Method of protecting a nuclear reactor in the event of a load increase

• US 5,169,592 A
• Filed: 07/17/1991
• Issued: 12/08/1992
• Est. Priority Date: 07/17/1990
• Status: Expired due to Term

• Current Assignee: Framatome
• Original Assignee: Framatome
• Inventors: Pavageau, Olivier, Mourlevat, Jean-Lucien, Kockerols, Pierre
• Primary Examiner(s): Hunt, Brooks H.
• Assistant Examiner(s): VOSS, FREDERICK
• Application Number:
  US07/731,330
• Time in Patent Office: 510 Days
• Field of Search: 376/277, 376/297, 376/241, 376/215, 376/216, 376/217, 376/244, 976/DIG. 300, 976/DIG. 302
• US Class Current: 376/215
• CPC Class Codes: G21D 3/04 Safety arrangements emergency protection of reactor G21C9/00
• CPC Class Codes: G21D 3/10 by a combination of a variable derived from neutron flux with other controlling variables, e.g. derived from temperature, cooling flow, pressure
• CPC Class Codes: Y02E 30/00 Energy generation of nuclear origin
• CPC Class Codes: Y02E 30/30 Nuclear fission reactors

Abstract

An emergency stop of a pressurized water reactor to be protected is triggered when the nuclear power (ET) thereof reaches an emergency stop limit (LP). The value of this limit is lower with lower operating temperatures (ST) of the reactor.

Claims

1. In a method for protecting a nuclear reactor in the event of an increase in its load, said method comprising the steps of:

(a) monitoring an operating temperature of said reactor;

(b) setting an emergency stop limit for nuclear power of said reactor;

(c) monitoring said nuclear power;

(d) comparing said monitored nuclear power to said emergency stop limit; and

(e) stopping said reactor when said monitored nuclear power exceeds said emergency stop limit;

the improvement wherein said method further comprises the steps of;

(f) setting a reference temperature for said operating temperature;

(g) comparing said monitored operating temperature to said reference temperature; and

(h) lowering said emergency stop limit when said monitored operating temperature becomes less than said reference temperature.

2. In a method for protecting a nuclear reactor in the event of an increase in its load, said reactor comprising:

a core (2) containing fuel rods in which a nuclear reaction takes place, giving off nuclear power which is spread between a top and a bottom of the core and which is transformed into heat;

a heat exchange circuit (4, 6,

     8) for causing a heat exchange fluid to penetrate into the core via an inlet duct (4), for causing it to flow through the core, and for causing it to leave the core via an outlet duct (6), thereby removing said heat, said circuit delivering the heat to a heat receiver (10) having varying needs; and

control clusters (12) penetrating in controlled manner into said core in order to control said nuclear reaction;

said method comprising the steps of;

(a) using at least one power measuring system (14) for delivering a total power signal (DT) representative of said nuclear power;

(b) using a temperature measuring system (18) for delivering an operating temperature signal (ST) representative of an operating temperature which is a temperature of said heat exchange fluid;

(c) using a power control system (24) for acting on some of said control clusters (12) in response to variations in the needs of said heat receiver (10) so that said heat receiver receives heat power that corresponds, at least approximately, to its needs;

(d) setting an emergency stop limit for said nuclear power; and

(e) supplying at least said total power signal and said operating temperature signal to an excess power protection system, said excess protection system delivering an emergency stop signal causing at least some of said control clusters to penetrate into said core so as to stop said nuclear reaction when the nuclear power represented by said total power signal (ET) exceeds said emergency stop limit (LP);

the improvement wherein said method further comprises the steps of;

(f) setting a reference temperature for said operating temperature;

(g) including a function generator in said excess power protection system for partially controlling said emergency stop limit; and

(h) supplying said reference temperature to said function generator, said function generator lowering said emergency stop limit when said operating temperature becomes less than said reference temperature.

3. A method according to claim 2, comprising the step of further using said function generator for further lowering said emergency stop limit when said operating temperature decreases from a value less than said reference temperature.

4. A method according to claim 2, comprising the step of further using said function generator for further lowering said emergency stop limit by a predetermined limit-lowering amount each time said operating temperature decreases by a predetermined value from a value less than said reference temperature.

5. A method according to claim 2, wherein said reference temperature (TR) lies in the range of 270°

C. to 320°

C.

6. A method according to claim 5, wherein said method is applied to a pressurized water reactor and said reference temperature (TR) lies in the range of 290°

C. to 300°

C.

7. A method according to claim 5, wherein said function generator gives to said emergency stop limit, when said operating temperature (ST) is 20°

C. less than said reference temperature (TR), a value which is less than one-half the value that said function generator gives to it when said operating temperature is close to but greater than said reference temperature.