RAPID ROUNDUP: Japanese nuclear reactor and health effects – experts respond

Wed Mar 16, 2011

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As the situation unfolds following the earthquake and tsunami in Japan, experts respond to the latest developments.

The Australian Radiation Protection and Nuclear Safety Agency (ARPANSA) have added more information to their website – please click: here

Feel free to use these quotes in your stories.  Any further comments will be posted here. If you would like to speak to an expert, please don’t hesitate to contact us on (08) 7120 8666 or by email.

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Special note from the Science Media Centre of Japan:

In the wake of the fluctuating levels of radiation coming out of the Fukushima Dai-ichi Nuclear Power Plant, locals have been told that wearing masks can help prevent them from breathing in radiation. Indeed, we’re seeing a lot of people wearing masks today in Tokyo and in disaster-stricken areas but this IS NOT entirely due to radiation scares. It is common practice in Japan for people to wear masks because:

- they have a cold, and don’t want to spread it (or they don’t have a cold but still wear a mask to stop breathing in the cold virus, although whether this really works is debatable)

- they have hayfever and are protecting themselves from breathing in pollen (pollen forecasts today are very high, and the weather has gone back to mid-winter temperatures with snow expected in northern Japan).

A lot of people will be wearing masks today for the above reasons and not because of possible radiation in the air.

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Peter Burns is former CEO of ARPANSA (Australian Radiation Protection and Nuclear Safety Agency)

1) How is the current Japanese situation different to Chernobyl?

“Chernobyl did not have a containment vessel and a large fraction of the inventory of volatile fission produces was released. Releases to date have been minor. If there is a major meltdown and the containment vessels are breached to some degree it is still likely that much of the radioactive material would be contained.”

2) Current reports state that the radiation levels at the plant reached 400 milli-Sieverts per hour (mSv/h). What does this number mean, is it comparable to other sources of radiation (x-ray etc)? How is it comparable to the radiation released at Chernobyl or 3 Mile Island?

“Current international recommendations allow for planned exposures up to 100mSv when dealing with accidents. At 400mSv this would occur in 15 minutes, so 400 mSv/h is a high exposure rate. A dose of 400mSv is comparable to the dose from 50 -100 CT Scans.”

3) How dangerous are these levels for the plant crews?

“The risk of fatal cancer from a dose of 100mSv is comparable to the risks associated with those from the high end of risky occupations, ie for other types of emergency responders.”

4) How dangerous are these levels for the general population in the surrounding area and further afield? There is currently a 20-km exclusion zone around the plant.

“Doses from the plant fall off quickly. With a 20km exclusion zone in place doses to the public would be low in comparison to those from natural background radiation.”

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Tony Irwin is a visiting lecturer in nuclear technology at the Australian National University and the University of Sydney. He worked for British Energy in the UK commissioning and operating 8 nuclear power plants and following the Chernobyl accident he helped review operating practices at Russian reactors. In 1999 he joined the Australian Nuclear Science and Technology Organisation (ANSTO) and was Reactor Manager during construction and operation of the OPAL research reactor. After retiring from ANSTO in late 2009, he became a visiting lecturer for Masters Courses in Nuclear Technology at the ANU and the University of Sydney:

1) How is the current Japanese situation different to Chernobyl?

“Chernobyl was the result of a badly-conceived and executed test on a reactor at power where many safety systems were defeated to enable the test to continue. The reactor was of a type (RBMK) that would not have been licensed in any western country. The reactor did not have the layers of containment systems that the Japanese reactors have. A dramatic power surge caused a steam explosion that lifted the top off the reactor releasing the radioactive core to the atmosphere. There were serious mistakes made by the plant operators.”

“The Japanese reactor is a Boiling Water Reactor (BWR) – a type licensed and in operation worldwide. The reactors safely shutdown automatically when the massive earthquake struck.  After the Tsunami stopped the cooling systems, the operators acted appropriately to ensure the reactors were kept cool and radioactive emissions were minimised.”

2) Current reports state that the radiation levels at the plant reached 400 milli-Sieverts per hour (mSv/h). What does this number mean, is it comparable to other sources of radiation (x-ray etc)? How is it comparable to the radiation released at Chernobyl or 3 Mile Island?

