UW Food Irradiation Education GroupHave there been major accidents atindustrial irradiation facilities?Medical sterilization facilities have been operated in theUS for more than 30 years, without a fatal accident. Over100 such facilities are currently licensed, along with atleast that many medical radiation treatment centers,and bone marrow transplant centers (which also useCobalt 60 to irradiate patients). No events have beendocumented in this country that led to exposure of thepopulation at large to radioactivity. In other countries, asmall number of fatal incidents have been documentedin which a worker by-passed multiple safety steps toenter the chamber while the source was exposed,resulting in a severe or even lethal radiation injury tothemselves.

Do irradiation facilities have radioactivewaste disposal problems?

No. The food irradiation facilities themselves do notbecome radioactive, and do not create radioactive waste.Cobalt 60 is manufactured in a commercial nuclearreactor, by exposing non-radioactive cobalt to intenseradiation in the reactor core. The cobalt sources usedin irradiation facilities decay by 50% in five years, andtherefore require periodic replacement. The sourcesare removed from the irradiator when the radioactivityfalls to a low level, usually between 6% and 12% of theinitial level (this takes 16 to 21 years for cobalt-60). Thesmall radioactive cobalt pencils are shipped back tothe original nuclear reactor, where they can be re-activated for further use. The shipment occurs in specialhardened steel canisters that have been designed andtested to survive crashes without breaking. Cobalt is asolid metal, and even if somehow something shouldbreak, it will not spread through the environment. Cobalt60 may also be disposed of as a radioactive waste.Given its relatively short half life (5 years) and its stablemetallic form, the material is not considered to be aproblematic waste.

E-beams and X-ray facilities do not involve radioactivesubstances.

Who makes sure that the irradiationfacilities are operated safely?The effectiveness of the treatment in eliminatingpathogens will be regulated as a food safety process,by either the USDA or the FDA, often in concert withState authorities, just as is the case now for milkpasteurization or retort canning.

The safety of operations of irradiation facilities isregulated separately. This requires extensive workertraining, supervision, and regulatory oversight. Facilitiesusing radioactive sources are regulated by the NuclearRegulatory Commission (NRC). To be licensed, thefacility must have been designed with multiple fail-safemeasures, and must establish extensive and welldocumented safety procedures, and worker training. Thesafe transport of the radioactive sources is regulated bythe Department of Transportation.

Can an accident at a irradiation facility leadto a meltdown with release ofradioactivity that would contaminate theenvironment and endanger people livingnearby?No. It is impossible for a meltdown to occur in a gammairradiator or for the radiation source to explode. Thesource of radiation used at irradiators cannot start afission chain reaction, and it does not emit neutronsthat could activate materials. The walls of the irradiationcell through which the food passes, the machineryinside the cell, and the product being processed cannotbecome radioactive. No radioactivity is released intothe environment.

TheFoodIrradiationProcessWhat is Food Irradiation?Food irradiation is a promising new food safetytechnology that can eliminate disease-causingmicroorganisms such as E. coli O157:H7,Campylobacter, and Salmonella from foods.

The Food and Drug Administration has approvedirradiation of meat and poultry and allows its use for avariety of other foods, including fresh fruits andvegetables, and spices. The agency determined thatthe process is safe and effective in decreasing oreliminating harmful bacteria. Irradiation also reducesspoilage bacteria, insects and parasites, and in certainfruits and vegetables it inhibits sprouting and delaysripening.

The effects of irradiation on the food and on animalsand people eating irradiated food have been studiedextensively for more than 40 years. These studies showclearly that when irradiation is used as approved onfoods:

Disease-causing microorganisms are reduced oreliminated

The nutritional value is essentially unchanged

The food does not become radioactive

Irradiation is a safe and effective technology that canprevent many foodborne diseases.

This brochure has been prepared by the UW FoodIrradiation Education Group, based on the informationprovided by:

http://www.iaea.org/worldatom/inforesource/other/food/http://www.cdc.gov/ncidod/dbmd/diseaseinfo/foodirradiation.htmhttp://www.food-irradiation.com/http://www.fda.gov/

For more information:

Email: uw-food-irradiation@engr.wisc.eduURL: uw-food-irradiation.engr.wisc.edu

The Food irradiation process

The radiation used in processing materials is limited toradiation from high-energy gamma rays, X-rays andaccelerated electrons. These types of radiation arecalled ionizing because their energy is high enough todislodge electrons from atoms and molecules and toconvert them to electrically charged particles called ions.

