Note: Descriptions are shown in the official language in which they were submitted.
~06643S
The present invention relates to a reactor plant
comprising a light-water-cooled reactor core with vertical fuel
assemblies, a reactor vessel with an inlet space and an outlet
space for cooling water flowing through the reactor core, a
heat-exchanger, a circulating pump for the primary circuit of
the heat-exchanger, and a water-filled pool, said inlet and
outlet spaces each being provided with at least one hydraulic
connection with the heat-exchanger, the reactor core being
contained in the reactor vessel and the reactor vessel arranged
in said pool, the coolant of the primary coolant circuit during
normal reactor operation being blocked from the pool water by
means of a blocking device with a liftable blocking effect.
In particular a nuclear reactor is aimed at which can
suitably be used in a district heating plant. Such a reactor
is described in "The American Nuclear Society Transactions",
Vol. 20, pp. 733-734. In the known reactor it is possible to
achieve emergency cooling with the pool as a heat sink. This
is done by operating two valves, by means of which the pool water
flows in through an inlet opening in the primary coolant circuit
of the reactor and steam and hot water flow out from this
through an outlet opening.
However, it is a disadvantage in the known device that
the emergency cooling function is dependent on the transport
and correct positioning of solid bodies, namely the valve
bodies included in the above-mentioned valves. A construction
according to the invention aims at avoiding this drawback.
Instead of valves with movable parts, a number of so-called
"gas lock tubes" are used according to the invention. In the
following, the term "gas lock tube" refers to a bent tube which
is immersed in a liquid and arranged with both its ends below
an intermediate tube portion, in which an amount of gas is
contained, or a device equivalent thereto.
' 1066435
~ s herein claimed, a reactor plant according to the
invention is characterized in that the primary coolant circuit,
through an outlet opening and an inlet opening in the walls
defining the primary coolant circuit, is constantly in an open
connection with the pool space, at least the outlet opening
being provided with a connecting means for this purpose in the
form of a gas lock tu~e.
.. . . . . .
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1066435
In the following the invention will be described with
reference to the accompanying schematic drawings in which
Figures 1 and 2 show two different embodiments of the invention
in vertical section and Figure 3 a partial section along III-III
of Figure 2~ Figure 2 is a section along II-II of Figure 3.
The reactors shown are of the pressurized water type, i.e.
boiling does not occur during normal operation since problems
of stability could arise at the low pressures which are used
in this connection.
In Figure 1, 1 designates a water-filled pool which
may suitably be designed with a maximum depth of about 25
metres. Near the bottom of the pool a reactor vessel 2 is
arranged, which contains a reactor core 3 and a plurality of
control rods 4. The reactor vessel is connected to the
primary side of a heat-exchanger 5 by means of a conduit 7 for
relatively cold water flowing into the reactor vessel, and a
conduit 6 for relatively hot water which leaves the reactor
core 3, a circulating pump 8 being included in the conduit 7.
The conduit 6 opens out into an inlet chamber 9 and the conduit
7 comes out from an outlet chamber 10 of the heat-exchanger.
From the inlet chamber 9 the water flows through vertical tubes
11 and up to a turning chamber 12 from which it 10ws bask
through vertical tubes 13 to the outlet chamber 10 of the heat-
exchanger. The parts 2, 6, 9, 11, 12, 13, 10, 7 and 8 together
form the primary coolant circuit of the core 3 which contains
only pure water. The corresponding secondary coolant circuit
consists of the spaces between the tubes 11 and 13, an outgoing
conduit 14 and a return conduit 15 and a number of consumers
connected to the conduits 14 and 15, preferably directly
connected heating-plants for room heating of houses and work
places. The secondary coolant circuit preferably has higher
water pressure than the primary circuit. The lower part of
~066435
the reactor vessel 2 is the inlet space and its upper part
the outlet space for the reactor core 3.
The primary coolant circuit is constructed with an
outlet opening 16 and an inlet opening 17, through which it
is in a permanent open communication with the pool space by
way of two gas lock tubes 18 and 19, which are connected to
the openings 16 and 17, respectively. As indicated in the
drawing, the gas lock tubes 18 and 19 each contains an enclosed
amount of gas, which are connected each to a pressure-regulated
gas tank 22 and 23 by way of relatively thin tubes 20 and 21,
respectively. The gas pressure in the gas tank 22 is chosen
approximately equal to the water pressure at the lower opening
of the gas lock tube 18, i.e. only so much higher than a slight
bubbling out of air can be observed at this opening. This
will give an indication that an even pressure is maintained in
the gas lock tube. Alternatively, the pressure in the gas
tanks 22 and 23 can be chosen much higher, for example more
than 150% of said water pressure, the pipes 20 and 21 then
being provided each with a throttling means.
