Induced nuclear reactions: processes – systems – and elements – Reactor protection or damage prevention
Patent
1995-02-07
1997-04-15
Wasil, Daniel D.
Induced nuclear reactions: processes, systems, and elements
Reactor protection or damage prevention
318161, H02J 906, G21C 900
Patent
active
056217773
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a drive system for a nuclear reactor, more particularly a drive system intended to drive a main recirculation pump for recirculation of coolant in a vessel arranged in the reactor.
BACKGROUND ART, PROBLEMS
A boiling water reactor normally comprises an external, substantially cylindrical, vertical container referred to as a reactor vessel, in the lower part of which a substantially cylindrical vertical moderator vessel is arranged. The moderator tank comprises a core of fuel rods. Between the outer wall of the moderator tank and the inner wall of the reactor vessel, there is an annular space referred to as a downcomer. The reactor vessel is partially filled with a coolant (water) for cooling a core of fuel rods arranged in the moderator tank.
During operation of the reactor, that is, during nuclear fission, the water starts boiling when it has reached to approximately one-fourth of the core. The steam thus formed is separated from the water at the upper part of the reactor vessel, partly in steam separators and partly in steam dryers arranged to separate the last moisture residues in the steam before it flows out of the reactor vessel. The separated water flows down into the downcomer. To replace the water which is taken out of the reactor vessel in the form of steam, the reactor vessel is supplied with water via a feedwater inlet. Thus, the downcomer contains a mixture of incoming feedwater and water which is separated from the steam in the steam separators and the steam dryers.
In the downcomer at the bottom of the reactor vessel, main recirculation pumps of plug-in type are arranged for recirculation of water from the downcomer and up through the core for continuous cooling of the fuel rods. The main recirculation pumps normally consist of vertical wet asynchronous machines operating in water under pressure.
The adjustable recirculation flow of the coolant is utilized for controlling the output power from the reactor in that an increased coolant flow, in addition to an increased cooling of the fuel rods, also results in an increased power production (increased neutron generation) in the fuel rods. As a result of the thermal inertia in the fuel rods, the time constant for increased power production in the fuel rods differs from the time constant for the corresponding increase of the cooling requirement. If the supply of energy to one or more main recirculation pumps is disturbed, the cooling and the power production are interrupted instantaneously whereas the surface temperature of the fuel rods rises since the fuel rods contain a decay power in the form of thermal energy which is not yet exhausted.
During normal operation of the reactor, the fuel rods are surrounded by a coolant film. At too rapid a reduction of the coolant flow, the decay power which is stored in the fuel rods will result in a brief overheating thereof. In those cases where this overheating leads to the heat flux from a fuel rods becoming very great in relation to the coolant flow, there may be a risk of dryout occurring, that is, the coolant film becomes so thin that it is unable to hold together. The coolant film is broken up and dry wall portions are formed, which locally leads to a considerably deteriorated thermal transmittance between the fuel rod and the coolant with an ensuing greatly increased surface temperature of the fuel rod. The increased surface temperature may lead to damage with serious consequences arising on the fuel rods, or to a shortening of the service life thereof.
To secure against dryout, the power output from the fuel rod is limited such that a margin with respect to dryout in case of transients in the coolant flow is obtained. This margin, referred to as dryout margin, means that the fuel cannot be utilized as efficiently as would otherwise be possible. Therefore, from the point of view of fuel economy, it is desirable to minimize the dryout margin. One of the dimensioning factors for the dryout margin is disturbance of the coolant flow as a result of line
REFERENCES:
patent: 4358719 (1982-11-01), Currier et al.
patent: 4920303 (1990-04-01), Perdriat
patent: 4937507 (1990-06-01), Masui et al.
ABB Atom AB
Wasil Daniel D.
LandOfFree
Pump drive system for recirculation of coolant flow in a nuclear does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Pump drive system for recirculation of coolant flow in a nuclear, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Pump drive system for recirculation of coolant flow in a nuclear will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-367480