Is the edifice of radiation protection built on a lie?

S & T

Published: January 26, 2012 01:39 IST | Updated: January 26, 2012 01:39 IST

Is the edifice of radiation protection built on a lie?

The Linear No Threshold concept assumes that the risk from radiation exposure varies linearly with total dose with no threshold

Recently, Edward Calabrese, an environmental toxicologist at the University of Amherst found out that Dr Hermann J. Muller, famous radiation geneticist knowingly lied in his Nobel Prize lecture when he claimed that there was “no escape from the conclusion that there is no threshold.” Calabrese described his discovery in September in Archives of Toxicology and Environmental and Molecular Mutagenesis

In 1927, Muller discovered that x-ray irradiation produces mutations in male fruit-fly germ cells. For this, he received the Nobel Prize in Physiology or Medicine in 1946. Many believe that Muller's assertion became a corner stone of radiation protection. This is the Linear No Threshold (LNT) concept which assumes that the risk from radiation exposure varies linearly with total dose with no threshold and any dose however small has an adverse effect.

Expert bodies accepted this model because of its simplicity in the management of radiation protection programmes.

“However, it has done much damage to speak of ‘no safe level of radiation' in scaring not only the public, but also those professionally involved in peacetime health physics who have not been involved in high levels and emergency situations,” Allen Brodsky, Adjunct Professor of Radiation Science, Georgetown University responded to an e-mail query.

In response to an e-mail query Calabrese disclosed that a reviewer of his article on the history of dose-response argued that he had not done a good job on the Muller section and key early radiation mutation studies. Calabrese found that a paper from the University of Rochester by Curt Stern and Casper on fruit-fly irradiation and germ cell mutation was published in 1948 but it was actually completed in August of 1946.

“This study was very important because it did not support a linear dose response and because it was the strongest study to date...using the lowest dose rate etc. I knew that Muller gave his Nobel Prize lecture on Dec. 12, 1946. So the question was whether Muller was aware of the new findings before his major speech,” Calabrese replied

By reviewing Stern's correspondence with Muller, Calabrese established that Muller knew of the findings which contradicted his theory a month prior to the Nobel Lecture.

Calabrese asserts that Muller's passionate beliefs influenced the way government and society viewed the risks of low doses of radiation. The 1956 recommendations of the US National Academy of Sciences (NAS) BEAR (Biological Effects of Atomic Radiation) I Committee reflected these views. Regulating ionizing radiation as if there was no safe dose began!

James Schwartz, a biographer of Muller, Kenneth Muller, Hermann Muller's grandson and Elof Axel Carlson, Muller's former student do not agree with Calabrese. Some feel that Calabrese, a supporter of radiation hormesis (beneficial effect) has conflict of interest. The balance of evidence shows that the edifice of radiation protection is not built on a lie.

Dr Evan B. Douple, Associate Chief of Research at the Radiation Effects Research Foundation, Hiroshima, does not think that the LNT hypothesis would have lost its applicability if Professor Muller would not have made the passionate statement in his speech.

“……. by the time the BEIR (Biological Effects of Ionizing Radiation) committees of the National Academy of Sciences began updating the risk estimates, the mutation risk was superseded by the risk of cancer. Having been intimately involved with the BEIR VI and BEIR VII studies, I can assure you that the voluminous data reviewed by the committee members that related to supporting or refuting LNT, was not swayed or overly influenced by the shape of a dose-response curve in the mutation work of Muller,” Douple responded. (Dr Douple was Director, Board on Radiation Effects Research, National Research Council)

He is not even sure that Calabrese's interpretation and assessment that Muller was deceptive in his presentation is necessarily accurate or fair.

“Although somatic mutations became a dogma for radiation carcinogenesis, the LNT for carcinogenesis was based on (a) analyses of cancer induction in rodent models, (b) biophysical characteristics of energy deposition, ionizations, and DNA damage in cells, and (c) the early epidemiological studies of cancer in the Japan A-bomb survivors,” he clarified in an e-mail.

He does not think that the conjecture and personal interpretation of an untestable accusation will have significant impact among the radiation protection community.

Prof Ludwig E. Feinendegen, Heinrich-Heine University, Germany thought that “the new revelations on low-dose effects in the realm of biological responses are making an impact on the radiation protection community — as it appears currently from the defensive manner of their arguments for keeping the LNT model, at least for the time being. Calabrese has done us a great favour by his new paper on Mueller's mistake.”

That there is no safe level of radiation continues to be a useful assumption in radiation protection. It is yet to be proved as a scientific fact.

Douple believes that the exhaustive efforts of those who claim that demonstrating hormesis (beneficial effect) or the presence of thresholds will revolutionize the radiation protection field are misguided.