“Dose is measured by the dose rate in mSv/hr x time. The 400mSv/hr measured is thought to have only existed for a very short period. Subsequent radiation levels are much lower – in the microSievert range. The internationally recognised dose limit for nuclear workers is 20 mSv/yr averaged over 5 years with a maximum of 50 mSv in any one year. In an emergency, most authorities permit doses up to 100mSv. An X-ray is typically <1 mSv, a CT scan is ~20mSv. Radiation doses at Chernobyl ranged up to 20,000 mSv on the first day and during the subsequent clean-up doses of 100 – 500 mSv were received.”

3) How dangerous are these levels for the plant crews?

“The plant crews work on shifts and will be rotated to ensure doses are minimised.”

4) How dangerous are these levels for the general population in the surrounding area and further afield? There is currently a 20-km exclusion zone around the plant.

“The effect of radiation on the general population will depend on the type of radiation they receive. As has been shown on the TV news, the population are being monitored for radiation.”

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Dr Don Higson, Fellow of the Institution of Engineers Australia and Fellow of the Australasian Radiation Protection Society, has given us his personal views drawn from his time as a nuclear safety specialist. He believes this situation is nothing like Chernobyl and that whilst there have been many deaths caused by the earthquake and tsunami, none are likely to be attributable to radiation even in the worst case scenario. Please click here for the link

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Mr Steve Crossley is a radiation physicist based in Perth.  He worked in the British nuclear industry for six years from 1996 to 2002.

1) How is the current Japanese situation different to Chernobyl?

“In the Chernobyl reactor incident the contents of the reactor core were exposed and on fire.  Large quantities of the fuel material itself were released into the environment. The design of the reactors in Japan prevent this kind of incident.  The reactor fuel assemblies are contained within a thick steel pressure vessel which is inside a containment structure, these structures are specifically designed to prevent release of core materials even during accident situations. Also boiling water reactors (BWR – the kind at Fukushima) are cooled and moderated by water which, unlike the graphite core at Chernobyl, cannot burn.”

2) Current reports state that the radiation levels at the plant reached 400 milli-Sieverts/hour. What does this number mean, is it comparable to other sources of radiation (X-Ray etc)? How is it comparable to the radiation released at Chernobyl or 3 Mile Island?

“Without an indication of where this level was measured, what was producing it and how long the radiation levels remained this high it is impossible to sensibly talk about health effects or to compare to other incidents.  It may have been very localised and transient.  Was this level measured within a shielded, unmanned structure or out in the open where people were working?”

3) How dangerous are these levels for the plant crews?

“The levels appear to be changing over time and with be very different in different areas of the site. No doubt the workers will be equipped with radiation detection equipment and an understanding of the readings and the workers and their managers will be taking decisions to keep worker doses to a minimum whilst carrying out the work required. In emergency situations it can be expected that the normal, very low, dose limits normally imposed on workers may be exceeded.”

4) How dangerous are these levels for the general population in the surrounding area and further afield? There is currently a 20-km exclusion zone around the plant.

“The 20km exclusion zone is part of the standard emergency response protocols which are established at every nuclear facility. The levels which have been reported from Tokyo are of no concern, there are many places in the world where the natural background radiation levels are higher than the reported ‘elevated’ levels in Tokyo.”

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Dr Pradip Deb is a Senior Lecturer in Medical Radiations at the School of Medical Sciences, RMIT University

“400 millisieverts is equivalent to 4000 x-ray exposure, which is very high, but if people are exposed for only a few minutes, even if for an hour – the dose is 400 mSv – which is sublethal.” [Please see exposure level classifications below]

“High levels of radiation exposure to human body can cause severe problems in human body functions.  An exposed person will show the symptoms of acute radiation sickness in different levels, depending on the amount and nature of radiation exposure. If a person is exposed to a significant amount of radiation over a short period of time, that is, acute exposure, this can cause radiation sickness or death shortly after exposure. If they survive there is a possibility of developing cancer in later years.”

“Each person differs in their biological response to a given amount of radiation depending on their age, sex, lifestyle, diet, body temperature, overall medical health etc. In general children and elderly person are more sensitive to radiation. The severity of acute radiation sickness depends on how much radiation is received, how much of the body is exposed and the sensitivity of the exposed individual to radiation.”

