Induced nuclear reactions: processes – systems – and elements – Reactor protection or damage prevention – Shield or barrier between radiation or heat source and...
Reexamination Certificate
2001-10-17
2004-10-26
Carone, Michael J. (Department: 3641)
Induced nuclear reactions: processes, systems, and elements
Reactor protection or damage prevention
Shield or barrier between radiation or heat source and...
C376S283000, C376S298000, C376S299000, C376S294000
Reexamination Certificate
active
06810099
ABSTRACT:
CROSS REFFERENCE TO RELOCATED APPLICATIONS
The present application is based on Japanese Application 317169/2000, filed Oct. 17, 2000, which is herein incorporated by reference in its entirety.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a boiling water reactor nuclear power plant with a natural circulation reactor, and particularly to a boiling water reactor nuclear power plant and its construction method with a simplified compact system configuration, having diversity to the power demand, and an improved economy and similar.
2. Description of the Related Technology
In conventional plants, as the configuration of reactor pressure vessel and internals of the boiling water reactor nuclear power plant, forced circulation method has been mainly adopted such that active pumps installed at the bottom of the reactor pressure vessel circulates reactor water, and jet pumps installed in the reactor are driven by the external loop active pumps. And as the control rod of power control means, bottom entry type which is inserted from the bottom of reactor pressure vessel has been adopted.
For the above configuration, the lower drywell space has been large in order to keep the circulating pumps and the control rod drive mechanism and its draw out space below the reactor pressure vessel. And this lower drywell is used for a large quantity of water storage space during loss of coolant accident since the suppression pool water injected into the reactor pressure vessel is drawn down to this space from the break cavity. And therefore this space has been wasteful to design the water quantity of the suppression pool.
And if core fuel is melted and dropped down onto the bottom of the reactor pressure vessel during assumed severe accident, the configuration with control rod driving mechanism and similar prevents from cooling the melted core from outside the reactor vessel.
As for the example of the conventional plant among these boiling water reactor nuclear plants, it is explained using the newest type reactor named ABWR referring to
FIG. 15
as follows.
On conventional boiling water reactor nuclear power plant, core shroud
3
which contains the core
2
is installed in the reactor pressure vessel
1
, many fuel bundles
6
are provided between core support plate
4
and upper lattice plate
5
which is installed in each at lower and upper portion in the core shroud.
Shroud head
7
is installed above the core shroud
3
, and steam separator
9
is installed above the shroud head
7
through the standpipes
8
. Steam dryer
10
is installed above the steam separator
9
. Control rod guide tubes
11
of the control rod (not figured) which are inserted into the core
2
and the control rod drive mechanism
12
which drives the control rods are installed below the core support plate
4
.
Plural reactor internal pumps
13
are installed in the circumferential direction at the bottom of the reactor pressure vessel
1
.
Main steam pipes
14
are provided on the sidewall of the reactor pressure vessel
1
alongside the steam dryer
10
to supply reactor steam to the turbine (not shown). Feed water pipes
15
are provided on the sidewall of the reactor pressure vessel
1
alongside the standpipes
8
of steam separators to supply cooling water to this reactor
1
.
In the boiling water reactor of this configuration, the coolant above the core is drawn into the internal pumps
13
from the gap area between the core shroud
3
and the reactor pressure vessel
1
, and it generates steam in the core
2
through the core bottom, and it is lead to the turbine through the main steam pipes
14
via. the standpipes
8
, the steam separators
9
and the steam dryer
10
. The steam which works in the turbine is condensed by the main condenser, and the condensed water is returned to the reactor upper portion through the feed water pipes
15
.
In these conventional type boiling water reactor nuclear power plants, the core and the pressure containment vessel is cooled during accident using active components in general, and for the severe accident means, in which these active components are assumed not to be used, passive cooling systems or alternate active cooling/injection systems have been added at present.
Therefore it requires additional exclusive passive equipments for the severe accident other than the design base accident equipments and system regardless of degree of these reliability and it has been given a large impact economically.
And as for the cooling method inside drywell during reactor normal operation, cooling heat exchanger (drywell cooler), for which cooling water is supplied from outside drywell, and fans for circulating the inner gas are installed in the drywell in general.
The conventional pressure containment vessel is made from steel or reinforced concrete. Namely, a gourd-shaped standalone type or a bell-shaped integrated building type is adopted for the steel containment vessel. And an integrated dual-cylinder type is adopted for the reinforced concrete containment vessel. The vessel sizing factors are mainly as follows; components arrangement inside drywell as for drywell, water and air space volume for the pressure suppression in the early stage of accident as for suppression pool.
In addition the pressure containment vessel strength is evaluated if its stress is below the limit in which hydrogen gas generated by metal-water reaction is stored assumed severe accident condition continuing the heat removal using passive containment cooling heat exchanger or alternate cooling/injection system.
Reactor building is made from reinforced concrete separated from turbine building, and is designed on each site conditions or plant power output. These buildings are constructed almost on site works.
FIG. 16
shows an example of the latest boiling water reactor plant under studying.
This plant is constituted of reactor building
421
, pressure containment vessel
422
, reactor pressure vessel
423
and its associated system and component. In this constituted plant, control rod and its driving mechanism
435
is provided below the reactor core
424
, and reactor coolant circulation components like reactor internal pumps
425
are provided on the reactor vessel bottom.
Emergency core cooling system pumps
426
are located on the lowest floor of the reactor building
421
, and residual heat removal pumps
427
and heat exchangers
428
for the containment vessel cooling as same manner.
On severe accident which exceeds design base accident, core and containment vessel
422
is continuously cooled using passive containment cooling heat exchanger
429
and alternate injection pumps
430
via alternate injection water supply tank
436
.
During annual plant inspection, core fuels are moved to spent fuel storage pool
432
on the condition of reactor well filled with water.
PROBLEMS TO BE SOLVED BY THE PRESENT INVENTION
Although there has been previously existed the idea of forced circulation type boiling water reactor with internal type upper entry control rod drive mechanism, the concept of natural circulation type boiling water reactor with it combining raised type suppression pool has not known before.
In the case of a conventional system of bottom entry control rod and bottom located suppression pool, when gravity driven cooling system of passive safety is adopted, additional exclusive tank of gravity driven cooling system is needed on the upper elevation portion of pressure containment vessel other than suppression pool and it causes large volume of pressure containment vessel.
And bottom entry control rod mechanism causes large lower drywell volume for the flooding by gravity driven cooling system to become large pool capacity of gravity driven cooling system. Furthermore many various nozzles, piping and control rod guide tubes etc. located under the core prevents IVR (In Vessel Retention), which stops the progress this event, of the molten core at severe accident.
Meanwhile, the present inventors and others have investigated the whole reactor pressure vessel remova
Arai Kenji
Heki Hideaki
Hiraiwa Kouji
Morooka Shinichi
Nakamaru Mikihide
Carone Michael J.
Foley & Lardner LLP
Kabushiki Kaisha Toshiba
Palabrica R
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