“We need to educate the public regarding the importance of ‘acceptable levels of risk'—levels that are believed to include risks, but risks for adverse effects that are so small that one would not be able to observe and measure an excess of the effects with a realistic study. Only then will the fear and paranoia associated with radiation effects gradually become less and less and sources for energy production can be fairly and objectively be evaluated,” Douple proposed as a realistic way forward.

Regulators want dose limits for enforcing radiation protection. What is the threshold dose value they will accept for enforcement? Calabrese and his followers have not yet responded to my query.

The French Academy of Sciences, the only scholarly body which has views closer to those of Calabrese on hormesis conceded that on the basis of present knowledge, it is not possible to define the threshold level (between 5 and 50 mSv) or to provide the evidence for it. The dose limit for workers recommended by the International Commission on Radiological Protection (ICRP) is 20 mSv per year averaged over five years with no year exceeding 50 mSv. The dose levels to radiation workers achievable are so low that the risk from them is negligible. Negligible risk is no risk at all. That we cannot rule out beneficial effects of radiation is also a comforting thought.

K.S. Parthasarathy

Raja Ramanna Fellow, Department of Atomic Energy (ksparth@yahoo.co.uk)

Keywords: radiation exposure

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Printable version | Jan 26, 2012 8:32:36 AM | http://www.thehindu.com/sci-tech/article2831847.ece

© The Hindu

Anti nuclear activists are lying or are ignorant

With malice towards none, and knowledge for all!

Those keen to sift facts from fiction may read the following note:

There is widespread wrong information about the status of nuclear power in USA after 1979, the year in which the accident occurred at the Three Mile Island nuclear power station.

Many anti nuclear activists state that since 1977, USA has not built any new nuclear power plant. There is a little confusion here. It is true that USA has not issued any new licence to construct a nuclear power plant. Government approved  up-rating the power of existing reactors by 6000MW from 1977 to 2011. From 2011 to 2015, 3211 MWe will be added.

Electric companies connected 50 out of the 104 currently operating nuclear power plants in USA to the grid after 1979, the year in which the Three Mile Island accident occurred. Nineteen of them after 1986, the year in which the Chernobyl accident occurred. Fifty three out of the 59 French reactors came on line after 1979.

The net capacity factor  of a power plant is the ratio of the actual output of a power plant over a period of time and its potential output if it had operated at full  capacity the entire time.

The capacity factor of nuclear power reactors in USA averaged about 57 % in 1980. It increased gradually. From 2004 till 2010 (the latest data)it averaged over 90%. Twenty two US nuclear power reactors out of the 104 exceeded  a capacity factor of 100%. In 2010 the capacity factors of other modes of power generation in % were: Biomass 85.5;.Geothermal 71.6;Coal (Steam turbine) 65.4;Gas(Combined cycle) 45.8;Hydro 29.4; Wind 29.1;Solar 17.7;Gas (Steam turbine) 12.9; oil (steam turbine) 8.9

Anti-nuclear critics claim that Russia stopped constructing nuclear power after 1986, the year in which the accident occurred at the Chernobyl nuclear power station.

What is the factual position?

 Russian power utilities started commercial operation of eight nuclear power reactors after 1986 . One of them in May 1986 a month after the Chernobyl accident. The last one of 950 Mgawatt became critical on November 11, 2011 and is operating at 50% power as one December 13, 2011.

Russia currently has an installed nuclear power capacity of 24,164 MWe from 33 reactors. It has started construction and  planned and proposed to erect 53 nuclear power reactors with a total capacity of over 50,000 MWe

China operates 15 reactors with a total capacity of 11,881 MWe starting from 1994. Nuclear power reactors under construction and  planned number 77 with a total capacity of 85,750MW.

Additional reactors are planned, including some of the world's most advanced, to give a five- or six-fold increase in nuclear capacity to at least 60 GWe by 2020, then 200 GWe by 2030, and 400 GWe by 2050. 

Until March 2011, Germany generated 25% of its electricity from nuclear energy using 17 reactors.In 1998, Germany decided to phase out nuclear power; in 2009 Government cancelled this policy but shut down eight reactors post Fukushima even before the factual position about the accident was known.

 French and Czechs are happy going to their banks. To compensate for the power generated by the seven reactors, Germany imports power from France and Czech Republic. France’s share of export to Germany increased by 50% in the first half of the year; Czech’s share went up by a whopping 673%(The Sydney Herald, November 26, 2011)

According to the paper, at peak times, up to four nuclear power stations in France and the Czech Republic are running just to cater to the demands of Germany

Kudankulam Reactors: Nuclear myths

PTI FEATURE

VOL NO XXVII(46)- 2011                                    November 12, 2011

           

                                                                                              SCIENCE & TECHNOLOGY

                                                                      PF-183/2011

Kudankulam Reactors: Nuclear Myths

By Dr K S Parthaarathy

Recently, an energy specialist showed that under realistic assumptions, India will not be able to maintain a modest  annual per capita power need of about 2000 kWh by 2070 by  renewable energy alone; the maximum potential for renewable will be 36.1%. (Current Science, Sept 10, 2011), Fossil fuel and nuclear will continue to play their role. He believes that hundred years later, India has to depend on nuclear power only.

