Oskarshamn (Sweden)

Map of Oskarshamn

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In Oskarshamn three BWRs and the Central Interim Storage CLAB are located.

Spent fuel of all Swedish npps and other high level waste is stored at the Central Interim Storage CLAB. The waste is stored in water pools in rock caverns at 25 m depth. The total capacity is 5000 tons of spent fuel. In 2003 4100 tons were stored. CLAB is now being expanded to increase the capacity to 8000 tons. The expansion is going to be commissioned in the end of 2004.

Facilities in Oskarshamn

plantreactor typconstruction startoperation startshut down
CLABInterim Storage for Spent Fuel1985
Oskarshamn-1BWR19661971
Oskarshamn-2BWR19691974
Oskarshamn-3BWR19801985
2008-10-01

"A routine annual control of Unit 3, a boiling water reactor, at Sweden's
Oskarshamn nuclear power plant in early October turned up a control
rod that had broken off. On closer inspection other rods were found to
be cracked. The Swedish Radiation Safety Authority (SSM)
immediately ordered an inspection of all Swedish BWRs of the same
construction, and especially a 'twin' reactor (Unit 3) at Forsmark."
source: nuclear monitor issue 679

2008-01-22

Oskarshamn-1 shut down on Tuesday because of a valve problem. There were no safety concerns related to the problem, the shutdown would only be temporary.

2007-11-07

A minor fire today occured at Oskarshamn-2, the plant was shut down.

2005-12-31

During 2005 in Oskarsham-1 five events occured that were below INES labelling: a fault in a turbine governing system, high vibrations in the turbine that resulted in a replacement of the turbine rotor, a steam leak, failure of the throttle valves, and a leak in connection with one of the main circulation pumps.

2005-12-31

During 2005 in Oskarsham-2 five events occured that were below INES labelling: a salt water leak to the turbine condenser, failure of a valve in the preheater system, power reduction because of high voltage levels in the Swedish poer grid, problems with the filtering because of jellyfis in the cooling water, and high level in a drainage vessel on the rheater.

2005-12-31

During 2005 in Oskarsham-3 eight events occured that were below INES labelling: fault in the excitation equipment, a salt water leak to the condenser and a fuel defect, a valve leakage in the feedwater system, reduction of power du to high voltage in the Swedish power grid, a defect valve on a main steam line, a defect measurement point in the feedwater system, and two fuel defects.

2003-12-31

Extensive stress corrosion cracking was observed years ago in consoles and supports of the emergency core spray systems. Most of the damaged supports were replaced. Follow-ups in 2002 showed that some of the remaining cracks had propagated, but no new cracks were identified. The core spray has been completely replaced to less sensitive material.

2003-09-30

In September Oskarshamn-3 had exceeded maximum permissible limits of temperature increase in the reactor pressure vessel. This event was rated INES level 1.

2002-07-26

Unit 1 should be back on line in October. The management of the plant has sent an application for restart to the Swedish Nuclear Power Inspectorate (SKI). The BWR is in the final phase of a massive modernisation program begun several years ago. Upgrading includes a new building for electrical cables, to improve safety system separation, and cleaning of the low pressure system, now under way.

1998-06-20

General Electric is having problems removing the unit's core shroud, which ABB is contracted to replace. Carlsson said that, despite years of planning for the job, it is going much more slowly than expected.
Two of the relays had malfunctioned, and one spare was temporarily connected, but management decided to replace all four as a permanent solution.

The relays, designed by ABB Atom AB, were installed as part of a massive modernization program that took three years to complete. Manager Carlsson said he believes "poor design" was responsible for the failure. Replacement will cost between 25 - and 30-million kronor (U.S. $3.2- and $3.8-million).

1998-05-10

In May 1998, a preliminary level 1 PSA at Oskarshamn-2 showed the frequency of an accident with core damage between 10-3 and 10-4. Sydkraft, which owns Barsebaeck and Oskarshamn, aims for a risk factor of 10-5, which Swedish regulators say is difficult for older units to achieve.

