atw 2018-03v6

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atw Vol. 63 (2018) | Issue 3 ı March

One of the most important feature of

this design is the small core, very

similar to the core of the AVR. The

results of the MCA tests with heat

rise by decay heat (Figure 20) can

be put into consideration. So, we

are able to increase the primary

maximum helium heat temperature to

the highest possible temperatures,

possibly to 1,100 °C, limited only

by the maximum allowable metallic

tube temperature of the He/He heat

exchanger inside the PCPV.

Design of important components

for a new 600 MW el /

1.500 MW th Pebble Bed

Reactor and potential risks

The Pre-stressed concrete

pressure vessel. (PCPV)

The reactor vessel is, for safety reasons,

the most important component

of every nuclear power station. The

calculation for larger cores for pebble

bed reactors showed that the diameter

of the core is too great for construction

using steel pressure vessels and

therefore cannot be manufactured

using metallic materials. It was

decided to look for other construction

materials for a large HTR pebble bed

design with high volume and high

pressure.

Two solutions had been taken into

consideration, a pre-stressed cast iron

vessel and a pre-stressed concrete

pressure vessel. The PCPV had been

chosen due to its excellent safety

advantages versus the cast iron vessel.

Several safety conditions could not be

reached with a pre-stressed cast iron

vessel and the construction would

have some fundamental problems.

This HTR design was a completely

new construction without any prior

experience and the operational

helium gas pressure was calculated

at 40 bar. It was decided to perform

experiments with a 1:20 scale model.

The model was pressurized with

warm water. Very small cracks began

to form at a pressure between 90-120

bar. The main crack was reached at

190 bar.

After the pressure dropped to 40

bar, the vessel was nearly gastight

again. After the pressure drop the

cables pulled the concrete together

[4]. These results were deemed very

important since this test proved that

oxygen could not enter into the vessel

in event of a crash. Throughout the

testing, all necessary factors were

measured and used as a baseline for

new calculation programs to calculate

the PCPV for the THTR-300.

| | Fig. 21.

Arrangement of stressing cables of the

THRT-PCPV.

| | Fig. 22.

Top of the steam generator of THTR-300.

| | Fig. 23.

Installation of the thermal shield.

Development, design and

erection of the THTR-300

pre-stressed concrete pressure

vessel

Figure 21 shows the cross section of

the reactor [26]. Located Inside are

the core, graphite and carbon brick

structures, thermal shield, six steam

generators, blowers, shut down rods,

measuring devices, and isolation with

liner and liner cooling system further

the penetrations for the steam generators,

the holes in the concrete are

reinforced by steel layers with steel

tops (Figure 22). There are 135 penetrations

in total, the largest of which

are for extracting the steam generators

at 2.25 m. All of the penetrations

are surrounded by cables and have

| | Fig. 24.

PCPV during manufacturing.

| | Fig. 25.

Model of bottom of THTR-300 core.

| | Fig. 26.

Results of pressure test of the THTR-PCPV.

encountered no design problems. The

construction phase is demonstrated in

Figures 23, 24 and 25.

The results of the pressure test

Figure 26 shows the accuracy between

the measured and calculated

factors. The pressure tests were performed

using nitrogen and helium to

ensure accurate measuring. The design

pressure was 39.2 bar and the

highest possible pressure in case of an

accident was calculated at 46.1 bar.

The test reached the calculated and

highest possible pressure (as required

RESEARCH AND INNOVATION 173

Research and Innovation

The Technology of TVHTR-Nuclear- Power Stations With Pebble Fuel Elements ı Urban Cleve

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