Recently anti nuclear activists scored over staunch nuclear power proponents by planning a fast of infants against Kudankulam project! Infants cannot protest; parents forced them to fast. Mercifully it was only for one hour. I do not know whether it is legal or whether it may be considered as child abuse. It was a clever ploy to get publicity. Next, the activists may argue that reactors will kill babies and babies’ babies!

Misinformation, misconcepts and other issues are coming in the way of commissioning the first Generation 3+ advanced nuclear power reactor in India.

In an article titled “India: People power vs. nuclear power (The Daily Star, October 17, 2011), Praful Bidwai claimed that  Kudankulam reactors will daily draw in millions of litre of freshwater, and release it at a high temperature into the sea, affecting the fish catch on which lakhs of livelihoods depend.

The reactors will not use fresh water but water from a desalination plant erected at site. The temperature of water from the reactors discharged in to the sea will be in compliance with the stipulations of the Ministry of Environment and Forests (MOEF), Government of India. This discharge will not affect fish catch nor will it adversely affect marine ecology.

Bidwai’s observation that the reactors are being built within a one-kilometre radius of major population-centres, violating the 1.6-km "nil-population" zone stipulation is not true.

Nuclear Power Corporation India Limited (NPCIL) keeps an area of 1.5 kilo-metre radius

around the reactors under its exclusive control as required by the Atomic Energy Regulatory Board (AERB) Code on Safety in Nuclear Power Plant Siting. The site satisfies other AERB stipulations.AERB allows the reactors to release effluents and emissions routinely. NPCIL ensures that the limits for releases prescribed by the Atomic Energy Regulatory Board (AERB) are not exceeded.

Bidwai scares people by describing radioactivity as “a regular poison you can’t see, touch or smell”. He knows that these shortcomings have not come in the way of using radiation in medical, industrial and research applications. That we can measure radioactivity and radiation accurately at extremely low levels helps to enforce regulatory limits on releases and emissions.

Bidwai notes that scientific studies covering 136 nuclear sites in seven countries showed some adverse health effects. The reference is to a paper by Baker and Hoel in the European Journal of Cancer Care (2007). It offered some evidence of elevated leukemia rates among children living near nuclear facilities. The authors described the limitations of the study and also referred to studies which did not show any effect. They referred to studies in which leukemia effect was seen before the nuclear facilities started operation!

 Specialists criticized the study for its methodological weaknesses, such as combining heterogeneous data (different age groups, sites that were not nuclear power plants, different zone definitions), arbitrary selection of 17 out of 37 individual studies, exclusion of sites with zero observed cases or deaths, etc (Wikipedia).

Though the paper deals with leukemia only and no other effects, Bidwai claimed that the study shows “abnormally high leukemia rates among children and higher incidence of cancers, congenital deformities, and immunity and organ damage”. Nuclear critics have a way of shaming epidemiologists and other specialists by cherry picking data and inventing conclusions!

 

 The Chernobyl accident caused two deaths immediately and 28 deaths within a few months. According to the United Nations Scientific Committee on the Effects of Atomic Radiation (2011), there were 15 more deaths due to thyroid cancers. Opinions on number of potential deaths differ.

Bidwai claimed (34,000 to 95,000) deaths, lot less than one million predicted by a Greenpeace supported report. He claimed that the numbers of deaths are still “climbing”. Such myths cloud the reality that no such dramatic increases have been identified. Actually radiation scaremongers caused 100,000 to 200,000 abortions in Europe!

A nuclear reactor will not explode like a nuclear bomb as its fuel contains only less than 5% enriched uranium. This is a basic lesson in reactor physics. Bidwai’s argument that a reactor is a barely controlled nuclear bomb has no scientific basis.

Bidwai recommends that “there are perfectly sound, safe, cost-competitive renewable energy alternatives to nuclear power”. We do not now have the luxury to choose any mode of power generation. The Government’s programme to erect solar generating capacity of 20,000 MWe by 2020, equal to that of the then nuclear capacity may be seen in that context.. On a percentage basis, India now produces more renewable energy than Germany.

Ranked fifth in the world, India’s installed wind-power capacity is 14,158 MW, three times our nuclear power capacity.

Recently, an energy specialist showed that under realistic assumptions, India will not be able to maintain a modest  annual per capita power need of about 2000 kWh by 2070 by  renewable energy alone; the maximum potential for renewable will be 36.1%. (Current Science, Sept 10, 2011), Fossil fuel and nuclear will continue to play their role. He believes that hundred years later, India has to depend on nuclear power only.

