<link rel="stylesheet" href="//fonts.googleapis.com/css?family=Open+Sans%3A400italic%2C700italic%2C400%2C700">Loss-of-coolant accident Archives « Aam JanataSkip to content

Dr. A. Gopalakrishnan, former chairman of the Atomic Energy Regulatory Board cautions, based on the sparse specifics available in the public domain and comments by authority figures that the government may be concealing information about the magnitude of the accident at KAPS (Kakrapar Atomic Power Station) Unit 1


The Kakrapar Unit-1 PHWR Primary System Leakage Incident on March 11, 2016

The Kakrapar Unit-I nuclear reactor in Gujarat is undergoing a moderately large leakage of heavy water from its Primary Heat Transport (PHT) system since 9.00 AM on March 11,2016. From the very limited information released by the Nuclear Power Corporation of India Limited (NPCIL) and the Atomic Energy Regulatory Board (AERB) of the government , as well as from the conversations I had with press people who have been in touch with nuclear officials, few inferences can be drawn.

Till 7.00 PM on March 12,2016 , the DAE officials have no clue as to where exactly the PHT leak is located and how big is the rate of irradiated heavy water that is leaking into the reactor containment . However, some reports indicate that the containment has been vented to the atmosphere at least once , if not more times , which I suspect indicates a tendency for pressure build up in that closed space due to release of hot heavy water and steam into the containment housing . If this is true, the leak is not small , but moderately large , and still continuing. No one confirms that any one has entered the containment (in protective clothing) for a quick physical assessment of the situation , perhaps it is not safe to do so because of the high radiationfields inside . When NPCIL officials state that the reactor cooling is maintained , I believe what they may be doing is to allow the heavy water or light water stored in the emergency cooling tanks to run once-through the system and continue to pour through the leak into the containment floor through the break .

All this points to the likelihood that what Kakrapar Unit-1 is undergoing is a small Loss-of-Coolant Accident (LOCA) in progress. It is most likely that one or more pressure tubes (PT) in the reactor (which contain the fuel bundles) have cracked open , leaking hot primary system heavy-water coolant into the containment housing . The reactor cooling is said to be maintained which , in view of the PT breach , can only be by supply of heavy water or light water from the storage tanks of the emergency cooling systems . While it may perhaps ensure bulk coolant temperatures in the PHT system to be well under control , it could still mean fuel centreline temperatures in the channel which may have a breach could be quite high . The seriousness of the accident and the potential high risks to the plant and personnel in the near vicinity are yet to be assessed , because NPCIL and AERB do not yet know where the location of the leak is or how to initiate actions to stop it. They were waiting for a team of AERB Specialists to reach Kakrapar in the afternoon of March 12 th. (today) to jointly decide between AERB & NPCIL how to proceed from here on. This is therefore a potentially serious accident in progress , and the DAE, NPCIL and AERB appear to be clearly saying at the moment that they know very little of what is happening. I was just told that a senior team from AERB has reached Kakrapar this evening and now the serious accident investigations will hopefully begin and decisions initiated .

In August 1983 , the Pickering Heavy Water Reactor in Canada had a serious Small LOCA , due to a sudden two-meter long rupture of a pressure tube (PT). Upon later analysis , the cause was found to be the mislocation of annulus gas spacer springs which allowed the pressure tube to sag and contact the calandria tube , leading to hydrogen enrichment of the cooler areas of the PT. This made the tube more brittle in such cooler locations and it ruptured due to the internal fluid pressure. In 1983 , when this accident in Canada occurred , India was under international nuclear sanctions following the Pokhran-1 test and it took some time before root causes of this accident were understood by our Department of Atomic Energy (DAE) institutions. But , the Bhabha Atomic Research Centre (BARC) did commendable work immediately in analysing the phenomenon of hydriding of PTs in a PHWR , and carried out experiments, developed computer programs and the appropriate PT Integrity Inspection Equipment within the next decade. Based on all this work , a Pressure Tube Aging & Integrity Management Program was develop jointly by BARC & NPCIL , for strict adherence to and use by NPCIL in all their PHWRs. Besides , it was found essential that the PT material has to be changed to Niobium-stabilized Zircalloy , and accordingly all previous Indian PHWRs including Kakrapar Unit-1 were re-tubed with the new alloy tubes in subsequent years . But , this re-tubing did not preclude the need for strictly following of the PT Aging Management Program and the periodic checking of the garter spring position between the PT and the Calandria tube to minimize the PT sagging within the calandria tube. It may be possible that , having built more than 20 PHWRs , NPCIL and AERB in recent years have become overconfident and relaxed their strict adherence to this Aging Management Program , which might have been the reason for the current accident.

