EP0135882B1 - Process for operating a nuclear reactor - Google Patents

Description

The invention relates to a method for operating a nuclear reactor with an exhaust gas source, in particular a coolant cleaning system, and an exhaust system connected to this exhaust gas source, which comprises at least one compressor, a gas cooler, a reducing valve, a moisture adsorber, a delay line and a chimney connection.

From DE-PS 2 302 905 a pressurized water reactor is known which comprises a cooling water cleaning system with a degassing device. The gases separated from the cooling water are first freed of hydrogen by combustion. You will then be taken to a drying plant where water is precipitated. Afterwards, they are fractionated in a gas separation plant by fractional liquefaction so that the noble gases, in particular krypton and xenon, can be stored in a small store, while the remaining gases are returned to the system if they are not discharged via a chimney connection.

In other known nuclear reactors, the gases are passed over a delay line so that their activity can decay. The delay line is either traversed in a circle or upstream of the chimney, as explained in the book "VGB Nuclear Power Plant Seminar 1970" on pages 43, 44 and 45.

The invention is based on the task of reducing the outlay caused by the exhaust gas treatment. Surprisingly, this is achieved in that the moisture adsorber and the delay line are operated in parallel in normal operation, the delay line being connected to the chimney connection, while the moisture adsorber is operated in a gas circuit to the compressor, and in the event of increased exhaust gas accumulation, in particular when the coolant is displaced during start-up. and shutdown of the reactor, the moisture adsorber and the delay line are connected in series and connected via a reducing valve to the chimney connection, which is set to a pressure which is at least twice as high as in normal operation.

The new process results in a significant reduction in the components required for exhaust gas treatment and a simpler system design without additional equipment. The advantages of the retention behavior, which is more favorable in the case of excess pressure, for the short-term operation of large gas accumulations are combined with the predominantly operating phases with less gas accumulation, in which the options of flash drying are used to reduce the effort of the previously usual drying facilities by reducing the operating pressure.

The method according to the invention can advantageously be developed further in that the gas path from the gas cooler to the moisture adsorber, including thermally insulated and / or cooled or heated.

For the transition from one operation (increased exhaust gas generation) to the other (normal operation), it has proven to be advantageous that the pressure is reduced over a period of several hours after an increased generation of exhaust gases. It is advisable to switch the moisture adsorber into the gas circuit to the compressor after the low operating pressure has been reached.

To explain the invention in more detail, an exemplary embodiment is described with reference to the accompanying drawing. 1 shows the exhaust system of a pressurized water reactor with two operating states represented by different arrows (solid and dashed) in a highly simplified manner. FIG. 2 shows a graph of the characteristic amount of exhaust gas in Nm ³ / h over time, an operating cycle with an operating time of at least 10 months being designated as 100%.

The exhaust gas sources are containers 1 and 2 with a liquid with a variable liquid level 4 or 5 and a gas atmosphere 6 or 7 above the liquid level, as well as degassing device 8. The gas atmosphere 6 or 7 and the degassing device 8 contain cracked gases. Therefore, the tops of the containers 1, 2 and the degassing device 8 are connected to an exhaust line 10. It leads through a recombiner 11 H _{2/0. 2} Behind this two compressors 12 and 13 are arranged redundantly. Its pressure side leads to a gas cooler 15 with a liquid outlet 16, which can be regulated by a condensate drain 17.

The gas cooler 15 is followed by a reducing valve 20, the actuator 21 of which can be actuated via lines 22. The low-pressure side leads via a line 23 to a changeover valve 24. From the changeover valve 24, a first line 26 leads to a further reducing valve 27, which is provided for gas recirculation. Its low pressure outlet is connected via a line 28 to the gas atmospheres 6, 7 of the exhaust gas containers 1, 2. The actuator 30 of the reducing valve 27 can be actuated via control lines 31.

The other outlet of the changeover valve 24 is connected via a line 33 to a branch 34, which leads to a moisture adsorber 35 on the one hand and a delay line 36 on the other hand. The moisture adsorber 35 is a container with an adsorbent 37, e.g. Gel or activated carbon, filled. Its outlet 38 leads to the line 26 and thus to the reducing valve 27.

The delay line 36 is designed as an activated carbon container which is flowed through from bottom to top. A chimney 42 is connected to the outlet 40 via a reducing valve 41. The actuator 43 of the reducing valve 41 can be actuated via control lines 44.

In Fig. 1 it is also emphasized that the lines between the gas cooler 15 and the changeover valve 24 as well as its line branch 26 and the line 38 from the outlet of the adsorber 35 are provided with an insulation 46 which also encloses a cooling possibility, for example with cooling water . The adsorber 35 can carry a cooling jacket 47, for example in the form of Peltier elements, the circuit of which has the connection terminals 48. It is also convenient if a pipe area heater 49 is connected upstream of the moisture adsorber 35 to improve regeneration. It captures the tube area between the top of the moisture adsorber 35 and the branch 34.

The amount of exhaust gas in the pressurized water reactor is very different, as shown in FIG. 2. Over more than 95% of the operating time, there is only a slight drop of less than 0.5 Nm ³ / h on average, as indicated in FIG. 1 in the areas 50, 51, 52, 53 and 54. In the periods indicated at 55, 56, 57 and 58, the amount of exhaust gas is practically zero. Only in the remaining 5% of the operating time does an increased emission of exhaust gas occur, which, however, is then for example 100 times for several hours. In FIG. 2, this is indicated by the area 60 for the case of start-up and the associated expansion of the cooling water during heating, which reduce the gas atmosphere volumes 6, 7 in the exhaust gas sources 1 and 2. At 61, purging of the exhaust gas sources is shown, for example, in front of a container opening. The area 63 comprises the lowering of the fill level in the reactor pressure vessel with a conceivable flushing at the end of the operating cycle, ie before the reactor pressure vessel is opened.