A Mumbai daily quoted Dr M P Parameswaran, a DAE veteran (whatever that may mean) as saying that “No N-plant in India safe”-an opinion, not based on facts.

“We are yet to master the technology to decommission a reactor. That is why we keep on extending the life period of some of the reactors which have outlived their utilities”, he added another skewed opinion.

Like other anti nuclear activists, he believes that since 1977, USA has not built any new nuclear power plant. There is a little confusion here. It is true that USA has not issued any new licence to construct a nuclear power plant.

Electric companies connected 50 out of the 104 currently operating nuclear power plants in USA to the grid after 1979, the year in which the Three Mile Island accident occurred. Nineteen of them after 1986, the year in which the Chernobyl accident occurred. Fifty three out of the 59 French reactors came on line after 1979.

He says that in 1974, all US Nobel Prize winners were opposed to nuclear power plants. It is very unlikely. In spite of the “opposition”, nuclear electricity has increased over seven fold during 1974 to 2010.

The one Nobel Laureate, Roald Hoffmann, I interviewed a few years ago, supports nuclear power; he wanted nuclear proponents to highlight its environmental advantages. Currently, Steven Chu, a Nobel Laureate is the US Energy Secretary ; he consistently votes for nuclear power

Dr Parameswaran asks why the Indian nuclear establishment is silent about the pollution caused to the marine wealth of the country by the coolant water discharged to the sea-another misconception!

A thermo-ecology study carried out at Kalpakkam and Kaiga stations with several experts from institutions such as the National Institute of Oceanography (NIO), Central Electro Chemical Research Institute (CECRI) and several universities in the country did not reveal any adverse impact on marine ecology near nuclear power plant sites.

With the erection, commissioning and operation of the reactors at Kudankulam, Indian scientists and engineers will demonstrate how they can effortlessly absorb and master Generation 3+ nuclear power technology. This will enable the country to face the challenges in electrical capacity addition with renewed vigour and confidence.

                       

                                                                                               -PTI Feature

How safe Kudankulam nuclear power reactors are

K S Parthasarathy

The Hindu SAFETY PRECAUTION: The reactor has double containment and the annulus between the two is kept at negative pressure to prevent any radioactivity if released, from escaping. Photo: A. Shaikmohideen

Twenty-five 1,000 MW VVER reactors are in operation in five countries. Kudankulam plants have more advanced safety features

The Unit 1 of the Kudankulam Nuclear Power Project (KKNPP) is under advanced stage of commissioning. Construction of Unit 2 is progressing well. In the meanwhile, sections of the public have expressed apprehensions about the safety of these reactors. Lack of understanding, misconceptions and misinformation contribute to this. Apparently, the Fukushima accident and other issues influence them.

Twenty-five VVER 1,000 MW reactors are in operation now in five countries. Nine more are under construction. The version offered to India is more recent and has more advanced safety features.

Satisfactory

Atomic Energy Regulatory Board (AERB) satisfied itself that the plant is of proven design. Indianspecialists visited Russia and had significant exchange of information from nuclear power plant designers. Indian engineers had completed licensing training process in either Balakova nuclear power plant (NPP) or Kalinin NPP.

The AERB and Bhabha Atomic Research Centre (BARC) and specialists from reputed academic institutions such as the Indian Institute of Technology, Mumbai, the Boilers Board and the Central Electricity Authority have spent over 7,000 man-days in carrying out the safety review and inspection of the Kudankulam reactors.

These system-wise reviews were comprehensive. AERB used relevant documents from the International Atomic Energy Agency (IAEA) and IAEA's peer reviews of VVER for safety assessment of these reactors.

These reactors belong to the Generation 3 + category (with more safety features than Generation 3) with a simpler and standardised design.

The Kudankulam site is located in the lowest seismic hazard zone in the country. The water level experienced at the site due to the December 26, 2004 tsunami, triggered by a 9.2 earthquake was 2.2 metres above the mean sea level. The safety-related buildings are located at higher elevation (SafetyDiesel Generators,9.3 metre) and belong to the highest seismic category and are closed with double sealed, water leak tight doors.

The reactors have redundant, diverse and thus reliable provisions needed to control nuclear reactions, to cool the fuel and to contain radioactive releases. They have in–built safety features to handle Station Black Out.

Besides fast acting control rods, the reactors also have a “quick boron injection system”, serving as a back-up to inject concentrated boric acid into the reactor coolant circuit in an emergency. Boron is an excellent neutron absorber.

Retains radioactivity

The enriched uranium fuel is contained in Zirconium-Niobium tubes. It can retain the radioactivity generated during the operation of the reactor. The fuel tubes are located in the 22 cm thick Reactor Pressure Vessel (RPV) which weighs 350 tonnes. RPV is kept inside a one metre thick concrete vault.