Let me caution the reader that the above conjecture is based on bits and pieces of reliable and not so reliable information gathered from different people close to the accident details and in positions of authority. Future detailed evaluation may or may not prove my entire set of conclusions or part of them to be not well-founded. But , technical experts are compelled to put out such conjectures because of the total lack of transparency of the Indian cilvilian nuclear power sector and the atomic energy commission (AEC) , the Dept. of Atomic Energy (DAE) , the NPCIL and the AERB . Public have a need to know and , therefore , the AEC and its sub-ordinate organizations need to promptly release status reports on the progressing safety incident which could affect their lives , to alleviate their concerns and anxieties . It is a series of such lapses in communication over the years which has built up the ever-increasing trust deficit in the DAE system among the general public. All future plans for expanding the civilian nuclear power sector should be put on hold until a truly independent nuclear safety regulator is put in place , who is not controlled by the AEC or the Prime Minister’s Office (PMO) , who will then be answerable to openly communicating with the public on all civilian nuclear power matters.

(Dr. Gopalakrishnan is a Former Chairman of the Atomic Energy Regulatory Board , Government of India. He can be reached at agk37@hotmail.com )

This article was originally published on the Dianuke website.


Twitter is ablaze with news of nuclear meltdown being imminent in Japan and some tweets are along the lines of "OMG! the reactors are going to explode! God save the world". This sounds a little extreme, and I thought I'd share what I found out in extremely non-tech terms for anyone to get an overall "panic-rating" kind of grip on the subject.

The Japanese reactors are light water reactors. Without getting into the scientifics of it, in the words of an expert, Naoto Sekimura, a professor at the University of Tokyo, a major radioactive disaster is unlikely.

"No Chernobyl is possible at a light water reactor. Loss of coolant means a temperature rise, but it also will stop the
reaction," he said.

"Even in the worst-case scenario, that would mean some radioactive leakage and equipment damage, but not an explosion. If venting is done carefully, there will be little leakage. Certainly not beyond the 3 km radius."

IAEA seems to agree on the whole, though they are concerned and actively monitoring.

Nuclear reactors use radioactive fuel to generate electricity. In the process, the fuel gets hot, and much like say, the engine of your car, it needs to be kept cool. This is a big deal, because unlike your car, if this stuff explodes, we can forget using that area of the earth for a long, long time because its radioactive contents will get scattered in the blast. Thus, the fuel is kept at desired temperatures and prevented from overheating. There is massive planning and enginnering around this, with several methods used simultaneously, each capable of cooling the core independently. In addition to that, each method has back ups and fail safes till a mind numbing redundancy is achieved. This is in order to set things up so that once the reactor is in operation, there is absolutely no possibility that there is a failure in cooling it down. The fuel needs to be cooled for a day or two after shutting a nuclear reactor down.

Another factor is the pressure. Evaporating coolant can create high pressures that can threaten the integrity of the containment dome. This can be released by venting, which is a management mechanism and not procedure, since it means that some quanitites of radiation can get released along with the steam. This isn't radioactive materials, but the water itself absorbing neutrons from the cooling process, which are shed off quickly. This radioactivity isn't supposed to last long because the water used is specially demineralized for the purpose, thus making it extremely resistant to this kind of radioactivity. Not that the core cares what cools it, but the water not being radioactive makes it easier for managing the plant.

Sometimes, this system can fail, like it is failing in Japan, right now. When the earthquake happened, the reactors were shut down. This was pretty much instantly. Well before the tsunami. It means the control rods came and fitted in between the fuel rods, so that the ricocheting neutrons had less space to move and less power and less targets, till it would finally wind down and stop in a day or two. This is normal. Nuclear reactions are like that.

