Secular Trends in Infection-Related Mortality after Kidney Transplantation

Background and objectives Infections are the most common noncardiovascular causes of death after kidney transplantation. We analyzed the current infection-related mortality among kidney transplant recipients in a nationwide cohort in Finland. Design, setting, participants, & measurements Altogether, 3249 adult recipients of a first kidney transplant from 1990 to 2012 were included. Infectious causes of death were analyzed, and the mortality rates for infections were compared between two eras (1990-1999 and 2000-2012). Risk factors for infectious deaths were analyzed with Cox regression and competing risk analyses. Results Altogether, 953 patients (29%) died during the follow-up, with 204 infection-related deaths. Mortality rate (per 1000 patient-years) due to infections was lower in the more recent cohort (4.6; 95% confidence interval, 3.5 to 6.1) compared with the older cohort (9.1; 95% confidence interval, 7.6 to 10.7); the incidence rate ratio of infectious mortality was 0.51 (95% confidence interval, 0.30 to 0.68). The main causes of infectious deaths were common bacterial infections: septicemia in 38% and pulmonary infections in 45%. Viral and fungal infections caused only 2% and 3% of infectious deaths, respectively (such as individual patients with Cytomegalovirus pneumonia, Herpes simplex virus meningoencephalitis, Varicella zoster virus encephalitis, and Pneumocystis jirovecii infection). Similarly, opportunistic bacterial infections rarely caused death; only one deathwas caused by Listeria monocytogenes, and two were caused by Mycobacterium tuberculosis. Only 23 (11%) of infection-related deaths occurred during the first post-transplant year. Older recipient age, higher plasma creatinine concentration at the end of the first post-transplant year, diabetes as a cause of ESKD, longer pretransplant dialysis duration, acute rejection, low albumin level, and earlier era of transplantation were associated with increased risk of infectious death in multivariable analysis. Conclusions The risk of death due to infectious causes after kidney transplantation in Finland dropped by one half since the 1990s. Common bacterial infections remained the most frequent cause of infection-related mortality, whereas opportunistic viral, fungal, or unconventional bacterial infections rarely caused deaths after kidney transplantation.Peer reviewe

Waste Management of Small Modular Nuclear Reactors in Finland

Small modular nuclear reactors (SMRs) represent advanced technology in nuclear energy aim-ing to produce low carbon energy at smaller unit size and enhanced passive safety in compar-ison to traditional nuclear power plants (NPPs). The management of spent nuclear fuel (SNF) and low- and intermediate-level waste (LILW) from SMRs is an issue that needs to be resolved as part of any deployment of SMR technology in Finland. Currently, spent nuclear fuel from NPPs in Finland is planned to be disposed in the ONKALO® deep geological repository applying the KBS-3V disposal concept. This concept should be applicable for spent fuel from SMRs using light-water reactor (LWR) technology. However, there are some differences in the waste forms, most obviously the length of the fuel assemblies, but also in the spent fuel characteristics that need to be considered in the further development of the concept for spent fuel from SMRs. Preliminary 2D calculations were made with the continuous-energy Monte Carlo code Serpent to compare the spent fuel characteristics from two example LWR-SMRs to spent nuclear fuel from currently operating NPPs in Finland. In one example case, a NuScale Power ModuleTM was considered as it is one of the most advanced LWR-SMRs in the world. The other example case is an SMR planned in Finland for district heating purposes. The main differences between the SMR and NPP spent fuels are linked to lower burnups in the SMRs. Lower discharge burnups are to be studied further from the point of view of criticality safety at disposal. Other-wise, the lower average discharge burnup of these SMR fuel types, in principle, generally tends to make the handling of spent fuel assemblies less demanding with respect to the decay heat and ionizing radiation emitted from the assembly. However, rigorous calculation of the dose rates would require 3D calculations to determine the axial burnup distribution within a fuel as-sembly, which was outside the scope of this study. Published studies indicate that possibly larger masses (per GWe-year) of SNF and other HLW and larger volumes (per GWe-year) of LLW will be produced in a LW-SMR compared to a large NPP. However, because of the lower decay heat in the SMR SF (due to the lower burnup), less excavated volume and, consequently, less clay-based filling material (deposition tunnel back-fill) may be needed in a repository. Depending on the number of SMR units located at sites in Finland, the amounts of spent fuel and other waste streams can be relatively small so that a centralised waste management facility and repository could be the most feasible option for processing and disposal of all the nuclear waste. Alternatively, the wastes can be disposed of locally (near SMR sites in smaller facilities) or a hybrid model, where, e.g., only SNF is disposed centrally, could be considered. These alternatives will depend strongly on the ownership structure of the SMRs deployed in Finland. Local stakeholder and public opinion will be very important as well. Other issues, such as ge-ological suitability of the SMR sites for disposal, transport and interim storage will need to be assessed. In terms of final disposal of SNF from LWR-SMRs, the only currently available option is the KBS-3V concept, especially considering the state of the licencing process for this concept in Finland. Deep borehole disposal represents an intriguing, particularly in the case of local disposal for relatively small amounts of waste, but not yet fully developed alternative. The suitability of deep borehole disposal in the crystalline rock conditions prevailing in Finland will be studied in the next phase of the project. Spent fuel from non-LWR SMRs, i.e., high-temperature-gas-cooled, fast neutron-spectrum and molten salt-type SMRs, was also discussed briefly. Challenges were identified in the pre-treat-ments needed for SNF from these reactors prior to disposal including lack of suitable facilities in Finland and potential proliferation issues. In some cases, e.g., reactors with graphite mod-erators, the disposal of the LILW waste streams was considered problematic as the current methodologies in use in Finland for disposal of LILW would not be applicable. More extensive studies would be required to specifically identify the waste streams from non-LWR SMRs and how the waste characteristics would need to be taken into account for disposal