Accelerated electrons: The electron beam is astream of high energy electrons, propelled out of anelectron gun. This electron gun apparatus is a largerversion of a standard television tube. The electronbeam generator can be simply switched on or off.There are no radioactive materials in the process. Theelectrons can penetrate food only to a depth of threecentimeters, or a little over an inch, so the food to betreated must be no thicker than that to be treated allthe way through. Two opposing beams can treat foodthat is twice as thick. E-beam medical sterilizers havebeen in use for at least fifteen years.

Gamma rays and X-rays form part of theelectromagnetic spectrum, like radio waves,microwaves, ultraviolet and visible light rays. Gammarays and X-rays are in the short wave length, high-energy region of the spectrum. Both Gamma and X-rays can penetrate foods to a depth of several feet.

! Gamma rays with specific energies normally comefrom the spontaneous disintegration ofradionuclides. Naturally occurring and man-maderadionuclides, also called radioactive isotopes orradioisotopes, are unstable, and emit radiation asthey spontaneously disintegrate, or decay, to astable state. The radionuclide used almost alwaysfor the irradiation of food by gamma rays is cobalt-60. It is produced by neutron bombardment in anuclear reactor of the metal cobalt-59, then doublyencapsulated in stainless steel pencils to preventany leakage during its use in a radiation plant.Cobalt-60 has a half-life of 5.3 years. Thistechnology has been used routinely for more thanthirty years to sterilize medical, dental andhousehold products, and it is also used forradiation treatment of cancer. Radioactivesubstances emit gamma rays all the time. Whennot in use, the gamma ray source is stored in apool of water which absorbs the radiationharmlessly and completely. To irradiate food orsome other product, the source is pulled out of thewater into a chamber with massive concrete wallsthat keep any rays from escaping. Medical productsor foods to be irradiated are brought into thechamber, and are exposed to the rays for a definedperiod of time. After it is used, the source is returnedto the water tank.

Only certain radiation sources can be used in foodirradiation. These are the radionuclides cobalt-60 orcesium-137 (used very rarely); X-ray machines havinga maximum energy of five million electron volts (MeV);or electron machines having a maximum energy of 10MeV. Energies from these radiation sources are too lowto induce radioactivity in any material, including food.

Radiation dose is the quantity of radiation energyabsorbed by the food as it passes through the radiationfield during processing. It is measured in Gray (Gy) [oneGray equals one Joule of energy absorbed per kilogramof food being irradiated] or in rad (1 Gy = 100 rads).International health and safety authorities haveendorsed the safety of irradiation for all foods up to adose level of 10,000 Gy (10 kGy).

How much does a typical food irradiationfacility cost?The cost to build a commercial food irradiation plant isin the range of US $3 million to $5 million, dependingon its size, processing capacity, and other factors. Thisis within the range of plant costs for other foodtechnologies. For example, a moderately-sized, ultra-high temperature plant for sterilizing milk, fruit juices,and other liquids costs about US $2 million. A smallvapor-heat treatment plant for disinfestation of fruitscosts about US $1 million.

! X-rays are caused by atomic transitions and theyare usually less energetic than gamma rays. Theyhave the same properties and effects on materials,their origin being the main difference between them.X-rays with varying energies are generated bymachines. The X-ray machine is a more powerfulversion of the machines used in many hospitalsand dental offices to take X-ray pictures. To producethe X-rays, a beam of electrons is directed at a thinplate of gold or other metal, producing a stream ofX-rays. Like gamma rays, X-rays can pass throughthick foods, and require heavy shielding for safety.However, like E-beams, the machine can beswitched on and off, and no radioactive substancesare involved. Four commercial X-ray irradiation unitshave been built throughout the world since 1996.

A typical gamma irradiation facitity: JS-8900 Unit Carrier Irradiation