The reactor has double containment, inner 1.2 metre-thick concrete wall lined on the inside with a 6 mm layer of steel and an outer 60 cm thick concrete wall. The annulus between the walls is kept at negative pressure so that if any radioactivity is released it cannot go out. Air carrying such activity will have to pass through filters before getting released through the stack. Multiple barriers and systems ensure that radioactivity is not released into the environment.

KKNPP-1&2 has many new safety systems in comparison with earlier models. The Four-train Safety-System instead of just one system leads to enhanced reliability. The reactors have many passive safety systems which depend on never-failing forces such as gravitation, conduction, convection etc.

Decay heat removal

Its Passive Heat Removal System (PHRS) is capable of removing decay heat of reactor core to the outside atmosphere, during Station Black Out (SBO) condition lasting up to 24 hours. It can maintain hot shutdown condition of the reactor, thus, delaying the need for boron injection.

It works without any external or diesel power or manual intervention.

The reactors are equipped with passive hydrogen recombiners to avoid formation of explosive mixtures .The reactors have a reliable Emergency Core Cooling System (ECCS).

Core catcher

Located outside the reactor vessel, a core catcher in the form of a vessel weighing 101 tonnes and filled with specially developed compound (oxides of Fe, Al & Gd) is provided to retain solid and liquid fragments of the damaged core, parts of the reactor pressure vessel and reactor internals under severe accident conditions.

The presence of gadolinium (Gd) which is a strong neutron absorber ensures that the molten mass does not go critical. The vessel prevents the molten material from spreading beyond the limits of containment. The filler compound has been developed to have minimum gas release during dispersal and retention of core melt.Rat

Fukushima plant spread gloom; the Onagawa plant close to it, in contrast, shut down safely; its gym served for three months as a shelter for those made homeless (Reuters, Oct 21). The plant showed that it is possible for nuclear facilities to withstand even the greatest shocks and to retain public trust.

Kudankulam reactors are more modern and safe. Exercising due diligence, AERB issued clearances to it at various stages. Public may rest assured thatIndian scientists and engineers will operate the reactor safely.AERB shall continue to enforce measures to maintain safe operation of these advanced nuclear power reactors.

The author is Raja Ramanna Fellow, Department of Atomic Energy and can be reached at ksparth@yahoo.co.uk

Keywords: Kudankulam nuclear plant, KNPP, nuclear safety, nuclear power

Published: July 7, 2011 01:55 IST | Updated: July 7, 2011 02:05 IST

Is radiation a must for cells' normal growth?

K.S. PARTHASARATHY

   

 

 

 

AP Scientists monitored the bacterial growth by assaying for protein, optical density of the cultures and cell agar plate counts. File photo

Both studies demonstrated a stress response when cells were grown under reduced radiation conditions

The March, 2011 issue of Health Physics published an interesting paper titled “Exploring Biological Effects of Low Level Radiation from the other Side of Background” summarizing the results from a Low Background Radiation Experiment carried out in Waste Isolation Pilot Plant (WIPP), an underground lab at New Mexico and those from a sister experiment conducted at the Lovelace Respiratory Research Institute, Albuquerque.

The recommendation

This was part of a $150 million, five-year long, low-dose research project recommended by 26 scientists highly regarded in radiobiology research community and representing competing radiation effects hypotheses.

WIPP is located at a depth of 650 metre in the middle of a 610 metre thick ancient salt deposit that has been stable for more than 200 million years. The radioactivity content of the salt deposit is extremely low.

The radiation levels in the lab are ten times lower than the normal natural background radiation levels. The contribution to the background from potassium-40, the only identifiable radionuclide present in the lab can also be reduced further by using a modest amount of shielding. Massive, 650 metre thick, salt reduced the cosmic ray background.

Highly resistant

Researchers incubated Deinococcus Radiodurans, a bacterium which is highly resistant to radiation, above-ground and in WIPP in a 15 cm thick pre-world war II steel chamber; that steel is not contaminated by traces of radio-nuclides from nuclear weapons fallout.

The surface radiation levels averaged 3.1 micro Roentgen per hour; the level underground was 0.6 microroentgen per hour and in the preWW II chamber it was as low as 0.2 microroentgen per hour. [Roentgen is a unit of radiation exposure. It depends on the ability of radiation to ionize air. Radiation exposure is one roentgen when the ionizing radiation releases one esu (electrostatic unit of charge) of charge in a cc of air at Normal temperature and Pressure (NTP)]

Scientists monitored the bacterial growth by assaying for protein, optical density of the cultures and cell agar plate counts. Though data had relatively high variability, the three indicators of cell growth demonstrated that the cells grown underground were inhibited and grew increasingly so with increasing time underground (Health Physics, 2011).

