Koodankulam Criticality: Tickling the Dragon’s Tail

V. Prakash, V.T. Padmanabhan, R. Ramesh, V. Pugazhendi,
Raminder Kaur, K. Sahadevan, Joseph Makkolil


inside reactorRS Sundar, the Station Director of Kudankulam Nuclear Power Plant has taken over the first reactor and his men will carefully lift the control rods from the reactor pressure vessel, and take the reactor to the “First Act of Criticality” [FAC] by midnight today. A comment and prayer from an eminent nuclear scientist: “if all engineering systems are “Go” (a big IF , considering the history of last few months), within the next week the approach to criticality will start! Let us pray for the country and especially for the people of Kudankulam , its neighbouring villages & the whole of Tamil Nadu”.

Prayer is the last option, because they have foreclosed the scientific-technological option, disregarding the following wise words of the IAEA:

“Despite all the precautions that are taken in the handling and use of fissile material there remains a possibility, while very small, that a failure (i.e. instrumentation and controls, electrical, mechanical or operational errors) or an incident may give rise to a criticality accident. In some cases, this may give rise to exposure or the release of radioactive materials within the facility and/or into the environment, which may necessitate emergency response actions. Adequate preparations should be established and maintained at local and national levels and, where agreed between States, at the international level to respond to nuclear or radiological emergencies”. International Atomic Energy Agency (IAEA) 2012


The Commissioning of the first VVER-1000 reactor at Kudankulam Nuclear Power Plant [KKNPP] has been delayed by 66 months. According to a report dated 19 June 2013 by Dr A Gopalakrishnan, formerly Chairman of the Atomic Energy Regulatory Board [AERB], the instrumentation and control cables in the reactor are giving out spurious signals which is the operator’s main headache now. KKNPP’s Station Director had appointed a committee of scientists to clarify this issue. The clarification has not been given so far. Instead, the authorities have decided to go for the first act of criticality [FAC]. There are eight other reactors in the world – 6 in South Korea and 2 in the Czech Republic, which have had cable-related problems. The problems in the Korean reactors have been due to counterfeit cables which the Korean regulator has decided to replace. Studies have shown that the KKNPP reactors have counterfeit equipment such as the reactor pressure vessel, polar cranes and safety-class valves. Taking the reactor to FAC without clarifying the safety issues is a high risk operation.

1. Introduction

The Atomic Energy Regulatory Board [AERB] has given clearance for the first approach to criticality of the Kudankulam Nuclear Power Plant reactor No 1 [KKNPP-1] on 11 July 2013. During this experiment, the control rods within the reactor pressure vessel [RPV] will be lifted to allow a sustained nuclear chain reaction. Successful completion of FAC will be followed by a series of physics experiments after which the power level of the reactor will be gradually raised. According to the press release, “the board had last September [date not given] granted the final permission for initial fuel loading (IFL) in the first unit.” As per the AERB website, the clearance for initial fuel loading and the first act of criticality of KKNPP-1 was given on 10th August 2012. There is only one AERB press release during September which details the annual report for 2011-12.

According to the AERB website, clearance for FAC was given on two dates.(i)

11-07-2013AERB grants Clearance for First Approach to Criticality for the first Pressurized Water Reactor in the country Latest


10-08-2012AERB grants Clearance for Initial Fuel Loading and First Approach to Criticality of Unit-1 of Kudankulam Nuclear Power Project


04-09-2012AERB releases the Annual Report for the year 2011-12

The IFL and FAC are statutory events and the regulator’s documentation is expected to be accurate and not a patchwork of information as it appears to be now. It appears that the Department of Atomic Energy [DAE] and its affiliates – the Nuclear Power Corporation of India [NPCIL] and AERB – are in a war against themselves and the nation, in a battle, it seems, at least from the secrecy and opacity of their actions. According to media reports, NPCIL had completed the IFL on 2 October 2012, some 250 days ago. The NPCIL or AERB did not say what they were doing or why they were idling so long with 80 tons of low enriched nuclear fuel inside the reactor. The last VVER-1000 reactor commissioned at Volgadonsk in Russia had achieved its FAC on the 29th day of IFL.

