Feasibility Study of Thorium-Plutonium Mixed Oxide Assembly In Light Water Reactors.

Thorium-plutonium mixed oxide, (Th,Pu)OX, is currently used as an alternative fuel in the light water reactors in the world. The main objective of this paper is not only to show the benefits of using the thorium, but mainly to study how the way thorium is introduced in the fuel affects the neutron parameters. Among these benefits is the possibility of extending the operating cycle length and the reduction of the increasing stockpiles of plutonium. The first investigated method is introducing thorium as (Th,Pu)OX. The second one is a homogeneous model of thorium plutonium oxide. It is carried out by adding an amount of plutonium separated from the uranium oxide cycle at 50 GWd/ton of heavy metal to the same amount of thorium. Thus, we studied three assemblies; the reference assembly is uranium oxide of 4.2% enrichment containing borated water as a moderator of concentration 500 ppm (part per million) of B-10. The second is a (Th,Pu)OX and the third one is an assembly with homogenized thorium plutonium. All three assemblies are modeled using MCNPX. A comparison is held between the results of the three lattices. The factors compared are the effective multiplication factor, the inventory of plutonium and uranium isotopes, and the depletion of B-10, the pin by pin power distribution at 0 and 60 GWd/ton and the relative pin radial power for the three lattices. The comparison is aimed to show the effect on the cycle length, the reduction in the Pu content and the power flattening across the assembly. It is found that the evolution of the multiplication factors shows a similar behaviour using (Th-Pu)OX fuel in the assembly as UOX cycle inspite of lowering the K-eff of fresh (Th-Pu)OX fuel (1.19847). The power flattening which is favorable in reactor operation is clearer in (Th,Pu)OX fuel. It is noticed that the mass of Pu-239 decreases by 1.07% from its initial value at the end of life. For homogeneous (Th,Pu)OX, the mass decreases by 0.0832%. The high power peaking factor for (Th,Pu)OX is not expected to cause significant effects during reactor operation but it can be reduced by adding burnable poisons.

Fricke gel dosimeter as a tool in quality assurance of the radiotherapy treatment plans.

Ferrous xylenol gel was evaluated as a dosimeter in verifications of treatment plans for treatments of female breast tumors in external-beam radiation therapy. The dosimeter was calibrated in a cubic wax phantom irradiated with 6 and 15MV beams of an Elekta clinical linear accelerator and then used for measurements of doses in an anthropomorphic phantom of a female torso, which mimicked female breasts after modified radical mastectomy and breast-conserving surgery. Doses measured with the gel in specific locations in the phantom were compared with values predicted by treatment plans created with the XiO treatment planning system (Elekta / IMPAQ) and with results of measurements with an IBA CC13 ionization chamber in the same locations. Differences between the values measured with the gel and predicted by the treatment planning system or measured with the ionization chamber were within 1.5% in most cases. In an area of as steep dose gradient, the difference reached 2.7%, which was explicable in terms of the finite size of the gel dosimeter. The dose response of the gel is dose rate and energy independent in the ranges used in most clinical linacs. The results have shown that ferrous xylenol gels can be used as dosimeters in quality assurance in radiation therapy.

Effect of perchloric acid on the performance of the Fricke xylenol gel dosimeter.

The conventional ferrous xylenol orange (XO) gel (FXG) dosimeter is being wildly investigated for radiotherapy dose measurements. Upon irradiation, its color turns red due to oxidation of Fe(2+) into Fe(3+), which forms a complex with xylenol orange. The effect of perchloric acid (PCA) on the dosimetric properties of the gel in the dose range of 1-15Gy was investigated using visual spectrophotometry. FXG-PCA responds to radiation dose linearly and exhibits higher radiation sensitivity than the conventional gel dosimeter. PCA in a concentration of 20mM enhances the radiation sensitivity ~44%. Stability of the absorbances of both the gels during storage under various conditions was investigated, and the uncertainty of dose measurements was estimated.

Full core analysis of IRIS reactor by using MCNPX.

This paper describes neutronic analysis for fresh fuelled IRIS (International Reactor Innovative and Secure) reactor by MCNPX code. The analysis included criticality calculations, radial power and axial power distribution, nuclear peaking factor and axial offset percent at the beginning of fuel cycle. The effective multiplication factor obtained by MCNPX code is compared with previous calculations by HELIOS/NESTLE, CASMO/SIMULATE, modified CORD-2 nodal calculations and SAS2H/KENO-V code systems. It is found that k-eff value obtained by MCNPX is closer to CORD-2 value. The radial and axial powers are compared with other published results carried out using SAS2H/KENO-V code. Moreover, the WIMS-D5 code is used for studying the effect of enriched boron in form of ZrB2 on the effective multiplication factor (K-eff) of the fuel pin. In this part of calculation, K-eff is calculated at different concentrations of Boron-10 in mg/cm at different stages of burnup of unit cell. The results of this part are compared with published results performed by HELIOS code.

Mobile mammography screening: the James Graham Brown Cancer Center three year experience. Implications for public and professional education.