In the second experiment, researchers exposed a type of human lung cells at 1.75 mGy per year; another sample of cells to 0.3 mGy per year by using a 10 cm lead shield. The former corresponds to a typical background radiation level. Gy is a unit of absorbed dose, when the radiation energy absorbed in material is one joule per kg.

Since Gy is a very large unit, submultiples such as mGy — milli Gy (one thousandths of Gy) are used.

They controlled the temperature, carbon dioxide and humidity levels in the two incubators in which the cells were placed ensuring that these parameters were statistically the same.

Standard methods

They analyzed the exposed cells directly by standard methods for the presence of heat shock proteins or by exposing the cells to a single x-ray dose of 10 cGy and then assayed for heat shock proteins.(cGy or centiGy is one hundredth of a Gy)

The researchers found that shielding cells from natural radiation upregulated ( initiated the process of increasing the response to a stimulus) the expression of two out of three stress proteins and follow on x-ray exposure further upregulated expression.

They obtained similar results with the bronchial epithelial cells. Both studies demonstrated a stress response when cells were grown under reduced radiation conditions. Does it show that radiation is necessary for normal growth of cells?

A few years ago, mainstream scientists should have shown a smirk on their face followed by a grin if they heard this conclusion. Not any more. Many outstanding specialists feel that at the end of five years, they may be able to develop a model based on exposing organisms to near zero levels of radiation, a model based on sound science.

Profound impact

It may lead to increasing the levels of radiation considered safe; it will have a profound impact on the economics of decommissioning nuclear facilities, long term storage of radioactive waste, construction of nuclear power facilities among others. This requires drastic changes in public perception.

Raja Ramanna Fellow, Department of Atomic Energy

ksparth@yahoo.co.uk

Keywords: radiation effects , K S Parthasarathy

Radiation dose limit for eye lens slashed

K.S. Parthasarathy

 

The Hindu A Phakonit Cataract operation in progress at a hospital in Guntur. File photo

The lens of the eye is one of the most radiation sensitive tissues in the body. If the eye lens which is normally crystal clear receives a high enough radiation dose it may become partly cloudy or totally opaque depending on the dose. Radiation protection agencies have prescribed dose limits to the lens to prevent induction of lens opacity or cataract.

On April 21, this year, the International Commission on Radiological Protection (ICRP) which issues recommendations on radiation protection, slashed the dose limit for the lens of the eye to 20mSv in a year, averaged over defined period of five years, with no single year exceeding 50 mSv.

Earlier dose limit

The earlier dose limit was 150mSv in a year. (Sv is a unit of biologically effective dose. The radiation energy absorbed in a sievert (Sv) is one Joule per kilogramme of material; since the unit is large, a sub-multiple such as one thousandth of a Sv or milliSv —mSv — is normally used).

Several studies over the past few years led the Commission to reduce the dose limit steeply.

There are three main forms of cataract depending on its anatomic location in the eye lens: nuclear, cortical and posterior sub capsular (PSC). Among these, PSC is the least common and is commonly associated with exposure to ionizing radiation. Radiation Effects Research foundation (RERF) describes the formation of radiation cataract thus: “There is a transparent layer of cells covering the interior frontal side of the capsule that covers the eye lens.

This layer maintains the function of the lens by slowly growing toward the centre, achieved through cell division at the periphery. Because irradiation is especially harmful to dividing cells, exposed cells at the equator are most prone to damage.

Unknown reasons

For unknown reasons, damaged cells move toward the rear of the lens before converging on the centre. Such cells prevent light from travelling straight forward resulting in opacity.”

So far, scientists believed that cataract will be formed only after the lens receives a typical radiation dose called the threshold. ICRP assumed that threshold was 2Gy for a single dose and 5 Gy when the exposure occurs in a protracted way.

Not any more. Recent studies appear to show the formation of radiation induced cataracts at much lower doses than the current standards. (Gy is the unit of absorbed dose; the dose is said to be one gray — Gy — when the ionizing radiation energy absorbed per kilogramme of material is one joule).

ICRP now considers that the threshold dose for cataract is 0.5Gy. ICRP also stated that although uncertainty remains, medical practitioners must be made aware that the absorbed dose threshold for circulatory disease may be as low as 0.5Gy to the heart or brain.

“Doses to patients of this magnitude could be reached during some complex interventional procedures, and therefore particular emphasis should be placed on optimization in these circumstances,” ICRP cautioned the specialists. The procedures include angioplasty.

The June 2010 on-line version of Catheterization and Cardiovascular Interventions and October 210 issue of Radiation Research have published studies on increased risk of cataracts among interventional cardiology professionals. Though the numbers of professionals monitored in the studies was limited, the results demand urgent action.