And the backup generators took over the cooling since the reactor was no longer producing electricity (and there were back up generators for the ones in operation too). This worked well for about an hour till the tsunami hit and took out all the generators. This was unfortunate, because the cooling system needs constant power. However, the third line of back up kicked in and the generator switched to battery power, which would last for 8 hours or so. Post this point, things seemed to go into chaos. For some reason, they were not able to use the time provided by the battery to rig up yet another power source, and when the battery was exhausted, the reactor started heating up. Without a circulation mechanism for the coolant, the whole thing is overheating and pressure is increasing from the evaporating water.

There are plans to let off steam. US has flown in coolant. Japan has been extremely transparent and proactive in dealing with the exposure to people. The area was evacuated well before any radiation could be found.

My suggestion would be to not panic. Yes, it can blow up, like the US Pennsylvania's Three Mile Island Meltdown. Mushroom cloud and all. Nothing is impossible. The venting could run into problems (though I don't see how). Everything to prevent a disaster could fail. But more likely it won't.

The domes that are so characteristic of nuclear reactors are basically built to contain any meltdowns. You can read about the architecture/engineering of a nuclear reactor facility, but I have, and without boring you with the details, there are vastly reassuring quantities of steel and very, very thick leak proof concrete structure. Its purpose is to contain any explosion/radiation that may occur. And there is no evidence that this integrity is breached.

Japan is a country with a reputation for engineering and efficiency. It has survived the only two atom bombs explosions in the world. I think its fair to say that they aren't going to give this up without a good fight. And, their expertise, ready aid from the world and the inherent safeguards built into every aspect of a reactor are on their side.

So, like the Hitchhiker's guide says, "Don't panic".... if the worst happens, I promise you you will have plenty of time.

Update: there has been an explosion OUTSIDE Japan's nuclear power plant at Fukushima 1. Doesn't seem to be a nuclear explosion, but building is damaged. 2killed, 4 workers injured. Uh... don't freak out just yet. Unlikely that a nuclear blast will result in 4 injuries at ground zero. More likely to do with the pressure building up or steam from some drastic cooling measure or hydrogen exploding from the venting. Let's wait for news. The only thing I am worried about is the radioactive stuff outside the containment - like spent fuel. Building gone means that is exposed, right? Or worse - exploded? But nothing in the news, so obviously I don't know as much as I imagine.

Update 2: Yep, like I said - steam. People within 20km asked to evacuate. Radiation leaking from damaged building. Residents advised to remain indoors, not drink tap water, and to cover their faces with wet towels (? for how long with covered face - but I guess for as long as it takes to get a green signal ?)

Update 3: Early, unconfirmed tweets on mushroom explosion spotted over reactor, but from an Australian, from the look of it. Could be a reaction to earlier blast, or something new? Scientists didn't seem to have invested much belief in the explosion idea for a light water reactor (like these are). Wait n watch  - you'll get to panic or breathe a sigh of relief soon.

Update 4: Stray initial tweets about pressure having been successfully released from the reactors, but paranoid Tweeters on and on about "Japanese reactor just exploded, OMG!!!" The links provided are all to the video footage of the earlier explosion OUTSIDE the reactor that damaged the building and *possibly* raised leakage. Nothing remotely like a nuclear explosion has happened yet, nor is it scheduled.

More quotes:

Robin Grimes, Professor of material physics at Imperial College, London

Despite the damage to the outer structure, as long as that steel inner vessel remains intact, then the vast majority of the radiation will be contained.

Professor Paddy Regan, Nuclear Physicist from Britain's Surrey University

"If the pressure vessel, which is the thing that actually holds all the nuclear fuel ... if that was to explode -- that's basically what happened at Chernobyl -- you get an enormous release of radioactive material.

"It doesn't look from the television pictures ... as though it's the vessel itself.

Update 5: For those who absolutely must follow microdetails (like me), a better source is http://www.tepco.co.jp/en/press/corp-com/release/index-e.html you will get all the techy things like timings for different things done, status of reactors, worker accident status, etc.

Update 6: News of problems at reactor 3 at Daichi.