three mile island, tmi - 2
DESCRIPTION
Three Mile Island, TMI - 2. TMI-2 normal operation. No true position indication of the valve. No temperature measurement upstream and downstream the valve. Erroneous level indication in the pressuriser. No water level measurement in the reactor vessel. TMI2 + 1 ½ h. - PowerPoint PPT PresentationTRANSCRIPT
American Nuclear Society 2001 Annual MeetingMilwaukee WI, June 17 - June 21
Safety Culture and its Relationship to Economic Valuein the Competitive Market:
A Global Perspective Worldwide
Embedded Topical Meeting:Nuclear Safety Goals and Safety Culture
Sponsored by ANS/AESJ
Promoting and Assessing an Improved Safety CultureAccident and Consequence Analyses
Lessons to learnThree Mile Island‘79, Chernobyl’86, Tokai Mura’99and the New Era of the European Nuclear Industry
Frigyes Reisch
KTH, Royal Institute of Technology(the technical university of
Stockholm, Sweden)[email protected]
Nuclear Industry, Lessons to LearnThree Mile Island´79, Chernobyl´86, Tokai Mura´99 and the
New Era of the European Nuclear [email protected]
AbstractThree Mile Island (Harrisburg, USA), Chernobyl (Ukraine) and Toka Mura (Japan) are the threemost publicised accidents of the nuclear industry. The plants are on different Continents, havevery different features and the accidents are very much unlike in nature. Nevertheless theseaccidents have many similar characteristics;
the precursors were not properly evaluated and consequently the proper conclusionswere not established, appropriate remedies were not applied to avoid similar accidents,
due to insufficient instrumentation the operators were denied much needed information -about the status of the process they controlled - to be able to make the correctdecisions,
the operators were not trained to recognise the importance - of the awareness - ofobserving deviations from normal conditions, at an early stage, to avoid accidents,
they were not trained either to be prepared to meet the challenges of unexpectedoccurrences,
the management did not see the activities at the plant through the operators’ eyes, the management did not realise the price of the “profit” of meeting time schedules by
pressuring people.
The new millennium started with an entirely new industrial landscape# The national and regional electrical grids are integrated into a huge European grid. The
rules of the electricity market changed entirely.# Reactor manufacturers are becoming fewer and bigger. For example the original
suppliers of the Swedish nuclear power plants are now in the hand of a single owner.
Common Features
- precursors were not thoroughly evaluated and consequently thecorrect conclusions were not deduced
- the operators lacked the necessary information about the statusof the process they controlled to be able to make the rightdecisions
- the operators lacked training to observe deviations at an earlystage to avoid accidents as well as their preparedness to meetthe challenges of unexpected occurrences was insufficient
- management did not see the activities at the plant through theoperators’ eyes
- the price of the “profit” of meeting time schedules by pressuringpeople was not assessed properly
[email protected] normal operation
Three Mile Island 1979
- The accident occurred in the middle of the night whenwork was to be rushed.
- After a transient, a valve on the pressurizer remainedopen and steam escaped continuously.
- The instruments erroneously indicated full pressurizerwhile the reactor vessel were emptied and the primarywater was amassed on the containment floor.
- Due to inadequate containment instrumentation theoperators could not recognize the actual situation.
- The operators were drilled to open the let down lineand stop water injection to the reactor vessel whenthe level measurement indicated full pressurizer.
- There were several precursors. Previous incidentsshowed the need for level measurement in the reactorvessel proper, at an other occasion the containmentfloor was flooded without the operators noticing it.
- After the accident neither the industry nor the safetyauthority admitted thier negligence. Thecomplementary instrumentation was installed yearslater and some is still missing.
RBMK Principal diagram
Excessive positive void coefficient +30pcm/%
Thermalisation
AbsorptionCapture and Fission
Fuel
Coolant
Graphite moderator Thermalisation
Absorption
Water&steam
Capture & Fission
Xe poisoning
Chernobyloperationalhistorypriorto theaccident
No indication of the Xe status
Chernobyl axial neutron flux shapeprior to the accident
No proper display of the axial neutron flux distribution
No interlock against unauthorised withdrawal of control rods
Remind
the
Perturbation
Theory
No temperature measurement in the suction line
No stability monitoring!