“There are four stages of acute radiation sickness – prodromal phase (within 48 hours), latent phase (days to weeks), manifest illness (weeks to months) and the fourth phase, which is recovery or death. If the radiation level is excessively high all four phases can appear within 48 hours.”

“Radiation exposure causes the changes in blood cells (white blood cells decrease very fast), effects in gastrointestinal cells (causing nausea, vomiting, diarrhoea), fever, non-specific flu-like symptoms, hair loss, fatigue. The basic three things about radiation protection is distance, shielding, and time. More distance from the radiation source, proper shielding, and less exposure time will reduce the exposure level of radiation. The exposed person should be isolated for treatment, as they can cause secondary radiation exposure to others.”

“Severity level of radiation dose can be estimated according to radiation level or effective dose. Radiation exposure levels (dose) can be classified as follows:

Less than 2.5 Sievert (2500 mSv) – sublethal dose

Symptoms may include:  malaise, fatigue, drowsiness, weight loss, fever, abdominal pain, insomnia, restlessness, blisters

2.5 Sv – 6.5 Sv (2500 mSv – 6500 mSv) – Potentially lethal dose

  • Significant reduction in production of blood cells
  • Nausea/vomiting which appears to get better in 3 days
  • WBC greatly reduced
  • After two weeks: chills, fatigue, ulceration of the mouth

6.5 Sv – 10 Sv (6500 mSv – 10000 mSv)  -  supralethal dose

  • Damage to the stomach lining and/or intestine -Causing decreased absorption, ulceration and dehydration
  • Seven Days After Exposure

-Severe infection, fluid loss, blood loss or collapse of the circulatory system and may result in death

Acute Doses over 10 Sv (10000 mSv)

  • Irreparable damage to the brain and spinal cord
  • Symptoms:

-Agitation
-Lack of coordination
-Breathing difficulty
-Occasional periods of disorientation
-Death occurs within hours to days

Comparison with diagnostic x-ray exposure:

Typical effective dose for one exposure of chest x-ray is 0.1 mSv. Which is very small compared to our normal radiation acceptance level (20 mSv per year).

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Statement from the Food Standards Australia New Zealand (FSANZ):

“Food Standards Australia New Zealand is conducting an investigation on the possible risk of radiation-contaminated food entering Australia from Japan and will provide advice to the Australian Quarantine and Inspection Service to assist them in determining what additional border action is needed, if any. Australia imports very little food from Japan and that is limited to a small range of specialty products (such as small volumes of seaweed and sake as well as other Japanese specialty food products such as mirin, soy sauce, dried noodles, pickled ginger, wasabi).”

You can contact FSANZ media on 0401 714 265

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The following comments are from our colleagues at the UK Science Media Centre

Prof Malcolm Sperrin is Professor of Medical Physics at the Royal Berkshire Hospital, UK:

“It is natural to seek hard facts to summarise the risk from exposure to radiation from the Fukuyama Nuclear Complex but at this time there is insufficient information to do so.  The long established link between radiation exposure (measured in Sieverts) and risk is quoted as 6% per Sievert of radiation exposure.  This can be applied to medical X-rays as much as the radiation in Japan.  This means that as a guide, there is an excess number of deaths equivalent to 1 in 17000 per 1mSv.  By comparison a chest X-ray gives typically 0.1mSv.

“For exposures of the magnitude being quoted in Japan, there is considerable caution needed, since these may be point measurements and may also be dose rates neither of which will represent the exposure received by staff.

“There is also caution needed in trying to identify ‘safe or dangerous levels’.  There is no such thing but the risk from radiation may be overwhelmingly swamped by the risk from other origins such as smoking, natural risk of cancer, etc etc. When thousands have died from the impact of the earthquake and tsunami, and the threat of infectious disease looms large as a result, the risks posed at Fukushima are limited in comparison.”

