17.08.2015   Integral design concepts of advanced water cooled reactors

Technical description of the NHR-200

For a nuclear distnet heating reactor it has to be located near the user due to the medium >f heat transmission (hot water or low pressure steam). It means a NHR is surrounded by a populous area Using emergency actions as an essential element in the ultimate protection of the public can thus become impractical Therefore, in all credible accidents the radioactive release from heatmg reactor has to be reduced to such low levels that off-site emergency actions, including sheltering, evacuation, relocation and field decontamination will not be necessary In the other hand there is a senous challenge to the economy for a NHR The capacity of a NHR can not be as big as that of NPP due to the limitation of heat transmission

Moreover the load factor is also much lower than that of NPP. It is obvious that to meet the safety requirement and lower the capital investment are the major concern in the design of a NHR. The only solution is to have a design with inherent safety characteristics and passive safety as much as possible instead of the complex engineering safety features.

The reactor structure and core cross section of NHR-200 are shown in Fig. l and Fig.2 respectively. The simplified schematic diagram is given in Fig.3. The main design data of NHR-200 arc listed in Table 1.

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1. primary beat exchanger containment

2. riser 5. pressure vessel

3. biological shield 6. oote

Fig. 1. The NHR-200 reactor.

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Name

Unit

Value

Rated thermal power

MW

200

Pressure of the primary coolant arcui;

MPa

2.5

Core miet/outiet temperature

*C

145/210

Core coolant flow rate

t/h

2376

Intermediate arcuit pressure

MPa

3.0

Intermediate circuit temperature

*C

95/145

Intermediate arcuit flow rate

t/h

3400

Heat grid temperature

*C

130/80

Fuel assembly type

! 12×12-2

Fuel assembly number (initial core)

1 96

Enrichment of fuel (initial core)

%

1 1 8/2 4/3 0

Average core power density

1 kW/l

! 36 23

Average fuel linear power density

і W/cm

! "7

The majoT features of the NHR-200 design are

(1) Integrated arrangement, self-pressunzea performance and dual vessel structure

(2) Natural circulation for primary loop

(3) Passive safety’ systems including Residual Heat Removal System and Boft Injection System

(4) Low operating parameters with large safety margin including temperature, pressure and power density

With these features, the probability of pressure boundary break is much lower than that of conventional NPP The mitigation of a LOCA is much easier and there is no ECCS m the NHR The supporting systems such as on-site diesel generators, component cooling system, service water system, instrument air system and ventilation svstem etc do not provide with safety functions, namely they are non safety-related m the NHR design While in a NPP these systems are safety-related and sometimes loss of them are dominant initiators resulting in core damage