Effect of temperature negative feedback on the power reduction process in a molten salt reactor

WANG Kai; CHEN Yixuan; WANG Chaoqun; YANG Qun; YUAN Guangpeng; HAN Yu; WANG Ziyun; HE Zhaozhong; ZHAO Qincai

doi:10.3724/j.0253-3219.2026.hjs.49.250471

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Effect of temperature negative feedback on the power reduction process in a molten salt reactor

Special Issue of Excellent Papers on The Second Academic Annual Conference of the Research Reactor and Innovative Reactor Association of Chinese Nuclear Society | 更新时间：2026-07-29

- Effect of temperature negative feedback on the power reduction process in a molten salt reactor
- NUCLEAR TECHNIQUES Vol. 49, Issue 7, Article number: 071125(2026)
- 作者机构：
  
  中国科学院上海应用物理研究所上海 201800
- 作者简介：
  
  WANG Kai, male, born in 1987, graduated from University of Chinese Academy of Sciences with a doctoral degree in 2025, focusing on nuclear safety analysis and reactor operation technology
  YANG Qun, E-mail: yangqun@sinap.ac.cn
- 基金信息：
  
  the Youth Innovation Promotion Association of Chinese Academy of Sciences(E329290101)
- DOI：10.3724/j.0253-3219.2026.hjs.49.250471
  CLC： TL99
- Received：07 January 2026，
  
  Revised：2026-03-14，
  
  Online First：29 July 2026，
  
  Published：15 July 2026
- 稿件说明：
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王凯,陈贻炫,王超群等.熔盐堆降功率过程中温度负反馈效应的影响研究[J].核技术,2026,49(07):071125.

WANG Kai,CHEN Yixuan,WANG Chaoqun,et al.Effect of temperature negative feedback on the power reduction process in a molten salt reactor[J].NUCLEAR TECHNIQUES,2026,49(07):071125.
王凯,陈贻炫,王超群等.熔盐堆降功率过程中温度负反馈效应的影响研究[J].核技术,2026,49(07):071125. DOI： 10.3724/j.0253-3219.2026.hjs.49.250471. CSTR： 32193.14.hjs.CN31-1342/TL.2026.49.250471.

WANG Kai,CHEN Yixuan,WANG Chaoqun,et al.Effect of temperature negative feedback on the power reduction process in a molten salt reactor[J].NUCLEAR TECHNIQUES,2026,49(07):071125. DOI： 10.3724/j.0253-3219.2026.hjs.49.250471. CSTR： 32193.14.hjs.CN31-1342/TL.2026.49.250471.

摘要

反应堆温度负反馈效应是保证反应堆稳定运行的关键因素之一，对抑制反应堆温度异常升高等具有良好效果，是反应堆重要的固有安全特性之一。熔盐堆具有较大的反应性温度系数，对功率升高或排热减小等原因引起的堆芯温度升高具有良好的抑制效果。但较大的反应性温度系数会对正常运行带来一定影响，尤其是在降功率过程中。若操作过程中由于设备故障或人因等导致温度降低过大时，在温度负反馈效应的作用下，将引入较大正反应性，导致功率快速升高，可能触发安全系统整定值进而引起紧急停堆。研究降功率过程中温度负反馈效应对堆芯功率的影响，为熔盐堆运行人员的安全操作和规程制定等提供依据。采用修改后的RELAP5/MOD4.0程序，建立熔盐堆分析模型，模拟分析在降功率过程中不同反应性引入量、插棒速度和空气流量下堆芯功率的变化趋势。引入的负反馈越大，功率波动也会越大，越容易触发功率保护限值（120%满功率（Full Power，FP））；降低反应性的引入速度可以有效降低功率波动，反应性引入越慢，功率波动越小；降低空冷空气流量能够防止功率波动触发保护限值，但无法较好地抑制功率和堆芯温度的波动幅度。降低单次反应性引入量和引入速度，并合理地调节空冷系统空气流量，能够有效降低功率的波动，避免因功率波动而触发功率保护限值。

Abstract

Background

The negative temperature feedback effect is a key inherent safety feature of nuclear reactors and effectively suppresses abnormal core temperature rises. Molten salt reactors (MSRs) feature a strongly negative temperature coefficient of reactivity

which mitigates temperature increases caused by power rises or reduced heat removal; however

the same strong feedback can adversely affect normal operation

especially during power reduction

when an excessive temperature drop may insert significant positive reactivity

drive a rapid power increase

and potentially trigger safety-system setpoints.

Purpose

This study aims to investigate the influence of temperature negative feedback on core power during the power reduction process and to provide a basis for the safe operation and procedure development of MSRs.

Methods

The RELAP5-TMSR code

developed on the basis of RELAP5/MOD4.0

was used to establish a MSR analysis model. Firstly

molten-salt fluid properties (e.g.

nitrate salts

FLiBe and FLiNaK)

heat-transfer correlations and liquid-fueled reactor models that had been validated against experiments were incorporated into the code. Then

a coupled system model consisting of the primary (fuel-salt) circuit

the secondary (coolant-salt) circuit and the air-cooling system was constructed. Finally

the core-power response during power reduction was simulated and analyzed under different reactivity insertion amounts

control-rod insertion speeds and air mass flow rates.

Results

Simulation analysis results show that larger single insertions of negative reactivity produce larger power oscillations and make it easier to reach the power protection limit of 120% full power (FP). At an initial power of 100% FP

insertion of -0.15$ drives the power peak to the 120% FP protection limit

whereas at 80% FP an insertion of -0.3$ still causes the peak to exceed 120% FP. Reducing the reactivity insertion rate effectively mitigates the oscillations: for a total insertion of -0.25$ at 100% FP

lowering the control-rod speed to 80% of the design maximum keeps the power peak below 120% FP. Decreasing the air mass flow rate of the air-cooling system can also prevent the peak from reaching the protection limit (e.g.

to 80% of the design flow for the same -0.25$ insertion)

but it does not adequately suppress the amplitudes of power and core-temperature oscillations.

Conclusions

During normal power reduction of a MSR

the single reactivity insertion should be limited (not exceeding 0.15$ at 100% FP)

the control-rod insertion rate needs to be reduced when necessary (e.g.

to about 80% of the design maximum for a -0.25$ insertion)

and the air-cooling flow should be adjusted in a coordinated manner. These measures effectively reduce power and temperature fluctuations and help avoid unnecessary actuation of the power protection system.

关键词

Keywords

references

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