• 1) Kontinuierlicher Dauerbetrieb ( > 95% der Betriebszeit eines DWR's). Hier liegt ständig ein relativ geringer Abgasanfall von durchschnittlich z. B. < 0,5 Nm³/h vor. Diese Abgasmenge sowie eine Spülgasmenge, die sich aus der Förderleistung des Kompressors 12, 13 ergibt, wird durch die Kompressionseinheit kontinuierlich oder diskontinuierlich komprimiert (z.B.: p_e = 8-25 bar). Im nachfolgenden Gaskühler 15, der z.B. mit Kaltwasser gekühlt wird, erfolgt die Kühlung und Reduzierung der absoluten Gasfeuchte. Im sich anschliessenden Reduzierventil 20 erfolgt die Gasentspannung mit entsprechender Reduktion der relativen Gasfeuchte (z.B.: p_e = 1-4 bar).

With the new process, the following three operating cycles can be distinguished:

• 1) Continuous continuous operation (> 95% of the operating time of a DWR). Here there is always a relatively low amount of exhaust gas, on average z. B. <0.5 Nm ³ / h before. This amount of exhaust gas and a purge gas amount, which results from the delivery capacity of the compressor 12, 13, is compressed continuously or discontinuously by the compression unit (for example: p _e = 8-25 bar). In the subsequent gas cooler 15, which is cooled, for example, with cold water, the cooling and reduction of the absolute gas moisture takes place. In the subsequent reducing valve 20, the gas is released with a corresponding reduction in the relative gas humidity (for example: p _e = 1-4 bar).

The gas, which has cooled slightly due to expansion and gas cooling, is then warmed to room temperature by appropriately guiding the pipeline through the ambient air or other auxiliary devices.

After passing the switch valve 24, the exhaust gas in the branch 34 is divided into two gas flows. Only the excess exhaust gas (for example <0.5 Nm ³ / h) is passed over the delay line 36, the rest is returned via the moisture adsorber 35 to the compressor suction side for the purpose of regeneration. The gas adsorption occurring in the delay line 36 at a reduced operating pressure brings the required delay time, despite the lower adsorption effect, due to the low amount of exhaust gas, for example in the first quarter of the adsorber, so that the remaining part is available for other operating cases.

2) The sliding gas case occurs e.g. with DWR systems practically only during start-up and lowering of the reactor pressure tank level and possibly subsequent rinsing processes of the primary circuit.

During this operating case, the delay section 36 is operated under increased operating pressure. The amount of exhaust gas now exceeds the aforementioned continuous amount of exhaust gas for several hours, e.g. 100 times.

The increase in operating pressure significantly improves the effective retention capacity of the delay line 36, in addition to the additional gas storage due to the pressure increase, due to the gas compression.

Depending on the exact operating conditions, e.g. at p _e = 8-25 bar for Xe isotopes, approx. 2 to 3 times and for the Kr isotopes relevant (in this case due to shorter adsorber breakthrough time) approx. 3 to 5 times improved Delay effect achieved.

The exhaust gas dehumidification is carried out here by means of the moisture adsorber 35 connected upstream in this operating case of the delay line by switching over the valve 24. For this design-determining operating case, that part of the delay line 36 which was previously practically not effective for reducing activity is now used under optimal conditions.

3) Operation directly after sliding gas fall.

The amount of exhaust gas produced drops again to values, for example <0.5 Nm ³ / h. The increased operating pressure is maintained for a short time in order to sufficiently delay the noble gas isotopes with relevant activity that are already shortly before they leave the delay line 36 (for example Kr 85 m at 5-10HWZ = 21.5-43 h).

Conservative then follows e.g. 40 h the slow lowering of the operating pressure by increasing the amount of exhaust gas to a fixed value to the design value, so that due to the low amount of exhaust gas, e.g. results in a corresponding reduction in operating pressure over approx. 10 h.

The changeover of the moisture adsorber 35 previously operating as a gas dryer for the purpose of regeneration takes place as soon as the reduced operating pressure is reached. The heater 49 can then be switched on and the cooling of the insulation 46 in the area of the line 38 can be set.

Claims (4)

1. A method of operating a nuclear reactor having a waste gas source (1, 2), particularly but not exclusively, of a coolant purification unit, and a waste gas system which is connected to said waste gas source and which comprises at least one compressor (12, 13), a gas cooler (15), a reducing valve (20), a moisture adsorber (35), a delay path (36) and a chimney connection (42), characterised in that the moisture adsorber and the delay path are operated in parallel during normal operation, the delay path being connected to the chimney connection, whilst the moisture adsorber is operated in a gas circuit to the compressor; and that, in the event of an increased formation of waste gas, particularly but not exclusively with coolant movement when a reactor is brought on or off stream, the moisture adsorber and the delay path are connected in series and are connected to the chimney connection by way of a reducing valve (41) which is set at a pressure which is twice as high as during normal operation.

2. A method as claimed in Claim 1, characterised in that the gas path from the gas cooler to the moisture adsorber inclusive is thermally insulated and/or cooled or heated, as the case may be.

3. A method as claimed in Claim 1 or Claim 2, characterised in that the reduction of the pressure after an increased formation of waste gases is effected over a period of several hours.

4. A method as claimed in Claim 3, characterised in that the switch-over of the moisture adsorber into the gas circuit to the compressor is effected when the low operating pressure has been reached.

Images