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Dr Jim Smith is Reader in Environmental Physics, School of Earth and Environmental Sciences at the University of Portsmouth:

In my opinion, a key risk at present is public panic in response to this incident. It is important to focus on the radiation risk, but experience from past nuclear incidents has shown that the stress and panic caused by these events can be as bad as, or worse than, the direct threat from radiation. Even after Chernobyl, although there were some severe health effects at the population level, the risk to individuals, except within the immediate vicinity of the plant, was very low. So: for people outside the immediate vicinity of the plant, even in meltdown on the scale of Chernobyl, the individual risk is likely to still be very low.”

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Prof Michael Reeks at the School of Mechanical & Systems, University of Newcastle, provided a backgrounder for the American Nuclear Association:

To begin, a sense of perspective is needed… right now, the Japanese earthquake/tsunami is clearly a catastrophe; the situation at impacted nuclear reactors is, in the words of IAEA, an “Accident with Local Consequences.

“The Japanese earthquake and tsunami are natural catastrophes of historic proportions. The death toll is likely to be in the thousands. While the information is still not complete at this time, the tragic loss of life and destruction caused by the earthquake and tsunami will likely dwarf the damage caused by the problems associated with the impacted Japanese nuclear plants.”

What happened?

“Recognizing that information is still not complete due to the destruction of the communication infrastructure, producing reports that are conflicting, here is our best understanding of the sequence of events at the Fukushima power station.”

- The plant was immediately shut down (scrammed) when the earthquake first hit. The automatic power system worked.

- All external power to the station was lost when the sea water swept away the power lines.

- Diesel generators started to provide backup electrical power to the plant’s backup cooling system. The backup worked.

- The diesel generators ceased functioning after approximately one hour due to tsunami induced damage, reportedly to their fuel supply.

- An Isolation condenser was used to remove the decay heat from the shutdown reactor.

- Apparently the plant then experienced a small loss of coolant from the reactor.

- Reactor Core Isolation Cooling (RCIC) pumps, which operate on steam from the reactor, were used to replace reactor core water inventory, however, the battery-supplied control valves lost DC power after the prolonged use.

- DC power from batteries was consumed after approximately 8 hours.

- At that point, the plant experienced a complete blackout (no electric power at all).

- Hours passed as primary water inventory was lost and core degradation occurred (through some combination of zirconium oxidation and clad failure).

- Portable diesel generators were delivered to the plant site.

- AC power was restored allowing for a different backup pumping system to replace inventory in reactor pressure vessel (RPV).

- Pressure in the containment drywell rose as wetwell became hotter.

- The Drywell containment was vented to outside reactor building which surrounds the containment.

- Hydrogen produced from zirconium oxidation was vented from the containment into the reactor building.

- Hydrogen in reactor building exploded causing it to collapse around the containment.

- The containment around the reactor and RPV were reported to be intact.

- The decision was made to inject seawater into the RPV to continue to the cooling process, another backup system that was designed into the plant from inception.

- Radioactivity releases from operator initiated venting appear to be decreasing.

Is a nuclear reactor “meltdown” a catastrophic event?

“Not necessarily. Nuclear reactors are built with redundant safety systems. Even if the fuel in the reactor melts, the reactor’s containment systems are designed to prevent the spread of radioactivity into the environment. Should an event like this occur, containing the radioactive materials could actually be considered a “success” given the scale of this natural disaster that had not been considered in the original design. The nuclear power industry will learn from this event, and redesign our facilities as needed to make them safer in the future.”

Can it happen here in the US? [note these comments from Michael Reeks were originally prepared for the American Nuclear Association]

“While there are risks associated with operating nuclear plants and other industrial facilities, the chances of an adverse event similar to what happened in Japan occurring in the US is small.

Since September 11, 2001, additional safeguards and training have been put in place at US nuclear reactors which allow plant operators to cool the reactor core during an extended power outage and/or failure of backup generators – “blackout conditions.”

What is the ANS doing?

“ANS has reached out to The Atomic Energy Society of Japan (AESJ) to offer technical assistance. ANS has established an incident communications response team. This team has compiling relevant news reports and other publicly available information on the ANS blog,

which can be found at ansnuclearcafe.org. The team is also fielding media inquiries and providing reporters with background information and technical perspective as the events unfold. Finally, the ANS is collecting information from publicly available sources, our sources in government agencies, and our sources on the ground in Japan, to better understand the extent and impact of the incident.”

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