion
30th September 1999 @ JCO small fuel preparation plant
• Criticality accident during conversion of enriched uranium hexafluoride (UF6)
to uranium dioxide (UO2) for use in nuclear fuel
• 18.8% in 235U for use in Joyo Fast Reactor (> 3-4% for conventional reactors)
INES = 4
A solution of uranyl nitrate was transferred into a large-volume precipitation tank,
rather than the smaller, cylindrical container required by regulations
• ~16 kg uranium poured in the precipitation tank Æ criticality safety limit is 2.4 kg
Æ supercriticality condition reached Æ γ and n irradiation
Æ intermittent process due to H2O boiling
Æ average power 0.7–4 kW
• wet process Æ water provided neutron
moderation/reflection and increase the reactivity
• water was drained from the tank and borated
water inserted in order to create subcriticality
• It was essentially an irradiation accident, not a
contamination accident Æ no substantial release
of noble gases
30
McLaughlin, A review of criticality accidents, LANL, 2000
11th December 2009
Tokai (1999) criticality excursion consequences
INES = 4
Most effects was due to γ and neutron direct dose
• 3 operators at the precipitation tank received 15 Sv, 8 Sv, 2 Sv Æ two died after
several weeks
• 56 plant workers exposed accidentally ranged up to 23 mSv
• 21 workers heavily exposed during the draining process (~100 msV)
• 7 workers immediately outside the plant received doses estimated at 6 - 15 mSv
• The maximum measured dose to the general public (including local residents) was
16 mSv, and the maximum estimated dose 21 mSv (thanks to evacuation)
• A total of 119 people received a radiation dose over 1 mSv from the
accident Æ direct effect, no contamination outside
Human error with violation of basic nuclear safety principles
31
11th December 2009
Japanese reactor incidents
Various incidents/accidents troubled Japan in recent years apart from Tokaimura 1999
• December 1995: Monju fast breeder reactor:
• sodium leakage from a secondary circuit pump, probably due to a bad welding
• hundreds of kg fell into the floor Æ hot fire reacted with air Æ caustic fumes +
temperatures reaching hundreds of C Æ melting of several steel structures
• scheduled to reopen in 2008
INES = 1
• 9th August 2004: Mihama-3
• Hot water and steam leaking from a broken pipe killed 5
workers and resulted in six others being injured.
INES = 0+
• most serious accident in Japan
•16th July 2007: Kashiwazaki-Kariwa, all 7 units
• 6.8 Richter scale quake stopped all the units, located 19 km 2002: TEPC falsification
scandal Æ all reactor
from epicenter
stopped for several months
• #2, #3, #4, and #7 all automatically powered down, while
units 1, 5, and 6 were already shut down
INES = 0• no significant radiation release, apart ~1.3 m3 from spent
pool totalling 90 kBq (80 Bq/l)
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11th December 2009
Reactor Safety Standards
Probability risk assessment that indicates the likelihood of an accident that
would cause a damage to a reactor core
NRC requirement, NUREG-1150 (1990) + SOARCA (state-of-the-art reactor
consequence analysis) in the making:
• Core damage probabilities:
• operating reactors (US avg.):1x10-6 – 4x10-5/RY (NUREG-1150)
• advanced systems:
“design objectives, not necessariliy to be
• ABWR: 2x10-7/RY
incorporated in the regulatory framework”,
• AP1000 : 5.1x10-7/RY
D. Bodanksy, 2004
-7
• EPR: 4x10 /RY
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11th December 2009
NUREG-1150 (12-3), WASH-1400 (1975)
• Average probability of an individual early fatality (increase of 0.1% over
non-nuclear sources):