Chernobyl effect

Cataract analysis of 8607 Chernobyl clean up workers,12 and 14 years after exposure, indicated that posterior sub-capsular or cortical cataracts appeared in 25 per cent of the participants (Radiation Research, February 2007). Researchers found evidence of a dose threshold of less than 0.7Gy.

The researchers noted that the workloads tend to increase in catheterization suites. This, together with lack of training in radiation protection and unavailability or non-use of radiation protection accessories may result in doses to the eyes of cardiology professionals sufficient to cause cataracts.

Studies show that leaded glass alone reduced the dose to the lens by 5 to 10 times; scatter-shielding drapes alone reduced the dose rate by 5 to 25 times; using both reduced the dose rate by 25 times or more

In BioMed Central Public Health (2010), Dr Sophie Jacob from the French Institute of Radiological Protection and Nuclear Safety (IRSN) and other specialists listed 14 peer reviewed studies showing evidence for low dose radiation-induced cataracts.

The results of their study on occupational cataracts and lens opacities in interventional cardiology involving 1700 interventional cardiologists in France is expected to be available this year.

The jury is no more out on radiation induction of cataract. The present ICRP recommendations must serve as a wake up call for interventional cardiology and radiology professionals.

 

Raja Ramanna Fellow, Department of Atomic Energy (ksparth@yahoo.co.uk)

Keywords: International Commission on Radiological Protection, eye lens, radiation dose limit

Online edition of India's National Newspaper
Thursday, Feb 03, 2011
Finland far ahead in nuclear waste management

— PHOTO:AFP

 

The solution: A general view of the Olkiluoto 3 European Pressurised Reactor (EPR) being built in Finland. Finland demonstrates that it has in place a popularly accepted technological solution.

Finland consumes nearly 17,000 units of electric power per capita annually; its share of nuclear electricity is about 28 per cent. Though its nuclear power programme is very modest compared to that of U.S. or U.K. it is far ahead in its universally applauded plans for nuclear waste management.
The general refrain of lay public (often reinforced by antinuclear rhetoric) is that there is no ultimate solution for managing high level nuclear waste. Finland demonstrates that it has in place a popularly accepted technological solution.
Finnish programme
Currently, Finland operates four nuclear power reactors with a total installed capacity of 2716 MWe. It produces about 70 tonnes of spent fuel annually. Finland has no plans to reprocess the spent fuel.
Finland started its preliminary preparations for its nuclear waste management shortly before the first reactors started operation 1n 1977-1978. In 1978, the first lot of spent fuel entered the facility for interim storage at Loviisa.
The Nuclear Energy Act 990/1987 passed by its parliament stated that nuclear waste generated in connection with or as a result of the use of nuclear energy in Finland shall be handled, stored and permanently disposed of in Finland.
In 1983, Finland started screening of potential sites for spent fuel disposal. Within the next four years, Finnish scientists started field research in five municipalities for selecting the final disposal site.
Final repository
In 2000, they chose Olkiluoto. They plan to dispose of spent fuel in an underground geological repository. Posiva, a Finnish company which is entrusted with the job has drilled a 6.5 metre –high, 5 m- wide and 5000m long Okalo tunnel. It has removed over 100,000 cubic metre of rock.
The company successfully located the place where no one would ever be likely to dig a deep hole later for exploiting minerals because the place is not mineral-rich. The idea is to abandon forever, the mostly natural, and partly engineered underground repository after filling it.
Canister design
After a few decades of interim storage, the levels radioactivity and heat of spent fuel reduce to about 0.1 per cent of the original values.
It is then encapsulated in a cast iron insert which in turn is covered by a 5 cm thick copper canister. Each insert may carry up to 12 fuel bundles.
They will be placed in neatly bored holes a few metre apart in the underground repository. The gaps between each canister and the hole will be filled with bentonite clay, which swells by absorbing water.
This clay provides cushioning to the canister in case of geological movements and ensures that there are no voids through which water can enter and corrode the container.
Finland hopes to start filling the repository by 2012 and completing it by 2120. They can cover the mouth of the tunnel and forget about it.
Canister integrity
Most of the radioactivity in the spent fuel is due to fission products.
They have a half life of about 30y. In 100,000 years, the radioactivity remaining in the fuel will be negligible. Finnish scientists proved that 1.5 cm of copper cladding would last over 100,000 years. Evidently, 5 cm of copper cladding will be more than adequate.
During the period, an ice age may come and cover the area under 2-3 km of ice. The pressure on the canister due to ice, tightly gripping bentonite clay and ground water may equal that experienced by it at an ocean depth of 4.5 km. Finns proved that their copper cylinders will withstand a pressure three times that before failing.
Waste management cost is manageable. Finland collects a few percentage of the electricity cost per unit of power to manage the waste and deposits it in an independent National Nuclear Waste Management Fund, controlled and administered by the Ministry of Trade and Industry.
The agency estimates and assesses the liability annually.
Finland's nuclear waste management programme was accepted by people because the Government took them into confidence at every stage.
Finland demonstrates that nuclear waste can be managed safely. This issue need not come in the way of harnessing nuclear power.
K.S.PARTHASARATHY
Raja Ramannna Fellow, Department of Atomic Energy
( ksparth@yahoo.co.uk)

Are the units 1 & 2 of Tarapur safe?

