Home | Contact usVVER 440 and 1000 with Horizontal Steam Generators
The ex-Soviet block or current Russian has designed a series of PWRs with horizontal steam generators. There are six-loop VVER-440 and 4-loop 1000 models. The number indicates its electric output in mega watts. For PCTRAN we model one single loop with the pressurizer at left and the remaining loops combined at right. The steam generators are horizontal in their shape. The remainder plant control and ECCS systems are similar to the western PWRs of vertical SGs. The reactor can be controlled either from the turbine to the reactor or from the reactor to the turbine. For VVER-440, there are two turbines for power generation. Trip of one turbine will result in the reactor runback to 50% power. Tripping both turbines will lead to a reactor scram.
VVER-440 is equipped with an isolation valve in each of its coolant loop. VVER is unique in its low power density, large coolant inventory and bubbling chamber containment design. In addition to the gravity-driven shutdown rod assemblies, there are mechanical-driven shutdown systems. In the event of a SG tube rupture, the troubled loop can be isolated. Some of the VVER-440 plants are equipped with two turbines. Trip of one turbine will result in the reactor runback to 50% power. Tripping both turbines will lead to a reactor scram.
For the RPS panel, in addition to the gravity-driven shutdown system HS1, there is a mechanical-driven shutdown system HS2. Any one of the following conditions will initiate HS2:
- High neutron flux (> 105%) after 10 sec
- High RC pressure (< 13.9 MPa) after 20 sec
- High Tavg (310°C) after 20 sec
- Low RC pressure (< 11.4 MPa)
- Manual trip
One of the six-rod groups (A to G) will be inserted. When one group is inserted to about 80% of its total length, the next group starts to move. The rod groups will be inserted successively until the signal is canceled.
The ECCS systems for a VVER440 Model 213 are similar to the PWRs of U-tube steam generators. They are high pressure injection, accumulators and low pressure injection. The containment has its unique accident localization and bubble-condenser system and localized compartments. At this moment they are not modeled yet. Therefore the containment response is still that for a conventional large-dry containment.
Steam Collector Break
For VVER’s with horizontal steam generators, there is a possibility for break at the cover on the top of primary collector. In January 1982 an accident occurred at Rovno plant in Ukraine. The incident was analyzed by assuming a large (1000%) SG leak from the primary to the secondary side in one steam generator. The faulty side's main steam safety valve was set to stick open after its first opening. After reactor and turbine trips following the primary-to-secondary leak, HPI and accumulators are initiated. PCTRAN calculated primary and secondary pressures, mass balance of the system, etc. are in good agreement with recorded data and published in literatures.