In order for the water levels of the two gas lock
tu~es to adjust themselves as indicated in the drawing, the tube
19 must be supplied with gas, the pressure of which - counting
in water columns - is equal to the gas pressure in the tube
18 plus the difference hl between the water levels of the
`two tubes. As indicated in the drawing, such a high pressuriza-
tion can be used that the water pressure at the outlet of the
core 3 will be considerably greater than what corresponds
to the water pressure in the pool. The vertical dimension
of the gas lock tube 18 can be chosen greater than, e.g. one-
fourth of the maximum water depth in the pool, thus achieving
a considerable increase in the water pressure in the core,
which means that a higher water temperature can be allowed at
~ _ 3 _
1066435
a given pool depth without getting too close to the boiling
point.
Also in the event that the gas amount contained in
the gas locks has a very small vertical dimension, the air
lock tubes have an important function since in normal operation
they effectively prevent the reactor water and the pool water
from being intermixed. When level variations occur, among
other things since the difference between the water levels of
the air lock tubes is greater when the pump 3 is in operation
than in the purely static case, the vertical dimensions of
the gas lock tubes must, however, be chosen so large that the
contained amount of air does not leave the gas lock tube during
normal operation. As a rule, it may be taken into account that
the gas lock tube shall be dimensioned to allow a contained
amount of air whose vertical dimension is greater than one
metre.
A reactor according to the invention is designed to
fulfil extrem~ security demands. Even in the very hypothetical
case that the circulating pump 8 seizes and the control rods
4 for some reason are jam~ed outside the core at the same time,
it may be counted on, with a great degree of security, that
no radioactive discharge will take place, and that there will
be no risk that the fuel rods will melt down.
If a sudden boiling takes place in the reactor core
3, for example because of an intentional or unintentional faulty
drawing of the control rods or an instantaneous pump stop
without a subsequent reactor trip, the steam formation will
first result in part of the water of the primary system being
pressed out through the gas lock tube 18. This does not
necessarily lead to a breakdown of the air locks. Since we
assume that there are negative void coefficients of reactivity,
the void contents will then result in the power being rapidly
~ - 3a -
1066435
reduced to less than 5 % of the normal power. The evaporation
continues and the gas lock tube 18 is filled with steam while
the water level slowly sinks.
- 3b -
.
~066435
B~ openlng the valves 24 ana 25 RO that the ~as pressure aiæappears ln the
tanks 22 snd 23, lt ~ould be pos~lble to aohie~e a relatirel~ rapid inno~
of pool ~ater into the primary ooolant olrouit of the reaotor. ~o~ver,
slnce the behaviour of the resotor under the ~orst i~agiDable condit~ons 18
of intere~t, ~c assu~e that the valves 24 and 25 are not operating.
If an evaporatlon ooours ln the reaotor oore, the dlfferenoe bet~een the l~ el
ln the heat-eschan~er ana the level in a connected branoh Or the lo~er gas
look tub~ ~ill deorease Rlo~ly, ~hioh eans that the pool water ~111 rlse to
such an e%tent ln the long branch of the lo~er &a8 loc~ tube that the pool
~ater finally passes the horlzontal part of bhe gas loc}s ana 18 suppllea
to the pri~ar1 coolant clrcuit of the reactor. Such replenishment oan be
repeated several times, but the water level in the heat-e%chan~er can n~rer
rlse hiBher than to a certain ~a~imu~ level, namel~ bhat ~hich coinclaes ~ith
the lo~er openlng of the upper ~as lock tube. It 18 i~portant that the ~hole
reactor core 18 arranBea belo~ this oa2imu~ level. Further, lt 18 es~ential
that the upper edg~ of the lo~er eas look tube 1~ arran~ea belo~ the abo e-
ntlond a~l~uo le~d , since other~ise lt ~ould be i~po~slble to flll lt
~lth ~ater co pletd ~ ~hen ~ater le flll d ln after ch nsln6~ which ~ould
inrolve that a per a~nent ~as plug ~Oula oocur at the upper ost part o~ th-
Bas loc~ tuOe 19, ~hlch ~Oula pr ront th fbrth r supply Or pool ~ater to
the r aotor. ~8 ~8 shown ln the ara~ing, both the Op~nln68 of the pri~ary
s~te , which arQ pro ldel ~lth Ras loc~s, are arransea in such a ~a~ that
the outl-t op nlng - coN~ting in th clrcul-tlng alr otlon of th prl-
ary clroult - has relatl~el~ ~hort alstance and the iDlet oponlng
a relatlr ly long alstan~- ~ror th space abo~e the reaotor core. The
lnlet opeul~6 17 ~houla Oe arran pa a~ ~ar down as posslbl-~ ho~er r lt
shoula be aOo - th oore . aounting~ln the clrcul-tlng alreotlon o~ th prl-
ary ooolant olrcult, th purp 8 18 looatd aft r the lnlet oponlng 17an~ before the oore ~, and therefore the pressurlsatlon ocourrin6 ~hen th
pu p 18 ~or~lng oaus-s an equally ~reat lncr~ se ln th pres~ure of th
coro 3, ~hereas th l- el ln the Bas loo~ tube 19 18 lnfluenosa to a r-la-
tl~el~ d l ae6re- ~h n the sps~a of the pu p 1~ o _ . _ _ _
In Flgures 2 ana 3~ 30 18 a reaotor oore ~hloh 18 arrsDBod ln a ~ater-fllld
r aotor essel 34 ana oonstruotsa fro a plurallt~ of ~ertloallJ arran~ea
fuol a~se~blle~. ~he r actor ssd 18 arraneed ln a ~ator-rilld pool spao-
31. ~he ~at r l~ el ln th- pool ~8 ~ho~n by the sy~bol J.
