JPS60252300A - Cost-reduction operation method of nuclear reactor - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a coastdown operation method using natural power reduction of a nuclear reactor.

[Technical background of the invention and its problems]

Generally speaking, once fuel is loaded into the core of a nuclear reactor, approximately 9
Output operation cannot be performed for several months. When this fuel is consumed,
When the reactor is temporarily shut down (1), the consumed fuel is removed from the reactor core and new fuel is loaded instead, and power operation is resumed. At the time of this fuel change, the reactor equipment is inspected at the same time, and these inspections are generally called periodic inspections.

These regular inspections have been carried out for about three months.

At present, in nuclear power plants, it is desired to improve the capacity utilization rate in order to reduce the amount of energy produced, and the capacity utilization rate F
is expressed in the fourth equation.

F=P-Do/(Po(Do1T.)) ・River・(4)
Note that Po: Rated output or allowable maximum cruising output (MW) Do
= Rated power operable period (days) To; Periodic inspection period (for the first loaded core, from fuel loading to the start of commercial operation) (days) P; Average output from the start of operation to the rated power operable period (MW ) For nuclear reactors, coast-down operation through natural reduction of output has been proposed in order to improve the above-mentioned capacity utilization factor. This coastdown operation will be explained below.

Nuclear reactors are designed so that as the power increases, the reactivity decreases. When the output of a nuclear reactor increases for some reason, negative feedback is applied to the reactor to suppress this increase in output. Furthermore, as the output decreases, the reactivity increases. When there is sufficient fuel at the beginning of reactor operation, the reactivity of this fuel is high. This operation continues, the fuel is gradually consumed by neutron irradiation, and the reactivity decreases.

Figures 2 and 3 show the characteristics of the core during this coastdown operation. Here, in Figure 2, the vertical axis represents the reactivity K,
A characteristic diagram of the core with burnup E and operation date is shown next to @. In this Figure 2, the operation is ``''. Then the burnup is E. Eggplant, reactivity becomes 0. When the reactivity of the nuclear reactor reaches O, it is no longer possible to maintain the rated output. A characteristic diagram of the core in this state is shown in Figure 3. Here, FIG. 3 is a characteristic diagram of the core, with output plotted on the vertical axis and burnup and operating days plotted on the horizontal axis. As shown in FIG. 3, the burnup E is where the reactivity becomes 0. If the reactor is left in this state without being shut down, the reactor's output will gradually decrease below its rated output. However, the decrease in reactivity due to the increase in burnup is offset by the increase in reactivity due to the decrease in power, so the reactor can remain in a critical state. This nuclear reactor beam. Until today, the control rods have been used to adjust the reactivity and increase the output to P.
. can be maintained. Furthermore, since the control rods are withdrawn from the core after the Do day, the reactivity cannot be adjusted using the control rods. Although the reactor output gradually decreases, operation continues, so the operating period can be extended. This is called coastdown driving. It is possible to increase the facility utilization rate by appropriately selecting the coastdown operation period. However, in the past, if the coastdown operation period was long, the operation at low output would be longer, resulting in a lower facility utilization rate. There was a problem in selecting the period efficiently, such as when it actually decreased.

[Purpose of the invention]

An object of the present invention is to determine an efficient end date of coastdown operation of a nuclear reactor in coastdown operation of a nuclear reactor so that the facility utilization factor is maximized.

[Summary of the invention]

The present invention is capable of operating at rated output for a long period of time. In the following coastdown operation method for a nuclear reactor in which the control rods are operated with the control rods pulled out of the reactor core, the periodic inspection period is T. Determine the average output P, and calculate the in-furnace reactivity coefficient α using the first equation using the in-furnace burnup increase ΔE and the in-furnace reactivity decrease ΔK, α2Δ/ΔE (1) Reactivity reduction amount Δ in the reactor and core rated power P. The power coefficient β of the reactivity in the reactor is determined by the second formula based on the amount of decrease in core power △P, and β−△, / (△P / P o ) ...
(2) Coast-down operation of a nuclear reactor characterized in that, when the specific power density is C, the coast-down operation period d max that maximizes the capacity factor of the reactor is set to a value determined by the third equation. Method VC, iru.