• NRC safety goal: 5x10-7/RY
• normal BWR (average): 5x10-11/RY
• normal PWR (average): 2x10-8/RY
Radiotherapy accidents
Less known but most deadly source of radiation accidents, few examples:
12th Sep.– 29th Sep 1987 Æ Goiania, Brazil
Accidental dispersal of lost radiography source
137Cs, 1.4 kCi
“The Radiological Accident in
5 fatalities, 250 injuries
Goiania”, IAEA report, 1998
INES = 5
Medical radiotherapy accidents
10th – 20th Dec 1990 Æ Zarragosa, Spain, errors in calibration of a linear accelerator
22nd Aug – 27th Sep 1996 Æ San Jose, Costa Rica, errors in calibration of a 60Co source
Aug 2000 – 24th Mar 2001 Æ Panama City, shielding error during radiotherapy
21st June 1990 Æ Soreq, Israel, commercial irradiator, 60Co source, 1 fatality
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11th December 2009
Military plants accidents
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Windscale pile accident (1957)
36
INES = 5
7.4 m
15.4 m
• Plutonium producing graphite-moderated/
air-cooled reactor
• Fuel was metallic uranium (pyrophoric) in
aluminum cans with fins
• Heating to anneal graphite moderator
defects in crystal lattice (Wigner effect)
• Heating and energy release was too rapid Æ
fuel overheated
• 5 days fire in U fuel and graphite
• CO2 and H2O used (dangerous
operation)
• Released 20 kCi (750 TBq) of 131I (t1/2~ 8
days)
• Milk production stopped for 6 weeks
• Estimated consequences 260 thyroid cancers
and 13 thyroid cancer fatalities
• Filter trapped most of the releases
(“Cockcroft's Folly”)
11th December 2009
Windscale pile fire aftermath (1957)
INES = 5
• Reactor unsalvageable, bioshield
sealed and left intact
• Partial fuel elements removed
• 10% of fuel cartridges and isotope
casks are still in the reactor
• Reactor fuel still warm due to
ongoing decay reactions
• Reactor is still in decommissioning
phase within the UKAEA
Damaged fuel cartridge after remote filming from UKAEA
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11th December 2009
Chelyabinsk-65
Source: BBC
• “Closed city” of Ozersk, known as
Chelyabinsk-65
• Location of the Mayak Production
Association (“Mayak”)
• Started in 1945 in the pace of the bomb
program
• Mayak fabricates plutonium and HEU
pits and tritium for the Russian nuclear
weapons program
• Mayak “Chemical Combine” hosts:
• production reactors
• 5 Pu prod. graphite A, IR, AV-1, AV-2, and AV-3 Æ shutdown
• + 2 for tritium production (Ruslan and Lyudmila) Æ in operation
• fissile material component fabrication plant
• reprocessing facilities
• MOX fuel production facilities
• vitrification plants
• fissile material storage facility
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Kyshtym disaster (1957)
• It has been a radiation contamination disaster, 29th September 1957 in
Mayak at a reprocessing facility
INES = 6
PRECURSORS
• 1949-1951: Mayak facilities were dumping high-level radioactive waste into the Techa
river (later a lake was added (*))
• Storage facility for liquid waste (1953) Æ 8.2 m steel tanks Æ fuel need to be cooled
EVENTS
• September 1957: failure of cooling system of one of the tank (70-80 tons of radioactive
waste):
• non-nuclear explosion of the dried waste Æ 70-100 tons TNT equivalent
• emission of 740 PBq (20 MCi) of radioactivity
• 137Cs, 90Sr
• a 2 MCi radioactive cloud moved towards the northeast, reaching 300-350
kilometers from the accident
39
11th December 2009
Kyshtym disaster - EURT
INES = 6
Eastern Urals Radioactive Trace (EURT) Æ disguised as Eastern Urals Natural Reserve
90Sr
Ci/km2
• 23000 km2 affected area
• 300 x 50 km was contaminated
by more than 0.1Ci/km² of 90Sr
(t1/2~29 y).