The reaotor oore 30 18 surrouna d by a flo w ontrolllng oadn6 32, the upp r
dge of ~hioh 1~ fastenea to a ooDlcal~ annular sore n 33~ th out-r dge o~
~hloh 18 attaoh~a to th reaotor essel 34 ~n a pressure-tlght ~nn r. Th
1066435
soreen 33 aeflnes an inlet space 35 bJ its under slae and b~ lts upper slde
it a-rines an outlet spaoe 36 for the cooling ~ater flo~g tbrough the reac-
tor core. The outlet space 36 1~ pro lded at its lo~er end ~ith a lo~er gaJ
loo~ tub- 37, the short branch 37' of ~hlch 18 ~ater-flllea, ~hereas the long
branch 37~ aurins nor~al operation is gas-flllea and arran6ea ~ith a predo l-
na~t part of lts length in a ~ell 58 the aepth of ~hich countlng ~ro the
pool botto 18 Breater th~n one-~ourth o~ the aqp~h of the pool.
The outlet ~pace 36 is ~urther pro~idea ~ith ~wo upper gas loo} tubes 3~, of
~hich the branch connect d to the r actor ~essel is in nor~al operation
~ater-filled ana the other branch gas-fillea.
~t th upper end of the reactor es~el an annnlar pump cha~ber 39 i8 definea
b~ mean~ of an annular pu~p ~ o~ 40 ana a hollo~ c~llnarloal ~11 41. ~t
lea~t on~ ~usp 57 1~ arrangea to pu~p ~ater ~ro~ the outlet spao- 36 to the
pu p ohu b r 39.
....
A plurallt~ Or heat-~ch~n~ru, Or ~hich only ona 18 ~ho~n ln Flgure 2, ar
arrane~a ln th reaotor -88-L ~ach h at-e~changer con d st~ of a tub- 42,
the upper end of ~hlch 1~ e~led ana pro id d ~it]h t~o conneotlon ~oo~ ts 43
ror ooonootlon Or tho lnlot a~a outl-t oondultc of th seoond~rJ olrc~lt,
~hioh are lnalcat d 1~ Flgur- 3 b~ th ~ots ~na da~he~ a-d4n~t d ~ and 45.
Th ~ ooJ~ar~ of th h at_~cotuo46~r oooslsts o~ a plurall b orLloo~ 46
arr ng d 1~ th tub- 42 and th ~rl~rr c~- of th 8paO- urroq~ d b~ th
tub- 42 and t oooupl d b~ t]h tub- loopc 46. Th tub- 42 ha- a yr~-s~r--
tlght pb~-ag thrcugh th r ~otor e-8 d 34, the snnular pu p d o~ 40 aod
th oooloal or- n 33 na OponJ out ~lth lt~ lower en~ into th lDl-t pac-
35~ th retur~ ~at r ~ro- tho pri brr ala- of the heat-~loh~D~r n o~ioB o~t
lnto th p o- 35. ~her tror th ~ator n 0~8 thso~gh th oore ~0 a~a lt~ o~t-
l-t oha ber 36 ~ro- ~h r~ lt pa~ th puap 57 an~ th pu p ohaab r 39 ana
then rlo~ at th upy r ~D~ of the Wbo 42 throogh a plurallt;r Or hol- 47
~hloh, tog ther ~lth th pu p oha ber, oo~stltut- a kvdsawllo oonn~otlon
bot~e~ the prl rr lde Or th heat-e~#h ry~r ana th o~tl-t ~pao- 36 o~
th roaotor es~-l.