1998-05-01

Initial improvements aimed at reducing the risk of a serious accident with core damage will be made within weeks at Sweden's Oskarshamn-2 and the two Barsebaeck units, and longer-term plans for changes are also being made.

In May, preliminary probabilistic safety analysis (PSA) at Oskarshamn-2 indicated that the likelihood of a serious accident with core damage was between 10E-3 and 10E-4 , because of station blackout sequences involving loss of power emergency generator failure.

Regulators expected a similar result at Barsebaeck, because the units are almost identical. Preliminary PSA results from Barsebaeck, sent to the Swedish Nuclear Power Inspectorate (SKI) June 12, show a frequency just over 10E-4. Plant management said the figures were better than Oskarshamn´s because the electrical systems at Barsebaeck are slightly different.
At Barsebaeck and Oskarshamn-2, work will begin during the upcoming maintenance outages to reduce the identified risks. At Oskarshamn-2, the plan calls for backup power for the core cooling system.

1998-05-01

Preliminary results from a prohabilistic safety analysis (PSA) indicate a serious problem, say regulators, who expect a similar result from ongoing PSAs at Barsebaeck-1 and -2.
The results show the likelihood of a serious accident with core damage is between 1 in 1000 (10E-3) and 1 in 10.000 (10E-4) at the 600-MW BWR.
The greatest contributor to the derived figure for core damage is common cause failure between the two diesel generators used for backup power. The generators have failed in the past, however.

1998-01-15

ABB Atom personnel are set to begin core shroud replacement at Oskarshamn-1 after replacing water-level measurement relays in the reactor vessel.

1997-05-01

OKG utility has just awarded key contracts to ABB and Siemens in the ongoing 1996-99 rejuvenation of Sweden's oldest commercial nuclear power unit - 25-year-old Oskarshamn-1. The order to ABB is worth nearly US $90 million.
ABB Atom will deliver new electrical and control equipment, and modernize the control room.
The Advantage technology was introduced during modernization of control systems at Sweden's Ringhals-1 and Forsmark-1 and -2, Finland's Olkiluoto-1 and -2, and South Korea's Ulchin-5 and -6.
ABB Stal will install one high-pressure steam turbine and six low-pressure turbines at Oskarshamn-1, thus boosting output by an expected 15 MW.
Siemens/KWU - under a contract worth about US $47 million - is providing the upgrade concept which will bring Oskarshamn-1´s accident prevention and accident control to the latest state of the art.
Siemens/KWU is responsible for implementation of the upgrade concept and will design, supply and install the new safety systems.

1996-11-15

Unit started up after a long period of maintenance and refuelling on November 6th, without the core spray being activated. spray pumps have been disconnected during tests and were not reconnected - by mistake. Unit operated during one week without completely available ECCS.

1996-01-22

Restart: Oskarshamn-1 began delivering electricity to the grid on January 22.
The reconnection marks the end of a long and often frustrating effort to rebuild the 23-year-old, 440-MW BWR, Sweden's oldest reactor. The initial 800-million-kronor (US $117-million) rehabilitation will be followed by 1-billion-kronor´s worth of upgrading o be finished in 1999.
Included in that work is replacement of a cracked moderator tank lid, scheduled for 1998.

1995-12-18

The unit was given permission to restart December 18, conditioned on a series of special safety checks including examination of the cracked moderator tank lid during this summer's annual maintenance outage.
In the fist INES incidents in January, an auxiliary condenser deactivated because of an improper temperature measurement. According to the report filed by INES officer F. Reisch, "the error was introduced by design work during modifications." The operator corrected the mistake within a couple of minutes and the incident was rated Level 1 (of seven severity levels).
On March 4, a containment isolation valve in the core spray system failed to close properly during a test. According to safety regulations, any problem with such a valve must be dealt with within 24 hours or the unit must shut down. However, operators failed to follow those instructions. The event was rated Level 1.

