[en] The following report shows, how to use operational experience for planning and realisation in dismantling of the Research Reactor SAPHIR (MTR Pool Reactor Type). The application of a PSI-internal QM-procedure regulation for set a radioprotection planning is given as an example at dismantling of reactor structures. With this procedure, basic demands of the Swiss regulation authority will be fulfilled by demands a radioprotection planning which complies with Quality Assurance. (orig.)

[en] The burnup of 20 irradiated LEU fuel elements has been determined as part of the annual series of reactivity-based burnup measurements at the SAPHIR reactor facility. It has ben shown that the target discharge burnup value of >60%, attained earlier with HEU fuel elements, can be easily reached with LEU fuel. This confirms - considering the much larger ²³⁵U loading of the LEU elements - that a considerably greater, integral energy production (MWD) is being achieved with LEU fuel elements in SAPHIr than with HEU. The accuracy of the reactivity method for burnup determination is estimated as ∼±5%, and high-resolution gamma-spectroscopy measurements are being planned to provide an independent check on the validity of the current results

[en] Short communication. 1 tab

[en] After 36 years in operation the former research reactor SAPHIR was decommissioned on December 23rd 1993. After removing the spent fuel, the highest activity was contained in the BeO-reflectors. Twenty reflectors were used; ten of BeO, in total 65.1 kg, and ten of Be-metal, in total 60.78 kg. Both types are in aluminum housings. The highest activation was built up in the Be-metal reflectors. The activity was calculated using the program ORIGEN resulting in 573 TBq ³H and 240 GBq ⁶⁰Co for the Be-metal reflectors and 181 TBq ³H and 21 GBq ⁶⁰Co for the BeO (December 1995). The corresponding dose rates due to the ⁶⁰Co were 4.64 Sv/h and 0.4 Sv/h from the Be-metal and BeO reflectors respectively. Due to the intrinsic toxicity, the high dose rate and the high ³H content, the following principles had to be followed: The reflectors should be conditioned without any additional dismantling; Due to the high ³H content the reflectors should be sealed in gas tight welded steel cans; The reflectors should be dried before welding to avoid corrosion; The void between the can and the reflector should be filled with quartz sand; The surface of the damaged BeO-reflectors should be sealed to avoid contamination from toxic BeO-dust; The dose rate should be reduced by using a shielded container; The volume should be minimized due to high costs of interim and final storage. These goals were achieved by sealing the dried reflectors in square section steel cans using a welding robot (type MOTOMAN SK6) in a shielded hot cell. The 20 cans were placed in a MOSAIK container Type II-15 U, using a steel grid to position the cans correctly. This container is stored in the Swiss Federal Interim Storage Facility to await the Swiss final repository. (author)

[en] The ionic dependence of the trout sperm plasma membrane potential was analysed by measuring the accumulation of the lipophilic ions ³H-tetraphenylphosphonium (TPP) and ¹⁴C-thiocyanate (SCN) following dilution in artificial media isotonic to the seminal fluid. Our data showed that the trout sperm plasma membrane has a mixed conductance: the plasma membrane potential is sensitive upon the transmembrane gradients of K+, Na+, and H+. This potential is negative (less than -40 mV) in a 125 mM choline chloride media (ChM) at pH 8.5. Replacement of choline by sodium has a small depolarizing effect. The membrane potential is about -15 mV in a 125 mM potassium chloride and falls near zero mV only if valinomycin is added. In ChM changing the external pH (pHe) greatly affects the membrane potential: its value rises from less than -40 mV at pHe 9.0 to -17 mV at pHe 5.0. This pH effect is observed also in presence of sodium or potassium. A decrease in the transmembrane proton gradient produced by increasing internal pH without changing pHe induces also a depolarisation of the plasma membrane. In the different media in which trout sperm remain immotile after dilution (media with [K+] greater than 20-40 mM or a pH less than 7.5) the plasma membrane is more depolarized than in media allowing motility, suggesting a relationship between the state of membrane polarization and the intracellular effectors of the axonemal movement

