The future of nuclear plan design - A post Fukushima assessment

For nuclear energy resurgence to continue, it will have to mend its ways dramatically, I  was , formerly Head of Information Systems NPCIL and served as a senior scientist with India's premier S&T establishment for a decade.

Japan’s nuclear crisis is a top most news story. Almost all media carry the same issues (on account of sketchy, ambiguous, often contradictory and combative information given by authorities and others).  

This is typical of nuclear industry all over the world whenever there is a problem? That is nothing new or peculiar to Japan, India, US or USSR over the last 30 years!.

This piece will try and ask some questions without resorting to technical speak or jargon.

What happened?

When the roof & outer walls of the reactor buildings No. 1, 2, 3 blew of (designed to blow out as versus implode to protect reactor vessel and critical internals), it was a sign of plant operators not being able to contain the runaway reaction inside the reactor building on account of loss of cooling capability within the reactor and spent fuel bays.

Why?

Cooling capability is driven by water pumps which run on electrical power. When the earthquake struck, the safety measures to shut down the normal operation of the reactor worked as per design (the earthquake was beyond what the design provided for). But even when the reactor is ‘off’ (unlike a car engine) it continues to produces about 6 percent of the heat of when it is at full power.

This residual heat has to be continuously removed from the system constantly. Now with no electrical back up to the main power – the 13 DG sets were swamped on account of flooding, no other secondary electrical power, and limited battery back up. Heat built up and the resultant mix of steam (radioactive in nature) and hydrogen gas (resultant from mixing of the zirconium fuel cladding & water above a certain temperature) accumulated within the building. In the absence of the in built emergency venting system ( paralysed due to bureaucratic delay and loss of power to the control system to open valves) to release the pressure. The  roof blew..

Why did the back up Diesel Generator power system fail? 

Because `of poor design and maintenance (corrosion and cracks). They assumed the 30 ft Tsunami sea wall around the plant would prevent ingress of water from tsunami into the ground level common areas which contains this machinery. Mainly (a) because the design did not account for such a severity of earthquake, and concomitant (b) 15 meter wall of water, rushing in within the hour! They could also have run short on fuel oil with no way to replenish.

What happens now?

With the roof , outer walls and primary containment seemingly compromised – steam venting is being done (to release pressure)  from time to time releasing radioactivity into the air – not visible to human eye or TV!

This invisible discharge then is carried by winds into whichever direction it is blowing. Result, back ground radiation in and around that area will show a rise. Though most of these will be short lived radiation (iodine 131) , there seems to be traces of cesium,  and strontium which are much longer lasting.  And when this ‘plume’ (for want of a better word) meets upper air circulatory systems, it will waft across Alaska, North America West Coast ultimately. It may also waft inland into western parts of Japan and offshore depending on wind circulation. It is already doing so.

Also they have started using sea water and fire hoses (belatedly) to cool the reactor and spent fuel bay, in a process called feed and bleed – sea water along with boron carbide ultimately corrodes the reactor core, leads to salt deposits preventing further cooling and ends the effective life of the reactor. Since Fukushima employs the old 60's GE Mark 1 single steam cycle system where cooling and extraction of steam for turbines takes place in one cycle (unlike secondary cycle in Indian reactor). What they call is a once thru cycle – sea water is ingested and needs to be topped up/treated/discharged.

Where is all this thousands of tonnes of radioactive  water (10000 tonnes)discharge going - into the sea or into special ponds and localised storage ?And what about another 100000 tonees still in Reactor Buildings waiting to be pumped out!

In short…?

There was a loss of coolant, temperature rose in core, partial (major) meltdown restricted to core, ( accompanied by breach in core and/or pipes, suppression chamber), hydrogen gas builds up in building and in the suppression chambers due to reaction, roof and sides of buildings blowout; spent fuel rods stored in same building also lose coolant (due to rip in stainless steel water containment pool & sloshing), so further reactions, explosion and emission of radiation from core, steam venting and spent fuel.

What lessons are apparent?

Definitely a wake up call for the nuclear industry, just when it was showing a belated resurgence. Ultimately, inspite of immediate political acceptance issues, there are few options for countries like India, Germany, France, Taiwan and USA. And yes, even Japan! Japan where over 30 % of its enery needs are from nuclear power!

For most of these countries nuclear is the most sustainable long range source of independent energy supply to meet their needs. For the resurgence to continue with a hiccup, honest soul searching around improved design philosophy and deployment strategy is required, as below;

·         A new design philosophy based on redundancy with diversity as versus the hitherto defense in depth principles. Actually, the latter does not actually prevent accidents from happening. It is not a prophylactic measure. And should be made clear to the audience. Only once accident happens, they come into play to stop egress of radiation from core into the environment.And that to as events unfold, not to well!The former approach will preempt an accident. 

Here is how it goes and this may sound as anathema for traditional designers;

-interim storage of spent fuel roads inside the same building (at near roof level) as the reactor core, is now out of the question. Regardless of the infrastructural/logistic efficiencies and economics of doing so. The earthquake cracked the spent fuel’s water containment pool, and may have also sloshed the water around and out. Adding to more distress than planned for. However reactors 5 & 6 are out of harms way now. 

-Common plant equipment and resources located in utility buildings, DG, auxiliary systems, switchboards, motors, etc has to be re thought – can’t have these ‘resources’ hooked onto servicing all reactors, from one contiguous area, or remain unprotected.

-Modular stand alone systems with each reactor islanded from others for any eventuality fire, local, missile strike, power, any man made or natural event. Even the reactors under maintenance are under crisis due to spent fuel overheating. Reactor 4 exploded not beacuse it was in distress but, there was exploseive hydrogen gas from Reactor 3 which leaked into it  from a common vent.

-Core catchers to be compulsory.

• New siting strategy. While there may not be much option from locating reactors on bluffs near coasts and other large water bodies, definitely not within our seismic zone more than Zone 2 (and an abundant measure of caution, I have dropped it one notch from 3 to 2 ), or at water/sea level.

• Emergency preparedness has to be constantly reviewed by third party (other operators/independent neutral agencies). The envisaged resources to fight emergency situation should be stored at plant site, and also at off site location. Remote plant operations are a must, as even control room was compromised with radiation on account of air cleaning system being knocked out. Pumping sea water in leads to crusts being formed, slowing heat transfer and water circulation.

• Design basis for accident (DBA) principles to make way for a new philosophy of design beyond expectations (DBE). The earthquake and breach of outer walls were stand alone events beyond expectations. There is a need to involve people from commercial airline manufacture, submarine designers, oil & gas, biologists, economics. Basically, people who are lateral thinkers or ‘out of box’ beyond just the arcane domain of people within the industry. This will be a societal obligation. And prevent key stakeholders colluding non transparently and giving each other a mutual back rub – operators and regulators !

• Design basis to consider ‘black swan’ event combinations – the current situation is a good example of such a scenario – no design manual would ever have this combination of such failures or events in this particular sequence. More scenarios have to be examined however outlandish they may seem to be on first impressions.

• The economics of nuclear will change, but technology, manufacturing & logistics innovations being such, they will mitigate costs to still remain financially competitive to other base load sources of power. And even then it is but a small price to pay for societal prosperity and survival in the very long term.

• Direct and lateral hires into senior and mid level for various key functions such as Public Awareness, Strategic Planning, Cloud computing,  Disaster Management, Outreach, International Relations, Crisis Management, Media Relations, Environmental Assessment, etc

• Plant performance reports & radiation data should be publicly available in real time.

So while nuclear power has clearly taken a sucker punch, it is not out for the count. yet.