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The 21st
century will be characterised by a numerous acts of sabotage against man-made
facilities and NPPs. Events of 9/11 in the USA
showed how it can happed.
The vulnerability of an NPP can be explained by the application of
fuel elements with zirconium claddings. Tubes from such an alloy can perfectly
well retain the fission products under the normal operation conditions. But in
accidents the temperature of the alloy rises to 1000°C. At that temperature the
strength deteriorates by several times. Due to that the fission products escape
from the fuel and the reactor. In case of a heavy aircraft crash the
containment and the reactor (of VVER type) can be destroyed. Radiation consequences of such an accident
will be comparable to those ones of Chernobyl.
The work of Russian scientists [1] proves that the application of
micro-fuel elements in VVER type reactors is very promising.
Micro-fuel elements are balls made of UO2 and covered by
several layers of graphite and silicon carbide. Originally this fuel was
designed for high-temperature reactors (HTGR) with helium coolant. For HTGR
micro-fuel elements proved to be excellent. They efficiently retained fission
products at 1300-1500°C.
It is well known that ceramics retains the strength at very high
temperatures. In high-temperature reactors the micro-fuel was used at the
nominal temperature of 1500°C and retrained the fission products. In accidental
conditions this was true even at 2000°C. This is a well known property of
ceramic materials. High temperature gas cooled reactors were not widely used
for competitive reasons.
Application of micro-fuel elements in VVER reactors may
significantly increase the radiation safety of NPPs.
In the work [1] the micro-fuel elements were placed in a fuel
assembly (as a layer of fuel or a pebble bed) directly washed by the coolant.
It is important to note that the fuel assembly with micro-fuel
elements can be made as an exact replica of the current FA with fuel rods
(keeping the same thermal, hydraulic and neutronic characteristics and
dimensions). It means that all existing NPPs can be loaded with new fuel
assemblies with micro-fuel elements and the radiation safety will be guaranteed
at any accidents, up to the deterministic level.
In the reactor with micro-fuel the residual heat is removed by a
natural convection at any failure of an active cooling system. If any positive
reactivity is inserted it is compensated by the evaporation of the coolant
which is a moderator also. This unique property is inherent only to VVER and PWR
reactors that use the same liquid for cooling and moderation. Even in case of
the vessel tank rapture after the aircraft crash or sabotage, the micro-fuels
elements scattered on the site will retain the fission products.
This way the application of micro-fuel in the existing NPPs will
allow large scale development of the nuclear power in the first half of the 21st
century.
Studies on the application of micro-fuel in VVER were started in Russia in
1992. Since 1994 this work is supported by Framatome. Up to now a number of
out-of-pile tests has been made, namely:
- Examination of corrosion resistance in water (3500, 19
MPa, 10 months)
- Examination of corrosion resistance in superheated steam (55000,
10 MPa, 14 months)
- Examination of corrosion resistance in superheated steam (900°C, 14
days);
- Examination of corrosion resistance in combustion gases (simulation
of water-steam mixture) at 1000-1670°C during 6 hours;
- Examination of the chemical interaction between micro-fuel and
stainless steel at temperatures above 1200°C;
- Mathematical modeling of accidents, including vessel tank rapture
These studies
showed the possibility to create a reactor of VVER type with unique safety
characteristics. Presently micro-fuel
elements are tested in-pile in a water loop of research reactor IVV-2M
(Zarechny near Yekaterinburg).
Studies on the
application of micro-fuel elements in boiling reactors of BWR type were
supported by Hitachi and the use of the same fuel in fast breeders is supported by
French Commissariat of Atomic Energy. Development of a concept for a vessel
type once-through reactor with super-heated steam and micro-fuel elements is
supported by PNNL (USA).
The goal of
this work is to develop a design of a micro-fuel element for existing NPP with
VVER (PWR) reactors.
The work will
be carried out by a number of Russian companies, including RRC KI, VNIIAM, NPO
Lutch, and OKB Gidropress.
97 experts and scientists will participate
in the project under the aegis of VNIIAM. Among them 55 earlier were involved
in the design and fabrication of weapons.
To realize that project is needed to
cooperate Russia and USA together.
Best Regards,
Nickolay Zhukov
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