[en] Several different core loadings were assembled at the SAPHIR research reactor in Switzerland combining the available types of MTR-type fuel elements, consisting mainly of both HEU and LEU fuel. Bearing in mind the well known problems which can occur in such configurations (especially power peaking), investigations have been carried out for each new loading with a 2D neutron transport code (BOXER). The axial effects were approximated by a global buckling value and therefore the radial effects could be studied in considerably detail. Some of the results were reported at earlier RERTR meetings and were compared to those obtained by other methods and with experimental values. For the explicit study of the third dimension of the core, another code (SILWER), which has been developed in PSI for LWR power plant cores, has been selected. With the help of an adapted model for the MTR-core of SAPHIR, several important questions have been addressed. Among other aspects, the estimation of the axial contribution to the hot channel factors, the influence of the control rod position and of the Xe-poisoning on the power distribution were studied. Special attention was given to a core position where a new element was assumed placed near a empty, water filled position. The comparison of elements of low and high enrichments at this position was made in terms of the induced power peaks, with explicit consideration of axial effects. The program SILWER has proven to be applicable to MTR-cores for the investigation of axial effects. For routine use as for the support of reactor operation, this 3D code is a good supplement to the standard 2D model

[en] Experience has been acquired in applying high-resolution gamma-spectroscopy of the primary coolant for early detection of small element defects during routine operation of the 10 MW_th research reactor, SAPHIR. With an effective delay of < 2 min between core exit and measurement position, it has been found possible to make use of several individual short-lived fission products (Kr and Xe isotopes) in the sampled coolant. Small fuel element defects - which would take hours for definite identification via the air-borne activity - have been shown to be detectable by the current method within as little as 5 minutes of their occurrence. The application of short-lived fission products, as compared to the longer-lived ones usually employed in power reactor studies, has been found to be particularly advantageous in the search for defective fuel elements during routine operation. Consistent results have been obtained in a series of fuel element tests carried out in three different SAPHIR core configurations

[en] The swimming pool research reactor SAPHIR (MTR type) became operational in 1957 on a power level of 1 MW. For 37 years it was the strongest neutron source within Switzerland for research purposes and industrial applications. The power level of 10 MW was reached in 1983 following the demands of the different facility users. In the framework of the RERTR program the different steps of reducing the fuel enrichment were practically applied. Because of the relative high U-235 content of the elements, the core configuration and the cooling conditions have to be considered very carefully. A number of problems could be solved by improving the loading procedures and by modifications of the cooling circuits. In 1994 it was decided to shut down the reactor. The owner of the facility (PSI) plans the decommissioning in several steps, starting with shipping all spent fuel elements back to their origin country USA and disposal in the DOE storage facilities. Considerations regarding criticality safety during storage of the fuel elements in the reactor pool, handling procedures and shipping in suited containers were performed. The decommission of the reactor facility will be done during the next years depending on the demands of the future users of the building and the advance in the licensing procedure. (author)

[en] The 10 MW_th open-pool research reactor, SAPHIR, meets the requirements for a range of neutron irradiation applications. These include radioisotope production for research, medicine and industry, radiation damage studies for fission and fusion reactor materials, radiochemistry and neutron activation analysis, industrial irradiations such as silicon transmutation doping and neutron radiography and - last but not least - neutron scattering research using the various beam tube facilities. The current paper describes the corresponding irradiation techniques developed and being applied at the reactor. (author) 11 figs., 1 tab., 13 refs

[en] On May 16th, 1994, PSI decided to discontinue its efforts to retrofit the SAPHIR reactor for operation at 10 MW. This decision was made because the effort and time for the retrofit work in progress had proven to be more complex than was anticipated. In view of the start-up of the new spallation-neutron source SINQ in 1996, the useful operating time between the eventual restart of SAPHIR and the start-up of SINQ became less than two years, which was regarded by PSI as too short a period to warrant the large retrofit effort. Following the decision of PSI not to re-use SAPHIR as a neutron source, several options for the further utilization of the facility were open. However, none of them appeared promising in comparison with other possibilities; it was therefore decided that SAPHIR should be decommissioned. A concerted effort was initiated to consolidate the nuclear and conventional safety for the post-operational period. (author) 3 figs., 3 tab