Note: Descriptions are shown in the official language in which they were submitted.
KN 5879
~ 1~876~
Fuel assembl,~ _ith a water ~1~el@a~arated f ' ~
The present invent:ion relates to a fuel assembly with a lower lattice
device and a plurality of fuel rods supported by said lattice de~ics,
a ~uel box which surrounds all the fuel rods~ and a base
with a downwardly-faoing inlet opening for reactor coolant, the fuel assembly
having at least one ~ertical water channel for a water flow flowing along
the fuel rods but being separated from these.
Dis~ g~ r ~r~
.
More p æticularly, the invention relates to a a fuel assembly which is
constructed in such a way that it shall be capable of being used, with
advantage, in a boiling water reactor which is originally intended ~or
fuel assemblies having no water channel Or the kind mentioned
f above, without it being necessary to introduce any considera~le ohange
of the other oomponents of the reaotor. A problem, which will then be
encountered, is how to achieve a necessary by-pass ~low through the central
water channel/channels when the reactor power is being reduced by reducing
the speed of the circulatin~ pumps. With a fuel assembly acoording to the
in~ention, an automatic adjuetment of the water flow supplied to the above-
mentioned vertioal water channels takes place in such a manner that the
magnitude of this ~low i9 dependent on the magDitude of the power supplied
to these water channels,
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Disclosure of the Invention
A fuel assembly according to the invention ic intended to be arranged in
a reactor core in a conventional manner, with four fuel assemblies in each
core module, water ~aps between adjacent asæemblies, and a control rod of
cruciform cross-section in each module. In addition to the flow flowing
along the filel rods and in contact therewith, the reactor core is traversed
by a first by-pass flow, which is located at the above-mentioned gaps formed
between the fuel assemblies, and by a second by-pass flow which iB located
at the above-mentioned vertical water channels.
According to the invention, there is provided a fuel a~sembly having a verti-
cal center line and comprising a lower lattice devi¢e and a plurality o' ver-
tical fuel rods supported by said lattice devioe, a fuel box which surrounds
all the fuel rods, and a sleeve-like base with a downwardly-faoing inlet
opening for reactor coolant, the fuel assembly having at least one vertical
water channel for a water flow flowing along the fuel rods and being sepa-
rated therefrom, wherein said at least one vertical water channel is hydraul-
ically connected at its lower end to at least one substantially radially
extending channel opening out at the side swrface of the fuel assembly, the
wall of said base being provided with at least one through-hole, said at
least one through-hole being positioned at a lower level than the outlet
openings of said substantially radial channels and being arranged in hydrawlic
connection with said inlet opening via a space s~rrounded by said base.
~rief ~escription of D a~
An embodiment of a fuel as6embly according to the in~ention will be described
in the following with reference to Figures 1 to 4 on the accompanying schema-
tic dxawings.
Figure 1 shows a vertical section along I-I of Figures 2 and 3; Figures 2
and 3 show horizontal seotions along II-II and III-III, respectively, of
Fig~re 1; Figure 4 6hows a partial vertical section along IV-IV of Figure 2.
.
In Figures 1, 2, 3 and 4, the numeral 1 designates a casing tube which is
attached to a sleeve-formed base 2. The casing tube 19 which
i8 composed of four mutually equal sheet-metal elements 1~, interconnected
by means of four vertical strips 1", surrounds sixty-four fuel rods 3 9
twelve smaller water tubes 4 and one larger, central watar tube 5. Each water
tube forms a vertical channel extending along the fuel rodsand oonducting a
--2--
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water flow flowing along the fuel rods but being separated therefrom.The water
tubes are mechanically connec-ted to each other by means of a plurality of long-ish linking members 6, which are attached with their ends to the strips 1".
The fuel rods 3 rest with their lower ends on a bottom lattice 7, which
rests on two vertical supporting plates 8, which are welded to a hollow~
cruciform water distributing member 9. This is provided wi-th connection
openings for the water tubes 4 and 5. The connection openings are constructed
with annular supporting æurfaces, aga:inst which the water tubes 4 and 5 rest
by their lower end surfaces. The water distributing member 9 is provided
with at least one (e.g. four) substantially radial tube 10, through which
the space surrounded by the member 9 oommunicates with the space located
radially outside the base 2. The fuel assembly has a circular,
downwardly-facing inlet opening which is surrounded by a substantially annu-
lar end surface 13 of the sleeve-formed base 2. A guide member
14, which consists of a ring 14" and ~ plurality of rods 14' attached thereto,
.... . . . .. _ _ . . . . .
is arranged below the sleeve-formed base 2. The fuel assembly sho~m has
a vertical center line and is intended to be suppor-ted, together with three
~imilar fuel assemblies, by a common supporting plate intended for four fuel
assemblies, said supporting plate being oonstructed with a conical supporting
surface and a circular throttling opening for each fuel assembly. ~elow the
radial tubes 10 and below the water distributing member 9, the wall of the
base 2 is provided with at least one through-hole 12.
.
When the flow paths of the described fuel assemblyare dimensioned in such a
way that an optimum by-pass flow through the water tubes 4 and 5 is obtained
at full reactor power, it cannot be avoided that a certain amount of boiling
takes place in the water tubes 4 and 5 when the reactor power is reduced to
a minimum by reducing the speed of the circulating pumps. ~o a certain extent
such boiling æives rise to void formation at the upper part of the water
tubes, which results in the pressure being considerably reduced in the water
distributor 9, water thus flowing in through the channels 10 from the gaps
located between the fuel assemblies. At a fully acceptable value of the
void formation, the corresponding increase of the water flow through the
radial channels 10 will be so ~reat that a state of equilibrium will be
created~