2. The spurious signals from instrumental and control cables

While the authorities have been silent on the issue, Dr A Gopalakrishnan, the formerly Chairman of AERB wrote that the “spurious signals of untraced origin are interfering with many of the instrumentation cables of paramount importance to safety, like the reactor neutron chamber output lines, wiring of the safety and shut-off rod control systems, etc.” According to Dr Gopalakrishnan, “such phenomena belong to a broad class of problems known as Electro-Magnetic Interference (EMI). A very rudimentary example of EMI, for instance, is that of a power-carrying, unshielded cable that would generate a surrounding electro-magnetic field, that in turn could induce a voltage/current in a nearby instrumentation or control cable. This spurious input can add to or subtract from the “real” signals, thereby sending erroneous control inputs to a variety of crucial safety systems, possibly leading to unpredictable and serious malfunctions or accidents.”i Responding to this revelation, KKNPP site director R.S. Sundar stated that “we will prove ourselves by commissioning the plant successfully” and “a small team of Nuclear Power Corporation of India Ltd (NPCIL) officials has been tasked to clarify the I&C [instrumentation and control] issues.”ii The promised clarifications have not been issued so far. Dr Gopalakrishnan is not anti-nuclear; he is an eminent nuclear scientist concerned with safety of the unit personnel and the downwinders and the downstreamers. His article was published as an opinion piece in an English national daily. If the neutron monitors and other instruments were all fine-tuned, the KKNPP station director could have shown them to him or if the security regime does not permit it, shown him all the relevant documentations. He himself would have retracted his article. However, the small committee has not come out with any clarification so far.

3. Three hundred Hiroshima bombs

The fresh batch of fuel in 163 fuel assemblies to be loaded in KKNPP-1 has a mass of 80 tons, of which the fissile isotope U235 will be about 3 tons, equal to the critical mass for some 300- 400 Hiroshima type bombs. In a reactor core, the chain reaction is initiated by a neutron. A fuel-loaded reactor pressure vessel [RPV] has two sources of neutrons: (a) from the spontaneous fission of U235 and U238 atoms and (b) neutrons produced by the cosmic rays. The fuel assemblies are immersed in demineralized and deionized water mixed with boric acid. The RPV is also loaded with 121 control rods, which also contain boron carbide. The boron in the coolant and the control rods eats up the neutrons and prevents a chain reaction from happening without an operator’s intervention.

The operators of an NPP cannot reach anywhere near the core where the fissions take place. There are neutron sensors kept in the fuel assemblies which send their signals through cables to the neutron flux monitor in the control room. This is the only source from which the operator knows the neutron density and the levels of fission activity inside the core – in a larger sense, it relays important information about how the reactor will perform. The neutron monitoring system has to be fully functional throughout the life of the reactor. If it does not work, the only option is to remove the fuel from the reactor pressure vessel immediately. If the spurious signals are interfering the functioning of neutron monitors, the reactor is in a danger zone. In 2008, the AERB “recommended that calibration/sensitivity checks of neutronic instruments should be done at site, as part of commissioning”.iii

4. Reactor’s instrumentation and control

The architecture of the instrumentation and control (I&C) system, together with plant operations personnel, serves as the “central nervous system” of a nuclear power plant (NPP). “Through its various constituent elements (e.g., equipment, modules, sensors, transmitters, redundancies, actuators, etc.), the plant I&C system senses basic physical parameters, monitors performance, integrates information, and makes automatic adjustments to plant operations as necessary. It also responds to failures and off-normal events, thus ensuring the goals of efficient power production and safety. Essentially, the purpose of the I&C system architecture at an NPP is to enable and ensure safe and reliable power generation.”iv

5. IAEA Guidelines on the commissioning of reactors

5.1 Initial Fuel loading [IFL]

IAEA’s Guidelines for the commissioning for nuclear power plants [2003] lists 13 prerequisites to be satisfied before fuel loading. The first one deals with the fuel itself and the second one is about the instrumentation and control system. Relevant excerpts from the IAEA document are given below.v

5.1.1. “operability of nuclear startup instrumentation, in terms of proper calibration, location (source–fuel–detector geometry) and functionality, including aural and visual alarm indications in the control room as well as the response of the instrumentation to a neutron”.