Nopean reaktorin laskentaa ERANOS-ohjelmistolla

The motivation behind this thesis was to study the suitability of the deterministic fast reactor steady-state neutronics code ERANOS to be used at VTT Technical Research Centre of Finland. A specific code for fast reactors is required, since codes developed for thermal reactor calculation have been optimized such that several fast spectrum specific phenomena are ignored. ERANOS is a modular code package consisting e.g. of the lattice code ECCO and core calculation modules BISTRO and VARIANT. For the present study, ERANOS was employed to calculate part of the critical sodium-cooled fast reactor with high Pu-240 core ZPR-6 Assembly 7 (Zero Power Reactor) reactor physics benchmark. The calculations were performed for the criticality safety model and two separate sodium void reactivity (SVR) core configurations. The purpose of the calculations was to determine the impact of various calculation methods, parameters and the applied geometry. Another subject of interest was the performance of ERANOS-2.2 with JEFF-3.1 and -3.1.1 nuclear data libraries against the ZPR-6/7 experimental results. Some of the calculations were performed also with the Serpent Monte Carlo code. The main tools to solve the transport equation were the discrete ordinates (SN) and variational nodal (VNM) methods, in addition to which methods based on diffusion approximation were utilized. The method proved to be a significant factor, as well as the geometry effect between the rectangular 3-D and 2-D cylindrical coordinate systems. The more detailed calculation parameters, such as the polynomial expansion orders and mesh size, showed lesser significance. The 3-D VNM proved to be able to provide the most accurate SVR results with respect to the experimental ones, as far as the parameters were set properly. The 2-D SN method did not show equally good consistency and it had the more difficulties the larger the voided area was. The discrepancy between these methods is somewhat contradictory to some previously published ERANOS calculations. For criticality calculation the SN method provided good results, but they became slightly deteriorated when the computational accuracy was increased.Työn tavoitteena oli selvittää aikariippumattoman nopean reaktorin neutroniikkalaskentaan kehitetyn deterministisen ERANOS-koodin käyttökelpoisuutta VTT:n tarpeisiin. Nopean reaktorin laskenta vaatii tarkoitusta varten erikseen kehitetyn koodin, sillä termisten reaktoreiden koodit on yleensä optimoitu siten, että monet nopean neutronispektrin ilmiöt on jätetty tarpeettomina huomioimatta. ERANOS on modulaarinen ohjelmistopaketti, jonka tärkeimpiä moduuleja ovat nippukoodi ECCO, sekä sydänlaskentakoodit BISTRO ja VARIANT. ERANOS-2.2 -koodia käytettiin natriumjäähdytteisen kriittisen ZPR-6 -nollatehoreaktorin mittauksista koostetun reaktorifysiikkabenchmarkin osittaiseen laskentaan. Työssä laskettiin benchmarkin kriittisyysturvallisuusmalli ja kaksi erilaista natriumin aukko-osuus-reaktiivisuusmallia. Laskujen tarkoitus oli selvittää eri laskentamenetelmien, -parametrien ja käytetyn geometrian vaikutuksia tuloksiin. Lisäksi tutkittiin, minkälaisia tuloksia ERANOS tuottaa suhteessa kokeellisiin tuloksiin JEFF-3.1 ja 3.1.1-pohjaisia ydinvakiokirjastoja käyttämällä. Joitain vertailulaskuja tehtiin myös Monte Carlo -koodi Serpentillä. Transport-laskuissa käytettiin diskreettiordinaatta- (SN) ja variaationodaalimenetelmiä (VNM). Lisäksi käytettiin diffuusioapproksimaatioon perustuvia menetelmiä. Laskentamenetelmä osoittautui merkittäväksi tekijäksi tulosten suhteen. Myös erot kolmiulotteisen suorakulmaisen ja kaksiulotteisen sylinterikoordinaatiston välillä olivat paikoin suuria. Sen sijaan yksityiskohtaisemmat laskentaparametrit vaikuttivat tuloksiin yleensä varsin vähän. VNM osoittautui parhaaksi menetelmäksi kokeellisten tulosten suhteen Na-aukko-osuusreaktiivisuuden laskennassa, kunhan käytettiin oikeita parametreja. Myös SN-menetelmä tuotti paikoin kohtalaisia tuloksia, mutta erityisesti laaja Na-aukkoalue osoittautui vaikeaksi laskettavaksi. Näin selvät erot menetelmien välillä ovat ristiriidassa eräiden aikaisemmin julkaistujen vastaavankaltaisten ERANOS-laskujen kanssa. Kriittisyyslaskussa 2-ulotteinen SN tuotti varsin hyviä tuloksia, mutta tarkkuuden kasvattaminen vaikutti heikentävästi