OBJECTIVE: Review the mobile mammography screening experience at the James Graham Brown Cancer Center during a 3 year interval. METHODS: Collect and analyze demographic and outcome data on the screened population. RESULTS: 4,864 women underwent two-view mammograms. One third of the mammograms were performed in women over 50 years of age. 232 mammograms were carried out per cancer detected. The number of mammograms per cancer detected was 2.5 times higher and the number of biopsies per cancer detected was 2.8 times higher in women under 50 years of age. Two thirds of the cancers detected were in the over 50 age group which represents one third of the study population. CONCLUSIONS: In this study, mammographic screening for breast cancer was more cost effective because a higher yield of cancers detected was obtained with fewer mammograms and fewer breast biopsies in women over 50 years of age, compared to women under 50 years. Resolving the question of the cost effectiveness of screening women aged 40 to 49, will require a large randomized prospective trial. In the near term, rather than to dwell on this issue, we would propose that this study suggests the need for greater emphasis in both public and professional education on breast cancer detection directed to women over 50 years of age.

Comparison of the cost-effectiveness of various therapies for common prostatic disorders.

Diseases of the prostate currently represent a major health problem worldwide. As the age of the male population increases in the future, so will the number of patients suffering from these disorders and the cost for treatment increase. Currently, benign prostatic hyperplasia (BPH) and prostate cancer are common in men over 50 years of age. In men after puberty, prostatic infections (prostatitis) are common. Each condition carries with it controversy regarding the most cost-effective treatment. Treatment for these disorders can include surgical intervention, drug therapy, or no treatment at all. In the United States, surgery is the usual treatment of BPH in men over 65 years of age, but most patients with BPH are asymptomatic and require no intervention. Aside from acute urinary retention or backpressure that compromises renal function, the indications to perform surgery are questionable. While some alpha-adrenergic antagonists are used to temporarily relieve symptoms, many patients with BPH will eventually require surgery. Transurethral resection of the prostate is the surgical treatment of choice in selected patients with BPH, accounting for over 90% of surgery performed in this area. The risk-to-benefit ratio for this procedure is favourable and cost-saving steps can be taken by the physician. Open prostatectomy, both suprapubic and retropubic, is performed to treat large prostates. However, both hospital stay and overall morbidity is higher for open prostatectomy than for transurethral prostatic resection. Radical prostatectomy and radiotherapy are commonly performed to treat patients with cancer of the prostate. For patients with the early stages of the disease, administering no treatment is also acceptable. Each therapeutic method has its advocates, and overall survival rates are similar for all treatments. Radiotherapy, however, is less expensive. We review the magnitude of these diseases, therapies available and relevant cost-effectiveness studies. When this sort of scientific information is not taken into account, the physician's decision of which therapy to choose is sometimes blinded by the prejudices and fears of the patient.

Carcinoma of the prostate simulating primary bladder cancer.

After encountering two patients who were diagnosed as having primary bladder cancer but were ultimately found to have carcinoma of the prostate invading the bladder, a prospective study was undertaken. In five patients with known carcinoma of the prostate invading the bladder, cup biopsies of the bladder lesions were reported as primary bladder cancer in four patients. To prevent this error, immunohistochemical studies are required and discussed in this paper.

Breast cancer risk: a review of definitions and assessments of risk.

The histopathological and biochemical characteristics of cells and multicellular structure of benign and malignant breast changes have highly significant implications as to the risk of acquiring and dying of breast cancer. Consequently, every breast biopsy merits highly specific histopathological characterization as well as assay for hormone receptors. Certain aspects of a woman's personal and family history may be associated with increased or decreased risk. Clinical application of these variables to the prediction of future outcome requires an understanding of the definitions of risk. These definitions must then be applied appropriately when assessing risk. The definition of risk used must be explicitly stated and consistently used. Provided is a review of the definitions of risk and the risk of acquiring breast cancer according to age, family history, and histopathological characteristics of benign breast biopsies. The highly variable relative risk of dying from breast cancer when diagnosed is also reviewed.

Blunt urethral injury: results of initial management.

Fourteen men with blunt urethral disruption were treated between 1979-1985. Injuries most commonly resulted from motor-vehicle accidents, as pedestrians or passengers. All patients had additional injuries, including pelvic fracture (13), extremity fractures (10), central nervous system (5), bladder (5) and rectal injury (3); the average injury severity score was 30. Pelvic fracture patterns included ten patients with a crushed pelvis, two with single anterior pelvic ring fractures and one with a double vertical fracture. Blood at the urethral meatus was noted in only five patients, gross hematuria without metal blood in another three, and a displaced prostate on rectal exam was found in 10 cases. All patients had a suprapubic cystostomy for management of the urethral injury. Thirteen of 14 patients survived (93%). The major complication was perineal sepsis. Based on this experience, it is concluded that: 1) the classical findings of urethral injury are not found consistently, 2) certain pelvic fracture patterns, particularly disruption of the anterior pelvic ring, are frequently associated with urethral injury and 3) aggressive and appropriate management of hemorrhage, pelvic fracture and concomitant injuries is important to minimize mortality.

Bipartite liver. A case report.

Bipartite liver is a rare anomaly that has no apparent phylogenetic significance but does represent a distinct category of congenital liver malformations. Although no associated complications have been known to occur, the potential for internal herniation of the gastrointestinal tract may exist.

The effect of samorin (isometamedium chloride) on Trypanosoma evansi infection in mice.

Samorin (isometamedium chloride) was effective against T. evansi in mice given in single i.p. doses of 1 to 10 mg/kg. The administration of 40 mg/kg of samorin or above caused rapid death of mice and there were severe haemorrhages, degeneration and congestion in the liver, heart and kidney. The lesions in the liver and kidney were accompanied with reduced activities of ATP-ase, 5-nucleotidase, succinic tetrazolium reductase and glucose-6-phosphatase.