5.1.2. “5.36. Fuel should be loaded in accordance with a written procedure to ensure safe and correct loading. Attention should be paid to adequate monitoring of the neutron flux for the timely indication of potential inadvertent criticality. Adequate means should be available to restore the shutdown margin in the event of an inadvertent approach to criticality.” (p.36)

5.1.3. “5.39. For the fuel loading procedure, the following should be required, as appropriate: periodic recording of data; audible indication of flux increases; monitoring of neutron count rate instruments when fuel is being inserted and/or when other operations are performed that could affect core reactivity. In addition, subcriticality checks should be performed at regular steps in the loading procedure in order to determine safe loading increments for subsequent loading. Predictions of the behaviour of the core in terms of its reactivity should be available for evaluation of the subcriticality margin. If actual measurements deviate from the predicted values, procedures should require loading to be stopped until the circumstances have been analysed, the reasons for the deviations have been determined and any appropriate corrective action has been taken”.(p.37)

5.1.4. “A–15. Tests on instrumentation and control systems cover control functions for normal operation and instrumentation to provide alarms for off-normal conditions in order to initiate corrective action and to monitor events. Instrumentation and control systems should be tested over the design operating range, and limiting malfunctions and failures should be tested by simulation. Any defensive measure to ensure the integrity of the instrumentation and control system also has to be tested (such as electromagnetic converter protection)”. (p.55)

5.2 First Act of Criticality [FAC]

5.2.1. “5.44. Before the approach to criticality is started, operability of the automatic reactivity shutdown devices shall be ensured and appropriate startup monitoring instrumentation shall be available to initiate shutdown devices when necessary.” [emphasis ours]

5.2.2. “5.45. Measures should be taken to ensure that the startup proceeds in a safe and orderly manner. For this purpose, changes in reactivity should be continuously monitored and evaluated so that the prediction of the point of criticality can be continually checked. The sequence and magnitude of changes in reactivity, made by means of removal of the absorber and/or adjustment of the moderator level, should be defined in the procedures.”

5.2.3. “5.46. Instruments for neutron monitoring at startup should be calibrated before the approach to criticality and the required minimum neutron count rate should be obtained, using in-core neutron sources if necessary. Trip set points should be reduced to the minimum level compatible with the demands of the tests scheduled in this substage.”

5.2.4. “5.47. The procedures for achieving criticality after significant subcritical multiplication has been experienced require a cautious approach, through continuous monitoring of the neutron flux and predictions of the point of criticality and successively smaller adjustments in positive reactivity. The objective of these actions is to avoid passing through the point of criticality with a high rate of change in neutron flux (i.e. with a short period of multiplication). After criticality has been achieved, a conservative startup rate of flux increase should be used in attaining low power”

6. The Repeat Hot tests after fuel loading

According to media reports, no abnormality was detected during the first hydro-test done in December 2010. Media reports said that the first reactor was fuel-loaded on 2 October 2012. On January 25, 2013, the Chairman of the AERB told PTI: ‘“We have given permission to repeat the hydro-tests (full systems test) at KKNPP-1 yesterday,” to be “carried out over the next fortnight. The systems will be heated up and a number of tests will be carried out. We will review the report and if everything is within the laid parameters, a go-ahead will be given for the next step.”vi On January 26, 2013, the Hindu, reported from New Delhi that “the plant was almost on the verge of being commissioned last month, but got stopped after the authorities decided to do some maintenance work when some of the parameters were found to be not falling within the prescribed norms in toto”.vii Hydro-test is conducted before fuel-loading. If it were to be conducted again, the fuel should be removed from the reactor.

7. The First Act of Criticality

As part of the Initial Start of the Unit [ISU] or the First Act of Criticality [FAC], the boron concentration in the coolant is reduced first and the control rods are removed. The neutron sources, such as Plutonium-238 [Pu-238], affixed on the control rods mentioned above are released so that the neutron population in the fuel assembly environment is gradually and systematically increased. Whilst this source of neutrons is not essential to start the chain reaction, it provides a shutdown neutron population that can be detected by instruments. The approach to criticality can thus be more observable. Whether or not a source is loaded, the reactor will go critical at the same control rod position. When the assembly is in the fuel pool (outside the reactor) such criticality is not possible because of its geometry [spacing]. Even without any operator action, like lifting of the control rods, the neutron density in the RPV may increase and if it increases abnormally, the operator has to act to prevent an inadvertent criticality. In the rarest of cases, a sustained chain reaction, known as inadvertent criticality, and a run-away reaction leading to a major accident is possible. In 1942, Enrico Fermi’s first nuclear reactor – known as Fermi’s Chicago pile, which attained criticality in December, 1942 did not have any neutron instrumentation. They still achieved a sustained chain reaction, which was maintained for 28 minutes. However, Fermi’s pile had only 30 kg of Uranium-235 and the US Army did not spend much money on instrumentation. The Kudankulam pile has 3000 kg of U-235 and NPCIL has spent more than Rs 1000 crores on instrumentation.

