Forsmark nuclear power plant

Reactors 1 and 2

location

Coordinates

60 ° 24 '12 " N , 18 ° 10' 0" E Coordinates: 60 ° 24 '12 " N , 18 ° 10' 0" E

Country:

Sweden

Data

Owner:

Forsmark Kraftgrupp AB

Operator:

Forsmark Kraftgrupp AB

Project start:

1971

Commercial operation:

Dec 10, 1980

Active reactors (gross):

3 (3157 MW)

Energy fed in in 2010:

19,648 GWh

Energy fed in since commissioning:

617,655 GWh

Was standing:

June 6, 2011

The data source of the respective entries can be found in the documentation .

The Forsmark nuclear power plant is one of three located in the operating nuclear power plants in Sweden . It generates about a sixth of all electricity in Sweden.

The nuclear power plant consists of three power plant blocks with boiling water reactors : Forsmark-1 (1011 megawatts of net electrical output, commissioned in 1980), Forsmark-2 (951 MW of net electrical output, commissioned in 1981) and Forsmark-3 (1190 MW of net electrical output, commissioned in 1985 ). Annual production since 2000 has been between 19.0 and 25.0 TWh . Units 1 and 2 are BWR-75 reactors. Unit 3 is a BWR-3000 reactor.

Sweden covers around 50 percent (69.5 TWh (e)) of its electricity needs with nuclear energy from three nuclear power plants (Forsmark, Oskarshamn , Ringhals ) with a total of 8 active reactor units. Two other plants with a total of three reactors ( Ågesta and Barsebäck ) have already been permanently shut down.

location

The village of Forsmark is located on the Upland coast about halfway between Gävle and Norrtälje . The reactor is located north of the village on the Baltic coast.

operator

Forsmark nuclear power plant is operated by Forsmark Kraftgrupp AB , a company owned by Vattenfall AB (66%), Mellansvensk Kraftgrupp (subsidiary of Fortum ) (25.5%) and Uniper Group (8.5%) (as of 2012 ). Vattenfall and Uniper are also active as energy supply companies in Germany.

history

Exposure of the Chernobyl disaster

Through the sensitive instruments of the nuclear power plant, On April 27, 1986, Forsmark was one of the first places outside the Soviet Union where signs of the Chernobyl disaster were noticed. At that time, increased radiation was found among workers and on the site of the power plant. First of all, the evacuation of Forsmark was initiated, as it was assumed that there was an incident in their own power plant. When looking for the cause of the increased radiation, it turned out that it came from outside.

Incident in July 2006

A short circuit outside the Forsmark-1 power plant on July 25, 2006 led to the plant being disconnected from the power grid and the automatic reactor shutdown. In order to dissipate the decay heat of the shutdown reactor, an emergency cooling system should have started automatically. But failed parts of the emergency power supply for the emergency cooling system, only two of four Siemens - diesel generators jumped and supplied the after-cooling with energy. Because part of the control system had also failed due to the power interruption, the operations team did not have a complete overview of the state of the reactor for more than twenty minutes. Then they could manually start the two emergency power generators that did not start automatically .

Scope of the incident

According to the state-of-the-art technology used in Forsmark-1, what impact the incident could have had in the worst case and how close the plant had come to a core meltdown as a result of the incident was assessed differently, since the emergency shutdown and essential parts of the emergency cooling system worked. According to a statement from a former construction manager of the power plant, Lars-Olov Höglund, a catastrophic outcome would have been possible because the power supply did not work properly.

The Swedish radiation protection authority SKI and the Finnish radiation protection authority STUK considered this statement to be exaggerated. An acute core meltdown was not to be expected at any time of the incident, but the incident was to be taken very seriously.

It is largely ignored that it was merely a coincidence that two emergency power subsystems (C and D) started up while two subsystems (A and B) failed. The reason for the failure of the subsystems C and D could not be conclusively clarified. The overvoltage caused by the short circuit could not only have paralyzed subsystems A and B, but also subsystems C and D. Failure to switch on all emergency diesel generators would have drastically worsened the situation. The cost of the incident is estimated at $ 12 million.