1995-12-11

Sweden's chief nuclear regulator has postponed a decision on the restart of Oskarshamn-1 because of new questions from an advisory committee about transients that could result in critical loads on some reactor components.
But Hoegberg said that the advisory board has asked for a further review of transients "to assure that we covered everything that could be significant." Hoegberg would not be more specific, except to confirm that the transient review does not include the cracked moderator tank lid.
The tank lid remains problematic. Cracking was discovered in the lid after the bulk of a massive upgrade program had been completed, delaying a restart decision that had been expected in September.
Oskarshamn-1 has been down since September 1992.
Restart end of Dec: operation allowed until 1996 summer refueling outage , conditioned on a series of strict special safety requirements.

Before restart permission is granted in 1996, regulators also want testing of the inner walls of the pressure vessels and a PSA demonstrating the anticipated effects of modernization on plant safety.
In 1997, additional testing of at least two valve housings and two pump housings in the primary system will be required. In 1998, new steam valves that meet modern safety standards must be installed and a Level 2 PSA must be completed.

1995-07-01

Operating costs for Swedens NPPs are on average higher than what the industry claims, according to a report done for the government's energy commission. The report was done by a Swedish accounting firm and the conclusions reported by a business paper.
Oskarshamn-1 curently undergoing major renovation is cited as the most expensive reactor: 22,6 oere/kWh (0,03 US$/kWh) compared with an average of 13 oere.

1995-03-28

Final inspections following the replacement of the core shroud support by ABB. Replacement was part of the Fenix project a $ 100 million 3-year modernization project of Swedens oldest BWR.
ABB dismantled the shroud and shroud support after the PRV had been emptied and decontaminated; radiation level was reduced to less then 0,5 mSv /h.
Cracks found also in MCP casings and connecting valves: deepest crack in a pump casing is 14 mm in a 50 mm wall.
pressure & temperature testing of RPV in august 1995. Restart is expected in september after two years of repairs & upgrading which costed US$ 100 million An additional 30 million $ will be spent for upgrades annually over the next 5 years.

1993-03-01

Two throughwall cracks 7 mm apart have been discovered during inspections in piping of reactor water clean-up system (part of RCS) one of the cracks was found by ultrasonic testing, the other because water is leaking from it. Further inspections revealed more cracks. Pipes replaced - no cracks were found at unit-2 which had a more normal water chemistry. It is assumed that sulfite is responsible for the stress-corrosion cracking in unit-1.
Planned restart in January 1995 was postponed to early summer. The 22 year old plant has been down for more than 2 years because of specific problems as well as generic flaws of ECCS. Refurbishment has included replacing cracked FW pipes and changing most of the cables in containment. The first phase of upgrade cost roughly US$ 95 million Additional 30 million US$ has been budgeted for upgrade from 1995 to 1999.

Unit was on the course for restart when cracking was discovered in stainless steel valve and pump casings under containment. a 400 mm long crack was also discovered in the moderator tank lid.

1991-08-01

Refueling and maintenance incidents: 1.) workers failed to use a video camera for monitoring the removal of spotlight parts that had fallen to the bottom of the reactor tank. 2.) a bridge at the interim spent fuel storage facility collided with a welding machine. The machine was pulled for 25 meters into an empty storage area.

1991-06-07

Delay of restart after refueling by high turbine vibrations - cracks in a bolt that secured a coupling in the turbine axle (cause vibration or improper fastening)

1988-08-01

Four dried out and damaged fuel rods in seperate assemblies were discovered at the plant. The failed rods were identified during refueling outage. The rods failed because they were operated under dryout conditions during steady state operation for an extended period of time (between 2 and 7 days). In each assembly with failed fuel the corner rod facing the adjacent control rod was heavily oxidized and the cladding was penetrated. There was also perforation near the bottom of the rods that resulted in loss of fuel . The rods looked sort of burned (NRC-note). Most of the radioactivity lost from the fuel channels was caught in ion exchange resin filters and rad. releases to the environment for 1988 were about 10% of reg. guidlines. Typically they are about 1%.