• An area measuring 17 km² was
contaminated by about
2.7kCi/km2 90Sr
• ≥ 1000 acknowledged victims
• prohibited any unauthorized access
to the affected area
• still heavily contaminated
Chernobyl Closed zone is > 40 Ci/km2 of 137Cs
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11th December 2009
Kyshtym disaster – Karachay lake (1968)
The lake was used for dumping
radioactive liquid effluent from
reprocessing operations
• Karachay is the “most polluted spot on
Earth” (Worldwatch Institute)
• 120 MCi of activity:
• 98 MCi of 137Cs (t1/2~30 y)
• 20 MCi of 90Sr (t1/2~29 y)
Currently, the lake is entirely
covered by concrete
41
• In 1968, following a drought in the region,
the wind carried radioactive dust
away from the dried area of the lake,
• 400000 people irradiated with 5
MCi
11th December 2009
Kyshtym disaster – Karachay lake
INES = 6
Aftermath of the emissions
US NRC S-97-04
1800 km2, 0.3-6 Ci/km2 of 137Cs
34 km2, 6-20 Ci/km2 of 137Cs
42
11th December 2009
Hanford nuclear reservation - USA
• Hanford Site is a nuclear
production complex on the
Columbia River, Washington
State, USA
• Established during ‘40s for
plutonium production
• B-Reactor: first full scale
plutonium producing reactor
1500 km2
~40 km
• 9 reactors + 5 Pu
processing complexes
• Operations began in
September 1944
• During operations large
amounts of radioactive
substances were released into air,
ground and water
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11th December 2009
Production of plutonium in fuel to be reprocessed through PUREX
• initially reactors were running in an once-through cycle
• later retention basins were used Æ not enough for LLFP and MA to decay
• during 50s/60s, releases up to 50 kCi/day
B reactor
KE/KW reactors
N reactor
44
11th December 2009
Irradiated fuel was
chemically processed to
separate and recover
plutonium
280 m
Weapons-grade Pu involves release of large
quantity of radioactivity
• GAS Æ releases through stacks (131I)
• LIQUID Æ critical storage in
single/double shells tanks
Æ Releases were part of routine
operations
45
11th December 2009
Series of air releases during 1945-1972 at
HNR
• The major radioactive releases occurred between 1944 and 1957
• No filters where installed in the stacks
Es. 40 MCi for Chernobyl, TMI ~30 Ci
• “Green run” Æ voluntary
dispersal of 8-12 kCi of volatile
radioisotopes 131I over two days
(2-3 December 1949)
46
Radionuclide
Released
Half-Life
Iodine-131
740 kCi
8 days
Tritium
200 kCi
12 years
Krypton-85
19 MCi
11 years
Strontium-89
700 Ci
50 days
Strontium-90
64 Ci
29 years
Zirconium-95
1.2 kCi
64 days
Ruthenium-106
390 Ci
370 days
Iodine-129
46 Ci
16 Myears
Tellurium-132
4 kCi
78 hours
Xenon-133
420 kCi
5 days
Cesium-137
42 Ci
30 years
Plutonium-239
1.8 Ci
24,000 years
11th December 2009
Hanford cleanup activities
Hanford “tank farm”
• Production shifted to clean-up in 1989
• Ongoing world largest clean-up
• Major activities ongoing since then:
• Restoring the Columbia River
• Converting the central plateau to long-term waste
treatment and storage
• Stabilization of 204,000 m3 of high-level
radioactive waste stored in 177 underground
tanks.
• Leaked waste into the soil and groundwater
• 12-50 years 4000 m3 of HLW will reach Columbia River
40 m
http://www.ecy.wa.gov/programs/nwp/index.html
http://www.hanford.gov/
47
• Recovery and stabilization of plutonium
(vitrification)
11th December 2009
Castle Bravo – nuclear test accident
Most significant radiological contamination of US
Æ Bikini Atoll, Marshall Islands, Pacific Ocean
7 km
Castle Bravo – 1st March 1954
1st deployable hydrogen bomb based on the
Teller-Ulam mechanism
Miscalculation resulted in the explosion over
twice as large as predicted
15 Mt (63 PJ), of which 10 Mt were fission
from the U-nat tamper (dirty component Æ
large fallout)
Radioactive fallout spread eastward, irradiating
Rongelap and Rongerik atolls + test personnel Æ
highest dose 3 Sv, 1 fatality, 93 injures
Castle Bravo became an international incident,
prompting calls for a ban on the atmospheric testing.
48
11th December 2009
Conclusions
1.
Most critical accidents since the beginning of nuclear era
i.
Chernobyl
ii.
Mayak “saga”
iii. Three Mile Island (?)
2.
Most incidents/accidents caused by:
i.
human error
ii.
negligence in safety provisions
iii. … few of them (not the worst) have been caused by structural failure
3.
Consequences:
i.
health outcome
ii.
alarmism in public opinion
iii. pressure in the design of subsequent reactor and plant generations
49
11th December 2009
Thanks a lot for your attention
50
11th December 2009

slides - INFN Sezione di Ferrara

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