Japan

Our analysts look at security and energy issues in Japan, where both nuclear weapons and nuclear power have a long and complex history.


Subscribe to our Japan feed

Latest Japan Posts

Transcript of Press Briefing on UCS Nuclear Power Recommendations

, co-director and senior scientist

On Wednesday, we released our report US.Nuclear Power After Fukushima: Common-Sense Recommendations for Safety and Security, which details our top recommendations for steps the Nuclear Regulatory Commission (NRC) should take to improve safety and security at US reactors.

An audio recording of the presentations by Dave Lochbaum and Ed Lyman, and a transcript of the full briefing, including Q&A with reporters, are now available.

Bookmark and Share

UCS Recommendations for Nuclear Power Safety and Security After Fukushima

, co-director and senior scientist

Following the disaster at the Fukushima Dai-Ichi nuclear plant in Japan, we began studying what lessons the US should learn from the event and developing a set of recommendations that would increase the safety and security of U.S. nuclear plants.

Today we released US.Nuclear Power After Fukushima: Common-Sense Recommendations for Safety and Security, which details our 23 recommendations for steps the Nuclear Regulatory Commission (NRC) should take. Many of the recommendations address problems that have been evident for decades, while others address problems brought to light during the Japanese crisis.

The top 8 recommendations, discussed in detail on our website are:

  • The NRC should extend the scope of regulations to include the prevention and mitigation of severe accidents.
  • The NRC should modify emergency planning requirements to ensure that everyone at significant risk from a severe accident—not just the people within the arbitrary 10-mile planning zone—is protected.
  • The NRC should require plant owners to move spent fuel at reactor sites from storage pools to dry casks when it has cooled enough to do so.
  • The NRC should enforce its fire protection regulations and compel the owners of more than three dozen reactors to comply with regulations they currently violate.
  • The NRC should establish timeliness goals for resolving safety issues while continuing to meet its timeliness goals for business-related requests from reactor owners.
  • The NRC should revise its assumptions about terrorists’ capabilities to ensure nuclear plants are adequately protected against credible threats, and these assumptions should be reviewed by U.S. intelligence agencies.
  • The NRC should require new reactor designs to be safer than existing reactors.
  • The NRC should increase the value it assigns to a human life in its cost-benefit analyses so the value is consistent with other government agencies.

In the wake of Fukushima, the NRC set up a 90-day task force to review insights from the accident; that task force released its recommendations today. UCS will post an analysis of those recommendations as soon as we have digested them.

Bookmark and Share

Fukushima Dai-Ichi Unit 3: The First 80 Minutes

, director, Nuclear Safety Project

As described in my first post, I reviewed the detailed data the Tokyo Electric Power Company (TEPCO) released, to understand the operation of Fukushima Units 1, 2, and 3.

The available information for Unit 3 does not extend long after the arrival of the tsunami, and does not extend to the point at which fuel in the reactor core was damaged by overheating. Much of the available information ends at 4:05 pm local time, about 80 minutes after the earthquake occurred at 2:46 pm.

The available information for the first 80 minutes following the earthquake shows:

  1. The reactor shut down around 2:46 pm local time and remained shut down.
  2. Normal power supplies to in-plant equipment were lost about a minute later. It is assumed that this occurred when the operators manually tripped the turbine/generator per procedure.
  3. Both emergency diesel generators on Unit 3 automatically started and connected to their in-plant electrical buses within seconds of the power loss, restoring power to essential plant equipment.
  4. The power interruption caused the main steam isolation valves to automatically close, disconnecting the reactor core from its normal heat sink and disabling the normal source of makeup water to the reactor vessel.
  5. A safety relief valve (SRV) automatically opened around 2:52 pm to control rising pressure inside the reactor vessel. This SRV automatically re-closed when reactor pressure dropped. This SRV followed by two other SRVs cycled opened/closed periodically over the next 73 minutes to control pressure inside the reactor vessel.
  6. The water level inside the reactor vessel steadily declined as cooling water was discharged through the open SRVs into the torus. By 4:00 pm, the water level had dropped below the bottom end of the level monitoring scale. There’s no compelling evidence that any system was used to provide makeup flow to the reactor vessel from the time that the MSIVs closed around 2:48 pm until 4:00 pm.
  7. Around 3:38 pm, one of the emergency diesel generators stopped running. About a minute later, the other emergency diesel generator stopped running. It is assumed that the tsunami caused these failures.
  8. Around 4:02 pm, the RCIC system appears to have been placed in service. The data ends shortly afterwards at 4:05 pm.

Details of my assessment of Unit 3 for the first 80 minutes after the March 11 earthquake are given here.

My assessments of the early behavior of Unit 1 and Unit 2 are available at these links.

Bookmark and Share

Fukushima Dai-Ichi Unit 2: The First 60 Minutes

, director, Nuclear Safety Project

As described in my first post, I reviewed the detailed data the Tokyo Electric Power Company (TEPCO) released, to understand the operation of Fukushima Units 1, 2, and 3.