pl~rallt~ Or oontrol roa eU~a tubos 48 ar- ~opt 1~ th- oorr ct posltlon
b~ eaDs Or ~ rlAg 49 whloh 1- ittaoh d to th- reaotor ess-l ~lth t~e h lp
of a plusallt~ Or ~t~o 50. ~ plursllt;r Or oontrol roas ar- oh faJt nea
to a oontrol ro~ sbart 51 ~r ~eans Or an ol otro~agnet, not ho~, th- ~lnd-
in~ of ~hloh 18 oerl-~-oonnsot d to a t~pera~uro fu~e in th for~ of a lt-
ing body ~hloh elt~ ana br a~- th ourront lf th te per~t~ in th ~at r
o~ tho re~otor 088-l tond~ to b oo e too hlgh, th t 1~, lr th r- 1B ~ rl-
~o~ bolling ooourrlDs ln th re~otor ese-l.
-5-
- .~ 1066435
~a¢h of the ¢ontrol rod shafts i8 conneotea to a control rd drl~e 53
attached to the reactor ~essel co~er 52 wbich control rod dri~es are oon-
neoted eaoh to an eleotric ~otor 55 b~ ~ay Or a plurality of shafts 54.
The motors are supported b~ a stana not sho~n attachd to the reactor
~essel oo~er. ~h oo ponents 48 51 52 53 54 ana 55 can be llftea as
o unlt in th oase o~ a refuelling.
The oonneotlon of the uppsr 8as lock tube to the vessel i~ dlr~ctl~ beloN
the pump deck To lid t the depth of the ~ell 58 of the lo~er 8as lock tube
this i8 oonneotea to the ~essel abo-e the core. During nor al operatlon this
requires a d l by-paJs flow pa~t the oore. During deca~ heat ooollng the
~ater supplied throu~h the lo~er 8as look then ~10N8 through a b~-pass ope-
nlD~ 56 ~sde for thls purpose to the iolet of the oore.
.
In th o~ont of a pu p stop ~ith falllng r aotor trlp the to p~rature of
the oor- o~tlot ~lll rl-- at th _ tl e a- th pr~ssu aiOps in a anner
a ter ~nd b~ th ¢o Jt do~n ¢hasaoterlstios of the pu p. For ~a pl- boil-
iog a~ ooour ft r about 6 second~ at about 4 bar and 145C in the oor~ out-
let. Thi~ te p~rature 18 far abov- the rolease temp~r~tur- of th fu~-- but
beoause of thelr lnertia th ~ are not l e~lat l~ r-leasd. Th pressure and
tho to p~rature ~lll ther~ror rlse ~h~ boiliog o¢ours #na Br~at a ounts of
~ator ana/or ~tea ar- pr~s~ d out through tho upper Ba8 l00~8. Tho pr esuro
arOp io these 18 UJUa~ 0 er at that oo r plenlsh- nt throu~h th- lo~r o~8
look oan bo oou~t d on. B oaus- of th ~olalDg tho po~r of th oor rall~
O oonJ~ rabl- ~nor J- of th fu l te~perature ooours. Th ~ater oon_
tonts of th r~ otor nsd abo e th oor aro unu~uall~ Br~at aoa a looB
tl~e before all thls oan be pressed out through th upper gas looks booau~e
of th- st _ doneloyo~nt~ the fcJ-s r l~s-~ the oontrol roa- fall do~n into
th oor ana onlJ the ~eoa~ po~er of th oore neea be ooold off
I~ a rea¢tor ~e~sel of the t~pe sho~n 1~ uros 2 aD~ ~ the alstanoe fro-
tho upper de- of the oor to the essd oo~er shoula b- at le Jt 60%
preferabl~ re than ?o% of the total heieht of tho reactor ~ess~ t
tho sa e tl e th- a~a eter of the ess d shoula be at lea~t 160~ pr f r-
abl~ re than 190% of th- ala eter o~ the reaotor oore. Beoaus- of the
Broat ala~eter an~ holdhe of the e88d a ~od separatl of st-an ana
~ater 18 obtaln~a ana ool~ 8 al1 prossure alffer~noos a regulrsa to
pre~s out the st~a~ throu~h th~ ~pper ou looks~ Thss th Yator upyl~
through the lo~er eaJ loo~ tub- 37 18 seourd.
The Bas of at least ono ~aJ look tubo ~a~ be vater stea~ upplld b~ a
speolal boller~ for -~ ple ~ a 8 al1 st~u~ oonkult.