[Embodiments of the invention]

The coastdown operation method for a nuclear reactor according to the present invention will be described below. First, the burnup coefficient α in the core is calculated using a calculation code. Burnup in the core is E. As the ratio of 1 to the in-core burnup increase ΔE2E F, o and the in-core reactivity decrease Δ near the fuel rods, the in-core burnup coefficient α is calculated as shown in equation 1. .

α=Δ+/ΔE (1) This ratio is determined by the fuel composition and shape within the reactor. It is also possible to calculate the value of burnup versus reactivity as shown in Figure 2 using the lattice combustion calculation code for light water reactors "LASER" and to preset α. In general, the burnup coefficient α is approximately -0.09X 10-
'[(MWD/ton)-').

Second, calculate the power coefficient β of the reactivity in the reactor using the calculation code. Let Po be the core rated power, and the core power number is small △P=1
)-Po and the ratio of 2 to the in-furnace reactivity increasing needle Δ, the power coefficient β of the in-furnace reactivity can be calculated as shown in the second equation.

β= Δ2/(△P/Po) ・・・=・(
2) Like the burnup coefficient α, this ratio is also a coefficient determined by the fuel composition and shape in the reactor. And the in-core power distribution calculation code for boiling water reactors "FT".

A.11. It is also possible to calculate 1β in advance by calculating the value of core power versus reactivity using E. Similarly, in a boiling water reactor, the power coefficient β of in-reactor reactivity is approximately -0.07
It is 5.

Thirdly, a formula for predicting the degree of decrease in in-core power is established. Burnup is E because d days have passed since the start of coastdown operation.

If the output increases by ΔE from then on, and the output at that point is P, then the amount of decrease in reactivity due to increase in burnup, Δ, 1 is offset by the amount of increase in reactivity due to decrease in output, Δ, which is 2, and the reactor returns to a critical state. maintain. The in-furnace burnup increase amount ΔE can be calculated as shown in Equation 6, assuming that the specific power density is O['MW/1on].

ΔE = /dO, P /Pn dt - (61 Then, by substituting this sixth equation into the fifth equation and setting the solution as rt and P=Poe, r2C·α/β can be found.

Therefore, the output P after 6 days of cost reduction operation is shown by the seventh equation.

P = Poe ``'''β... Song (Equation 8 can be found as an approximation of Equation 7).

P= Pa (1-cd-a/β) (8) In the same boiling water reactor, C is approximately 22.5 [MW/lon
:] is. From this, the rate of power reduction in the furnace can be determined by Equation 9 by substituting the above values for α, β, and C in Equation 8.

P/PO=1-C, -dα7β= 1-0.0027d
- By using calculation steps of +91 or higher, it is possible to predict how the in-core power output will decrease as time passes from the start of coastdown operation.

Next, as the fourth step, determine the coastdown operation period during which the capacity utilization rate is maximum. The capacity utilization rate under normal conditions is the 4th
Formula 1. It can be seen as shown in C. When coast down operation is performed, by substituting the seventh equation for the output P of the fourth equation, the equipment utilization rate during coast down operation can be determined, and this is shown in equation 10.

...(10) In this 10th equation, in order to determine the coastdown operation period d during which the capacity factor F is maximum, it is sufficient to differentiate the 10th equation with respect to dlc so that it becomes zero. . When you put this on, it looks like @11 type.

...... (11) Solving this 11th equation for d, we obtain the 8th equation, which is an approximate equation for P.
Substituting the expression gives the result as shown in the third expression.

dmax −(Do-1-'[”o) C(Do 1T
. )2-2(To +Do (P'/"'0)Do)
/(αC/β)]+ ・・・・・・(3) d in this third equation
max is taken as the period that maximizes F.