The article titled "Are the units 1 & 2  of Tarapur safe? in The Economic Times (28 May 2011) summarizes the safety upgrades carried out by the Nuclear Power Corporation of India limited (NPCIL) at Units 1 & 2 of TAPS. In view of Fukushima accident NPCIL plans to carry out further steps to enhance safety.

Background radiation and radioactivity in India

                                                                      May 5, 2011

Background radiation and radioactivity in India

We live in a sea of radiation. In any city, an unsuspecting owner of a 0.1 acre backyard garden may not know that the top one metre of soil from his garden contains 11,200 kg of potassium, 1.28 kg which is of potassium- 40 (K-40, a radioactive isotope of potassium), 3.6 kg of thorium and one kg of uranium.

These values may be higher or lower depending on the soil. Uranium and thorium decay through several radio-nuclides to lead, a stable element. The presence of radioactive nuclides does not pose any significant risk.

Total dose

The total annual external dose from sources in soil and cosmic rays in Mumbai, Kolkata, Chennai, Delhi and Bengaluru is 0.484, 0.81, 0.79, 0.70 and 0.825 milligray respectively. Gray is a unit for absorbed dose; when the radiation energy imparted to a kg of material is one joule, it is called a gray. Since gray is very large, milligray (one thousandth of a gray), and microgray (one millionth of a gray), are commonly used.

Cosmic rays come from outer space. Their intensity at a place depends on the altitude. Cosmic rays alone contribute 0.28 milligray at the first three cities as they are at sea level; the column of air helps to reduce their intensity. At high altitudes, the protection from the column of air is less.

The cosmic ray contributions are higher at 0.31 milligray and 0.44 milligray respectively at Delhi and Bengaluru as these cities are at altitudes of 216 metre and 921 metre. Air passengers receive 5 microgray per hour from cosmic rays.

Parts of Kerala and Tamil Nadu are high background radiation areas (HBRA) because of the presence of large quantities of monazite in the soil. Thorium content in monazite ranges from 8-10.5 per cent. Researchers found that the radiation levels in 12 Panchayats in Karunagappally varied between 0.32 to 76 milligrays per year; the levels in 90 per cent of over 71,000 houses were more than one milligray per year.

The average value of population dose in HBRA is 3.8 milligray per year. One milligray is the average value for areas of normal background radiation. The units milligray and millisievert are the same in these instances. Study at the HBRA during 1990-99 by the researchers from the Regional Cancer Centre and Bhabha Atomic Research Centre did not show any health effect attributable to radiation.

Radon, which occurs in uranium series present in soil seeps into homes. In temperate areas radon decay products build up in air due to poor ventilation and deliver high doses to the lungs of millions of people. In tropics ventilation is adequate to disperse radon .In the United Kingdom persons in 5 per cent of the homes are exposed to doses above 23.7 mSv/year. One per cent of the population receives doses above 55.8 mSv/year. The highest estimated dose was 320 mSv/year in Cornwall.

All foodstuffs contain potassium-40 (K-40). We need potassium for sustenance. K-40 is 0.012 per cent of potassium. Once ingested, most of the potassium enters the blood stream directly and gets distributed to all tissues and organs.

Homeostatic control

The potassium content in the human body is strictly under homeostatic control. The body retains only the amounts in the normal range essential for its functioning; it is independent of the variations in the environmental levels.

The body excretes excess amounts with a biological half life of 30 days. K-40 delivers a constant annual radiation dose of 0.18 mSv to soft tissue. This dose is unavoidable as potassium is an essential element. Every time we eat a banana, we are introducing 14 Bq of K-40 in to our body. Trucks containing bananas have triggered radiation alarms at border posts in the U.S.

Brazil nut

Brazil nut is probably the most radioactive food. Scientists have measured 700Bq of radium per kg of Brazil nut.

The roots of the Brazil nut tree pass through acres of land; They have a tendency to concentrate barium; along with barium, the roots collect radium as well. Radium appears in the nuts. Many vegetables like brinjal, carrot etc. also contain the radioactive isotope.

Indian researchers have measured polonium-210 in fish and other marine organisms. Our whole body is hit by particles coming from all sides. Radiation is a part of our life. We cannot avoid eating food just because it contains radioactivity

(Raja Ramanna fellow, Department of Atomic Energy)

ksparth@yahoo.co.uk

Keywords: radio activity, potassium, radiation in food