The available information for Unit 2 does not extend long after the arrival of the tsunami, and does not extend to the point at which fuel in the reactor core was damaged by overheating. Much of the available information ends at 3:47 pm local time, about 60 minutes after the earthquake occurred at 2:46 pm.

The available information for the first hour following the earthquake shows:

  1. The reactor shut down around 2:46 pm local time and remained shut down.
  2. Normal power supplies to in-plant equipment were lost about a minute later. It is assumed that this occurred when the operators manually tripped the turbine/generator per procedure.
  3. Both emergency diesel generators on Unit 2 automatically started and connected to their in-plant electrical buses within seconds of the power loss, restoring power to essential plant equipment.
  4. The power interruption caused the main steam isolation valves to automatically close, disconnecting the reactor core from its normal heat sink and disabling the normal source of makeup water to the reactor vessel.
  5. A safety relief valve (SRV) automatically opened around 2:52 pm to control rising pressure inside the reactor vessel. This SRV automatically re-closed when reactor pressure dropped. This SRV cycled opened/closed periodically over the next hour to control pressure inside the reactor vessel.
  6. The operators manually started the reactor core isolation cooling (RCIC) system around 2:51 pm,when stopped it about a minute later. The RCIC system was restarted around 3:03 pm and provided makeup flow to the reactor vessel to compensate for the inventory being lost when the SRV opened.
  7. The operators manually placed one loop of the residual heat removal (RHR) system in the toruswater-cooling mode of operation. This step removed the heat being added to the torus water from repeated SRV openings and RCIC system operation.
  8. The operators removed the RCIC system from service around 3:28 pm. The water level inside the reactor vessel at that time was above normal, so continued makeup was not needed.
  9. Around 3:38 pm, one of the emergency diesel generators stopped running. About four minutes later, the other emergency diesel generator stopped running. It is assumed that the tsunami caused these failures.
  10. Around 3:39 pm, the operators returned the RCIC system to service. The system continued to provide makeup to the reactor vessel until the available data ends at 3:47 pm.

Details of my assessment of Unit 2 for the first 60 minutes after the March 11 earthquake are given here.

Bookmark and Share

Fukushima Dai-Ichi Unit 1: The First 30 Minutes

, director, Nuclear Safety Project

In the middle of May 2011, the Tokyo Electric Power Company (TEPCO) posted information such as scans from paper recorders in the control rooms, computer alarm printouts, parameters plotted from high-speed data recorders (the nuclear equivalent to aircraft black boxes), and operator log books online.

I reviewed the information for Units 1, 2, and 3. While working as a shift technical advisor in the early 1980s at the Browns Ferry nuclear plant in Alabama (with three boiling water reactors (BWRs) having Mark I containment designs like those at Fukushima Dai-Ichi Units 1-3), I authored several reports for unplanned reactor shut downs. To prepare those reports, I reviewed many of the same materials.

More recently while working as a BWR technology instructor for the U.S. Nuclear Regulatory Commission, I taught during the two-week R504B course. During that course, we covered transients both in classroom and control room simulator settings. In the classroom sessions, we would provide students with control room chart recorder plots of seven key parameters (average power range monitor power level, reactor vessel pressure, reactor steam flow, turbine steam flow, feedwater flow, reactor vessel narrow range water level, and total core flow) and ask them to determine what transient explained all the squiggles on the charts. Later in the control room simulator, we’d demonstrate the transients for the students.

The available information for Unit 1 stops before the arrival of the tsunami, and well before the point at which fuel in the reactor core was damaged by overheating. Much of the available information ends at 3:17 pm local time, about 30 minutes after the earthquake occurred at 2:46 pm. This available information for the first 30 minutes following the earthquake shows:

  1. Sensors detecting ground motion caused by the earthquake triggered an automatic shut down of the reactor at 2:46 pm local time. All of the control rods fully inserted into the reactor core.
  2. When the operators manually tripped the turbine/generator per procedure 50 seconds after the reactor shut down, normal power supplies to in-plant equipment were lost.
  3. Both emergency diesel generators on Unit 1 automatically started and connected to their in-plant electrical buses within 6 seconds of the power loss, restoring power to essential plant equipment.
  4. The power interruption caused the main steam isolation valves to automatically close, disconnecting the reactor core from its normal heat sink and disabling the normal source of makeup water to the reactor vessel.
  5. Both isolation condensers were placed in service about 5 minutes after the reactor shut down to control a rising pressure trend inside the reactor vessel.
  6. It appears that both isolation condensers were removed from service after approximately 11 minutes due to an excessive cool down of the water inside the reactor vessel.
  7. Around the time the isolation condensers were removed from service, there was an unexpectedly large downward step change in the indicated water level inside the reactor vessel.
  8. After the isolation condensers were removed from service, there was an excessive heatup of the water inside the reactor vessel.

Details of my assessment of Unit 1 for the first 30 minutes after the March 11 earthquake are given here.

My assessments of the early behavior of Unit 2 and Unit 3 are available at these links.

Bookmark and Share