Uranium contamination, fission product

Control had been established with no further hazard likely, although a state of emergency was still considered to exist. Office areas immediately adjacent (40 ft) to the process area were cleared (T-t-1 day) by health physics for occupancy. Contamination was cbi ined to the process area by uranium and fission products with maximum penetrating radiation levels of SO R. There was no evidence that uranium or fission products had been deposited off site. The radioactive materials ivere contained primarily within the plant building and were concentrated in the Immediate vicinity of the reacting vessel (the solvent extraction area). 

The electrometallurgical recycle technology does not involve separation of plutonium. The plutonium product is inherently commingled together with minor actinides (i.e. americium, curium, and neptunium), uranium, and fission products. The minor actinides contribute substantial decay heat and contamination with alpha, beta, gamma, and neutron radiation emitters. The fresh fuel product is highly radioactive, which complicates thefts and diversion. 

After irradiation of the uranium target, it is dissolved in nitric acid and the final solution adsorbed on an alumina column that is washed with nitric acid to remove uranium (and other fission products). Molybdenum is finally eluted with ammonium hydroxide and further purified by absorption on an anion exchange column from which ammonium molibdate is eluted with dilute hydrochloric acid after washing the resin with concentrated HC1. The "Mo is obtained in no-carrier-added conditions, and the most common contaminants can be 131I and 103Ru. 

With the help of this multicyclic extraction the contamination of uranium and plutonium with fission products is reduced to 0.1 to 1 ppm. The residual concentration of plutonium in uranium may not exceed 10 ppb, since the uranium must be able to be processed without protective measures. The recovery efficiency for uranium and plutonium is 98 to 99%. 

An important objective of dissolution and the preconditioning of feed solution prior to extraction is to convert these fission-product elements into states that will not contaminate uranium, plutonium, or solvent in subsequent solvent extraction. 

A well-designed Purex plant aims for as complete recycle of solvent as possible, to minimize costs of solvent makeup and disposal. Solvent from the uranium purification section usually contains so few contaminants or degradation products that it can be reused a number of times without cleanup. On the other hand, solvent that has processed solutions containing hi activity of fission products and plutonium carries traces of these contaminants, uranium, nitric acid, dibutyl phosphate, and other radiolytic degradation products of TBP and dodecane. Uranium and plutonium should be recovered because of their value. Fission products should be removed to prevent product contamination in later cycles. Dibutyl phosphate should be removed because it forms strong complexes with tetravalent zirconium and plutonium that would impair ability of the solvent to reject zirconium and separate plutonium from uranium. 

Solvent recovery. To prevent cross-contamination of products and to allow for the greater degradation of solvent by high concentrations of fission products and plutonium, two independent solvent recovery systems are provided. Solvent recovery system 1 processes solvent ICW, stream 13, which has been used in the high-activity codecontamination, partitioning, and plutonium purification cycles. System 2 processes the low-activity solvent 2EW, stream 23, which has been used only for final uranium decontamination. Solvent in both systems is processed before recycle by a sodium carbonate wash, filtration and a nitric acid wash. System 1 also uses a second sodium carbonate wash. 

The isotope °Sr is a 3-emitter h = 29.1 yr) and a fission product of uranium. In the event of a nuclear energy plant disaster or through the dumping of nuclear waste, there is a danger that grass, and then milk, may be contaminated with Sr and that it may be incorporated with calcium phosphate into bone. For discussion of Ra, see Section 11.1. 

The facility produces radioisotopes by chemically processing the fission products of irradiated uranium dioxide. These processes involve the generation of liquid solutions, the evolution of volatile radioactive gases, and the generation of significant inventories of residual radioactive materials that are solidified for temporary storage in the facility. These processes must be conducted in shielded locations with adequate ventilation and appropriate filtration for the control of contamination and the prevention of unmitigated releases of hazardous materials to the environment. 

In a modern PUREX plant, the fuel pins are first cut into pieces that are 3-5 cm long. The fuel is then dissolved in 6-11 M nitric acid, while the cladding hulls do not dissolve. Sometimes <0.05 M AIF3 is added to the nitric acid to improve dissolution of, e.g., zirconium by complex formation. The solution is then diluted to 3-4 M and nitrite is added to assure that plutonium is present as Pu(IV) and uranium as U(VI). Plutonium and uranium are then selectively extracted into TBP in aliphatic kerosene. Fission products and trivalent actinides remain in the aqueous phase. The extract is scrubbed with nitric acid to remove all contaminants except traces of ruthenium, neptunium, and zirconium. 

Windscale The Windscale (now called Shellafield) Reactor No. 1 was partially consumed by combustion in October 1957, resulting in the release of fission products to the surrounding countryside. The reactor was an air-cooled graphite-moderated natural-uranium reactor employed primarily for plutonium production. The radionuclides (740 TBq), Cs (22 TBq), Ru (3 TBq), and Xe (1.2 PBq) were released. In addition to those fission products, 8.8 TBq of Po was also released, because the nuclide was produced by neutron irradiation of bismuth. The released radionuclides moved from Windscale to the south, southeast, and to London, and they contaminated vast grasslands. The collective dose is estimated to be 2,000 man-Sv in the contaminated area. 

The water of the primary circuit always contains trace amounts of fission products. These may stem from a small outer contamination of the fuel rods by traces of uranium. (The total surface area of the fuel rods exposed to the primary coolant amounts to about 7,000 m, equal to the size of a soccer field.) The fission products may also stem from pinholes in a fuel rod. The measurement of the fission product spectrum and the nuclidic composition allows the radiochemist to decide between the two possibilities. Consequently, the defective fuel rod can be isolated and removed. 

Use of a steam generator to separate the primary loop from the secondary loop largely confines the radioactive materials to a single building during normal power operation and eliminates the extensive turbine maintenance problems that would result from radio-actively contaminated steam. Radioactivity sources are the activation products from the small amount of corrosion that is present in the primary loop over the 12-18-month reactor cycle, as well as from the occasional (<1 in 10,000) fuel rod that develops a crack and releases a small portion of its volatile fission products. Uranium dioxide fuel is very resistant to erosion by the coolant, so the rod does not dump its entire fission product inventory into the RCS. 

According to Hiittig et al. (1990), the amount of uranium released from defective fuel rods and deposited on in-core surfaces can be assessed from the coolant activity levels of various short-lived fission products such as I, I, Cs, calculating their source strengths under the assumption of a direct and instantaneous release to the coolant. Though the releases of these isotopes from failed fuel rods are quite small (due to their short halflives), such data can provide only an upper limit for the uranium contamination if there are simultaneously fuel rod failures in... 

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