Decreasing system pressure due to dump valve opening
Neutron Kinetics equations
n = n0
. e
t/T l = 1 msec void increase 10% 60% = 50%, void coefficient 30 pcm/% (1pcm = 10-5 ) 50 x 30.10-5 = 1.5%
β = 0,5 % Pu & U235 δk - β = 1%
T = 10-3/10-2 = 0,1 = 100 . 10-3 = 100 msec
icn
l
k
dt
dn.
nl
k
dt
dn
k
lT
k
%5.1k In 0.1 sec 2.7 times power increase
In 1 sec 22026 times power increase
Nuclear Chain ReactionPower Excursion- Fuel Fragmentation, Melt, Gas
Chemical Reactions* Hydrogen production, explosion;
- Radiolysis- Metal Water Reaction- Cladding (Zr) temperature- exceeds 1200 0C
* Graphite Fire* Steam Explosion
Chernobyl 1986
- This disaster happened in the middle of the nightwhen an experiment was due to be rushedthrough to make place to the refueling crew.
- During the experiment large amount of steamwas produced in the reactor which in conjunctionwith the positive void coefficient caused supercriticality and blew up the reactor.
- The immediate past history of power productioncreated a heavily xenon poisoned reactor corewith a most peculiar axial power profile.
- The operators were not aware of this because ofthe lacking instrumentation.
- There were several precursors, incidents at otherRBMK plants which were not properly evaluatedand the lessons were not applied.
- After the incident all the blame was put on thegrass roots.
- Nevertheless major changes were made in thedesign.
- Still there is much left to do.
Tokai-Muraprocessdiagram
No weight measurement
No sign of maximum permitted weight
No sign of actuall enrichment
No interlock
Neutron energy spectrumfrom 10-9 to 101 MeVT
o
k
a
i
M
u
r
a
Mixed Spectrum Reactor
Tokai Mura 1999
- The workers during the night shift were cuttingcorners to save time.
- Due to a non existing weighing instrument theywere not aware that they overcharged a vessel,
- neither were they aware that they handledmaterial with higher enrichment as usual asthere was no indication anywhere about theenrichment.
- Their training was insufficient in such extent thatthey were hardly aware of the dangers theerroneous handling of fissionable material cancause.
- There were plenty of criticality accidentspreviously which could serve as precursors.
- After the accident most of the blame were put onthe worker.
- The responsibility of the management and theauthorities was not much talked about,
- neither was the necessary improvements of theinstrumentation discussed.
[email protected] Power Plants in Northern Europe
Northern Europe- Around the Baltic Sea there is a cluster of the most widely used
reactor types in operation;- There are pressurised water reactors of both western (PWR) and- Russian (VVER) types,- boiling water reactors (BWR) of Swedish and German manufacture,- a boiling heavy water reactor (BHWR) in Norway and- graphite moderated boiling water cooled pressure tube reactors (RBMK)
of Russian design.- - These reactors are not only of different types, they are also of
different sizes.- The BHWR is a low power research reactor of some 10 MWt while- the BWRs, PWRs and VVERs are of medium to large sizes, from some
100 to more than 1000 MWe.- RBMKs are among the most powerful reactors of all categories – well
over a GWe.
- The Baltic Ring Project, now under development in Scandinavia, isintended to link all the nuclear reactors surrounding the Baltic Sea into apowerful grid.
European Industry: Fewer and Bigger Manufacturers
- Since the beginning of this new century all the original suppliers of theSwedish reactors ABB and Westinghouse are owned by BNFL, BritishNuclear Fuel Limited controlled from London by the government, whilethe
- original supplier of the German plants, Siemens is controlled by thelargely Paris government owned Framatom, the supplier of the Frenchnuclear power plants.
*Both companies have plants in all the Continents