Block 1

Reactor 2 of the Forsmark nuclear power plant

Block 3

Aerial view of the nuclear power plant

Consequences of the accident in Sweden

As a consequence of the incident, the affected reactor block 1 in Forsmark and the structurally identical unit 2, which at the time of the incident had already been shut down for the annual inspection and the fuel element replacement, remained shut down for the time being, as did two structurally identical reactor blocks in the Oskarshamn nuclear power plant . The operating license for these four boiling water reactors with the same technology was withdrawn and had to be renewed before they were put back into operation.

The Swedish Radiation Protection Agency (SKI) rated the error as an incident (level two) in a first response on the International Assessment Scale for Nuclear Events (INES), which ranges from zero to seven . Four weeks after the incident, the chairman of the SKI's Reactor Safety Committee, Björn Karlsson, admitted that "the clarification of details had significantly worsened the picture".

Electricity prices in Sweden rose to a record level.

After Forsmark employees criticized a “collapse of the safety culture”, Vattenfall admitted safety deficiencies and the responsible public prosecutor's office started investigations on suspicion of a criminal delay in the shutdown of the reactor. After further technical problems, which again led to reactor shutdowns, the head of the nuclear power plant, Lars Fagerberg, resigned in February 2007. The safety of the plant is now to be checked by the International Atomic Energy Agency .

Recommissioning subject to conditions

About two months after the incident, the Swedish radiation protection authority SKI initially refused a new operating license due to safety deficiencies and imposed requirements to increase safety. On September 28, 2006, the SKI agreed to restart reactor units 1 and 2. The operators had complied with the requirements of the SKI, but had to further improve safety and work out a plan of action. Before operations in Forsmark could be resumed, the contingency plans had to be revised, plans for the training of the staff developed and maintenance work improved.

Reactions to the accident in Germany

The partial failure of the emergency power supply also raised questions about the safety of their nuclear facilities in other countries . The Forsmark incident initially went largely unnoticed in the German media. It was classified by the German Federal Ministry for the Environment, Nature Conservation and Nuclear Safety on August 3, 2006 as a "safety-related serious incident" - with the result that all nuclear power plants in Germany were also checked again. Within a few days, the competent supervisory authorities of the federal states passed reports from the nuclear power plant operators, which had been assessed by their experts, to the Federal Environment Ministry. The central question for the Federal Environment Ministry was whether similar incidents could occur in German nuclear power plants.

According to information from the Society for Plant and Reactor Safety (GRS), Germany's central specialist institution in the field of nuclear safety, these reports are not sufficient. A whole series of breakdowns caused the accident in the plant. The GRS therefore called for a more thorough inspection of German nuclear power plants.

Course of the incident and any breakdowns

procedure

On July 25, 2006, the Forsmark-1 reactor was automatically disconnected from the power supply after a short circuit in connection with maintenance work in the substation through which the nuclear power plant feeds its electricity into the public grid. This led to a load shedding on the generator and the heat produced in the reactor could no longer be converted into electrical power. The reactor was shut down to 25% of its rated output via a rapid shutdown; that is, the nuclear chain reaction was reduced to the internal power station supply. However, the short circuit was not disconnected in the usual short time of around 100 ms, which is why there was initially undervoltage and, after disconnection, excess voltage ( transients ) of 120% for one second. The electricity for the control of the nuclear power plant and the feed pumps , which have to dissipate the decay heat, failed in two of the four internal network areas. The internal supply was then switched to the emergency power system.

