Process for preparing sintered uranium dioxide nuclear fuel

Claim 2

A SINTERING CONTROL PROCESS WHEREIN THE SINTERING ATMOSPHERE CONTAINS SUBSTANTIALLY CONTANTLY A PREDETERMINED MONITORED OXYGEN PARTIAL PRESSURE WHICH MAINTAINS A BODY CONSISTING ESSENTIALLY OF URANIUM DIOXIDE AT A PRESELECTED OXYGEN TO URANIUM RATIO DURING SINTERING OF SUCH BODY IN THE PRODUCTION OF A URANIUM DIOXIDE NUCLEAR FUEL BODY HAVING SAID PRESELECTED OXYGEN TO URANIUM RATIO COMPRISING THE STEPS OF PROVIDING URANIUM DIOXIDE PARTICLES HAVING AN OXYGEN TO URANIUM ATOMIC RATIO OF 1.7 TO 2.25 AND A SURFACE AREA RANGING FROM ABOUT 2 TO 12 SQUARE METERS PER GRAM, PRESSING SAID URANIUM DIOXIDE PARTICLES TO FORM A GREEN BODY, HEATING SAID B GREEN BODY TO A SINTERING TEMPERATURE RANGING FROM ABOUT 100:C TO 1400*C IN A CHEMICALLY BUFFERED SINTERING GAS ATMOSPHERE CONSISTING ESSENTIALLY OF A GAS MIXTURE OF AT LEAST TWO GASES, WHICH ARE MAINTAINED IN A RATIOWHICH IN EQUILIBRIUM AT SAID SINTERING TEMPERATURE PROVIDES SAID PREDETERMINED MONITORED OXYGEN PARTIAL PRESSURE TO MAINTAIN THE URANIUM DIOXIDE AT SAID PRESELECTED OXYGEN TO URANIUM RATIO DURING SINTERING, AND SINTERING SAID BODY AT SAID TEMPERATURE, SAID OXYGEN PARTIAL PRESSURE BEING SOLELY PREDETERMINED BY SAID PRESENECTED OXYGEN TO URANIUM RATIO AND SAID SINTERING TEMPERATURE, SAID PRESELECTED OXYGEN TO URANIUM RATIO BEING A MINIMUM OF 2,0005, AND SAID SINTERING BEING CARRIED OUT TO PRODUCE A SINTERED BODY OF URANIUM DIOXIDE HAVING A DENSITY OF AT LEAST ABOUT 92 PERCENT OF THEORETICAL.

Claim 3

A process according to claim 1 wherein said gas mixture consists essentially of carbon monoxide and carbon dioxide.

Claim 4

A process according to claim 1 wherein said gas mixture consists essentially of hydrogen and steam.

Claim 5

A process according to claim 1 wherein said gas mixture is formed from combusted air and methane.

Claim 6

A process according to claim 1 wherein said sintering temperature ranges from aoubt 1000*C to 1250*C, said oxygen to uranium ratio ranges from 2.005 to 2.01, and said density ranges from about 92 to 96.9 percent of theoretical.

Claim 7

A process according to claim 1 wherein said oxygen to uranium ratio ranges from 2.005 to 2.05.

Claim 8

A sintering control process which produces a sintered nuclear fuel body of uranium dioxide having a preselected oxygen to urnaium ratio which ranges from 2.005 to 2.05 and a density of at least about 92% of theoretical which comprises the steps of preselecting said oxygen to uranium ratio for said sintered body of uranium dioxide, preselecting a sintering temperature from the range of about 1000*C to 1400*C, calculating the required oxygen partial pressure to be maintained substantially constantly at said preselected sintering temperature to produce said sintered body having said preselected oxygen to uranium ratio, said required oxygen partial pressure being solely determined by said preselected sintering temperature and said preselected oxygen to uranium ratio of said sintered product, providing a gas mixture of at least two gases which in equilibrium produces a partial pressure of oxygen, calculating from said calculated required oxygen partial pressure and said preselected sintering temperature the required ratio of gases in said gas mixture which in equilibrium at said sintering temperature produces said required partial pressure of oxygen, providing a sintering gas atmosphere consisting essentially of said gas mixture which in equilibrium at said sintering temperature produces said required oxygen partial pressure, providing uranium dioxide particles having an oxygen to uranium ratio of 1.7 to 2.25 and a surface area ranging from about 2 to 12 square meters per gram, pressing said uranium dioxide particles to form a green body, heating said green body in said sintering gas atmosphere to said preselected sintering temperature, sintering said body to said density, monitoring the oxygen partial pressure of said sintering atmosphere during sintering and maintaining said calculated required oxygen partial pressure in said sintering atmosphere substantially constantly at said preselected temperature by adjusting the equilibrium of said gas mixture by adjusting said gas mixture ratio.

Claim 9

A sintering control process which produces a sintered nuclear fuel body of uranium dioxide having a preselected oxygen to urnaium ratio which ranges from 2.005 to 2.05 and a density of at least about 92% of theoretical which comprises the steps of preselecting said oxygen to uranium ratio for said sintered body of uranium dioxide, preselecting a sintering temperature from the range of about 1000*C to 1400*C, calculating the required oxygen partial pressure to be maintained substantially constantly at said preselected sintering temperature to produce said sintered body having said preselected oxygen to uranium ratio, said required oxygen partial pressure being solely determined by said preselected sintering temperature and said preselected oxygen to uranium ratio of said sintered product, providing a gas mixture of at least two gases which in equilibrium produces a partial pressure of oxygen, calculating from said calculated required oxygen partial pressure and said preselected sintering temperature the required ratio of gases in said gas mixture which in equilibrium at said sintering temperature produces said required partial pressure of oxygen, providing a sintering gas atmosphere consisting essentially of said gas mixture which in equilibrium at said sintering temperature produces said required oxygen partial pressure, providing uranium dioxide particles having an oxygen to uranium ratio of 1.7 to 2.25 and a surface area ranging from about 2 to 12 square meters per gram, pressing said uranium dioxide particles to form a green body, heating said green body in said sintering gas atmosphere to said preselected sintering temperature, sintering said body to said density, monitoring the oxygen partial pressure of said sintering atmosphere during sintering and maintaining said calculated required oxygen partial pressure in said sintering atmosphere substantially constantly at said preselected temperature by adjusting the equilibrium of said gas mixture by adjusting said gas mixture ratio.