Hereinafter, a coastdown operation method for a nuclear reactor according to the present invention will be explained with reference to FIG. In addition, there are generally burrs. +T
O is input first (block 1), but in this description it is I). , To will be explained as variables.

In a general boiling water reactor, p==po.

a = -0,09X 10-' ((FvfWD/1
on)'), β=-0,075.

0 = 22, 5 [:MW/t on ) (Block 2.3), so if this is used, the coastdown operation period dmax and the capacity factor F at that time will be the first
2 and 13 (block 4).

dmax=Do+To ((DO+TO)”-2TO1
0,0027)"・" o3 Table 1 shows formula 13 and 1
Type 4 glue. , To are variables, and dmax and F are calculated (block 5).

This is a case where the day when F becomes maximum in the vicinity of the first table row is determined by trial and error. From Table 1 and Equation 13, it can be seen that the capacity factor F increases slowly with dmaxH, and then gradually decreases.

This is it! In the current boiling water reactor, D0 = 2.
70 days and To=90 days, therefore, by performing coast-down operation for 95 days, the facility utilization rate improves by about 4% compared to the conventional method (block 6).

In addition, in this coastdown operation, it is possible to select the optimal day with flexibility due to issues such as the power supply plan due to reactor shutdown and the availability of periodic inspection tools when the reactor is shut down.

Furthermore, during coastdown operation, no control rods are inserted into the core, so the three-dimensional power distribution is flattened. This is because in areas with high output, fuel consumption progresses quickly, resulting in a decrease in output, while in areas with low output, fuel consumption slows down, so the output of the entire reactor core is leveled out without reducing the output too much. It is from. In a nuclear reactor, one fuel exchange is % to % of the total fuel, so the output distribution at the beginning of the next cycle operation is influenced by the previous cycle operation. Therefore, if the output distribution in the previous cycle operation is flattened, the output distribution at the beginning of the next cycle operation will also be flattened, leading to an increase in the thermal margin of the operation.

[Effects of the Invention] According to the present invention, in coastdown operation of a nuclear reactor, it is possible to determine an efficient end date of coastdown operation of the nuclear reactor and maximize the facility utilization rate.

[Brief explanation of the drawing]

Figure 1 is a block diagram showing the process for determining the operating period in the coastdown operation method of the present invention, Figure 2 is a characteristic diagram of a conventional core, and Figure 3 is a characteristic diagram of a core showing conventional coastdown operation. be. Do... Rated output operation period To... Periodic inspection period P... Average power ΔE... In-furnace burnup increase no amount ΔK... In-furnace reactivity α... Burn-up coefficient of in-furnace reactivity Po...Core rated power ΔP...Core power reduction amount β...Power coefficient of reactor reactivity C...Specific power density dmax...Coastdown operation period Agent Patent attorney Noriyuki Chika (and others) 1 person) Figure 1 Figure 2 Figure 3 0 1 Turning (l:)'Heart''

Claims (1)

[Claims] Rated output operation period. In the subsequent coastdown operation method for a nuclear reactor that operates with control rods pulled out of the core, periodic inspection period ITI. Determine the average output P, and calculate the burnup coefficient α of the in-furnace reactivity using the first equation using the in-furnace burnup increase △E and the in-furnace reactivity decrease △K, α=Δ/ΔE ・Old・(1) When the reactivity in the reactor decreases by 1·Δ, the core rated power P. Based on the amount of decrease in core power △Pvtc, the power coefficient β of the reactivity inside the reactor is determined by the second formula, β = Δ, /(ΔP /P o ) ・Song (2) When the specific power density is C, the atomic A coastdown operation method for a nuclear reactor, characterized in that the coastdown operation period d max that maximizes the capacity utilization rate of the reactor is set to a value determined by the third formula (%)) (3).