The safety systems of the Forsmark 1 power plant are designed to be fourfold redundant, i. H. the four subsystems (A to D) are physically separate and include electrical and mechanical safety devices. In the event of undervoltage, the internal 230 V supply network should be fed from four separate, battery-operated inverters designed as an uninterruptible power supply (UPS) (without delay) and the 6 kV network from four diesel generators (after they have started up). Of the four systems, two UPS and two assigned diesel systems (subsystems C and D) went into operation as intended, the other two UPS (subsystems A and B) had shut down due to the malfunctions; the diesels assigned had started up, but could not go into operation due to a lack of UPS voltage.

This meant that there was no power supply for some of the 230 V-fed measuring devices in the control room and other components:

Sensors, transmitters, controllers and event logging
Displays and monitoring devices in the control room, e.g. B. Display "control rods in the core" (for systems A and B), display for neutron monitoring and for pressure and water level in the reactor pressure vessel
Fine movement of the drives for the control rods (all rods were retracted by the hydraulic quick shutdown system)
Motor operated isolation and pressure reducing valves had increased response times
The motor drives for four circulation pumps failed

The pressure in the reactor pressure vessel was reduced to 1.2 MPa for a period of 30 minutes. The water level in the pressure vessel was stabilized at 1.9 m above the core. The saturation temperature decreased with the pressure. Such a strong temperature change has been calculated in advance and must not occur more than 25 times during the entire service life of the reactor pressure vessel.

The supply and safeguarding of the reactor by removing the decay heat requires two emergency power generators, as each can provide 50 percent of the necessary emergency power.

After 22 minutes, the maintenance staff re-established the connection between the dead 500 V rails of the diesel-supported subsystems A and B and the 6 kV network, which was supplied from the external 70 kV network during the entire incident. These manual actions put the entire electrical supply of the power plant back into operation. The operating team was able to determine again that the control rods had all retracted into the reactor core. From now on, all sub-areas of the auxiliary feedwater system went back into operation and the reactor soon reached its nominal water level. The activated safety systems were manually reset (on standby) and the opened relief valves closed. After a total of 45 minutes, the operating team was able to confirm that the reactor was in a safe and stable shutdown mode.

causes

The critical situation arose from two causes:

The protection system of the 400 kV substation was not working fast enough. This was because the network operator Svenska kraftnät , the owner of the substation , had neglected to install an earth fault safety switch that would have quickly disconnected the earth fault in 100 ms. The resulting transients caused two of the four UPS units (subsystems A and B) to be disconnected from the emergency power supply rails by their internal protective devices for their electronic rectifiers and inverters, even before they started operating as a power supplier from the batteries to the emergency power grid could record. Insufficient selectivity between rectifier protection (for battery charging) and inverter protection (for AC voltage generation from the battery voltage) caused the failure of both UPS units in connection with the overvoltage. As a direct consequence of this, the two assigned diesel generators, which had already started, could not be started up due to the lack of a 230 V voltage supply for speed control using the tachometer generator . They were disconnected from the 500 V network and switched off.

The shutdown system of the power plant generators in the event of a frequency deviation failed due to a design error because two phases were reversed. This phase dependency had not been tested. After the external short circuit - due to insufficient hydraulic pressure in the control valve system - a turbine had fallen below nominal speed, the frequency of the generator fell below 47.5 Hz. If the frequency deviation occurred, the shutdown system would have automatically switched the power plant's internal emergency power network to the external 70 kV If you had to switch the supply, the power failure would have been limited to seconds instead of minutes.

A third mistake had no effect. The start signal for an existing 70 kV gas turbine generator did not reach it because an automatic processor was not working properly. However, this was irrelevant because the external 70 kV network was available for the internal power plant supply all the time.

One weakness of the power plant's safety concept was mainly shown in the fact that the startup of an emergency diesel generator depends on the correct functioning of the associated UPS unit. In this way, the UPS and diesel generator together hardly provide any higher security for the 500 V network. Other power plants feed the diesel run-up control directly from batteries. The fact that the same fault occurred in two out of four systems is classified by the Swedish authority SKI as a "fault with a common cause", which considerably reduces the safety design of the emergency power supply.