8. The First Inadvertent Criticality

The first inadvertent criticality happened in the US weapon laboratories, where young and brave scientists were tinkering with the materials produced in Fermi’s factories. During the Manhattan Project days of nuclear experiments critical mass of fissile materials such as Uranium-235 and Plutonium-239 was done by bringing masses of fissile materials to near-critical levels to their critical mass values. Richard Feynman, compared those experiments to “tickling the tail of a sleeping dragon”. Louis Slotin, a scientist of the Manhattan Project, who assembled the core for Trinity, the first detonated atomic device, was known as the “chief armorer of the United States”. On 16 July 1945, Slotin tasted the nuclear criticality, 23 days ahead of thousands of children, women and men in Hiroshima. Slotin died a slow and painful death due to acute radiation syndrome.viii Reactor operators may forget Fermi and Feynman, but not Slotin. There have been 65 criticality accidents worldwide since the nuclear age began in 1942, 33 of them occurred in the United States and 19 in the former Soviet Union. One study on accidents up until 2000 showed that “these inadvertent critical excursions yielded prodigious amounts of neutrons and ionizing radiation within very short periods of time. Of these, 23 have occurred in the direct vicinity of individuals killing 21 and injuring 27 persons. All of the injured victims were reported to have suffered from acute radiation sickness, and at least 7 suffered permanent disabilities, including at least 4 with amputations of arms or legs”.ix The IAEA’s 2003 Guideline on the commissioning of commercial reactors discusses inadvertent criticality four times. In USA, 10 CFR 70.24 deals with the action to be taken to avoid inadvertent criticality.x

9. Summary of the events thus far:

9.1. AERB gave consent for IFL and FAC on10 August 2012. This event in recorded on their website.
9.2. AERB abruptly withdrew the consent on 13 September 2012, permitted fuel loading on 20 September 2012, fuel loading began on 22 September 2012 and was completed on 2 October 2012. On 25 January 2013, AERB permits NPCIL to repeat a hydro-test. The first hydro-test was done in December 2010. If the reactor failed in 2010 hydro-test, fuel loading should not have taken place. Moreover, hydro-test is not done on a fuel-loaded reactor. There is no record of any of the events in this paragraph on the NPCIL or AERB websites.

9.3. On 19 June 2013, Dr Gopalakrishnan says that there are serious problems with the neutron monitors and other instrumentations at KKNPP. IAEA states that if neutron monitors and related instrumentations are not fine-tuned, fuel loading or approach to criticality should not be pursued.

9.4. The KKNPP Station Director states that a committee of NPCIL scientists will give clarifications on the points raised by Dr Gopalakrishnan.

9.5. On 11 July 2013, on the 21st day of Dr Gopalakrishnan’s revelation, the AERB gives permission for the first act of criticality. This is recorded on the AERB website.

10. Conclusion

IFL and FAC are risky reactor operations which could be linked to a possibility of an event known as inadvertent criticality. A recent IAEA draft document has the following wise words: “Despite all the precautions that are taken in the handling and use of fissile material there remains a possibility, while very small, that a failure (i.e. instrumentation and controls, electrical, mechanical or operational errors) or an incident may give rise to a criticality accident. In some cases, this may give rise to exposure or the release of radioactive materials within the facility and/or into the environment, which may necessitate emergency response actions. Adequate preparations should be established and maintained at local and national levels and, where agreed between States, at the international level to respond to nuclear or radiological emergencies”.xi [emphasis ours] We expect that India’s political and scientific leadership also shares the wisdom of IAEA and desist from tickling the dragon’s tail.

Dr. V. Prakash
Prof V. Prakash, Ph.D., teaches in a reputed engineering college in South India. He has developed new means of Energy Efficiency Improvement measures in Electrical Motors, which form major part of the electrical load. The outcome of his research is particularly applicable to conditions prevailing in developing countries including India. He has written articles highlighting the importance of decentralized energy production. Email: sugiprakash@gmail.com

Dr Joseph Makkolil is a physicist [nano-sciences] with the Inter-University Centre for Nanomaterials and Devices [IUCND], Cochin University for Science and Technology [CUSAT]. He has been active in the Peoples’ Science Movement for three decades.

K Sahadevan is a science writer, specializing on environmental issues and also part of the movement-Youth for Environment and Justice.

VT Padmanabhan is an independent expert on radiation and human health, has done studies genetic effects of radiation and has written extensively on the safety lapses of KKNPP.

Drs R Ramesh and V Pugazhendi are family physicians and part of the Doctors for a Safe Environment [DOSE]. Their recent book on the volcanoes in sea off Kalpakkam has been appreciated by the nuclear establishment and AERB is planning more detailed studies.

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