Corrective Action Status (September 14, 2006)

In the meantime, the voltage supply for the diesel run-up control in Forsmark 1 has been switched to DC voltage supply from the battery systems, and a protection system has been set up and tested in the external 400 kV switching station. The other causes of errors mentioned have also been eliminated. A revision of the safety analysis report and plans for preventive maintenance are planned as longer-term measures.

safety

In October 2012, the results of a stress test that the EU had carried out after the Fukushima nuclear disaster became known . In addition to the Olkiluoto nuclear power plant in Finland, the Forsmark nuclear power plant was one of the particularly criticized nuclear power plants. Accordingly, z. For example, the operating teams in these power plants have less than an hour to restore an interrupted power supply to maintain the essential reactor cooling, in Forsmark even only 35 minutes.

Bomb threats

After a bomb threat , the area had to be evacuated on March 21, 2007 except for an emergency occupation .

Data of the reactor blocks

The Forsmark nuclear power plant has a total of three blocks :

Reactor block	Reactor type	net power	gross power	start of building	Network synchronization	Commercialization of essential operation	switching off processing
Forsmark - 1	Boiling water reactor	987 MW	1025 MW	June 1, 1973	June 6, 1980	December 10, 1980	(approx. 2040)Template: future / in 5 years
Forsmark - 2nd	Boiling water reactor	1000 MW	1038 MW	1st January 1975	January 26, 1981	7th July 1981	(approx. 2040)Template: future / in 5 years
Forsmark - 3rd	Boiling water reactor	1170 MW	1212 MW	1st January 1979	March 5th 1985	August 18, 1985	(approx. 2040)Template: future / in 5 years

Web links

List of incidents from July 25, 2006
Website of the power plant operator Forsmark Kraftgrupp (English / Swedish)
Swedish Nuclear Power Inspectorate website with details on the Forsmark 1 incident

pdf report of the Swedish Nuclear Power Inspectorate with the exact course of the incident (English)

Interview on Deutschlandfunk on the topic (German)

Article of the time to the incident

Individual evidence

↑ Vattenfall : Forsmark ( Memento of the original from July 17, 2012 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.

↑ IAEA - Nuclear Power Reactors in the World - Series 2 2008 (English; PDF file; 1.6 MB)

↑ IAEA , Power Reactor Information System : "Sweden, Kingdom of Power Reactors" (English)

↑ Om Forsmark ( Memento of the original from October 7, 2012 in the Internet Archive ) Info: The @1@ 2 archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. , Vattenfall homepage (Swedish), accessed October 19, 2012

↑ UPI : "Nuclear plant faced possible meltdown" (August 1, 2006) (English)

↑ GRS specialist forum: Mastery of electrical voltage transients . June 15, 2009. Retrieved April 29, 2015.

↑ GRS: Event in the Swedish Forsmark Nuclear Power Plant ( Memento of the original from September 4, 2006 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. , also contains a sketch of the power supply for Forsmark 1 (November 14, 2007)

↑ KSA: On the incident of July 25, 2006 at the Forsmark 1 nuclear power plant (Sweden) (October 2007)

↑ Billion investments without income from October 22, 2015, accessed on March 27, 2018

^ ZDF news from August 24, 2006

^ "Frankfurter Allgemeine Zeitung", August 25, 2006, page 5

↑ Spiegel Online : "Four nuclear power plants shut down after a serious incident" (August 3, 2006)

↑ Frankfurter Allgemeine Zeitung, February 10, 2007, p. 6.

↑ Vattenfall admits safety deficiencies in the Forsmark nuclear power plant

↑ Head of the Forsmark nuclear power plant resigns (tagesschau.de archive)

↑ Spiegel Online : "German nuclear reactors are checked for design errors" (August 3, 2006)

↑ Archived copy ( Memento of the original from September 28, 2007 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. Brief information on the incident prepared by GRS and Öko-Institut on behalf of the BMU